note: project gutenberg also has an html version of this file which includes the original illustrations. see 13476-h.htm or 13476-h.zip: (http://www.gutenberg.net/dirs/1/3/4/7/13476/13476-h/13476-h.htm) or (http://www.gutenberg.net/dirs/1/3/4/7/13476/13476-h.zip) experiments with alternate currents of high potential and high frequency a lecture delivered before the institution of electrical engineers, london by nikola tesla with a portrait and biographical sketch of the author new york 1892 biographical sketch of nikola tesla. while a large portion of the european family has been surging westward during the last three or four hundred years, settling the vast continents of america, another, but smaller, portion has been doing frontier work in the old world, protecting the rear by beating back the "unspeakable turk" and reclaiming gradually the fair lands that endure the curse of mohammedan rule. for a long time the slav people--who, after the battle of kosovopjolje, in which the turks defeated the servians, retired to the confines of the present montenegro, dalmatia, herzegovina and bosnia, and "borderland" of austria--knew what it was to deal, as our western pioneers did, with foes ceaselessly fretting against their frontier; and the races of these countries, through their strenuous struggle against the armies of the crescent, have developed notable qualities of bravery and sagacity, while maintaining a patriotism and independence unsurpassed in any other nation. it was in this interesting border region, and from among these valiant eastern folk, that nikola tesla was born in the year 1857, and the fact that he, to-day, finds himself in america and one of our foremost electricians, is striking evidence of the extraordinary attractiveness alike of electrical pursuits and of the country where electricity enjoys its widest application. mr. tesla's native place was smiljan, lika, where his father was an eloquent clergyman of the greek church, in which, by the way, his family is still prominently represented. his mother enjoyed great fame throughout the countryside for her skill and originality in needlework, and doubtless transmitted her ingenuity to nikola; though it naturally took another and more masculine direction. the boy was early put to his books, and upon his father's removal to gospic he spent four years in the public school, and later, three years in the real school, as it is called. his escapades were such as most quick witted boys go through, although he varied the programme on one occasion by getting imprisoned in a remote mountain chapel rarely visited for service; and on another occasion by falling headlong into a huge kettle of boiling milk, just drawn from the paternal herds. a third curious episode was that connected with his efforts to fly when, attempting to navigate the air with the aid of an old umbrella, he had, as might be expected, a very bad fall, and was laid up for six weeks. about this period he began to take delight in arithmetic and physics. one queer notion he had was to work out everything by three or the power of three. he was now sent to an aunt at cartstatt, croatia, to finish his studies in what is known as the higher real school. it was there that, coming from the rural fastnesses, he saw a steam engine for the first time with a pleasure that he remembers to this day. at cartstatt he was so diligent as to compress the four years' course into three, and graduated in 1873. returning home during an epidemic of cholera, he was stricken down by the disease and suffered so seriously from the consequences that his studies were interrupted for fully two years. but the time was not wasted, for he had become passionately fond of experimenting, and as much as his means and leisure permitted devoted his energies to electrical study and investigation. up to this period it had been his father's intention to make a priest of him, and the idea hung over the young physicist like a very sword of damocles. finally he prevailed upon his worthy but reluctant sire to send him to gratz in austria to finish his studies at the polytechnic school, and to prepare for work as professor of mathematics and physics. at gratz he saw and operated a gramme machine for the first time, and was so struck with the objections to the use of commutators and brushes that he made up his mind there and then to remedy that defect in dynamo-electric machines. in the second year of his course he abandoned the intention of becoming a teacher and took up the engineering curriculum. after three years of absence he returned home, sadly, to see his father die; but, having resolved to settle down in austria, and recognizing the value of linguistic acquirements, he went to prague and then to buda-pesth with the view of mastering the languages he deemed necessary. up to this time he had never realized the enormous sacrifices that his parents had made in promoting his education, but he now began to feel the pinch and to grow unfamiliar with the image of francis joseph i. there was considerable lag between his dispatches and the corresponding remittance from home; and when the mathematical expression for the value of the lag assumed the shape of an eight laid flat on its back, mr. tesla became a very fair example of high thinking and plain living, but he made up his mind to the struggle and determined to go through depending solely on his own resources. not desiring the fame of a faster, he cast about for a livelihood, and through the help of friends he secured a berth as assistant in the engineering department of the government telegraphs. the salary was five dollars a week. this brought him into direct contact with practical electrical work and ideas, but it is needless to say that his means did not admit of much experimenting. by the time he had extracted several hundred thousand square and cube roots for the public benefit, the limitations, financial and otherwise, of the position had become painfully apparent, and he concluded that the best thing to do was to make a valuable invention. he proceeded at once to make inventions, but their value was visible only to the eye of faith, and they brought no grist to the mill. just at this time the telephone made its appearance in hungary, and the success of that great invention determined his career, hopeless as the profession had thus far seemed to him. he associated himself at once with telephonic work, and made various telephonic inventions, including an operative repeater; but it did not take him long to discover that, being so remote from the scenes of electrical activity, he was apt to spend time on aims and results already reached by others, and to lose touch. longing for new opportunities and anxious for the development of which he felt himself possible, if once he could place himself within the genial and direct influences of the gulf streams of electrical thought, he broke away from the ties and traditions of the past, and in 1881 made his way to paris. arriving in that city, the ardent young likan obtained employment as an electrical engineer with one of the largest electric lighting companies. the next year he went to strasburg to install a plant, and on returning to paris sought to carry out a number of ideas that had now ripened into inventions. about this time, however, the remarkable progress of america in electrical industry attracted his attention, and once again staking everything on a single throw, he crossed the atlantic. mr. tesla buckled down to work as soon as he landed on these shores, put his best thought and skill into it, and soon saw openings for his talent. in a short while a proposition was made to him to start his own company, and, accepting the terms, he at once worked up a practical system of arc lighting, as well as a potential method of dynamo regulation, which in one form is now known as the "third brush regulation." he also devised a thermo-magnetic motor and other kindred devices, about which little was published, owing to legal complications. early in 1887 the tesla electric company of new york was formed, and not long after that mr. tesla produced his admirable and epoch-marking motors for multiphase alternating currents, in which, going back to his ideas of long ago, he evolved machines having neither commutator nor brushes. it will be remembered that about the time that mr. tesla brought out his motors, and read his thoughtful paper before the american institute of electrical engineers, professor ferraris, in europe, published his discovery of principles analogous to those enunciated by mr. tesla. there is no doubt, however, that mr. tesla was an independent inventor of this rotary field motor, for although anticipated in dates by ferraris, he could not have known about ferraris' work as it had not been published. professor ferraris stated himself, with becoming modesty, that he did not think tesla could have known of his (ferraris') experiments at that time, and adds that he thinks tesla was an independent and original inventor of this principle. with such an acknowledgment from ferraris there can be little doubt about tesla's originality in this matter. mr. tesla's work in this field was wonderfully timely, and its worth was promptly appreciated in various quarters. the tesla patents were acquired by the westinghouse electric company, who undertook to develop his motor and to apply it to work of different kinds. its use in mining, and its employment in printing, ventilation, etc., was described and illustrated in _the electrical world_ some years ago. the immense stimulus that the announcement of mr. tesla's work gave to the study of alternating current motors would, in itself, be enough to stamp him as a leader. mr. tesla is only 35 years of age. he is tall and spare with a clean-cut, thin, refined face, and eyes that recall all the stories one has read of keenness of vision and phenomenal ability to see through things. he is an omnivorous reader, who never forgets; and he possesses the peculiar facility in languages that enables the least educated native of eastern europe to talk and write in at least half a dozen tongues. a more congenial companion cannot be desired for the hours when one "pours out heart affluence in discursive talk," and when the conversation, dealing at first with things near at hand and next to us, reaches out and rises to the greater questions of life, duty and destiny. in the year 1890 he severed his connection with the westinghouse company, since which time he has devoted himself entirely to the study of alternating currents of high frequencies and very high potentials, with which study he is at present engaged. no comment is necessary on his interesting achievements in this field; the famous london lecture published in this volume is a proof in itself. his first lecture on his researches in this new branch of electricity, which he may be said to have created, was delivered before the american institute of electrical engineers on may 20, 1891, and remains one of the most interesting papers read before that society. it will be found reprinted in full in _the electrical world_, july 11, 1891. its publication excited such interest abroad that he received numerous requests from english and french electrical engineers and scientists to repeat it in those countries, the result of which has been the interesting lecture published in this volume. the present lecture presupposes a knowledge of the former, but it may be read and understood by any one even though he has not read the earlier one. it forms a sort of continuation of the latter, and includes chiefly the results of his researches since that time. experiments with alternate currents of high potential and high frequency i cannot find words to express how deeply i feel the honor of addressing some of the foremost thinkers of the present time, and so many able scientific men, engineers and electricians, of the country greatest in scientific achievements. the results which i have the honor to present before such a gathering i cannot call my own. there are among you not a few who can lay better claim than myself on any feature of merit which this work may contain. i need not mention many names which are world-known--names of those among you who are recognized as the leaders in this enchanting science; but one, at least, i must mention--a name which could not be omitted in a demonstration of this kind. it is a name associated with the most beautiful invention ever made: it is crookes! when i was at college, a good time ago, i read, in a translation (for then i was not familiar with your magnificent language), the description of his experiments on radiant matter. i read it only once in my life--that time--yet every detail about that charming work i can remember this day. few are the books, let me say, which can make such an impression upon the mind of a student. but if, on the present occasion, i mention this name as one of many your institution can boast of, it is because i have more than one reason to do so. for what i have to tell you and to show you this evening concerns, in a large measure, that same vague world which professor crookes has so ably explored; and, more than this, when i trace back the mental process which led me to these advances--which even by myself cannot be considered trifling, since they are so appreciated by you--i believe that their real origin, that which started me to work in this direction, and brought me to them, after a long period of constant thought, was that fascinating little book which i read many years ago. and now that i have made a feeble effort to express my homage and acknowledge my indebtedness to him and others among you, i will make a second effort, which i hope you will not find so feeble as the first, to entertain you. give me leave to introduce the subject in a few words. a short time ago i had the honor to bring before our american institute of electrical engineers[a] some results then arrived at by me in a novel line of work. i need not assure you that the many evidences which i have received that english scientific men and engineers were interested in this work have been for me a great reward and encouragement. i will not dwell upon the experiments already described, except with the view of completing, or more clearly expressing, some ideas advanced by me before, and also with the view of rendering the study here presented self-contained, and my remarks on the subject of this evening's lecture consistent. [footnote a: for mr. tesla's american lecture on this subject see the electrical world of july 11, 1891, and for a report of his french lecture see the electrical world of march 26, 1892.] this investigation, then, it goes without saying, deals with alternating currents, and, to be more precise, with alternating currents of high potential and high frequency. just in how much a very high frequency is essential for the production of the results presented is a question which even with my present experience, would embarrass me to answer. some of the experiments may be performed with low frequencies; but very high frequencies are desirable, not only on account of the many effects secured by their use, but also as a convenient means of obtaining, in the induction apparatus employed, the high potentials, which in their turn are necessary to the demonstration of most of the experiments here contemplated. of the various branches of electrical investigation, perhaps the most interesting and immediately the most promising is that dealing with alternating currents. the progress in this branch of applied science has been so great in recent years that it justifies the most sanguine hopes. hardly have we become familiar with one fact, when novel experiences are met with and new avenues of research are opened. even at this hour possibilities not dreamed of before are, by the use of these currents, partly realized. as in nature all is ebb and tide, all is wave motion, so it seems that; in all branches of industry alternating currents--electric wave motion--will have the sway. one reason, perhaps, why this branch of science is being so rapidly developed is to be found in the interest which is attached to its experimental study. we wind a simple ring of iron with coils; we establish the connections to the generator, and with wonder and delight we note the effects of strange forces which we bring into play, which allow us to transform, to transmit and direct energy at will. we arrange the circuits properly, and we see the mass of iron and wires behave as though it were endowed with life, spinning a heavy armature, through invisible connections, with great speed and power--with the energy possibly conveyed from a great distance. we observe how the energy of an alternating current traversing the wire manifests itself--not so much in the wire as in the surrounding space--in the most surprising manner, taking the forms of heat, light, mechanical energy, and, most surprising of all, even chemical affinity. all these observations fascinate us, and fill us with an intense desire to know more about the nature of these phenomena. each day we go to our work in the hope of discovering,--in the hope that some one, no matter who, may find a solution of one of the pending great problems,--and each succeeding day we return to our task with renewed ardor; and even if we _are_ unsuccessful, our work has not been in vain, for in these strivings, in these efforts, we have found hours of untold pleasure, and we have directed our energies to the benefit of mankind. we may take--at random, if you choose--any of the many experiments which may be performed with alternating currents; a few of which only, and by no means the most striking, form the subject of this evening's demonstration: they are all equally interesting, equally inciting to thought. here is a simple glass tube from which the air has been partially exhausted. i take hold of it; i bring my body in contact with a wire conveying alternating currents of high potential, and the tube in my hand is brilliantly lighted. in whatever position i may put it, wherever i may move it in space, as far as i can reach, its soft, pleasing light persists with undiminished brightness. here is an exhausted bulb suspended from a single wire. standing on an insulated support. i grasp it, and a platinum button mounted in it is brought to vivid incandescence. here, attached to a leading wire, is another bulb, which, as i touch its metallic socket, is filled with magnificent colors of phosphorescent light. here still another, which by my fingers' touch casts a shadow--the crookes shadow, of the stem inside of it. here, again, insulated as i stand on this platform, i bring my body in contact with one of the terminals of the secondary of this induction coil--with the end of a wire many miles long--and you see streams of light break forth from its distant end, which is set in violent vibration. here, once more, i attach these two plates of wire gauze to the terminals of the coil. i set them a distance apart, and i set the coil to work. you may see a small spark pass between the plates. i insert a thick plate of one of the best dielectrics between them, and instead of rendering altogether impossible, as we are used to expect, i _aid_ the passage of the discharge, which, as i insert the plate, merely changes in appearance and assumes the form of luminous streams. is there, i ask, can there be, a more interesting study than that of alternating currents? in all these investigations, in all these experiments, which are so very, very interesting, for many years past--ever since the greatest experimenter who lectured in this hall discovered its principle--we have had a steady companion, an appliance familiar to every one, a plaything once, a thing of momentous importance now--the induction coil. there is no dearer appliance to the electrician. from the ablest among you, i dare say, down to the inexperienced student, to your lecturer, we all have passed many delightful hours in experimenting with the induction coil. we have watched its play, and thought and pondered over the beautiful phenomena which it disclosed to our ravished eyes. so well known is this apparatus, so familiar are these phenomena to every one, that my courage nearly fails me when i think that i have ventured to address so able an audience, that i have ventured to entertain you with that same old subject. here in reality is the same apparatus, and here are the same phenomena, only the apparatus is operated somewhat differently, the phenomena are presented in a different aspect. some of the results we find as expected, others surprise us, but all captivate our attention, for in scientific investigation each novel result achieved may be the centre of a new departure, each novel fact learned may lead to important developments. usually in operating an induction coil we have set up a vibration of moderate frequency in the primary, either by means of an interrupter or break, or by the use of an alternator. earlier english investigators, to mention only spottiswoode and j.e.h. gordon, have used a rapid break in connection with the coil. our knowledge and experience of to-day enables us to see clearly why these coils under the conditions of the tests did not disclose any remarkable phenomena, and why able experimenters failed to perceive many of the curious effects which have since been observed. in the experiments such as performed this evening, we operate the coil either from a specially constructed alternator capable of giving many thousands of reversals of current per second, or, by disruptively discharging a condenser through the primary, we set up a vibration in the secondary circuit of a frequency of many hundred thousand or millions per second, if we so desire; and in using either of these means we enter a field as yet unexplored. it is impossible to pursue an investigation in any novel line without finally making some interesting observation or learning some useful fact. that this statement is applicable to the subject of this lecture the many curious and unexpected phenomena which we observe afford a convincing proof. by way of illustration, take for instance the most obvious phenomena, those of the discharge of the induction coil. here is a coil which is operated by currents vibrating with extreme rapidity, obtained by disruptively discharging a leyden jar. it would not surprise a student were the lecturer to say that the secondary of this coil consists of a small length of comparatively stout wire; it would not surprise him were the lecturer to state that, in spite of this, the coil is capable of giving any potential which the best insulation of the turns is able to withstand: but although he may be prepared, and even be indifferent as to the anticipated result, yet the aspect of the discharge of the coil will surprise and interest him. every one is familiar with the discharge of an ordinary coil; it need not be reproduced here. but, by way of contrast, here is a form of discharge of a coil, the primary current of which is vibrating several hundred thousand times per second. the discharge of an ordinary coil appears as a simple line or band of light. the discharge of this coil appears in the form of powerful brushes and luminous streams issuing from all points of the two straight wires attached to the terminals of the secondary. (fig. 1.) [illustration: fig. 1.--discharge between two wires with frequencies of a few hundred thousand per second.] now compare this phenomenon which you have just witnessed with the discharge of a holtz or wimshurst machine--that other interesting appliance so dear to the experimenter. what a difference there is between these phenomena! and yet, had i made the necessary arrangements--which could have been made easily, were it not that they would interfere with other experiments--i could have produced with this coil sparks which, had i the coil hidden from your view and only two knobs exposed, even the keenest observer among you would find it difficult, if not impossible, to distinguish from those of an influence or friction machine. this may be done in many ways--for instance, by operating the induction coil which charges the condenser from an alternating-current machine of very low frequency, and preferably adjusting the discharge circuit so that there are no oscillations set up in it. we then obtain in the secondary circuit, if the knobs are of the required size and properly set, a more or less rapid succession of sparks of great intensity and small quantity, which possess the same brilliancy, and are accompanied by the same sharp crackling sound, as those obtained from a friction or influence machine. another way is to pass through two primary circuits, having a common secondary, two currents of a slightly different period, which produce in the secondary circuit sparks occurring at comparatively long intervals. but, even with the means at hand this evening, i may succeed in imitating the spark of a holtz machine. for this purpose i establish between the terminals of the coil which charges the condenser a long, unsteady arc, which is periodically interrupted by the upward current of air produced by it. to increase the current of air i place on each side of the arc, and close to it, a large plate of mica. the condenser charged from this coil discharges into the primary circuit of a second coil through a small air gap, which is necessary to produce a sudden rush of current through the primary. the scheme of connections in the present experiment is indicated in fig. 2. [illustration: fig. 2.--imitating the spark of a holtz machine.] g is an ordinarily constructed alternator, supplying the primary p of an induction coil, the secondary s of which charges the condensers or jars cc. the terminals of the secondary are connected to the inside coatings of the jars, the outer coatings being connected to the ends of the primary pp of a second induction coil. this primary pp has a small air gap ab. the secondary s of this coil is provided with knobs or spheres kk of the proper size and set at a distance suitable for the experiment. a long arc is established between the terminals ab of the first induction coil. mm are the mica plates. each time the arc is broken between a and b the jars are quickly charged and discharged through the primary pp, producing a snapping spark between the knobs kk. upon the arc forming between a and b the potential falls, and the jars cannot be charged to such high potential as to break through the air gap ab until the arc is again broken by the draught. in this manner sudden impulses, at long intervals, are produced in the primary pp, which in the secondary s give a corresponding number of impulses of great intensity. if the secondary knobs or spheres, kk, are of the proper size, the sparks show much resemblance to those of a holtz machine. but these two effects, which to the eye appear so very different, are only two of the many discharge phenomena. we only need to change the conditions of the test, and again we make other observations of interest. when, instead of operating the induction coil as in the last two experiments, we operate it from a high frequency alternator, as in the next experiment, a systematic study of the phenomena is rendered much more easy. in such case, in varying the strength and frequency of the currents through the primary, we may observe five distinct forms of discharge, which i have described in my former paper on the subject[a] before the american institute of electrical engineers, may 20, 1891. [footnote a: see the electrical world, july 11, 1891.] it would take too much time, and it would lead us too far from the subject presented this evening, to reproduce all these forms, but it seems to me desirable to show you one of them. it is a brush discharge, which is interesting in more than one respect. viewed from a near position it resembles much a jet of gas escaping under great pressure. we know that the phenomenon is due to the agitation of the molecules near the terminal, and we anticipate that some heat must be developed by the impact of the molecules against the terminal or against each other. indeed, we find that the brush is hot, and only a little thought leads us to the conclusion that, could we but reach sufficiently high frequencies, we could produce a brush which would give intense light and heat, and which would resemble in every particular an ordinary flame, save, perhaps, that both phenomena might not be due to the same agent--save, perhaps, that chemical affinity might not be _electrical_ in its nature. as the production of heat and light is here due to the impact of the molecules, or atoms of air, or something else besides, and, as we can augment the energy simply by raising the potential, we might, even with frequencies obtained from a dynamo machine, intensify the action to such a degree as to bring the terminal to melting heat. but with such low frequencies we would have to deal always with something of the nature of an electric current. if i approach a conducting object to the brush, a thin little spark passes, yet, even with the frequencies used this evening, the tendency to spark is not very great. so, for instance, if i hold a metallic sphere at some distance above the terminal you may see the whole space between the terminal and sphere illuminated by the streams without the spark passing; and with the much higher frequencies obtainable by the disruptive discharge of a condenser, were it not for the sudden impulses, which are comparatively few in number, sparking would not occur even at very small distances. however, with incomparably higher frequencies, which we may yet find means to produce efficiently, and provided that electric impulses of such high frequencies could be transmitted through a conductor, the electrical characteristics of the brush discharge would completely vanish--no spark would pass, no shock would be felt--yet we would still have to deal with an _electric_ phenomenon, but in the broad, modern interpretation of the word. in my first paper before referred to i have pointed out the curious properties of the brush, and described the best manner of producing it, but i have thought it worth while to endeavor to express myself more clearly in regard to this phenomenon, because of its absorbing interest. when a coil is operated with currents of very high frequency, beautiful brush effects may be produced, even if the coil be of comparatively small dimensions. the experimenter may vary them in many ways, and, if it were nothing else, they afford a pleasing sight. what adds to their interest is that they may be produced with one single terminal as well as with two--in fact, often better with one than with two. but of all the discharge phenomena observed, the most pleasing to the eye, and the most instructive, are those observed with a coil which is operated by means of the disruptive discharge of a condenser. the power of the brushes, the abundance of the sparks, when the conditions are patiently adjusted, is often amazing. with even a very small coil, if it be so well insulated as to stand a difference of potential of several thousand volts per turn, the sparks may be so abundant that the whole coil may appear a complete mass of fire. curiously enough the sparks, when the terminals of the coil are set at a considerable distance, seem to dart in every possible direction as though the terminals were perfectly independent of each other. as the sparks would soon destroy the insulation it is necessary to prevent them. this is best done by immersing the coil in a good liquid insulator, such as boiled-out oil. immersion in a liquid may be considered almost an absolute necessity for the continued and successful working of such a coil. it is of course out of the question, in an experimental lecture, with only a few minutes at disposal for the performance of each experiment, to show these discharge phenomena to advantage, as to produce each phenomenon at its best a very careful adjustment is required. but even if imperfectly produced, as they are likely to be this evening, they are sufficiently striking to interest an intelligent audience. before showing some of these curious effects i must, for the sake of completeness, give a short description of the coil and other apparatus used in the experiments with the disruptive discharge this evening. [illustration: fig. 3.--disruptive discharge coil.] it is contained in a box b (fig. 3) of thick boards of hard wood, covered on the outside with zinc sheet z, which is carefully soldered all around. it might be advisable, in a strictly scientific investigation, when accuracy is of great importance, to do away with the metal cover, as it might introduce many errors, principally on account of its complex action upon the coil, as a condenser of very small capacity and as an electrostatic and electromagnetic screen. when the coil is used for such experiments as are here contemplated, the employment of the metal cover offers some practical advantages, but these are not of sufficient importance to be dwelt upon. the coil should be placed symmetrically to the metal cover, and the space between should, of course, not be too small, certainly not less than, say, five centimetres, but much more if possible; especially the two sides of the zinc box, which are at right angles to the axis of the coil, should be sufficiently remote from the latter, as otherwise they might impair its action and be a source of loss. the coil consists of two spools of hard rubber rr, held apart at a distance of 10 centimetres by bolts c and nuts n, likewise of hard rubber. each spool comprises a tube t of approximately 8 centimetres inside diameter, and 3 millimetres thick, upon which are screwed two flanges ff, 24 centimetres square, the space between the flanges being about 3 centimetres. the secondary, ss, of the best gutta percha-covered wire, has 26 layers, 10 turns in each, giving for each half a total of 260 turns. the two halves are wound oppositely and connected in series, the connection between both being made over the primary. this disposition, besides being convenient, has the advantage that when the coil is well balanced--that is, when both of its terminals t_1 t_1 are connected to bodies or devices of equal capacity--there is not much danger of breaking through to the primary, and the insulation between the primary and the secondary need not be thick. in using the coil it is advisable to attach to _both_ terminals devices of nearly equal capacity, as, when the capacity of the terminals is not equal, sparks will be apt to pass to the primary. to avoid this, the middle point of the secondary may be connected to the primary, but this is not always practicable. the primary pp is wound in two parts, and oppositely, upon a wooden spool w, and the four ends are led out of the oil through hard rubber tubes tt. the ends of the secondary t_1 t_1 are also led out of the oil through rubber tubes t_1 t_1 of great thickness. the primary and secondary layers are insulated by cotton cloth, the thickness of the insulation, of course, bearing some proportion to the difference of potential between the turns of the different layers. each half of the primary has four layers, 24 turns in each, this giving a total of 96 turns. when both the parts are connected in series, this gives a ratio of conversion of about 1:2.7, and with the primaries in multiple, 1:5.4; but in operating with very rapidly alternating currents this ratio does not convey even an approximate idea of the ratio of the e.m.fs. in the primary and secondary circuits. the coil is held in position in the oil on wooden supports, there being about 5 centimetres thickness of oil all round. where the oil is not specially needed, the space is filled with pieces of wood, and for this purpose principally the wooden box b surrounding the whole is used. the construction here shown is, of course, not the best on general principles, but i believe it is a good and convenient one for the production of effects in which an excessive potential and a very small current are needed. in connection with the coil i use either the ordinary form of discharger or a modified form. in the former i have introduced two changes which secure some advantages, and which are obvious. if they are mentioned, it is only in the hope that some experimenter may find them of use. [illustration: fig. 4.--arrangement of improved discharger and magnet.] one of the changes is that the adjustable knobs a and b (fig. 4), of the discharger are held in jaws of brass, jj, by spring pressure, this allowing of turning them successively into different positions, and so doing away with the tedious process of frequent polishing up. the other change consists in the employment of a strong electromagnet ns, which is placed with its axis at right angles to the line joining the knobs a and b, and produces a strong magnetic field between them. the pole pieces of the magnet are movable and properly formed so as to protrude between the brass knobs, in order to make the field as intense as possible; but to prevent the discharge from jumping to the magnet the pole pieces are protected by a layer of mica, mm, of sufficient thickness. s_1 s_1 and s_2 s_2 are screws for fastening the wires. on each side one of the screws is for large and the other for small wires. ll are screws for fixing in position the rods rr, which support the knobs. in another arrangement with the magnet i take the discharge between the rounded pole pieces themselves, which in such case are insulated and preferably provided with polished brass caps. the employment of an intense magnetic field is of advantage principally when the induction coil or transformer which charges the condenser is operated by currents of very low frequency. in such a case the number of the fundamental discharges between the knobs may be so small as to render the currents produced in the secondary unsuitable for many experiments. the intense magnetic field then serves to blow out the arc between the knobs as soon as it is formed, and the fundamental discharges occur in quicker succession. instead of the magnet, a draught or blast of air may be employed with some advantage. in this case the arc is preferably established between the knobs ab, in fig. 2 (the knobs ab being generally joined, or entirely done away with), as in this disposition the arc is long and unsteady, and is easily affected by the draught. when a magnet is employed to break the arc, it is better to choose the connection indicated diagrammatically in fig. 5, as in this case the currents forming the arc are much more powerful, and the magnetic field exercises a greater influence. the use of the magnet permits, however, of the arc being replaced by a vacuum tube, but i have encountered great difficulties in working with an exhausted tube. [illustration: fig. 5.--arrangement with low-frequency alternator and improved discharger.] [illustration: fig. 6.--discharger with multiple gaps.] the other form of discharger used in these and similar experiments is indicated in figs. 6 and 7. it consists of a number of brass pieces cc (fig. 6), each of which comprises a spherical middle portion m with an extension e below--which is merely used to fasten the piece in a lathe when polishing up the discharging surface--and a column above, which consists of a knurled flange f surmounted by a threaded stem l carrying a nut n, by means of which a wire is fastened to the column. the flange f conveniently serves for holding the brass piece when fastening the wire, and also for turning it in any position when it becomes necessary to present a fresh discharging surface. two stout strips of hard rubber rr, with planed grooves gg (fig. 7) to fit the middle portion of the pieces cc, serve to clamp the latter and hold them firmly in position by means of two bolts cc (of which only one is shown) passing through the ends of the strips. [illustration: fig. 7.--discharger with multiple gaps.] in the use of this kind of discharger i have found three principal advantages over the ordinary form. first, the dielectric strength of a given total width of air space is greater when a great many small air gaps are used instead of one, which permits of working with a smaller length of air gap, and that means smaller loss and less deterioration of the metal; secondly by reason of splitting the arc up into smaller arcs, the polished surfaces are made to last much longer; and, thirdly, the apparatus affords some gauge in the experiments. i usually set the pieces by putting between them sheets of uniform thickness at a certain very small distance which is known from the experiments of sir william thomson to require a certain electromotive force to be bridged by the spark. it should, of course, be remembered that the sparking distance is much diminished as the frequency is increased. by taking any number of spaces the experimenter has a rough idea of the electromotive force, and he finds it easier to repeat an experiment, as he has not the trouble of setting the knobs again and again. with this kind of discharger i have been able to maintain an oscillating motion without any spark being visible with the naked eye between the knobs, and they would not show a very appreciable rise in temperature. this form of discharge also lends itself to many arrangements of condensers and circuits which are often very convenient and time-saving. i have used it preferably in a disposition similar to that indicated in fig. 2, when the currents forming the arc are small. i may here mention that i have also used dischargers with single or multiple air gaps, in which the discharge surfaces were rotated with great speed. no particular advantage was, however, gained by this method, except in cases where the currents from the condenser were large and the keeping cool of the surfaces was necessary, and in cases when, the discharge not being oscillating of itself, the arc as soon as established was broken by the air current, thus starting the vibration at intervals in rapid succession. i have also used mechanical interrupters in many ways. to avoid the difficulties with frictional contacts, the preferred plan adopted was to establish the arc and rotate through it at great speed a rim of mica provided with many holes and fastened to a steel plate. it is understood, of course, that the employment of a magnet, air current, or other interrupter, produces no effect worth noticing, unless the self-induction, capacity and resistance are so related that there are oscillations set up upon each interruption. i will now endeavor to show you some of the most noteworthy of these discharge phenomena. i have stretched across the room two ordinary cotton covered wires, each about 7 metres in length. they are supported on insulating cords at a distance of about 30 centimetres. i attach now to each of the terminals of the coil one of the wires and set the coil in action. upon turning the lights off in the room you see the wires strongly illuminated by the streams issuing abundantly from their whole surface in spite of the cotton covering, which may even be very thick. when the experiment is performed under good conditions, the light from the wires is sufficiently intense to allow distinguishing the objects in a room. to produce the best result it is, of course, necessary to adjust carefully the capacity of the jars, the arc between the knobs and the length of the wires. my experience is that calculation of the length of the wires leads, in such case, to no result whatever. the experimenter will do best to take the wires at the start very long, and then adjust by cutting off first long pieces, and then smaller and smaller ones as he approaches the right length. a convenient way is to use an oil condenser of very small capacity, consisting of two small adjustable metal plates, in connection with this and similar experiments. in such case i take wires rather short and set at the beginning the condenser plates at maximum distance. if the streams for the wires increase by approach of the plates, the length of the wires is about right; if they diminish the wires are too long for that frequency and potential. when a condenser is used in connection with experiments with such a coil, it should be an oil condenser by all means, as in using an air condenser considerable energy might be wasted. the wires leading to the plates in the oil should be very thin, heavily coated with some insulating compound, and provided with a conducting covering--this preferably extending under the surface of the oil. the conducting cover should not be too near the terminals, or ends, of the wire, as a spark would be apt to jump from the wire to it. the conducting coating is used to diminish the air losses, in virtue of its action as an electrostatic screen. as to the size of the vessel containing the oil, and the size of the plates, the experimenter gains at once an idea from a rough trial. the size of the plates _in oil_ is, however, calculable, as the dielectric losses are very small. in the preceding experiment it is of considerable interest to know what relation the quantity of the light emitted bears to the frequency and potential of the electric impulses. my opinion is that the heat as well as light effects produced should be proportionate, under otherwise equal conditions of test, to the product of frequency and square of potential, but the experimental verification of the law, whatever it may be, would be exceedingly difficult. one thing is certain, at any rate, and that is, that in augmenting the potential and frequency we rapidly intensify the streams; and, though it may be very sanguine, it is surely not altogether hopeless to expect that we may succeed in producing a practical illuminant on these lines. we would then be simply using burners or flames, in which there would be no chemical process, no consumption of material, but merely a transfer of energy, and which would, in all probability emit more light and less heat than ordinary flames. [illustration: fig. 8.--effect produced by concentrating streams.] the luminous intensity of the streams is, of course, considerably increased when they are focused upon a small surface. this may be shown by the following experiment: i attach to one of the terminals of the coil a wire w (fig. 8), bent in a circle of about 30 centimetres in diameter, and to the other terminal i fasten a small brass sphere s, the surface of the wire being preferably equal to the surface of the sphere, and the centre of the latter being in a line at right angles to the plane of the wire circle and passing through its centre. when the discharge is established under proper conditions, a luminous hollow cone is formed, and in the dark one-half of the brass sphere is strongly illuminated, as shown in the cut. by some artifice or other, it is easy to concentrate the streams upon small surfaces and to produce very strong light effects. two thin wires may thus be rendered intensely luminous. in order to intensify the streams the wires should be very thin and short; but as in this case their capacity would be generally too small for the coil--at least, for such a one as the present--it is necessary to augment the capacity to the required value, while, at the same time, the surface of the wires remains very small. this may be done in many ways. here, for instance, i have two plates, rr, of hard rubber (fig. 9), upon which i have glued two very thin wires ww, so as to form a name. the wires may be bare or covered with the best insulation--it is immaterial for the success of the experiment. well insulated wires, if anything, are preferable. on the back of each plate, indicated by the shaded portion, is a tinfoil coating tt. the plates are placed in line at a sufficient distance to prevent a spark passing from one to the other wire. the two tinfoil coatings i have joined by a conductor c, and the two wires i presently connect to the terminals of the coil. it is now easy, by varying the strength and frequency of the currents through the primary, to find a point at which, the capacity of the system is best suited to the conditions, and the wires become so strongly luminous that, when the light in the room is turned off the name formed by them appears in brilliant letters. [illustration: fig. 9.--wires rendered intensely luminous.] it is perhaps preferable to perform this experiment with a coil operated from an alternator of high frequency, as then, owing to the harmonic rise and fall, the streams are very uniform, though they are less abundant then when produced with such a coil as the present. this experiment, however, may be performed with low frequencies, but much less satisfactorily. [illustration: fig. 10.--luminous discs.] when two wires, attached to the terminals of the coil, are set at the proper distance, the streams between them may be so intense as to produce a continuous luminous sheet. to show this phenomenon i have here two circles, c and c (fig. 10), of rather stout wire, one being about 80 centimetres and the other 30 centimetres in diameter. to each of the terminals of the coil i attach one of the circles. the supporting wires are so bent that the circles may be placed in the same plane, coinciding as nearly as possible. when the light in the room is turned off and the coil set to work, you see the whole space between the wires uniformly filled with streams, forming a luminous disc, which could be seen from a considerable distance, such is the intensity of the streams. the outer circle could have been much larger than the present one; in fact, with this coil i have used much larger circles, and i have been able to produce a strongly luminous sheet, covering an area of more than one square metre, which is a remarkable effect with this very small coil. to avoid uncertainty, the circle has been taken smaller, and the area is now about 0.43 square metre. the frequency of the vibration, and the quickness of succession of the sparks between the knobs, affect to a marked degree the appearance of the streams. when the frequency is very low, the air gives way in more or less the same manner, as by a steady difference of potential, and the streams consist of distinct threads, generally mingled with thin sparks, which probably correspond to the successive discharges occurring between the knobs. but when the frequency is extremely high, and the arc of the discharge produces a very _loud_ but _smooth_ sound--showing both that oscillation takes place and that the sparks succeed each other with great rapidity--then the luminous streams formed are perfectly uniform. to reach this result very small coils and jars of small capacity should be used. i take two tubes of thick bohemian glass, about 5 centimetres in diameter and 20 centimetres long. in each of the tubes i slip a primary of very thick copper wire. on the top of each tube i wind a secondary of much thinner gutta-percha covered wire. the two secondaries i connect in series, the primaries preferably in multiple arc. the tubes are then placed in a large glass vessel, at a distance of 10 to 15 centimetres from each other, on insulating supports, and the vessel is filled with boiled out oil, the oil reaching about an inch above the tubes. the free ends of the secondary are lifted out of the oil and placed parallel to each other at a distance of about 10 centimetres. the ends which are scraped should be dipped in the oil. two four-pint jars joined in series may be used to discharge through the primary. when the necessary adjustments in the length and distance of the wires above the oil and in the arc of discharge are made, a luminous sheet is produced between the wires which is perfectly smooth and textureless, like the ordinary discharge through a moderately exhausted tube. i have purposely dwelt upon this apparently insignificant experiment. in trials of this kind the experimenter arrives at the startling conclusion that, to pass ordinary luminous discharges through gases, no particular degree of exhaustion is needed, but that the gas may be at ordinary or even greater pressure. to accomplish this, a very high frequency is essential; a high potential is likewise required, but this is a merely incidental necessity. these experiments teach us that, in endeavoring to discover novel methods of producing light by the agitation of atoms, or molecules, of a gas, we need not limit our research to the vacuum tube, but may look forward quite seriously to the possibility of obtaining the light effects without the use of any vessel whatever, with air at ordinary pressure. such discharges of very high frequency, which render luminous the air at ordinary pressures, we have probably often occasion to witness in nature. i have no doubt that if, as many believe, the aurora borealis is produced by sudden cosmic disturbances, such as eruptions at the sun's surface, which set the electrostatic charge of the earth in an extremely rapid vibration, the red glow observed is not confined to the upper rarefied strata of the air, but the discharge traverses, by reason of its very high frequency, also the dense atmosphere in the form of a _glow_, such as we ordinarily produce in a slightly exhausted tube. if the frequency were very low, or even more so, if the charge were not at all vibrating, the dense air would break down as in a lightning discharge. indications of such breaking down of the lower dense strata of the air have been repeatedly observed at the occurrence of this marvelous phenomenon; but if it does occur, it can only be attributed to the fundamental disturbances, which are few in number, for the vibration produced by them would be far too rapid to allow a disruptive break. it is the original and irregular impulses which affect the instruments; the superimposed vibrations probably pass unnoticed. when an ordinary low frequency discharge is passed through moderately rarefied air, the air assumes a purplish hue. if by some means or other we increase the intensity of the molecular, or atomic, vibration, the gas changes to a white color. a similar change occurs at ordinary pressures with electric impulses of very high frequency. if the molecules of the air around a wire are moderately agitated, the brush formed is reddish or violet; if the vibration is rendered sufficiently intense, the streams become white. we may accomplish this in various ways. in the experiment before shown with the two wires across the room, i have endeavored to secure the result by pushing to a high value both the frequency and potential: in the experiment with the thin wires glued on the rubber plate i have concentrated the action upon a very small surface--in other words, i have worked with a great electric density. a most curious form of discharge is observed with such a coil when the frequency and potential are pushed to the extreme limit. to perform the experiment, every part of the coil should be heavily insulated, and only two small spheres--or, better still, two sharp-edged metal discs (dd, fig. 11) of no more than a few centimetres in diameter--should be exposed to the air. the coil here used is immersed in oil, and the ends of the secondary reaching out of the oil are covered with an air-tight cover of hard rubber of great thickness. all cracks, if there are any, should be carefully stopped up, so that the brush discharge cannot form anywhere except on the small spheres or plates which are exposed to the air. in this case, since there are no large plates or other bodies of capacity attached to the terminals, the coil is capable of an extremely rapid vibration. the potential may be raised by increasing, as far as the experimenter judges proper, the rate of change of the primary current. with a coil not widely differing from the present, it is best to connect the two primaries in multiple arc; but if the secondary should have a much greater number of turns the primaries should preferably be used in series, as otherwise the vibration might be too fast for the secondary. it occurs under these conditions that misty white streams break forth from the edges of the discs and spread out phantom-like into space. with this coil, when fairly well produced, they are about 25 to 30 centimetres long. when the hand is held against them no sensation is produced, and a spark, causing a shock, jumps from the terminal only upon the hand being brought much nearer. if the oscillation of the primary current is rendered intermittent by some means or other, there is a corresponding throbbing of the streams, and now the hand or other conducting object may be brought in still greater proximity to the terminal without a spark being caused to jump. [illustration: fig. 11.--phantom streams.] among the many beautiful phenomena which may be produced with such a coil i have here selected only those which appear to possess some features of novelty, and lead us to some conclusions of interest. one will not find it at all difficult to produce in the laboratory, by means of it, many other phenomena which appeal to the eye even more than these here shown, but present no particular feature of novelty. early experimenters describe the display of sparks produced by an ordinary large induction coil upon an insulating plate separating the terminals. quite recently siemens performed some experiments in which fine effects were obtained, which were seen by many with interest. no doubt large coils, even if operated with currents of low frequencies, are capable of producing beautiful effects. but the largest coil ever made could not, by far, equal the magnificent display of streams and sparks obtained from such a disruptive discharge coil when properly adjusted. to give an idea, a coil such as the present one will cover easily a plate of 1 metre in diameter completely with the streams. the best way to perform such experiments is to take a very thin rubber or a glass plate and glue on one side of it a narrow ring of tinfoil of very large diameter, and on the other a circular washer, the centre of the latter coinciding with that of the ring, and the surfaces of both being preferably equal, so as to keep the coil well balanced. the washer and ring should be connected to the terminals by heavily insulated thin wires. it is easy in observing the effect of the capacity to produce a sheet of uniform streams, or a fine network of thin silvery threads, or a mass of loud brilliant sparks, which completely cover the plate. since i have advanced the idea of the conversion by means of the disruptive discharge, in my paper before the american institute of electrical engineers at the beginning of the past year, the interest excited in it has been considerable. it affords us a means for producing any potentials by the aid of inexpensive coils operated from ordinary systems of distribution, and--what is perhaps more appreciated--it enables us to convert currents of any frequency into currents of any other lower or higher frequency. but its chief value will perhaps be found in the help which it will afford us in the investigations of the phenomena of phosphorescence, which a disruptive discharge coil is capable of exciting in innumerable cases where ordinary coils, even the largest, would utterly fail. considering its probable uses for many practical purposes, and its possible introduction into laboratories for scientific research, a few additional remarks as to the construction of such a coil will perhaps not be found superfluous. it is, of course, absolutely necessary to employ in such a coil wires provided with the best insulation. good coils may be produced by employing wires covered with several layers of cotton, boiling the coil a long time in pure wax, and cooling under moderate pressure. the advantage of such a coil is that it can be easily handled, but it cannot probably give as satisfactory results as a coil immersed in pure oil. besides, it seems that the presence of a large body of wax affects the coil disadvantageously, whereas this does not seem to be the case with oil. perhaps it is because the dielectric losses in the liquid are smaller. i have tried at first silk and cotton covered wires with oil immersion, but i have been gradually led to use gutta-percha covered wires, which proved most satisfactory. gutta-percha insulation adds, of course, to the capacity of the coil, and this, especially if the coil be large, is a great disadvantage when extreme frequencies are desired; but on the other hand, gutta-percha will withstand much more than an equal thickness of oil, and this advantage should be secured at any price. once the coil has been immersed, it should never be taken out of the oil for more than a few hours, else the gutta-percha will crack up and the coil will not be worth half as much as before. gutta-percha is probably slowly attacked by the oil, but after an immersion of eight to nine months i have found no ill effects. i have obtained in commerce two kinds of gutta-percha wire: in one the insulation sticks tightly to the metal, in the other it does not. unless a special method is followed to expel all air, it is much safer to use the first kind. i wind the coil within an oil tank so that all interstices are filled up with the oil. between the layers i use cloth boiled out thoroughly in oil, calculating the thickness according to the difference of potential between the turns. there seems not to be a very great difference whatever kind of oil is used; i use paraffine or linseed oil. to exclude more perfectly the air, an excellent way to proceed, and easily practicable with small coils, is the following: construct a box of hard wood of very thick boards which have been for a long time boiled in oil. the boards should be so joined as to safely withstand the external air pressure. the coil being placed and fastened in position within the box, the latter is closed with a strong lid, and covered with closely fitting metal sheets, the joints of which are soldered very carefully. on the top two small holes are drilled, passing through the metal sheet and the wood, and in these holes two small glass tubes are inserted and the joints made air-tight. one of the tubes is connected to a vacuum pump, and the other with a vessel containing a sufficient quantity of boiled-out oil. the latter tube has a very small hole at the bottom, and is provided with a stopcock. when a fairly good vacuum has been obtained, the stopcock is opened and the oil slowly fed in. proceeding in this manner, it is impossible that any big bubbles, which are the principal danger, should remain between the turns. the air is most completely excluded, probably better than by boiling out, which, however, when gutta-percha coated wires are used, is not practicable. for the primaries i use ordinary line wire with a thick cotton coating. strands of very thin insulated wires properly interlaced would, of course, be the best to employ for the primaries, but they are not to be had. in an experimental coil the size of the wires is not of great importance. in the coil here used the primary is no. 12 and the secondary no. 24 brown & sharpe gauge wire; but the sections may be varied considerably. it would only imply different adjustments; the results aimed at would not be materially affected. i have dwelt at some length upon the various forms of brush discharge because, in studying them, we not only observe phenomena which please our eye, but also afford us food for thought, and lead us to conclusions of practical importance. in the use of alternating currents of very high tension, too much precaution cannot be taken to prevent the brush discharge. in a main conveying such currents, in an induction coil or transformer, or in a condenser, the brush discharge is a source of great danger to the insulation. in a condenser especially the gaseous matter must be most carefully expelled, for in it the charged surfaces are near each other, and if the potentials are high, just as sure as a weight will fall if let go, so the insulation will give way if a single gaseous bubble of some size be present, whereas, if all gaseous matter were carefully excluded, the condenser would safely withstand a much higher difference of potential. a main conveying alternating currents of very high tension may be injured merely by a blow hole or small crack in the insulation, the more so as a blowhole is apt to contain gas at low pressure; and as it appears almost impossible to completely obviate such little imperfections, i am led to believe that in our future distribution of electrical energy by currents of very high tension liquid insulation will be used. the cost is a great drawback, but if we employ an oil as an insulator the distribution of electrical energy with something like 100,000 volts, and even more, become, at least with higher frequencies, so easy that they could be hardly called engineering feats. with oil insulation and alternate current motors transmissions of power can be effected with safety and upon an industrial basis at distances of as much as a thousand miles. a peculiar property of oils, and liquid insulation in general, when subjected to rapidly changing electric stresses, is to disperse any gaseous bubbles which may be present, and diffuse them through its mass, generally long before any injurious break can occur. this feature may be easily observed with an ordinary induction coil by taking the primary out, plugging up the end of the tube upon which the secondary is wound, and filling it with some fairly transparent insulator, such as paraffine oil. a primary of a diameter something like six millimetres smaller than the inside of the tube may be inserted in the oil. when the coil is set to work one may see, looking from the top through the oil, many luminous points--air bubbles which are caught by inserting the primary, and which are rendered luminous in consequence of the violent bombardment. the occluded air, by its impact against the oil, heats it; the oil begins to circulate, carrying some of the air along with it, until the bubbles are dispersed and the luminous points disappear. in this manner, unless large bubbles are occluded in such way that circulation is rendered impossible, a damaging break is averted, the only effect being a moderate warming up of the oil. if, instead of the liquid, a solid insulation, no matter how thick, were used, a breaking through and injury of the apparatus would be inevitable. the exclusion of gaseous matter from any apparatus in which the dielectric is subjected to more or less rapidly changing electric forces is, however, not only desirable in order to avoid a possible injury of the apparatus, but also on account of economy. in a condenser, for instance, as long as only a solid or only a liquid dielectric is used, the loss is small; but if a gas under ordinary or small pressure be present the loss may be very great. whatever the nature of the force acting in the dielectric may be, it seems that in a solid or liquid the molecular displacement produced by the force is small; hence the product of force and displacement is insignificant, unless the force be very great; but in a gas the displacement, and therefore this product, is considerable; the molecules are free to move, they reach high speeds, and the energy of their impact is lost in heat or otherwise. if the gas be strongly compressed, the displacement due to the force is made smaller, and the losses are reduced. in most of the succeeding experiments i prefer, chiefly on account of the regular and positive action, to employ the alternator before referred to. this is one of the several machines constructed by me for the purposes of these investigations. it has 384 pole projections, and is capable of giving currents of a frequency of about 10,000 per second. this machine has been illustrated and briefly described in my first paper before the american institute of electrical engineers, may 20, 1891, to which i have already referred. a more detailed description, sufficient to enable any engineer to build a similar machine, will be found in several electrical journals of that period. the induction coils operated from the machine are rather small, containing from 5,000 to 15,000 turns in the secondary. they are immersed in boiled-out linseed oil, contained in wooden boxes covered with zinc sheet. i have found it advantageous to reverse the usual position of the wires, and to wind, in these coils, the primaries on the top; this allowing the use of a much bigger primary, which, of course, reduces the danger of overheating and increases the output of the coil. i make the primary on each side at least one centimetre shorter than the secondary, to prevent the breaking through on the ends, which would surely occur unless the insulation on the top of the secondary be very thick, and this, of course, would be disadvantageous. when the primary is made movable, which is necessary in some experiments, and many times convenient for the purposes of adjustment, i cover the secondary with wax, and turn it off in a lathe to a diameter slightly smaller than the inside of the primary coil. the latter i provide with a handle reaching out of the oil, which serves to shift it in any position along the secondary. i will now venture to make, in regard to the general manipulation of induction coils, a few observations bearing upon points which have not been fully appreciated in earlier experiments with such coils, and are even now often overlooked. the secondary of the coil possesses usually such a high self-induction that the current through the wire is inappreciable, and may be so even when the terminals are joined by a conductor of small resistance. if capacity is added to the terminals, the self-induction is counteracted, and a stronger current is made to flow through the secondary, though its terminals are insulated from each other. to one entirely unacquainted with the properties of alternating currents nothing will look more puzzling. this feature was illustrated in the experiment performed at the beginning with the top plates of wire gauze attached to the terminals and the rubber plate. when the plates of wire gauze were close together, and a small arc passed between them, the arc _prevented_ a strong current from passing through the secondary, because it did away with the capacity on the terminals; when the rubber plate was inserted between, the capacity of the condenser formed counteracted the self-induction of the secondary, a stronger current passed now, the coil performed more work, and the discharge was by far more powerful. the first thing, then, in operating the induction coil is to combine capacity with the secondary to overcome the self-induction. if the frequencies and potentials are very high gaseous matter should be carefully kept away from the charged surfaces. if leyden jars are used, they should be immersed in oil, as otherwise considerable dissipation may occur if the jars are greatly strained. when high frequencies are used, it is of equal importance to combine a condenser with the primary. one may use a condenser connected to the ends of the primary or to the terminals of the alternator, but the latter is not to be recommended, as the machine might be injured. the best way is undoubtedly to use the condenser in series with the primary and with the alternator, and to adjust its capacity so as to annul the self-induction of both the latter. the condenser should be adjustable by very small steps, and for a finer adjustment a small oil condenser with movable plates may be used conveniently. i think it best at this juncture to bring before you a phenomenon, observed by me some time ago, which to the purely scientific investigator may perhaps appear more interesting than any of the results which i have the privilege to present to you this evening. it may be quite properly ranked among the brush phenomena--in fact, it is a brush, formed at, or near, a single terminal in high vacuum. in bulbs provided with a conducting terminal, though it be of aluminium, the brush has but an ephemeral existence, and cannot, unfortunately, be indefinitely preserved in its most sensitive state, even in a bulb devoid of any conducting electrode. in studying the phenomenon, by all means a bulb having no leading-in wire should be used. i have found it best to use bulbs constructed as indicated in figs. 12 and 13. in fig. 12 the bulb comprises an incandescent lamp globe l, in the neck of which is sealed a barometer tube b, the end of which is blown out to form a small sphere s. this sphere should be sealed as closely as possible in the centre of the large globe. before sealing, a thin tube t, of aluminium sheet, may be slipped in the barometer tube, but it is not important to employ it. the small hollow sphere s is filled with some conducting powder, and a wire w is cemented in the neck for the purpose of connecting the conducting powder with the generator. [illustration: fig. 12. fig. 13. bulbs for producing rotating brush.] the construction shown in fig. 13 was chosen in order to remove from the brush any conducting body which might possibly affect it. the bulb consists in this case of a lamp globe l, which has a neck n, provided with a tube b and small sphere s, sealed to it, so that two entirely independent compartments are formed, as indicated in the drawing. when the bulb is in use, the neck n is provided with a tinfoil coating, which is connected to the generator and acts inductively upon the moderately rarefied and highly conducting gas inclosed in the neck. from there the current passes through the tube b into the small sphere s to act by induction upon the gas contained in the globe l. it is of advantage to make the tube t very thick, the hole through it very small, and to blow the sphere s very thin. it is of the greatest importance that the sphere s be placed in the centre of the globe l. [illustration: fig. 14.--forms and phases of the rotating brush.] figs. 14, 15 and 16 indicate different forms, or stages, of the brush. fig. 14 shows the brush as it first appears in a bulb provided with a conducting terminal; but, as in such a bulb it very soon disappears--often after a few minutes--i will confine myself to the description of the phenomenon as seen in a bulb without conducting electrode. it is observed under the following conditions: when the globe l (figs. 12 and 13) is exhausted to a very high degree, generally the bulb is not excited upon connecting the wire w (fig. 12) or the tinfoil coating of the bulb (fig. 13) to the terminal of the induction coil. to excite it, it is usually sufficient to grasp the globe l with the hand. an intense phosphorescence then spreads at first over the globe, but soon gives place to a white, misty light. shortly afterward one may notice that the luminosity is unevenly distributed in the globe, and after passing the current for some time the bulb appears as in fig. 15. from this stage the phenomenon will gradually pass to that indicated in fig. 16, after some minutes, hours, days or weeks, according as the bulb is worked. warming the bulb or increasing the potential hastens the transit. [illustration: fig. 15. fig. 16. forms and phases of the rotating brush.] when the brush assumes the form indicated in fig. 16, it maybe brought to a state of extreme sensitiveness to electrostatic and magnetic influence. the bulb hanging straight down from a wire, and all objects being remote from it, the approach of the observer at a few paces from the bulb will cause the brush to fly to the opposite side, and if he walks around the bulb it will always keep on the opposite side. it may begin to spin around the terminal long before it reaches that sensitive stage. when it begins to turn around principally, but also before, it is affected by a magnet, and at a certain stage it is susceptible to magnetic influence to an astonishing degree. a small permanent magnet, with its poles at a distance of no more than two centimetres, will affect it visibly at a distance of two metres, slowing down or accelerating the rotation according to how it is held relatively to the brush. i think i have observed that at the stage when it is most sensitive to magnetic, it is not most sensitive to electrostatic, influence. my explanation is, that the electrostatic attraction between the brush and the glass of the bulb, which retards the rotation, grows much quicker than the magnetic influence when the intensity of the stream is increased. when the bulb hangs with the globe l down, the rotation is always clockwise. in the southern hemisphere it would occur in the opposite direction and on the equator the brush should not turn at all. the rotation may be reversed by a magnet kept at some distance. the brush rotates best, seemingly, when it is at right angles to the lines of force of the earth. it very likely rotates, when at its maximum speed, in synchronism with the alternations, say 10,000 times a second. the rotation can be slowed down or accelerated by the approach or receding of the observer, or any conducting body, but it cannot be reversed by putting the bulb in any position. when it is in the state of the highest sensitiveness and the potential or frequency be varied the sensitiveness is rapidly diminished. changing either of these but little will generally stop the rotation. the sensitiveness is likewise affected by the variations of temperature. to attain great sensitiveness it is necessary to have the small sphere s in the centre of the globe l, as otherwise the electrostatic action of the glass of the globe will tend to stop the rotation. the sphere s should be small and of uniform thickness; any dissymmetry of course has the effect to diminish the sensitiveness. the fact that the brush rotates in a definite direction in a permanent magnetic field seems to show that in alternating currents of very high frequency the positive and negative impulses are not equal, but that one always preponderates over the other. of course, this rotation in one direction may be due to the action of two elements of the same current upon each other, or to the action of the field produced by one of the elements upon the other, as in a series motor, without necessarily one impulse being stronger than the other. the fact that the brush turns, as far as i could observe, in any position, would speak for this view. in such case it would turn at any point of the earth's surface. but, on the other hand, it is then hard to explain why a permanent magnet should reverse the rotation, and one must assume the preponderance of impulses of one kind. as to the causes of the formation of the brush or stream, i think it is due to the electrostatic action of the globe and the dissymmetry of the parts. if the small bulb s and the globe l were perfect concentric spheres, and the glass throughout of the same thickness and quality, i think the brush would not form, as the tendency to pass would be equal on all sides. that the formation of the stream is due to an irregularity is apparent from the fact that it has the tendency to remain in one position, and rotation occurs most generally only when it is brought out of this position by electrostatic or magnetic influence. when in an extremely sensitive state it rests in one position, most curious experiments may be performed with it. for instance, the experimenter may, by selecting a proper position, approach the hand at a certain considerable distance to the bulb, and he may cause the brush to pass off by merely stiffening the muscles of the arm. when it begins to rotate slowly, and the hands are held at a proper distance, it is impossible to make even the slightest motion without producing a visible effect upon the brush. a metal plate connected to the other terminal of the coil affects it at a great distance, slowing down the rotation often to one turn a second. i am firmly convinced that such a brush, when we learn how to produce it properly, will prove a valuable aid in the investigation of the nature of the forces acting in an electrostatic or magnetic field. if there is any motion which is measurable going on in the space, such a brush ought to reveal it. it is, so to speak, a beam of light, frictionless, devoid of inertia. i think that it may find practical applications in telegraphy. with such a brush it would be possible to send dispatches across the atlantic, for instance, with any speed, since its sensitiveness may be so great that the slightest changes will affect it. if it were possible to make the stream more intense and very narrow, its deflections could be easily photographed. i have been interested to find whether there is a rotation of the stream itself, or whether there is simply a stress traveling around in the bulb. for this purpose i mounted a light mica fan so that its vanes were in the path of the brush. if the stream itself was rotating the fan would be spun around. i could produce no distinct rotation of the fan, although i tried the experiment repeatedly; but as the fan exerted a noticeable influence on the stream, and the apparent rotation of the latter was, in this case, never quite satisfactory, the experiment did not appear to be conclusive. i have been unable to produce the phenomenon with the disruptive discharge coil, although every other of these phenomena can be well produced by it--many, in fact, much better than with coils operated from an alternator. it may be possible to produce the brush by impulses of one direction, or even by a steady potential, in which case it would be still more sensitive to magnetic influence. in operating an induction coil with rapidly alternating currents, we realize with astonishment, for the first time, the great importance of the relation of capacity, self-induction and frequency as regards the general result. the effects of capacity are the most striking, for in these experiments, since the self-induction and frequency both are high, the critical capacity is very small, and need be but slightly varied to produce a very considerable change. the experimenter may bring his body in contact with the terminals of the secondary of the coil, or attach to one or both terminals insulated bodies of very small bulk, such as bulbs, and he may produce a considerable rise or fall of potential, and greatly affect the flow of the current through the primary. in the experiment before shown, in which a brush appears at a wire attached to one terminal, and the wire is vibrated when the experimenter brings his insulated body in contact with the other terminal of the coil, the sudden rise of potential was made evident. i may show you the behavior of the coil in another manner which possesses a feature of some interest. i have here a little light fan of aluminium sheet, fastened to a needle and arranged to rotate freely in a metal piece screwed to one of the terminals of the coil. when the coil is set to work, the molecules of the air are rhythmically attracted and repelled. as the force with which they are repelled is greater than that with which they are attracted, it results that there is a repulsion exerted on the surfaces of the fan. if the fan were made simply of a metal sheet, the repulsion would be equal on the opposite sides, and would produce no effect. but if one of the opposing surfaces is screened, or if, generally speaking, the bombardment on this side is weakened in some way or other, there remains the repulsion exerted upon the other, and the fan is set in rotation. the screening is best effected by fastening upon one of the opposing sides of the fan insulated conducting coatings, or, if the fan is made in the shape of an ordinary propeller screw, by fastening on one side, and close to it, an insulated metal plate. the static screen may, however, be omitted, and simply a thickness of insulating material fastened to one of the sides of the fan. to show the behavior of the coil, the fan may be placed upon the terminal and it will readily rotate when the coil is operated by currents of very high frequency. with a steady potential, of course, and even with alternating currents of very low frequency, it would not turn, because of the very slow exchange of air and, consequently, smaller bombardment; but in the latter case it might turn if the potential were excessive. with a pin wheel, quite the opposite rule holds good; it rotates best with a steady potential, and the effort is the smaller the higher the frequency. now, it is very easy to adjust the conditions so that the potential is normally not sufficient to turn the fan, but that by connecting the other terminal of the coil with an insulated body it rises to a much greater value, so as to rotate the fan, and it is likewise possible to stop the rotation by connecting to the terminal a body of different size, thereby diminishing the potential. instead of using the fan in this experiment, we may use the "electric" radiometer with similar effect. but in this case it will be found that the vanes will rotate only at high exhaustion or at ordinary pressures; they will not rotate at moderate pressures, when the air is highly conducting. this curious observation was made conjointly by professor crookes and myself. i attribute the result to the high conductivity of the air, the molecules of which then do not act as independent carriers of electric charges, but act all together as a single conducting body. in such case, of course, if there is any repulsion at all of the molecules from the vanes, it must be very small. it is possible, however, that the result is in part due to the fact that the greater part of the discharge passes from the leading-in wire through the highly conducting gas, instead of passing off from the conducting vanes. in trying the preceding experiment with the electric radiometer the potential should not exceed a certain limit, as then the electrostatic attraction between the vanes and the glass of the bulb may be so great as to stop the rotation. a most curious feature of alternate currents of high frequencies and potentials is that they enable us to perform many experiments by the use of one wire only. in many respects this feature is of great interest. in a type of alternate current motor invented by me some years ago i produced rotation by inducing, by means of a single alternating current passed through a motor circuit, in the mass or other circuits of the motor, secondary currents, which, jointly with the primary or inducing current, created a moving field of force. a simple but crude form of such a motor is obtained by winding upon an iron core a primary, and close to it a secondary coil, joining the ends of the latter and placing a freely movable metal disc within the influence of the field produced by both. the iron core is employed for obvious reasons, but it is not essential to the operation. to improve the motor, the iron core is made to encircle the armature. again to improve, the secondary coil is made to overlap partly the primary, so that it cannot free itself from a strong inductive action of the latter, repel its lines as it may. once more to improve, the proper difference of phase is obtained between the primary and secondary currents by a condenser, self-induction, resistance or equivalent windings. i had discovered, however, that rotation is produced by means of a single coil and core; my explanation of the phenomenon, and leading thought in trying the experiment, being that there must be a true time lag in the magnetization of the core. i remember the pleasure i had when, in the writings of professor ayrton, which came later to my hand, i found the idea of the time lag advocated. whether there is a true time lag, or whether the retardation is due to eddy currents circulating in minute paths, must remain an open question, but the fact is that a coil wound upon an iron core and traversed by an alternating current creates a moving field of force, capable of setting an armature in rotation. it is of some interest, in conjunction with the historical arago experiment, to mention that in lag or phase motors i have produced rotation in the opposite direction to the moving field, which means that in that experiment the magnet may not rotate, or may even rotate in the opposite direction to the moving disc. here, then, is a motor (diagrammatically illustrated in fig. 17), comprising a coil and iron core, and a freely movable copper disc in proximity to the latter. [illustration: fig. 17.--single wire and "no-wire" motor.] to demonstrate a novel and interesting feature, i have, for a reason which i will explain, selected this type of motor. when the ends of the coil are connected to the terminals of an alternator the disc is set in rotation. but it is not this experiment, now well known, which i desire to perform. what i wish to show you is that this motor rotates with _one single_ connection between it and the generator; that is to say, one terminal of the motor is connected to one terminal of the generator--in this case the secondary of a high-tension induction coil--the other terminals of motor and generator being insulated in space. to produce rotation it is generally (but not absolutely) necessary to connect the free end of the motor coil to an insulated body of some size. the experimenter's body is more than sufficient. if he touches the free terminal with an object held in the hand, a current passes through the coil and the copper disc is set in rotation. if an exhausted tube is put in series with the coil, the tube lights brilliantly, showing the passage of a strong current. instead of the experimenter's body, a small metal sheet suspended on a cord may be used with the same result. in this case the plate acts as a condenser in series with the coil. it counteracts the self-induction of the latter and allows a strong current to pass. in such a combination, the greater the self-induction of the coil the smaller need be the plate, and this means that a lower frequency, or eventually a lower potential, is required to operate the motor. a single coil wound upon a core has a high self-induction; for this reason principally, this type of motor was chosen to perform the experiment. were a secondary closed coil wound upon the core, it would tend to diminish the self-induction, and then it would be necessary to employ a much higher frequency and potential. neither would be advisable, for a higher potential would endanger the insulation of the small primary coil, and a higher frequency would result in a materially diminished torque. it should be remarked that when such a motor with a closed secondary is used, it is not at all easy to obtain rotation with excessive frequencies, as the secondary cuts off almost completely the lines of the primary--and this, of course, the more, the higher the frequency--and allows the passage of but a minute current. in such a case, unless the secondary is closed through a condenser, it is almost essential, in order to produce rotation, to make the primary and secondary coils overlap each other more or less. but there is an additional feature of interest about this motor, namely, it is not necessary to have even a single connection between the motor and generator, except, perhaps, through the ground: for not only is an insulated plate capable of giving off energy into space, but it is likewise capable of deriving it from an alternating electrostatic field, though in the latter case the available energy is much smaller. in this instance one of the motor terminals is connected to the insulated plate or body located within the alternating electrostatic field, and the other terminal preferably to the ground. it is quite possible, however, that such "no-wire" motors, as they might be called, could be operated by conduction through the rarefied air at considerable distances. alternate currents, especially of high frequencies, pass with astonishing freedom through even slightly rarefied gases. the upper strata of the air are rarefied. to reach a number of miles out into space requires the overcoming of difficulties of a merely mechanical nature. there is no doubt that with the enormous potentials obtainable by the use of high frequencies and oil insulation luminous discharges might be passed through many miles of rarefied air, and that, by thus directing the energy of many hundreds or thousands of horse-power, motors or lamps might be operated at considerable distances from stationary sources. but such schemes are mentioned merely as possibilities. we shall have no need to transmit power in this way. we shall have no need to _transmit_ power at all. ere many generations pass, our machinery will be driven by a power obtainable at any point of the universe. this idea is not novel. men have been led to it long ago by instinct or reason. it has been expressed in many ways, and in many places, in the history of old and new. we find it in the delightful myth of antheus, who derives power from the earth; we find it among the subtile speculations of one of your splendid mathematicians, and in many hints and statements of thinkers of the present time. throughout space there is energy. is this energy static or kinetic? if static our hopes are in vain; if kinetic--and this we know it is, for certain--then it is a mere question of time when men will succeed in attaching their machinery to the very wheelwork of nature. of all, living or dead, crookes came nearest to doing it. his radiometer will turn in the light of day and in the darkness of the night; it will turn everywhere where there is heat, and heat is everywhere. but, unfortunately, this beautiful little machine, while it goes down to posterity as the most interesting, must likewise be put on record as the most inefficient machine ever invented! the preceding experiment is only one of many equally interesting experiments which may be performed by the use of only one wire with alternate currents of high potential and frequency. we may connect an insulated line to a source of such currents, we may pass an inappreciable current over the line, and on any point of the same we are able to obtain a heavy current, capable of fusing a thick copper wire. or we may, by the help of some artifice, decompose a solution in any electrolytic cell by connecting only one pole of the cell to the line or source of energy. or we may, by attaching to the line, or only bringing into its vicinity, light up an incandescent lamp, an exhausted tube, or a phosphorescent bulb. however impracticable this plan of working may appear in many cases, it certainly seems practicable, and even recommendable, in the production of light. a perfected lamp would require but little energy, and if wires were used at all we ought to be able to supply that energy without a return wire. it is now a fact that a body may be rendered incandescent or phosphorescent by bringing it either in single contact or merely in the vicinity of a source of electric impulses of the proper character, and that in this manner a quantity of light sufficient to afford a practical illuminant may be produced. it is, therefore, to say the least, worth while to attempt to determine the best conditions and to invent the best appliances for attaining this object. some experiences have already been gained in this direction, and i will dwell on them briefly, in the hope that they might prove useful. the heating of a conducting body inclosed in a bulb, and connected to a source of rapidly alternating electric impulses, is dependent on so many things of a different nature, that it would be difficult to give a generally applicable rule under which the maximum heating occurs. as regards the size of the vessel, i have lately found that at ordinary or only slightly differing atmospheric pressures, when air is a good insulator, and hence practically the same amount of energy by a certain potential and frequency is given off from the body, whether the bulb be small or large, the body is brought to a higher temperature if inclosed in a small bulb, because of the better confinement of heat in this case. at lower pressures, when air becomes more or less conducting, or if the air be sufficiently warmed as to become conducting, the body is rendered more intensely incandescent in a large bulb, obviously because, under otherwise equal conditions of test, more energy may be given off from the body when the bulb is large. at very high degrees of exhaustion, when the matter in the bulb becomes "radiant," a large bulb has still an advantage, but a comparatively slight one, over the small bulb. finally, at excessively high degrees of exhaustion, which cannot be reached except by the employment of special means, there seems to be, beyond a certain and rather small size of vessel, no perceptible difference in the heating. these observations were the result of a number of experiments, of which one, showing the effect of the size of the bulb at a high degree of exhaustion, may be described and shown here, as it presents a feature of interest. three spherical bulbs of 2 inches, 3 inches and 4 inches diameter were taken, and in the centre of each was mounted an equal length of an ordinary incandescent lamp filament of uniform thickness. in each bulb the piece of filament was fastened to the leading-in wire of platinum, contained in a glass stem sealed in the bulb; care being taken, of course, to make everything as nearly alike as possible. on each glass stem in the inside of the bulb was slipped a highly polished tube made of aluminium sheet, which fitted the stem and was held on it by spring pressure. the function of this aluminium tube will be explained subsequently. in each bulb an equal length of filament protruded above the metal tube. it is sufficient to say now that under these conditions equal lengths of filament of the same thickness--in other words, bodies of equal bulk--were brought to incandescence. the three bulbs were sealed to a glass tube, which was connected to a sprengel pump. when a high vacuum had been reached, the glass tube carrying the bulbs was sealed off. a current was then turned on successively on each bulb, and it was found that the filaments came to about the same brightness, and, if anything, the smallest bulb, which was placed midway between the two larger ones, may have been slightly brighter. this result was expected, for when either of the bulbs was connected to the coil the luminosity spread through the other two, hence the three bulbs constituted really one vessel. when all the three bulbs were connected in multiple arc to the coil, in the largest of them the filament glowed brightest, in the next smaller it was a little less bright, and in the smallest it only came to redness. the bulbs were then sealed off and separately tried. the brightness of the filaments was now such as would have been expected on the supposition that the energy given off was proportionate to the surface of the bulb, this surface in each case representing one of the coatings of a condenser. accordingly, time was less difference between the largest and the middle sized than between the latter and the smallest bulb. an interesting observation was made in this experiment. the three bulbs were suspended from a straight bare wire connected to a terminal of the coil, the largest bulb being placed at the end of the wire, at some distance from it the smallest bulb, and an equal distance from the latter the middle-sized one. the carbons glowed then in both the larger bulbs about as expected, but the smallest did not get its share by far. this observation led me to exchange the position of the bulbs, and i then observed that whichever of the bulbs was in the middle it was by far less bright than it was in any other position. this mystifying result was, of course, found to be due to the electrostatic action between the bulbs. when they were placed at a considerable distance, or when they were attached to the corners of an equilateral triangle of copper wire, they glowed about in the order determined by their surfaces. as to the shape of the vessel, it is also of some importance, especially at high degrees of exhaustion. of all the possible constructions, it seems that a spherical globe with the refractory body mounted in its centre is the best to employ. in experience it has been demonstrated that in such a globe a refractory body of a given bulk is more easily brought to incandescence than when otherwise shaped bulbs are used. there is also an advantage in giving to the incandescent body the shape of a sphere, for self-evident reasons. in any case the body should be mounted in the centre, where the atoms rebounding from the glass collide. this object is best attained in the spherical bulb; but it is also attained in a cylindrical vessel with one or two straight filaments coinciding with its axis, and possibly also in parabolical or spherical bulbs with the refractory body or bodies placed in the focus or foci of the same; though the latter is not probable, as the electrified atoms should in all cases rebound normally from the surface they strike, unless the speed were excessive, in which case they _would_ probably follow the general law of reflection. no matter what shape the vessel may have, if the exhaustion be low, a filament mounted in the globe is brought to the same degree of incandescence in all parts; but if the exhaustion be high and the bulb be spherical or pear-shaped, as usual, focal points form and the filament is heated to a higher degree at or near such points. to illustrate the effect, i have here two small bulbs which are alike, only one is exhausted to a low and the other to a very high degree. when connected to the coil, the filament in the former glows uniformly throughout all its length; whereas in the latter, that portion of the filament which is in the centre of the bulb glows far more intensely than the rest. a curious point is that the phenomenon occurs even if two filaments are mounted in a bulb, each being connected to one terminal of the coil, and, what is still more curious, if they be very near together, provided the vacuum be very high. i noted in experiments with such bulbs that the filaments would give way usually at a certain point, and in the first trials i attributed it to a defect in the carbon. but when the phenomenon occurred many times in succession i recognized its real cause. in order to bring a refractory body inclosed in a bulb to incandescence, it is desirable, on account of economy, that all the energy supplied to the bulb from the source should reach without loss the body to be heated; from there, and from nowhere else, it should be radiated. it is, of course, out of the question to reach this theoretical result, but it is possible by a proper construction of the illuminating device to approximate it more or less. for many reasons, the refractory body is placed in the centre of the bulb, and it is usually supported on a glass stem containing the leading-in wire. as the potential of this wire is alternated, the rarefied gas surrounding the stem is acted upon inductively, and the glass stem is violently bombarded and heated. in this manner by far the greater portion of the energy supplied to the bulb--especially when exceedingly high frequencies are used--may be lost for the purpose contemplated. to obviate this loss, or at least to reduce it to a minimum, i usually screen the rarefied gas surrounding the stem from the inductive action of the leading-in wire by providing the stem with a tube or coating of conducting material. it seems beyond doubt that the best among metals to employ for this purpose is aluminium, on account of its many remarkable properties. its only fault is that it is easily fusible, and, therefore, its distance from the incandescing body should be properly estimated. usually, a thin tube, of a diameter somewhat smaller than that of the glass stem, is made of the finest aluminium sheet, and slipped on the stem. the tube is conveniently prepared by wrapping around a rod fastened in a lathe a piece of aluminium sheet of the proper size, grasping the sheet firmly with clean chamois leather or blotting paper, and spinning the rod very fast. the sheet is wound tightly around the rod, and a highly polished tube of one or three layers of the sheet is obtained. when slipped on the stem, the pressure is generally sufficient to prevent it from slipping off, but, for safety, the lower edge of the sheet may be turned inside. the upper inside corner of the sheet--that is, the one which is nearest to the refractory incandescent body--should be cut out diagonally, as it often happens that, in consequence of the intense heat, this corner turns toward the inside and comes very near to, or in contact with, the wire, or filament, supporting the refractory body. the greater part of the energy supplied to the bulb is then used up in heating the metal tube, and the bulb is rendered useless for the purpose. the aluminium sheet should project above the glass stem more or less--one inch or so--or else, if the glass be too close to the incandescing body, it may be strongly heated and become more or less conducting, whereupon it may be ruptured, or may, by its conductivity, establish a good electrical connection between the metal tube and the leading-in wire, in which case, again, most of the energy will be lost in heating the former. perhaps the best way is to make the top of the glass tube, for about an inch, of a much smaller diameter. to still further reduce the danger arising from the heating of the glass stem, and also with the view of preventing an electrical connection between the metal tube and the electrode, i preferably wrap the stem with several layers of thin mica, which extends at least as far as the metal tube. in some bulbs i have also used an outside insulating cover. the preceding remarks are only made to aid the experimenter in the first trials, for the difficulties which he encounters he may soon find means to overcome in his own way. to illustrate the effect of the screen, and the advantage of using it, i have here two bulbs of the same size, with their stems, leading-in wires and incandescent lamp filaments tied to the latter, as nearly alike as possible. the stem of one bulb is provided with an aluminium tube, the stem of the other has none. originally the two bulbs were joined by a tube which was connected to a sprengel pump. when a high vacuum had been reached, first the connecting tube, and then the bulbs, were sealed off; they are therefore of the same degree of exhaustion. when they are separately connected to the coil giving a certain potential, the carbon filament in the bulb provided with the aluminium screen is rendered highly incandescent, while the filament in the other bulb may, with the same potential, not even come to redness, although in reality the latter bulb takes generally more energy than the former. when they are both connected together to the terminal, the difference is even more apparent, showing the importance of the screening. the metal tube placed on the stem containing the leading-in wire performs really two distinct functions: first: it acts more or less as an electrostatic screen, thus economizing the energy supplied to the bulb; and, second, to whatever extent it may fail to act electrostatically, it acts mechanically, preventing the bombardment, and consequently intense heating and possible deterioration of the slender support of the refractory incandescent body, or of the glass stem containing the leading-in wire. i say _slender_ support, for it is evident that in order to confine the heat more completely to the incandescing body its support should be very thin, so as to carry away the smallest possible amount of heat by conduction. of all the supports used i have found an ordinary incandescent lamp filament to be the best, principally because among conductors it can withstand the highest degrees of heat. the effectiveness of the metal tube as an electrostatic screen depends largely on the degree of exhaustion. at excessively high degrees of exhaustion--which are reached by using great care and special means in connection with the sprengel pump--when the matter in the globe is in the ultra-radiant state, it acts most perfectly. the shadow of the upper edge of the tube is then sharply defined upon the bulb. at a somewhat lower degree of exhaustion, which is about the ordinary "non-striking" vacuum, and generally as long as the matter moves predominantly in straight lines, the screen still does well. in elucidation of the preceding remark it is necessary to state that what is a "non-striking" vacuum for a coil operated, as ordinarily, by impulses, or currents, of low-frequency, is not, by far, so when the coil is operated by currents of very high frequency. in such case the discharge may pass with great freedom through the rarefied gas through which a low-frequency discharge may not pass, even though the potential be much higher. at ordinary atmospheric pressures just the reverse rule holds good: the higher the frequency, the less the spark discharge is able to jump between the terminals, especially if they are knobs or spheres of some size. finally, at very low degrees of exhaustion, when the gas is well conducting, the metal tube not only does not act as an electrostatic screen, but even is a drawback, aiding to a considerable extent the dissipation of the energy laterally from the leading-in wire. this, of course, is to be expected. in this case, namely, the metal tube is in good electrical connection with the leading-in wire, and most of the bombardment is directed upon the tube. as long as the electrical connection is not good, the conducting tube is always of some advantage, for although it may not greatly economize energy, still it protects the support of the refractory button, and is a means for concentrating more energy upon the same. to whatever extent the aluminium tube performs the function of a screen, its usefulness is therefore limited to very high degrees of exhaustion when it is insulated from the electrode--that is, when the gas as a whole is non-conducting, and the molecules, or atoms, act as independent carriers of electric charges. in addition to acting as a more or less effective screen, in the true meaning of the word, the conducting tube or coating may also act, by reason of its conductivity, as a sort of equalizer or dampener of the bombardment against the stem. to be explicit, i assume the action as follows: suppose a rhythmical bombardment to occur against the conducting tube by reason of its imperfect action as a screen, it certainly must happen that some molecules, or atoms, strike the tube sooner than others. those which come first in contact with it give up their superfluous charge, and the tube is electrified, the electrification instantly spreading over its surface. but this must diminish the energy lost in the bombardment for two reasons: first, the charge given up by the atoms spreads over a great area, and hence the electric density at any point is small, and the atoms are repelled with less energy than they would be if they would strike against a good insulator: secondly, as the tube is electrified by the atoms which first come in contact with it, the progress of the following atoms against the tube is more or less checked by the repulsion which the electrified tube must exert upon the similarly electrified atoms. this repulsion may perhaps be sufficient to prevent a large portion of the atoms from striking the tube, but at any rate it must diminish the energy of their impact. it is clear that when the exhaustion is very low, and the rarefied gas well conducting, neither of the above effects can occur, and, on the other hand, the fewer the atoms, with the greater freedom they move; in other words, the higher the degree of exhaustion, up to a limit, the more telling will be both the effects. what i have just said may afford an explanation of the phenomenon observed by prof. crookes, namely, that a discharge through a bulb is established with much greater facility when an insulator than when a conductor is present in the same. in my opinion, the conductor acts as a dampener of the motion of the atoms in the two ways pointed out; hence, to cause a visible discharge to pass through the bulb, a much higher potential is needed if a conductor, especially of much surface, be present. for the sake of clearness of some of the remarks before made, i must now refer to figs. 18, 19 and 20, which illustrate various arrangements with a type of bulb most generally used. [illustration: fig. 18.--bulb with mica tube and aluminium screen.] [illustration: fig. 19.--improved bulb with socket and screen.] fig. 18 is a section through a spherical bulb l, with the glass stem s, containing the leading-in wire w; which has a lamp filament l fastened to it, serving to support the refractory button m in the centre. m is a sheet of thin mica wound in several layers around the stem s, and a is the aluminium tube. fig. 19 illustrates such a bulb in a somewhat more advanced stage of perfection. a metallic tube s is fastened by means of some cement to the neck of the tube. in the tube is screwed a plug p, of insulating material, in the centre of which is fastened a metallic terminal t, for the connection to the leading-in wire w. this terminal must be well insulated from the metal tube s, therefore, if the cement used is conducting--and most generally it is sufficiently so--the space between the plug p and the neck of the bulb should be filled with some good insulating material, as mica powder. [illustration: fig. 20.--bulb for experiments with conducting tube.] fig. 20 shows a bulb made for experimental purposes. in this bulb the aluminium tube is provided with an external connection, which serves to investigate the effect of the tube under various conditions. it is referred to chiefly to suggest a line of experiment followed. since the bombardment against the stem containing the leading-in wire is due to the inductive action of the latter upon the rarefied gas, it is of advantage to reduce this action as far as practicable by employing a very thin wire, surrounded by a very thick insulation of glass or other material, and by making the wire passing through the rarefied gas as short as practicable. to combine these features i employ a large tube t (fig. 21), which protrudes into the bulb to some distance, and carries on the top a very short glass stem s, into which is sealed the leading-in wire w, and i protect the top of the glass stem against the heat by a small, aluminium tube a and a layer of mica underneath the same, as usual. the wire w, passing through the large tube to the outside of the bulb, should be well insulated--with a glass tube, for instance--and the space between ought to be filled out with some excellent insulator. among many insulating powders i have tried, i have found that mica powder is the best to employ. if this precaution is not taken, the tube t, protruding into the bulb, will surely be cracked in consequence of the heating by the brushes which are apt to form in the upper part of the tube, near the exhausted globe, especially if the vacuum be excellent, and therefore the potential necessary to operate the lamp very high. fig. 22 illustrates a similar arrangement, with a large tube t protruding in to the part of the bulb containing the refractors button m. in this case the wire leading from the outside into the bulb is omitted, the energy required being supplied through condenser coatings cc. the insulating packing p should in this construction be tightly fitting to the glass, and rather wide, or otherwise the discharge might avoid passing through the wire w, which connects the inside condenser coating to the incandescent button m. the molecular bombardment against the glass stem in the bulb is a source of great trouble. as illustration i will cite a phenomenon only too frequently and unwillingly observed. a bulb, preferably a large one, may be taken, and a good conducting body, such as a piece of carbon, may be mounted in it upon a platinum wire sealed in the glass stem. the bulb may be exhausted to a fairly high degree, nearly to the point when phosphorescence begins to appear. [illustration: fig. 21.--improved bulb with non-conducting button.] [illustration: fig. 22.--type of bulb without leading-in wire.] when the bulb is connected with the coil, the piece of carbon, if small, may become highly incandescent at first, but its brightness immediately diminishes, and then the discharge may break through the glass somewhere in the middle of the stem, in the form of bright sparks, in spite of the fact that the platinum wire is in good electrical connection with the rarefied gas through the piece of carbon or metal at the top. the first sparks are singularly bright, recalling those drawn from a clear surface of mercury. but, as they heat the glass rapidly, they, of course, lose their brightness, and cease when the glass at the ruptured place becomes incandescent, or generally sufficiently hot to conduct. when observed for the first time the phenomenon must appear very curious, and shows in a striking manner how radically different alternate currents, or impulses, of high frequency behave, as compared with steady currents, or currents of low frequency. with such currents--namely, the latter--the phenomenon would of course not occur. when frequencies such as are obtained by mechanical means are used, i think that the rupture of the glass is more or less the consequence of the bombardment, which warms it up and impairs its insulating power; but with frequencies obtainable with condensers i have no doubt that the glass may give way without previous heating. although this appears most singular at first, it is in reality what we might expect to occur. the energy supplied to the wire leading into the bulb is given off partly by direct action through the carbon button, and partly by inductive action through the glass surrounding the wire. the case is thus analogous to that in which a condenser shunted by a conductor of low resistance is connected to a source of alternating currents. as long as the frequencies are low, the conductor gets the most, and the condenser is perfectly safe: but when the frequency becomes excessive, the _role_ of the conductor may become quite insignificant. in the latter case the difference of potential at the terminals of the condenser may become so great as to rupture the dielectric, notwithstanding the fact that the terminals are joined by a conductor of low resistance. [illustration: fig. 23.--effect produced by a ruby drop.] it is, of course, not necessary, when it is desired to produce the incandescence of a body inclosed in a bulb by means of these currents, that the body should be a conductor, for even a perfect non-conductor may be quite as readily heated. for this purpose it is sufficient to surround a conducting electrode with a non-conducting material, as, for instance, in the bulb described before in fig. 21, in which a thin incandescent lamp filament is coated with a non-conductor, and supports a button of the same material on the top. at the start the bombardment goes on by inductive action through the non-conductor, until the same is sufficiently heated to become conducting, when the bombardment continues in the ordinary way. a different arrangement used in some of the bulbs constructed is illustrated in fig. 23. in this instance a non-conductor m is mounted in a piece of common arc light carbon so as to project some small distance above the latter. the carbon piece is connected to the leading-in wire passing through a glass stem, which is wrapped with several layers of mica. an aluminium tube a is employed as usual for screening. it is so arranged that it reaches very nearly as high as the carbon and only the non-conductor m projects a little above it. the bombardment goes at first against the upper surface of carbon, the lower parts being protected by the aluminium tube. as soon, however, as the non-conductor m is heated it is rendered good conducting, and then it becomes the centre of the bombardment, being most exposed to the same. i have also constructed during these experiments many such single-wire bulbs with or without internal electrode, in which the radiant matter was projected against, or focused upon, the body to be rendered incandescent. fig. 24 illustrates one of the bulbs used. it consists of a spherical globe l, provided with a long neck n, on the top, for increasing the action in some cases by the application of an external conducting coating. the globe l is blown out on the bottom into a very small bulb b, which serves to hold it firmly in a socket s of insulating material into which it is cemented. a fine lamp filament f, supported on a wire w, passes through the centre of the globe l. the filament is rendered incandescent in the middle portion, where the bombardment proceeding from the lower inside surface of the globe is most intense. the lower portion of the globe, as far as the socket s reaches, is rendered conducting, either by a tinfoil coating or otherwise, and the external electrode is connected to a terminal of the coil. the arrangement diagrammatically indicated in fig. 24 was found to be an inferior one when it was desired to render incandescent a filament or button supported in the centre of the globe, but it was convenient when the object was to excite phosphorescence. in many experiments in which bodies of a different kind were mounted in the bulb as, for instance, indicated in fig. 23, some observations of interest were made. it was found, among other things, that in such cases, no matter where the bombardment began, just as soon as a high temperature was reached there was generally one of the bodies which seemed to take most of the bombardment upon itself, the other, or others, being thereby relieved. this quality appeared to depend principally on the point of fusion, and on the facility with which the body was "evaporated," or, generally speaking, disintegrated--meaning by the latter term not only the throwing off of atoms, but likewise of larger lumps. the observation made was in accordance with generally accepted notions. in a highly exhausted bulb electricity is carried off from the electrode by independent carriers, which are partly the atoms, or molecules, of the residual atmosphere, and partly the atoms, molecules, or lumps thrown off from the electrode. if the electrode is composed of bodies of different character, and if one of these is more easily disintegrated than the others, most of the electricity supplied is carried off from that body, which is then brought to a higher temperature than the others, and this the more, as upon an increase of the temperature the body is still more easily disintegrated. it seems to me quite probable that a similar process takes place in the bulb even with a homogeneous electrode, and i think it to be the principal cause of the disintegration. there is bound to be some irregularity, even if the surface is highly polished, which, of course, is impossible with most of the refractory bodies employed as electrodes. assume that a point of the electrode gets hotter, instantly most of the discharge passes through that point, and a minute patch is probably fused and evaporated. it is now possible that in consequence of the violent disintegration the spot attacked sinks in temperature, or that a counter force is created, as in an arc; at any rate, the local tearing off meets with the limitations incident to the experiment, whereupon the same process occurs on another place. to the eye the electrode appears uniformly brilliant, but there are upon it points constantly shifting and wandering around, of a temperature far above the mean, and this materially hastens the process of deterioration. that some such thing occurs, at least when the electrode is at a lower temperature, sufficient experimental evidence can be obtained in the following manner: exhaust a bulb to a very high degree, so that with a fairly high potential the discharge cannot pass--that is, not a _luminous_ one, for a weak invisible discharge occurs always, in all probability. now raise slowly and carefully the potential, leaving the primary current on no more than for an instant. at a certain point, two, three, or half a dozen phosphorescent spots will appear on the globe. these places of the glass are evidently more violently bombarded than others, this being due to the unevenly distributed electric density, necessitated, of course, by sharp projections, or, generally speaking, irregularities of the electrode. but the luminous patches are constantly changing in position, which is especially well observable if one manages to produce very few, and this indicates that the configuration of the electrode is rapidly changing. from experiences of this kind i am led to infer that, in order to be most durable, the refractory button in the bulb should be in the form of a sphere with a highly polished surface. such a small sphere could be manufactured from a diamond or some other crystal, but a better way would be to fuse, by the employment of extreme degrees of temperature, some oxide--as, for instance, zirconia--into a small drop, and then keep it in the bulb at a temperature somewhat below its point of fusion. interesting and useful results can no doubt be reached in the direction of extreme degrees of heat. how can such high temperatures be arrived at? how are the highest degrees of heat reached in nature? by the impact of stars, by high speeds and collisions. in a collision any rate of heat generation may be attained. in a chemical process we are limited. when oxygen and hydrogen combine, they fall, metaphorically speaking, from a definite height. we cannot go very far with a blast, nor by confining heat in a furnace, but in an exhausted bulb we can concentrate any amount of energy upon a minute button. leaving practicability out of consideration, this, then, would be the means which, in my opinion, would enable us to reach the highest temperature. but a great difficulty when proceeding in this way is encountered, namely, in most cases the body is carried off before it can fuse and form a drop. this difficulty exists principally with an oxide such as zirconia, because it cannot be compressed in so hard a cake that it would not be carried off quickly. i endeavored repeatedly to fuse zirconia, placing it in a cup or arc light carbon as indicated in fig. 23. it glowed with a most intense light, and the stream of the particles projected out of the carbon cup was of a vivid white: but whether it was compressed in a cake or made into a paste with carbon, it was carried off before it could be fused. the carbon cup containing the zirconia had to be mounted very low in the neck of a large bulb, as the heating of the glass by the projected particles of the oxide was so rapid that in the first trial the bulb was cracked almost in an instant when the current was turned on. the heating of the glass by the projected particles was found to be always greater when the carbon cup contained a body which was rapidly carried off--i presume because in such cases, with the same potential, higher speeds were reached, and also because, per unit of time, more matter was projected--that is, more particles would strike the glass. the before mentioned difficulty did not exist, however, when the body mounted in the carbon cup offered great resistance to deterioration. for instance, when an oxide was first fused in an oxygen blast and then mounted in the bulb, it melted very readily into a drop. generally during the process of fusion magnificent light effects were noted, of which it would be difficult to give an adequate idea. fig. 23 is intended to illustrate the effect observed with a ruby drop. at first one may see a narrow funnel of white light projected against the top of the globe, where it produces an irregularly outlined phosphorescent patch. when the point of the ruby fuses the phosphorescence becomes very powerful; but as the atoms are projected with much greater speed from the surface of the drop, soon the glass gets hot and "tired," and now only the outer edge of the patch glows. in this manner an intensely phosphorescent, sharply defined line, _l_, corresponding to the outline of the drop, is produced, which spreads slowly over the globe as the drop gets larger. when the mass begins to boil, small bubbles and cavities are formed, which cause dark colored spots to sweep across the globe. the bulb may be turned downward without fear of the drop falling off, as the mass possesses considerable viscosity. i may mention here another feature of some interest, which i believe to have noted in the course of these experiments, though the observations do not amount to a certitude. it _appeared_ that under the molecular impact caused by the rapidly alternating potential the body was fused and maintained in that state at a lower temperature in a highly exhausted bulb than was the case at normal pressure and application of heat in the ordinary way--that is, at least, judging from the quantity of the light emitted. one of the experiments performed may be mentioned here by way of illustration. a small piece of pumice stone was stuck on a platinum wire, and first melted to it in a gas burner. the wire was next placed between two pieces of charcoal and a burner applied so as to produce an intense heat, sufficient to melt down the pumice stone into a small glass-like button. the platinum wire had to be taken of sufficient thickness to prevent its melting in the fire. while in the charcoal fire, or when held in a burner to get a better idea of the degree of heat, the button glowed with great brilliancy. the wire with the button was then mounted in a bulb, and upon exhausting the same to a high degree, the current was turned on slowly so as to prevent the cracking of the button. the button was heated to the point of fusion, and when it melted it did not, apparently, glow with the same brilliancy as before, and this would indicate a lower temperature. leaving out of consideration the observer's possible, and even probable, error, the question is, can a body under these conditions be brought from a solid to a liquid state with evolution of _less_ light? when the potential of a body is rapidly alternated it is certain that the structure is jarred. when the potential is very high, although the vibrations may be few--say 20,000 per second--the effect upon the structure may be considerable. suppose, for example, that a ruby is melted into a drop by a steady application of energy. when it forms a drop it will emit visible and invisible waves, which will be in a definite ratio, and to the eye the drop will appear to be of a certain brilliancy. next, suppose we diminish to any degree we choose the energy steadily supplied, and, instead, supply energy which rises and falls according to a certain law. now, when the drop is formed, there will be emitted from it three different kinds of vibrations--the ordinary visible, and two kinds of invisible waves: that is, the ordinary dark waves of all lengths, and, in addition, waves of a well defined character. the latter would not exist by a steady supply of the energy; still they help to jar and loosen the structure. if this really be the case, then the ruby drop will emit relatively less visible and more invisible waves than before. thus it would seem that when a platinum wire, for instance, is fused by currents alternating with extreme rapidity, it emits at the point of fusion less light and more invisible radiation than it does when melted by a steady current, though the total energy used up in the process of fusion is the same in both cases. or, to cite another example, a lamp filament is not capable of withstanding as long with currents of extreme frequency as it does with steady currents, assuming that it be worked at the same luminous intensity. this means that for rapidly alternating currents the filament should be shorter and thicker. the higher the frequency--that is, the greater the departure from the steady flow--the worse it would be for the filament. but if the truth of this remark were demonstrated, it would be erroneous to conclude that such a refractory button as used in these bulbs would be deteriorated quicker by currents of extremely high frequency than by steady or low frequency currents. from experience i may say that just the opposite holds good: the button withstands the bombardment better with currents of very high frequency. but this is due to the fact that a high frequency discharge passes through a rarefied gas with much greater freedom than a steady or low frequency discharge, and this will say that with the former we can work with a lower potential or with a less violent impact. as long, then, as the gas is of no consequence, a steady or low frequency current is better; but as soon as the action of the gas is desired and important, high frequencies are preferable. in the course of these experiments a great many trials were made with all kinds of carbon buttons. electrodes made of ordinary carbon buttons were decidedly more durable when the buttons were obtained by the application of enormous pressure. electrodes prepared by depositing carbon in well known ways did not show up well; they blackened the globe very quickly. from many experiences i conclude that lamp filaments obtained in this manner can be advantageously used only with low potentials and low frequency currents. some kinds of carbon withstand so well that, in order to bring them to the point of fusion, it is necessary to employ very small buttons. in this case the observation is rendered very difficult on account of the intense heat produced. nevertheless there can be no doubt that all kinds of carbon are fused under the molecular bombardment, but the liquid state must be one of great instability. of all the bodies tried there were two which withstood best--diamond and carborundum. these two showed up about equally, but the latter was preferable, for many reasons. as it is more than likely that this body is not yet generally known, i will venture to call your attention to it. it has been recently produced by mr. e.g. acheson, of monongahela city, pa., u.s.a. it is intended to replace ordinary diamond powder for polishing precious stones, etc., and i have been informed that it accomplishes this object quite successfully. i do not know why the name "carborundum" has been given to it, unless there is something in the process of its manufacture which justifies this selection. through the kindness of the inventor, i obtained a short while ago some samples which i desired to test in regard to their qualities of phosphorescence and capability of withstanding high degrees of heat. carborundum can be obtained in two forms--in the form of "crystals" and of powder. the former appear to the naked eye dark colored, but are very brilliant; the latter is of nearly the same color as ordinary diamond powder, but very much finer. when viewed under a microscope the samples of crystals given to me did not appear to have any definite form, but rather resembled pieces of broken up egg coal of fine quality. the majority were opaque, but there were some which were transparent and colored. the crystals are a kind of carbon containing some impurities; they are extremely hard, and withstand for a long time even an oxygen blast. when the blast is directed against them they at first form a cake of some compactness, probably in consequence of the fusion of impurities they contain. the mass withstands for a very long time the blast without further fusion; but a slow carrying off, or burning, occurs, and, finally, a small quantity of a glass-like residue is left, which, i suppose, is melted alumina. when compressed strongly they conduct very well, but not as well as ordinary carbon. the powder, which is obtained from the crystals in some way, is practically non-conducting. it affords a magnificent polishing material for stones. the time has been too short to make a satisfactory study of the properties of this product, but enough experience has been gained in a few weeks i have experimented upon it to say that it does possess some remarkable properties in many respects. it withstands excessively high degrees of heat, it is little deteriorated by molecular bombardment, and it does not blacken the globe as ordinary carbon does. the only difficulty which i have found in its use in connection with these experiments was to find some binding material which would resist the heat and the effect of the bombardment as successfully as carborundum itself does. i have here a number of bulbs which i have provided with buttons of carborundum. to make such a button of carborundum crystals i proceed in the following manner: i take an ordinary lamp filament and dip its point in tar, or some other thick substance or paint which may be readily carbonized. i next pass the point of the filament through the crystals, and then hold it vertically over a hot plate. the tar softens and forms a drop on the point of the filament, the crystals adhering to the surface of the drop. by regulating the distance from the plate the tar is slowly dried out and the button becomes solid. i then once more dip the button in tar and hold it again over a plate until the tar is evaporated, leaving only a hard mass which firmly binds the crystals. when a larger button is required i repeat the process several times, and i generally also cover the filament a certain distance below the button with crystals. the button being mounted in a bulb, when a good vacuum has been reached, first a weak and then a strong discharge is passed through the bulb to carbonize the tar and expel all gases, and later it is brought to a very intense incandescence. when the powder is used i have found it best to proceed as follows: i make a thick paint of carborundum and tar, and pass a lamp filament through the paint. taking then most of the paint off by rubbing the filament against a piece of chamois leather, i hold it over a hot plate until the tar evaporates and the coating becomes firm. i repeat this process as many times as it is necessary to obtain a certain thickness of coating. on the point of the coated filament i form a button in the same manner. there is no doubt that such a button--properly prepared under great pressure--of carborundum, especially of powder of the best quality, will withstand the effect of the bombardment fully as well as anything we know. the difficulty is that the binding material gives way, and the carborundum is slowly thrown off after some time. as it does not seem to blacken the globe in the least, it might be found useful for coating the filaments of ordinary incandescent lamps, and i think that it is even possible to produce thin threads or sticks of carborundum which will replace the ordinary filaments in an incandescent lamp. a carborundum coating seems to be more durable than other coatings, not only because the carborundum can withstand high degrees of heat, but also because it seems to unite with the carbon better than any other material i have tried. a coating of zirconia or any other oxide, for instance, is far more quickly destroyed. i prepared buttons of diamond dust in the same manner as of carborundum, and these came in durability nearest to those prepared of carborundum, but the binding paste gave way much more quickly in the diamond buttons: this, however, i attributed to the size and irregularity of the grains of the diamond. it was of interest to find whether carborundum possesses the quality of phosphorescence. one is, of course, prepared to encounter two difficulties: first, as regards the rough product, the "crystals," they are good conducting, and it is a fact that conductors do not phosphoresce; second, the powder, being exceedingly fine, would not be apt to exhibit very prominently this quality, since we know that when crystals, even such as diamond or ruby, are finely powdered, they lose the property of phosphorescence to a considerable degree. the question presents itself here, can a conductor phosphoresce? what is there in such a body as a metal, for instance, that would deprive it of the quality of phosphorescence, unless it is that property which characterizes it as a conductor? for it is a fact that most of the phosphorescent bodies lose that quality when they are sufficiently heated to become more or less conducting. then, if a metal be in a large measure, or perhaps entirely, deprived of that property, it should be capable of phosphorescence. therefore it is quite possible that at some extremely high frequency, when behaving practically as a non-conductor, a metal or any other conductor might exhibit the quality of phosphorescence, even though it be entirely incapable of phosphorescing under the impact of a low-frequency discharge. there is, however, another possible way how a conductor might at least _appear_ to phosphoresce. considerable doubt still exists as to what really is phosphorescence, and as to whether the various phenomena comprised under this head are due to the same causes. suppose that in an exhausted bulb, under the molecular impact, the surface of a piece of metal or other conductor is rendered strongly luminous, but at the same time it is found that it remains comparatively cool, would not this luminosity be called phosphorescence? now such a result, theoretically at least, is possible, for it is a mere question of potential or speed. assume the potential of the electrode, and consequently the speed of the projected atoms, to be sufficiently high, the surface of the metal piece against which the atoms are projected would be rendered highly incandescent, since the process of heat generation would be incomparably faster than that of radiating or conducting away from the surface of the collision. in the eye of the observer a single impact of the atoms would cause an instantaneous flash, but if the impacts were repeated with sufficient rapidity they would produce a continuous impression upon his retina. to him then the surface of the metal would appear continuously incandescent and of constant luminous intensity, while in reality the light would be either intermittent or at least changing periodically in intensity. the metal piece would rise in temperature until equilibrium was attained--that is until the energy continuously radiated would equal that intermittently supplied. but the supplied energy might under such conditions not be sufficient to bring the body to any more than a very moderate mean temperature, especially if the frequency of the atomic impacts be very low--just enough that the fluctuation of the intensity of the light emitted could not be detected by the eye. the body would now, owing to the manner in which the energy is supplied, emit a strong light, and yet be at a comparatively very low mean temperature. how could the observer call the luminosity thus produced? even if the analysis of the light would teach him something definite, still he would probably rank it under the phenomena of phosphorescence. it is conceivable that in such a way both conducting and non-conducting bodies may be maintained at a certain luminous intensity, but the energy required would very greatly vary with the nature and properties of the bodies. these and some foregoing remarks of a speculative nature were made merely to bring out curious features of alternate currents or electric impulses. by their help we may cause a body to emit _more_ light, while at a certain mean temperature, than it would emit if brought to that temperature by a steady supply; and, again, we may bring a body to the point of fusion, and cause it to emit _less_ light than when fused by the application of energy in ordinary ways. it all depends on how we supply the energy, and what kind of vibrations we set up: in one case the vibrations are more, in the other less, adapted to affect our sense of vision. some effects, which i had not observed before, obtained with carborundum in the first trials, i attributed to phosphorescence, but in subsequent experiments it appeared that it was devoid of that quality. the crystals possess a noteworthy feature. in a bulb provided with a single electrode in the shape of a small circular metal disc, for instance, at a certain degree of exhaustion the electrode is covered with a milky film, which is separated by a dark space from the glow filling the bulb. when the metal disc is covered with carborundum crystals, the film is far more intense, and snow-white. this i found later to be merely an effect of the bright surface of the crystals, for when an aluminium electrode was highly polished it exhibited more or less the same phenomenon. i made a number of experiments with the samples of crystals obtained, principally because it would have been of special interest to find that they are capable of phosphorescence, on account of their being conducting. i could not produce phosphorescence distinctly, but i must remark that a decisive opinion cannot be formed until other experimenters have gone over the same ground. the powder behaved in some experiments as though it contained alumina, but it did not exhibit with sufficient distinctness the red of the latter. its dead color brightens considerably under the molecular impact, but i am now convinced it does not phosphoresce. still, the tests with the powder are not conclusive, because powdered carborundum probably does not behave like a phosphorescent sulphide, for example, which could be finely powdered without impairing the phosphorescence, but rather like powdered ruby or diamond, and therefore it would be necessary, in order to make a decisive test, to obtain it in a large lump and polish up the surface. if the carborundum proves useful in connection with these and similar experiments, its chief value will be found in the production of coatings, thin conductors, buttons, or other electrodes capable of withstanding extremely high degrees of heat. the production of a small electrode capable of withstanding enormous temperatures i regard as of the greatest importance in the manufacture of light. it would enable us to obtain, by means of currents of very high frequencies, certainly 20 times, if not more, the quantity of light which is obtained in the present incandescent lamp by the same expenditure of energy. this estimate may appear to many exaggerated, but in reality i think it is far from being so. as this statement might be misunderstood i think it necessary to expose clearly the problem with which in this line of work we are confronted, and the manner in which, in my opinion, a solution will be arrived at. any one who begins a study of the problem will be apt to think that what is wanted in a lamp with an electrode is a very high degree of incandescence of the electrode. there he will be mistaken. the high incandescence of the button is a necessary evil, but what is really wanted is the high incandescence of the gas surrounding the button. in other words, the problem in such a lamp is to bring a mass of gas to the highest possible incandescence. the higher the incandescence, the quicker the mean vibration, the greater is the economy of the light production. but to maintain a mass of gas at a high degree of incandescence in a glass vessel, it will always be necessary to keep the incandescent mass away from the glass; that is, to confine it as much as possible to the central portion of the globe. in one of the experiments this evening a brush was produced at the end of a wire. this brush was a flame, a source of heat and light. it did not emit much perceptible heat, nor did it glow with an intense light; but is it the less a flame because it does not scorch my hand? is it the less a flame because it does not hurt my eye by its brilliancy? the problem is precisely to produce in the bulb such a flame, much smaller in size, but incomparably more powerful. were there means at hand for producing electric impulses of a sufficiently high frequency, and for transmitting them, the bulb could be done away with, unless it were used to protect the electrode, or to economize the energy by confining the heat. but as such means are not at disposal, it becomes necessary to place the terminal in a bulb and rarefy the air in the same. this is done merely to enable the apparatus to perform the work which it is not capable of performing at ordinary air pressure. in the bulb we are able to intensify the action to any degree--so far that the brush emits a powerful light. the intensity of the light emitted depends principally on the frequency and potential of the impulses, and on the electric density of the surface of the electrode. it is of the greatest importance to employ the smallest possible button, in order to push the density very far. under the violent impact of the molecules of the gas surrounding it, the small electrode is of course brought to an extremely high temperature, but around it is a mass of highly incandescent gas, a flame photosphere, many hundred times the volume of the electrode. with a diamond, carborundum or zirconia button the photosphere can be as much as one thousand times the volume of the button. without much reflecting one would think that in pushing so far the incandescence of the electrode it would be instantly volatilized. but after a careful consideration he would find that, theoretically, it should not occur, and in this fact--which, however, is experimentally demonstrated--lies principally the future value of such a lamp. at first, when the bombardment begins, most of the work is performed on the surface of the button, but when a highly conducting photosphere is formed the button is comparatively relieved. the higher the incandescence of the photosphere the more it approaches in conductivity to that of the electrode, and the more, therefore, the solid and the gas form one conducting body. the consequence is that the further is forced the incandescence the more work, comparatively, is performed on the gas, and the less on the electrode. the formation of a powerful photosphere is consequently the very means for protecting the electrode. this protection, of course, is a relative one, and it should not be thought that by pushing the incandescence higher the electrode is actually less deteriorated. still, theoretically, with extreme frequencies, this result must be reached, but probably at a temperature too high for most of the refractory bodies known. given, then, an electrode which can withstand to a very high limit the effect of the bombardment and outward strain, it would be safe no matter how much it is forced beyond that limit. in an incandescent lamp quite different considerations apply. there the gas is not at all concerned: the whole of the work is performed on the filament; and the life of the lamp diminishes so rapidly with the increase of the degree of incandescence that economical reasons compel us to work it at a low incandescence. but if an incandescent lamp is operated with currents of very high frequency, the action of the gas cannot be neglected, and the rules for the most economical working must be considerably modified. in order to bring such a lamp with one or two electrodes to a great perfection, it is necessary to employ impulses of very high frequency. the high frequency secures, among others, two chief advantages, which have a most important bearing upon the economy of the light production. first, the deterioration of the electrode is reduced by reason of the fact that we employ a great many small impacts, instead of a few violent ones, which shatter quickly the structure; secondly, the formation of a large photosphere is facilitated. in order to reduce the deterioration of the electrode to the minimum, it is desirable that the vibration be harmonic, for any suddenness hastens the process of destruction. an electrode lasts much longer when kept at incandescence by currents, or impulses, obtained from a high-frequency alternator, which rise and fall more or less harmonically, than by impulses obtained from a disruptive discharge coil. in the latter case there is no doubt that most of the damage is done by the fundamental sudden discharges. one of the elements of loss in such a lamp is the bombardment of the globe. as the potential is very high, the molecules are projected with great speed; they strike the glass, and usually excite a strong phosphorescence. the effect produced is very pretty, but for economical reasons it would be perhaps preferable to prevent, or at least reduce to the minimum, the bombardment against the globe, as in such case it is, as a rule, not the object to excite phosphorescence, and as some loss of energy results from the bombardment. this loss in the bulb is principally dependent on the potential of the impulses and on the electric density on the surface of the electrode. in employing very high frequencies the loss of energy by the bombardment is greatly reduced, for, first, the potential needed to perform a given amount of work is much smaller; and, secondly, by producing a highly conducting photosphere around the electrode, the same result is obtained as though the electrode were much larger, which is equivalent to a smaller electric density. but be it by the diminution of the maximum potential or of the density, the gain is effected in the same manner, namely, by avoiding violent shocks, which strain the glass much beyond its limit of elasticity. if the frequency could be brought high enough, the loss due to the imperfect elasticity of the glass would be entirely negligible. the loss due to bombardment of the globe may, however, be reduced by using two electrodes instead of one. in such case each of the electrodes may be connected to one of the terminals; or else, if it is preferable to use only one wire, one electrode may be connected to one terminal and the other to the ground or to an insulated body of some surface, as, for instance, a shade on the lamp. in the latter case, unless some judgment is used, one of the electrodes might glow more intensely than the other. but on the whole i find it preferable when using such high frequencies to employ only one electrode and one connecting wire. i am convinced that the illuminating device of the near future will not require for its operation more than one lead, and, at any rate, it will have no leading-in wire, since the energy required can be as well transmitted through the glass. in experimental bulbs the leading-in wire is most generally used on account of convenience, as in employing condenser coatings in the manner indicated in fig. 22, for example, there is some difficulty in fitting the parts, but these difficulties would not exist if a great many bulbs were manufactured; otherwise the energy can be conveyed through the glass as well as through a wire, and with these high frequencies the losses are very small. such illuminating devices will necessarily involve the use of very high potentials, and this, in the eyes of practical men, might be an objectionable feature. yet, in reality, high potentials are not objectionable--certainly not in the least as far as the safety of the devices is concerned. there are two ways of rendering an electric appliance safe. one is to use low potentials, the other is to determine the dimensions of the apparatus so that it is safe no matter how high a potential is used. of the two the latter seems to me the better way, for then the safety is absolute, unaffected by any possible combination of circumstances which might render even a low-potential appliance dangerous to life and property. but the practical conditions require not only the judicious determination of the dimensions of the apparatus; they likewise necessitate the employment of energy of the proper kind. it is easy, for instance, to construct a transformer capable of giving, when operated from an ordinary alternate current machine of low tension, say 50,000 volts, which might be required to light a highly exhausted phosphorescent tube, so that, in spite of the high potential, it is perfectly safe, the shock from it producing no inconvenience. still, such a transformer would be expensive, and in itself inefficient; and, besides, what energy was obtained from it would not be economically used for the production of light. the economy demands the employment of energy in the form of extremely rapid vibrations. the problem of producing light has been likened to that of maintaining a certain high-pitch note by means of a bell. it should be said a _barely audible_ note; and even these words would not express it, so wonderful is the sensitiveness of the eye. we may deliver powerful blows at long intervals, waste a good deal of energy, and still not get what we want; or we may keep up the note by delivering frequent gentle taps, and get nearer to the object sought by the expenditure of much less energy. in the production of light, as far as the illuminating device is concerned, there can be only one rule--that is, to use as high frequencies as can be obtained; but the means for the production and conveyance of impulses of such character impose, at present at least, great limitations. once it is decided to use very high frequencies, the return wire becomes unnecessary, and all the appliances are simplified. by the use of obvious means the same result is obtained as though the return wire were used. it is sufficient for this purpose to bring in contact with the bulb, or merely in the vicinity of the same, an insulated body of some surface. the surface need, of course, be the smaller, the higher the frequency and potential used, and necessarily, also, the higher the economy of the lamp or other device. this plan of working has been resorted to on several occasions this evening. so, for instance, when the incandescence of a button was produced by grasping the bulb with the hand, the body of the experimenter merely served to intensify the action. the bulb used was similar to that illustrated in fig. 19, and the coil was excited to a small potential, not sufficient to bring the button to incandescence when the bulb was hanging from the wire; and incidentally, in order to perform the experiment in a more suitable manner, the button was taken so large that a perceptible time had to elapse before, upon grasping the bulb, it could be rendered incandescent. the contact with the bulb was, of course, quite unnecessary. it is easy, by using a rather large bulb with an exceedingly small electrode, to adjust the conditions so that the latter is brought to bright incandescence by the mere approach of the experimenter within a few feet of the bulb, and that the incandescence subsides upon his receding. [illustration: fig. 24.--bulb without leading-in wire, showing effect of projected matter.] in another experiment, when phosphorescence was excited, a similar bulb was used. here again, originally, the potential was not sufficient to excite phosphorescence until the action was intensified--in this case, however, to present a different feature, by touching the socket with a metallic object held in the hand. the electrode in the bulb was a carbon button so large that it could not be brought to incandescence, and thereby spoil the effect produced by phosphorescence. [illustration: fig. 25.--improved experimental bulb.] again, in another of the early experiments, a bulb was used as illustrated in fig. 12. in this instance, by touching the bulb with one or two fingers, one or two shadows of the stem inside were projected against the glass, the touch of the finger producing the same result as the application of an external negative electrode under ordinary circumstances. in all these experiments the action was intensified by augmenting the capacity at the end of the lead connected to the terminal. as a rule, it is not necessary to resort to such means, and would be quite unnecessary with still higher frequencies; but when it _is_ desired, the bulb, or tube, can be easily adapted to the purpose. [illustration: fig. 26.--improved bulb with intensifying reflector.] in fig. 24, for example, an experimental bulb l is shown, which is provided with a neck n on the top for the application of an external tinfoil coating, which may be connected to a body of larger surface. such a lamp as illustrated in fig. 25 may also be lighted by connecting the tinfoil coating on the neck n to the terminal, and the leading-in wire w to an insulated plate. if the bulb stands in a socket upright, as shown in the cut, a shade of conducting material may be slipped in the neck n, and the action thus magnified. a more perfected arrangement used in some of these bulbs is illustrated in fig. 26. in this case the construction of the bulb is as shown and described before, when reference was made to fig. 19. a zinc sheet z, with a tubular extension t, is slipped over the metallic socket s. the bulb hangs downward from the terminal t, the zinc sheet z, performing the double office of intensifier and reflector. the reflector is separated from the terminal t by an extension of the insulating plug p. [illustration: fig. 27.--phosphorescent tube with intensifying reflector.] a similar disposition with a phosphorescent tube is illustrated in fig. 27. the tube t is prepared from two short tubes of a different diameter, which are sealed on the ends. on the lower end is placed an outside conducting coating c, which connects to the wire w. the wire has a hook on the upper end for suspension, and passes through the centre of the inside tube, which is filled with some good and tightly packed insulator. on the outside of the upper end of the tube t is another conducting coating c_1 upon which is slipped a metallic reflector z, which should be separated by a thick insulation from the end of wire w. the economical use of such a reflector or intensifier would require that all energy supplied to an air condenser should be recoverable, or, in other words, that there should not be any losses, neither in the gaseous medium nor through its action elsewhere. this is far from being so, but, fortunately, the losses may be reduced to anything desired. a few remarks are necessary on this subject, in order to make the experiences gathered in the course of these investigations perfectly clear. suppose a small helix with many well insulated turns, as in experiment fig. 17, has one of its ends connected to one of the terminals of the induction coil, and the other to a metal plate, or, for the sake of simplicity, a sphere, insulated in space. when the coil is set to work, the potential of the sphere is alternated, and the small helix now behaves as though its free end were connected to the other terminal of the induction coil. if an iron rod be held within the small helix it is quickly brought to a high temperature, indicating the passage of a strong current through the helix. how does the insulated sphere act in this case? it can be a condenser, storing and returning the energy supplied to it, or it can be a mere sink of energy, and the conditions of the experiment determine whether it is more one or the other. the sphere being charged to a high potential, it acts inductively upon the surrounding air, or whatever gaseous medium there might be. the molecules, or atoms, which are near the sphere are of course more attracted, and move through a greater distance than the farther ones. when the nearest molecules strike the sphere they are repelled, and collisions occur at all distances within the inductive action of the sphere. it is now clear that, if the potential be steady, but little loss of energy can be caused in this way, for the molecules which are nearest to the sphere, having had an additional charge imparted to them by contact, are not attracted until they have parted, if not with all, at least with most of the additional charge, which can be accomplished only after a great many collisions. from the fact that with a steady potential there is but little loss in dry air, one must come to such a conclusion. when the potential of the sphere, instead of being steady, is alternating, the conditions are entirely different. in this case a rhythmical bombardment occurs, no matter whether the molecules after coming in contact with the sphere lose the imparted charge or not; what is more, if the charge is not lost, the impacts are only the more violent. still if the frequency of the impulses be very small, the loss caused by the impacts and collisions would not be serious unless the potential were excessive. but when extremely high frequencies and more or less high potentials are used, the loss may be very great. the total energy lost per unit of time is proportionate to the product of the number of impacts per second, or the frequency and the energy lost in each impact. but the energy of an impact must be proportionate to the square of the electric density of the sphere, since the charge imparted to the molecule is proportionate to that density. i conclude from this that the total energy lost must be proportionate to the product of the frequency and the square of the electric density; but this law needs experimental confirmation. assuming the preceding considerations to be true, then, by rapidly alternating the potential of a body immersed in an insulating gaseous medium, any amount of energy may be dissipated into space. most of that energy then, i believe, is not dissipated in the form of long ether waves, propagated to considerable distance, as is thought most generally, but is consumed--in the case of an insulated sphere, for example--in impact and collisional losses--that is, heat vibrations--on the surface and in the vicinity of the sphere. to reduce the dissipation it is necessary to work with a small electric density--the smaller the higher the frequency. but since, on the assumption before made, the loss is diminished with the square of the density, and since currents of very high frequencies involve considerable waste when transmitted through conductors, it follows that, on the whole, it is better to employ one wire than two. therefore, if motors, lamps, or devices of any kind are perfected, capable of being advantageously operated by currents of extremely high frequency, economical reasons will make it advisable to use only one wire, especially if the distances are great. when energy is absorbed in a condenser the same behaves as though its capacity were increased. absorption always exists more or less, but generally it is small and of no consequence as long as the frequencies are not very great. in using extremely high frequencies, and, necessarily in such case, also high potentials, the absorption--or, what is here meant more particularly by this term, the loss of energy due to the presence of a gaseous medium--is an important factor to be considered, as the energy absorbed in the air condenser may be any fraction of the supplied energy. this would seem to make it very difficult to tell from the measured or computed capacity of an air condenser its actual capacity or vibration period, especially if the condenser is of very small surface and is charged to a very high potential. as many important results are dependent upon the correctness of the estimation of the vibration period, this subject demands the most careful scrutiny of other investigators. to reduce the probable error as much as possible in experiments of the kind alluded to, it is advisable to use spheres or plates of large surface, so as to make the density exceedingly small. otherwise, when it is practicable, an oil condenser should be used in preference. in oil or other liquid dielectrics there are seemingly no such losses as in gaseous media. it being impossible to exclude entirely the gas in condensers with solid dielectrics, such condensers should be immersed in oil, for economical reasons if nothing else; they can then be strained to the utmost and will remain cool. in leyden jars the loss due to air is comparatively small, as the tinfoil coatings are large, close together, and the charged surfaces not directly exposed; but when the potentials are very high, the loss may be more or less considerable at, or near, the upper edge of the foil, where the air is principally acted upon. if the jar be immersed in boiled-out oil, it will be capable of performing four times the amount of work which it can for any length of time when used in the ordinary way, and the loss will be inappreciable. it should not be thought that the loss in heat in an air condenser is necessarily associated with the formation of _visible_ streams or brushes. if a small electrode, inclosed in an unexhausted bulb, is connected to one of the terminals of the coil, streams can be seen to issue from the electrode and the air in the bulb is heated; if, instead of a small electrode, a large sphere is inclosed in the bulb, no streams are observed, still the air is heated. nor should it be thought that the temperature of an air condenser would give even an approximate idea of the loss in heat incurred, as in such case heat must be given off much more quickly, since there is, in addition to the ordinary radiation, a very active carrying away of heat by independent carriers going on, and since not only the apparatus, but the air at some distance from it is heated in consequence of the collisions which must occur. owing to this, in experiments with such a coil, a rise of temperature can be distinctly observed only when the body connected to the coil is very small. but with apparatus on a larger scale, even a body of considerable bulk would be heated, as, for instance, the body of a person; and i think that skilled physicians might make observations of utility in such experiments, which, if the apparatus were judiciously designed, would not present the slightest danger. a question of some interest, principally to meteorologists, presents itself here. how does the earth behave? the earth is an air condenser, but is it a perfect or a very imperfect one--a mere sink of energy? there can be little doubt that to such small disturbance as might be caused in an experiment the earth behaves as an almost perfect condenser. but it might be different when its charge is set in vibration by some sudden disturbance occurring in the heavens. in such case, as before stated, probably only little of the energy of the vibrations set up would be lost into space in the form of long ether radiations, but most of the energy, i think, would spend itself in molecular impacts and collisions, and pass off into space in the form of short heat, and possibly light, waves. as both the frequency of the vibrations of the charge and the potential are in all probability excessive, the energy converted into heat may be considerable. since the density must be unevenly distributed, either in consequence of the irregularity of the earth's surface, or on account of the condition of the atmosphere in various places, the effect produced would accordingly vary from place to place. considerable variations in the temperature and pressure of the atmosphere may in this manner be caused at any point of the surface of the earth. the variations may be gradual or very sudden, according to the nature of the general disturbance, and may produce rain and storms, or locally modify the weather in any way. from the remarks before made one may see what an important factor of loss the air in the neighborhood of a charged surface becomes when the electric density is great and the frequency of the impulses excessive. but the action as explained implies that the air is insulating--that is, that it is composed of independent carriers immersed in an insulating medium. this is the case only when the air is at something like ordinary or greater, or at extremely small, pressure. when the air is slightly rarefied and conducting, then true conduction losses occur also. in such case, of course, considerable energy may be dissipated into space even with a steady potential, or with impulses of low frequency, if the density is very great. when the gas is at very low pressure, an electrode is heated more because higher speeds can be reached. if the gas around the electrode is strongly compressed, the displacements, and consequently the speeds, are very small, and the heating is insignificant. but if in such case the frequency could be sufficiently increased, the electrode would be brought to a high temperature as well as if the gas were at very low pressure; in fact, exhausting the bulb is only necessary because we cannot produce (and possibly not convey) currents of the required frequency. returning to the subject of electrode lamps, it is obviously of advantage in such a lamp to confine as much as possible the heat to the electrode by preventing the circulation of the gas in the bulb. if a very small bulb be taken, it would confine the heat better than a large one, but it might not be of sufficient capacity to be operated from the coil, or, if so, the glass might get too hot. a simple way to improve in this direction is to employ a globe of the required size, but to place a small bulb, the diameter of which is properly estimated, over the refractory button contained in the globe. this arrangement is illustrated in fig. 28. [illustration: fig. 28.--lamp with auxiliary bulb for confining the action to the centre.] the globe l has in this case a large neck n, allowing the small bulb b to slip through. otherwise the construction is the same as shown in fig. 18, for example. the small bulb is conveniently supported upon the stem s, carrying the refractory button m. it is separated from the aluminium tube a by several layers of mica m, in order to prevent the cracking of the neck by the rapid heating of the aluminium tube upon a sudden turning on of the current. the inside bulb should be as small as possible when it is desired to obtain light only by incandescence of the electrode. if it is desired to produce phosphorescence, the bulb should be larger, else it would be apt to get too hot, and the phosphorescence would cease. in this arrangement usually only the small bulb shows phosphorescence, as there is practically no bombardment against the outer globe. in some of these bulbs constructed as illustrated in fig. 28 the small tube was coated with phosphorescent paint, and beautiful effects were obtained. instead of making the inside bulb large, in order to avoid undue heating, it answers the purpose to make the electrode m larger. in this case the bombardment is weakened by reason of the smaller electric density. many bulbs were constructed on the plan illustrated in fig. 29. here a small bulb b, containing the refractory button m, upon being exhausted to a very high degree was sealed in a large globe l, which was then moderately exhausted and sealed off. the principal advantage of this construction was that it allowed of reaching extremely high vacua, and, at the same time use a large bulb. it was found, in the course of experiences with bulbs such as illustrated in fig. 29, that it was well to make the stem s near the seal at e very thick, and the leading-in wire w thin, as it occurred sometimes that the stem at e was heated and the bulb was cracked. often the outer globe l was exhausted only just enough to allow the discharge to pass through, and the space between the bulbs appeared crimson, producing a curious effect. in some cases, when the exhaustion in globe l was very low, and the air good conducting, it was found necessary, in order to bring the button m to high incandescence, to place, preferably on the upper part of the neck of the globe, a tinfoil coating which was connected to an insulated body, to the ground, or to the other terminal of the coil, as the highly conducting air weakened the effect somewhat, probably by being acted upon inductively from the wire w, where it entered the bulb at e. another difficulty--which, however, is always present when the refractory button is mounted in a very small bulb--existed in the construction illustrated in fig. 29, namely, the vacuum in the bulb b would be impaired in a comparatively short time. [illustration: fig. 29.--lamp with independent auxiliary bulb.] the chief idea in the two last described constructions was to confine the heat to the central portion of the globe by preventing the exchange of air. an advantage is secured, but owing to the heating of the inside bulb and slow evaporation of the glass the vacuum is hard to maintain, even if the construction illustrated in fig. 28 be chosen, in which both bulbs communicate. but by far the better way--the ideal way--would be to reach sufficiently high frequencies. the higher the frequency the slower would be the exchange of the air, and i think that a frequency may be reached at which there would be no exchange whatever of the air molecules around the terminal. we would then produce a flame in which there would be no carrying away of material, and a queer flame it would be, for it would be rigid! with such high frequencies the inertia of the particles would come into play. as the brush, or flame, would gain rigidity in virtue of the inertia of the particles, the exchange of the latter would be prevented. this would necessarily occur, for, the number of the impulses being augmented, the potential energy of each would diminish, so that finally only atomic vibrations could be set up, and the motion of translation through measurable space would cease. thus an ordinary gas burner connected to a source of rapidly alternating potential might have its efficiency augmented to a certain limit, and this for two reasons--because of the additional vibration imparted, and because of a slowing down of the process of carrying off. but the renewal being rendered difficult, and renewal being necessary to maintain the _burner_, a continued increase of the frequency of the impulses, assuming they could be transmitted to and impressed upon the flame, would result in the "extinction" of the latter, meaning by this term only the cessation of the chemical process. i think, however, that in the case of an electrode immersed in a fluid insulating medium, and surrounded by independent carriers of electric charges, which can be acted upon inductively, a sufficiently high frequency of the impulses would probably result in a gravitation of the gas all around toward the electrode. for this it would be only necessary to assume that the independent bodies are irregularly shaped; they would then turn toward the electrode their side of the greatest electric density, and this would be a position in which the fluid resistance to approach would be smaller than that offered to the receding. the general opinion, i do not doubt, is that it is out of the question to reach any such frequencies as might--assuming some of the views before expressed to be true--produce any of the results which i have pointed out as mere possibilities. this may be so, but in the course of these investigations, from the observation of many phenomena i have gained the conviction that these frequencies would be much lower than one is apt to estimate at first. in a flame we set up light vibrations by causing molecules, or atoms, to collide. but what is the ratio of the frequency of the collisions and that of the vibrations set up? certainly it must be incomparably smaller than that of the knocks of the bell and the sound vibrations, or that of the discharges and the oscillations of the condenser. we may cause the molecules of the gas to collide by the use of alternate electric impulses of high frequency, and so we may imitate the process in a flame; and from experiments with frequencies which we are now able to obtain, i think that the result is producible with impulses which are transmissible through a conductor. in connection with thoughts of a similar nature, it appeared to me of great interest to demonstrate the rigidity of a vibrating gaseous column. although with such low frequencies as, say 10,000 per second, which i was able to obtain without difficulty from a specially constructed alternator, the task looked discouraging at first, i made a series of experiments. the trials with air at ordinary pressure led to no result, but with air moderately rarefied i obtain what i think to be an unmistakable experimental evidence of the property sought for. as a result of this kind might lead able investigators to conclusions of importance i will describe one of the experiments performed. it is well known that when a tube is slightly exhausted the discharge may be passed through it in the form of a thin luminous thread. when produced with currents of low frequency, obtained from a coil operated as usual, this thread is inert. if a magnet be approached to it, the part near the same is attracted or repelled, according to the direction of the lines of force of the magnet. it occurred to me that if such a thread would be produced with currents of very high frequency, it should be more or less rigid, and as it was visible it could be easily studied. accordingly i prepared a tube about 1 inch in diameter and 1 metre long, with outside coating at each end. the tube was exhausted to a point at which by a little working the thread discharge could be obtained. it must be remarked here that the general aspect of the tube, and the degree of exhaustion, are quite different than when ordinary low frequency currents are used. as it was found preferable to work with one terminal, the tube prepared was suspended from the end of a wire connected to the terminal, the tinfoil coating being connected to the wire, and to the lower coating sometimes a small insulated plate was attached. when the thread was formed it extended through the upper part of the tube and lost itself in the lower end. if it possessed rigidity it resembled, not exactly an elastic cord stretched tight between two supports, but a cord suspended from a height with a small weight attached at the end. when the finger or a magnet was approached to the upper end of the luminous thread, it could be brought locally out of position by electrostatic or magnetic action; and when the disturbing object was very quickly removed, an analogous result was produced, as though a suspended cord would be displaced and quickly released near the point of suspension. in doing this the luminous thread was set in vibration, and two very sharply marked nodes, and a third indistinct one, were formed. the vibration, once set up, continued for fully eight minutes, dying gradually out. the speed of the vibration often varied perceptibly, and it could be observed that the electrostatic attraction of the glass affected the vibrating thread; but it was clear that the electrostatic action was not the cause of the vibration, for the thread was most generally stationary, and could always be set in vibration by passing the finger quickly near the upper part of the tube. with a magnet the thread could be split in two and both parts vibrated. by approaching the hand to the lower coating of the tube, or insulated plate if attached, the vibration was quickened; also, as far as i could see, by raising the potential or frequency. thus, either increasing the frequency or passing a stronger discharge of the same frequency corresponded to a tightening of the cord. i did not obtain any experimental evidence with condenser discharges. a luminous band excited in a bulb by repeated discharges of a leyden jar must possess rigidity, and if deformed and suddenly released should vibrate. but probably the amount of vibrating matter is so small that in spite of the extreme speed the inertia cannot prominently assert itself. besides, the observation in such a case is rendered extremely difficult on account of the fundamental vibration. the demonstration of the fact--which still needs better experimental confirmation--that a vibrating gaseous column possesses rigidity, might greatly modify the views of thinkers. when with low frequencies and insignificant potentials indications of that property may be noted, how must a gaseous medium behave under the influence of enormous electrostatic stresses which may be active in the interstellar space, and which may alternate with inconceivable rapidity? the existence of such an electrostatic, rhythmically throbbing force--of a vibrating electrostatic field--would show a possible way how solids might have formed from the ultra-gaseous uterus, and how transverse and all kinds of vibrations may be transmitted through a gaseous medium filling all space. then, ether might be a true fluid, devoid of rigidity, and at rest, it being merely necessary as a connecting link to enable interaction. what determines the rigidity of a body? it must be the speed and the amount of moving matter. in a gas the speed may be considerable, but the density is exceedingly small; in a liquid the speed would be likely to be small, though the density may be considerable; and in both cases the inertia resistance offered to displacement is practically _nil_. but place a gaseous (or liquid) column in an intense, rapidly alternating electrostatic field, set the particles vibrating with enormous speeds, then the inertia resistance asserts itself. a body might move with more or less freedom through the vibrating mass, but as a whole it would be rigid. there is a subject which i must mention in connection with these experiments: it is that of high vacua. this is a subject the study of which is not only interesting, but useful, for it may lead to results of great practical importance. in commercial apparatus, such as incandescent lamps, operated from ordinary systems of distribution, a much higher vacuum than obtained at present would not secure a very great advantage. in such a case the work is performed on the filament and the gas is little concerned; the improvement, therefore, would be but trifling. but when we begin to use very high frequencies and potentials, the action of the gas becomes all important, and the degree of exhaustion materially modifies the results. as long as ordinary coils, even very large ones, were used, the study of the subject was limited, because just at a point when it became most interesting it had to be interrupted on account of the "non-striking" vacuum being reached. but presently we are able to obtain from a small disruptive discharge coil potentials much higher than even the largest coil was capable of giving, and, what is more, we can make the potential alternate with great rapidity. both of these results enable us now to pass a luminous discharge through almost any vacua obtainable, and the field of our investigations is greatly extended. think we as we may, of all the possible directions to develop a practical illuminant, the line of high vacua seems to be the most promising at present. but to reach extreme vacua the appliances must be much more improved, and ultimate perfection will not be attained until we shall have discarded the mechanical and perfected an _electrical_ vacuum pump. molecules and atoms can be thrown out of a bulb under the action of an enormous potential: _this_ will be the principle of the vacuum pump of the future. for the present, we must secure the best results we can with mechanical appliances. in this respect, it might not be out of the way to say a few words about the method of, and apparatus for, producing excessively high degrees of exhaustion of which i have availed myself in the course of these investigations. it is very probable that other experimenters have used similar arrangements; but as it is possible that there may be an item of interest in their description, a few remarks, which will render this investigation more complete, might be permitted. [illustration: fig. 30.--apparatus used for obtaining high degrees of exhaustion.] the apparatus is illustrated in a drawing shown in fig. 30. s represents a sprengel pump, which has been specially constructed to better suit the work required. the stop-cock which is usually employed has been omitted, and instead of it a hollow stopper s has been fitted in the neck of the reservoir r. this stopper has a small hole h, through which the mercury descends; the size of the outlet o being properly determined with respect to the section of the fall tube t, which is sealed to the reservoir instead of being connected to it in the usual manner. this arrangement overcomes the imperfections and troubles which often arise from the use of the stopcock on the reservoir and the connection of the latter with the fall tube. the pump is connected through a u-shaped tube t to a very large reservoir r_1. especial care was taken in fitting the grinding surfaces of the stoppers p and p_1, and both of these and the mercury caps above them were made exceptionally long. after the u-shaped tube was fitted and put in place, it was heated, so as to soften and take off the strain resulting from imperfect fitting. the u-shaped tube was provided with a stopcock c, and two ground connections g and g_1--one for a small bulb b, usually containing caustic potash, and the other for the receiver r, to be exhausted. the reservoir r_1 was connected by means of a rubber tube to a slightly larger reservoir r_2, each of the two reservoirs being provided with a stopcock c_1 and c_2, respectively. the reservoir r_2 could be raised and lowered by a wheel and rack, and the range of its motion was so determined that when it was filled with mercury and the stopcock c_2 closed, so as to form a torricellian vacuum in it when raised, it could be lifted so high that the mercury in reservoir r_1 would stand a little above stopcock c_1; and when this stopcock was closed and the reservoir r_2 descended, so as to form a torricellian vacuum in reservoir r_1, it could be lowered so far as to completely empty the latter, the mercury filling the reservoir r_2 up to a little above stopcock c_2. the capacity of the pump and of the connections was taken as small as possible relatively to the volume of reservoir r_1, since, of course, the degree of exhaustion depended upon the ratio of these quantities. with this apparatus i combined the usual means indicated by former experiments for the production of very high vacua. in most of the experiments it was convenient to use caustic potash. i may venture to say, in regard to its use, that much time is saved and a more perfect action of the pump insured by fusing and boiling the potash as soon as, or even before, the pump settles down. if this course is not followed the sticks, as ordinarily employed, may give moisture off at a certain very slow rate, and the pump may work for many hours without reaching a very high vacuum. the potash was heated either by a spirit lamp or by passing a discharge through it, or by passing a current through a wire contained in it. the advantage in the latter case was that the heating could be more rapidly repeated. generally the process of exhaustion was the following:--at the start, the stop-cocks c and c_1 being open, and all other connections closed, the reservoir r_2 was raised so far that the mercury filled the reservoir r_1 and a part of the narrow connecting u-shaped tube. when the pump was set to work, the mercury would, of course, quickly rise in the tube, and reservoir r_2 was lowered, the experimenter keeping the mercury at about the same level. the reservoir r_2 was balanced by a long spring which facilitated the operation, and the friction of the parts was generally sufficient to keep it almost in any position. when the sprengel pump had done its work, the reservoir r_2 was further lowered and the mercury descended in r_1 and filled r_2, whereupon stopcock c_2 was closed. the air adhering to the walls of r_1 and that absorbed by the mercury was carried off, and to free the mercury of all air the reservoir r_2 was for a long time worked up and down. during this process some air, which would gather below stopcock c_2, was expelled from r_2 by lowering it far enough and opening the stopcock, closing the latter again before raising the reservoir. when all the air had been expelled from the mercury, and no air would gather in r_2 when it was lowered, the caustic potash was resorted to. the reservoir r_2 was now again raised until the mercury in r_1 stood above stopcock c_1. the caustic potash was fused and boiled, and the moisture partly carried off by the pump and partly re-absorbed; and this process of heating and cooling was repeated many times, and each time, upon the moisture being absorbed or carried off, the reservoir r_2 was for a long time raised and lowered. in this manner all the moisture was carried off from the mercury, and both the reservoirs were in proper condition to be used. the reservoir r_2 was then again raised to the top, and the pump was kept working for a long time. when the highest vacuum obtainable with the pump had been reached the potash bulb was usually wrapped with cotton which was sprinkled with ether so as to keep the potash at a very low temperature, then the reservoir r_2 was lowered, and upon reservoir r_1 being emptied the receiver r was quickly sealed up. when a new bulb was put on, the mercury was always raised above stopcock c_1 which was closed, so as to always keep the mercury and both the reservoirs in fine condition, and the mercury was never withdrawn from r_1 except when the pump had reached the highest degree of exhaustion. it is necessary to observe this rule if it is desired to use the apparatus to advantage. by means of this arrangement i was able to proceed very quickly, and when the apparatus was in perfect order it was possible to reach the phosphorescent stage in a small bulb in less than 15 minutes, which is certainly very quick work for a small laboratory arrangement requiring all in all about 100 pounds of mercury. with ordinary small bulbs the ratio of the capacity of the pump, receiver, and connections, and that of reservoir r was about 1-20, and the degrees of exhaustion reached were necessarily very high, though i am unable to make a precise and reliable statement how far the exhaustion was carried. what impresses the investigator most in the course of these experiences is the behavior of gases when subjected to great rapidly alternating electrostatic stresses. but he must remain in doubt as to whether the effects observed are due wholly to the molecules, or atoms, of the gas which chemical analysis discloses to us, or whether there enters into play another medium of a gaseous nature, comprising atoms, or molecules, immersed in a fluid pervading the space. such a medium surely must exist, and i am convinced that, for instance, even if air were absent, the surface and neighborhood of a body in space would be heated by rapidly alternating the potential of the body; but no such heating of the surface or neighborhood could occur if all free atoms were removed and only a homogeneous, incompressible, and elastic fluid--such as ether is supposed to be--would remain, for then there would be no impacts, no collisions. in such a case, as far as the body itself is concerned, only frictional losses in the inside could occur. it is a striking fact that the discharge through a gas is established with ever increasing freedom as the frequency of the impulses is augmented. it behaves in this respect quite contrarily to a metallic conductor. in the latter the impedance enters prominently into play as the frequency is increased, but the gas acts much as a series of condensers would: the facility with which the discharge passes through seems to depend on the rate of change of potential. if it act so, then in a vacuum tube even of great length, and no matter how strong the current, self-induction could not assert itself to any appreciable degree. we have, then, as far as we can now see, in the gas a conductor which is capable of transmitting electric impulses of any frequency which we may be able to produce. could the frequency be brought high enough, then a queer system of electric distribution, which would be likely to interest gas companies, might be realized: metal pipes filled with gas--the metal being the insulator, the gas the conductor--supplying phosphorescent bulbs, or perhaps devices as yet uninvented. it is certainly possible to take a hollow core of copper, rarefy the gas in the same, and by passing impulses of sufficiently high frequency through a circuit around it, bring the gas inside to a high degree of incandescence; but as to the nature of the forces there would be considerable uncertainty, for it would be doubtful whether with such impulses the copper core would act as a static screen. such paradoxes and apparent impossibilities we encounter at every step in this line of work, and therein lies, to a great extent, the claim of the study. i have here a short and wide tube which is exhausted to a high degree and covered with a substantial coating of bronze, the coating allowing barely the light to shine through. a metallic clasp, with a hook for suspending the tube, is fastened around the middle portion of the latter, the clasp being in contact with the bronze coating. i now want to light the gas inside by suspending the tube on a wire connected to the coil. any one who would try the experiment for the first time, not having any previous experience, would probably take care to be quite alone when making the trial, for fear that he might become the joke of his assistants. still, the bulb lights in spite of the metal coating, and the light can be distinctly perceived through the latter. a long tube covered with aluminium bronze lights when held in one hand--the other touching the terminal of the coil--quite powerfully. it might be objected that the coatings are not sufficiently conducting; still, even if they were highly resistant, they ought to screen the gas. they certainly screen it perfectly in a condition of rest, but not by far perfectly when the charge is surging in the coating. but the loss of energy which occurs within the tube, notwithstanding the screen, is occasioned principally by the presence of the gas. were we to take a large hollow metallic sphere and fill it with a perfect incompressible fluid dielectric, there would be no loss inside of the sphere, and consequently the inside might be considered as perfectly screened, though the potential be very rapidly alternating. even were the sphere filled with oil, the loss would be incomparably smaller than when the fluid is replaced by a gas, for in the latter case the force produces displacements; that means impact and collisions in the inside. no matter what the pressure of the gas may be, it becomes an important factor in the heating of a conductor when the electric density is great and the frequency very high. that in the heating of conductors by lightning discharges air is an element of great importance, is almost as certain as an experimental fact. i may illustrate the action of the air by the following experiment: i take a short tube which is exhausted to a moderate degree and has a platinum wire running through the middle from one end to the other. i pass a steady or low frequency current through the wire, and it is heated uniformly in all parts. the heating here is due to conduction, or frictional losses, and the gas around the wire has--as far as we can see--no function to perform. but now let me pass sudden discharges, or a high frequency current, through the wire. again the wire is heated, this time principally on the ends and least in the middle portion; and if the frequency of the impulses, or the rate of change, is high enough, the wire might as well be cut in the middle as not, for practically all the heating is due to the rarefied gas. here the gas might only act as a conductor of no impedance diverting the current from the wire as the impedance of the latter is enormously increased, and merely heating the ends of the wire by reason of their resistance to the passage of the discharge. but it is not at all necessary that the gas in the tube should he conducting; it might be at an extremely low pressure, still the ends of the wire would be heated--as, however, is ascertained by experience--only the two ends would in such, case not be electrically connected through the gaseous medium. now what with these frequencies and potentials occurs in an exhausted tube occurs in the lightning discharges at ordinary pressure. we only need remember one of the facts arrived at in the course of these investigations, namely, that to impulses of very high frequency the gas at ordinary pressure behaves much in the same manner as though it were at moderately low pressure. i think that in lightning discharges frequently wires or conducting objects are volatilized merely because air is present and that, were the conductor immersed in an insulating liquid, it would be safe, for then the energy would have to spend itself somewhere else. from the behavior of gases to sudden impulses of high potential i am led to conclude that there can be no surer way of diverting a lightning discharge than by affording it a passage through a volume of gas, if such a thing can be done in a practical manner. there are two more features upon which i think it necessary to dwell in connection with these experiments--the "radiant state" and the "non-striking vacuum." any one who has studied crookes' work must have received the impression that the "radiant state" is a property of the gas inseparably connected with an extremely high degree of exhaustion. but it should be remembered that the phenomena observed in an exhausted vessel are limited to the character and capacity of the apparatus which is made use of. i think that in a bulb a molecule, or atom, does not precisely move in a straight line because it meets no obstacle, but because the velocity imparted to it is sufficient to propel it in a sensibly straight line. the mean free path is one thing, but the velocity--the energy associated with the moving body--is another, and under ordinary circumstances i believe that it is a mere question of potential or speed. a disruptive discharge coil, when the potential is pushed very far, excites phosphorescence and projects shadows, at comparatively low degrees of exhaustion. in a lightning discharge, matter moves in straight lines as ordinary pressure when the mean free path is exceedingly small, and frequently images of wires or other metallic objects have been produced by the particles thrown off in straight lines. [illustration: fig. 31.--bulb showing radiant lime stream at low exhaustion.] i have prepared a bulb to illustrate by an experiment the correctness of these assertions. in a globe l (fig. 31) i have mounted upon a lamp filament f a piece of lime l. the lamp filament is connected with a wire which leads into the bulb, and the general construction of the latter is as indicated in fig. 19, before described. the bulb being suspended from a wire connected to the terminal of the coil, and the latter being set to work, the lime piece l and the projecting parts of the filament f are bombarded. the degree of exhaustion is just such that with the potential the coil is capable of giving phosphorescence of the glass is produced, but disappears as soon as the vacuum is impaired. the lime containing moisture, and moisture being given off as soon as heating occurs, the phosphorescence lasts only for a few moments. when the lime has been sufficiently heated, enough moisture has been given off to impair materially the vacuum of the bulb. as the bombardment goes on, one point of the lime piece is more heated than other points, and the result is that finally practically all the discharge passes through that point which is intensely heated, and a white stream of lime particles (fig. 31) then breaks forth from that point. this stream is composed of "radiant" matter, yet the degree of exhaustion is low. but the particles move in straight lines because the velocity imparted to them is great, and this is due to three causes--to the great electric density, the high temperature of the small point, and the fact that the particles of the lime are easily torn and thrown off--far more easily than those of carbon. with frequencies such as we are able to obtain, the particles are bodily thrown off and projected to a considerable distance; but with sufficiently high frequencies no such thing would occur: in such case only a stress would spread or a vibration would be propagated through the bulb. it would be out of the question to reach any such frequency on the assumption that the atoms move with the speed of light; but i believe that such a thing is impossible; for this an enormous potential would be required. with potentials which we are able to obtain, even with a disruptive discharge coil, the speed must be quite insignificant. as to the "non-striking vacuum," the point to be noted is that it can occur only with low frequency impulses, and it is necessitated by the impossibility of carrying off enough energy with such impulses in high vacuum since the few atoms which are around the terminal upon coming in contact with the same are repelled and kept at a distance for a comparatively long period of time, and not enough work can be performed to render the effect perceptible to the eye. if the difference of potential between the terminals is raised, the dielectric breaks down. but with very high frequency impulses there is no necessity for such breaking down, since any amount of work can be performed by continually agitating the atoms in the exhausted vessel, provided the frequency is high enough. it is easy to reach--even with frequencies obtained from an alternator as here used--a stage at which the discharge does not pass between two electrodes in a narrow tube, each of these being connected to one of the terminals of the coil, but it is difficult to reach a point at which a luminous discharge would not occur around each electrode. a thought which naturally presents itself in connection with high frequency currents, is to make use of their powerful electro-dynamic inductive action to produce light effects in a sealed glass globe. the leading-in wire is one of the defects of the present incandescent lamp, and if no other improvement were made, that imperfection at least should be done away with. following this thought, i have carried on experiments in various directions, of which some were indicated in my former paper. i may here mention one or two more lines of experiment which have been followed up. many bulbs were constructed as shown in fig. 32 and fig. 33. in fig. 32 a wide tube t was sealed to a smaller w-shaped tube u, of phosphorescent glass. in the tube t was placed a coil c of aluminium wire, the ends of which were provided with small spheres t and t_1 of aluminium, and reached into the u tube. the tube t was slipped into a socket containing a primary coil through which usually the discharges of leyden jars were directed, and the rarefied gas in the small u tube was excited to strong luminosity by the high-tension currents induced in the coil c. when leyden jar discharges were used to induce currents in the coil c, it was found necessary to pack the tube t tightly with insulating powder, as a discharge would occur frequently between the turns of the coil, especially when the primary was thick and the air gap, through which the jars discharged, large, and no little trouble was experienced in this way. [illustration: fig. 32.--electro-dynamic induction tube.] [illustration: fig. 33--electro-dynamic induction lamp.] in fig. 33 is illustrated another form of the bulb constructed. in this case a tube t is sealed to a globe l. the tube contains a coil c, the ends of which pass through two small glass tubes t and t_1, which are sealed to the tube t. two refractory buttons m and m_1 are mounted on lamp filaments which are fastened to the ends of the wires passing through the glass tubes t and t_1. generally in bulbs made on this plan the globe l communicated with the tube t. for this purpose the ends of the small tubes t and t_1 were just a trifle heated in the burner, merely to hold the wires, but not to interfere with the communication. the tube t, with the small tubes, wires through the same, and the refractory buttons m and m_1, was first prepared, and then sealed to globe l, whereupon the coil c was slipped in and the connections made to its ends. the tube was then packed with insulating powder, jamming the latter as tight as possible up to very nearly the end, then it was closed and only a small hole left through which the remainder of the powder was introduced, and finally the end of the tube was closed. usually in bulbs constructed as shown in fig. 33 an aluminium tube a was fastened to the upper end s of each of the tubes t and t_1, in order to protect that end against the heat. the buttons m and m_1 could be brought to any degree of incandescence by passing the discharges of leyden jars around the coil c. in such bulbs with two buttons a very curious effect is produced by the formation of the shadows of each of the two buttons. another line of experiment, which has been assiduously followed, was to induce by electro-dynamic induction a current or luminous discharge in an exhausted tube or bulb. this matter has received such able treatment at the hands of prof. j.j. thomson that i could add but little to what he has made known, even had i made it the special subject of this lecture. still, since experiences in this line have gradually led me to the present views and results, a few words must be devoted here to this subject. it has occurred, no doubt, to many that as a vacuum tube is made longer the electromotive force per unit length of the tube, necessary to pass a luminous discharge through the latter, gets continually smaller; therefore, if the exhausted tube be made long enough, even with low frequencies a luminous discharge could be induced in such a tube closed upon itself. such a tube might be placed around a ball or on a ceiling, and at once a simple appliance capable of giving considerable light would be obtained. but this would be an appliance hard to manufacture and extremely unmanageable. it would not do to make the tube up of small lengths, because there would be with ordinary frequencies considerable loss in the coatings, and besides, if coatings were used, it would be better to supply the current directly to the tube by connecting the coatings to a transformer. but even if all objections of such nature were removed, still, with low frequencies the light conversion itself would be inefficient, as i have before stated. in using extremely high frequencies the length of the secondary--in other words, the size of the vessel--can be reduced as far as desired, and the efficiency of the light conversion is increased, provided that means are invented for efficiently obtaining such high frequencies. thus one is led, from theoretical and practical considerations, to the use of high frequencies, and this means high electromotive forces and small currents in the primary. when he works with condenser charges--and they are the only means up to the present known for reaching these extreme frequencies--he gets to electromotive forces of several thousands of volts per turn of the primary. he cannot multiply the electro-dynamic inductive effect by taking more turns in the primary, for he arrives at the conclusion that the best way is to work with one single turn--though he must sometimes depart from this rule--and he must get along with whatever inductive effect he can obtain with one turn. but before he has long experimented with the extreme frequencies required to set up in a small bulb an electromotive force of several thousands of volts he realizes the great importance of electrostatic effects, and these effects grow relatively to the electro-dynamic in significance as the frequency is increased. now, if anything is desirable in this case, it is to increase the frequency, and this would make it still worse for the electro-dynamic effects. on the other hand, it is easy to exalt the electrostatic action as far as one likes by taking more turns on the secondary, or combining self-induction and capacity to raise the potential. it should also be remembered that, in reducing the current to the smallest value and increasing the potential, the electric impulses of high frequency can be more easily transmitted through a conductor. these and similar thoughts determined me to devote more attention to the electrostatic phenomena, and to endeavor to produce potentials as high as possible, and alternating as fast as they could be made to alternate. i then found that i could excite vacuum tubes at considerable distance from a conductor connected to a properly constructed coil, and that i could, by converting the oscillatory current of a condenser to a higher potential, establish electrostatic alternating fields which acted through the whole extent of a room, lighting up a tube no matter where it was held in space. i thought i recognized that i had made a step in advance, and i have persevered in this line; but i wish to say that i share with all lovers of science and progress the one and only desire--to reach a result of utility to men in any direction to which thought or experiment may lead me. i think that this departure is the right one, for i cannot see, from the observation of the phenomena which manifest themselves as the frequency is increased, what there would remain to act between two circuits conveying, for instance, impulses of several hundred millions per second, except electrostatic forces. even with such trifling frequencies the energy would be practically all potential, and my conviction has grown strong that, to whatever kind of motion light may be due, it is produced by tremendous electrostatic stresses vibrating with extreme rapidity. of all these phenomena observed with currents, or electric impulses, of high frequency, the most fascinating for an audience are certainly those which are noted in an electrostatic field acting through considerable distance, and the best an unskilled lecturer can do is to begin and finish with the exhibition of these singular effects. i take a tube in the hand and move it about, and it is lighted wherever i may hold it; throughout space the invisible forces act. but i may take another tube and it might not light, the vacuum being very high. i excite it by means of a disruptive discharge coil, and now it will light in the electrostatic field. i may put it away for a few weeks or months, still it retains the faculty of being excited. what change have i produced in the tube in the act of exciting it? if a motion imparted to the atoms, it is difficult to perceive how it can persist so long without being arrested by frictional losses; and if a strain exerted in the dielectric, such as a simple electrification would produce, it is easy to see how it may persist indefinitely, but very difficult to understand why such a condition should aid the excitation when we have to deal with potentials which are rapidly alternating. since i have exhibited these phenomena for the first time, i have obtained some other interesting effects. for instance, i have produced the incandescence of a button, filament, or wire enclosed in a tube. to get to this result it was necessary to economize the energy which is obtained from the field and direct most of it on the small body to be rendered incandescent. at the beginning the task appeared difficult, but the experiences gathered permitted me to reach the result easily. in fig. 34 and fig. 35 two such tubes are illustrated which are prepared for the occasion. in fig. 34 a short tube t_1, sealed to another long tube t, is provided with a stem s, with a platinum wire sealed in the latter. a very thin lamp filament l is fastened to this wire, and connection to the outside is made through a thin copper wire w. the tube is provided with outside and inside coatings, c and c_1 respectively, and is filled as far as the coatings reach with conducting, and the space above with insulating powder. these coatings are merely used to enable me to perform two experiments with the tube--namely, to produce the effect desired either by direct connection of the body of the experimenter or of another body to the wire w, or by acting inductively through the glass. the stem s is provided with an aluminium tube a, for purposes before explained, and only a small part of the filament reaches out of this tube. by holding the tube t_1 anywhere in the electrostatic field the filament is rendered incandescent. [illustration: fig. 34.--tube with filament rendered incandescent in an electrostatic field.] [illustration: fig. 35.--crookes' experiment in electrostatic field.] a more interesting piece of apparatus is illustrated in fig. 35. the construction is the same as before, only instead of the lamp filament a small platinum wire p, sealed in a stem s, and bent above it in a circle, is connected to the copper wire w, which is joined to an inside coating c. a small stem s_1 is provided with a needle, on the point of which is arranged to rotate very freely a very light fan of mica v. to prevent the fan from falling out, a thin stem of glass g is bent properly and fastened to the aluminium tube. when the glass tube is held anywhere in the electrostatic field the platinum wire becomes incandescent, and the mica vanes are rotated very fast. intense phosphorescence may be excited in a bulb by merely connecting it to a plate within the field, and the plate need not be any larger than an ordinary lamp shade. the phosphorescence excited with these currents is incomparably more powerful than with ordinary apparatus. a small phosphorescent bulb, when attached to a wire connected to a coil, emits sufficient light to allow reading ordinary print at a distance of five to six paces. it was of interest to see how some of the phosphorescent bulbs of professor crookes would behave with these currents, and he has had the kindness to lend me a few for the occasion. the effects produced are magnificent, especially by the sulphide of calcium and sulphide of zinc. from the disruptive discharge coil they glow intensely merely by holding them in the hand and connecting the body to the terminal of the coil. to whatever results investigations of this kind may lead, their chief interest lies for the present in the possibilities they offer for the production of an efficient illuminating device. in no branch of electric industry is an advance more desired than in the manufacture of light. every thinker, when considering the barbarous methods employed, the deplorable losses incurred in our best systems of light production, must have asked himself, what is likely to be the light of the future? is it to be an incandescent solid, as in the present lamp, or an incandescent gas, or a phosphorescent body, or something like a burner, but incomparably more efficient? there is little chance to perfect a gas burner; not, perhaps, because human ingenuity has been bent upon that problem for centuries without a radical departure having been made--though this argument is not devoid of force-but because in a burner the higher vibrations can never be reached except by passing through all the low ones. for how is a flame produced unless by a fall of lifted weights? such process cannot be maintained without renewal, and renewal is repeated passing from low to high vibrations. one way only seems to be open to improve a burner, and that is by trying to reach higher degrees of incandescence. higher incandescence is equivalent to a quicker vibration; that means more light from the same material, and that, again, means more economy. in this direction some improvements have been made, but the progress is hampered by many limitations. discarding, then, the burner, there remain the three ways first mentioned, which are essentially electrical. suppose the light of the immediate future to be a solid rendered incandescent by electricity. would it not seem that it is better to employ a small button than a frail filament? from many considerations it certainly must be concluded that a button is capable of a higher economy, assuming, of course, the difficulties connected with the operation of such a lamp to be effectively overcome. but to light such a lamp we require a high potential; and to get this economically we must use high frequencies. such considerations apply even more to the production of light by the incandescence of a gas, or by phosphorescence. in all cases we require high frequencies and high potentials. these thoughts occurred to me a long time ago. incidentally we gain, by the use of very high frequencies, many advantages, such as a higher economy in the light production, the possibility of working with one lead, the possibility of doing away with the leading-in wire, etc. the question is, how far can we go with frequencies? ordinary conductors rapidly lose the facility of transmitting electric impulses when the frequency is greatly increased. assume the means for the production of impulses of very great frequency brought to the utmost perfection, every one will naturally ask how to transmit them when the necessity arises. in transmitting such impulses through conductors we must remember that we have to deal with _pressure_ and _flow_, in the ordinary interpretation of these terms. let the pressure increase to an enormous value, and let the flow correspondingly diminish, then such impulses--variations merely of pressure, as it were--can no doubt be transmitted through a wire even if their frequency be many hundreds of millions per second. it would, of course, be out of question to transmit such impulses through a wire immersed in a gaseous medium, even if the wire were provided with a thick and excellent insulation for most of the energy would be lost in molecular bombardment and consequent heating. the end of the wire connected to the source would be heated, and the remote end would receive but a trifling part of the energy supplied. the prime necessity, then, if such electric impulses are to be used, is to find means to reduce as much as possible the dissipation. the first thought is, employ the thinnest possible wire surrounded by the thickest practicable insulation. the next thought is to employ electrostatic screens. the insulation of the wire may be covered with a thin conducting coating and the latter connected to the ground. but this would not do, as then all the energy would pass through the conducting coating to the ground and nothing would get to the end of the wire. if a ground connection is made it can only be made through a conductor offering an enormous impedance, or though a condenser of extremely small capacity. this, however, does not do away with other difficulties. if the wave length of the impulses is much smaller than the length of the wire, then corresponding short waves will be sent up in the conducting coating, and it will be more or less the same as though the coating were directly connected to earth. it is therefore necessary to cut up the coating in sections much shorter than the wave length. such an arrangement does not still afford a perfect screen, but it is ten thousand times better than none. i think it preferable to cut up the conducting coating in small sections, even if the current waves be much longer than the coating. if a wire were provided with a perfect electrostatic screen, it would be the same as though all objects were removed from it at infinite distance. the capacity would then be reduced to the capacity of the wire itself, which would be very small. it would then be possible to send over the wire current vibrations of very high frequencies at enormous distance without affecting greatly the character of the vibrations. a perfect screen is of course out of the question, but i believe that with a screen such as i have just described telephony could be rendered practicable across the atlantic. according to my ideas, the gutta-percha covered wire should be provided with a third conducting coating subdivided in sections. on the top of this should be again placed a layer of gutta-percha and other insulation, and on the top of the whole the armor. but such cables will not be constructed, for ere long intelligence--transmitted without wires--will throb through the earth like a pulse through a living organism. the wonder is that, with the present state of knowledge and the experiences gained, no attempt is being made to disturb the electrostatic or magnetic condition of the earth, and transmit, if nothing else, intelligence. it has been my chief aim in presenting these results to point out phenomena or features of novelty, and to advance ideas which i am hopeful will serve as starting points of new departures. it has been my chief desire this evening to entertain you with some novel experiments. your applause, so frequently and generously accorded, has told me that i have succeeded. in conclusion, let me thank you most heartily for your kindness and attention, and assure you that the honor i have had in addressing such a distinguished audience, the pleasure i have had in presenting these results to a gathering of so many able men--and among them also some of those in whose work for many years past i have found enlightenment and constant pleasure--i shall never forget. [transcriber's note: corrected the following typesetting errors: 1) 'preceived' to 'perceived', page 16. 2) 'disharging' to 'discharging', page 30. 3) 'park' to 'spark', page 33. 4) 'pssition' to 'position', page 50. 5) 'to th opposite side' to 'to the opposite side', page 56. 6) 's resses' to 'stresses', page 147.] tom swift and his wireless message or the castaways of earthquake island by victor appleton author of "tom swift and his motor-cycle," "tom swift and his motor boat," "tom swift and his airship," "tom swift and his submarine boat," "tom swift and his electric runabout," etc. illustrated books by victor appleton the tom swift series tom swift and his motor-cycle or fun and adventures on the road tom swift and his motor-boat or the rivals of lake carlopa tom swift and his airship or the stirring cruise of the red cloud tom swift and his submarine boat or under the ocean for sunken treasure tom swift and his electric runabout or the speediest car on the road tom swift and his wireless message or the castaways of earthquake island tom swift among the diamond makers or the secret of phantom mountain tom swift in the caves of ice or the wreck of the airship tom swift and his sky racer or the quickest flight on record tom swift and his electric rifle or daring adventures in elephant land (other volumes in preparation) tom swift and his wireless message contents i. an appeal for aid ii. miss nestor's news iii. tom knocks out andy iv. mr. damon will go along v. vol-planing to earth vi. the new airship vii. making some changes viii. andy foger's revenge ix. the whizzer flies x. over the ocean xi. a night of terror xii. a downward glide xiii. on earthquake island xiv. a night in camp xv. the other castaway xvi. an alarming theory xvii. a mighty shock xviii. mr. jenks has diamonds xix. secret operations xx. the wireless plant xxi. messages into space xxii. anxious days xxiii. a reply in the dark xxiv. "we are lost!" xxv. the rescue-conclusion chapter i an appeal for aid tom swift stepped from the door of the machine shop, where he was at work making some adjustments to the motor of his airship, and glanced down the road. he saw a cloud of dust, which effectually concealed whatever was causing it. "some one must be in a hurry this morning," the lad remarked, "looks like a motor speeding along. my! but we certainly do need rain," he added, as he looked up toward the sky. "it's very dusty. well, i may as well get back to work. i'll take the airship out for a flight this afternoon, if the wind dies down a bit." the young inventor, for tom swift himself had built the airship, as well as several other crafts for swift locomotion, turned to re-enter the shop. something about the approaching cloud of dust, however, held his attention. he glanced more intently at it. "if it's an automobile coming along," he murmured, "it's moving very slowly, to make so much fuss. and i never saw a motor-cycle that would kick up as much sand, and not speed along more. it ought to be here by now. i wonder what it can be?" the cloud of highway dirt rolled along, making some progress toward tom's house and the group of shops and other buildings surrounding it. but, as the lad had said, the dust did not move at all quickly in comparison to any of the speedy machines that might be causing it. and the cloud seemed momentarily to grow thicker and thicker. "i wonder if it could be a miniature tornado, or a cyclone or whirlwind?" and tom spoke aloud, a habit of his when he was thinking, and had no one to talk to. "yet it can hardly be that." he went on. "guess i'll watch and see what it is." nearer and nearer came the dust cloud. tom peered anxiously ahead, a puzzled look on his face. a few seconds later there came from the midst of the obscuring cloud a voice, exclaiming: "g'lang there now, boomerang! keep to' feet a-movin' an' we sho' will make a record. 'tain't laik we was a autermobiler, er a electricity car, but we sho' hab been goin' sence we started. yo' sho' done yo'se'f proud t'day, boomerang, an' i'se gwine t' keep mah promise an' gib yo' de bestest oats i kin find. ah reckon massa tom swift will done say we brought dis yeah message t' him as quick as anybody could." then there followed the sound of hoofbeats on the dusty road, and the rattle of some many-jointed vehicle, with loose springs and looser wheels. "eradicate sampson!" exclaimed tom. "but who would ever think that the colored man's mule could get up such speed as that cloud of dust indicates. his mule's feet must be working overtime, but he goes backward about as often as he moves forward. that accounts for it. there's lots of dust, but not much motion." once more, from the midst of the ball-like cloud of dirt came the voice of the colored man: "now behave yo'se'f, boomerang. we'm almost dere an' den yo' kin sit down an' rest if yo' laik. jest keep it up a little longer, an' we'll gib massa tom his telephone. g'lang now, boomerang." the tattoo of hoofbeats was slowing up now, and the cloud of dust was not so heavy. it was gradually blowing away. tom swift walked down to the fence that separated the house, grounds and shops from the road. as he got there the sounds of the mule's progress, and the rattle of the wagon, suddenly ceased. "g'lang! g'lang! don't yo' dare t' stop now, when we am most dere!" cried eradicate sampson. "keep a-movin', boomerang!" "it's all right, eradicate. i'm here," called tom, and when the last of the dust had blown away, the lad waved his hand to an aged colored man, who sat upon the seat of perhaps the most dilapidated wagon that was ever dignified by such a name. it was held together with bits of wire, rope and strings, and each of the four wheels leaned out at a different angle. it was drawn by a big mule, whose bones seemed protruding through his skin, but that fact evidently worried him but little, for now the animal was placidly sleeping, while standing up, his long ears moving slowly to and fro. "am dat yo', massa tom?" asked eradicate, ceasing his task of jerking on the lines, to which operation the mule paid not the least attention. "yes, i'm here, rad," replied tom, smiling. "i came out of my shop to see what all the excitement was about. how did you ever get your mule to make so much dust?" "i done promise him an extra helpin' ob oats ef he make good time," said the colored man. "an' he done it, too. did yo' see de dust we made?" "i sure did, but you didn't do much else. and you didn't make very good time. i watched you, and you came along like an ice wagon after a day's work on the fourth of july. you were going fast, but moving slow." "i 'spects we was, massa tom," was the colored man's answer. "but boomerang done better dan i 'spected he would. i done tole him yo'd be in a hurry t' git yo' telephone, an' he sho' did trot along." "my telephone?" repeated tom, wonderingly. "what have you and your mule boomerang to do with my telephone? that's up in the house." "no, it ain't! it's right yeah in mah pocket," chuckled eradicate, opening a ragged coat, and reaching for something. "i got yo' telephone right yeah." he went on. "de agent at de station see me dribin' ober dis way, an' he done ast he t' deliber it. he said as how he ain't got no messenger boy now, 'cause de one he done hab went on a strike fo' five cents mo' a day. so i done took de telephone," and with that the colored man pulled out a crumpled yellow envelope. "oh, you mean a telegram," said tom, with a laugh, as he took the message from the odd colored man. "well, maybe it's telegraf, but i done understood de agent t' say telephone. anyhow, dere it is. an' i s'pects we'd better git along, boomerang." the mule never moved, though eradicate yanked on the reins, and used a splintered whip with energy. "i said as how we'd better git along, boomerang," went on the darkey, raising his voice, "dinnah am mos' ready, an' i'm goin' t' giv yo' an extra helpin' ob oats." the effect of these words seemed magical. the mule suddenly came to life, and was about to start off. "i done thought dat would cotch yo', boomerang," chuckled eradicate. "wait a minute, rad," called tom, who was tearing open the envelope of the telegram. "i might want to send an answer back by you. i wonder who is wiring me now?" he read the message slowly, and eradicate remarked: "'taint no kind ob use, massa tom, fo' t' send a message back wif me." "why not?" asked the young inventor, looking up from the sheet of yellow paper. "'case as how i done promised boomerang his airman, an' he won't do nothin' till he has it. ef i started him back t' town now he would jest lay down in de road. i'll take de answer back fo' you dis arternoon." "all right, perhaps that will do," assented tom. "i haven't quite got the hang of this yet. drop around this afternoon, rad," and as the colored man, who, with his mule boomerang, did odd jobs around the village, started off down the highway, in another cloud of dust, tom swift resumed the reading of the message. "hum, this is rather queer," he mused, when having read it once, he began at it again. "it must have cost him something to send all this over the wire. he could just as well have written it. so he wants my help, eh? well, i never heard of him, and he may be all right, but i had other plans, and i don't know whether i can spare the time to go to philadelphia or not. i'll have to think it over. an electric airship, eh? he's sort of following along the lines of my inventions. wants my aid--hum--well, i don't know--" tom's musings were suddenly cut short by the approach of an elderly gentleman, who was walking slowly down the path that led from the house to the country highway which ran in front of it. "a telegram, tom?" asked the newcomer. "yes, dad," was the reply. "i was just coming in to ask your advice about it. eradicate brought it to me." "what, with his mule, boomerang?" and the gentleman seemed much amused. "how did he ever get up speed enough to deliver a telegram?" "oh, eradicate has some special means he uses on his mule when he's in a hurry. but listen to this message, dad. it's from a mr. hosmer fenwick, of philadelphia. he says:" "'tom swift--can you come on to philadelphia at once and aid me in perfecting my new electric airship? i want to get it ready for a flight before some government experts who have promised to purchase several if it works well. i am in trouble, and i can't get it to rise off the ground. i need help. i have heard about your airship, and the other inventions you and your father have perfected, and i am sure you can aid me. i am stuck. can you hurry to the quaker city? i will pay you well. answer at once!'" "well?" remarked mr. swift, questioningly, as his son finished reading the telegram. "what are you going to do about it, tom?" "i don't exactly know, dad. i was going to ask your advice. what would you do? who is this mr. fenwick?" "well, he is an inventor of some note, but he has had many failures. i have not heard of him in some years until now. he is a gentleman of wealth, and can be relied upon to do just as he says. we are slightly acquainted. perhaps it would be well to aid him, if you can spare the time. not that you need the money, but inventors should be mutually helpful. if you feel like going to philadelphia, and aiding him in getting his electric airship in shape, you have my permission." "i don't know," answered tom, doubtfully. "i was just getting my monoplane in shape for a little flight. it was nothing particular, though. dad, i think i will take a run to philadelphia, and see if i can help mr. fenwick. i'll wire him that i am coming, to-morrow or next day." "very well," assented mr. swift, and then he and his son went into one of the shops, talking of a new invention which they were about to patent. tom little knew what a strange series of adventures were to follow his decision to go to the quaker city, nor the danger involved in aiding mr. fenwick to operate his electric airship. chapter ii miss nestor's news "when do you think you will go to philadelphia, tom?" asked mr. swift, a little later, as the aged inventor and his son were looking over some blueprints which garret jackson, an engineer employed by them, had spread out on a table. "i don't exactly know," was the answer. "it's quite a little run from shopton, because i can't get a through train. but i think i'll start tomorrow." "why do you go by train?" asked mr. jackson. "why--er--because--" was tom's rather hesitating reply. "how else would i go?" "your monoplane would be a good deal quicker, and you wouldn't have to change cars," said the engineer. "that is if you don't want to take out the big airship. why don't you go in the monoplane?" "by jove! i believe i will!" exclaimed tom. "i never thought of that, though it's a wonder i didn't. i'll not take the red cloud, as she's too hard to handle alone. but the butterfly will be just the thing," and tom looked over to where a new monoplane rested on the three bicycle wheels which formed part of its landing frame. "i haven't had it out since i mended the left wing tip," he went on, "and it will also be a good chance to test my new rudder. i believe i will go to philadelphia by the butterfly." "well, as long as that's settled, suppose you give us your views on this new form of storage battery," suggested mr. swift, with a fond glance at his son, for tom's opinion was considered valuable in matters electrical, as those of you, who have read the previous books in this series, well know. the little group in the machine shop was soon deep in the discussion of ohms, amperes, volts and currents, and, for a time, tom almost forgot the message calling him to philadelphia. taking advantage of the momentary lull in the activities of the young inventor, i will tell my readers something about him, so that those who have no previous introduction to him may feel that he is a friend. tom swift lived with his father, barton swift, a widower, in the village of shopton, new york. there was also in the household mrs. baggert, the aged housekeeper, who looked after tom almost like a mother. garret jackson, an engineer and general helper, also lived with the swifts. eradicate sampson might also be called a retainer of the family, for though the aged colored man and his mule boomerang did odd work about the village, they were more often employed by tom and his father than by any one else. eradicate was so called because, as he said, he "eradicated" the dirt. he did whitewashing, made gardens, and did anything else that was needed. boomerang was thus named by his owner, because, as eradicate said, "yo' nebber know jest what dat mule am goin' t' do next. he may go forward or he may go backward, jest laik them australian boomerangs." there was another valued friend of the family, wakefield damon by name, to whom the reader will be introduced in due course. and then there was mary nestor, about whom i prefer to let tom tell you himself, for he might be jealous if i talked too much about her. in the first book of this series, called "tom swift and his motor-cycle," there was told how he became possessed of the machine, after it had nearly killed mr. damon, who was learning to ride it. mr. damon, who had a habit of "blessing" everything from his collar button to his shoe laces, did not "bless" the motor-cycle after it tried to climb a tree with him; and he sold it to tom very cheaply. tom repaired it, invented some new attachments for it, and had a number of adventures on it. not the least of these was trailing after a gang of scoundrels who tried to get possession of a valuable patent model belonging to mr. swift. our second book, called "tom swift and his motor-boat," related some exciting times following the acquisition by the young inventor of a speedy craft which the thieves of the patent model had stolen. in the boat tom raced with andy foger, a town bully, and beat him. tom also took out on pleasure trips his chum, ned newton, who worked in a shopton bank, and the two had fine times together. need i also say that mary nestor also had trips in the motor-boat? besides some other stirring adventures in his speedy craft tom rescued, from a burning balloon that fell into the lake, the aeronaut, john sharp. later mr. sharp and tom built an airship, called the red cloud, in which they had some strenuous times. their adventures in this craft of the air form the basis for the third book of the series, entitled "tom swift and his airship." in the red cloud, tom and his friends, including mr. damon, started to make a record flight. they left shopton the night when the bank vault was blown open, and seventy-five thousand dollars stolen. because of evidence given by andy foger, and his father, suspicion pointed to tom and his friends as the robbers, and they were pursued. but they turned the tables by capturing the real burglars, and defeating the mean plans of the fogers. not satisfied with having mastered the air tom and his father turned their attention to the water. mr. swift perfected a new type of craft, and in the fourth book of the series, called "tom swift and his submarine," you may read how he went after a sunken treasure. the party had many adventures, and were in no little danger from their enemies before they reached the wreck with its store of gold. the fifth book of the series, named "tom swift and his electrical runabout," told how tom built the speediest car on the road, and won a prize with it, and also saved a bank from ruin. tom had to struggle against odds, not only in his inventive work, but because of the meanness of jealous enemies, including andy foger, who seemed to bear our hero a grudge of long standing. even though tom had, more than once, thrashed andy well, the bully was always seeking a chance to play some mean trick on the young inventor. sometimes he succeeded, but more often the tables were effectually turned. it was now some time since tom had won the prize in his electric car and, in the meanwhile he had built himself a smaller airship, or, rather, monoplane, named the butterfly. in it he made several successful trips about the country, and gave exhibitions at numerous aviation meets; once winning a valuable prize for an altitude flight. in one trip he had met with a slight accident, and the monoplane had only just been repaired after this when he received the message summoning him to philadelphia. "well, tom," remarked his father that afternoon, "if you are going to the quaker city, to see mr. fenwick to-morrow, you'd better be getting ready. have you wired him that you will come?" "no, i haven't, dad," was the reply. "i'll get a message ready at once, and when eradicate comes back i'll have him take it to the telegraph office." "i wouldn't do that, tom." "do what?" "trust it to eradicate. he means all right, but there's no telling when that mule of his may lie down in the road, and go to sleep. then your message won't get off, and mr. fenwick may be anxiously waiting for it. i wouldn't like to offend him, for, though he and i have not met in some years, yet i would be glad if you could do him a favor. why not take the message yourself?" "guess i will, dad. i'll run over to mansburg in my electric car, and send the message from there. it will go quicker, and, besides, i want to get some piano wire to strengthen the wings of my monoplane." "all right, tom, and when you telegraph to mr. fenwick, give him my regards, and say that i hope his airship will be a success. so it's an electric one, eh? i wonder how it works? but you can tell me when you come back." "i will, dad. mr. jackson, will you help me charge the batteries of my car? i think they need replenishing. then i'll get right along to mansburg." mansburg was a good-sized city some miles from the village of shopton, and tom and his father had frequent business there. the young inventor and the engineer soon had the electric car in readiness for a swift run, for the charging of the batteries could be done in much less than the time usual for such an operation, owing to a new system perfected by tom. the latter was soon speeding along the road, wondering what sort of an airship mr. fenwick would prove to have, and whether or not it could be made to fly. "it's easy enough to build an airship," mused tom, "but the difficulty is to get them off the ground, and keep them there." he knew, for there had been several failures with his monoplane before it rose like a bird and sailed over the tree-tops. the lad was just entering the town, and had turned around a corner, twisting about to pass a milk wagon, when he suddenly saw, darting out directly in the path of his car, a young lady. "look out!" yelled tom, ringing his electric gong, at the same time shutting off the current, and jamming on the powerful brakes. there was a momentary scream of terror from the girl, and then, as she looked at tom, she exclaimed: "why, tom swift! what are you trying to do? run me down?" "mary--miss nestor!" ejaculated our hero, in some confusion. he had brought his car to a stop, and had thrown open the door, alighting on the crossing, while a little knot of curious people gathered about. "i didn't see you," went on the lad. "i came from behind the milk wagon, and--" "it was my fault," miss nestor hastened to add. "i, too, was waiting for the milk wagon to pass, and when it got out of my way, i darted around the end of it, without looking to see if anything else was coming. i should have been more careful, but i'm so excited that i hardly know what i'm doing." "excited? what's the matter?" asked tom, for he saw that his friend was not her usual calm self. "has anything happened, mary?" "oh, i've such news to tell you!" she exclaimed. "then get in here, and we'll go on." advised tom. "we are collecting a crowd. come and take a ride; that is if you have time." "of course i have," the girl said, with a little blush, which tom thought made her look all the prettier. "then we can talk. but where are you going?" "to send a message to a gentleman in philadelphia, saying that i will help him out of some difficulties with his new electric airship. i'm going to take a run down there in my monoplane, butterfly, to-morrow, and--" "my! to hear you tell it, one would think it wasn't any more to make an airship flight than it was to go shopping," interrupted mary, as she entered the electric car, followed by tom, who quickly sent the vehicle down the street. "oh, i'm getting used to the upper air," he said. "but what is the news you were to tell me?" "did you know mamma and papa had gone to the west indies?" asked the girl. "no! i should say that was news. when did they go? i didn't know they intended to make a trip." "neither did they; nor i, either. it was very sudden. they sailed from new york yesterday. mr. george hosbrook, a business friend of papa's, offered to take them on his steam yacht, resolute. he is making a little pleasure trip, with a party of friends, and he thought papa and mamma might like to go." "he wired to them, they got ready in a rush, caught the express to new york, and went off in such a hurry that i can hardly realize it yet. i'm left all alone, and i'm in such trouble!" "well, i should say that was news," spoke tom. "oh, you haven't heard the worst yet," went on mary. "i don't call the fact that papa and mamma went off so suddenly much news. but the cook just left unexpectedly, and i have invited a lot of girl friends to come and stay with me, while mamma and papa are away; and now what shall i do without a cook? i was on my way down to an intelligence office, to get another servant, when you nearly ran me down! now, isn't that news?" "i should say it was--two kinds," admitted tom, with a smile. "well, i'll help you all i can. i'll take you to the intelligence office, and if you can get a cook, by hook or by crook, i'll bundle her into this car, and get her to your house before she can change her mind. and so your people have gone to the west indies?" "yes, and i wish i had the chance to go." "so do i," spoke tom, little realizing how soon his wish might be granted. "but is there any particular intelligence office you wish to visit?" "there's not much choice," replied mary nestor, with a smile, "as there's only one in town. oh. i do hope i can get a cook! it would be dreadful to have nothing to eat, after i'd asked the girls to spend a month with me; wouldn't it?" tom agreed that it certainly would, and they soon after arrived at the intelligence office. chapter iii tom knocks out andy "do you want me to come in and help you?" asked the young inventor, of miss nestor. "do you know anything about hiring a cook?" she inquired, with an arch smile. "i'm afraid i don't," the lad was obliged to confess. "then i'm a little doubtful of your ability to help me. but i'm ever so much obliged to you. i'll see if i can engage one. the cook who just left went away because i asked her to make some apple turnovers. some of the girls who are coming are very fond of them." "so am i," spoke tom, with a smile. "are you, indeed? then, if the cook i hope to get now will make them, i'll invite you over to have some, and--also meet my friends." "i'd rather come when just you, and the turnovers and the cook are there," declared tom, boldly, and mary, with a blush, made ready to leave the electric car. "thank you," she said, in a low voice. "if i can't help you select a cook," went on tom, "at least let me call and take you home when you have engaged one." "oh, it will be too much trouble," protested miss nestor. "not at all. i have only to send a message, and get some piano wire, and then i'll call back here for you. i'll take you and the new cook back home flying." "all right, but don't fly so fast. the cook may get frightened, and leave before she has a chance to make an apple turnover." "i'll go slower. i'll be back in fifteen minutes," called tom, as he swung the car out away from the curb, while mary nestor went into the intelligence office. tom wrote and sent this message to mr. hostner fenwick, of philadelphia: "will come on to-morrow in my aeroplane, and aid you all i can. will not promise to make your electric airship fly, though. father sends regards." "just rush that, please," he said to the telegraph agent, and the latter, after reading it over, remarked: "it'll rush itself, i reckon, being all about airships, and things like that," and he laughed as tom paid him. selecting several sizes of piano wire of great strength, to use as extra guy-braces on the butterfly, tom re-entered his electric car, and hastened back to the intelligence office, where he had left his friend. he saw her standing at the front door, and before he could alight, and go to her, miss nestor came out to meet him. "oh, tom!" she exclaimed, with a little tragic gesture, "what do you think?" "i don't know," he answered good-naturedly. "does the new cook refuse to come unless you do away with apple turnovers?" "no, it isn't that. i have engaged a real treasure, i'm sure, but as soon as i mentioned that you would take us home in the electric automobile, she flatly refused to come. she said walking was the only way she would go. she hasn't been in this country long. but the worst of it is that a rich woman has just telephoned in for a cook, and if i don't get this one away, the rich lady may induce her to come to her house, and i'll be without one! oh, what shall i do?" and poor mary looked quite distressed. "humph! so she's afraid of electric autos; eh?" mused tom. "that's queer. leave it to me, mary, and perhaps i can fix it. you want to get her away from here in a hurry; don't you?" "yes, because servants are so scarce, that they are engaged almost as soon as they register at the intelligence office. i know the one i have hired is suspicious of me, since i have mentioned your car, and she'll surely go with mrs. duy puyster when she comes. i'm sorry i spoke of the automobile." "well, don't worry. it's partly my fault, and perhaps i can make amends. i'll talk to the new cook," decided the young inventor. "oh, tom, i don't believe it will do any good. she won't come, and all my girl friends will arrive shortly." miss nestor was quite distressed. "leave it to me," suggested the lad, with an assumed confidence he did not feel. he left the car, and walked toward the office. entering it, with miss nestor in his wake, he saw a pleasant-faced irish girl, sitting on a bench, with a bundle beside her. "and so you don't want to ride in an auto?" began tom. "no, an' it's no use of the likes of you askin' me, either," answered the girl, but not impudently. "i am afeered of thim things, an' i won't work in a family that owns one." "but we don't own one," said mary. the girl only sniffed. "it is the very latest means of traveling," tom went on, "and there is absolutely no danger. i will drive slowly." "no!" snapped the new cook. tom was rather at his wits' ends. at that moment the telephone rang, and tom and mary, listening, could hear the proprietress of the intelligence office talking to mrs. duy puyster over the wire. "we must get her away soon," whispered mary, with a nod at the irish girl, "or we'll lose her." tom was thinking rapidly, but no plan seemed to come to him. a moment later one of the assistants of the office led out from a rear room another irish girl,--who, it seems, had just engaged herself to work in the country. "good-by, bridget," said this girl, to the one mary nestor had hired. "i'm off now. the carriage has just come for me. i'm goin' away in style." "good luck, sarah," wished bridget. tom looked out of the window. a dilapidated farm wagon, drawn by two rusty-looking horses, just drawing up at the curb. "there is your employer, sarah," said the proprietress of the office. "you will have a nice ride to the country and i hope you will like the place." a typical country farmer alighted from the wagon, leaving a woman, evidently his wife, or the seat. he called out: "i'll git th' servant-gal, 'mandy, an' we'll drive right out hum. then you won't have such hard work any more." "an' so that's the style you was tellin' me of; eh, sarah?" asked the cook whom miss nestor had engaged. "that's queer style, sarah." sarah was blushing from shame and mortification. tom was quick to seize the advantage thus offered. "bridget, if you appreciate style," he said, "you will come in the automobile. i have one of the very latest models, and it is very safe. but perhaps you prefer a farm wagon." "indade an' i don't!" was the ready response. "i'll go wid you now if only to show sarah malloy thot i have more style than her! she was boastin' of the fine place she had, an' th' illigant carriage that was comin' t' take her to the counthry. if that's it i want none of it! i'll go wid you an' th' young gintleman. style indade!" and, gathering up her bundle she followed tom and mary to the waiting auto. they entered it and started off, just as mrs. duy puyster drove up in her elegantly appointed carriage, while sarah, with tears of mortification in her eyes, climbed up beside the farmer and his wife. "you saved the day for me, tom," whispered miss nestor, as the young inventor increased the speed of his car. "it was only just in time." "don't forget the apple turnovers," he whispered back. once she had made the plunge, the new cook seemed to lose her fears of the auto, and enjoyed the ride. in a short time she had been safely delivered at miss nestor's home, while that young lady repeated her thanks to tom, and renewed her invitation for him to come and sample the apple turnovers, which tom promised faithfully to do, saying he would call on his return from philadelphia. musing on the amusing feature of his trip, tom was urging his auto along at moderate speed, when, as he turned down a country road, leading to his home, he saw, coming toward him, a carriage, drawn by a slow-moving, white horse, and containing a solitary figure. "why, that looks like andy foger," spoke tom, half aloud. "i wonder what he's doing out driving? his auto must be out of commission. but that's not strange, considering the way he abuses the machine. it's in the repair shop half the time." he slowed down still more, for he did not know but that andy's horse might be skittish. he need have no fears, however, for the animal did not seem to have much more life than did eradicate's mule, boomerang. as tom came nearer the carriage, he was surprised to see andy deliberately swing his horse across the road, blocking the highway by means of the carriage and steed. "well, andy foger, what does that mean?" cried tom, indignantly, as he brought his car to a sudden stop. "why do you block the road?" "because i want to," snarled the bully, taking out a notebook and pencil, and pretending to make some notes about the property in front of which he had halted. "i'm in the real estate business now," went on andy, "and i'm getting descriptions of the property i'm going to sell. guess i've got a right to stop in the road if i want to!" "but not to block it up," retorted tom. "that's against the law. pull over and let me pass!" "suppose i don't do it?" "then i'll make you!" "huh! i'd like to see you try it!" snapped andy. "if you make trouble for me, it will be the worse for you." "if you pull to one side, so i can pass, there'll be no trouble," said tom, seeing that andy wished to pick a quarrel. "well, i'm not going to pull aside until i finish putting down this description," and the bully continued to write with tantalizing slowness. "look here!" exclaimed tom swift, with sudden energy. "i'm not going to stand for this! either you pull to one side and let me pass, or--" "well, what will you do?" demanded the bully. "i'll shove you to one side, and you can take the consequences!" "you won't dare to!" "i won't, eh? just you watch." tom threw forward the lever of his car. there was a hum of the motor, and the electric moved ahead. andy had continued to write in the book, but at this sound he glanced up. "don't you dare to bunk into me!" yelled andy. "if you do i'll sue you for damages!" "get out of the way, or i'll shove you off the road!" threatened tom, calmly. "i'll not go until i get ready." "oh, yes you will," responded our hero quietly. he sent his car ahead slowly but surely. it was within a few feet of the carriage containing andy. the bully had dropped his notebook, and was shaking his fist at tom. as for the young inventor he had his plans made. he saw that the horse was a quiet, sleepy one, that would not run away, no matter what happened, and tom only intended to gently push the carriage to one side, and pass on. the front of his auto came up against the other vehicle. "here, you stop!" cried andy, savagely. "it's too late now," answered tom, grimly. andy reached for the horsewhip. tom put on a little more power, and the carriage began to slide across the road, but the old horse never opened his eyes. "take that!" cried andy, raising his whip, with the intention of slashing tom across the face, for the front of the auto was open. but the blow never fell, for, the next instant, the carriage gave a lurch as one of the wheels slid against a stone, and, as andy was standing up, and leaning forward, he was pitched head first out into the road. "by jove! i hope i haven't hurt him!" gasped tom, as he leaped from his auto, which he had brought to a stop. the young inventor bent over the bully. there was a little cut on andy's forehead, and his face was white. he had been most effectually knocked out entirely by his own meanness and fault, but, none the less, tom was frightened. he raised up andy's head on his arm, and brushed back his hair. andy was unconscious. chapter iv mr. damon will go along at first tom was greatly frightened at the sight of andy's pale face. he feared lest the bully might be seriously hurt. but when he realized that the fall from the carriage, which was a low one, was not hard, and that andy had landed on his outstretched hands before his head came in contact with the earth, our hero was somewhat reassured. "i wish i had some water, with which to bathe his head," tom murmured, and he looked about in vain for some. but it was not needed, for, a moment later, andy opened his eyes, and, when he saw tom bending over, and holding him, the bully exclaimed: "here! you let me go! don't you hit me again, tom swift, or i'll punch you!" "i didn't hit you," declared tom, while andy tore himself away, and struggled to his feet. "yes, you did, too, hit me!" "i did not! you tried to strike me with your whip, as i was shoving your carriage out of the way, which i had a perfect right to do, as you were blockading the highway. you lost your balance and fell. it was your own fault." "well, you'll suffer for it, just the same, snarled andy, and then, putting his hand to his head, and bringing it away, with some drops of blood on it, he cried out:" "oh, i'm hurt! i'm injured! get a doctor, or maybe i'll bleed to death!" he began blubbering, for andy, like all bullies, was a coward. "you're not hurt," asserted tom, trying not to laugh. "it's only a scratch. next time don't try to blockade the whole street, and you won't get into trouble. are you able to drive home; or shall i take you in my car?" "i wouldn't ride in your car!" snapped the ugly lad. "you go on, and mind your business now, and i'll pay you back for this, some day. i could have you arrested!" "and so could i have you locked up for obstructing traffic. but i'll not. your rig isn't damaged, and you'd better drive home." the old white horse had not moved, and was evidently glad of the rest. a glance satisfied tom that the carriage had not been damaged, and, getting into his car, while andy was brushing the dust from his clothes, our hero started the motor. there was now room enough to pass around the obstructing carriage, and soon tom was humming down the road, leaving a much discomfited bully behind him. "tom swift is too smart--thinking he can run everybody, and everything, to suit himself," growled andy, as he finished dusting off his clothes, and wiping the blood from his face. as tom had said, the wound was but a scratch, though the bully's head ached, and he felt a little dizzy. "i wish i'd hit him with the horsewhip," he went on, vindictively. "i'll get square with him some day." andy had said this many times, but he had never yet succeeded in permanently getting the best of tom. pondering on some scheme of revenge the rich lad--for mr. foger, his father, was quite wealthy--drove on. meanwhile tom, rather wishing the little encounter had not taken place, but refusing to blame himself for what had occurred, was speeding toward home. "let's see," he murmured, as he drove along in his powerful car. "i've got quite a lot to do if i make an early start for philadelphia, in my airship, to-morrow. i want to tighten the propeller on the shaft a trifle, and give the engine a good try-out. then, too, i think i'd better make the landing springs a little stiffer. the last time i made a descent the frame was pretty well jarred up. yes, if i make that air trip to-morrow i'll have to do some tall hustling when i get home." the electric runabout swung into the yard of the swift house, and tom brought it to a stop opposite the side door. he looked about for a sight of his father, mrs. baggert or garret jackson. the only person visible was eradicate sampson, working in the garden. "hello, rad," called tom. "anybody home?" "yais, massa tom," answered the colored man. "yo' dad an' anodder gen'mans hab jest gone in de house." "who's the other gentleman, rad?" asked tom, and the negro, glad of an excuse to cease the weeding of the onion bed, came shuffling forward. "it's de gen'mans what is allers saying his prayers," he answered. "saying his prayers?" repeated tom. "yep. yo' knows what i means, massa tom. he's allers askin' a blessin' on his shoes, or his rubbers, or his necktie." "oh, you mean mr. wakefield damon." "yais, sah, dat's who i done means. mr. wakefull lemon--dat's sho' him." at that moment there sounded, within the house, the voices of mr. swift, and some one else in conversation. "and so tom has decided to make a run to the quaker city in the butterfly, to-morrow," mr. swift was saying, "and he's going to see if he can be of any service to this mr. fenwick." "bless my watch chain!" exclaimed the other voice. "you don't say so! why i know mr. fenwick very well--he and i used to go to school together, but bless my multiplication tables--i never thought he'd amount to anything! and so he's built an airship; and tom is going to help him with it? why, bless my collar button, i've a good notion to go along and see what happens. bless my very existence, but i think i will!" "that's mr. damon all right," observed tom, with a smile, as he advanced toward the dining-room, whence the voices proceeded. "dat's what i done tole you!" said eradicate, and, with slow and lagging steps he went back to weed the onion bed. "how are you, mr. damon," called our hero, as he mounted the steps of the porch. "why, it's tom--he's back!" exclaimed the eccentric man. "why, bless my shoe laces, tom! how are you? i'm real glad to see you. bless my eyeglasses, but i am! i just returned from a little western trip, and i thought i'd run over and see how you are. i came in my car--had two blowouts on the way, too. bless my spark plug, but the kind of tires one gets now-a-days are a disgrace! however, i'm here, and your father has just told me about you going to philadelphia in your monoplane, to help a fellow-inventor with his airship. it's real kind of you. bless my topknot if it isn't! do you know what i was just saying?" "i heard you mention that you knew mr. fenwick," replied tom, with a smile, as he shook hands with mr. damon. "so i do, and, what's more, i'd like to see his airship. will your butterfly carry two passengers?" "easily, mr. damon." "then i'll tell you what i'm going to do. if you'll let me i'll take that run to philadelphia with you!" "glad to have you come along," responded tom, heartily. "then i'll go, and, what's more, if fenwick's ship will rise, i'll go with you in that--bless my deflection rudder if i don't, tom!" and puffing up his cheeks, as he exploded these words, mr. damon fairly raised himself on his tiptoes, and shook tom's hand again. chapter v vol-planing to earth for a moment after mr. damon's announcement tom did not reply. mr. swift, too, seemed a little at a loss for something to say. they did not quite know how to take their eccentric friend at times. "of course i'll be glad of your company, mr. damon," said tom: "but you must remember that my butterfly is not like the red cloud. there is more danger riding in the monoplane than there is in the airship. in the latter, if the engine happens to stop, the sustaining gas will prevent us from falling. but it isn't so in an aeroplane. when your engine stops there--" "well, what happens?" asked mr. damon, impatiently, for tom hesitated. "you have to vol-plane back to earth." "vol-plane?" and there was a questioning note in mr. damon's voice. "yes, glide down from whatever height you are at when the engine stalls. come down in a series of dips from the upper currents. vol-planing, the french call it, and i guess it's as good a word as any." "have you ever done it?" asked the odd character. "oh, yes, several times." "then, bless my fur overcoat! i can do it, too, tom. when will you be ready to start?" "to-morrow morning. now you are sure you won't get nervous and want to jump, if the engine happens to break down?" "not a bit of it. i'll vol-plane whenever you are ready," and mr. damon laughed. "well, we'll hope we won't have to," went on tom. "and i'll be very glad of your company. mr. fenwick will, no doubt, be pleased to see you. i've never met him, and it will be nice to have some one to introduce me. suppose you come out and see what sort of a craft you are doomed to travel in to-morrow, mr. damon. i believe you never saw my new monoplane." "that's right, i haven't, but i'd be glad to. i declare, i'm getting to be quite an aviator," and mr. damon chuckled. a little later, tom, having informed his father of the sending of the message, took his eccentric friend out to the shop, and exhibited the butterfly. as many of you have seen the ordinary monoplane, either on exhibition or in flight, i will not take much space to describe tom's. sufficient to say it was modeled after the one in which bleriot made his first flight across the english channel. the body was not unlike that of a butterfly or dragon fly, long and slender, consisting of a rectangular frame with canvas stretched over it, and a seat for two just aft of the engine and controlling levers. back of the seat stretched out a long framework, and at the end was a curved plane, set at right angles to it. the ends of the plane terminated in flexible wings, to permit of their being bent up or down, so as to preserve the horizontal equilibrium of the craft. at the extreme end was the vertical rudder, which sent the monoplane to left or right. forward, almost exactly like the front set of wings of the dragon fly, was the large, main plane, with the concave turn toward the ground. there was the usual propeller in front, operated by a four cylinder motor, the cylinders being air cooled, and set like the spokes of a wheel around the motor box. the big gasolene tank, and other mechanism was in front of the right-hand operator's seat, where tom always rode. he had seldom taken a passenger up with him, though the machine would easily carry two, and he was a little nervous about the outcome of the trip with mr. damon. "how do you like the looks of it?" asked the young inventor, as he wheeled the butterfly out of the shed, and began pumping up the tires of the bicycle wheels on which it ran over the ground, to get impetus enough with which to rise. "it looks a little frail, compared to the big red cloud, tom," answered the eccentric man, "but i'm going up in her just the same; bless my buttons if i'm not." tom could not but admire the grit of his friend. the rest of the day was busily spent making various adjustments to the monoplane, putting on new wire stays, changing the rudder cables, and tuning up the motor. the propeller was tightened on the shaft, and toward evening tom announced that all was in readiness for a trial flight. "want to come, mr. damon?" he asked. "i'll wait, and see how it acts with you aboard," was the answer. "not that i'm afraid, for i'm going to make the trip in the morning, but perhaps it won't work just right now." "oh, i guess it will," ventured tom, and in order to be able to know just how his butterfly was going to behave, with a passenger of mr. damon's weight, the young inventor placed a bag of sand on the extra seat. the monoplane was then wheeled to the end of the starting ground. tom took his place in the seat, and mr. jackson started the propeller. at first the engine failed to respond, but suddenly with a burst of smoke, and a spluttering of fire the cylinders began exploding. the hat of mr. damon, who was standing back of the machine, was blown off by the wind created by the propeller. "bless my gaiters!" he exclaimed, "i never thought it was as strong as that!" "let go!" cried tom to mr. jackson and eradicate, who were holding back the monoplane from gliding over the ground. "all right," answered the engineer. an instant later the explosions almost doubled, for tom turned on more gasolene. then, like some live thing, the butterfly rushed across the starting ground. faster and faster it went, until the young inventor, knowing that he had motion enough, tilted his planes to catch the wind. up he went from earth, like some graceful bird, higher and higher, and then, in a big spiral, he began ascending until he was five hundred feet in the air. up there he traveled back and forth, in circles, and in figure eights, desiring to test the machine in various capacities. suddenly the engine stopped, and to those below, anxiously watching, the silence became almost oppressive, for tom had somewhat descended, and the explosions had been plainly heard by those observing him. but now they ceased! "his engine's stalled!" cried garret jackson. mr. swift heard the words, and looked anxiously up at his son. "is he in any danger?" gasped mr. damon. no one answered him. like some great bird, disabled in mid flight, the monoplane swooped downward. a moment later a hearty shout from tom reassured them. "he shut off the engine on purpose," said mr. jackson. "he is vol-planing back to earth!" nearer and nearer came the butterfly. it would shoot downward, and then, as tom tilted the planes, would rise a bit, losing some of the great momentum. in a series of maneuvers like this, the young inventor reached the earth, not far from where his father and the others stood. down came the butterfly, the springs of the wheel frame taking the shock wonderfully well. "she's all right--regular bird!" cried tom, in enthusiasm, when the machine had come to a stop after rolling over the ground, and he had leaped out. "we'll make a good flight to-morrow, mr. damon, if the weather holds out this way." "good!" cried the eccentric man. "i shall be delighted." they made the start early the next morning, there being hardly a breath of wind. there was not a trace of nervousness noticeable about mr. damon, as he took his place in the seat beside tom. the lad had gone carefully over the entire apparatus, and had seen to it that, as far as he could tell, it was in perfect running order. "when will you be back, tom?" asked his father. "to-night, perhaps, or to-morrow morning. i don't know just what mr. fenwick wants me to do. but if it is anything that requires a long stay, i'll come back, and let you know, and then run down to philadelphia again. i may need some of my special tools to work with. i'll be back to-night perhaps." "shall i keep supper for you?" asked mrs. baggert, the housekeeper. "i don't know," answered tom, with a laugh. "perhaps i'll drop down at miss nestor's, and have some apple turnovers," for he had told them or the incident of hiring the new cook. "well," he went on to mr. damon, "are you all ready?" "as ready as i ever shall be. do you think we'll have to do any vol-planing, tom?" "hard to say, but it's not dangerous when there's no wind. all right, garret. start her off." the engineer whirled the big wooden, built-up propeller, and with a rattle and roar of the motor, effectually drowning any but the loudest shouts, the butterfly was ready for her flight. tom let the engine warm up a bit before calling to his friends to let go, and then, when he had thrown the gasolene lever forward, he shouted a good-by and cried: "all right! let go!" forward, like a hound from the leash, sprang the little monoplane. it ran perhaps for five hundred feet, and then, with a tilting of the wings, to set the air currents against them, it sprang into the air. "we're off!" cried mr. damon, waving his hand to those on the ground below. "yes, we're off," murmured tom. "now for the quaker city!" he had mapped out a route for himself the night before, and now, picking out the land-marks, he laid as straight a course as possible for philadelphia. the sensation of flying along, two thousand feet high, in a machine almost as frail as a canoe, was not new to tom. it was, in a degree, to mr. damon, for, though the latter had made frequent trips in the large airship, this mode of locomotion, as if he was on the back of some bird, was much different. still, after the first surprise, he got used to it. "bless my finger ring!" he exclaimed, "i like it!" "i thought you would," said tom, in a shout, and he adjusted the oil feed to send more lubricant into the cylinders. the earth stretched out below them, like some vari-colored relief map, but they could not stop to admire any particular spot long, for they were flying fast, and were beyond a scene almost as quickly as they had a glimpse of it. "how long will it take us?" yelled mr. damon into tom's ear. "i hope to do it in three hours," shouted back the young inventor. "what! why it takes the train over five hours." "yes, i know, but we're going direct, and it's only about two hundred and fifty miles. that's only about eighty an hour. we're doing seventy-five now, and i haven't let her out yet." "she goes faster than the red cloud," cried mr. damon. tom nodded. it was hard work to talk in that rush of air. for an hour they shot along, their speed gradually increasing. tom called out the names of the larger places they passed over. he was now doing better than eighty an hour as the gage showed. the trip was a glorious one, and the eyes of the young inventor and his friend sparkled in delight as they rushed forward. two hours passed. "going to make it?" fairly howled mr. damon. tom nodded again. "be there in time for dinner," he announced in a shout. it lacked forty minutes of the three hours when tom, pointing with one hand down below, while with the other he gripped the lever of the rudder, called: "north philadelphia!" "so soon?" gasped mr. damon. "well, we certainly made speed! where are you going to land?" "i don't know," answered the young inventor, "i'll have to pick out the best place i see. it's no fun landing in a city. no room to run along, after you're down." "what's the matter with franklin field?" cried mr. damon. "out where they play football." "good! the very thing!" shouted tom. "mr. fenwick lives near there," went on mr. damon, and tom nodded comprehendingly. they were now over north philadelphia, and, in a few minutes more were above the quaker city itself. they were flying rather low, and as the people in the streets became aware of their presence there was intense excitement. tom steered for the big athletic field, and soon saw it in the distance. with a suddenness that was startling the motor ceased its terrific racket. the monoplane gave a sickening dip, and tom had to adjust the wing tips and rudder quickly to prevent it slewing around at a dangerous angle. "what's the matter?" cried mr. damon, "did you shut it off on purpose?" "no!" shouted tom, "something's gone wrong!" "gone wrong! bless my overshoes! is there any danger?" "we'll have to vol-plane to earth," answered tom, and there was a grim look on his face. he had never executed this feat with a passenger aboard. he was wondering how the butterfly would behave. but he would know very soon, for already the tiny monoplane was shooting rapidly toward the big field, which was now swarming with a curious crowd. chapter vi the new airship for a brief instant after the stopping of the motor, and the consequent sudden dropping toward the earth of the monoplane, tom glanced at mr. damon. the latter's face was rather pale, but he seemed calm and collected. his lips moved slightly, and tom, even in those tense moments, wondered if the odd gentleman was blessing anything in particular, or everything in general. tom threw up the tilting plane, to catch more air beneath it, and bring the butterfly in a more parallel position to the earth. this, in a manner, checked the downward flight, and they glided along horizontally for a hundred feet or more. "is--is there any great danger, tom?" asked mr. damon. "i think not," answered the young inventor, confidently. "i have done this same thing before, and from greater heights. the only thing that bothers me is that there are several cross-currents of air up here, which make it difficult to manage the planes and wing tips. but i think we'll make a good landing." "bless my overcoat!" exclaimed mr. damon "i certainly hope so." conversation was more easily carried on now, as the motor was not spitting fire and throbbing like a battery of gatling guns. tom thought perhaps it might start on the spark, as the propeller was slowly swinging from the force of air against it. he tried, but there was no explosion. he had scarcely hoped for it, as he realized that some part of the mechanism must have broken. down they glided, coming nearer and nearer to the earth. the crowd in the big athletic field grew larger. shouts of wonder and fear could be heard, and people could be seen running excitedly about. to tom and mr. damon they looked like dolls. reaching the limit of the parallel glide the monoplane once more shot down on an incline toward the earth with terrible speed. the ground seemed to rush up to meet mr. damon. "look out!" he cried to tom. "we're going to hit something!" "not yet," was the calm answer "i'm going to try a new stunt. hold fast!" "what are you going to do?" "some spirals. i think that will let us down easier, but the craft is likely to tilt a bit, so hold on." the young inventor shifted the movable planes and rudder, and, a moment later, the butterfly swung violently around, like a polo pony taking a sudden turn after the ball. mr. damon slid to one side of his seat, and made a frantic grab for one of the upright supports. "i made too short a turn!" cried tom, easing off the craft, which righted itself in an instant. "the air currents fooled me." under his skillful guidance, the monoplane was soon slowly approaching the earth in a series of graceful curves. it was under perfect control, and a smile of relief came on the face of the young inventor. seeing it mr. damon took courage, and his hands, which had grasped the uprights with such firmness that his knuckles showed white with the strain, were now removed. he sat easily in his seat. "we're all right now," declared tom. "i'll take a couple of forward glides now, and we'll land." he sent the machine straight ahead. it gathered speed in an instant. then, with an upward tilt it was slackened, almost as if brakes had been applied. once more it shot toward the earth, and once more it was checked by an up-tilted plane. then with a thud which shook up the occupants of the two seats, the butterfly came to the ground, and ran along on the three bicycle wheels. swiftly it slid over the level ground. a more ideal landing place would have been hard to find. scores of willing hands reached out, and checked the momentum of the little monoplane, and tom and mr. damon climbed from their seats. the crowd set up a cheer, and hundreds pressed around the aviators. several sought to reach, and touch the machine, for they had probably never been so close to one before, though airship flights are getting more and more common. "where did you come from?" "are you trying for a record?" "how high did you get?" "did you fall, or come down on purpose?" "can't you start your motor in mid-air?" these, and scores of other questions were fairly volleyed at tom and mr. damon. the young inventor good-naturedly answered them as best he could. "we were coming down anyhow," he explained, "but we did not calculate on vol-planing. the motor was stalled, and i had to glide. please keep away from the machine. you might damage it." the arrival of several policemen, who were attracted by the crowd, served to keep the curious ones back away from the butterfly, or the men, boys and women (for there were a number of the latter in the throng) might have caused serious trouble. tom made a hasty examination of the motor, and, having satisfied himself that only a minor difficulty had caused it to stop, he decided to put the monoplane in some safe place, and proceed to mr. fenwick's house. the lad was just asking one of the officers if the air craft could not be put in one of the grandstands which surrounded the field, when a voice on the outskirts of the crowd excitedly exclaimed: "let me pass, please. i want to see that airship. i'm building one myself, and i need all the experience i can get. let me in, please." a man pushed his way into the crowd, and wormed his way to where tom and mr. damon stood. at the sight of him, the eccentric individual cried out: "why bless my pocket-knife! if it isn't mr. fenwick!" "mr. fenwick?" gasped tom. "yes. the inventor we came to see!" at the same moment the newcomer cried out: "wakefield damon!" "that's who i am," answered tom's friend, "and let me introduce you to mr. swift, the inventor of more machines than i can count. he and i were coming to see you, when we had a slight accident, and we landed here. but that didn't matter, for we intended to land here anyhow, as i knew it was near your house. only we had to vol-plane back to earth, and i can't say that i'd care for that, as a steady diet. bless my radiator, but i'm glad we've arrived safely." "did you come all the way from your home in that?" asked mr. fenwick of tom, as he shook hands with him, and nodded at the monoplane. "oh, yes. it's not much of a trip." "well, i hope my airship will do as well. but something seems to be wrong with it, and i have hopes that you can help me discover what it is, i know your father, and i have heard much of your ability. that is why i requested your aid." "i'm afraid i've been much overrated," spoke tom, modestly, "but i'll do all i can for you. i must now leave my monoplane in a safe place, however." "i'll attend to that," mr. fenwick hastened to assure him. "leave it to me." by this time a lieutenant of police, in charge of several reserve officers, had arrived on the scene, for the crowd was now very large, and, as mr. fenwick knew this official, he requested that tom's machine be protected from damage. it was arranged that it could be stored in a large, empty shed, and a policeman would be left on guard. then, seeing that it was all right, tom, mr. damon and mr. fenwick started for the latter's house. "i am very anxious to show you the whizzer," said mr. fenwick, as they walked along. "the whizzer?" repeated tom, wonderingly. "yes, that's what i call my electric airship. it hasn't 'whizzed' any to speak of yet, but i have hopes that it will, now that you are here to help me. we will take one of these taxicabs, and soon be at my house. i was out for a stroll, when i saw your monoplane coming down, and i hastened to franklin field to see it." the three entered an automobile, and were soon being driven to the inventor's home. a little later he led them out to a big shed which occupied nearly all of a large lot, in back of mr. fenwick's house. "does it take up all that room?" asked tom. "oh, yes, the whizzer is pretty good size. there she is!" cried mr. fenwick proudly, as he threw open the doors of the shed, and tom and mr. damon, looking in, saw a large triplane, with a good-sized gas bag hovering over it, and a strange collection of rudders, wings and planes sticking out from either side. amidships was an enclosed car, or cabin, and a glimpse into it served to disclose to the young inventor a mass of machinery. "there she is! that's the whizzer!" cried mr. fenwick, with pride in his voice. "what do you think of her, tom swift?" tom did not immediately answer. he looked dubiously at the electric airship and shrugged his shoulders. it seemed to him, at first glance, that, it would never sail. chapter vii making some changes "well, what do you think of it?" asked mr. fenwick again, as tom walked all about the electric airship, still without speaking. "it's big, certainly," remarked the lad. "bless my shoe horn! i should say it was!" burst out mr. damon. "it's larger than your red cloud, tom." "but will it go? that's what i want to know," insisted the inventor. "do you think it will fly, tom? i haven't dared to try it yet, though a small model which i made floated in the air for some time. but it wouldn't move, except as the wind blew it." "it would be hard to say, without a careful examination, whether this large one will fly or not," answered tom. "then give it a careful examination," suggested mr. fenwick. "i'll pay you well for your time and trouble." "oh if i can help a fellow inventor, and assist in making a new model of airship fly, i'm only too glad to do it without pay," retorted tom, quickly. "i didn't come here for that. suppose we go in the cabin, and look at the motor. that's the most important point, if your airship is to navigate." there was certainly plenty of machinery in the cabin of the whizzer. most of it was electrical, for on that power mr. fenwick intended to depend to sail through space. there was a new type of gasolene engine, small but very powerful, and this served to operate a dynamo. in turn, the dynamo operated an electrical motor, as mr. fenwick had an idea that better, and more uniform, power could be obtained in this way, than from a gasolene motor direct. one advantage which tom noticed at once, was that the whizzer had a large electric storage battery. this was intended to operate the electric motor in case of a break to the main machinery, and it seemed a good idea. there were various other apparatuses, machines, and appliances, the nature of which tom could not readily gather from a mere casual view. "well, what's your opinion, now that you have seen the motor?" asked mr. fenwick, anxiously. "i'd have to see it in operation," said tom. "and you shall, right after dinner," declared the inventor. "i'd like to start it now, and hear what you have to say, but i'm not so selfish as that. i know you must be hungry after your trip from shopton, as they say aeroplaning gives one an appetite." "i don't know whether it's that or not," answered tom with a laugh, "but i am certainly hungry." "then we'll postpone the trial until after dinner. it must be ready by this time, i think," said mr. fenwick, as he led the way back to the house. it was magnificently furnished, for the inventor was a man of wealth, and only took up aeroplaning as a "fad." an excellent dinner was served, and then the three returned once more to the shed where the whizzer was kept. "shall i start the motor in here?" asked mr. fenwick, when he had summoned several of the machinists whom he employed, to aid himself and the young inventor. "it would be better if we could take it outside," suggested tom, "yet a crowd is sure to gather, and i don't like to work in a mob of people." "oh, we can easily get around that," said mr. fenwick. "i have two openings to my aeroplane shed. we can take the whizzer out of the rear door, into a field enclosed by a high fence. that is where i made all my trials, and the crowd couldn't get in, though some boys did find knot-holes and use them. but i don't mind that. the only thing that bothers me is that i can't make the whizzer go up, and if it won't go up, it certainly won't sail. that's my difficulty, and i hope you can remedy it, tom swift." "i'll do the best i can. but let's get the airship outside." this was soon accomplished, and in the open lot tom made a thorough and careful examination of the mechanism. the motor was started, and the propellers, for there were two, whirled around at rapid speed. tom made some tests and calculations, at which he was an expert, and applied the brake test, to see how much horse power the motor would deliver. "i think there is one trouble that we will have to get over," he finally said to mr. fenwick. "what is that?" "the motor is not quite powerful enough because of the way in which you have it geared up. i think by changing some of the cogs, and getting rid of the off-set shaft, also by increasing the number of revolutions, and perhaps by using a new style of carburetor, we can get more speed and power." "then we'll do it!" cried mr. fenwick, with enthusiasm. "i knew i hadn't got everything just right. do you think it will work after that?" "well," remarked tom, hesitatingly, "i think the arrangement of the planes will also have to be changed. it will take quite some work, but perhaps, after a bit, we can get the whizzer up in the air." "can you begin work at once?" asked the inventor, eagerly. tom shook his head. "i can't stay long enough on this trip," he said. "i promised father i would be back by to-morrow at the latest, but i will come over here again, and arrange to stay until i have done all i can. i need to get some of my special tools, and then, too, you will require some other supplies, of which i will give you a list. i hope you don't mind me speaking in this way, mr. fenwick, as though i knew more about it than you do," added tom, modestly. "not a bit of it!" cried the inventor heartily. "i want the benefit of your advice and experience, and i'll do just as you say. i hope you can come back soon." "i'll return the first of the week," promised tom, "and then we'll see what can be done. now i'll go over the whole ship once more, and see what i need. i also want to test the lifting capacity of your gas bag." the rest of the day was a busy one for our hero. with the aid of mr. damon and the owner of the whizzer, he went over every point carefully. then, as it was too late to attempt the return flight to shopton, he telegraphed his father, and he and mr. damon remained over night with mr. fenwick. in the morning, having written out a list of the things that would be needed, tom went out to franklin field, and repaired his own monoplane. it was found that one of the electric wires connected with the motor had broken, thus cutting off the spark. it was soon repaired, and, in the presence of a large crowd, tom and mr. damon started on their return flight. "do you think you can make the whizzer work, tom?" asked mr. damon, as they were flying high over philadelphia. "i'm a little dubious about it," was the reply. "but after i make some changes i may have a different opinion. the whole affair is too big and clumsy, that's the trouble; though the electrical part of it is very good." shopton was reached without incident, in about three hours, and there was no necessity, this time, of vol-planing back to earth. after a short rest, tom began getting together a number of special tools and appliances, which he proposed taking back to philadelphia with him. the young inventor made another trip to mr. fenwick's house the first of the following week. he went by train this time, as he had to ship his tools, and mr. damon did not accompany him. then, with the assistance of the inventor of the whizzer, and several of his mechanics, tom began making the changes on the airship. "do you think you can make it fly?" asked mr. fenwick, anxiously, after several days of labor. "i hope so," replied our hero, and there was more confidence in his tone than there had been before. as the work progressed, he began to be more hopeful. "i'll make a trial flight, anyhow, in a few days," he added. "then i must send word to mr. damon," decided mr. fenwick. "he wants to be on hand to see it, and, if possible, go up; so he told me." "all right," assented tom. "i only hope it does go up," he concluded, in a low tone. chapter viii andy foger's revenge during the following week, tom was kept busy over the airship. he made many important changes, and one of these was to use a new kind of gas in the balloon bag. he wanted a gas with a greater lifting power than that of the ordinary illuminating vapor which mr. fenwick had used. "well," remarked tom, as he came from the airship shed one afternoon, "i think we can give it a try-out, mr. fenwick, in a few days more. i shall have to go back to shopton to get some articles i need, and when i come back i will bring mr. damon with me, and we will see what the whizzer can do." "do you mean we will make a trial flight?" "yes." "for how long a distance?" "it all depends on how she behaves," answered tom, with a smile. "if possible, we'll make a long flight." "then i'll tell you what i'm going to do," went on the inventor, "i'm going to put aboard a stock of provisions, and some other supplies and stores, in case we are two or three days in the air." "it might not be a bad plan," agreed tom, "though i hardly think we will be gone as long as that." "well, being out in the air always makes me hungry," proceeded mr. fenwick, "so i'm going to take plenty of food along." the time was to come, and that very soon, when this decision of the inventor of the whizzer stood the adventurers in good stead. tom returned to shopton the next day, and sent word to have mr. damon join him in time to go back to the quaker city two days later. "but why don't you start right back to philadelphia to-morrow," asked mr. swift of his son. "because," answered tom, and that was all the reason he would give, though had any one seen him reading a certain note a few minutes before that, which note was awaiting him on his arrival from the quaker city, they would not have wondered at his decision. the note was brief. it merely said: "won't you come, and have some apple turnovers? the new cook is a treasure, and the girls are anxious to meet you." it was signed: mary nestor. "i think i could enjoy some apple turnovers," remarked tom, with a smile. having gotten ready the few special appliances he wished to take back to philadelphia with him, tom went, that evening, to call on miss nestor. true to her promise, the girl had a big plate full of apple turnovers, which she gaily offered our hero on his arrival, and, on his laughing declination to partake of so many, she ushered him into a room full of pretty girls, saying: "they'll help you eat them, tom. girls, here is mr. swift, who doesn't mind going up in the air or under the ocean, or even catching runaway horses," by which last she referred to the time tom saved her life, and first made her acquaintance. as for the young inventor, he gave a gasp, almost as if he had plunged into a bath of icy water, at the sight of so many pretty faces staring at him. he said afterward that he would rather have vol-planed back to earth from a seven-mile height, than again face such a battery of sparkling eyes. but our hero soon recovered himself, and entered into the merriment of the evening, and, before he knew it he was telling miss nestor and her attractive guests something of his exploits. "but i'm talking altogether too much about myself." he said, finally. "how is the new cook miss nestor; and have you heard from your father and mother since they sailed on the resolute for the west indies?" "as to the new cook, she is a jewel of the first water," answered miss nestor. "we all like her, and she is anxious for another ride in a taxicab, as she calls your auto." "she shall have it," declared tom, "for those are the best apple turnovers i ever ate." "i'll tell her so," declared mary. "she'll appreciate it coming from an inventor of your ability." "have you heard from your parents?" asked tom, anxious to change the subject. "oh, yes. i had a wire to-day. they stopped at st. augustine to let me know they were having a glorious time aboard the yacht. mr. hosbrook, the owner, is an ideal host, mamma said. they are proceeding directly to the west indies, now. i do hope they will arrive safely. they say there are bad storms down there at this time of year." "perhaps, if they are shipwrecked, mr. swift will go to their rescue in one of his airships, or a submarine," suggested mabel jackson, one of the several pretty girls. "oh, i hope he doesn't have to!" exclaimed mary. "don't speak of shipwrecks! it makes me shudder," and she seemed unduly alarmed. "of course they won't have any trouble," asserted tom, confidently, more to reassure miss nestor, than from any knowledge he possessed; "but if they do get cast away on a desert island, i'll certainly go to their rescue," he added. it was late when tom started for home that night, for the society of miss nestor and her friends made the time pass quickly. he promised to call again, and try some more samples of the new cook's culinary art, as soon as he had gotten mr. fenwick's airship in shape for flying. as, later that night, the young inventor came in sight of his home, and the various buildings and shops surrounding it, his first glance was toward the shed which contained his monoplane, butterfly. that little craft was tom's pet. it had not cost him anything like as much as had his other inventions, either in time or money, but he cared more for it than for his big airship, red cloud. this was principally because the butterfly was so light and airy, and could be gotten ready so quickly for a flight across country. it was capable of long endurance, too, for an extra large supply of gasolene and oil was carried aboard. so it was with rather a start of surprise that tom saw a light in the structure where the butterfly was housed. "i wonder if dad or mr. jackson can be out there?" he mused. "yet, i don't see why they should be. they wouldn't be going for a flight at night. or perhaps mr. damon arrived, and is out looking it over." a moment's reflection, however, told tom that this last surmise could not be true, since the eccentric man had telegraphed, saying he would not arrive until the next day. "somebody's out there, however," went on tom, "and i'm going to see who it is. i hope it isn't eradicate monkeying with the monoplane. he's very curious, and he might get it out of order." tom increased his pace, and moved swiftly but softly toward the shed. if there was an intruder inside he wanted to surprise him. there were large windows to the place, and they would give a good view of the interior. as tom approached, the light within flickered, and moved to and fro. tom reached one of the casements, and peered in. he caught a glimpse of a moving figure, and he heard a peculiar ripping sound. then, as he sprang toward the front door, the light suddenly went out, and the young inventor could hear some one running from the shop. "they've seen me, and are trying to get away," thought the lad. "i must catch them!" he fairly leaped toward the portal, and, just as he reached it, a figure sprang out. so close was tom that the unknown collided with him, and our hero went over on his back. the other person was tossed back by the force of the impact, but quickly recovered himself, and dashed away. not before, however, tom had had a chance to glance at his face, and, to the chagrin of the young inventor, he recognized, by the dim light of a crescent moon, the countenance of andy foger! if additional evidence was needed tom fully recognized the form as that of the town bully. "hold on there, andy foger!" shouted the young inventor. "what are you doing in my shed? what right have you in there? what did you do?" back came the answer through the night: "i told you i'd get square with you, and i've done it," and then andy's footsteps died away, while a mocking laugh floated back to tom. what was andy's revenge? chapter ix the whizzer flies for a moment, tom gazed after the fleeting figure of the cowardly bully. he was half-minded to give pursuit, and then, realizing that he could find andy later if he wanted him, the young inventor decided his best plan would be to see what damage had been done. for that damage would follow andy's secret visit to the shop, tom was certain. nor was his surmise wrong. stepping into the building, the lad switched on the lights, and he could not repress an exclamation of chagrin as he looked toward his trim little monoplane, the butterfly. now it was a butterfly with broken wings, for andy had slashed the canvas of the planes in a score of places. "the scoundrel!" growled tom. "i'll make him suffer for this! he's all but ruined my aeroplane." tom walked around his pet machine. as he came in front, and saw the propeller, he gave another exclamation. the fine wooden blades of several layers, gracefully curved, which had cost him so much in time and labor to build up, and then fashion to the right shape, had been hacked, and cut with an axe. the propeller was useless! "more of andy's work," murmured tom. "this is about the worst yet!" there came over him a feeling of great despondency, which was succeeded by a justifiable rage. he wanted to take after the bully, and give him a merciless beating. then a calmer mood came over tom. "after all, what's the use?" he reasoned. "whipping andy wouldn't mend the butterfly. she's in bad shape, but i can repair her, when i get time. luckily, he didn't meddle with the engine. that's all right." a hasty examination had shown this. "i guess i won't do anything now," went on tom. "i'll have my hands full getting mr. fenwick's airship to run. after that i can come back here and fix up my own. it's a good thing i don't have to depend on her for making the trip to philadelphia. poor butterfly! you sure are in a bad way," and tom felt almost as if he was talking to some living creature, so wrapped up was he in his trim little monoplane. after another disheartening look at his air craft, the young inventor started to leave the shop. he looked at a door, the fastening of which andy had broken to gain admittance. "i should have had the burglar alarm working, and this would never have happened," reasoned tom. all the buildings were arranged so that if any one entered them after a certain hour, an alarm would ring in the house. but of late, the alarm had not been set, as tom and his father were not working on any special inventions that needed guarding. it was due to this oversight that andy was able to get in undetected. "but it won't happen again," declared tom, and he at once began connecting the burglar-apparatus. he went into the house, and told his father and the engineer what had occurred. they were both indignant, and the engineer declared that he would sleep with one eye open all night, ready to respond to the first alarm. "oh, there's no danger of andy coming back right away," said tom. "he's too frightened. i wouldn't be surprised if he disappeared for a time. he'll be thinking that i'm after him." this proved true, as andy had left town next morning, and to all inquiries his mother said he had gone to visit relatives. she was not aware of her son's meanness, and tom did not tell her. mr. damon arrived from his home in waterfield that day, and, with many "blessings," wanted to know if tom was ready for the trial of the electrical airship. "yes, we'll leave for philadelphia to-morrow," was the answer. "are we going in the butterfly? bless my watch chain, but i like that little machine!" "it will be some time before you again have a flight in her," said tom, sorrowfully, as he told of andy's act of vandalism. "why, bless my individuality!" cried mr. damon, indignantly. "i never heard of such a thing! never!" it did little good to talk of it, however, and tom wanted to forget about it. he wished he had time to repair the monoplane before he left home, but there was much to do to get ready for the trial of the whizzer. "when will you be back, tom?" asked mr. swift, as his son and mr. damon departed for the quaker city the following morning. "hard to say, dad. if i can make a long flight in the whizzer i'll do so. i may even drop down here and pay you a visit. but if i find there are many more changes to make in her construction, which is more than likely, i can't say when i'll return. i'll keep you posted, however, by writing." "can't you arrange to send me some wireless messages?" asked the older inventor, with a smile. "i could, if i had thought to rig up the apparatus on mr. fenwick's airship," was the reply. "i'll hardly have time to do it now, though." "send wireless messages from an aeroplane?" gasped mr. damon. "bless my gizzard! i never heard of such a thing!" "oh, it can be done," tom assured him. and this was a fact. tom had installed a wireless apparatus on his red cloud recently, and it is well known that several of the modern biplanes can send wireless messages. the crossing and bracing wires of the frame are used for sending wires, and in place of ground conductors there are trailers which hang below the aeroplane. the current is derived directly from the engine, and the remaining things needed are a small step-up transformer, a key and a few other small parts. tom had gone a step farther than this, and had also arranged to receive wireless messages, though few modern aeroplanes are thus equipped as yet. but, of course, there was no time now to install a wireless apparatus on mr. fenwick's craft. tom thought he would be lucky if he got the whizzer to make even a short flight. "well, let me hear from you when you can," requested mr. swift, and tom promised. it was some time after that, and many strange things happened before tom swift again communicated with his father, at any length. the young inventor had bidden farewell to miss nestor the night previous. she stated that she had a message that day from her parents aboard the resolute, which spoke a passing steamer. mr. and mrs. nestor, and the other guests of mr. hosbrook were well, and anticipated a fine time on reaching the west indies. tom now said good-by to his father, the housekeeper and mr. jackson, not forgetting, of course, eradicate sampson. "don't let andy foger come sneaking around here, rad," cautioned the young inventor. "'deed an' i won't!" exclaimed the colored man. "ef he do, i'll hab boomerang kick him t' pieces, an' den i'll whitewash him so his own folks won't know him! oh, don't you worry, massa tom. dat andy won't do no funny business when i'm around!" tom laughed, and started for the station with mr. damon. they arrived in philadelphia that afternoon, the trip being very slow, as compared with the one made by the monoplane. they found mr. fenwick anxiously awaiting them, and tom at once started work on the airship. he kept at it until late that night, and resumed early the next morning. many more changes and adjustments were made, and that afternoon, the young inventor said: "i think we'll give it a try-out, mr. fenwick." "do you mean make a flight?" "yes, if she'll take it; but only a short one. i want to get her up in the air, and see how she behaves." "well, if you find out, after you're up, that she does well, you may want to take a long flight," suggested mr. fenwick. "if you do, why i have everything aboard necessary for a long voyage. the whizzer is well stocked with provisions." an hour later, the big electric machine was wheeled out into the yard, for, in spite of her size, four men could easily move the craft about, so well was she balanced. aside from a few personal friends of the inventor, himself, his machinists, tom and mr. damon, no one was present at the try-out. tom, mr. damon and mr. fenwick climbed into the car which was suspended below the gas bag, and between the wing-like planes on either side. the young inventor had decided to make the whizzer rise by scudding her across the ground on the bicycle wheels, with which she was equipped, and then by using the tilting planes to endeavor to lift her off the earth. he wanted to see if she would go up that way, without the use of the gas bag. all was in readiness. the motor was started and the machinery began to hum and throb. the propellers gained speed with every revolution. the airship had been made fast by a rope, to which was attached a strong spring balance, as it was desired to see how much pull the engine would give. "eight hundred pounds," announced one of the machinists. "a thousand would be better, but we'll try it," murmured tom. "cast off!" the rope was loosened, and, increasing the speed of the engine, tom signalled to the men to give a little momentum to the craft. she began running over the smooth ground. there was a cheer from the few spectators. certainly the whizzer made good time on the earth. tom was anxiously watching the gages and other instruments. he wanted a little more speed, but could not seem to get it. he ran the motor to the utmost, and then, seeing the necessity of making an attempt to get up into the air, before the end of the speeding ground was reached, he pulled the elevating plane lever. the front of the whizzer rose, and then settled down. tom quickly shut off the power, and jammed on the brake, an arrangement of spikes that dug into the earth, for the high board fence loomed up before him. "what's the matter?" cried mr. fenwick, anxiously. "couldn't get up speed enough," answered the young inventor. "we must have more momentum to make her rise." "can it be gotten?" "i think so. i'll gear the motor higher." it took an hour to do this. once more the scale test was applied. it registered a pull of fifteen hundred pounds now. "we'll go up," said tom, grimly. once more the motors spit out fire, and the propellers whirled so that they looked like mere circles of light. once more the whizzer shot over the ground, but this time, as she neared the fence, she rose up like a bird, cleared it like a trick horse, and soared off into the air! the whizzer was flying! chapter x over the ocean "hurrah!" cried mr. fenwick in delight. "my machine is really flying at last!" "yes," answered tom, as he adjusted various levers and gears, "she is going. it's not as high as i'd like, but it is doing very well, considering the weight of the craft, and the fact that we have not used the gas bag. i'm going to let that fill now, and we'll go up. don't you want to steer, mr. fenwick?" "no, you manage it, tom, until it's in good running shape. i don't want to 'hoodoo' it. i worked as hard as i could, and never got more than two feet off the ground. now i'm really sailing. it's great!" he was very enthusiastic, and tom himself was not a little pleased at his own success, for certainly the airship had looked to be a very dubious proposition at first. "bless my gaiters! but we are doing pretty well," remarked mr. damon, looking down on the field where mr. fenwick's friends and the machinists were gathered, cheering and waving their hands. "we'll do better," declared tom. he had already set the gas machine in operation, and was now looking over the electric apparatus, to see that it was working well. it needed some adjustments, which he made. all this while the whizzer was moving about in a big circle, for the rudder had been automatically set to so swing the craft. it was about two hundred feet high, but soon after the gas began to enter the bag it rose until it was nearly five thousand feet high. this satisfied tom that the airship could do better than he expected, and he decided to return nearer earth. in going down, he put the craft through a number of evolutions designed to test her ability to answer the rudders promptly. the lad saw opportunity for making a number of changes, and suggested them to mr. fenwick. "are you going any farther?" asked the owner of the whizzer, as he saw that his craft was slowly settling. "no, i think we've done enough for the first day," said tom, "but i'd like you to handle her now, mr. fenwick. you can make the landing, while i watch the motor and other machines." "yes. i guess i can make a landing all right," assented the inventor. "i'm better at coming down than going up." he did make a good descent, and received the congratulation of his friends as he stepped from the airship. tom was also given much praise for his success in making the craft go at all, for mr. fenwick and his acquaintances had about given up hope that she ever would rise. "well, what do you think of her?" mr. fenwick wanted to know of the young inventor, who replied that, as soon as some further changes had been made, they would attempt a long flight. this promise was kept two days later. they were busy days for tom, mr. fenwick and the latter's assistants. tom sent a short note to his father telling of the proposed long flight, and intimated that he might make a call in shopton if all went well. he also sent a wire to miss nestor, hinting that she might have some apple turnovers ready for him. but tom never called for that particular pastry, though it was gotten ready for him when the girl received his message. all was in readiness for the long flight, and a preliminary test had demonstrated that the whizzer had been wonderfully improved by the changes tom made. the young inventor looked over the supply of food mr. fenwick had placed aboard, glanced at the other stores, and asked: "how long do you expect to be gone, mr. fenwick?" "why, don't you think we can stay out a week?" "that's quite a while," responded tom. "we may be glad to return in two days, or less. but i think we're all ready to start. are any of your friends going?" "i've tried to pursuade some of them to accompany me, but they are a bit timid," said the inventor. "i guess we three will make up the party this time, though if our trip is a successful one i'll be overwhelmed with requests for rides, i suppose." as before, a little crowd gathered to see the start. the day was warm, but there was a slight haziness which tom did not like. he hoped, though, that it would pass over before they had gone far. "do you wish to head for any particular spot, mr. fenwick?" asked tom, as they were entering the cabin. "yes, i would like to go down and circle cape may, new jersey, if we could. i have a friend who has a summer cottage there, and he was always laughing at my airship. i'd just like to drop down in front of his place now, and pay him a call." "we'll try it," assented tom, with a smile. an auspicious start was made, the whizzer taking the air after a short flight across the ground, and then, with the lifting gas aiding in pulling the craft upward, the airship started to sail high over the city of philadelphia. so swiftly did it rise that the cheers of the little crowd of mr. fenwick's friends were scarcely heard. up and up it went, and then a little later, to the astonishment of the crowds in the streets, tom put the airship twice in a circle around the statue of william penn, on the top of the city hall. "now you steer," the lad invited mr. fenwick. "take her straight across the delaware river, and over camden, new jersey, and then head south, for cape may. we ought to make it in an hour, for we are getting up good speed." leaving the owner in charge of his craft, to that gentleman's no small delight, tom and mr. damon began an inspection of the electrical and other machinery. there was much that needed attention, but tom soon had the automatic apparatus in working order, and then less attention need be given to it. several times the young investor looked out of the windows with which the cabin was fitted. mr. damon noticed this. "bless my shoe laces, tom," he said. "what's the matter?" "i don't like the looks of the weather," was the answer. "i think we're in for a storm." "then let's put back." "no, it would be too bad to disappoint mr. fenwick, now that we have made such a good start. he wants to make a long flight, and i can't blame him," spoke tom, in a low voice. "but if there's danger--" "oh, well, we can soon be at cape may, and start back. the wind is freshening rather suddenly, though," and tom looked at the anemometer, which showed a speed of twenty miles an hour. however, it was in their favor, aiding them to make faster time. the speed of the whizzer was now about forty miles an hour, not fast for an air craft, but sufficiently speedy in trying out a new machine. tom looked at the barograph, and noted that they had attained an altitude of seven thousand five hundred feet. "that's better than millionaire daxtel's distance of seven thousand one hundred and five feet," remarked the lad, with a smile, "and it breaks jackson's climb of seven thousand three hundred and three feet, which is pretty good for your machine, mr. fenwick." "do you really think so?" asked the pleased inventor. "yes. and we'll do better than that in time, but it's best to go slow at first, until we see how she is standing the strain. this is high and fast enough for the present." they kept on, and as tom saw that the machinery was working well, he let it out a little, the whizzer at once leaped forward, and, a little later they came within sight of cape may, the jersey coast resort. "now to drop down and visit my friend," said mr. fenwick, with a smile. "won't he be surprised!" "i don't think we'd better do it," said tom. "why not?" "well, the wind is getting stronger every minute and it will be against us on the way back. if we descend, and try to make another ascension we may fail. we're up in the air now, and it may be easy to turn around and go back. then, again, it may not, but it certainly will be easier to shift around up here than down on the ground. so i'd rather not descend--that is, not entirely to the ground." "well, just as you say, though i wanted my friend to know i could build a successful airship." "oh, we can get around that. i'll take her down as low as is safe, and fly over his house, if you'll point it out, and you can drop him a message in one of the pasteboard tubes we carry for that purpose." "that's a good idea," assented mr. fenwick. "i'll do it." tom sent the whizzer down until the hotels and cottages could be made out quite plainly. after looking with a pair of opera glasses, mr. fenwick picked out the residence of his friend, and tom prepared to circle about the roof. by this time the presence of the airship had become known to hundreds, and crowds were eagerly watching it. "there he is! there's my friend who didn't believe i would ever succeed!" exclaimed mr. fenwick, pointing to a man who stood in the street in front of a large, white house. "i'll drop him a message!" one was in readiness in a weighted pasteboard cylinder, and soon it was falling downward. the airship was moving slowly, as it was beating against the wind. leaning out of the cabin window, mr. fenwick shouted to his friend: "hey, will! i thought you said my airship would never go! i'll come and give you a ride, some day!" whether the gentleman understood what mr. fenwick shouted at him is doubtful, but he saw the inventor waving his hand, and he saw the falling cylinder, and a look of astonishment spread over his face, as he ran to pick up the message. "we're going up now, and will try to head for home," said tom, a moment later, as he shifted the rudder. "bless my storage battery!" cried mr. damon. "but we have had a fine trip." "a much better one than we'll have going back," observed tom, in a low voice. "why; what's the matter?" asked the eccentric man. "the wind has increased to a gale, and will be dead against us," answered tom. mr. fenwick was busy writing another message to drop, and he paid little attention to the young inventor. tom sent the craft well up into the air, and then tried to turn it about, and head back for philadelphia. no sooner had he done so than the airship was met by the full force of the wind, which was now almost a hurricane. it had steadily increased, but, as long as they were moving with it, they did not notice it so much. once they attempted to stem its fury they found themselves almost helpless. tom quickly realized this, and, giving up his intention of beating up against the wind, he turned the craft around, and let it fly before the gale, the propellers aiding to get up a speed of seventy miles an hour. mr. fenwick, who had dropped the last of his messages, came from his small private cabin, to where mr. damon and tom were in a low-voiced conversation near the engines. the owner of the whizzer, happened to look down through a plate-glass window in the floor of car. what he saw caused him to give a gasp of astonishment. "why--why!" he exclaimed. "we--we're over the ocean." "yes," answered tom, quietly, as he gazed down on the tumbling billows below them. they had quickly passed over cape may, across the sandy beach, and were now well out over the atlantic. "why--why are we out here?" asked mr. fenwick. "isn't it dangerous--in an airship that hasn't been thoroughly tried yet?" "dangerous? yes, somewhat," replied tom, slowly. "but we can't help ourselves, mr. fenwick. we can't turn around and go back in this gale, and we can't descend." "then what's to be done?" "nothing, except to keep on until the gale blows itself out." "and how long will that be?" "i don't know--a week, maybe." "bless my coffee pot, i'm glad we've got plenty on board to eat!" exclaimed mr. damon. chapter xi a night of terror after the first shock of tom's announcement, the two men, who were traveling with him in the airship, showed no signs of fear. yet it was alarming to know that one was speeding over the mighty ocean, before a terrific gale, with nothing more substantial under one that a comparatively frail airship. still mr. damon knew tom of old, and had confidence in his ability, and, while mr. fenwick was not so well acquainted with our hero, he had heard much about him, and put faith in his skill to carry them out of their present difficulty. "are you sure you can't turn around and go back?" asked mr. fenwick. his knowledge of air-currents was rather limited. "it is out of the question," replied tom, simply. "we would surely rip this craft to pieces if we attempted to buffet this storm." "is it so bad, then?" asked mr. damon, forgetting to bless anything in the tense excitement of the moment. "it might be worse," was the reply of the young inventor. "the wind is blowing about eighty miles an hour at times, and to try to turn now would mean that we would tear the planes loose from the ship. true, we could still keep up by means of the gas bag, but even that might be injured. going as we are, in the same direction as that in which the wind is blowing, we do not feel the full effect of it." "but, perhaps, if we went lower down, or higher up, we could get in a different current of air," suggested mr. fenwick, who had made some study of aeronautics. "i'll try," assented tom, simply. he shifted the elevating rudder, and the whizzer began to go up, slowly, for there was great lateral pressure on her large surface. but tom knew his business, and urged the craft steadily. the powerful electric engines, which were the invention of mr. fenwick, stood them in good stead, and the barograph soon showed that they were steadily mounting. "is the wind pressure any less?" inquired mr. damon, anxiously. "on the contrary, it seems to be increasing," replied tom, with a glance at the anemometer. "it's nearly ninety miles an hour now." "then, aided by the propellers, we must be making over a hundred miles an hour." said the inventor. "we are,--a hundred and thirty," assented tom. "we'll be blown across the ocean at this rate," exclaimed mr. damon. "bless my soul! i didn't count on that." "perhaps we had better go down," suggested mr. fenwick. "i don't believe we can get above the gale." "i'm afraid not," came from tom. "it may be a bit better down below." accordingly, the rudder was changed, and the whizzer pointed her nose downward. none of the lifting gas was let out, as it was desired to save that for emergencies. down, down, down, went the great airship, until the adventurers within, by gazing through the plate glass window in the floor of the cabin, could see the heaving, white-capped billows, tossing and tumbling below them. "look out, or we'll be into them!" shouted mr. damon. "i guess we may as well go back to the level where we were," declared tom. "the wind, both above and below that particular strata is stronger, and we will be safer up above. our only chance is to scud before it, until it has blown itself out. and i hope it will be soon." "why?" asked mr. damon, in a low voice. "because we may be blown so far that we can not get back while our power holds out, and then--" tom did not finish, but mr. damon knew what he meant--death in the tossing ocean, far from land, when the whizzer, unable to float in the air any longer, should drop into the storm-enraged atlantic. they were again on a level, where the gale blew less furiously than either above or below, but this was not much relief. it seemed as if the airship would go to pieces, so much was it swayed and tossed about. but mr. fenwick, if he had done nothing else, had made a staunch craft, which stood the travelers in good stead. all the rest of that day they swept on, at about the same speed. there was nothing for them to do, save watch the machinery, occasionally replenishing the oil tanks, or making minor adjustments. "well," finally remarked mr. damon, when the afternoon was waning away, "if there's nothing else to do, suppose we eat. bless my appetite, but i'm hungry! and i believe you said, mr. fenwick, that you had plenty of food aboard." "so we have, but the excitement of being blown out to sea on our first real trip, made me forget all about it. i'll get dinner at once, if you can put up with an amateur's cooking." "and i'll help," offered mr. damon. "tom can attend to the airship, and we'll serve the meals. it will take our minds off our troubles." there was a well equipped kitchen aboard the whizzer and soon savory odors were coming from it. in spite of the terror of their situation, and it was not to be denied that they were in peril, they all made a good meal, though it was difficult to drink coffee and other liquids, owing to the sudden lurches which the airship gave from time to time as the gale tossed her to and fro. night came, and, as the blackness settled down, the gale seemed to increase in fury. it howled through the slender wire rigging of the whizzer, and sent the craft careening from side to side, and sometimes thrust her down into a cavern of the air, only to lift her high again, almost like a ship on the heaving ocean below them. as darkness settled in blacker and blacker, tom had a glimpse below him, of tossing lights on the water. "we just passed over some vessel," he announced. "i hope they are in no worse plight than we are." then, there suddenly came to him a thought of the parents of mary nestor, who were somewhere on the ocean, in the yacht resolute bound for the west indies. "i wonder if they're out in this storm, too?" mused tom. "if they are, unless the vessel is a staunch one, they may be in danger." the thought of the parents of the girl he cared so much for being in peril, was not reassuring to tom, and he began to busy himself about the machinery of the airship, to take his mind from the presentiment that something might happen to the resolute. "we'll have our own troubles before morning," the lad mused, "if this wind doesn't die down." there was no indication that this was going to be the case, for the gale increased rather than diminished. tom looked at their speed gage. they were making a good ninety miles an hour, for it had been decided that it was best to keep the engine and propellers going, as they steadied the ship. "ninety miles an hour," murmured tom. "and we've been going at that rate for ten hours now. that's nearly a thousand miles. we are quite a distance out to sea." he looked at a compass, and noted that, instead of being headed directly across the atlantic they were bearing in a southerly direction. "at this rate, we won't come far from getting to the west indies ourselves," reasoned the young inventor. "but i think the gale will die away before morning." the storm did not, however. more fiercely it blew through the hours of darkness. it was a night of terror, for they dared not go to sleep, not knowing at what moment the ship might turn turtle, or even rend apart, and plunge with them into the depths of the sea. so they sat up, occasionally attending to the machinery, and noting the various gages. mr. damon made hot coffee, which they drank from time to time, and it served to refresh them. there came a sudden burst of fury from the storm, and the airship rocked as if she was going over. "bless my heart!" cried mr. damon, springing up. "that was a close call!" tom said nothing. mr. fenwick looked pale and alarmed. the hours passed. they were swept ever onward, at about the same speed, sometimes being whirled downward, and again tossed upward at the will of the wind. the airship was well-nigh helpless, and tom, as he realized their position, could not repress a fear in his heart as he thought of the parents of the girl he loved being tossed about on the swirling ocean, in a frail pleasure yacht. chapter xii a downward glide they sat in the cabin of the airship, staring helplessly at each other. occasionally tom rose to attend to one of the machines, or mr. fenwick did the same. occasionally, mr. damon uttered a remark. then there was silence, broken only by the howl of the gale. it seemed impossible for the whizzer to travel any faster, yet when tom glanced at the speed gage he noted, with a feeling of surprise, akin to horror, that they were making close to one hundred and fifty miles an hour. only an aeroplane could have done it, and then only when urged on by a terrific wind which added to the speed produced by the propellers. the whole craft swayed and trembled, partly from the vibration of the electrical machinery, and partly from the awful wind. mr. fenwick came close to tom, and exclaimed: "do you think it would be any use to try once more to go above or below the path of the storm?" tom's first impulse was to say that it would be useless, but he recollected that the craft belonged to fenwick, and surely that gentleman had a right to make a suggestion. the young inventor nodded. "we'll try to go up," he said. "if that doesn't work, i'll see if i can force her down. it will be hard work, though. the wind is too stiff." tom shifted the levers and rudders. his eyes were on the barograph--that delicate instrument, the trembling hand of which registered their height. tom had tilted the deflection rudder to send them up, but as he watched the needle he saw it stationary. they were not ascending, though the great airship was straining to mount to an upper current where there might be calm. it was useless, however, and tom, seeing the futility of it, shifted the rudder to send them downward. this was more easily accomplished, but it was a change for the worse, since, the nearer to the ocean they went, the fiercer blew the wind. "back! go back up higher!" cried mr. damon, "we can't!" yelled tom. "we've got to stay here now!" "oh, but this is awful!" exclaimed mr. fenwick. "we can never stand this!" the airship swaged more than ever, and the occupants were tossed about in the cabin, from side to side. indeed, it did seem that human beings never could come alive out of that fearful ordeal. as tom looked from one of the windows of the cabin, he noted a pale, grayish sort of light outside. at first he could not understand what it was, then, as he observed the sickly gleams of the incandescent electric lamps, he knew that the hour of dawn was at hand. "see!" he exclaimed to his companions, pointing to the window. "morning is coming." "morning!" gasped mr. damon. "is the night over? now, perhaps we shall get rid of the storm." "i'm afraid not," answered tom, as he noted the anemometer and felt the shudderings of the whizzer as she careened on through the gale. "it hasn't blown out yet!" the pale light increased. the electrics seemed to dim and fade. tom looked to the engines. some of the apparatus was in need of oil, and he supplied it. when he came back to the main cabin, where stood mr. damon and mr. fenwick, it was much lighter outside. "less than a day since we left philadelphia," murmured the owner of the whizzer, as he glanced at a distance indicator, "yet we have come nearly sixteen hundred miles. we certainly did travel top speed. i wonder where we are?" "still over the ocean," replied mr. damon, as he looked down at the heaving billows rolling amid crests of foam far below them. "though what part of it would be hard to say. we'll have to reckon out our position when it gets calmer." tom came from the engine room. his face wore a troubled look, and he said, addressing the older inventor: "mr. fenwick, i wish you'd come and look at the gas generating apparatus. it doesn't seem to be working properly." "anything wrong?" asked mr. damon, suspiciously. "i hope not," replied tom, with all the confidence he could muster. "it may need adjusting. i am not so familiar with it as i am with the one on the red cloud. the gas seems to be escaping from the bag, and we may have to descend, for some distance." "but the aeroplanes will keep us up," said mr. daman. "yes--they will," and tom hesitated. "that is, unless something happens to them. they are rather frail to stand alone the brunt of the gale, and i wish--" tom did not complete the sentence. instead, he paused suddenly and seemed to be intently listening. from without there came a rending, tearing, crashing sound. the airship quivered from end to end, and seemed to make a sudden dive downward. then it appeared to recover, and once more glided forward. tom, followed by mr. fenwick, made a rush for the compartment where the machine was installed. they had no sooner reached it than there sounded an explosion, and the airship recoiled as if it had hit a stone wall. "bless my shaving brush! what's that?" cried mr. damon. "has anything happened?" "i'm rather afraid there has," answered tom, solemnly. "it sounded as though the gas bag went up. and i'm worried over the strength of the planes. we must make an investigation!" "we're falling!" almost screamed mr. fenwick, as he glanced at the barograph, the delicate needle of which was swinging to and fro, registering different altitudes. "bless my feather bed! so we are!" shouted mr. damon. "let's jump, and avoid being caught under the airship!" he darted for a large window, opening from the main cabin, and was endeavoring to raise it when tom caught his hand. "what are you trying to do," asked the lad, hoarsely. "save my life! i want to get out of this as soon as i can. i'm going to jump!" "don't think of it! you'd be instantly killed. we're too high for a jump, even into the ocean." "the ocean! oh, is that still below us? is there any chance of being saved? what can be done?" mr. damon hesitated. "we must first find out how badly we are damaged," said tom, quietly. "we must keep our heads, and be calm, no matter what happens. i need your help, mr. damon." this served to recall the rather excited man to his senses. he came back to the centre of the cabin, which was no easy task, for the floor of it was tilted at first one angle, and then another. he stood at tom's side. "what can i do to help you?" he asked. mr. fenwick was darting here and there, examining the different machines. none of them seemed to be damaged. "if you will look and see what has happened to our main wing planes, i will see how much gas we have left in the bag," suggested tom. "then we can decide what is best to be done. we are still quite high, and it will take some time to complete our fall, as, even if everything is gone, the material of the bag will act as a sort of parachute." mr. damon darted to a window in the rear of the cabin, where he could obtain a glimpse of the main wing planes. he gave a cry of terror and astonishment. "two of the planes are gone!" he reported. "they are torn and are hanging loose." "i feared as much," retorted tom, quietly, "the gale was too much for them." "what of the lifting gas?" asked mr. fenwick, quickly. "it has nearly all flowed out of the retaining bag." "then we must make more at once. i will start the generating machine." he darted toward it. "it will be useless," spoke tom, quietly. "why?" "because there is no bag left to hold it. the silk and rubber envelope has been torn to pieces by the gale. the wind is even stronger than it was last night." "then what's to be done?" demanded mr. damon, with a return of his alarmed and nervous manner. "bless my fingernails! what's to be done?" for an instant tom did not answer. it was constantly getting lighter, though there was no sun, for it was obscured by scudding clouds. the young inventor looked critically at the various gages and indicators. "is--is there any chance for us?" asked mr. fenwick, quietly. "i think so," answered tom, with a hopeful smile. "we have about two thousand feet to descend, for we have fallen nearly that distance since the accident." "two thousand feet to fall!" gasped mr. damon. "we can never do it and live!" "i think so," spoke tom. "bless my gizzard! how?" fairly exploded mr. damon. "by vol-planing down!" "but, even if we do, we will fall into the ocean!" cried mr. fenwick. "we will be drowned!" "no," and tom spoke more quietly than before. "we are over a large island." he went on, "and i propose to let the disabled airship vol-plane down to it. that is our only chance." "over an island!" cried mr. damon. he looked down through the floor observation window. tom had spoken truly. at that moment they were over a large island, which had suddenly loomed up in the wild and desolate waste of the ocean. they had reached its vicinity just in time. tom stepped to the steering and rudder levers, and took charge. he was going to attempt a most difficult feat--that of guiding a disabled airship back to earth in the midst of a hurricane, and landing her on an unknown island. could he do it? there was but one answer. he must try. it was the only chance of saving their lives, and a slim one at best. down shot the damaged whizzer like some giant bird with broken wings, but tom swift was in charge, and it seemed as if the craft knew it, as she began that earthward glide. chapter xiii on earthquake island mingled feelings possessed the three adventurers within the airship. mr. damon and mr. fenwick had crowded to the window, as tom spoke, to get a glimpse of the unknown island toward which they were shooting. they could see it more plainly now, from the forward casement, as well as from the one in the bottom of the craft. a long, narrow, rugged piece of land it was, in the midst of the heaving ocean, for the storm still raged and lashed the waves to foam. "can you make it?" asked mr. damon, in a low voice. "i think so," answered tom, more cheerfully. "shall i shut down the motor?" inquired the older inventor. "yes, you might as well. we don't need the propellers now, and i may be better able to make the glide without them." the buzzing and purring electrical apparatus was shut down. silence reigned in the airship, but the wind still howled outside. as tom had hoped, the ship became a little more steady with the stopping of the big curved blades, though had the craft been undamaged they would have served to keep her on an even keel. with skillful hand he so tilted the elevating planes that, after a swift downward glide, the head of the whizzer would be thrown up, so to speak, and she would sail along in a plane parallel to the island. this had the effect of checking her momentum, just as the aviator checks the downward rush of his monoplane or biplane when he is making a landing. tom repeated this maneuver several times, until a glance at his barograph showed that they had but a scant sixty feet to go. there was time but for one more upward throwing of the whizzer's nose, and tom held to that position as long as possible. they could now make out the topography of the island plainly, for it was much lighter. tom saw a stretch of sandy beach, and steered for that. downward shot the airship, inert and lifeless. it was not like gliding his little butterfly to earth after a flight, but tom hoped he could make it. they were now within ten feet of the earth, skimming forward. tom tried another upward tilt, but the forward planes would not respond. they could get no grip on the air. with a crash that could have been heard some distance the whizzer settled to the sand. it ran along a slight distance, and then, as the bicycle wheels collapsed under the pressure, the airship seemed to go together in a shapeless mass. at the first impact with the earth, tom had leaped away from the steering wheel and levers, for he did not want to be crushed against them. mr. damon and mr. fenwick, in pursuance of a plan adopted when they found that they were falling, had piled a lot of seat cushions around them. they had also provided some as buffers for tom, and our hero, at the instant of the crash, had thrown himself behind and upon them. it seemed as if the whole ship went to pieces. the top of the main cabin crashed down, as the side supports gave way, but, fortunately, there were strong main braces, and the roof did not fall completely upon our friends. the whole bottom of the craft was forced upward and had it not been for the protecting cushions, there might have been serious injuries for all concerned. as it was they were badly bruised and shaken up. after the first crash, and succeeding it an instant later, there came a second smash, followed by a slight explosion, and a shower of sparks could be seen in the engine room. "that's the electrical apparatus smashing through the floor!" called tom. "come, let's get out of here before the gasolene sets anything on fire. are you all right, mr. damon, and you, mr. fenwick?" "yes, i guess so," answered the inventor. "oh, what a terrible crash! my airship is ruined!" "you may be glad we are alive," said mr. damon. "bless my top knot, i feel--" he did not finish the sentence. at that moment a piece of wood, broken from the ceiling, where it had hung by a strip of canvas came crashing down, and hit mr. damon on the head. the eccentric man toppled over on his pile of cushions, from which he was arising when he was struck. "oh, is he killed?" gasped mr. fenwick. "i hope not!" cried tom. "we must get him out of here, at all events. there may be a fire." they both sprang to mr. damon's aid, and succeeded in lifting him out. there was no difficulty in emerging from the airship as there were big, broken gaps, on all sides of what was left of the cabin. once in the outer air mr. damon revived, and opened his eyes. "much hurt?" asked tom, feeling of his friend's head. "no--no, i--i guess not," was the slow answer. "i was stunned for a moment. i'm all right now. nothing broken, i guess," and his hand went to his head. "no, nothing broken," added tom, cheerfully, "but you've got a lump there as big as an ostrich egg. can you walk?" "oh, i'm all right. bless my stars, what a wreck!" mr. damon looked at the remains of the airship. it certainly was a wreck! the bent and twisted planes were wrapped about the afterpart, the gas bag was but a shred, the frame was splintered and twisted, and the under part, where the starting wheels were placed, resembled a lot of broken bicycles. the cabin looked like a shack that had sustained an explosion of dynamite. "it's a wonder we came out alive," said mr. fenwick, in a low voice. "indeed it is," agreed tom, as he came back with a tin can full of sea water, with which to bathe mr. damon's head. the lad had picked up the can from where it had rolled from the wreck, and they had landed right on the beach. "it doesn't seem to blow so hard," observed mr. damon, as he was tenderly sopping his head with a handkerchief wet in the salt water. "no, the wind is dying out, but it happened too late to do us any good," remarked tom, sorrowfully. "though if it hadn't blown us this far, we might have come to grief over the ocean, and be floundering in that, instead of on dry land." "that's so," agreed mr. fenwick, who was carefully feeling of some bruises on his legs. "i wonder where we are, anyhow?" "i haven't the least idea," responded tom. "it's an island, but which one, or where it is i don't know. we were blown nearly two thousand miles, i judge." he walked over and surveyed the wreck. now that the excitement was over he was beginning to be aware of numerous bruises and contusions, his legs felt rather queer, and on rolling up his trousers he found there was a deep cut in the right shin, just below his knee. it was bleeding, but he bandaged it with a spare handkerchief, and walked on. peering about, he saw that nearly the whole of the machinery in the engine room, including most of the electrical apparatus, had fallen bodily through the floor, and now rested on the sand. "that looks to be in pretty good shape." mused tom, "but it's a question whether it will ever be any good to us. we can't rebuild the airship here, that's certain." he walked about the wreck, and then returned to his friends. mr. damon was more like himself, and mr. fenwick had discovered that he had only minor bruises. "bless my coffee cup!" exclaimed mr. damon. "i declare, i feel hungry. i wonder if there's anything left to eat in the wreck?" "plenty," spoke tom, cheerfully. "i'll get it out. i can eat a sandwich or too myself, and perhaps i can set up the gasolene stove, and cook something." as the young inventor was returning to the wreck, he was halted halfway by a curious trembling feeling. at first he thought it was a weakness of his legs, caused by his cut, but a moment later he realized with a curious, sickening sensation that it was the ground--the island itself--that was shaking and trembling. the lad turned back. mr. damon and mr. fenwick were staring after him with fear showing on their faces. "what was that?" cried the inventor. "bless my gizzard! did you feel that, tom?" cried mr. damon. "the whole place is shaking!" indeed, there was a stronger tremor now, and it was accompanied by a low, rumbling sound, like distant thunder. the adventurers were swaying to and fro. suddenly they were tossed to the ground by a swaying motion, and not far off a great crack opened in the earth. the roaring, rumbling sound increased in volume. "an earthquake! it's an earthquake!" cried tom. "we're in the midst of an earthquake!" chapter xiv a night in camp the rumbling and roaring continued for perhaps two minutes, during which time the castaways found it impossible to stand, for the island was shaking under their feet with a sickening motion. off to one side there was a great fissure in the earth, and, frightened as he was, tom looked to see if it was extending in their direction. if it was, or if a crack opened near them, they might be precipitated into some bottomless abyss, or into the depths of the sea. but the fissure did not increase in length or breadth, and, presently the rumbling, roaring sound subsided. the island grew quiet and the airship travelers rose to their feet. "bless my very existence! what happened?" cried mr. damon. "it was an earthquake; wasn't it, tom?" asked mr. fenwick. "it sure was," agreed the young inventor. "rather a hard one, too. i hope we don't have any more." "do you think there is any likelihood of it?" demanded mr. damon. "bless my pocketbook! if i thought so i'd leave at once." "where would you go?" inquired tom, looking out across the tumbling ocean, which had hardly had a chance to subside from the gale, ere it was again set in a turmoil by the earth-tremor. "that's so--there isn't a place to escape to," went on the eccentric man, with something like a groan. "we are in a bad place--do you think there'll be more quakes, tom?" "it's hard to say. i don't know where we are, and this island may be something like japan, subject to quakes, or it may be that this one is merely a spasmodic tremor. perhaps the great storm which brought us here was part of the disturbance of nature which ended up with the earthquake. we may have no more." "and there may be one at any time," added mr. fenwick. "yes," assented tom. "then let's get ready for it," proposed mr. damon. "let's take all the precautions possible." "there aren't any to take," declared tom. "all we can do is to wait until the shocks come--if any more do come, which i hope won't happen, and then we must do the best we can." "oh, dear me! bless my fingernails!" cried mr. damon, wringing his hands. "this is worse than falling in an airship! there you do have some chance. here you haven't any." "oh, it may not be so bad," tom cried to reassure him. "this may have been the first shock in a hundred years, and there may never be another." but, as he looked around on the island, he noted evidences that it was of volcanic origin, and his heart misgave him, for he knew that such islands, created suddenly by a submarine upheaval, might just as suddenly be destroyed by an earthquake, or by sinking into the ocean. it was not a pleasant thought--it was like living over a mine, that might explode at any moment. but there was no help for it. tom tried to assume a cheerfulness he did not feel. he realized that, in spite of his youth, both mr. damon and mr. fenwick rather depended on him, for tom was a lad of no ordinary attainments, and had a fund of scientific knowledge. he resolved to do his best to avoid making his two companions worry. "let's get it off our minds," suggested the lad, after a while. "we were going to get something to eat. suppose we carry out that program. my appetite wasn't spoiled by the shock." "i declare mine wasn't either," said mr. damon, "but i can't forget it easily. it's the first earthquake i was ever in." he watched tom as the latter advanced once more toward the wreck of the airship, and noticed that the lad limped, for his right leg had been cut when the whizzer had fallen to earth. "what's the matter, tom; were you hurt in the quake?" asked the eccentric man. "no--no," tom hastened to assure him. "i just got a bump in the fall--that's all. it isn't anything. if you and mr. fenwick want to get out some food from the wrecked store room i'll see if i can haul out the gasolene stove from the airship. perhaps we can use it to make some coffee." by delving in about the wreck, tom was able to get out the gasolene stove. it was broken, but two of the five burners were in commission, and could be used. water, and gasolene for use in the airship, was carried in steel tanks. some of these had been split open by the crash, but there was one cask of water left, and three of gasolene, insuring plenty of the liquid fuel. as for the water, tom hoped to be able to find a spring on the island. in the meanwhile, mr. damon and mr. fenwick had been investigating the contents of the storeroom. there was a large supply of food, much larger than would have been needed, even on a two weeks' trip in the air, and the inventor of the whizzer hardly knew why he had put so much aboard. "but if we have to stay here long, it may come in handy," observed tom, with a grim smile. "why; do you think we will be here long?" asked mr. damon. the young inventor shrugged his shoulders. "there is no telling," he said. "if a passing steamer happens to see us, we may be taken off to-day or to-morrow. if not we may be here a week, or--" tom did not finish. he stood in a listening attitude. there was a rumbling sound, and the earth seemed again to tremble. then there came a great splash in the water at the foot of a tall, rugged cliff about a quarter of a mile away. a great piece of the precipice had fallen into the ocean. "i thought that was another earthquake coming," said mr. damon, with an air of relief. "so did i," admitted mr. fenwick. "it was probably loosened by the shock, and so fell into the sea," spoke tom. their momentary fright over, the castaways proceeded to get their breakfast. tom soon had water boiling on the gasolene stove, for he had rescued a tea-kettle and a coffee pot from the wreck of the kitchen of the airship. shortly afterward, the aroma of coffee filled the air, and a little later there was mingled with it the appetizing odor of sizzling bacon and eggs, for mr. fenwick, who was very fond of the latter, had brought along a supply, carefully packed in sawdust carriers, so that the shock had broken only a few of them. "well, i call this a fine breakfast," exclaimed mr. damon, munching his bacon and eggs, and dipping into his coffee the hard pilot biscuit, which they had instead of bread. "we're mighty lucky to be eating at all, i suppose." "indeed we are," chimed in mr. fenwick. "i'm awfully sorry the airship is wrecked, though," spoke tom. "i suppose it's my fault. i should have turned back before we got over the ocean, and while the storm was not at its height. i saw that the wind was freshening, but i never supposed it would grow to a gale so suddenly. the poor old whizzer--there's not much left of her!" "now don't distress yourself in the least," insisted mr. fenwick. "i'm proud to have built a ship that could navigate at all. i see where i made lots of mistakes, and as soon as i get back to philadelphia, i'm going to build a better one, if you'll help me, tom swift." "i certainly will," promised the young inventor. "and i'll take a voyage with you!" cried mr. damon. "bless my teaspoon, tom, but will you kindly pass the bacon and eggs again!" there was a jolly laugh at the eccentric man, in which he himself joined, and the little party felt better. they were seated on bits of broken boxes taken from the wreck, forming a little circle about the gasolene stove, which tom had set up on the beach. the wind had almost entirely died away, though the sea was still heaving in great billows, and masses of surf. they had no exact idea of the time, for all their watches had stopped when the shock of the wreck came, but presently the sun peeped out from the clouds, and, from knowing the time when they had begun to fall, they judged it was about ten o'clock, and accordingly set their timepieces. "well," observed tom, as he collected the dishes, which they had also secured from the wreck, "we must begin to think about a place to spend the night. i think we can rig up a shelter from some of the canvas of the wing-planes, and from what is left of the cabin. it doesn't need to be very heavy, for from the warmth of the atmosphere, i should say we were pretty well south." it was quite warm, now that the storm was over, and, as they looked at the vegetation of the island, they saw that it was almost wholly tropical. "i shouldn't be surprised if we were on one of the smaller of the west indian islands," said tom. "we certainly came far enough, flying a hundred miles or more an hour, to have reached them. but this one doesn't appear to be inhabited." "we haven't been all over it yet," said mr. damon. "we may find cannibals on the other side." "cannibals don't live in this part of the world," tom assured him. "no, i think this island is practically unknown. the storm brought us here, and it might have landed us in a worse place." as he spoke he thought of the yacht resolute, and he wondered how her passengers, including the parents of mary nestor, had fared during the terrible blow. "i hope they weren't wrecked, as we were," mused tom. but there was little time for idle thoughts. if they were going to build a shelter, they knew that they must speedily get at it. accordingly, with a feeling of thankfulness that their lives had been spared, they set to work taking apart such of the wreck as could the more easily be got at. boards, sticks, and planks were scattered about, and, with the pieces of canvas from the wing-planes, and some spare material which was carried on board, they soon had a fairly good shack, which would be protection enough in that warm climate. next they got out the food and supplies, their spare clothing and other belongings, few of which had been harmed in the fall from the clouds. these things were piled under another rude shelter which they constructed. by this time it was three o'clock, and they ate again. then they prepared to spend the night in their hastily made camp. they collected driftwood, with which to make a fire, and, after supper, which was prepared on the gasolene stove, they sat about the cheerful blaze, discussing their adventures. "to-morrow we will explore the island," said tom, as he rolled himself up in his blankets and turned over to sleep. the others followed his example, for it was decided that no watch need be kept. thus passed several hours in comparative quiet. it must have been about midnight that tom was suddenly awakened by a feeling as if someone was shaking him. he sat up quickly and called out: "what's the matter?" "eh? what's that? bless my soul! what's going on?" shouted mr. damon. "did you shake me?" inquired tom. "i? no. what--?" then they realized that another earth-tremor was making the whole island tremble. tom leaped from his blankets, followed by mr. damon and mr. fenwick, and rushed outside the shack. they felt the earth shaking, but it was over in a few seconds. the shock was a slight one, nothing like as severe as the one in the morning. but it set their nerves on edge. "another earthquake!" groaned mr. damon. "how often are we to have them?" "i don't know," answered tom, soberly. they passed the remainder of the night sleeping in blankets on the warm sands, near the fire, for they feared lest a shock might bring the shack down about their heads. however, the night passed with no more terrors. chapter xv the other castaways "well, we're all alive, at any rate," announced tom, when the bright sun, shining into his eyes, had awakened him. he sat up, tossed aside his blankets, and stood up. the day was a fine one, and the violence of the sea had greatly subsided during the night, their shack had suffered not at all from the slight shock in the darkness. "now for a dip in old briney," the lad added, as he walked down to the surf, "i think it will make me feel better." "i'm with you," added mr. fenwick, and mr. damon also joined the bathers. they came up from the waves, tingling with health, and their bruises and bumps, including tom's cut leg, felt much better. "you did get quite a gash; didn't you," observed mr. fenwick, as he noticed tom's leg. "better put something on it. i have antiseptic dressings and bandages in the airship, if we can find them." "i'll look for them, after breakfast," tom promised, and following a fairly substantial meal, considering the exigencies under which it was prepared, he got out the medicine chest, of which part remained in the wreck of the whizzer, and dressed his wound. he felt much better after that. "well, what's our program for to-day?" mr. damon wanted to know, as they sat about, after they had washed up what few dishes they used. "let's make a better house to stay in," proposed mr. fenwick. "we may have to remain here for some time, and i'd like a more substantial residence." "i think the one we now have will do," suggested tom. "i was going to propose making it even less substantial." "why so?" "because, in the event of an earthquake, while we are sleeping in it, we will not be injured. made of light pieces of wood and canvas it can't harm us very much if it falls on us." "that's right," agreed mr. damon. "in earthquake countries all the houses are low, and built of light materials." "ha! so i recollect now," spoke mr. fenwick. "i used to read that in my geography, but i never thought it would apply to me. but do you think we will be subject to the quakes?" "i'm afraid so," was tom's reply. "we've had two, now, within a short time, and there is no way of telling when the next will come. we will hope there won't be any more, but--" he did not finish his sentence, but the others knew what he meant. thereupon they fell to work, and soon had made a shelter that, while very light and frail, would afford them all the protection needed in that mild climate, and, at the same time, there would be no danger should an earthquake collapse it, and bring it down about their heads while they were sleeping in it. for they decided that they needed some shelter from the night dews, as it was exceedingly uncomfortable to rest on the sands even wrapped in blankets, and with a driftwood fire burning nearby. it was noon when they had their shack rebuilt to their liking, and they stopped for dinner. there was quite a variety of stores in the airship, enough for a much larger party than that of our three friends, and they varied their meals as much as possible. of course all the stuff they had was canned, though there are some salted and smoked meats. but canned food can be had in a variety of forms now-a-days, so the castaways did not lack much. "what do you say to an exploring expedition this afternoon?" asked tom, as they sat about after dinner. "we ought to find out what kind of an island we're on." "i agree with you," came from mr. fenwick. "perhaps on the other side we will stand a much better chance of speaking some passing vessel. i have been watching the horizon for some time, now, but i haven't seen the sign of a ship." "all right, then we'll explore, and see what sort of an island we have taken possession of," went on tom. "and see if it isn't already in possession of natives--or cannibals," suggested mr. damon. "bless my frying pan! but i should hate to be captured by cannibals at my time of life." "don't worry; there are none here," tom assured him again. they set out on their journey around the island. they agreed that it would be best to follow the beach around, as it was easier walking that way, since the interior of the place consisted of rugged rocks in a sort of miniature mountain chain. "we will make a circuit of the place," proposed tom, "and then, if we can discover nothing, we'll go inland. the centre of the island is quite high, and we ought to be able to see in any direction for a great distance from the topmost peak. we may be able to signal a vessel." "i hope so!" cried mr. damon. "i want to send word home that i am all right. my wife will worry when she learns that the airship, in which i set out, has disappeared." "i fancy we all would like to send word home," added mr. fenwick. "my wife never wanted me to build this airship, and, now that i have sailed in it, and have been wrecked, i know she'll say 'i told you so,' as soon as i get back to philadelphia." tom said nothing, but he thought to himself that it might be some time before mrs. fenwick would have a chance to utter those significant words to her husband. following the beach line, they walked for several miles. the island was larger than they had supposed, and it soon became evident that it would take at least a day to get all around it. "in which case we will need some lunch with us." said tom. "i think the best thing we can do now is to return to camp, and get ready for a longer expedition to-morrow." mr. fenwick was of the same mind, but mr. damon called out: "let's go just beyond that cliff, and see what sort of a view is to be had from there. then we'll turn back." to oblige him they followed. they had not gone more than a hundred yards toward the cliff, than there came the preliminary rumbling and roaring that they had come to associate with an earthquake. at the same time, the ground began to shiver and shake. "here comes another one!" cried tom, reeling about. he saw mr. damon and mr. fenwick topple to the beach. the roaring increased, and the rumbling was like thunder, close at hand. the island seemed to rock to its very centre. suddenly the whole cliff toward which they had been walking, appeared to shake itself loose. in another instant it was flung outward and into the sea, a great mass of rock and stone. the island ceased trembling, and the roaring stopped. tom rose to his feet, followed by his companions. he looked toward the place where the cliff had been. its removal by the earthquake gave them a view of a part of the beach that had hitherto been hidden from them. and what tom saw caused him to cry out in astonishment. for he beheld, gathered around a little fire on the sand, a party of men and women. some were standing, clinging to one another in terror. some were prostrate on the ground. others were running to and fro in bewilderment. "more castaways!" cried tom. "more castaways," and, he added under his breath, "more unfortunates on earthquake island!" chapter xvi an alarming theory for a few seconds, following tom's announcement to his two companions, neither mr. damon nor mr. fenwick spoke. they had arisen from the beach, where the shock of the earthquake had thrown them, and were now staring toward the other band of castaways, who, in turn were gazing toward our three friends. there was a violent agitation in the sea, caused by the fall of the great cliff, and immense waves rushed up on shore, but all the islanders were beyond the reach of the rollers. "is it--do i really--am i dreaming or not?" at length gasped mr. damon. "is this a mirage, or do we really see people, tom?" inquired mr. fenwick. "they are real enough people," replied the lad, himself somewhat dazed by the unexpected appearance of the other castaways. "but how--why--how did they get here?" went on the inventor of the whizzer. "as long as they're not cannibals, we're all right," murmured mr. damon. "they seem to be persons like ourselves, tom." "they are," agreed the lad, "and they appear to be in the same sort of trouble as ourselves. let's go forward, and meet them." the tremor of the earthquake had now subsided, and the little band that was gathered about a big fire of driftwood was calmer. those who had fallen, or who had thrown themselves on the sand, arose, and began feeling of their arms and legs to see if they had sustained any injuries. others advanced toward our friends. "nine of them," murmured tom, as he counted the little band of castaways, "and they don't seem to have been able to save much from the wreck of their craft, whatever it was." the beach all about them was bare, save for a boat drawn up out of reach of high water. "do you suppose they are a party from some disabled airship, tom," asked mr. fenwick. "not from an airship," answered the lad. "probably from some vessel that was wrecked in the gale. but we will soon find out who they are." tom led the way for his two friends. the fall of the cliff had made a rugged path around the base of it, over rocks, to where the other people stood. tom scrambled in and out among the boulders, in spite of the pain it caused his wounded leg. he was anxious to know who the other castaways were, and how they had come there. several of the larger party were now advancing to meet the lad and his friends. tom could see two women and seven men. a moment later, when the lad had a good view of one of the ladies and a gentleman, he could not repress a cry of astonishment. then he rubbed his eyes to make sure it was not some blur or defect of vision. no, his first impression had been correct. "mr. nestor!" cried tom, recognizing the father of his girl friend. "and mrs. nestor!" he added a moment later. "why--of all things--look--amos--it's--it can't be possible--and yet--why, it's tom swift!" cried the lady. "tom--tom swift--here?" ejaculated the man at her side. "yes--tom swift--the young inventor--of shopton--don't you know--the lad who saved mary's life in the runaway--tom swift!" "tom swift!" murmured mr. nestor. "is it possible!" "i'm tom swift, all right," answered the owner of that name, "but how in the world did you get on this island, mr. nestor?" "i might ask you the same thing, tom. the yacht resolute, on which we were making a voyage to the west indies, as guests of mr. george hosbrook, was wrecked in the awful gale. we took to the boats and managed to reach this island. the yacht sunk, and we only had a little food. we are almost starved! but how came you here?" "mr. fenwick's airship was wrecked, and we dropped down here. what a coincidence! to think that i should meet you here! but if you're hungry, it's the best thing in the world that we met you, for, though our airship was wrecked, we have a large supply of food. come over to our camp, and we'll give you all you want!" tom had rushed forward, and was shaking hands with mary's parents, so unexpectedly met with, when mr. nestor called out: "come over here, mr. hosbrook. i want you to meet a friend of mine." a moment later, the millionaire owner of the ill-fated resolute was shaking hands with tom. "i can't understand it," mr. hosbrook said. "to think of meeting other people on this desolate island--this island of earthquakes." "oh, please don't speak of earthquakes!" cried mrs. nestor. "we are in mortal terror! there have been several since we landed in the most terrible storm day before yesterday. isn't it awful! it is a regular earthquake island!" "that's what i call it," spoke tom, grimly. the others of the larger party of refugees now came up. besides mr. and mrs. nestor, and mr. hosbrook, there was mr. and mrs. floyd anderson, friends of the millionaire; mr. ralph parker, who was spoken of as a scientist, mr. barcoe jenks, who seemed an odd sort of individual, always looking about suspiciously, captain mentor, who had been in command of the yacht, and jake fordam, the mate of the vessel. "and are these all who were saved?" asked tom, as he introduced his two friends, and told briefly of their air voyage. "no," answered mr. hosbrook, "two other boatloads, one containing most of the crew, and the other containing some of my guests, got away before our boat left. i trust they have been rescued, but we have heard nothing about them. however, our own lives may not long be safe, if these earthquakes continue." "but did i understand you to say, mr. swift, that you had food?" he went on. "if you have, i will gladly pay you any price for some, especially for these two ladies, who must be faint. i have lost all my ready cash, but if we ever reach civilization, i will--" "don't speak of such a thing as pay," interrupted mr. fenwick. "all that we have we'll gladly share with you. come over to our camp. we have enough for all, and we can cook on our gasolene stove. don't speak of pay, i beg of you." "ah--er, if mr. hosbrook has no money, perhaps i can offer an equivalent," broke in the man who had been introduced as barcoe jenks. "i have--er--some securities--" he stopped and looked about indefinitely, as though he did not know exactly what to say, and he was fumbling at a belt about his waist; a belt that might contain treasure. "don't speak of reimbursing us," went on mr. fenwick, with rather a suspicious glance at mr. jenks. "you are welcome to whatever we have." "bless my topknot; certainly, yes!" joined in mr. damon, eagerly. "well, i--er--i only spoke of it," said mr. jenks, hesitatingly, and then he turned away. mr. hosbrook looked sharply at him, but said nothing. "suppose we go to our camp," proposed tom. "we may be able to get you up a good meal, before another earthquake comes." "i wonder what makes so many of them?" asked mrs. nestor, with a nervous shiver. "yes, indeed, they are terrifying! one never knows when to expect them," added mrs. anderson. "i have a theory about them," said mr. parker, the scientist, who, up to this time had spoken but little. "a theory?" inquired tom. "yes. this island is one of the smaller of the west indies group. it is little known, and has seldom been visited, i believe. but i am sure that what causes the earthquakes is that the whole island has been undermined by the sea, and it is the wash of great submarine waves and currents which cause the tremors." "undermined by the sea?" repeated tom. "yes. it is being slowly washed away." "bless my soul! washed away!" gasped mr. damon. "and, in the course of a comparatively short time, it will sink," went on the scientist, as cheerfully as though he was a professor propounding some problem to his class. "sink!" ejaculated mrs. nestor. "the whole island undermined! oh, what an alarming theory!" "i wish i could hold to a different one, madam," was mr. parker's answer, "but i cannot. i think the island will sink after a few more shocks." "then what good will my--" began barcoe jenks, but he stopped in confusion, and again his hand went to his belt with a queer gesture. chapter xvii a mighty shock tom swift turned to gaze at mr. barcoe jenks. that individual certainly had a strange manner. perhaps it might be caused by the terror of the earthquakes, but the man seemed to be trying to hold back some secret. he was constrained and ill at ease. he saw the young inventor looking at him, and his hands, which had gone to his belt, with a spasmodic motion, dropped to his side. "you don't really mean to say, parker, that you think the whole island is undermined, do you?" asked the owner of the resolute. "that's my theory. it may be a wrong one, but it is borne out by the facts already presented to us. i greatly fear for our lives!" "but what can we do?" cried mrs. nestor. "nothing," answered the scientist, with a shrug of his shoulders. "absolutely nothing, save to wait for it to happen." "don't say that!" begged mrs. andersen. "can't you gentlemen do something--build a boat and take us away. why, the boat we came here in--" "struck a rock, and stove a hole in the bottom as big as a barrel, madam," interrupted captain mentor. "it would never do to put to sea in that." "but can't something else be done?" demanded mrs. nestor. "oh, it is awful to think of perishing on this terrible earthquake island. oh, amos! think of it, and mary home alone! have you seen her lately, mr. swift?" tom told of his visit to the nestors' home. our hero was almost in despair, not so much for himself, as for the unfortunate women of the party--and one of them was mary's mother! yet what could he do? what chance was there of escaping from the earthquake? "bless my gizzard!" exclaimed mr. damon. "don't let's stand here worrying! if you folks are hungry come up to our camp. we have plenty. afterward we can discuss means of saving ourselves." "i want to be saved!" exclaimed mr. jenks. "i must be saved! i have a great secret--a secret--" once more he paused in confusion, and once more his hands nervously sought his belt. "i would give a big reward to be saved," he murmured. "and so, i fancy, we all would," added captain mentor. "but we are not likely to. this island is out of the track of the regular line of vessels." "where are we, anyhow?" inquired mr. fenwick. "what island is this?" "it isn't down on the charts, i believe," was the captain's reply, "but we won't be far out, if we call it earthquake island. that name seems to fit it exactly." they had walked on, while talking, and now had gone past the broken cliff. tom and his two friends of the airship led the way to the camp they had made. on the way, mr. hosbrook related how his yacht had struggled in vain against the tempest, how she had sprung a leak, how the fires had gone out, and how, helpless in the trough of the sea, the gallant vessel began to founder. then they had taken to the boats, and had, most unexpectedly come upon the island. "and since we landed we have had very little to eat," said mrs. nestor. "we haven't had a place to sleep, and it has been terrible. then, too, the earthquakes! and my husband and i worried so about mary. oh, mr. swift! do you think there is any chance of us ever seeing her again?" "i don't know," answered tom, softly. "i'll do all i can to get us off this island. perhaps we can build a raft, and set out. if we stay here there is no telling what will happen, if that scientist's theory is correct. but there is our camp, just ahead. you will be more comfortable, at least for a little while." in a short time they were at the place where tom and the others had built the shack. the ruins of the airship were examined with interest, and the two women took advantage of the seclusion of the little hut, to get some much needed rest until a meal should be ready. one was soon in course of preparation by tom and mr. damon, aided by mate fordam, of the resolute. fortunate it was that mr. fenwick had brought along such a supply of food, for there were now many mouths to feed. that the supper (which the meal really was, for it was getting late) was much enjoyed, goes without saying. the yacht castaways had subsisted on what little food had been hurriedly put into the life boat, as they left the vessel. at tom's request, while it was yet light, captain mentor and some of the men hunted for a spring of fresh water, and found one, for, with the increase in the party, the young inventor saw the necessity for more water. the spring gave promise of supplying a sufficient quantity. there was plenty of material at hand for making other shacks, and they were soon in course of construction. they were made light, as was the one tom and his friends first built, so that, in case of another shock, no one would be hurt seriously. the two ladies were given the larger shack, and the men divided themselves between two others that were hastily erected on the beach. the remainder of the food and stores was taken from the wreck of the airship, and when darkness began to fall, the camp was snug and comfortable, a big fire of driftwood burning brightly. "oh, if only we can sleep without being awakened by an earthquake!" exclaimed mrs. nestor, as she prepared to go into the shack with mrs. anderson. "but i am almost afraid to close my eyes!" "if it would do any good to stay up and watch, to tell you when one was coming, i'd do so," spoke tom, with a laugh, "but they come without warning." however, the night did pass peacefully, and there was not the least tremor of the island. in the morning the castaways took courage and, after breakfast, began discussing their situation more calmly. "it seems to me that the only solution is to build some sort of a raft, or other craft and leave the island," said mr. fenwick. "bless my hair brush!" cried mr. damon. "why can't we hoist a signal of distress, and wait for some steamer to see it and call for us? it seems to me that would be more simple than going to sea on a raft. i don't like the idea." "a signal would be all right, if this island was in the path of the steamers," said captain mentor. "but it isn't. our flag might fly for a year, and never be seen." his words seemed to strike coldness to every heart. tom, who was looking at the wreck of the airship, suddenly uttered an exclamation. he sprang to his feet. "what is it?" demanded mr. fenwick. "does your sore leg hurt you?" "no, but i have just thought of a plan!" fairly shouted the young inventor. "i have it! wait and see if i can work it!" "work what?" cried mr. damon. tom did not get a chance to answer, for, at that moment, there sounded, at the far end of the island, whence the yacht castaways had come, a terrific crash. it was accompanied, rather than followed, by a shaking, trembling and swaying of the ground. "another earthquake!" screamed mrs. nestor, rushing toward her husband. the castaways gazed at each other affrighted. suddenly, before their eyes, they saw the extreme end of that part of the island on which they were camping, slip off, and beneath the foaming waves of the sea, while the echoes of the mighty crash came to their ears! chapter xviii mr. jenks has diamonds stunned, and well-nigh paralyzed by the suddenness of the awful crash, and the recurrence of the earthquake, the castaways gazed spell-bound at one another. succeeding the disappearance of the end of the island there arose a great wave in the ocean, caused by the immersion of such a quantity of rock and dirt. "look out!" yelled tom, "there may be a flood here!" they realized his meaning, and hastened up the beach, out of reach of the water if it should come. and it did. at first the ocean retreated, as though the tide was going out, then, with a rush and roar, the waves came leaping back, and, had the castaways remained where they had been standing they would have been swept out to sea. as it was the flood reached part of the wreck of the airship, that lay on the beach, and washed away some of the broken planks. but, after the first rush of water, the sea grew less troubled, and there was no more danger from that source. true, the whole island was rumbling and trembling in the throes of an earthquake, but, by this time, the refugees had become somewhat used to this, and only the two ladies exhibited any outward signs of great alarm, though mr. barcoe jenks, tom observed, was nervously fingering the belt which he wore about his waist. "i guess the worst is over," spoke mr. fenwick, as they stood looking toward where part of the island had vanished. "the shock expended itself on tearing that mass of rock and earth away." "let us hope so," added mr. hosbrook, solemnly. "oh, if we could only get away from this terrible place! we must hoist a signal of distress, even if we are out of the track of regular vessels. some ship, blown out of her course may see it. captain mentor, i wish you and mr. fordam would attend to that." "i will, sir," answered the commander of the ill-fated resolute. "the signal shall be hoisted at once. come on, mr. fordam," he added, turning to the first mate. "if you don't mind," interrupted tom, "i wish you would first help me to get what remains of the airship up out of reach of any more possible high waves. that one nearly covered it, and if there are other big rollers, the wreck may be washed out to sea." "i can't see that any great harm would result from that," put in mr. jenks. "there isn't anything about the wreck that we could use to make a boat or raft from." indeed, there was little left of the airship, save the mass of machinery. "well, it may come in handy before we leave here," said tom, and there was a quiet determined air about him, that caused mr. damon to look at him curiously. the odd gentleman started to utter one of his numerous blessings, and to ask tom a question, but he thought better of it. by this time the earthquake had ceased, and the castaways were calmer. tom started toward the airship wreck, and began pulling off some broken boards to get at the electrical machinery. "i guess you had better give mr. swift a hand, captain mentor," spoke the millionaire yacht owner. "i don't know what good the wreck can be, but we owe considerable to mr. swift and his friends, and the least we can do is to aid them in anything they ask. so, captain, if you don't mind, you and the mate bear a hand. in fact, we'll all help, and move the wreck so far up that there will be no danger, even from tidal waves." tom looked pleased at this order, and soon he and all the men in the little party were busy taking out the electrical apparatus, and moving it farther inland. "what are you going to do with it, tom?" asked mr. damon, in a low voice, as he assisted the young inventor to carry a small dynamo, that was used for operating the incandescent lights. "i hardly know myself. i have a half-formed plan in my mind. i may be able to carry it out, and i may not. i don't want to say anything until i look over the machinery, and see if all the parts which i need are here. please say nothing about it." "bless my toothpick! of course, i'll not," promised mr. damon. when the removal of most of the machinery of the wrecked airship had been completed, mrs. nestor exclaimed: "well, since you are moving that out of harm's way, don't you think it would be a good idea to change our camp, also? i'm sure i'll never sleep a wink, thinking that part of the island may fall into the ocean at any moment in the night, and create a wave that may wash us all out to sea. can't we move the camp, mr. swift?" "no reason why we can't," answered the lad, smiling. "i think it would be a good plan to take it farther back. we are likely to be here some time, and, while we are about it, we might build more complete shelters, and have a few more comforts." the others agreed with this idea, so the little shacks that had been erected were taken down, and moved to higher ground, where a better outlook could be had of the surrounding ocean. at the same time as safe a place as possible, considering the frequent earthquakes, was picked out--a place where there were no overhanging rocks or cliffs. three huts were built, one for the two ladies, one for the men, and third where the cooking could be done. this last also held the food supplies and stores, and tom noted, with satisfaction, that there was still sufficient to eat to last over a week. mr. fenwick had not stinted his kitchen stores. this work done, captain mentor and mate fordam went to the highest part of the island, where they erected a signal, made from pieces of canvas that had been in the life boat. the boat itself was brought around to the new camp, and at first it was hoped that it could be repaired, and used. but too large a hole had been stove in the bottom, so it was broken up, and the planks used in making the shacks. this work occupied the better part of two days, and during this time, there were no more earthquakes. the castaways began to hope that the island would not be quiet for a while. mrs. anderson and mrs. nestor assumed charge of the "housekeeping" arrangements, and also the cooking, which relieved tom from those duties. the two ladies even instituted "wash-day," and when a number of garments were hung on lines to dry, the camp looked like some summer colony of pleasure-seekers, out for a holiday. in the meanwhile, tom had spent most of his time among the machinery which had been taken from the airship. he inspected it carefully, tested some of the apparatus, and made some calculations on a bit of paper. he seemed greatly pleased over something, and one afternoon, when he was removing some of the guy and stay wires from the collapsed frame of the whizzer, he was approached by mr. barcoe jenks. "planning something new?" asked mr. jenks, with an attempt at jollity, which, however, failed. the man had a curious air about him, as if he was carrying some secret that was too much for him. "well, nothing exactly new," answered tom. "at best i am merely going to try an experiment." "an experiment, eh?" resumed mr. jenks, "and might i ask if it has anything to do with rescuing us from this island?" "i hope it will have," answered tom, gravely. "good!" exclaimed mr. jenks. "well, now i have a proposition to make to you. i suppose you are not very wealthy, mr. swift?" he gazed at tom, quizzically. "i am not poor," was the young inventor's proud answer, "but i would be glad to make more money--legitimately." "i thought so. most every one would. look here!" he approached closer to tom, and, pulling his hand from his pocket, held it extended, in the palm were a number of irregularly-shaped objects--stones or crystals the lad took them to be, yet they did not look like ordinary stones or crystals. "do you know what those are?" asked mr. jenks. "i might guess," replied tom. "i'll save you the trouble. they are diamonds! diamonds of the very first water, but uncut. now to the point. i have half a million dollars worth of them. if you get me safely off this island, i will agree to make you a quarter of a million dollars worth of diamonds!" "make me a quarter of a million dollars worth of diamonds?" asked tom, struck by the use of the work "make." "yes, 'make,'" answered mr. jenks. "that is if i can discover the secret--the secret of phantom mountain. get me away from the island and i will share my knowledge with you--i need help--help to learn the secret and help to make the diamonds--see, there are some of the first ones made, but i have been defrauded of my rights--i need the aid of a young fellow like you. will you help? see, i'll give you some diamonds now. they are genuine, though they are not like ordinary diamonds. i made them. will you--" before tom could answer, there came a warning rumble of the earth, and a great fissure opened, almost at the feet of mr. jenks, who, with a cry of fear, leaped toward the young inventor. chapter xix secret operations "help me save this machinery!" yelled tom, whose first thought was for the electrical apparatus. "don't let it fall into that chasm!" for the crack had widened, until it was almost to the place where the parts of the wrecked airship had been carried. "the machinery? what do i care about the machinery?" cried mr. jenks. "i want to save my life!" "and this machinery is our only hope!" retorted tom. he began tugging at the heavy dynamos and gasolene engine, but he might have saved himself the trouble, for with the same suddenness with which it opened, the crack closed again. the shock had done it, and, as if satisfied with that phenomena, the earthquake ceased, and the island no longer trembled. "that was a light one," spoke tom, with an air of relief. he was becoming used to the shocks now, and, when he saw that his precious machinery was not damaged he could view the earth tremors calmly. "slight!" exclaimed mr. jenks. "well, i don't call it so. but i see captain mentor and mr. hosbrook coming. please don't say anything to them about the diamonds. i'll see you again," and with that, the queer mr. jenks walked away. "we came to see if you were hurt," called the captain, as he neared the young inventor. "no, i'm all right. how about the others?" "only frightened," replied the yacht owner. "this is getting awful. i hoped we were free from the shocks, but they still continue." "and i guess they will," added tom. "we certainly are on earthquake island!" "mr. parker, the scientist, says this last shock bears out his theory," went on the millionaire. "he says it will be only a question of a few days when the whole island will disappear." "comforting, to say the least," commented tom. "i should say so. but what are you doing, mr. swift?" "trying an experiment," answered the young inventor, in some confusion. he was not yet ready to talk about his plans. "we must begin to think seriously of building some sort of a boat or raft, and getting away from the island," went on the millionaire. "it will be perilous to go to sea with anything we can construct, but it is risking our lives to stay here. i don't know what to do." "perhaps captain mentor has some plan," suggested tom, hoping to change the subject. "no," answered the commander, "i confess i am at a loss to know what to do. there is nothing with which to do anything, that is the trouble! but i did think of hoisting another signal, on this end of the island, where it might be seen if our first one wasn't. i believe i'll do that," and he moved away, to carry out his intention. "well, i think i'll get back, tom, and tell the others that you are all right," spoke mr. hosbrook. "i left the camp, after the shock, because mrs. nestor was worried about you." the place to which the airship machinery had been removed was some distance from the camp, and out of sight of the shacks. "oh, yes. i'm all right," said tom. then, with a sudden impulse, he asked: "do you know much about this mr. barcoe jenks, mr. hosbrook?" "not a great deal," was the reply. "in fact, i may say i do not know him at all. why do you ask?" "because i thought he acted rather strangely." "just what the rest of us think," declared the yacht owner. "he is no friend of mine, though he was my guest on the resolute. it came about in this way. i had invited a mr. frank jackson to make the trip with me, and he asked if he could bring with him a mr. jenks, a friend of his. i assented, and mr. jackson came aboard with mr. jenks. just as we were about to sail mr. jackson received a message requiring his presence in canada, and he could not make the trip." "but mr. jenks seemed so cut-up about being deprived of the yachting trip, and was so fond of the water, that i invited him to remain on board, even if his friend did not. so that is how he came to be among my guests, though he is a comparative stranger to all of us." "i see," spoke tom. "has he been acting unusually strange?" asked mr. hosbrook suspiciously. "no, only he seemed very anxious to get off the island, but i suppose we all are. he wanted to know what i planned to do." "did you tell him?" "no, for the reason that i don't know whether i can succeed or not, and i don't want to raise false hopes." "then you would prefer not to tell any of us?" "no one--that is except mr. fenwick and mr. damon. i may need them to help me." "i see," responded mr. hosbrook. "well, whatever it is, i wish you luck. it is certainly a fearful place--this island," and busy with many thoughts, which crowded upon him, the millionaire moved away, leaving tom alone. a little while after this tom might have been seen in close conversation with mr. damon and mr. fenwick. the former, on hearing what the young inventor had to say, blessed himself and his various possessions so often, that he seemed to have gotten out of breath. mr. fenwick exclaimed: "tom, if you can work that it will be one of the greatest things you have ever done!" "i hope i can work it," was all the young inventor replied. for the next three days tom, and his two friends, spent most of their time in the neighborhood of the pile of machinery and apparatus taken from the wrecked whizzer. mr. jenks hung around the spot, but a word or two from mr. hosbrook sent him away, and our three friends were left to their work in peace, for they were inclined to be secretive about their operations, as tom did not want his plans known until he was ready. the gasolene motor was overhauled, and put in shape to work. then it was attached to the dynamo. when this much had been done, tom and his friends built a rude shack around the machinery shutting it from view. "humph! are you afraid we will steal it?" asked mr. parker, the scientist, who held to his alarming theory regarding the ultimate disappearance of the island. "no, i simply want to protect it from the weather," answered tom. "you will soon know all our plans. i think they will work out." "you'd better do it before we get another earthquake, and the island sinks," was the dismal response. but there had been no shocks since the one that nearly engulfed mr. jenks. as for that individual he said little to any one, and wandered off alone by himself. tom wondered what kind of diamonds they were that the odd man had, and the lad even had his doubts as to the value of the queer stones he had seen. but he was too busy with his work to waste much time in idle speculation. chapter xx the wireless plant the castaways had been on earthquake island a week now, and in that time had suffered many shocks. some were mere tremors, and some were so severe as to throw whole portions of the isle into the sea. they never could tell when a shock was coming, and often one awakened them in the night. but, in spite of this, the refugees were as cheerful as it was possible to be under the circumstances. only mr. jenks seemed nervous and ill at ease, and he kept much by himself. as for tom, mr. damon and mr. fenwick, the three were busy in their shack. the others had ceased to ask questions about what they were doing, and mr. nestor and his wife took it for granted that tom was building a boat. captain mentor and the mate spent much time gazing off to sea, hoping for a sight of the sail of some vessel, or the haze that would indicate the smoke of a steamer. but they saw nothing. "i haven't much hope of sighting anything," the captain said. "i know we are off the track of the regular liners, and our only chance would be that some tramp steamer, or some ship blown off her course, would see our signal. i tell you, friends, we're in a bad way." "if money was any object--," began mr. jenks. "what good would money be?" demanded mr. hosbrook. "what we need to do is to get a message to some one--some of my friends--to send out a party to rescue us." "that's right," chimed in mr. parker, the scientist. "and the message needs to go off soon, if we are to be saved." "why so?" asked mr. anderson. "because i think this island will sink inside of a week!" a scream came from the two ladies. "why don't you keep such thoughts to yourself?" demanded the millionaire yacht owner, indignantly. "well, it's true," stubbornly insisted the scientist. "what if it is? it doesn't do any good to remind us of it." "bless my gizzard, no!" exclaimed mr. damon. "suppose we have dinner. i'm hungry." that seemed to be his remedy for a number of ills. "if we only could get a message off, summoning help, it would be the very thing," sighed mrs. nestor. "oh, how i wish i could send my daughter, mary, word of where we are. she may hear of the wreck of the resolute, and worry herself to death." "but it is out of the question to send a message for help from earthquake island," added mrs. anderson. "we are totally cut off from the rest of the world here." "perhaps not," spoke tom swift, quietly. he had come up silently, and had heard the conversation. "what's that you said?" cried mr. nestor, springing to his feet, and crossing the sandy beach toward the lad. "i said perhaps we weren't altogether cut off from the rest of the world," repeated tom. "why not," demanded captain mentor. "you don't mean to say that you have been building a boat up there in your little shack, do you?" "not a boat," replied tom, "but i think i have a means of sending out a call for help!" "oh, tom--mr. swift--how?" exclaimed mrs. nestor. "do you mean we can send a message to my mary?" "well, not exactly to her," answered the young inventor, though he wished that such a thing were possible. "but i think i can summon help." "how?" demanded mr. hosbrook. "have you managed to discover some cable line running past the island, and have you tapped it?" "not exactly." was tom's calm answer, "but i have succeeded, with the help of mr. damon and mr. fenwick, in building an apparatus that will send out wireless messages!" "wireless messages!" gasped the millionaire. "are you sure?" "wireless messages!" exclaimed mr. jenks. "i'll give--" he paused, clasped his hands on his belt, and turned away. "oh, tom!" cried mrs. nestor, and she went up to the lad, threw her arms about his neck, and kissed him; whereat tom blushed. "perhaps you'd better explain," suggested mr. anderson. "i will," said the lad. "that is the secret we have been engaged upon--mr. damon, mr. fenwick and myself. we did not want to say anything about it until we were sure we could succeed." "and are you sure now?" asked captain mentor. "fairly so." "how could you build a wireless station?" inquired mr. hosbrook. "from the electrical machinery that was in the wrecked whizzer," spoke tom. "fortunately, that was not damaged by the shock of the fall, and i have managed to set up the gasolene engine, and attach the dynamo to it so that we can generate a powerful current. we also have a fairly good storage battery, though that was slightly damaged by the fall." "i have just tested the machinery, and i think we can send out a strong enough message to carry at least a thousand miles." "then that will reach some station, or some passing ship," murmured captain mentor. "there is a chance that we may be saved." "if it isn't too late," gloomily murmured the scientist. "there is no telling when the island will disappear beneath the sea." but they were all so interested in tom's announcement that they paid little attention to this dire foreboding. "tell us about it," suggested mr. nestor. and tom did. he related how he had set up the dynamo and gasolene engine, and how, by means of the proper coils and other electrical apparatus, all of which, fortunately, was aboard the whizzer, he could produce a powerful spark. "i had to make a key out of strips of brass, to produce the morse characters," the lad said. "this took considerable time, but it works, though it is rather crude. i can click out a message with it." "that may be," said mr. hosbrook, who had been considering installing a wireless plant on his yacht, and who, therefore, knew something about it, "you may send a message, but can you receive an answer?" "i have also provided for that," replied tom. "i have made a receiving instrument, though that is even more crude than the sending plant, for it had to be delicately adjusted, and i did not have just the magnets, carbons, coherers and needles that i needed. but i think it will work." "did you have a telephone receiver to use?" "yes. there was a small interior telephone arrangement on mr. fenwick's airship, and part of that came in handy. oh, i think i can hear any messages that may come in answer to ours." "but what about the aerial wires for sending and receiving messages?" asked mr. nestor. "don't you have to have several wires on a tall mast?" "yes, and that is the last thing to do," declared tom. "i need all your help in putting up those wires. that tall tree on the crest of the island will do," and he pointed to a dead palm that towered gaunt and bare like a ship's mast, on a pile of rocks in the centre of earthquake island. chapter xxi messages into space tom swift's announcement of the practical completion of his wireless plant brought hope to the discouraged hearts of the castaways. they crowded about him, and asked all manner of questions. mr. fenwick and mr. damon came in for their share of attention, for tom said had it not been for the aid of his friends he never could have accomplished what he did. then they all trooped up to the little shack, and inspected the plant. as the young inventor had said, it was necessarily crude, but when he set the gasolene motor going, and the dynamo whizzed and hummed, sending out great, violet-hued sparks, they were all convinced that the young inventor had accomplished wonders, considering the materials at his disposal. "but it's going to be no easy task to rig up the sending and receiving wires," declared tom. "that will take some time." "have you got the wire?" asked mr. jenks. "i took it from the stays of the airship," was tom's reply, and he recalled the day he was at that work, when the odd man had exhibited the handful of what he said were diamonds. tom wondered if they really were, and he speculated as to what might be the secret of phantom mountain, to which mr. jenks had referred. but now followed a busy time for all. under the direction of the young inventor, they began to string the wires from the top of the dead tree, to a smaller one, some distance away, using five wires, set parallel, and attached to a wooden spreader, or stay. the wires were then run to the dynamo, and the receiving coil, and the necessary ground wires were installed. "but i can't understand how you are going to do it," said mrs. nestor. "i've read about wireless messages, but i can't get it through my head. how is it done, mr. swift?" "the theory is very simple," said the young inventor. "to send a message by wire, over a telegraph system, a battery or dynamo is used. this establishes a current over wires stretched between two points. by means of what is called a 'key' this current is interrupted, or broken, at certain intervals, making the sounding instrument send out clicks. a short click is called a dot, and a long click a dash. by combinations of dots, dashes, and spaces between the dots and dashes, letters are spelled out. for instance, a dot and a space and a dash, represent the letter 'a' and so on." "i understand so far," admitted mrs. nestor. "in telegraphing without wires," went on tom, "the air is used in place of a metallic conductor, with the help of the earth, which in itself is a big magnet, or a battery, as you choose to regard it. the earth helps to establish the connection between places where there are no wires, when we 'ground' certain conductors." "to send a wireless message a current is generated by a dynamo. the current flows along until it gets to the ends of the sending wires, which we have just strung. then it leaps off into space, so to speak, until it reaches the receiving wires, wherever they may be erected. that is why any wireless receiving station, within a certain radius, can catch any messages that may be flying through the air--that is unless certain apparatus is tuned, or adjusted, to prevent this." "well, once the impulses, or electric currents, are sent out into space, all that is necessary to do is to break, or interrupt them at certain intervals, to make dots, dashes and spaces. these make corresponding clicks in the telephone receiver which the operator at the receiving station wears on his ear. he hears the code of clicks, and translates them into letters, the letters into words and the words into sentences. that is how wireless messages are sent." "and do you propose to send some that way?" asked mrs. anderson. "i do," replied tom, with a smile. "where to?" mrs. nestor wanted to know. "that's what i can't tell," was tom's reply. "i will have to project them off into space, and trust to chance that some listening wireless operator will 'pick them up,' as they call it, and send us aid." "but are wireless operators always listening?" asked mr. nestor. "somewhere, some of them are--i hope," was tom's quiet answer. "as i said, we will have to trust much to chance. but other people have been saved by sending messages off into space; and why not we? sinking steamers have had their passengers taken off when the operator called for help, merely by sending a message into space." "but how can we tell them where to come for us--on this unknown island?" inquired mrs. anderson. "i fancy captain mentor can supply our longitude and latitude," answered tom. "i will give that with every message i send out, and help may come--some day." "it can't come any too quick for me!" declared mr. damon. "bless my door knob, but my wife must be worrying about my absence!" "what message for help will you send?" captain mentor wanted to know. "i am going to use the old call for aid," was the reply of the young inventor. "i shall flash into space the three letters 'c.q.d.' they stand for 'come quick--danger.' a new code call has been instituted for them, but i am going to rely on the old one, as, in this part of the world, the new one may not be so well understood. then i will follow that by giving our position in the ocean, as nearly as captain mentor can figure it out. i will repeat this call at intervals until we get help--" "or until the island sinks," added the scientist, grimly. "here! don't mention that any more," ordered mr. hosbrook. "it's getting on my nerves! we may be rescued before that awful calamity overtakes us." "i don't believe so," was mr. parker's reply, and he actually seemed to derive pleasure from his gloomy prophecy. "it's lucky you understand wireless telegraphy, tom swift," said mr. nestor admiringly, and the other joined in praising the young inventor, until, blushing, he hurried off to make some adjustments to his apparatus. "can you compute our longitude and latitude, captain mentor," asked the millionaire yacht owner. "i think so," was the reply. "not very accurately, of course, for all my papers and instruments went down in the resolute. but near enough for the purpose, i fancy. i'll get right to work at it, and let mr. swift have it." "i wish you would. the sooner we begin calling for help the better. i never expected to be in such a predicament as this, but it is wonderful how that young fellow worked out his plan of rescue. i hope he succeeds." it took some little time for the commander to figure their position, and then it was only approximate. but at length he handed tom a piece of paper with the latitude and longitude written on it. in the meanwhile, the young inventor had been connecting up his apparatus. the wires were now all strung, and all that was necessary was to start the motor and dynamo. a curious throng gathered about the little shack as tom announced that he was about to flash into space the first message calling for help. he took his place at the box, to which had been fastened the apparatus for clicking off the morse letters. "well, here we go," he said, with a smile. his fingers clasped the rude key he had fashioned from bits of brass and hard rubber. the motor was buzzing away, and the electric dynamo was purring like some big cat. just as tom opened the circuit, to send the current into the instrument, there came an ominous rumbling of the earth. "another quake!" screamed mrs. anderson. but it was over in a second, and calmness succeeded the incipient panic. suddenly, overhead, there sounded a queer crackling noise, a vicious, snapping, as if from some invisible whips. "mercy! what's that?" cried mrs. nestor. "the wireless," replied tom, quietly. "i am going to send a message for help, off into space. i hope some one receives it--and answers," he added, in a low tone. the crackling increased. while they gathered about him, tom swift pressed the key, making and breaking the current until he had sent out from earthquake island the three letters--"c.q.d." and he followed them by giving their latitude and longitude. over and over again he flashed out this message. would it be answered? would help come? if so, from where? and if so, would it be in time? these were questions that the castaways asked themselves. as for tom, he sat at the key, clicking away, while, overhead, from the wires fastened to the dead tree, flashed out the messages. chapter xxii anxious days after the first few minutes of watching tom click out the messages, the little throng of castaways that had gathered about the shack, moved away. the matter had lost its novelty for them, though, of course, they were vitally interested in the success of tom's undertaking. only mr. damon and mr. fenwick remained with the young inventor, for he needed help, occasionally, in operating the dynamo, or in adjusting the gasolene motor. mrs. nestor, who, with mrs. anderson, was looking after the primitive housekeeping arrangements, occasionally strolled up the hill to the little shed. "any answer yet, mr. swift?" she would ask. "no." was the reply. "we can hardly expect any so soon," and mrs. nestor would depart, with a sigh. knowing that his supply of gasolene was limited, tom realized that he could not run the dynamo steadily, and keep flashing the wireless messages into space. he consulted with his two friends on the subject, and mr. damon said: "well, the best plan, i think, would be only to send out the flashes over the wires at times when other wireless operators will be on the lookout, or, rather, listening. there is no use wasting our fuel. we can't get any more here." "that's true," admitted tom, "but how can we pick out any certain time, when we can be sure that wireless operators, within a zone of a thousand miles, will be listening to catch clicks which call for help from the unknown?" "we can't," decided mr. fenwick. "the only thing to do is to trust to chance. if there was only some way so you would not have to be on duty all the while, and could send out messages automatically, it would be good." tom shook his head. "i have to stay here to adjust the apparatus," he said. "it works none too easily as it is, for i didn't have just what i needed from which to construct this station. anyhow, even if i could rig up something to click out 'c.q.d.' automatically, i could hardly arrange to have the answer come that way. and i want to be here when the answer comes." "have you any plan, then?" asked mr. damon. "bless my shoe laces! there are enough problems to solve on this earthquake island." "i thought of this," said tom. "i'll send out our call for help from nine to ten in the morning. then i'll wait, and send out another call from two to three in the afternoon. around seven in the evening i'll try again, and then about ten o'clock at night, before going to bed." "that ought to be sufficient," agreed mr. fenwick. "certainly we must save our gasolene, for there is no telling how long we may have to stay here, and call for help." "it won't be long if that scientist parker has his way," spoke mr. damon, grimly. "bless my hat band, but he's a most uncomfortable man to have around; always predicting that the island is going to sink! i hope we are rescued before that happens." "i guess we all do," remarked mr. fenwick. "but, tom, here is another matter. have you thought about getting an answer from the unknown--from some ship or wireless station, that may reply to your calls? how can you tell when that will come in?" "i can't." "then won't you or some of us, have to be listening all the while?" "no, for i think an answer will come only directly after i have sent out a call, and it has been picked up by some operator. still there is a possibility that some operator might receive my message, and report to his chief, or some one in authority over him, before replying. in that time i might go away. but to guard against that i will sleep with the telephone receiver clamped to my ear. then i can hear the answer come over the wires, and can jump up and reply." "do you mean you will sleep here?" asked mr. damon, indicating the shack where the wireless apparatus was contained. "yes," answered tom, simply. "can't we take turns listening for the answer?" inquired mr. fenwick, "and so relieve you?" "i'm afraid not, unless you understand the morse code," replied tom. "you see there may be many clicks, which result from wireless messages flying back and forth in space, and my receiver will pick them up. but they will mean nothing. only the answer to our call for help will be of any service to us." "do you mean to say that you can catch messages flying back and forth between stations now?" asked mr. fenwick. "yes," replied the young inventor, with a smile. "here, listen for yourself," and he passed the head-instrument over to the whizzer's former owner. the latter listened a moment. "all i can hear are some faint clicks," he said. "but they are a message," spoke tom. "wait, i'll translate," and he put the receiver to his ear. "'steamship "falcon" reports a slight fire in her forward compartment,'" said tom, slowly. "'it is under control, and we will proceed.'" "do you mean to say that was the message you heard?" cried mr. damon. "bless my soul, i never can understand it!" "it was part of a message," answered tom. "i did not catch it all, nor to whom it was sent." "but why can't you send a message to that steamship then, and beg them to come to our aid?" asked mr. fenwick. "even if they have had a fire, it is out now, and they ought to be glad to save life." "they would come to our aid, or send," spoke tom, "but i can not make their wireless operator pick up our message. either his apparatus is not in tune, or in accord with ours, or he is beyond our zone." "but you heard him," insisted mr. damon. "yes, but sometimes it is easier to pick up messages than it is to send them. however, i will keep on trying." putting into operation the plan he had decided on for saving their supply of gasolene, tom sent out his messages the remainder of the day, at the intervals agreed upon. then the apparatus was shut down, but the lad paid frequent visits to the shack, and listened to the clicks of the telephone receiver. he caught several messages, but they were not in response to his appeals for aid. that night there was a slight earthquake shock, but no more of the island fell into the sea, though the castaways were awakened by the tremors, and were in mortal terror for a while. three days passed, days of anxious waiting, during which time tom sent out message after message by his wireless, and waited in vain for an answer. there were three shocks in this interval, two slight, and one very severe, which last cast into the ocean a great cliff on the far end of the island. there was a flooding rush of water, but no harm resulted. "it is coming nearer," said mr. parker. "what is?" demanded mr. hosbrook. "the destruction of our island. my theory will soon be confirmed," and the scientist actually seemed to take pleasure in it. "oh, you and your theory!" exclaimed the millionaire in disgust. "don't let me hear you mention it again! haven't we troubles enough?" whereat mr. parker went off by himself, to look at the place where the cliff had fallen. each night tom slept with the telephone receiver to his ear, but, though it clicked many times, there was not sounded the call he had adopted for his station--"e. i."--earthquake island. in each appeal he sent out he had requested that if his message was picked up, that the answer be preceded by the letters "e.i." it was on the fourth day after the completion of the wireless station, that tom was sending out his morning calls. mrs. nestor came up the little hill to the shack where tom was clicking away. "no replies yet, i suppose?" she inquired, and there was a hopeless note in her voice. "none yet, but they may come any minute," and tom tried to speak cheerfully. "i certainly hope so," added mary's mother, "but i came up more especially now, mr. swift, to inquire where you had stored the rest of the food." "the rest of the food?" "yes, the supply you took from the wrecked airship. we have used up nearly all that was piled in the improvised kitchen, and we'll have to draw on the reserve supply." "the reserve," murmured tom. "yes, there is only enough in the shack where mrs. anderson and i do the cooking, to last for about two days. isn't there any more?" tom did not answer. he saw the drift of the questioning. their food was nearly gone, yet the castaways from the resolute thought there was still plenty. as a matter of fact there was not another can, except those in the kitchen shack. "get out wherever there is left some time to-day, if you will, mr. swift," went on mrs. nestor, as she turned away, "and mrs. anderson and i will see if we can fix up some new dishes for you men-folks." "oh--all right," answered tom, weakly. his hand dropped from the key of the instrument. he sat staring into space. food enough for but two days more, with earthquakes likely to happen at any moment, and no reply yet to his appeals for aid! truly the situation was desperate. tom shook his head. it was the first time he had felt like giving up. chapter xxiii a reply in the dark the young inventor looked out of the wireless shack. down on the beach he saw the little band of castaways. they were gathered in a group about mr. jenks, who seemed to be talking earnestly to them. the two ladies were over near the small building that served as a kitchen. "more food supplies needed, eh?" mused tom. "well, i don't know where any more is to come from. we've stripped the whizzer bare." he glanced toward what remained of the airship. "i guess we'll have to go on short rations, until help comes," and, wondering what the group of men could be talking about, tom resumed his clicking out of his wireless message. he continued to send it into space for several minutes after ten o'clock, the hour at which he usually stopped for the morning, for he thought there might be a possible chance that the electrical impulses would be picked up by some vessel far out at sea, or by some station operator who could send help. but there came no answering clicks to the "e. i." station--to earthquake island--and, after a little longer working of the key, tom shut down the dynamo, and joined the group on the beach. "i tell you it's our only chance," mr. jenks was saying. "i must get off this island, and that's the only way we can do it. i have large interests at stake. if we wait for a reply to this wireless message we may all be killed, though i appreciate that mr. swift is doing his best to aid us. but it is hopeless!" "what do you think about it, tom?" asked mr. damon, turning to the young inventor. "think about what?" "why mr. jenks has just proposed that we build a big raft, and launch it. he thinks we should leave the island." "it might be a good idea," agreed the lad, as he thought of the scant food supply. "of course, i can't say when a reply will be received to my calls for aid, and it is best to be prepared." "especially as the island may sink any minute," added mr. parker. "if it does, even a raft will be little good, as it may be swamped in the vortex. i think it would be a good plan to make one, then anchor it some distance out from the island. then we can make a small raft, and paddle out to the big one in a hurry if need be." "yes, that's a good idea, too," conceded tom. "and we must stock it well with provisions," said mr. damon. "put plenty of water and food aboard." "we can't," spoke tom, quietly. "why not?" "because we haven't plenty of provisions. that's what i came down to speak about," and the lad related what mrs. nestor had said. "then there is but one thing to do," declared mr. fenwick. "what?" asked captain mentor. "we must go on half rations, or quarter rations, if need be. that will make our supply last longer. and another thing--we must not let the women folks know. just pretend that we're not hungry, but take only a quarter, or at most, not more than a half of what we have been in the habit of taking. there is plenty of water, thank goodness, and we may be able to live until help comes." "then shall we build the raft?" asked mr. hosbrook. it was decided that this would be a good plan, and they started it that same day. trees were felled, with axes and saws that had been aboard the whizzer, and bound together, in rude fashion, with strong trailing vines from the forest. a smaller raft, as a sort of ferry, was also made. this occupied them all that day, and part of the next. in the meanwhile, tom continued to flash out his appeals for help, but no answers came. the men cut down their rations, and when the two ladies joked them on their lack of appetite, they said nothing. tom was glad that mrs. nestor did not renew her request to him to get out the reserve food supply from what remained in the wreck of the airship. perhaps mr. nestor had hinted to her the real situation. the large raft was towed out into a quiet bay of the island, and anchored there by means of a heavy rock, attached to a rope. on board were put cans of water, which were lashed fast, but no food could be spared to stock the rude craft. all the castaways could depend on, was to take with them, in the event of the island beginning to sink, what rations they had left when the final shock should come. this done, they could only wait, and weary was that waiting. tom kept faithfully to his schedule, and his ear ached from the constant pressure of the telephone receiver. he heard message after message flash through space, and click on his instrument, but none of them was in answer to his. on his face there came a grim and hopeless look. one afternoon, a week following the erection of the wireless station, mate fordam came upon a number of turtles. he caught some, by turning them over on their backs, and also located a number of nests of eggs under the warm sands. "this will be something to eat," he said, joyfully, and indeed the turtles formed a welcome food supply. some fish were caught, and some clams were cast up by the tide, all of which eked out the scanty food supply that remained. the two ladies suspected the truth now and they, too, cut down their allowance. tom, who had been sitting with the men in their sleeping shack, that evening, rose, as the hour of ten approached. it was time to send out the last message of the night, and then he would lie down on an improvised couch, with the telephone receiver clamped to his ear, to wait, in the silence of the darkness, for the message saying that help was on the way. "well, are you off?" asked mr. damon, kindly. "i wish some of us could relieve you, tom." "oh, i don't mind it," answered the lad "perhaps the message may come to-night." hardly had he spoken than there sounded the ominous rumble and shaking that presaged another earthquake. the shack rocked, and threatened to come down about their heads. "we must be doomed!" cried mr. parker. "the island is about to sink! make for the raft!" "wait and see how bad it is," counseled mr. hosbrook. "it may be only a slight shock." indeed, as he spoke, the trembling of the island ceased, and there was silence. the two ladies, who had retired to their own private shack, ran out screaming, and mr. anderson and mr. nestor hastened over to be with their wives. "i guess it's passed over," spoke mr. fenwick. an instant later there came another tremor, but it was not like that of an earthquake shock. it was more like the rumble and vibration of an approaching train. "look!" cried tom, pointing to the left. their gaze went in that direction, and, under the light of a full moon they saw, sliding into the sea, a great portion of one of the rocky hills. "a landslide!" cried captain mentor. "the island is slowly breaking up." "it confirms my theory!" said mr. parker, almost in triumph. "forget your theory for a while, parker, please," begged mr. hosbrook. "we're lucky to have left a place on which to stand! oh, when will we be rescued?" he asked hopelessly. the worst seemed to be over at least for the present, and, learning that the two ladies were quieted, tom started up the hill to his wireless station. mr. damon and mr. fenwick went with him, to aid in starting the motor and dynamo. then, after the message had been clicked out as usual tom would begin his weary waiting. they found that the earthquake shock had slightly disturbed the apparatus, and it took them half an hour to adjust it. as there had been a delay on account of the landslide, it was eleven o'clock before tom began sending out any flashes, and he kept it up until midnight. but there came no replies, so he shut off the power, and prepared to get a little rest. "it looks pretty hopeless; doesn't it?" said mr. fenwick, as he and mr. damon were on their way back to the sleeping shack. "yes, it does. our signal hasn't been seen, no ships have passed this way, and our wireless appeal isn't answered. it does look hopeless but, do you know, i haven't given up yet." "why not?" "because i have faith in tom swift's luck!" declared the eccentric man. "if you had been with him as much as i have, up in the air, and under the water, and had seen the tight places he has gotten out of, you'd feel the same, too!" "perhaps, but here there doesn't seem to be anything to do. it all depends on some one else." "that's all right. you leave it to tom. he'll get an answer yet, you see if he doesn't." it was an hour past midnight. tom tossed uneasily on the hard bed in the wireless shack. the telephone receiver on his ear hurt him, and he could not sleep. "i may as well sit up for a while," he told himself, and he arose. in the dimness of the shack he could see the outlines of the dynamo and the motor. "guess i'll start her up, and send out some calls," he murmured. "i might just happen to catch some ship operator who is up late. i'll try it." the young inventor started the motor, and soon the dynamo was purring away. he tested the wireless apparatus. it shot out great long sparks, which snapped viciously through the air. then, in the silence of the night, tom clicked off his call for help for the castaways of earthquake island. for half an hour he sent it away into space, none of the others in their shacks below him, awakening. then tom, having worked off his restless fit, was about to return to bed. but what was this? what was that clicking in the telephone receiver at his ear? he listened. it was not a jumble of dots and dashes, conveying through space a message that meant nothing to him. no! it was his own call that was answered. the call of his station--"e. i."--earthquake island! "where are you? what's wanted?" that was the message that was clicked to tom from somewhere in the great void. "i get your message 'e. i.' what's wanted? do i hear you right? repeat." tom heard those questions in the silence of the night. with trembling fingers tom pressed his own key. out into the darkness went his call for help. "we are on earthquake island." he gave the longitude and latitude. "come quickly or we will be engulfed in the sea! we are castaways from the yacht 'resolute,' and the airship 'whizzer.' can you save us?" came then this query: "what's that about airship?" "never mind airship," clicked tom. "send help quickly! who are you?" the answer flashed to him through space: "steamship 'cambaranian' from rio de janeiro to new york. just caught your message. thought it a fake." "no fake," tom sent back. "help us quickly! how soon can you come?" there was a wait, and the wireless operator clicked to tom that he had called the captain. then came the report: "we will be there within twenty-four hours. keep in communication with us." "you bet i will," flashed back tom, his heart beating joyously, and then he let out a great shout. "we are saved! we are saved! my wireless message is answered! a steamer is on her way to rescue us!" he rushed from the shack, calling to the others. "what's that?" demanded mr. hosbrook. tom briefly told of how the message had come to him in the night. "tell them to hurry," begged the rich yacht owner. "say that i will give twenty thousand dollars reward if we are taken off!" "and i'll do the same," cried mr. jenks. "i must get to the place where--" then he seemed to recollect himself, and stopped suddenly. "tell them to hurry," he begged tom. the whole crowd of castaways, save the women, were gathered about the wireless shack. "they'll need to hurry," spoke mr. parker, the gloomy scientist. "the island may sink before morning!" mr. hosbrook and the others glared at him, but he seemed to take delight in his prediction. suddenly the wireless instruments hummed. "another message," whispered tom. he listened. "the 'cambaranian' will rush here with all speed," he announced, and not a heart there on that lonely and desolate island but sent up a prayer of thankfulness. chapter xxiv "we are lost!" there was little more sleep for any one that night. they sat up, talking over the wonderful and unexpected outcome of tom swift's wireless message, and speculating as to when the steamer would get there. "bless my pocket comb! but i told you it would come out all right, if we left it to tom!" declared mr. damon. "but it hasn't come out yet," remarked the pessimistic scientist. "the steamer may arrive too late." "you're a cheerful sort of fellow to take on a yachting trip," murmured mr. hosbrook, sarcastically. "i'll never invite you again, even if you are a great scientist." "i'm going to sit and watch for the steamer," declared mr. damon, as he went outside the shack. the night was warm, and there was a full moon. "which way will she come from, tom?" "i don't know, but i should think, that if she was on her way north, from south america, she'd pass on the side of the island on which we now are." "that's right," agreed captain mentor. "she'll come up from over there," and he pointed across the ocean directly in front of the shacks and camp. "then i'm going to see if i can't be the first to sight her lights," declared mr. damon. "she can't possibly get here inside of a day, according to what the operator said," declared tom. "wire them to put on all the speed they can," urged the eccentric man. "no, don't waste any more power or energy than is needed," suggested mr. hosbrook. "you may need the gasolene before we are rescued. they are on their way, and that is enough for now." the others agreed with this, and so tom, after a final message to the operator aboard the cambaranian stating that he would call him up in the morning, shut down the motor. mr. damon took up his position where he could see far out over the ocean, but, as the young inventor had said, there was no possible chance of sighting the relief steamer inside of a day. still the nervous, eccentric man declared that he would keep watch. morning came, and castaways brought to breakfast a better appetite than they had had in some time. they were allowed larger rations, too, for it was seen that they would have just enough food to last until taken off. "we didn't need to have made the big raft," said mr. fenwick, as tom came down from his station, to report that he had been in communication with the camabarian and that she was proceeding under forced draught. "we'll not have to embark on it, and i'm glad of it." "oh, we may need it yet," asserted mr. parker. "i have been making some observations just now, and the island is in a very precarious state. it is, i believe, resting on only a slim foundation, and the least shock may break that off, and send it into the sea. that is what my observations point out." "then i wish you wouldn't make any more observations!" exclaimed mrs. nestor, with spirit. "you make me nervous." "and me, also," added mrs. anderson. "science can not deceive, madam," retorted mr. parker. "well it can keep quiet about what it knows, and not make a person have cold chills," replied mary's mother. "i'm sure we will be rescued in time." there was a slight tremor of an earthquake, as they were eating dinner that day, but, aside from causing a little alarm it did no damage. in the afternoon, tom again called up the approaching steamer, and was informed that, because of a slight accident, it could not arrive until the next morning. every effort would be made to keep up speed, it was said. there was much disappointment over this, and mr. damon was observed to be closely examining the food supply, but hope was too strong to be easily shattered now. mr. parker went off alone, to make some further "observations" as he called them, but mr. hosbrook warned him never again to speak of his alarming theories. mr. barcoe jenks called tom aside just before supper that evening. "i haven't forgotten what i said to you about my diamonds," he remarked, with many nods and winks. "i'll show you how to make them, if you will help me. did you ever see diamonds made?" "no, and i guess very few persons have." replied the lad, thinking perhaps mr. jenks might not be quite right, mentally. the night passed without alarm, and in the morning, at the first blush of dawn, every one was astir, looking eagerly across the sea for a sight of the steamer. tom had just come down from the wireless station, having received a message to the effect that a few hours more would bring the cambaranian within sight of the island. suddenly there was a tremendous shock, as if some great cannon had been fired, and the whole island shook to its very centre. "another earthquake! the worst yet!" screamed mrs. anderson. "we are lost!" cried mrs. nestor, clinging to her husband. an instant later they were all thrown down by the tremor of the earth, and tom, looking toward his wireless station, saw nearly half of the island disappear from sight. his station went down in collapse with it, splashing into the ocean, and the wave that followed the terrible crash washed nearly to the castaways, as they rose and kneeled on the sand. "the island is sinking!" cried mr. parker. "make for the raft!" "i guess it's our only chance," murmured captain mentor, as he gazed across the water. there was no steamer in sight. could it arrive on time? the tremors and shaking of the island continued. chapter xxv the rescue--conclusion down to where the small raft was moored ran mr. parker. he was followed by some of the others. "we must put off at once!" he cried. "half the island is gone! the other half may disappear any moment! the steamer can not get here on time, but if we put off they may pick us up, if we are not engulfed in the ocean. help, everybody!" tom gave one more look at where his wireless station had been. it had totally disappeared, there being, at the spot, now but a sheer cliff, which went right down into the sea. the women were in tears. the men, with pale faces, tried to calm them. gradually the earthquake tremor passed away; but who could tell when another would come? captain mentor, mr. hosbrook and the others were shoving out the small raft. they intended to get aboard, and paddle out to the larger one, which had been moored some distance away, in readiness for some such emergency as this. "come on!" cried mr. fenwick to tom who was lingering behind. "come on, ladies. we must all get aboard, or it may be too late!" the small raft was afloat. mrs. anderson and mrs. nestor, weeping hysterically, waded out through the water to get aboard. "have we food?" cried mr. damon. "bless my kitchen range! but i nearly forgot that." "there isn't any food left to take," answered mrs. anderson. "shove off!" cried captain mentor. at that instant a haze which had hung over the water, was blown to one side. the horizon suddenly cleared. tom swift looked up and gave a cry. "the steamer! the steamer! the cambaranian!" he shouted, pointing to it. the others joined in his exclamations of joy, for there, rushing toward earthquake island was a great steamer, crowding on all speed! "saved! saved!" cried mrs. nestor, sinking to her knees even in the water. "it came just in time!" murmured mr. hosbrook. "now i can make my diamonds," whispered mr. jenks to tom. "push off! push off!" cried mr. parker. "the island will sink, soon!" "i think we will be safer on the island than on the raft," declared captain mentor. "we had better land again." they left the little raft, and stood on the shore of the island. eagerly they watched the approach of the steamer. they could make out hands and handkerchiefs waving to them now. there was eager hope in every heart. suddenly, some distance out in the water, and near where the big raft was anchored, there was a curious upheaval of the ocean. it was as if a submarine mine had exploded! the sea swirled and foamed! "it's a good thing we didn't go out there," observed captain mentor. "we would have been swamped, sure as guns." almost as he spoke the big raft was tossed high into the air, and fell back, breaking up. the castaways shuddered. yet were they any safer on the island? they fancied they could feel the little part of it that remained trembling under their feet. "the steamer is stopping!" cried mr. damon. surely enough the cambaranian had slowed up. was she not going to complete the rescue she had begun? "she's going to launch her lifeboats," declared captain mentor. "her commander dare not approach too close, not knowing the water. he might hit on a rock." a moment later and two lifeboats were lowered, and, urged on by the sturdy arms of the sailors, they bounded over the waves. the sea seemed to be more and more agitated. "it is the beginning of the end," murmured mr. parker. "the island will soon disappear." "will you be quiet?" demanded mr. damon, giving the scientist a nudge in the ribs. the lifeboats were close at hand now. "are you all there?" shouted some one, evidently in command. "all here," answered tom. "then hurry aboard. there seems to be something going on in these waters--perhaps a submarine volcano eruption. we must get away in a hurry!" the boats came in to the shelving beach. there was a little stretch of water between them and the sand. through this the castaways waded, and soon they were grasped by the sailors and helped in. in the reaction of their worriment mrs. anderson and mrs. nestor were both weeping, but their tears were those of joy. "give way now, men!" cried the mate in charge of the boats. "we must get back to the ship!" the sea was now swirling angrily, but the sailors, who had been in worse turmoils than this, rowed on steadily. "we feared you would not get here in time," said tom to the mate. "we were under forced draught most of the way," was his answer. "your wireless message came just in time. an hour later and our operator would have gone to bed." the young inventor realized by what a narrow margin they had been rescued. "the island will soon sink," predicted mr. parker, as they reached the steamer, and boarded her. captain valasquez, who was in command, warmly welcomed the castaways. "we will hear your story later," he said. "just now i want to get out of these dangerous waters." he gave the order for full speed, and, as the cambaranian got under way, tom, and the others, standing on the deck, looked back at earthquake island. suddenly there sounded a dull, rumbling report. the whole ocean about the island seemed to upheave. there was a gigantic shower of spray, a sound like an explosion, and when the waters subsided the island had sunk from sight. "i told you it would go," cried mr. parker, triumphantly, but the horror of it all--the horror of the fate that would have been theirs had they remained there an hour longer--held the castaways dumb. the scientist's honor of having correctly predicted the destruction of the island was an empty one. the agitation of the sea rocked even the mighty cambaranian and, had our friends been aboard the frail raft, they would surely have perished in the sea. as it was, they were safe--saved by tom swift's wireless message. the steamer resumed her voyage, and the castaways told their story. captain valasquez refused to receive the large amount of money mr. hasbrook and mr. jenks would have paid him for the rescue, accepting only a sum he figured that he had lost by the delay, which was not a great deal. the castaways were given the best aboard the ship, and their stories were listened to by the other passengers with bated breath. in due time they were landed in new york, and mr. and mrs. nestor accompanied tom to shopton. mr. damon, with many blessings also accompanied them, going to his home in waterfield. later it was learned that the other boats from the resolute had been picked up, and the sailors and guests were all saved. of course, as soon as our friends had been rescued by the steamer, the wireless operator aboard her, with whom tom soon struck up an acquaintance, sent messages to the relatives of the castaways, apprising them of their safety. and the joy of mary nestor, when she found that it was tom who had saved her parents, can well be imagined. as for our hero, well, he was glad too--for mary's sake. "i won't forget my promise to you, tom swift," said mr. barcoe jenks, as he parted from the young inventor, and what the promise was will be told in the next volume of this series, to be called: "tom swift among the diamond makers; or, the secret of phantom mountain." in that tom is destined to have many more surprising adventures, as is also mr. damon, who learned new ways to call down blessings on himself and his possessions. and now, for a time, we will take leave of the young inventor and also of his many friends, who never ceased to wonder over tom swift's skill with the wireless. the end [transcriber's notes all apparent printer's errors and variations in spelling have been retained, there are also some inconsistencies in the hyphenation of words. all these have been detailed at the end of the text. there are a number of mathematical equations in the text, these have been rendered into a text representation that attempts to make them as clear as possible while matching the text as closely as possible. multi-line fractions have been rendered on one line with the addition of extra brackets if required to ensure clarity. superscripts are denoted with ^ followed by the superscripted term in {}. subscripts are denoted by _ with the subscripted term in {}. square roots are denoted by [\sq] followed by the rooted term in {}. some equations have following punctuation, both commas or full stops, in the original text as though the equation is part of the sentence. the middle dot has been used in the original text, both as a multiplication symbol and as a decimal point. these have been kept but the middle dot as a multiplication symbol in formulae is surrounded by single spaces. italicised text in the original text is represented by _text_, bold text is represented by =bold=.] * * * * * hertzian wave wireless telegraphy. by dr. j. a. fleming, f.r.s. [from the popular science monthly, june-december, 1903.] * * * * * [from the "popular science monthly," june, 1903.] hertzian wave wireless telegraphy.[1] by dr. j. a. fleming, f.r.s., professor of electrical engineering, university college, london. the immense public interest which has been aroused of late years in the subject of telegraphy without connecting wires has undoubtedly been stimulated by the achievements of mr. marconi in effecting communication over great distances by means of hertzian waves. the periodicals and daily journals, which are the chief avenues through which information reaches the public, whilst eager to describe in a sensational manner these wonderful applications of electrical principles, have done little to convey an intelligible explanation of them. hence it appeared probable that a service would be rendered by an endeavour to present an account of the present condition of electric wave telegraphy in a manner acceptable to those unversed in the advanced technicalities of the subject, but acquainted at least with the elements of electrical science. it is the purpose of these articles to attempt this task. we shall, however, limit the discussion to an account of the scientific principles underlying the operation of this particular form of wireless telegraphy, omitting, as far as possible, references to mere questions of priority and development. the practical problem of electric wave wireless telegraphy, which has been variously called hertzian wave telegraphy, marconi telegraphy, or spark telegraphy (_funkentelegraphie_), is that of the production of an effect called an electric wave or train of electric waves, which can be sent out from one place, controlled, detected at another place, and interpreted into an alphabetic code. up to the present time, the chief part of that intercommunication has been effected by means of the morse code, in which a group of long and short signs form the letter or symbol. some attempts have been made with more or less success to work printing telegraphs and even writing or drawing telegraphs by hertzian waves, but have not passed beyond the experimental stage, whilst wireless telephony by this means is still a dream of the future. we shall, in the first place, consider the transmitting arrangements and, incidentally, the nature of the effect or wave transmitted; in the second place, the receiving appliances; and, finally, discuss the problem of the isolation or secrecy of the intelligence conveyed between any two places. the transmitter used in hertzian wave telegraphy consists essentially of a device for producing electric waves of a type which will travel over the surface of the land or sea without speedy dissipation, and the important element in this arrangement is the _radiator_, by which these waves are sent out. it will be an advantage to begin by explaining the electrical action of the radiator, and then proceed to discuss the details of the transmitting appliances. it will probably assist the reader to arrive most easily at a general idea of the functions of the various portions of the transmitting arrangements, and in particular of the radiator, if we take as our starting point an analogy which exists between electric wave generation for telegraphic purposes and air wave generation for sound signal purposes. most persons have visited some of the large lighthouses which exist around our coasts and have there seen a steam or air _siren_, as used for the production of sound signals during fogs. if they have examined this appliance, they will know that it consists, in the first place, of a long metal tube, generally with a trumpet-shaped mouthpiece. at the bottom of this tube there is a fixed plate with holes in it, against which revolves another similarly perforated plate. these two plates separate a back chamber or wind chest from the tube, and the wind chest communicates with a reservoir of compressed air or a high-pressure steam boiler. in the communication pipe there is a valve which can be suddenly opened for a longer or shorter time. when the movable plate revolves, the coincidence or non-coincidence of the holes in the two plates opens or shuts the air passage way very rapidly. hence when the blast of air or steam is turned on, the flow is cut up by the revolving plates into a series of puffs which inflict blows upon the stationary air in the siren tube. if these blows come at the rate, say, of a hundred a second, they give rise to aerial oscillations in the tube, which impress the ear as a deep, musical note or roar; and this continuous sound can be cut up by closing the valve intermittently into long and short periods, and so caused to signal a letter according to the morse code, denoting the name of the lighthouse. in this case the object is to produce: first, aerial vibrations in the tube, giving rise to a train of powerful air waves; secondly, to intermit this wave-train so as to produce an intelligible signal; and thirdly, to transmit this wave as far as possible through space. the production of a sound or air wave can only be achieved by administering a very sudden blow to the general mass of the air in the tube. this impulse must be sufficient to call into operation the inertia and elastic qualities of the air. it is found, moreover, that the amplitude of the resulting wave, or the loudness of the sound, is increased by suitably proportioning the length of the siren pipe and the frequency of the air puffs; whilst the distance at which it is heard depends also in some degree upon the form of the mouthpiece. inside the siren tube, when it is in operation, the air molecules are in rapid vibratory motion in the direction of the length of the tube. if we could at any one instant examine the distribution and changes of air pressure in the tube, we should find that at some places there are large, and at others small, variations in air pressure. these latter places are called the _nodes_ of pressure. at the pressure nodes, however, we should find large variations in the velocity of the air particles, and these points are called the _antinodes_ of velocity. in those places at which the pressure variation is greatest, the velocity changes are least, and _vice versa_. outside the tube, as a result of these air motions in it, we have a hemispherical air wave produced, which travels out from the mouthpiece as a centre; and if we could examine the distribution of air pressure and velocity through all external space, we should find a distribution which is periodic in space as well as time, constituting the familiar phenomenon of an air wave. turning then to consider the production of an electric, instead of an air wave, we notice in the first place that the medium with which we are concerned is the _ether_ filling all space. this ether permits the production of physical changes in it which are analogous to, but not identical in nature with, the pressures and movements which constitute a sound wave. the hertzian radiator is an appliance for acting on the ether as the siren acts on the air. it produces a wave in it, and it can be shown that all the parts of the above described siren apparatus have their electrical equivalents in the transmitter employed in hertzian wave wireless telegraphy. to understand the nature of an electric wave we must consider, in the first place, some properties of the ether. in this medium we can at any place produce a state called _electric displacement_ or _ether strain_ as we can produce compression or rarefaction in air; and, just as the latter changes are said to be created by mechanical force, so the former is said to be due to _electric force_. we can not define more clearly the nature of this ether strain or displacement until we know much more about the structure of the ether than we do at present. we can picture to ourselves the operation of compressing air as an approximation of the air molecules, but the difficulty of comprehending the nature of an electric wave arises from the fact that we cannot yet definitely resolve the notion of electric strain into any simpler or more familiar ideas. we have to be content, therefore, to disguise our present ignorance by the use of some descriptive term, such as _electric strain_, _electrostatic strain_ or _ether strain_, to describe the directed condition of the space around a body in a state of electrification which is produced by electric force. this electric strain is certainly not of the nature of a compression in the ether, but much more akin to a twist or rotational strain in a solid body. for our present purpose it is not so necessary to postulate any particular theory of the ether as it is to possess some consistent hypothesis, in terms of which we can describe the phenomena which will concern us. these effects are, as we shall see, partly states of electrification on the surface or distributions of electric current in wires or rods, and partly conditions in the space outside them, which we are led to recognise as distributions of electric strain and of an associated effect called _magnetic flux_. we find such a theory at hand at the present time in the electronic theory of electricity, which has now been sufficiently developed and popularised to make it useful as a descriptive hypothesis.[2] this theory has the great recommendation that it offers a means of abolishing the perplexing dualism of ether and ponderable matter, and gives a definite and, in a sense, objective meaning to the word electricity. in this physical speculation, the chief subject of contemplation is the electron, or ultimate particle of negative electricity, which, when associated in greater or less number with a matrix of some description, forms the atom of ponderable matter. to avoid further hypothesis, this matrix may be called the _co-electron_; and we shall adopt the view that a single chemical atom is a union of a _co-electron_ with a surrounding envelope or group of electrons, one or more of the latter being detachable. we need not stop to speculate on the structure of the atomic core or co-electron, whether it is composed of positive and negative electrons or of something entirely different. the single electron is the indivisible unit or atomic element of so-called negative electricity, and the neutral chemical atom deprived of one electron is the unit of positive electricity. on this hypothesis, the chemical atom is to be regarded as a microcosm, a sort of a solar system in miniature, the component electrons being capable of vibration relatively to the atomic centre of mass. furthermore, from this point of view it is the electron which is the effective cause of radiation. it alone has a grip on the ether whereby it is able to establish wave motion in the latter. dr. larmor has developed in considerable detail an hypothesis of the nature of an electron which makes it the centre or convergence-point of lines of a self-locked ether strain of a torsional type. the notion of an atom merely as a "centre of force" was one familiar to faraday and much supported by boscovich and others. the fatal objection to the validity of this notion as originally stated was that it offers no possibility of explaining the inertia of matter. on the electronic hypothesis, the source of all inertia is the inertia of the ether, and until we are able to dissect this last quality into anything simpler than the time-element involved in the production of an ether strain or displacement, we must accept it as an ultimate fact, not more elucidated because we speak of it as the inductance of the electron. we postulate, therefore, the following ideas: we have to think of the ether as a homogeneous medium in which a strain of some kind, most probably of a rotational type, is possible. this strain appears only under the influence of an appropriate stress called the electric force, and disappears when the force is removed. hence to create this strain necessitates the expenditure of energy. an electron is a centre or convergence-point of lines of permanent ether strain of such nature that it cannot release itself. to obtain some idea of the nature of such a structure, let us imagine a flat steel band formed into a ring by welding the ends together. there is then no torsional strain. if, however, we suppose the band cut in one place, one end then given half a turn and the cut ends again welded, we shall have on the band a self-locked twist, which can be displaced on the band, but which can not release itself or be released except by cutting the ring. hence we see that to make an electron in an ether possessing torsional elasticity would require creative energy, and when made, the electron cannot destroy itself except by occupying simultaneously the same place as an electron of opposite type. every electron extends, therefore, as faraday said of the atom, throughout the universe, and the properties that we find in the electron are only there because they are first in the universal medium, the ether. every line of ether or electric strain must, therefore, be a self-closed line, or else it must terminate on an electron and a co-electron. so far we have only considered the electron at rest. if, however, it moves, it can be mathematically demonstrated that it must give rise to a second form of ether strain which is related to the electric strain as a twist is related to a thrust or a vortex ring to a squirt in liquid or a rotation to a linear progression. the ether strain which results from the lateral movement of lines of electric strain is called the _magnetic flux_, and it can be mathematically shown that the movement of an electron, consisting when a rest of a radial convergence of lines of electric strain, must be accompanied by the production of self-closed lines of magnetic flux, distributed in concentric circles or rings round it, the planes of these circles being perpendicular to the direction of motion of the electron. this electronic hypothesis, therefore, affords a basis on which we can build up a theory affording an explanation of the nature of the intimate connection known to exist between ether, matter and electricity. the electron is the connecting link between them all, for it is in itself a centre of convergent ether strain; isolated, it presents itself as electricity of the negative or resinous kind; and, in combination with co-electrons and other electrons, it forms the atoms of ponderable matter. at rest the electron or the co-electron constitutes an electric charge, and when in motion it is an electric current. a steady flux or drift of electrons in one direction and co-electrons in the opposite direction is a continuous electric current, whilst their mere oscillation about a mean position is an alternating current. furthermore, the vibration of an electron, if sufficiently rapid, enables it to establish what are called electric waves in the ether, but which are really detached and self-closed lines of ether strain distributed in a periodic manner through space. we have, therefore, to start with, three conceptions concerning the electron, viz.: its condition when at rest; its state when in uniform motion; and its operations when in vibration or rapid oscillation. in the first case, by our fundamental supposition, it consists of lines of ether strain of a type called the electric strain, radiating uniformly in all directions. when in uniform motion, it can be shown that these lines of electric strain tend to group themselves in a plane perpendicular to the line of motion drawn through the electron, and their lateral motion generates another class of strain called the magnetic strain, disposed in concentric circles described round the electron and lying in this equatorial plane. the proof of the above propositions cannot be given verbally, but requires the aid of mathematical analysis of an advanced kind. the reader must be referred for the complete demonstration to the writings of professor j. j. thomson[3] and mr. oliver heaviside.[4] in the third case, when the electron vibrates, we have a state in which self-closed lines of electric strain and magnetic flux are thrown off and move away through the ether constituting electric radiation, the manner in which this happens was first described by hertz in a paper on "electric oscillations treated according to the method of maxwell."[5] as this phenomenon lies at the very root of hertzian wave wireless telegraphy, we must spend a moment or two in its careful examination. let us imagine two metal rods placed in line and constituting what is called a linear oscillator. let these rods have adjacent ends separated by a very small air space, and let one rod be charged with positive and the other with negative electricity. on the electronic theory this is explained by stating that there is an accumulation of electrons in one and of co-electrons in the other. these charges create a distribution of electric strain throughout their neighbourhood, which follows approximately the same law of distribution as the lines of magnetic force of a bar magnet, and may be roughly represented as in fig. 1. suppose then that the air gap is destroyed, these charges move towards each other and disappear by uniting, the lines of electric strain then collapse, and as they shrink in give rise to circular lines of magnetic flux embracing the rods. this external distribution of magnetism constitutes an electric current in the rods produced by the movement of the two opposite electric charges. at this stage it may be explained that the electrons or atoms of electricity can in some cases make their way freely between the atoms of ponderable matter. the former are incomparably smaller than the latter, and in those cases in which this electronic movement can take place easily, we call the material a good conductor. [illustration: fig. 1.--lines of electric strain between a positive and negative electron at rest.] suppose then the electric charges reappear in reversed positions and go through an oscillatory motion. the result in the external space would be the alternate production of lines of electric strain and magnetic flux, the direction of these lines being reversed each half cycle. inside the rods we have a movement of electrons and co-electrons to and fro, electric charges at the ends of the rods alternating with electric currents in the rods, the charges being at a maximum when the current is zero, and the current at a maximum when the charges have for the moment disappeared. outside the rods we have a corresponding set of charges, lines of electric strain stretching from end to end of the rod, alternating with rings of magnetic flux embracing the rod. so far we have supposed the oscillation to be relatively a slow one. [illustration: fig. 2.--successive stages in the deformation of a line of strain between positive and negative electrons in rapid oscillation, showing closed loop of electric strain thrown off.] imagine next that the to and fro movement of the electrons or charges is sufficiently rapid to bring into play the inertia quality of the medium. we then have a different state of affairs. the lines of strain in the external medium cannot contract or collapse quickly enough to keep up with the course of events, or movements of the electrons in the rods, and hence their regular contraction and absorption is changed into a process of a different kind. as the electrons and co-electrons, _i.e._, the electric charges, vibrate to and fro, the lines of electric strain connecting them are nipped in and thrown off as completely independent and closed lines of electric strain, and at each successive alternation, groups or batches of these loops of strain are detached from the rod, and, so to speak, take on an independent existence. the whole process of the formation of these self-closed lines of electric strain is best understood by examining a series of diagrams which roughly represent the various stages of the process. in fig. 2 we have a diagram (_a_) the curved line in which delineates approximately the form of one line of electric strain round a linear oscillator, with spark gap in the centre, one half being charged positively and the other negatively. let us then suppose that the insulation of the spark gap is destroyed, so that the opposite electric charges rush together and oscillate to and fro. the strain lines at each oscillation are then crossed or decussate, and the result, as shown in fig. 2, _d_, is that a portion of the energy of the field is thrown off in the form of self-closed lines of strain (see fig. 2, _e_). at each oscillation of the charges the direction of the lines of strain springing from end to end of the radiator is reversed. it is a general property of lines of strain whether electric or magnetic, that there is a tension along the line and a pressure at right angles. in other words, these lines of electric strain are like elastic threads, they tend to contract in the direction of their length and press sideways on each other when in the same direction. hence it is not difficult to see that as each batch of self-closed lines of strain is thrown off, the direction of the strain round each loop is alternately in one direction and in the other. hence these loops of electric strain press each other out, and each one that is formed squeezes the already formed loops further and further from the radiator. the loops, therefore, march away into space (see fig. 2, _f_). if we imagine ourselves standing at a little distance at a point on the equatorial line and able to see these loops of strain as they pass, we should recognise a procession of loops, consisting of alternately directed strain lines marching past. this movement through the ether of self-closed lines of electric strain constitutes what is called electric radiation. hence along a line drawn perpendicular to the radiator through its centre, there is a distribution of electric strain normal to that line, which is periodic in space and in time. moreover, in addition to these lines of electric strain, there are at right angles to them another set of self-closed lines of magnetic flux. alternated between the instants when the electric charges at the ends of the radiator are at their maximum, we have instants when the radiator rod is the seat of an electric current, and hence the field round it is filled with circular lines of magnetic flux coaxial with the radiator. as the current alternates in direction each half period, these rings of magnetic flux alternate in direction as regards the flux, and hence we must complete our mental picture of the space round the radiator rods when the charges are oscillating by supposing it filled with concentric rings of magnetic flux which are periodically reversed in direction, and have their maximum values at those instants and places where the lines of electric strain have their zero values. accordingly, along the equatorial line we have two sets of strains in the ether, distributed periodically in space and in time. first, the lines of electric strain in the plane of the radiator, and, secondly, the lines of magnetic flux at right angles to these. at any one point in space these two changes, the strain and the flux, succeed each other periodically, being, however, at right angles in direction. at any one moment these two effects are distributed periodically or cyclically through space, and these changes in time and space constitute an _electric wave_ or electromagnetic wave. we may then summarise the above statements by saying that the most recent hypothesis as to the nature of electrical action and of electricity itself is briefly comprised in the following statements: the universally diffused medium called the ether has had created in it certain centres of strain or radiating points from which proceed lines of strain, and these centres of force are called electrons. electrons must, therefore, be of two kinds, positive and negative, according to the direction of the strain radiating from the centre. these electrons in their free condition constitute what we call electricity, and the electrons themselves are the atoms of electricity which, in one sense, is, therefore, as much material as that which we call ordinary gross or ponderable matter. collocations of these electrons constitute the atoms of gross matter, and we must consider that the individuality of any atom is not determined merely by the identity of the electrons composing it, but by the permanence of their arrangement or form. in any mass of material substance there is probably a continual exchange of electrons from one atom to another, and hence at any one given moment, whilst a number of the electrons are an association forming material atoms, there will be a further number of isolated but intermingled electrons, which are called the free electrons. in substances which we call good conductors, we must imagine that the free electrons have the power of moving freely through or between the material atoms, and this movement of the electrons constitutes a current of electricity; whilst a superfluity of electrons of either type in any one mass of matter constitutes what we call a charge of electricity. hence an electrical oscillation, which is merely a very rapid alternating current taking place in a conductor, is on this hypothesis assumed to consist in a rapid movement to and fro of the free electrons. we may picture to ourselves, therefore, a rod of metal in which electrical oscillations are taking place, as similar to an organ-pipe or siren tube in which movements of the air particles are taking place to and fro, the free electrons corresponding with the air particles. owing to the nature of the structure of an electron, it follows, however, that every movement of an electron is accompanied by changes in the distribution of the electric strain or ether strain taking place throughout all surrounding space, and, as already explained, certain very rapid movements of the electrons have the effect of detaching closed lines of strain in the ether which move off through space, forming, when cyclically distributed, an electric wave. [illustration: fig. 3.--simple marconi radiator. b, battery; i, induction coil; k, signalling key; s, spark gap; a, aerial wire; e, earth plate.] we may next proceed to apply these principles to the explanation of the action of the simplest form of hertzian wave telegraphic radiator, viz., the marconi aerial wire. in its original form this consists of a long vertical insulated wire, a, the lower end of which is attached to one of the spark balls s of an induction coil, i, the other spark ball being connected to earth e, and the two spark balls being placed a few millimetres apart (see fig. 3). when the coil is set in action oscillatory or hertzian sparks pass between the balls, electric oscillations are set up in the wire and electric waves are radiated from it. deferring for the moment a more detailed examination of the operations of the coil and at the spark gap, we may here say that the action which takes place in the aerial wire is as follows: the wire is first charged to a high potential, let us suppose, with negative electricity. we may imagine this process to consist in forcing additional electrons into it, the induction coil acting as an electron pump. up to a certain pressure the spark gap is a perfect insulator, but at a critical pressure, which for spark gap lengths of four or five millimetres and balls about one centimetre in diameter approximates to three thousand volts per millmetre, the insulation of the air gives way, and the charge in the wire rushes into the earth. in consequence, however, of the inertia of the medium or of the electrons, the charge, so to speak, overshoots the mark, and the wire is then left with a charge of opposite sign. this again in turn rebounds, and so the wire is discharged by a series of electrical oscillations, consisting of alternations of static charge and electric discharge. we may fasten our attention either on the events taking place in the vertical wire or in the medium outside, but the two sets of phenomena are inseparably connected and go on together. when the aerial wire is statically charged, we may describe it by saying that there is an accumulation of electrons or co-electrons in it. outside the wire there is, however, a distribution of electric strain the strain lines proceeding from the wire to the earth (see fig. 4). [illustration: fig. 4.--lines of electric strain (dotted lines) extending between a marconi aerial, a, and the earth _ee_ before discharge.] the wire has _capacity_ with respect to the earth, and it acts like the inner coating of a leyden jar, of which the dielectric is the air and ether around it, and the outer coating is the earth's surface. when the discharge takes place, we may consider that electrons rush out of the wire and then rush back again into it. at the moment when the electrons rush out of or into the aerial wire, we say there is an electric current flowing into or out of the wire, and this electron movement, therefore, creates the magnetic flux which is distributed in concentric circles round the wire. this current, and, therefore, motion of electrons, can be proved to exist by its heating effect upon a fine wire inserted in series with the aerial, and in the case of large aerials it may have a mean value of many amperes and a maximum value of hundreds of amperes. inside the aerial wire we have, therefore, alternations of electric potential or charge and electric current, or we may call it electron-pressure and electron-movement. there is, therefore, an oscillation of electrons in the aerial wire, just as in the case of an organ-pipe there is an oscillation of air molecules in the pipe. outside the aerial we have variations and distributions of electric strain and magnetic flux. the resemblance between the closed organ-pipe and the simple marconi aerial is, in fact, very complete. in the case of the closed organ-pipe, we have a longitudinal oscillation of air molecules in the pipe. at the open end or mouthpiece, where we have air moving in and out, the air movement is alternating and considerable, but there is little or no variation of air pressure. at the upper or closed end of the pipe we have great variation of air pressure, but little or no air movement (see fig. 5). compare this now with the electrical phenomena of the aerial. at the spark ball or lower end we have little or no variation of potential or electron pressure, but we have electrons rushing into and out of the aerial at each half oscillation, forming the electric discharge or current. at the upper or insulated end we have little or no current, but great variations of potential or electron pressure. supposing we could examine the wire inch by inch, all the way up from the spark balls at the bottom to the top, we should find at each stage of our journey that the range of variation and maximum value of the current in the wire became less and those of the potential became greater. at the bottom we have nearly zero potential or no electric pressure, but large current, and at the top end, no current, but great variation of potential. [illustration: fig. 5.--amplitude of pressure variation in a closed organ pipe, indicated by the ordinates of the dotted line _xy_.] we can represent the amplitude of the current and potential values along the aerial by the ordinates of a dotted line so drawn that its distance from the aerial represents the potential oscillation or current oscillation at that point (see fig. 6). this distribution of potential and current along the wire does not necessarily imply that any one electron moves far from its normal position. the actual movement of any particular air molecule in the case of a sound wave is probably very small, and reckoned in millionths of an inch. so also we must suppose that any one electron may have a small individual amplitude of movement, but the displacement is transferred from one to another. conduction in a solid may be effected by the movement of free electrons intermingled with the chemical atoms, but any one electron may be continually passing from a condition of freedom to one of combination. [illustration: fig. 6.--(_a_) distribution of electric pressure in a marconi aerial, a, (_b_) distribution of electric current in a marconi aerial, as shown by the ordinates of the dotted line _xy_.] so much for the events inside the wire, but now outside the wire its electric charge is represented by lines of electric strain springing from the aerial to the earth. it must be remembered that every line of strain terminates on an electron or a co-electron. hence, when the discharge or spark takes place between the spark balls, the rapid movement of the electrons in the wire is accompanied by a redistribution and movement of the lines of strain outside. as the negative charge flows out of the aerial the ends of the strain lines abutting on to it run down the wire and are transferred to the earth, and at the next instant this semi-loop of electric or ether strain, with its ends on the earth, is pushed out sideways from the wire by the growth of a new set of lines of ether strain in an opposite direction. the process is best understood by consulting a series of diagrams which represent the distribution and approximate form of a few of the strain lines at successive instants (see fig. 7). in between the lines of formation of the successive strain lines between the aerial and the earth, corresponding to the successive alternate electric charges of the aerial with opposite sign, there are a set of concentric rings of magnetic flux formed round it which are alternately in opposite directions, and these expand out, keeping step with the progress of the detached strain loops and having their planes at right angles to the latter. as the semi-loops of electric strain march outwards with their feet on the ground, these strain lines must always be supposed to terminate on electrons, but not continually on the same electrons. since the earth is a conductor, we must suppose that there is a continual migration of the electrons forming the atoms of the earth, and that when one electron enters an atom, another leaves it. hence, corresponding to the electric wave in the space above, there are electrical changes in the ground beneath. this view is confirmed by the well-known fact that the achievement of hertzian wave telegraphy is much dependent on the nature of the surface over which it is conducted, and can be carried on more easily over good conducting material, like sea water, than over badly conducting dry land. [illustration: fig. 7.--successive stages in the production of a semi-loop of electric strain by a marconi aerial radiator.] the matter may be viewed, however, from another standpoint. good conductors are opaque to hertzian waves; in other words, are non-absorptive. the energy of the electric wave is not so rapidly absorbed when it glides over a sea surface as when it is passing over a surface which is an indifferent conductor, like dry land. in fact, it is possible by the improvement of the signals to detect a heavy fall of rain in the space between two stations separated only by dry land. it is, however, clear that on the electronic theory the progression of the lines of electric strain can only take place if the surface over which they move is a fairly good conductor, unless these lines of strain form completely closed loops. hence we may sum up by saying that there are three set of phenomena to which we must pay attention in formulating any complete theory of the aerial. the first is the operation taking place in the vertical wire, which is described by saying that electrical oscillations or vibratory movements of electrons are taking place in it, and, on our adopted theory, it may be said to consist in a longitudinal vibration of electrons of such a nature that we may appropriately call the aerial an ether organ-pipe. then in the next place, we have the distribution and movement of the lines of electric strain and magnetic flux in the space outside the wire, constituting the electric wave; and lastly, there are the electrical changes in the conductor over which the wave travels, which is the earth or water surrounding the aerial. in subsequently dealing with the details of transmitting arrangements, attention will be directed to the necessity for what telegraphists call a "good earth" in connection with hertzian wave telegraphy. this only means that there must be a perfectly free egress and ingress for the electrons leaving or entering the aerial, so that nothing hinders their access to the conducting surface over which the wave travels. there must be nothing to stop or throttle the rush of electrons into or out of the aerial wire, or else the lines of strain cannot be detached and and travel away. we may next consider more particularly the energy which is available for radiation and which is radiated. in the original form of simple marconi aerial, the aerial itself when insulated forms one coating or surface of a condenser, the dielectric being the air and ether around it, and the other conductor being the earth. the electric energy stored up in it just before discharge takes place is numerically equal to the product of the capacity of the aerial and half the square of the potential to which it is charged. if we call c the capacity of the aerial in microfarads, and v the potential in volts to which it is raised before discharge, then the energy storage in joules e is given by the equation, e = (cv^{2}) / (2 â· 10^{6}). since one joule is nearly equal to three-quarters of a foot-pound, the energy storage in foot-pounds f is roughly given by the rule f = (3/8)cv^{2}/10^{6}. for spark lengths of the order of five to fifteen millimetres, the disruptive voltage in air of ordinary pressure is at the rate of 3,000 volts per millimetre. hence, if s stands for the spark length in millimetres, and c for the aerial capacity in microfarads, it is easy to see that the energy storage in foot-pound is f = (27cs^{2}) / 8. if the aerial consists of a stranded wire formed of 7/22 and has a length of 150 feet, and is insulated and held vertically with its lower end near the earth, it would have a capacity of about one three ten-thousandths of a microfarad or 0â·0003 mfd.[6] hence, if it is used as a marconi aerial and operated with a spark gap of one centimetre in length, the energy stored up in the wire before each discharge would be only one-tenth (0â·1) of a foot-pound. by no means can all of this energy be radiated as hertzian waves; part of it is dissipated as heat and light in the spark, and yet such an aerial can, with a sensitive receiver such as that devised by mr. marconi, make itself felt for a hundred miles over sea in every direction. this fact gives us an idea of the extremely small energy which, when properly imparted to the ether, can effect wireless telegraphy over immense distances. of course, the minimum telegraphic signal, say the morse dot, may involve a good many, perhaps half-a-dozen, discharges of the wire, but even then the amount of energy concerned in affecting the receiver at the distant place is exceedingly small. the problem, therefore, of long-distance telegraphy by hertzian waves is largely, though not entirely, a matter of associating sufficient energy with the aerial wire or radiator. there are obviously two things which may be done; first, we may increase the capacity of the aerial, and secondly, we may increase the charging voltage or, in other words, lengthen the spark gap. there is, however, a well-defined limit to this last achievement. if we lengthen the spark gap too much, its resistance becomes too great and the spark ceases to be oscillatory. we can make a discharge, but we obtain no radiation. when using an induction coil, about a centimetre, or at most a centimetre and a half, is the limiting length of oscillatory sparks; in other words, our available potential difference is restricted to 30,000 or 40,000 volts. by other appliances we can, however, obtain oscillatory sparks having a voltage of 100,000 or 200,000 volts, and so obtain what hertz called "active sparks" five or six centimetres in length. turning then to the question of capacity, we may enquire in the next place how the capacity of an aerial wire can be increased. this has generally been done by putting up two or more aerial wires in contiguity and joining them together, and so making arrangements called in the admitted slang of the subject "multiple aerials." the measurement of the capacity of insulated wires can be easily carried out by means of an appliance devised by the author and mr. w. c. clinton, consisting of a rotating commutator which alternately charges the insulated wire at a source of known electromotive force and then discharges it through a galvanometer. if this galvanometer is subsequently standardised, so that the ampere value of its deflection is known, we can determine easily the capacity c of the aerial or insulated conductor, reckoned in microfarads, when it is charged to a potential of v volts, and discharged _n_ times a second through a galvanometer. the series of discharges are equivalent to a current, of which the value in amperes a is given by the equation a = (nvc) / (10^{6}), and hence, if the value of the current resulting is known, we have the capacity of the aerial or conductor expressed in microfarads, given by the formula c = (a10^{6}) / (nv). a series of experiments made on this plan have revealed the fact that if a number of vertical insulated wires are hung up in the air and rather near together, the electrical capacity of the whole of the wires in parallel is not nearly equal to the sum of their individual capacities. if a number of parallel insulated wires are separated by a distance equal to about 3 per cent. of their length, the capacity of the whole lot together varies roughly as the square root of their number. thus, if we call the capacity of one vertical wire in free space unity, then the capacity of four wires placed rather near together will only be about twice that of one wire, and that of twenty-five wires will only be about five times one wire. this approximate rule has been confirmed by experiments made with long wires one hundred or two hundred feet in length in the open air. hence it points to the fact that the ordinary plan of endeavouring to obtain a large capacity by putting several wires in parallel and not very far apart is very uneconomical in material. the diagrams in fig. 8 show the various methods which have been employed by mr. marconi and others in the construction of such multiple wire aerials. if, for instance, we put four insulated stranded 7/22 wires each 100 feet long, about six feet apart, all being held in a vertical position, the capacity of the four together is not much more than twice that of a single wire. in the same manner, if we arrange 150 similar wires, each 100 feet long, in the form of a conical aerial, the wires being distributed at the top round a circle 100 feet in diameter, the whole group will not have much more than twelve times the capacity of one single wire, although it weighs 150 times as much. [illustration: fig. 8.--various forms of aerial radiator. _a_, single wire; _b_, multiple wire; _c_, fan shape; _d_, cylindrical; _g_, conical.] the author has designed an aerial in which the wires, all of equal length, are arranged sufficiently far apart not to reduce each other's capacity. as a rough guide in practice, it may be borne in mind that a wire about one tenth of an inch in diameter and one hundred feet long, held vertical and insulated, with its bottom end about six feet from the ground, has a capacity of 0â·0002 of a microfarad, if no other earthed vertical conductors are very near it. the moral of all this is that the amount of electric energy which can be stored up in a simple marconi aerial is very limited, and is not much more than one-tenth of a joule or one-fourteenth of a foot-pound, per hundred feet of 7/22 wire. the astonishing thing is that with so little storage of energy it should be possible to transmit intelligence to a distance of a hundred miles without connecting wires. one consequence, however, of the small amount of energy which can be accumulated in a simple marconi aerial is that this energy is almost entirely radiated in one oscillation or wave. hence, strictly speaking, a simple aerial of this type does not create a train of waves in the ether, but probably at most a single impulse or two. [illustration: fig. 9.--marconi-braun system of inducing electromotive force in an aerial, a. b, battery; k, key; i, induction coil; s, spark gap; c, leyden jar; e, earth plate; _ps_, oscillation transformer.] we shall later on consider some consequences which follow from this fact. meanwhile, it may be explained that there are methods by which not only a much larger amount of energy can be accumulated in connection with an aerial, but more sustained oscillations created than by the original marconi method. one of these methods originated with professor braun, of strasburg, and a modification was first described by mr. marconi in a lecture before the society of arts of london.[7] in this method the charge in the aerial is not created by the direct application to it of the secondary electromotive force of an induction coil, but by means of an induced electromotive force created in the aerial by an oscillation transformer. the method due to professor braun is as follows: a condenser or leyden jar has one terminal, say, its inside, connected to one spark ball of an induction coil. the other spark ball is connected to the outside of the leyden jar or condenser through the primary coil of a transformer of a particular kind, called an oscillation transformer (see fig. 9). the spark balls are brought within a few millimetres of each other. when the coil is set in operation, the jar is charged and discharged through the spark gap, and electrical oscillations are set up in the circuit consisting of the dielectric of the jar, the primary coil of the oscillation transformer and the spark gap. the secondary circuit of this oscillation transformer is connected in between the earth and the insulated aerial wire; hence, when the oscillations take place in the primary circuit, they induce other oscillations in the aerial circuit. but the arrangement is not very effective unless, as is shown by mr. marconi, the two circuits of the oscillation transformer are tuned together. we shall return presently to the consideration of this form of transmitter; meanwhile we may notice that by means of such an arrangement it is possible to create in the aerial a far greater charging electromotive force than would be the case if the aerial were connected directly to one terminal of the secondary circuit of the induction coil, the other terminal being to earth, and the two terminals connected as usual by spark balls. by the inductive arrangement it is possible to create in an aerial electromotive forces which are equivalent to a spark of a foot in length, and when the length of the aerial is also properly proportioned the potential along it will increase all the way up, until at the top or insulated end of the aerial it may reach an amount capable of giving sparks several feet in length. from the remarks already made on the analogy between the closed organ-pipe and the marconi aerial wire, it will be seen that the wave which is radiated from the aerial must have a wave length four times that of the aerial if the aerial is vibrating in its fundamental manner. it is also possible to create electrical oscillations in a vertical wire which are the harmonics of the fundamental. all musicians are aware that in the case of an organ-pipe if the pipe is blown gently it sounds a note which is called the fundamental of the pipe. the celebrated mathematician, daniel bernouilli, discovered that an organ-pipe can be made to yield a succession of musical notes by properly varying the pressure of the current of air blown into it. if the pipe is an open pipe, and if we call the frequency of the primary note obtained when the pipe is gently blown, unity, then when we blow more strongly the pipe yields notes which are the harmonics of the fundamental one; that is to say, notes which have frequencies represented by the numbers 2, 3, 4, 5, &c. if, however, the pipe is closed at the top, then over-blowing the pipe makes it yield the odd harmonics or the tones which are related to the primary tone in the ratio of 3, 5, 7, &c., to unity. accordingly, if a stopped pipe gives as its fundamental the note c, its first overtone will be the fifth above the octave or g'. [illustration: fig. 10.--seibt's apparatus for showing stationary waves in long solenoid a. i, induction coil; s, spark gap; l, inductance coil; c_{1}c_{2}, leyden jars; e, earth wire.] as already remarked, the aerial wire or radiator as used in marconi telegraphy may be looked upon as a kind of ether organ-pipe or siren tube, and its electrical phenomena are in every respect similar to the acoustic phenomena of the ordinary closed organ-pipe. when the aerial is sounding its fundamental ether note, the conditions which pertain are that there is a current flowing into the aerial at the lower end, but at that point the variation in potential is very small, whereas at the upper end there is no current, but the variations of potential are very large. accordingly, we say that at the upper end of the aerial there is an antinode of potential and a node of current, and at the bottom an antinode of current and a node of potential. by altering the frequency of the electrical impulses we can create in the aerial an arrangement of nodes of current or potential corresponding to the overtones of a closed organ-pipe. but whatever may be the arrangement the conditions must always hold that there is a node of current at the upper end and an antidote of current at the lower end. in other words, there are large variations of current at the place where the aerial terminates on the spark-gap and no current at the upper end. the first harmonic is formed where there is a node of potential at one-third of the length of the aerial from the top. in this case we have a node of potential not only at the lower end of the wire, but at two-thirds of the way up. in the same way we can create in the closed organ-pipe, by properly overblowing the pipe, a region about two-thirds of the way up the pipe, where the pressure changes in the air are practically no greater than they are at the mouthpiece. we can make evident visually in a beautiful manner the existence of similar stationary electrical waves in an aerial by means of an ingenious arrangement devised by dr. georg seibt, of berlin. it consists of a very long silk-covered copper wire, a (see fig. 10), wound in a close spiral of single layer round a wooden rod six feet long and about two inches in diameter. this rod is insulated, and at the lower end the wire is connected to a leyden jar circuit, consisting of a leyden jar or jars and an inductance coil, l, the inductance of which can be varied. oscillations are set up in this jar circuit by means of an induction-coil discharge, and the lower end of the long spiral wire is attached to one point on the jar circuit. in this manner we can communicate to the bottom end of the long spiral wire a series of electric impulses, the time period of which depends upon the capacity of the jar and the inductance of the discharge circuit. we can, moreover, vary this frequency over wide limits. parallel to the long spiral wire is suspended another copper wire, e (see fig. 10), and between this wire and the silk-covered copper wire discharges take place due to the potential difference between each part of the wire and this long aerial wire. if we arrange matters so that the impulses communicated to the bottom end of the long spiral wire correspond to its fundamental note or periodic time, then in a darkened room we shall see a luminous glow or discharge between the vertical wire and the spiral wire, which increases in intensity all the way up to the top of the spiral wire. the luminosity of this brush discharge at any point is evidence of the potential of the spiral wire at that point, and its distribution clearly demonstrates that the difference of potential between the spiral wire and the aerial increases all the way up from the bottom to the top of the spiral wire. in the next place, by making a little adjustment and by varying the inductance of the jar circuit, we can increase the frequency of the impulses which are falling upon the spiral wire; and then it will be noticed that the distribution of the brush discharge or luminosity is altered, and that there is a maximum now at about one-third of the height of the spiral wire, and a dark place at about two-thirds of the height, and another bright place at the top, thus showing that we have a node of potential at about two-thirds the way up the wire (see fig. 11), and we have therefore set up in the spiral wire electrical oscillations corresponding to the first overtone. it is possible to show in the same way the existence of the second harmonic in the coil, but the luminosity then becomes too faint to be seen at a distance. [illustration: fig. 11.--harmonic oscillations in long solenoid shown with seibt's apparatus.] an interesting form of aerial devised by professor slaby, of berlin, depends for its action entirely on the fact that the electrical oscillations set up in it which radiate are harmonics of the fundamental tone. [illustration: fig. 12.--non-radiative closed loop aerial.] [illustration: fig. 13.--slaby's loop radiator.] a closed vertical loop, a_{1}a_{2} (see fig. 12), is formed by erecting two parallel insulated wires vertically a few feet apart and joining them together at the top. at the bottom these wires are connected, with the secondary terminals of an induction coil, a condenser, c, or leyden jar, being bridged across the terminals and a pair of spark balls, s, inserted in one side of the loop. it will readily be seen that on setting the coil in action, oscillations will take place in these vertical wires, but that if the oscillations are simply the fundamental note of the system, then at any moment corresponding to a current going up one side of the loop of wire there must be a current coming down the other. accordingly, an arrangement of this kind, forming what is called a closed circuit, will not radiate or radiates but very feebly. professor slaby found, however, that it might be converted into a powerful radiator if we give the two sides of the loop unequal capacity or inductance and at the same time earth one of the lower ends of the loop, as shown in fig. 13. by this means it is possible to set up in the loop electrical overtones or harmonics of the fundamental oscillation, and if we cause the system to vibrate so as to produce its first odd harmonic, there is a potential node at the lower end of both vertical sides of the loop, a potential node on both vertical sides at two-thirds of the way up, and a potential antinode at the summit of the loop; then, under these circumstances, the closed loop of wire is in the same electrical condition as if two simple marconi aerials, both emitting their first odd harmonic oscillation, were placed side by side and joined together at the top. it is a little difficult without the employment of mathematical analysis to explain precisely the manner in which earthing one side of the loop or making the loop unsymmetrical as regards inductance has the effect of creating overtones in it. the following rough illustration may, however, be of some assistance. imagine a long spiral metallic spring supported horizontally by threads. let this represent a conductor, and let any movement to or fro of a part of the spring represent a current in that conductor. suppose we take hold of the spring at one end, we can move it bodily to and fro as a whole. in this case, every part of the spring is moving one way or the other in the same manner at the same time. this corresponds with the case in which the discharge of the condenser through the uniform loop conductor is a flow of electricity, all in one direction one way or the other. the current is in the same direction in all parts of the loop at the same time, and, therefore, if the current is going up one side of the loop it is at the same time coming down the other side. hence the two sides of the loop are always in exact opposition as regards the effect of the current in them on the external space, and the loop does not radiate. returning again to the case of the spring. supposing that we add a weight to one end of the spring by attaching to it a metal ball, and then move the other end to and fro with certain periodic motion, it will be found quite easy to set up in the spring a pulsatory motion resembling the movement of the air in an open organ-pipe. under these circumstances both ends of the spring will be moving inwards or outwards at the same time, and the central portions of the spring, although being pressed and expanded slightly, are moving to and fro very little. this corresponds in the case of the looped aerial with a current flowing up or down both sides at the same time; in other words, when this mode of electrical oscillation is established in the loop, its electrical condition is just that of two simple marconi aerials joined together at the top and vibrating in their fundamental manner. accordingly, if one side of the double loop is earthed, we then have an arrangement which radiates waves. professor slaby found that by giving one side of the loop less inductance than the other, and at the same time earthing the side having greater inductance at the bottom, he was able to make an arrangement which radiated, not in virtue of the normal oscillations of the condenser, but in virtue of the harmonic oscillations set up in the conductor itself. the mathematical theory of this radiator has been very fully developed by dr. georg seibt. it will be seen, therefore, that there are several ways in which we may start into existence oscillations in an aerial. first, the aerial may be insulated, and we may charge it to a high potential and allow this charge suddenly to rush out. although this process gives rise to a disturbance in the ether, as already explained, it is analogous to a pop or explosion in the air, rather than to a sustained musical note. the exact acoustic analogue would be obtained if we imagine a long pipe pumped full of air and then suddenly opened at one end. the air would rush out, and, communicating a blow to the outer air, would create an atmospheric disturbance appreciated as a noise or small explosion. this is what happens when we cut the string and let the cork fly out from a bottle of champagne. at the same time, the inertia of the air rushing out of the tube would cause it to overshoot the mark, and a short time after opening the valve the tube, so far from containing compressed air, would contain air slightly rarefied near its mouth, and this rarefication would travel back up the tube in the form of wave motion, and, being reflected as condensation at the closed end, travel down again; and so after being reflected once or twice at the open or closed end, become damped out very rapidly in virtue of both air friction and the radiation of the energy. in the case, however, of the ordinary organ-pipe, we do not depend merely upon a store of compressed air put into the pipe, but we have a store of energy to draw upon in the form of the large amount of compressed air contained in a wind chest, which is being continually supplied by the bellows. this store of compressed air is fed into the organ-pipe, with the result that we obtain a continuous radiation of sound waves. the first case, in which the only store of energy is the compressed air originally contained in the pipe, illustrates the operation of the simple marconi aerial. the second case, in which there is a larger store of energy to draw upon, the organ-pipe being connected to a wind chest, illustrates the marconi-braun method, in which an aerial is employed to radiate a store of electric energy contained in a condenser, gradually liberated by the aerial in the form of a series of electrical oscillations and waves. in this arrangement the condenser corresponds to the wind chest, and it is continually kept full of electrical energy by means of the induction coil or transformer, which answers to the bellows of the organ. from the condenser, electrical energy is discharged each time the spark discharge passes at a spark gap in the form of electrical oscillations set up in the primary circuit of an oscillation transformer. the secondary circuit of this transformer is connected in between the earth and the aerial, and therefore may be considered as part of it, and, accordingly, the energy which is radiated from the aerial is not simply that which is stored up in it in virtue of its own small capacity, but that which is stored up in the much larger capacity represented by the primary condenser or, as it may be called, the electrical wind chest. by the second arrangement we have therefore the means of radiating more or less continuous trains of electric waves, corresponding with each spark discharge. to create powerful oscillations in the aerial, one condition of success is that there shall be an identity in time-period between the circuit of the aerial and that of the primary condenser. the aerial is an open circuit which has capacity with respect to the earth, and it has also inductance, partly due to the wire of the aerial and partly due to the secondary circuit of the oscillation transformer in series with it. the primary circuit or spark circuit has capacity--viz., the capacity of the energy-storing condenser--and it has also inductance--viz., the inductance of the primary circuit of the oscillation transformer. we shall consider at a later stage more particularly the details of syntonising arrangements, but meanwhile it may be said that one condition for setting up powerful waves by means of the above arrangement is that the electrical time-period of both the two circuits mentioned shall be the same. this involves adjusting the inductance and capacity so that the product of conductance and capacity for each of these two circuits is numerically the same. instead of employing an oscillation transformer between the condenser circuit and the aerial, the aerial may be connected directly to some point on the condenser circuit at which the potential oscillations are large, and we have then another arrangement devised by professor braun (see fig. 14). in this case, in order to accumulate large potential oscillations at the top of the aerial, it is, as we have seen, necessary that the length of the aerial shall be one quarter the length of the wave. if, therefore, the electrical oscillations in the condenser circuit are at the rate of n per second, in other words, have a frequency n, the wave-length correponding to this frequency is given by the expression, 3ã�10^{10}/n cms. the number 3ã�10^{10} is the value in centimetres per second of the velocity of the electromagnetic wave, and is identical with that of light. the corresponding resonant length of the aerial is therefore one-fourth of this wave-length, or 3ã�10^{10}/4n. generally speaking, however, it will be found that with any length of aerial which is practicable, say, 200 feet or 6,000 cms., this proportion necessitates rather a high frequency in the primary oscillation circuit. in the case considered--viz., for an aerial 200 feet in height--the oscillations in the primary circuit must have a frequency of one and a quarter million. this high frequency can only be obtained either by greatly reducing the inductance of the primary discharge circuit, or reducing the capacity. if we reduce the capacity, we thereby greatly reduce the storage of energy, and it is not practicable to reduce the inductance below a certain amount. [illustration: fig. 14.--braun's radiator. b, battery; i, induction coil; k, key; s, spark-gap; l, inductance coil; c, condenser; a, aerial.] summing up, it may be said that there are three, and, as far as the writer is aware, at present only three, modes of exciting the electrical oscillations in an aerial wire. first, the aerial may itself be used as an electrical reservoir and charged to a high potential and suddenly discharged to the earth. this is the original marconi method. the second method, due to braun, consist of attaching the aerial to some point on an oscillation circuit consisting of a condenser, an inductance coil and a spark gap, in series with one another, and charging and discharging the condenser across the spark gap so as to create alterations of potential at some point on the oscillation circuit. the length of the aerial must then be so proportioned as above described that it is resonant to this frequency. thirdly, we may employ the arrangement involving an oscillation transformer, in which the oscillations in the primary condenser circuit are made to induce others in the aerial circuit, the time-period of the two circuits being the same. this method may be called the braun-marconi method. professor slaby has combined together in a certain way the original marconi simple aerial with the resonant quarter-wave-length wire of braun. he constructs what he calls a _multiplicator_, which is really a wire wound into a loose spiral connected at one point to an oscillation circuit consisting of a condenser inductance, the length of this wire being proportioned so that there is a great resonance or multiplication of tension or potential at its free end. this free end is then attached to the lower end of an ordinary marconi aerial, and serves to charge it with a higher potential than could be obtained by the use of the induction coil directly attached to it. * * * * * we have next to consider the appliances for creating the necessary charging electromotive force, and for storing and releasing this charge at pleasure, so as to generate the required electrical oscillations in the aerial. it is essential that this generator should be able to create not only large potential difference, but also a certain minimum electric current. accordingly, we are limited at the present moment to one of two appliances--viz., the induction coil or the alternating current transformer. it will not be necessary to enter into an explanation of the action of the induction coil. the coil generally employed for wireless telegraphy is technically known as a ten-inch coil--_i.e._, a coil which is capable of giving a ten-inch spark between pointed conductors in air at ordinary pressure. the construction of a large coil of this description is a matter requiring great technical skill, and is not to be attempted without considerable previous experience in the manufacture of smaller coils. the secondary circuit of a ten-inch coil is formed of double silk-covered copper wire; generally speaking, the gauge called no. 36, or else no. 34 s.w.g. is used, and a length of ten to seventeen miles of wire is employed on the secondary circuit, according to the gauge of wire selected. for the precautions necessary in constructing the secondary coil, practical manuals must be consulted.[8] very great care is required in the insulation of the secondary circuit of an induction coil to be used in hertzian wave telegraphy, because the secondary circuit is then subjected to impulsive electromotive forces lasting for a short time, having a much higher electromotive force than that which the coil itself normally produces. the primary circuit of a ten-inch coil generally consists of a length of 300 or 400 feet of thick insulated copper wire. in such a coil the secondary circuit would require about ten miles of no. 34 h.c. copper wire, making 50,000 turns round the core. it would have a resistance at ordinary temperatures of 6,600 ohms, and an inductance of 460 henrys. the primary circuit, if formed of 360 turns of no. 12 h.c. copper wire, would have a resistance of 0â·36 of an ohm, and an inductance of 0â·02 of a henry. an important matter in connection with an induction coil to be used for wireless telegraphy is the resistance of the secondary circuit. the purpose for which we employ the coil is to charge a condenser of some kind. if a constant electromotive force (v) is applied to the terminals of a condenser having a capacity c, then the difference of potential (_v_) of the terminals of the condenser at any time that the contact is made is given by the expression: v = v(1 e^{-t/rc}). in the above equation, the letter e stands for the number 2â·71828, the base of the napierian logarithms, and r is the resistance in series with the condenser, of which the capacity is c, to which the electromotive force is applied. this equation can easily be deduced from first principles,[9] and it shows that the potential difference _v_ of the terminals of the condenser does not instantly attain a value equal to the impressed electromotive force v, but rises up gradually. thus, for instance, suppose that a condenser of one microfarad is being charged through a resistance of one megohm by an impressed voltage of 100 volts, the equation shows that at the end of the first second after contact, the terminal potential difference of the condenser will be only 63 volts, at the end of the second second, 86 volts, and so on. since _e_^{-10} is an exceedingly small number, it follows that in 10 seconds the condenser would be practically charged with a voltage equal to 100 volts. the product cr in the above equation is called the _time-constant_ of the condenser, and we may say that the condenser is practically charged after an interval of time equal to ten times the time-constant, counting from the moment of first contact between the condenser and the source of constant voltage. the time-constant is to be reckoned as the product of the capacity (c) in microfarads, by the resistance of the charging circuit (r) in megohms. to take another illustration. supposing we are charging a condenser having a capacity of one-hundreth of a microfarad, through a resistance of ten thousand ohms. since ten thousand ohms is equal to one-hundredth of a megohm, the time-constant would be equal to one-ten-thousandth of a second, and ten times this time-constant would be equal to a thousandth of a second. hence, in order to charge the above capacity through the above resistance, it is necessary that the contact between the source of voltage and the condenser should be maintained for at least one-thousandth part of a second. in discussing the methods of interrupting the circuit, we shall return to this matter, but, meanwhile, it may be said that in order to secure a small time-constant for the charging circuit, it is desirable that the secondary circuit of the induction coil should have as low a resistance as possible. this, of course, involves winding the secondary circuit with a rather thick wire. if, however, we employ a wire larger in size than no. 34, or at the most no. 32, the bulk and the cost of the induction coil began to rise very rapidly. hence, as in all other departments of electrical construction, the details of the design are more or less a matter of compromise. generally speaking, however, it may be said that the larger the capacity which is to be charged, the lower should be the resistance of the secondary circuit of the induction coil. in the practical construction of induction coils for wireless telegraphy, manufacturers have departed from the stock designs. we are all familiar with the appearance of the instrument maker's induction coil; its polished mahogany base, its lacquered brass fittings, and its secondary bobbin constructed of and covered with ebonite. but such a coil, although it may look very pretty on the lecture table, is yet very unsuited to positions in which it may be used in connection with hertzian wave telegraphy. three important adjuncts of the induction coil are the primary condenser, the interrupter and the primary key. the interrupter is the arrangement for intermitting the primary current. we have in some way or other to rapidly interrupt the primary current, and the torrent of sparks that then appears between the secondary terminals of the coil is due to the electromotive force set up in the secondary circuit at each break or interruption of the primary circuit. we may divide interrupters into five classes. we have first the well-known hammer interrupter which continental writers generally attribute to neef or wagner.[10] in this interrupter, the magnetisation of the iron core of the coil is caused to attract a soft-iron block fixed at the top of a brass spring, and by so doing to interrupt the primary circuit between two platinum contacts. mr. apps, of london, added an arrangement for pressing back the spring against the back contact, and the form of hammer that is now generally employed is therefore called an apps break. as the ten-inch coil takes a primary current of ten amperes at sixteen volts when in operation, it requires very substantial platinum contacts to withstand the interruption of this current continuously without damage. the small platinum contacts that are generally put on these coils by instrument makers are very soon worn out in practical wireless telegraph work. if a hammer break is used at all, it is essential to make the contacts of very stout pieces of platinum, and from time to time, as they get burnt away or roughened, they must be smoothed up with a fine file. it does not require much skill to keep the hammer contacts in good order and prevent them from sticking together and becoming damaged by the break spark. by regulating the pressure of the spring against the back contact, by means of an adjusting screw, the rate at which the break vibrates can be regulated, but as a rule it is not possible, with a hammer break, to obtain more than about 800 interruptions per minute, or, say, twelve a second. the hammer break is usually operated by the magnetism of the iron core of the coil, but for some reasons it is better to separate the break from the coil altogether, and to work it by an independent electromagnet, which, however, may be excited by a current from the same battery supplying the induction coil. for coils up to the ten-inch size the hammer break can be used when very rapid interruptions are not required. it is not in general practicable to work coils larger than the ten-inch size with a platinum contact hammer break, as such a butt contact becomes overheated and sticks if more than ten amperes is passed through it. in the case of larger coils, we have to employ some form of interrupter in which mercury or a conducting liquid forms one of the contact surfaces. the next class of interrupter is the vibrating or hand-worked mercury break, in which a platinum or steel pin is made to vibrate in and out of mercury. this movement may be effected by the attraction of an iron armature by an electromagnet, or by the varying magnetism of the core of the coil, or it may be effected more slowly by hand. the mercury surface must be covered with water, alcohol, paraffin or creosote oil to prevent oxidation and to extinguish the break spark. the interruption of the primary current obtained by the mercury break is more sudden than that obtained by the platinum contact in air, in consequence of the more rapid extinction of the spark; hence the sparks obtained from coils fitted with mercury interrupters are generally from twenty to thirty per cent. longer than those obtained from the same coil under the same conditions, with platinum contact interrupters. the mercury breaks will not, however, work well unless cleaned at regular intervals by emptying off the oil and rinsing well with clean water, and hence they require rather more attention than platinum interrupters. it is not generally possible to obtain so many interruptions per minute with the simple vibrating mercury interrupter as with the ordinary hammer interrupter. the mercury interrupter has, however, the advantage that the contact time during which the circuit is kept closed may be made longer than is the case with the hammer break. also, if fresh water is allowed to flow continuously over the mercury surface, it can be kept clean, and the break will then operate for considerable periods of time without attention. the mercury interrupter may be worked by a separate electromagnet or by the magnetism of the core of the induction coil. the third class of interrupter may be called the motor interrupter, of which a large number have been invented in recent years. in this interrupter some form of a continuously-rotating electromotor is employed to make and break a mercury or other liquid contact. in one simple form the motor shaft carries an eccentric, which simply dips a platinum point into mercury, or else a platinum horseshoe into two mercury surfaces, making in this manner an interruption of the primary circuit at one or two places. as a small motor can easily be run at twelve hundred revolutions per minute, or twenty per second, it is possible to secure easily in this manner a uniform rate of interruption of the primary current at the rate of about twenty per second. if, however, much higher speeds are employed, then the time of contact becomes abbreviated, and the ability of the coil to charge a capacity is diminished. professor j. trowbridge has described an effective form of motor break for large coils, in which the interruption is caused by withdrawing a stout platinum wire from a dilute solution of sulphuric acid, and by this means he increased the spark given by a coil provided with hammer break and condenser from fifteen inches to thirty inches when using the liquid break and no condenser.[11] a good form of motor-interrupter, due to dr. mackenzie davidson, consists of a slate disc bearing pin contacts fixed on the prolonged steel axle of a motor placed in an inclined position; the disc and the lower part of the axle lie in a vessel filled one-third with mercury and two-thirds with paraffin oil. the circuit is made and broken by the revolution of the disc causing the pins to enter and leave the mercury. the speed of the motor can be regulated by a small resistance, and can be adapted to the electromotive force used in the primary circuit. when the motor is running slowly the interrupter can be used with a low electromotive force, that is to say, something between twelve and twenty volts, but with a higher speed a large electromotive force can be used without danger of overheating the primary coil, and with an electromotive force of about fifty volts, the interruptions may be so rapid that an unbroken arc of flame, resembling an alternating-current arc, springs between the secondary terminals of the coil. mr. tesla has devised numerous forms of rotating mercury break. in one, a star-shaped metal disc revolves in a box so that its points dip into mercury covered with oil, and make and break contact. in another form, a jet of mercury plays against a similar shaped rotating wheel. for details, the reader must consult the fuller descriptions in _the electrical world_ of new york, vol. xxxii., p. 111, 1898; also vol. xxxiii., p. 247; or _science abstracts_, vol. ii., pp. 46 and 47, 1898. the fourth class of interrupter is called a turbine interrupter. in this appliance, a jet of mercury is forced out of a small aperture by means of a centrifugal pump, and is made to squirt against a metal plate, and interrupted intermittently by a toothed wheel made of insulating material rotated by the motor which drives the pump. the current supplying the coil passes through or along this jet of mercury, and is therefore rendered intermittent when the wheel revolves. in the case of this interrupter, the duration of the contacts, as well as the number of interruptions per second, is under control, and for this reason better results are probably obtained with it than with any other form of break. a description of a turbine mercury break devised by m. max levy was given in the _elektrotechnische zeitschrift_, vol. xx., p. 717, october 12, 1899 (see also _science abstracts_, vol. iii., p. 63, abstract no. 165) as follows:-a toothed wheel made of insulating material carries from 6 to 24 teeth, and can be made to rotate from 300 to 1,000 times per minute, the interruptions being thus regulated between 5 and 400 per second. by raising or lowering the position of the jet of mercury and that of the plate against which it strikes, the duration of the contact can be varied, so that it is possible to regulate this period without disturbing the number of interruptions per second. the sparks obtained from a coil worked with a turbine interrupter have more quantity than the sparks obtained with any other interrupter under similar conditions, and the coil can be worked with a far higher voltage than is possible when using the hammer break. in this manner, the appearance of the secondary sparks can be varied from the thin snappy sparks given by the hammer break to the thick flame-like arc sparks given by the electrolytic break. this break can be adapted for any voltage from twelve to two hundred and fifty volts, and the primary circuit cannot be closed before the interrupter is acting. the mercury in the break is generally covered with alcohol or paraffin oil to reduce oxidation, and the appliance is nearly noiseless when in operation. the mercury has to be cleaned at intervals, if the interrupter is much used. if alcohol is used to cover the mercury, the cleaning is very simple; the break requires only to be rinsed under a water tap. when paraffin oil is used, the cleaning is generally effected with the help of a few ounces of sulphuric acid in a very few minutes. it is best, however, to clean the mercury continuously by allowing the water to flow over it. the motor driving the centrifugal pump and the fan can be wound for any voltage, and it is best to have it so arranged that this motor works on the same battery which supplies the primary circuit of the coil, the two circuits working parallel together. a rheostat can be added to the motor circuit to regulate the speed. the turbine break driven by an independent motor, which is kept always running, has another advantage over the hammer break in practical wireless telegraphy, viz., that a useful secondary spark can be secured with a shorter time of closure of the primary circuit, since there is no inertia to overcome as in the case of the hammer break. this latter form has only continued in use because of its simplicity and ease of management by ordinary operators. the mercury turbine interrupter has been extensively adopted both in the german and british navies in connection with induction coils used for wireless telegraphy. lastly we have the electrolytic interrupters, the first of which was introduced by dr. wehnelt, of charlottenburg, in the year 1899, and modified by subsequent inventors. in its original form, a glass vessel filled with dilute sulphuric acid (one of acid to five or else ten parts of water) contains two electrodes of very different sizes; one is a large lead electrode formed of a piece of sheet lead laid round the interior of the vessel, and the other is a short piece of platinum wire projecting from the end of a glass or porcelain tube. the smaller of these electrodes is made the positive, and the large one the negative. if this electrolytic cell is connected in series with the primary circuit of the induction coil (the condenser being cut out) and supplied with an electromotive force from forty to eighty volts, an electrolytic action takes place which interrupts the current periodically.[12] an enormous number of interruptions can, by suitable adjustment, be produced per second, and the appearance of a discharge from the secondary terminals of the coil, while using the wehnelt break, more resembles an alternate-current arc than the usual disruptive spark. at the time when the wehnelt break was first introduced, great interest was excited in it, and the technical journals in 1899 were full of discussions as to the theory of its operation.[13] the general facts concerning the wehnelt break are that the electrolyte must be dilute sulphuric acid in the proportion of one of acid to five or ten of water. the large lead plate must be the cathode or negative pole, and the anode or positive pole must be a platinum wire, about a millimetre in diameter, and projecting one or two millimetres from the pointed end of a porcelain, glass or other acid-proof insulating tube. the aperture through which the platinum wire works must be so tight that acid cannot enter, yet it is desirable that the platinum wire should be capable of being projected more or less from the aperture by means of an adjusting screw. the glass vessel which contains these two electrodes should be of considerable size, holding, say, a quart of fluid, and it is better to include this vessel in a larger one in which water can be placed to cool the electrolyte, as the latter gets very warm when the break is used continuously. if such an electrolytic cell has a continuous electromotive force applied to it tending to force a current through the electrolyte from the platinum wire to the lead plate, we can distinguish three stages in its operation, which are determined by the electromotive force and the inductance in the circuit. first, if the electromotive force is below sixteen or twenty volts, then ordinary and silent electrolysis of the liquid proceeds, bubbles of oxygen being liberated from the platinum wire and hydrogen set free against the lead plate. if the electromotive force is raised above twenty-five volts, then if there is no inductance in the circuit, the continuous flow of current proceeds, but if the circuit of the electrolyte possesses a certain minimum inductance, the character of the current flow changes, and it becomes intermittent, and the cell acts as an interrupter, the current being interrupted from 100 to 2,000 times per second, according to the electromotive force and the inductance of the circuit. under these conditions, the cell produces a rattling noise and a luminous glow appears round the tip of the platinum wire. thus, in a particular case, with an inductance of 0â·004 millihenry in the circuit of a wehnelt break, no interruption of the circuit took place, but with one millihenry of inductance in the circuit, and with an electromotive force of 48 volts, the current became intermittent at the rate of 930 per second, and by increasing the voltage to 120 volts, the intermittency rose to 1,850 a second. the wehnelt break acts best as an interrupter with an electromotive force from 40 to 80 volts. at higher voltages a third stage sets in: the luminous glow round the platinum wire disappears, and it becomes surrounded with a layer of vapour, as observed by mm. violle and chassagny; the interruptions of current cease, and the platinum wire becomes red hot. if there is no inductance in the circuit, the interrupter stage never sets in at all, but the first stage passes directly into the third stage. in the first stage bubbles of oxygen rise steadily from the platinum wire, and in the interrupted stage they rise at longer intervals, but regularly. the cell will not, however, act as a break at all unless some inductance exists in the circuit. in applying the wehnelt break to an induction coil, the condenser is discarded and also the ordinary hammer break, and the wehnelt break is placed in circuit with the primary coil. in some cases, the inductance of the primary coil alone is sufficient to start the break in operation, but with voltages above 50 or 60, it is generally necessary to supplement the inductance of the primary coil by another inductive coil. the best form of wehnelt break for operating induction coils is the one with multiple anodes (see dr. marchant, _the electrician_, vol. xlii., p. 841, 1899), and when it has to be used for long periods, the cathode may advantageously be formed of a spiral of lead pipe, through which cold water is made to circulate. another form of electrolytic break was introduced by mr. caldwell. in this, a vessel containing dilute sulphuric acid is divided into two parts. in the partition is a small hole, and in the two compartments are electrodes of sheet lead. the small hole causes an intermittency in the current which converts the arrangement into a break. mr. campbell swinton modified the above arrangement by making the partition to consist of a sort of porcelain test-tube with a hole in the bottom. this hole can be more or less plugged up by a glass rod drawn out to a point, and this is used to more or less close the hole. this porcelain vessel contains dilute acid and stands in a larger vessel of acid, and lead electrodes are placed in both compartments. the current and intermittency can be regulated by more or less closing the aperture between the two regions. when the wehnelt break is applied to an ordinary ten-inch induction coil, and the inductance of the primary circuit and the electromotive force varied until the break interrupts the current regularly and with the frequency of some hundred a second, the character of the secondary discharge is entirely different from its appearance with the ordinary hammer break. the thin blue lightning-like sparks are then replaced by a thicker mobile flaming discharge, which resembles an alternating-current arc, and, when carefully examined or photographed, is found to consist of a number of separate discharges superimposed upon one another in slightly different positions. many theories have been adopted as to the action of the break, but time will not permit us to examine these. professor s. p. thompson and dr. marchant have suggested a theory of resonance.[14] one difficulty in explaining the action of the break is created by the fact that it will not work if the platinum wire is made a cathode. although the wehnelt break has some advantages in connection with the use of the induction coil for rã¶ntgen ray work, its utility as far as regards hertzian wave telegraphy is not by any means so marked. it has already been explained that, in order to charge a condenser of a given capacity at a constant voltage, the electromotive force must be applied for a certain minimum time, which is determined by the value of the capacity and the resistance of the secondary circuit of the induction coil. if the coil is a ten-inch coil and has a secondary resistance of, say, 6,000 ohms, and if the capacity to be charged has a value, say, of one-thirtieth of a microfarad, then the time-constant of the circuit is 1/5,000 of a second. therefore, the contact with the condenser must be maintained for at least 1/500 of a second, during the time that the secondary electromotive force of the coil is at its maximum, so that the condenser may become charged to a voltage which the coil is then capable of producing. in the induction coil, the electromotive force generated in the secondary coil at the "break" of the primary current is higher than that at the "make," and this electromotive force, other things being equal, depends upon the rate at which the magnetism of the iron core dies away, and its duration is shorter in proportion as the whole time occupied in the disappearance of the magnetism is less. the wehnelt break does not increase the actual secondary electromotive force, nor apparently its duration, but it greatly increases the number of times per second this electromotive force makes it appearance. hence this break increases the current, but not the electromotive force in the secondary coil. it, therefore, does not assist us in the direction required--viz., in prolonging the duration of the secondary electromotive force to enable larger capacities to be charged. the important point in connection with the working of a coil used for charging a condenser is not the length of spark which the coil can give alone, but the length of spark which can be obtained between small balls attached to the secondary terminals, when these terminals are also connected to the two surfaces of the condenser. thus, a coil may give a ten-inch spark if worked alone, but on a capacity of one-thirtieth of a microfarad it may not be able to give more than a five-millimetre spark. hence, in describing the value of a coil for wireless telegraph purposes, it is not the least use to state the length of spark which the coil will give between the pointed conductors in air, but we must know the spark length which it will give between brass balls, say, 1 centimetre in diameter, connected to the secondary terminals, when these terminals are also short-circuited by a stated capacity, the spark not exceeding that length at which it becomes non-oscillatory. a good way of describing the value of an induction coil for wireless telegraph purposes is to state the length of oscillatory spark which can be produced between balls one centimetre in diameter connected to the secondary terminals, when these balls are short-circuited by a condenser having a capacity, say, of one-hundredth of a microfarad, and also one-tenth of a microfarad. if a hammer or motor interrupter is employed with the coil, then a primary condenser must be connected across the points between which the primary circuit is broken. this condenser generally consists of sheets of tinfoil alternated with sheets of paraffin paper, and for a ten-inch coil may have a capacity of about 0â·4 or 0â·5 of a microfarad.[15] lord rayleigh discovered that if the interruption of the primary circuit is sufficiently sudden and complete, as when the primary circuit is severed by a bullet from a gun, the primary condenser can be removed and yet the sparks obtained from the secondary circuit are actually longer than those obtained with the condenser and the ordinary break.[16] in the use, however, of the coil for hertzian wave telegraphy, with all interrupters except the wehnelt break a condenser of suitable capacity must be joined across the break points. turning in the next place to the primary key, or signalling interrupter, it is necessary to be able to control the torrent of sparks between the secondary terminals of the coil, and to cut them up into long and short periods in accordance with the letters of the morse alphabet. this is done by means of the primary key. the primary key generally consists of an ordinary massive single contact key with heavy platinum contacts. as the current to be interrupted amounts to about ten amperes and is flowing in a highly inductive circuit, the spark at break is considerable. if the attempt is made to extinguish this spark by making the contacts move rapidly away from one another through a long distance, in other words, by using a key with a wide movement, then the speed at which the signals can be set is greatly diminished. the speed of sending greatly depends upon the time taken to move the key up and down between sending two dots, and hence a short range key sends quicker than a long range key. if it is desired to use a short range key, then some method must be employed to extinguish the spark at the contacts. this is done in one of three ways: either by using a high resistance coil to short-circuit these contacts, or by a condenser, or by a magnetic blow-out, as in the case of an electric tramcar circuit controller. of these, the magnetic blow-out is probably the best. mr. marconi has designed a signalling key which performs the function not only of interrupting the primary circuit, but at the same time breaks connection between the receiving appliance and the aerial. the author has designed for signalling purposes a multiple contact key which interrupts the circuit simultaneously in ten or twelve different places. the particular point about this break is the means which are taken to make the twelve interruptions absolutely simultaneous. if these interruptions are not simultaneous, the spark always takes place at the contact which is broken first, but if the circuit is interrupted in a dozen places quite simultaneously, then the spark is cut up into a dozen different portions, and the spark at each contact is very much diminished. by this break, voltages up to two thousand volts may be quite easily dealt with. various forms of break have been devised in which the circuit is broken under oil or insulating fluids, but, generally speaking, these devices are not very portable, and a dry contact between platinum surfaces with appropriate means for cutting up the spark and blowing it out so that the mechanical movement of the switch may be small is the best thing to use. the signalling key is really a very important part of the transmitting arrangement, because whatever may be the improvements in receiving instruments, it is not possible to receive faster than we can send. a great many statements have appeared in the daily papers as to the possibility of receiving hundreds of words a minute by hertzian wave telegraphy, but the fact remains that whatever may be the sensibility of the receiving appliance, the rate at which telegraphy of any kind can be conducted is essentially dependent upon the rate at which the signals can be sent, and this in turn is largely dependent upon the mechanical movement which the key has to make to interrupt the primary circuit, and so interrupt the secondary discharge. in order to make the separation of the contact points of the switch as small as possible, and yet prevent an arc being established, various blow-out devices have been employed. the simplest arrangement for this purpose is a powerful permanent magnet so placed that its inter-polar field embraces the contact points and is at right angles to them. as already explained, the applicability of the induction coil in wireless telegraphy is limited by the fact of the high resistance of the secondary circuit and the small current that can be supplied from it. data are yet wanting to show what is the precise efficiency of the induction coil, as used in hertzian wave telegraphy, but there are reasons for believing that it does not exceed 50 or 60 per cent. where large condensers have to be charged--in other words, where we have to deal with larger powers--we are obliged to discard the induction coil and to employ the alternating-current transformer. but this introduces us to a new class of difficulties. if an alternating-current transformer wound for a secondary voltage, say, of 20,000 or 30,000 volts, has its primary circuit connected to an alternator, then if the secondary terminals, to which are connected two spark balls, are gradually brought within striking distance of one another, the moment we do this an alternating-current arc starts between these balls. if the transformer is a small one, there is no difficulty in extinguishing this arc by withdrawing the secondary terminals, but if the transformer is a large one, say, of ten or twenty kilowatts, dangerous effects are apt to ensue when such an experiment is tried. the short circuiting of the secondary circuit almost entirely annuls the inductance of the primary circuit. there is, therefore, a rush of current into the transformer, and if it is connected to an alternator of low armature resistance the fuses are generally blown and other damage done. let us supppse, then, that the secondary terminals of the transformer are also connected to a condenser. on bringing together the spark balls connected with the secondary terminals we may have one or more oscillatory discharges, but the process will not be continuous, because the moment that the alternating-current arc starts between the spark balls it reduces their difference of potential to a comparatively low value, and hence the charge taken by the condenser is very small, and, moreover, the circuit is not interrupted periodically so as to re-start a train of oscillations. when, therefore, we desire to employ an alternating-current transformer as a source of electromotive force, although it may have the advantage that the resistance of the secondary circuit of the transformer is generally small compared with that of the secondary circuit of an induction coil, yet, nevertheless, we are confronted with two practical difficulties: (1) how to control the primary current flowing into the transformer, and (2) how to destroy the alternating-current arc between the spark balls and reduce the discharge entirely to the disruptive or oscillatory discharge of the condenser. the control over the current can be obtained, in accordance with a plan suggested by the author, by inserting in the primary circuit of the transformer two variable choking coils. the form in which it is preferred to construct these is that of a cylindrical bobbin standing upon a laminated cross-piece of iron. these bobbins can have let down into them an =e=-shaped piece of laminated iron, so as to complete the magnetic circuit, and thus raise the inductance of the bobbin. by placing two of these variable choking coils in series with the primary circuit, the current is under perfect control. we can fix a minimum value below which the current shall not fall, by adjusting the position of the cores of these two choking coils, and we can then cause that current to be increased up to a certain limit which it cannot exceed, by short-circuiting one of these choking coils by an appropriate switch. several ways have been suggested for extinguishing the alternating current arc which forms between the spark balls connected to the secondary terminals when these are brought within a certain distance of one another. one of these is due to mr. tesla. he places a strong electromagnet so that its lines of magnetic flux pass transversely between the spark balls. when the discharge takes place the electric arc is blown out, but if the balls are short-circuited by a condenser the oscillatory discharge of the condenser still takes place across the spark gap. professor elihu thomson achieves the same result by employing a blast of air thrown on the spark gap. this has the effect of destroying the alternating-current arc, but still leaves the oscillating discharge of the condenser. the action is somewhat tedious to explain in words, but it can easily be understood that the blast of air, by continually breaking down the alternating-current arc which tends to form, allows the condenser connected to the spark balls to become charged with the potential of the secondary circuit of the transformer, and that this condenser then discharges across the spark gap, producing an oscillatory discharge in the usual manner. the author has found that, without the use of any air blast or electromagnet, simple adjustment of the double choking coil in the primary circuit of the transformer, as above described, is sufficient to bring about the desired result, when the capacity of the condenser is adjusted to be in resonance. another method, which has been adopted by m. d'arsonval, is to cause the spark to pass between two balls placed at the extremities of metal rods, which are in rapid rotation like the spokes of a wheel. in this case, the draught of air produced by the passage of the spark balls blows out the arc and performs the same function as the blast of air in professor elihu thomson's method. when these adjustments are properly made, it is possible, by means of a condenser and an alternating-current transformer supplied with current from an alternator, to create a rapidly intermittent oscillatory discharge, the sparks of which succeed one another so quickly that it appears almost continuous. when using a large transformer and condenser, the noise and brilliancy of these sparks are almost unbearable, and the eyes may be injured by looking at this spark for more than a moment. in the construction of transformers intended to be used in this manner, very special precautions have to be taken in the insulation of the primary and secondary circuits, and the insulation of these from the core. it may be remarked in passing that experimenting with large high-tension transformers coupled to condensers of large capacity is exceedingly dangerous work, and the greatest precautions are necessary to avoid accident. in the light, however, of sufficient experience there is no difficulty in employing high-tension transformers in the above-described manner, and in obtaining electromotive forces of upwards of a hundred thousand volts supplied through transformers capable of yielding any required amount of current. on occasions where continuous current alone is available, a motor generator has to be employed converting the continuous current into an alternating current. this is best achieved by the employment of a small alternator directly coupled to a continuous-current motor; or by providing the shaft of a continuous-current motor with two rings connected to two opposite portions of its armature, so that when continuous current is supplied to the brushes pressing against the commutator, an alternating current can be drawn off from two other brushes touching the above-mentioned insulated rings. the next element of importance in the transmitting arrangement is the spark gap. in the case of those transmitters employing an ordinary induction coil, the secondary spark, or the discharge of any condenser connected to the secondary terminals can be taken between the brass balls about half an inch or one inch in diameter, with which the terminals of the secondary coil are usually furnished; and it is generally the custom to allow this spark discharge to take place in air at ordinary pressure. in the very early days of his work mr. marconi adopted the discharger devised by professor rhigi, in which the spark takes place between two brass balls placed in vaseline or other highly insulating oil.[17] but whatever advantage may accrue from using oil as the dielectric in which the spark discharge takes place, when carrying out simple laboratory experiments on hertzian waves, there is no advantage in the case of wireless telegraphy. the rhigi discharger was, therefore, soon discarded. if discharges having large quantity are passed through oil, it is rapidly decomposed or charred, and ceases to retain the special insulating and self-restoring character which is necessary in the medium in which an oscillating spark is formed. the conditions when the discharges of large condensers are passed between spark balls are entirely different from those when the quantity of the spark, or to put it in more exact language, the current passing, is very small. in the case of hertzian experiments it is necessary, as shown by hertz, to maintain a high state of polish on the spark balls when they are employed for the production of short waves of small energy, but when we are dealing with large quantities of energy at each discharge, those methods which succeed for laboratory experiments are perfectly impracticable. the conditions necessary to be fulfilled by a discharger for use in hertzian wave telegraphy are that the surfaces shall maintain a constant condition and not be fused or eaten away by the spark, and, next, that the medium in which the discharge takes place shall not be decomposed by the passage of the spark, but shall maintain the property of giving way suddenly when a certain critical pressure is reached, and passing instantly from a condition in which it is a very perfect insulator to one in which it is a very good conductor; and, thirdly, that on the cessation of the discharge, the medium shall immediately restore itself to its original condition. when using the ordinary ten-inch induction coil, and when the capacity charged by it does not exceed a small fraction of a microfarad, it is quite sufficient to employ brass or steel balls separated by a certain distance in air, at the ordinary pressure, as the arrangement of the discharger. when, however, we come to deal with the discharges of very large condensers, at high electromotive forces, then it is necessary to have special arrangements to prevent the destruction of the surfaces between which the spark passes, or their continual alteration, and many devices have been invented for this purpose. the author has devised an arrangement which fulfils the above conditions very perfectly for use in large power stations, but the details of this cannot be made public at the present time. * * * * * we have to consider in connection with this part of the subject the dielectric strength of air under different pressures and for different thicknesses. it was shown by lord kelvin, in 1860, that the dielectric strength of very thin layers of air is greater than that of thick layers.[18] the electric force, reckoned in volts per centimetre, required to pierce a thickness of air from two to ten millimetres in thickness, at atmospheric pressure, may be taken at 30,000 volts per centimetre. the same force in electrostatic units is represented by the number 100, since a gradient of 300 volts per centimetre corresponds to a force of one electrostatic unit. it appears also that for air and other gases there is a certain minimum voltage (approximately 400 volts) below which no discharge takes place, however near the conducting surfaces may be approximated. in this particular practical application, however, we are only concerned with spark lengths which are measured in millimetres or centimetres, lying, say, between one or two millimetres and five or six centimetres. over this range of spark length we shall not generally be wrong in reckoning the voltage required to produce a spark between metal balls in air at the ordinary pressure to be given by the rule: _disruptive voltage_ = 3,000 ã� _spark-gap length in millimetres_. if, however, the air pressure is increased above the normal by including the spark balls in a vessel in which air can be compressed, then the spark length, corresponding to a given potential difference, very rapidly decreases. mr. f. j. jervis-smith[19] found that by increasing the air pressure from one atmosphere to two atmospheres round a pair of spark balls he reduced the spark length given by a certain voltage from 2â·5 to 0â·75 centimetre. professor r. a. fessenden has also made some interesting observations on the effect of using compressed air round spark gaps. he found that if a certain voltage between metal surfaces would yield a spark four inches in length, at the ordinary pressure of the air, if the spark balls were enclosed in a cylinder, the air round them compressed at 50lb. per square inch, the spark length for the same potential difference of the balls was only one quarter of an inch, or one-sixteenth of its former value. the writer has also made experiments with an apparatus designed to study the effect of compressed air round the spark gap. the experimental arrangements are as follows: a ten-inch induction coil has one of its terminals connected to the internal coating of a battery of leyden jars. the external coating is connected through the primary coil of an oscillation transformer with the other secondary terminal of the coil, and these secondary terminals are also connected to a spark gap consisting of two brass balls enclosed in a glass vessel into which air can be forced by a pump, the air pressure being measured by a gauge. the balls in the glass vessel are set at a distance of about three millimetres apart. the secondary circuit of the oscillation transformer is connected to another pair of spark balls, the distance of which can be varied. suppose we begin with the air in the glass vessel containing the balls connected to the secondary terminals of the induction coil, which may be called the secondary balls, at atmospheric pressure, and create oscillatory discharges in the primary coil of the oscillation transformer, we have a spark between the balls, which may be called the tertiary balls, connected to the secondary terminals of the oscillation transformer. if the secondary balls are placed, say, three millimetres apart, the air in the glass vessel enclosing them being at the ordinary atmospheric pressure, then with one particular arrangement of jars used, a spark twenty-five or twenty-six millimetres long between the tertiary balls will take place. suppose, then, we increase the pressure of the air round the secondary balls, pumping it by degrees to 10, 20, 30, 40 and 50lb. per square inch above the atmospheric pressure. we find that the spark between the tertiary balls will gradually leap a greater and greater distance, and when the pressure of the air is 50lb. per square inch, we can obtain a fifty-millimetre spark between the tertiary balls, whereas when the air in the glass vessel is at atmospheric pressure, we can only obtain a spark between the tertiary balls of half that length. this experiment demonstrates that the effect of compressing the air round the secondary terminals of the induction coil is to greatly increase the difference of potential between these balls before the spark passes. in fact, it requires about double the voltage to force a spark of the same length through air compressed at 50lb. on the square inch that it does to make a spark of identical length between the same balls in air at normal pressure. this shows that there is a very great advantage in taking the discharge spark in compressed air. a better effect can be produced by substituting dry gaseous hydrochloric acid for air at ordinary pressures. one other incidental advantage is that the noise of the spark is very much reduced. the continual crackle, of the discharge spark of the induction coil in connection with wireless telegraphy is very annoying to sensitive ears, but in this manner we can render it perfectly silent. professor fessenden also states that when the spark balls are surrounded by compressed air, and if one of the balls is connected with a radiator, the compression of the air, although it shortens the spark-gap corresponding to a given voltage, does not in any way increase the radiation. when, however, the air in the spark-ball vessel is compressed to 60lb. in the square inch, there is a marked increase in the effective radiation, and at 80lb. per square inch the energy emitted in the form of waves is nearly three and a-half times greater than at 50lb., the potential difference between the balls remaining the same. this effect is no doubt connected with the fact that the production of a wave, whether in ether or in any other material, is not so much dependent upon the absolute force applied as upon the suddenness of its application. to translate it into the language of the electronic theory, we may say that the electron radiates only whilst it is being accelerated, and that its radiating power, therefore, depends not so much upon its motion as upon the rate at which its motion is changing. the advantage in using compressed air round the spark gap is that we can increase the effective potential difference between the balls without rendering the spark non-oscillatory. in air of the ordinary pressure there is a certain well-defined limit of spark length for each voltage, beyond which the discharge becomes non-oscillatory, but by the employment of spark balls in compressed air, we can increase the potential difference between the balls corresponding to a given distance apart before a discharge takes place, or employ higher potentials with the same length of spark gap. in addition to this, we have, perhaps, the production of a more effective radiation, as asserted by fessenden, when the air pressure exceeds a certain critical value. the next element which we have to consider in the transmitting arrangements is a condenser of some kind for storing the energy which is radiated at intervals. where a condenser other than the aerial is employed for storing the electric energy which is to be radiated by the aerial, some form of it must be constructed which will withstand high potentials. as the dielectric for such a condenser, only two materials seem to be of any practical use, viz., glass and micanite. glass condensers in the form of leyden jars have been extensively employed, but they have the disadvantage that they are very bulky in proportion to their electrical capacity. the instrument maker's quart leyden jar has a capacity of about one-five hundredth of a microfarad, but it occupies about 150 cubic inches or more. professor braun has employed in his transmitting arrangements condensers consisting of small glass tubes like test tubes, lined on the inside and outside with tinfoil, which are more economical in space. the author has found that condensers for this purpose are best made of sheet glass about one-eighth or one-tenth of an inch in thickness, coated to within one inch of their edge on both sides with tinfoil, and arranged in a vessel containing resin or linseed oil, like the plates of a storage battery. m. d'arsonval has employed micanite, but although this material has a considerably higher dielectric strength than glass, it is much more expensive to obtain a given capacity by means of micanite than by glass, although the bulk of the condenser for a given capacity is less. to store up a certain amount of electric energy in a condenser, we require a certain definite volume of dielectric, no matter how we may arrange it, and the volume required per unit of energy is determined by the dielectric strength of the material. thus, for instance, ordinary sheet glass cannot be safely employed with a greater electric force than is represented by 20,000 volts for one-tenth of an inch in thickness, or, say, a potential gradient of 160,000 volts per centimetre. this is equivalent to an electric force of about 500 electrostatic units. this may be called the safe-working force. the electrostatic capacity of a condenser formed of two metal surfaces a foot square separated by glass three millimetres in thickness is between 1/360 and 1/400 of a microfarad. if this condenser is charged to 20,000 volts, we have stored up in it half a joule of electric energy, and the volume of the dielectric is 270 cubic centimetres. hence, to store up in a glass condenser electric energy represented by one joule at a pressure of 20,000 volts, we require 500 cubic centimetres of glass, and it will be found that if we double the pressure and double the thickness of the glass, we still require the same volume.[20] hence, in the construction of high-tension condensers to store up a given amount of energy, the economical problem is how to obtain the greatest energy-storing capacity for the least money. glass fulfils this condition better than any other material. although some materials may have very high dielectric strength, such as paper saturated with various oils, or resins, yet they cannot be used for the purpose of making condensers to yield oscillatory discharges, because the oscillations are damped out of existence too soon by the dielectric. in arranging condensers to attain a given capacity, regard has to be taken of the fact that for a given potential difference there must be a certain total thickness of dielectric, and that if condensers of equal size are being arranged in parallel it adds to their capacity, whilst joining them in series divides their capacity. if n equal condensers or leyden jars have each a capacity represented by c, and if they are joined _n_ in series and _m_ in parallel, the joint capacity of the whole number is _m_c/_n_, where the product _mn_ = n. passing on next to the consideration of oscillation transformers of various kinds--these are appliances of the nature of induction coils for transforming the current or electromotive force of electrical oscillations in a required ratio. these coils are, however, destitute of any iron core, and they generally consist of coils of wire wound on a fibre, wooden or ebonite frame, and must be immersed in a vat of oil to preserve the necessary insulation. no dry insulation of the nature of indiarubber or gutta-percha will withstand the high pressures that are brought to bear upon the circuits of an oscillation transformer. in constructing these transformers we have to set aside all previous notions gathered from the design of low-frequency iron-core transformers. the chief difficulty we have to contend against in the construction of an effective oscillation transformer is the inductance of the primary circuit and the magnetic leakage that takes place. in other words, the failure of the whole of the flux generated by the primary circuit to pass through or be linked with the secondary circuit. mr. marconi has employed an excellent form of oscillation transformer, in the design of which he was guided by a large amount of experience. in this transformer the two circuits are wound round a square wooden frame. the primary circuit consists of a number of strands of thick insulated cable laid on in parallel, so that it consists of only one turn of a stranded conductor. the secondary circuit consists of a number of turns, say, ten to twenty, of thinner insulated wire laid over the primary circuit and close to it, so that the transformer has the transformation ratio of one to ten or one to twenty. in the arrangements devised and patented by mr. marconi, these two circuits, with their respective capacities in series with them, are tuned to one another, so that the time-period of each circuit is exactly the same, and without this tuning the device becomes ineffective as a transformer.[21] there is no advantage in putting a number of turns on the primary circuit, because such multiplication simply increases the inductance, and, therefore, diminishes the primary current in the same ratio which it multiplies the turns, and hence the magnetic field due to the primary circuit remains the same. where it is desired to put a number of turns upon a coil, and yet at the same time keep the inductance down, the writer has adopted the device of winding a silk or hemp rope well paraffined between the turns of the circuit, so as to keep them further apart from one another, and as the inductance depends on the turns per centimetre, this has the effect of reducing the inductance. the next and most important element in any transmitting station is the aerial or radiator, and it was the introduction of this element by mr. marconi which laid the foundation for hertzian wave telegraphy as opposed to mere experiments with the hertzian waves. we may consider the different varieties of aerial which have been evolved from the fundamental idea. the simple single marconi aerial consists of a bare or insulated wire, generally about 100ft. or 150ft. in length, suspended from a sprit attached to a tall mast. as these masts have generally to be erected in exposed positions, considerable care has to be taken in erecting them with a large margin of strength. to the end of a sprit is attached an insulator of some kind, which may be a simple ebonite rod, or sometimes a more elaborate arrangement of oil insulators, and to the lower end of this insulator is attached the aerial wire. as at the top of the aerial we have to deal with potentials capable sometimes of giving sparks several feet in length, the insulation of the upper end of the aerial is an important matter. in the original marconi system, the lower end of the aerial was simply attached to one spark ball connected to one terminal of the induction coil, and the other terminal and spark ball were connected to the earth. in this arrangement, the aerial acted not only as radiator, but as energy-storing capacity, and as already explained, its radiating power was on that account limited. the earth connection is an important matter. for long distance work, a good earth is essential. this earth must be made by embedding a metal plate in the soil, and many persons are under the impression that the efficiency of the earth plate depends upon its area, but this is not the fact. it depends much more upon its shape, and principally upon the amount of its "edge." it has been shown by professor a. tanakadate, of japan, that if a metal plate of negligible resistance is embedded in an infinite medium having a resistivity _r_, the electrical conductance of this plate is equal to 4pi/_r_ times the electrostatic capacity of the same plate placed in a dielectric of infinite extent. hence in designing an earth plate, we have to consider not how to give it the utmost amount of surface, but how to give it the greatest electrostatic capacity, and for this purpose it is far better to divide a given amount of metal into long strips radiating out in different directions, rather than to employ it in the form of one big square or circular plate. the importance of the "good earth" will have been seen from our discussion on the mode of formation of electric waves. there must be a perfectly free access for the electrons to pass into and out of the aerial. hence, if the soil is dry, or badly conductive in the neighbourhood, we have to go down to a level at which we get a good moist earth. in fact, the precautions which have to be taken in making a good earth for hertzian wave telegraphy are exactly those which should be taken in making a good earth for a lightning conductor. whilst on the subject of aerials, a word may be said on the localisation of wireless telegraph stations on the marconi system. for reasons which were explained previously, the transmission of signals is effected more easily over water than over dry land, and it is hindered if the soil in the neighbourhood of the sending station is a poor conductor. hence, all active hertzian wave telegraph stations, like all active volcanoes, are generally found near the sea. in those cases in which a multiple aerial has to be put up consisting of many wires, one mast may be insufficient to support the structure, and several masts arranged in the form of a square or a circle have to be employed. the illustrated papers have reproduced numerous pictures of the marconi power stations at poldhu in cornwall, glace bay in nova scotia, and cape cod in the united states. in these stations, after preliminary failures to obtain the necessary structural strength with ordinary masts, tall lattice girder wooden towers have been built, about 215 feet in height, well stayed against wind pressure, and which so far have proved themselves capable of withstanding any storm of wind which has come against them. an important question in connection with the sending power of an aerial is that of the relation of its height to the distance covered. some time ago mr. marconi enunciated a law, as the result of his experiments, connecting these two quantities, which may be called marconi's law. he stated that the height of the aerial to cover a given distance, other things remaining the same, varies as the square root of the distance. let d be the distance and let l be the length of the aerial, then if both the transmitting and receiving aerial are the same height, we may say that d varies as l^{2}. this relation may be theoretically deduced as follows:--any given receiving apparatus for hertzian wave telegraphy requires a certain minimum energy to be imparted to it to make it yield a signal. if the resistance and the capacity of the receiver is taken as constant, this minimum working energy is proportional to the square of the electromotive force set up in the receiving aerial by the impact on it of the electric waves. this electromotive force varies as the length of the receiving aerial and as the magnetic force due to the wave cutting across it, and the magnetic force varies as the current in the transmitting aerial, and therefore, for any given voltage varies as the capacity, and therefore as the length of the transmitting aerial. if, therefore, the transmitting and receiving aerial have the same length, the minimum energy varies as the square of the electromotive force in the receiving aerial, and therefore as the fourth power of the length of either aerial, since the electromotive force varies as the product of the lengths of the aerials. hence, when the distance between the aerials is constant, the minimum working energy varies as the fourth power of the height of either aerial, but when the lengths of the aerials are constant, the energy caught up by the receiving aerial must vary inversely as the square of the distance d between the aerials. hence, if we call _e_ this minimum working energy, _e_ must vary as 1/d^{2} when l is constant, or as l^4 when d is constant, and since _e_ is a constant quantity for any given arrangements of receiver and transmitter, it follows that when the height of aerial and distance vary, the ratio l^4/d^2 is constant, or, in other words, d^2 varies as l^4 or d varies as l^2--_i.e._, distance varies as the square of the height of the aerial, which is marconi's law. the curve, therefore, connecting height of aerial with sending distance for given arrangements is a portion of a parabola. otherwise, the law may be stated in the form l = _a_[\sq]{d}, where _a_ is a numerical coefficient. if l and d are both measured in metres, then, for recent marconi apparatus as used on ships, _a_ = 0â·15 roughly. (see a report on experiments made for the italian navy, 1900-1901, by captain quintino bonomo--"telegrafia senza fili," rome, 1902.) this law, however, must not be used without discretion. after mr. marconi had transmitted signals across the british channel, some people, forgetting that a little knowledge is a dangerous thing, predicted that aerials a thousand feet in height would be required to signal across the atlantic, but mr. marconi has made such improvements of late years in the receiving arrangements that he has been able to receive signals over three thousand miles in 1903 with aerials only thirty-three per cent. longer than those which, in 1899, he employed to cover twenty miles across the english channel. [illustration: fig. 15.--alternating-current double-transformation power plant for generating electric waves (fleming). _a_, alternator; h_{1}h_{2}, choking coil; k, signalling key; t, step-up transformer; s_{1}s_{2} spark-gap; c_{1}c_{2} condensers; t_{1}t_{2}, oscillation transformers; a, aerial; e, earthplate.] we turn, in the next place, to the consideration of those devices for putting more power into the aerial than can be achieved when the aerial itself is simply employed as the reservoir of energy. professor braun, of strassburg, in 1899, described a method for doing this by inducing oscillations in the aerial by means of an oscillation transformer, these oscillations being set up by the discharges from a leyden jar or battery of leyden jars, which formed the reservoir of energy. the induction coil is employed to produce a rapidly intermittent series of electrical oscillations in the primary coil of an oscillation transformer by the discharge through it of a leyden jar. mr. marconi immensely improved this arrangement, as described by him in a lecture given before the society of arts on may 17, 1901, by syntonising the two circuits and making the circuit, consisting of the capacity of the aerial and the inductance of the secondary circuit of the oscillation transformer, have the same time-period as the circuit consisting of the leyden jars, or energy-storing condenser, and the primary circuit of the oscillation transformer, and by so doing immensely added to the power and range of the apparatus. starting from these inventions of braun and marconi, the author devised a double transmission system in which the oscillations are twice transformed before being generated in the aerial, each time with a multiplication of electromotive force and a multiplication of the number of groups of oscillations per second. this arrangement can best be understood from the diagram (see fig. 15). in this case a transformer, t, or transformers receive alternating low-frequency current from an alternator, _a_, being regulated by passing through two variable choking coils, h_{1} and h_{2}, so as to control it. this alternating current is transformed up from a potential of two thousand to twenty, forty or a hundred thousand, and is employed to charge a large condenser, c_{1}, which discharges across a primary spark-gap, s_{1}, through the primary coil of an oscillation transformer, t_{1}. the secondary circuit of the oscillation transformer is connected to a second pair of spark balls, s_{2}, which in turn are connected by a secondary condenser, c_{2}, and the primary circuit of a third transformer, t_{2} and the secondary circuit of this last transformer are inserted between a marconi aerial, a, and the earth e. when all these circuits are tuned to resonance by mr. marconi's methods, we have an enormously powerful arrangement for creating electric waves, or rather trains of electric waves, sent out from the aerial, and the oscillations are controlled and the signals made by short-circuiting one of the choking coils. another transmitting arrangement, which involves a slightly different principle, and employs no oscillation transformer, is one due also to professor braun. in this case, a condenser and inductance are connected in series to the spark balls of an induction coil, and oscillations are set up in this circuit. accordingly, there are rapid fluctuations of potential at one terminal of the condenser. if to this we connect a long aerial, the length of which has been adjusted to be one quarter of the length of wave corresponding to the frequency, in other words, to make it a quarter-wave resonator, then powerful oscillations will be accumulated in this rod. the relation between the height (h) of the aerial and the frequency is given by the equation 3 ã� 10^{10} = 4_n_h, where _n_ is the frequency of the oscillations and h the height of the aerial in centimetres. the frequency of the oscillations is determined by the capacity (c) and inductance (l) of the condenser circuit, and can be calculated from the formula n = (5,000,000) / ([\sq]{c (in mfds.) ã� l (in cms.)}). that is, the frequency is obtained by dividing into the number 5,000,000, the square root of the product of the capacity in microfarads, and inductance in centimetres, of the condenser circuit. it will be found, on applying these rules, that it is impossible to unite together any aerial of a length obtainable in practice with a condenser circuit of more than a very moderate capacity. it has been shown that for an aerial two hundred feet in height the corresponding resonating frequency is about one and a quarter million.[22] as we are limited in the amount to which we can reduce the inductance of a discharge circuit, probably to something like a thousand centimetres, a simple calculation shows that the largest capacity we can employ is about a sixtieth of a microfarad. this capacity, even if charged at 60,000 volts, would only contain thirty joules of energy, or about 22â·5 foot-pounds, which is a small storage compared to that which can be achieved when we are employing the above-described methods, which involve the use of an oscillation transformer. in such a case, however, it is an advantage to employ a spark-gap in compressed air, because we can then raise the voltage to a much higher value than in air of ordinary pressure without lengthening the spark so much as to render it non-oscillatory. when employing methods involving the use of an oscillation transformer, it is possible to use multiple aerials having large capacity, and hence to store up a very large amount of energy in the aerial, which is liberated at each discharge. the most effective arrangement is one in which the radiator draws off gradually a large supply of energy from a non-radiating circuit, and so sends out a true train of waves, and not mere impulses, into the ether, and as we shall see later on, it is only when the radiation takes place in the form of true wave trains that anything like syntony can be obtained. there are a number of variants of the above methods of arranging the radiator and associated energy-storing in circuit. descriptions of these arrangements will be found in patents by mr. marconi, professor slaby and count von arco, sir oliver lodge, dr. muirhead, professor popoff, professor fessenden and others. in all cases, however, they are variations of the three simple forms of radiator already described. returning to the analogy with the air or steam siren suggested at the commencement of this article, the reader will see in the light of the explanations already given, that all parts of the air-wave producing apparatus have their analogues in the electrical radiator as used in hertzian wave telegraphy. the object in the one case is to produce rapid oscillations of air particles in a tube, which result in the production of an air wave in external space; in the other case, the arrangement serves to produce oscillations of electrons or electrical particles in a wire, the movements of which create a disturbance in the ether called an electrical wave. comparing together, item by item, it will be seen, therefore, that the induction coil or transformer used in connection with electric-wave apparatus is analogous to the air pump in the siren plant. in the electrical apparatus, this electron pump is employed to put an electrical charge into a condenser; in the air wave apparatus, the air pump is employed to charge an air vessel with high pressure air. from the electrical condenser the charge is released in the form of a series of electrical oscillations, and in the air wave producing appliance, the compressed air is released in the form of a series of intermittent puffs or blasts. in the electrical wave producing apparatus, these electrical oscillations in the condenser circuit are finally made to produce other oscillations in an air wire or open circuit, just as the puffs of air finally expend themselves in producing aerial oscillations in the siren tube. finally, in the one case we have a series of air waves and in the other case, a series of electrical waves. these trains of electric waves or air waves, as the case may be, are intermitted into long and short groups, in accordance with the signals of the morse alphabet, and, therefore, the hertzian wave transmitter, in whatever form it may be employed, when operated by means of a marconi aerial, is in fact an electrical siren apparatus, the function of which is to create periodic disturbances in the universal ether of the same character as those which the siren produces in atmospheric air. * * * * * we have to consider in the next place the arrangements of the receiving station and the various forms of receivers that have been devised for effecting telegraphy by hertzian waves. just as the transmitting station consists essentially of two parts, viz., a part for creating electrical oscillations and a part for throwing out or radiating electric waves, so the receiving-station appliances may be divided into two portions; the function of one being to catch up a portion of the energy of the passing wave, and that of the other to make a record or intelligible signal in some manner in the form of an audible or visible sign. accordingly, there must be at the receiving station an arrangement called a receiving aerial, which in general takes the form of a long vertical wire or wires, similar in form to the transmitting aerial, there is, however, a distinct difference in the function of the transmitting aerial and the receiving aerial. the function of the first is effective radiation, and for this purpose the aerial must have associated with it a store of energy to be released as wave energy; but the function of the receiving aerial is to be the seat of an electromotive force which is created by the electric force and the magnetic force of the incident electric wave. in tracing out the mode of operation of the transmitting aerial, it was pointed out that the electric waves emitted consisted of alternations of electric force in a direction which is perpendicular to the surface of the earth, and magnetic force parallel to the surface of the earth. these two quantities, the electric force and the magnetic force, are called the _wave vectors_, and they both lie in a plane perpendicular to the direction in which the wave is travelling and at right angles to one another, the electric force being perpendicular to the surface of the earth. in optical language, the wave sent out by the aerial would be called a plane polarised wave, the plane of polarisation being parallel to the magnetic force. hence, if at any point in the path of the wave we erect a vertical conductor, as the wave passes over it, it is cut transversely by the magnetic force of the wave and longitudinally by the electric force. both of these operations result in the creation of an alternating electromotive force in the receiving aerial wire. as in all other cases of oscillatory motion, the principle of resonance may here be brought into play to increase immensely the amplitude of the current oscillations thereby set up in the receiving aerial. as already explained, any vertical insulated wire placed with its lower end near the earth has capacity with respect to the earth, and it has also inductance, the value of these factors depending on its shape and height. accordingly, it has a natural electrical time-period of its own, and if the periodic electromotive impulses which are set up in it by the passage of the waves over it agree in period with its own natural time-period, then the amplitude of the current vibrations in it may become enormously greater than when there is a disagreement between these two periods. before concluding these articles we shall return to this subject of electric resonance and syntony, and discuss it with reference to what is called the tuning of hertzian wave stations. meanwhile, it may be said that for the sake of obtaining, at any rate in an approximate degree, this coincidence of time-period, it is generally usual to make the receiving aerial as far as possible identical with the transmitting aerial. if the receiving aerial is not insulated, but is connected to the earth at its lower end through the primary coil of an oscillation transformer, we can still set up in it electrical oscillations by the impact on it of an electric wave of proper period; and if the oscillation transformer is properly constructed we can draw from its secondary circuit electric oscillations in a similar period. one problem in connection with the design of a receiving aerial is that of increasing its effective length and capacity so as to increase correspondingly the electromotive force or current oscillations in it. it is clear that if we put a number of receiving wires in parallel so that each one of them is operated upon by the wave separately, although we can increase in this way the magnitude of the alternating current which can be drawn off from the aerial, we cannot increase the electromotive force in it except by increasing the actual height of the wires. unfortunately, there is a limit to the height of the receiving aerial. it has to be suspended, like the transmitting aerial, from a mast or tower, and the engineering problem of constructing such a permanent supporting structure higher than, say, two hundred feet is a difficult one. since any one station has to send as well as receive, it is usual to make one and the same aerial wire or wires do double duty. it is switched over from the transmitting to the receiving apparatus, as required. this, however, is a concession to convenience and cost. in some respects it would be better to have two separate aerials at each station, the one of the best form for sending, and the other of the best form for receiving. in mr. marconi's early arrangements, the so-called coherer or sensitive wave-detecting appliance, to be described more in detail presently, was inserted between the base of the insulated receiving aerial and the earth, but it was subsequently found by him to be a great improvement to act upon the receiving device, not directly by the electromotive force set up in the aerial, but by the induced electromotive force of a special form of step-up oscillation transformer he calls a "jigger," the primary circuit of which was inserted in between the receiving aerial and the earth plate, and the secondary circuit was connected to the sensitive organ of the telegraphic receiving arrangements.[23] a suggestion to employ transformed oscillations in affecting a coherer, had also been described in a patent specification by sir oliver lodge, in 1897, but the essence of success in the use of this device is not merely the employment of a transformer, but of a transformer constructed specially to transform electrical oscillations. turning, then, to the consideration of the relation existing between the transmitting and receiving aerials, we note that in their simplest form these consist of two similar tall rods of metal placed upright, with their feet in good connection with the earth at two places. we may think of them as two identical lightning conductors, well earthed at the bottom, and supported by non-conducting masts or towers. these rods must be in good connection with the earth, and therefore with it form, as it were, one conductor. if, as usual, these aerials are separated by the sea, the intermediate portion of this circuit is an electrolyte. the operations which take place when a signal is sent are as follows:-at the transmitting station, we set up in the transmitting aerial electric oscillations, of which the frequency may be of the order of a million, _i.e._, the oscillations as long as they last are at the rate of a million a second. each spark discharge at the transmitter results, however, only in the production of a train of a dozen or two oscillations, and these trains succeed each other at a rate depending upon the transmitting arrangements used. each oscillation in the transmitting aerial is accompanied by the detachment from it of semi-loops of electric strain, as already explained. the alterations of electric strain directed perpendicularly to the earth, and of the associated magnetic force parallel to the earth, constitute an electric wave in the ether, just as the alternations of pressure and motion of air molecules constitute an air wave. associated with these physical actions above ground, there is a propagation through the earth of electric action, which may consist in a motion or atomic exchange of electrons. each change or movement of a semi-loop of electric strain above ground has its equivalent below ground in inter-atomic exchanges or movements of the electrons, on which the ends of these semi-loops of electric strain terminate. the earth must play, therefore, a very important part in so-called "wireless telegraphy," and we might also say the earth does as much as the ether in its production. the function of the receiving aerial is to bring about a union between these two operations above and below ground. when the electric waves fall upon it, they give rise to electromotive force in the receiving aerial, and, therefore, produce oscillations in it which, in fact, are electric currents flowing into and out of the receiving aerial. we may say that the transmitting aerial, the receiving aerial and the earth form one gigantic hertz oscillator. in one part of this system, electric oscillations of a certain period are set up by the discharge of a condenser and are propagated to the other part. in the earth, there is a propagation of electric oscillations; in the space above and between the aerials, there is a propagation of electric waves. the receiving aerial _feels_, therefore, what is happening at the distant aerial and can be made to record it.[24] we have next to consider the question of the wave-detecting devices which enable us to appreciate and record the impact of a wave or wave train against the aerial. at the very outset it will be necessary to coin a new word to apply generally to these appliances. most readers are probably familiar with the term "coherer," which was applied by sir oliver lodge, in the first instance, to an electric wave-detecting device of one particular kind--viz., that in which a metal point was lightly pressed against another metal surface and caused to stick to it when an electric wave fell upon it. as our knowledge increased, it was found that there were many cases in which the effect of the electric radiation was to cause a severance and not a coherence, and hence such clumsy phrases as "anticoherer" and "self-decohering coherer" have come into use. moreover, we have now many kinds of electric wave detectors based on quite different physical principles. at the risk of incurring reprobation for adding to scientific nomenclature, the author ventures to think that the time has arrived when a simple and inclusive term will be found useful to describe all the devices, whatever their nature, which are employed for detecting the presence of an electric wave. for this purpose the term _kumascope_, from the greek [greek: kuma] (a wave), is suggested. the scientific study of waves has already been called _kumatology_, and in view of our familiarity with such terms as _microscope_, _electroscope_ and _hygroscope_, there does not seem to be any objection to enlarging our vocabulary by calling a wave-detecting appliance a _kumascope_. we are then able to look at the subject broadly and to classify kumascopes of different kinds. we may, in the first place, arrange them according to the principle on which they act. thus, we may have electric, magnetic, thermal, chemical and physiological operations involved; and finally, we may divide them into those which are self-restoring, in the sense that after the passage or action of a wave upon them they return to their original sensitive condition; and those which are non-restoring, in that they must be subjected to some treatment to bring them back again to a condition in which they are fit to respond again to the action of a wave. we have no space to refer to the whole of the steps of discovery which led up to the invention of all the various forms of the modern electric kumascope or wave detector. suffice it to say that the researches of hertz in 1887 threw a flood of light upon many previously obscure phenomena, and enabled us to see that an electric spark, and especially an oscillatory spark, creates a disturbance in the ether, which has a resemblance in nature to the expanding ripples produced by a stone hurled into water. scientific investigation then returned with fresh interest to previously incomprehensible effects, and a new meaning was read into many old observations. again and again it had been noticed that loose metallic contacts, loose aggregations of metallic filings or fragments, had a mysterious way of altering their conductivity under the action of electric sparks, lightning discharges and high electromotive forces. as far back as 1852, mr. varley had noticed that masses of powdered metals had a very small conductivity, which increased in a remarkable way during thunderstorms;[25] and in 1866, c. and s. a. varley patented a device for protecting telegraphic instruments from lightning, which consisted of a small box of powdered carbon in which were buried two nearly touching metal points, and they stated that "powdered conducting matter offers a great resistance to a current of moderate tension, but offers but little resistance to currents of high tension."[26] we then pass over a long interval and find that the next published account of similar observations was due to professor t. calzecchi-onesti, who described in an italian journal, _il nuovo cimento_ (see vol. xvi., p. 58, and vol. xvii., p. 38), in 1884 and 1885 his observations on the decrease in resistance of metal powders when the spark from an induction coil was sent through them.[27] these observations did not attract much attention until professor e. branly, of paris, in 1890 and 1891, repeated them on an extended scale and with great variations, making the important observation that an electric spark _at a distance_ had a similar effect in increasing the conductivity of metallic powders.[28] branly, however, noticed that in some cases of conductors in powder, such as the peroxide of lead or antimony, the effect of the spark was to cause a decrease of conductivity. to professor e. branly unquestionably belongs the honour of giving to science a new weapon in the shape of a tube containing metallic filings or powder rather loosely packed between metal plugs, and of showing that when the pressure on the powder was adjusted such a tube may be a conductor of very high resistance, but that the electrical conductivity is enormously increased if an electric spark is made in its neighbourhood. he also proved that the same effect occurred in the case of two slightly oxidised steel or copper wires laid across one another with light pressure, and that this loose or imperfect contact was extraordinarily sensitive to an electric spark, dropping in resistance from thousands of ohms to a few ohms when a spark was made many yards away. it is curious to notice how long some important researches take to become generally known. branly's work did not attract much attention in england until 1892, when dr. dawson turner described his own repetition of branly's experiments with the metallic filings tube at a meeting of the british association in edinburgh. in the discussion which followed, professor george forbes made an important remark. he asked whether it was possible that the decrease in resistance could be brought about by hertz waves.[29] this question shows that even in 1892 the idea that the effect of the spark on the branly tube was really due to hertzian waves was only just beginning to arise. the following year, however, mr. w. b. croft repeated branly's experiment with copper filings before the physical society of london, and entitled his short paper "electric radiation on copper filings."[30] he exhibited a tube containing copper filings loosely held between two copper plugs and joined in series with a galvanometer and cell. the effect of an electric spark at a distance, in causing increase of conductivity, was shown, and the return of the tube to its non-conducting state when tapped was also noticed. in the discussion which followed the reading of this paper, professor minchin described the effects of electric radiation on his impulsion cells. he followed up this by reading a paper to the physical society on november 24, 1893, on the action of hertzian radiation on films containing metallic powders, and expressed the opinion that the change in resistance of the branly tube was due to electric radiation.[31] thus, at the end of 1893, a few physicists clearly recognised that a new means had been given to us for detecting those invisible ether waves, the chief properties of which hertz had unravelled with surpassing skill six years before, by means of a detector consisting of a ring of wire having a small spark-gap in it. in june, 1894, sir oliver lodge delivered a discourse at the royal institution, entitled "the work of hertz," and at this lecture use was made of the branly tube as a hertz wave detector. the chief object of the lecture was to describe the properties of hertzian waves and their reflection, absorption and transmission, and many brilliant quasi-optical experiments were exhibited. although a branly tube, or imperfect metallic contact, then named by him a _coherer_, was employed by sir oliver lodge to detect an electric wave generated in another room, there was no mention in this lecture of any use of the instrument for telegraphic purposes.[32] as we are here concerned only with the applications in telegraphy, we shall not spend any more time discussing the purely scientific work done with laboratory forms of this wave detector. without attempting to touch the very delicate question as to the precise point at which laboratory research passed into technical application, we shall briefly describe the forms of kumascope which have been devised with special reference to hertzian wave telegraphic work. a very exact classification is at present impossible, but we may say that telegraphic kumascopes may be roughly divided into six classes. the first class includes all those that depend for their action on the "coherer principle" or the reduction of the resistance of a metallic microphone by the action of electromotive force. as they depend upon an imperfect contact, they may be called _contact kumascopes_. this class is furthermore subdivided into the self-restoring and the non-self-restoring varieties. the second class comprises the _magnetic kumascopes_ which depend upon the action of an electrical oscillation as a magnetising or demagnetising agency. the third class comprises the _electrolytic responders_, in which the action of electric oscillations either promotes or destroys the results of electrolysis. the fourth class consists of the _electrothermal detectors_, in which the power of an electrical oscillation as a high frequency electric current to heat a conductor is utilised. the fifth class comprises the _electromagnetic_ or _electro-dynamic_ instruments, which are virtually very sensitive alternating-current ammeters, adapted for immensely high frequency. the sixth class must be made to contain all those which cannot be well fitted at present into any of the others, such as the sensitive responder of schã¤fer, the action of which is not very clearly made out. we may proceed briefly to describe the construction of the principal forms of kumascope coming under the above headings. in the first place, let us consider those which are commonly called the "coherers" or, as the writer prefers to call them, the _contact kumascopes_. the simplest of these is the crossed needle or single contact, which originated with professor e. branly.[33] the pressure of the point of a steel needle against an aluminium plate was subsequently found by sir oliver lodge to be a very sensitive arrangement when so adjusted that a single cell sends little or no current through the contact.[34] when an electric wave passes over it, good conducting contact ensues. the point is, in fact, welded to the plate, and can only be detached by giving the plate or needle a light shock or vibration. a variation of the above form is a pair of crossed needles, one resting on the other. professor branly found, in 1891, that if a pair of slightly-oxidised copper wires rest across one another the contact-resistance may fall from 8,000 to 7 ohms by the impact of an electric wave. he has recently devised a tripod arrangement, in which a light metal stool with three slightly-oxidised legs stands on a polished plate of steel. the contact points must be oxidised, but not too heavily, and the stool makes a bad electrical contact until a wave falls upon it.[35] the decoherence is effected by giving the stool a tilt by means of an electromagnet. these single or multiple-point kumascopes labour under the disadvantage that only a very small current can be passed through the variable contact when used as a relay arrangement, without welding them together so much that a considerable mechanical shock is required to break the contact and reset the trap. the logical development of the single contact is, therefore, the infinite number of contacts existing in the tube of metallic filings, which has been the form of kumascope most used for many years. in its typical form it consists of a tube of insulating material with metallic plugs at each end, and between them a mass of metallic powder, filings, borings, granules or small spheres, lightly touching one another. imperfect contact must be arranged by light pressure, and in the majority of cases the resistance is very large until an electric wave falls upon the tube, when it drops suddenly to a small value and remains there until the tube is given a slight shake or the granules disturbed in any way, when the resistance suddenly rises again. this type of responder is a non-restoring kumascope, and requires the continual operation of some external agency to keep it in a condition in which it is receptive or sensitive to electric waves. much discussion and considerable research have taken place in connection with the action and improvement of these metallic powder kumascopes. as regards materials, the magnetic metals, nickel, iron and cobalt, in the order named, appear to give the best results. the noble metals, gold, silver and platinum, are too sensitive, and the very oxidisable metals too insensitive, for telegraphic work, but an admixture may be advantageously made. omitting the intermediate developments of invention, it may be said that mr. marconi was the first to recognise that to secure great sensibility in an electric wave detector of this type the following conditions must be fulfilled: an exceedingly small mass of metallic filings must be placed in a very narrow gap between two plugs, the whole being contained in a vessel which is wholly or partly exhausted of its air. mr. marconi devoted himself with great success to the development of this instrument, and in a very short time succeeded in transforming it from an uncertain laboratory appliance, capable of yielding results only in very skilled hands, into an instrument certain and simple in its operations as an ordinary telegraphic relay. he did this, partly by reducing its size, and partly by a most judicious selection of materials for its construction. as made at present, the marconi metallic filings tube consists of a small glass tube, the interior diameter of which is not much more than one-eighth of an inch, which has in it two silver plugs which are bevelled off obliquely. these are placed opposite to each other, so as to form a wedge-shaped gap, about a millimetre in width at the bottom and two, or at most three, millimetres in width at the top (see fig. 16). the silver plugs exactly fill the aperture of the tube, and are connected to platinum wires sealed through the glass. the tube has a lateral glass tube fused into it, by which the exhaustion is made, which is afterwards sealed off, and this tube projects on the side of the wider portion of the gap between the silver plugs. the sensitive material consists of a mixture of metallic filings, five per cent. silver and ninety-five per cent. nickel, being carefully mixed and sifted to a certain standard fineness. in the manufacture of these tubes, great care is taken to make them as far as possible absolutely identical. each tube when finished is exhausted, but not to a very high vacuum. the tube so finished is attached to a bone holder, by which it can be held in a horizontal position. the object of bevelling off the plugs in the marconi tube is to enable the sensitiveness of the tube to be varied by turning it round, so that the small quantity of filings lie in between a wider or narrower part of the gap.[36] [illustration: fig. 16.--marconi sensitive tube or metallic filings kumascope. pp, silver plugs; tt, platinum wires; f, nickel and silver filings.] other ways of adjusting the quantity of the filings to the width of the gap have been devised. sometimes one of the plugs is made movable. in other cases, such as the tubes devised by m. blondel and sir oliver lodge, there is a pocket in the glass receptacle to hold square filings, from which more or less can be shaken into the gap. an interesting question, which we have not time to discuss in full, is the cause of the initial coherence of the metallic filings in a branly tube. it does not seem to be a simple welding action due to heat, and it certainly takes place with a difference of potential, which is very far indeed below that which we know is required to produce a spark. on the other hand, it seems to be proved that in a banly tube, when acted upon by electric waves, chains of metallic particles are produced. the effect is not peculiar to electric waves. it can be accomplished by the application of any high electromotive force. thus branly found that coherence may be produced by the application of an electromotive force of twenty or thirty volts, operating through a very high water resistance, and thus precluding the passage of any but an excessively small current. again, the coherence seems to take place in some cases when metallic particles are immersed in a liquid, or even in a solid, insulator. processor branly has, therefore, preferred to speak of masses of metallic granules as _radio-conductors_, and professor bose has divided substances into positive and negative, according as the operation of electromotive force is to increase the coherence of the particles or to decrease it. it has been asserted that for every particular branly tube, there is a critical electromotive force, in the neighbourhood of two or three volts which causes the tube to break down and pass instantly from a non-conductive to a conductive condition, and that this critical electromotive force may become a measure of the utility of the tube for telegraphic purposes. thus, c. kinsley (_physical review_, vol. xii., p. 177, 1901) has made measurements of this supposed critical potential for different "coherers," and subsequently tested the same as receivers at a wireless telegraph station of the u.s.a. signal corps. the average of twenty-four experiments gave in one case 2â·2 volts as the breaking down potential of one of these coherers or branly tubes, 3â·8 volts for a second and 5â·5 volts for the third. these same instruments, tested as telegraphic kumascopes, showed that the first of the three was most sensitive. on the other hand, w. h. eccles (_electrician_, vol. xlvii., pp. 682 and 715, 1901) has made experiments with marconi nickel-silver sensitive tubes, using a liquid potentiometer made with copper sulphate, to apply the potential so that infinitesimal spark contacts might be avoided and the changes in potential made without any abruptness. he states that if the coherer tube is continuously tapped, say at the rate of fifty vibrations per second, whilst at the same time an increasing potential is applied to its terminals and the current passing through it measured on a galvanometer, there is no abrupt change in current at any point. he found that when the current and voltage were plotted against each other, a regular curve was obtained, which after a time becomes linear. a decided change occurs in the conductivity of the mass of metallic filings when treated in this manner at voltages lower than the critical voltage obtained by previous methods. he ascertained that there was a complete correspondence between the sensitiveness of the tubes used as telegraphic instruments and the form of the characteristic curve of current and voltage drawn by the above-described method. in the same manner, k. e. guthe and a. trowbridge (_physical review_, vol. ii., p. 22, 1900) investigated the action of a simple ball coherer formed of half a dozen steel, lead or phosphor-bronze balls in slight contact. they measured the current _i_ passing through the series under the action of a difference of potential _v_ between the ends, and found a relation which could be expressed in the form v = v(1 e^{ki}), where v and _k_ are constants. the current through this ball coherer is, therefore, a logarithmic function of the potential difference between its ends, of the form i = log(v v) and exhibits no discontinuity. the inference was drawn that the "resistance" is due to films of water adhering to the metallic particles through which electrolytic action occurs. a good metallic filings tube for use as a receiver in hertzian wave telegraphy should exhibit a constancy of action and should cohere and decohere, to use the common terms, sharply, at the smallest possible tap. it should not have a current passed through it by the external cell of more than a fraction of a milliampere, or else it becomes wounded and unsensitive. the investigations which have already taken place seem to show pretty clearly that the agency causing the masses of filings to pass from a non-conductive to a conductive condition is electromotive force, and that, therefore, it is the electromotive force set up in the aerial by the incident waves which is the effective agent in causing the change in the metallic filings tube, when this is used as a telegraphic kumascope. this transformation of the tube from a non-conductor to a conductor is made to act as a circuit-closer, completing the circuit, by means of which a single cell of a local battery is made to send current through an ordinary telegraph relay, and so by the aid of a second battery operate a telegraphic printer or recorder of any kind. hence it is clear that after one impact, the metallic filings tube has to be brought back to its non-conductive condition, and this may be achieved in several ways. (1) by the administration of carefully-regulated taps or shocks or by rotating the tube on its axis; (2) by the aid of an alternating current; (3) in those cases where filings of magnetic metals are employed, by magnetism. the decoherence by taps was discovered by branly,[37] and popoff, following the example of sir oliver lodge, employed an electric bell arrangement for this purpose.[38] mr. marconi, in his original receiving instruments, placed an electromagnet under the coherer tube with a vibrating armature like an electric bell.[39] this armature carries a small hammer or tapper, which, when set in action, hits the tube on the under side, and various adjusting screws are arranged for regulating exactly the force and amplitude of the blows. this tapper is actuated by the same current as the morse printer, or other telegraphic recorder, so that when the signal is received and the metallic filings tube passes into the conductive condition and closes the relay circuit, this latter in turn closes the circuit of the morse printer or other recorder, and at the same time, a current passes through the electromagnet of the tapper and the tube is tapped back. this sequence of operations requires a certain time which limits the speed of receiving. the tapper has to be so arranged that it is possible to receive and to record not only the _dot_ but a _dash_ on the morse system. the _dash_ is really a series of closely adjacent dots, which run together in virtue of the inertia and inductance of the different parts of the whole receiving apparatus. the adjustment has so to be made that, whilst the _dash_ is being recorded and a continuous tapping is kept up, yet, nevertheless the continued electromotive force in the aerial, due to the continually arriving trains of waves, is able to act against the tapping and to keep the filings in the tube in the conductive condition. hence, the successful operation of the arrangement requires attention to a number of adjustments, but these are not more difficult, or even as difficult, as those involved in the use of many telegraphic receivers employed in ordinary telegraphy with wires. mr. marconi also introduced devices for preventing the sparks at the contacts of the electromagnetic hammer from directly affecting the tube, and also to prevent the electric oscillations which are set up in the aerial from being partly shunted through other circuits than that of the sensitive tube. we pass on to notice the remaining devices for restoring the metallic filings tube to a condition of sensitiveness or receptiveness. a method for doing this by alternating currents is due to mr. s. g. brown.[40] the pole pieces of the coherer tube are made of iron, and they are enveloped in magnetising coils traversed by an alternating electric current. between these pole pieces is placed a small quantity of nickel or iron filings, and under the action of the electromotive force, due to an electric wave acting on them, may be made to cohere in the usual fashion; but the moment that the wave ceases, the alternating magnetism of the electrodes causes the filings to drop apart or decohere. in place of the alternating current, mr. brown finds that a revolving permanent magnet can be used to produce the alternating magnetisation of the pole pieces of the sensitive tube or coherer. the third method of causing the decoherence of the filings is that due to t. tommasina. he found that when a branly tube is made with filings of a magnetic metal, such as iron, nickel and cobalt, the decoherence of the filings can be produced by means of an electromagnet placed in a suitable position under the tube.[41] the explanation of this fact seems to be that, when an electric wave falls upon the tube or when any other source of electromotive force acts upon it, chains of metallic particles are formed, stretching from one electrode to the other. tommasina contends that he has proved the existence of these chains of particles by experiments made with iron filings; and r. malagoli,[42] in referring to tommasina's assertion, states that it can be witnessed in the case of brass filings placed between two plates of metal and immersed in vaseline oil, when a difference of potential is made between the plates. t. sundorph[43] says he has confirmed tommasina's discovery of the formation of these chains of metallic particles in the coherer. the filings do not all cling together, but certain chains are formed which afford a conducting path for the current subsequently passed through the coherer from an external source. accordingly, tommasina's method of causing decoherence in the case of filings of magnetic metals is to pull them apart by an external magnetic field; and he stated that decoherence can be effected more easily and regularly in this way than by tapping. whilst on this point, it may be mentioned that c. tissot[44] says that he has found that the sensitiveness of a coherer formed of nickel and iron filings can be increased by placing it in the magnetic field, the lines of which are parallel to the axis of the tube. according to mm. a. blondel and g. dobkevitch, this is merely the result of an increased coherence of the particles. * * * * * quite recently, sir oliver lodge and dr. muirhead have employed as a self-restoring coherer or kumascope a steel disc revolved by clockwork, the edge of which just touches a globule of mercury covered with a thin film of paraffin oil. the contact is made between the mercury and the steel by the electric wave generating an electromotive force in the aerial, sufficient to break through the thin film of oil. when the wave stops, the circuit is again interrupted automatically. this device is used without a relay to actuate directly a syphon recorder as used in submarine telegraphy. the working battery employed with it must only have an electromotive force of about a tenth of a volt. it may be used also with a telephone in circuit and can, therefore, be employed either for telegraphic or telephonic reception.[45] [illustration: fig. 17.--italian navy self-restoring kumascope. c, carbon plug; i, iron plug; m, mercury globule; a, aerial; b, battery; t, telephone; s, adjusting screw.] one of the most sensitive of these self-restoring kumascopes is the carbon-steel-mercury coherer, the invention of which has been attributed to castelli, a signalman in the italian navy,[46] but also stated on good authority to have been the invention of officers in the royal italian navy, and has, therefore, been called the italian navy coherer.[47] this instrument has been arranged in several forms, but in the simplest of these it consists of a glass tube, having in it a plug of iron and a plug of arc-lamp carbon, or two plugs of iron with a plug of carbon between them. the plugs of iron, or of iron and carbon, are separated by an exceedingly small globule of mercury, the size of which should be between one and a-half and three millimetres. the plugs closing the tube must be capable of movement, one of them by means of a screw, as shown in the diagram (fig. 17), taken from a patent specification communicated to mr. marconi by the marchese luigi solari, of the royal italian navy. one of the plugs of this tube is connected to the aerial and the other to the earth, and they are also connected through another circuit composed of a single dry cell and a telephone. the arrangement then forms an extremely sensitive detector of electric waves or of small electromotive forces, or, if a wave falls on the aerial, the electromotive force at once improves the contact between the mercury and the plugs, and therefore causes a sudden increase in the current through the telephone, giving rise to a sound; but when the wave ceases, or the electromotive force is withdrawn, the resistance falls back again to its origin value, and the arrangement is, therefore, self-acting, requiring no tapping or other device for restoring it to receptivity. a very ingenious form of combined telephone and coherer has been devised by t. tommasina.[48] in this instrument the diaphragm of an ordinary bell telephone carries upon it a very small carbon or metallic coherer. this coherer is connected in between the aerial and the earth, and is also in circuit with a battery and the electromagnet of a telegraphic relay. when this relay operates it closes the circuit of another battery which is placed in series with the telephone coil. the moment the current passes through the telephone coil it attracts, and therefore vibrates, the diaphragm and shakes up the metallic filings. if an observer, therefore, places the telephone to his ear, he hears a sound corresponding to every train of waves incident upon the aerial. with this arrangement, one can obtain two different kinds of results, according to the nature of the cohering powder placed in the cavity in the diaphragm. first, if the powder consists of a non-magnetic metal, gold, silver, platinum or the like, the receiver will be very sensitive; and at the same time the current passing through it when it is cohered will be sufficient to work a sensive recording apparatus in series with the telephone coil. secondly, if the metallic powder placed in the cavity is a magnetic metal, the receiver will be somewhat less sensitive, but will work with more precision, because of the magnetic action of the magnet of the telephone upon the cohering powder. if no recording apparatus is used, the observer must write down the signals as heard in the telephone, since corresponding to a short spark at the transmitting station, a single tick or short sound is heard at the telephone, and corresponding to a series of rapidly successive sparks, a more prolonged sound is heard in the telephone. these two sounds, as already explained, constitute the dot and the dash of the morse signals. we may, in the next place, refer to that form of kumascope in which the action of the wave or of electromotive force is not to decrease the resistance of a contact, but to increase that of an imperfect contact. as already mentioned, professor branly discovered long ago that peroxide of lead acts in an opposite manner to metallic filings, in that when placed in a branly tube it increases its resistance under the action of an electric spark, instead of decreasing it. again, professor bose has found that fragments of metallic potassium in kerosene oil behave in a similar manner, and that certain varieties of silver, antimony and of arsenic, and a few other metals, have a similar property. branly tubes, therefore, made with these materials, or any arrangements which act in a similar manner, have been called "anti-coherers." the most interesting arragement which has been called by this name is that of schã¤fer.[49] schã¤fer's kumascope is made in the following manner: a very thin film of silver is deposited upon glass, and a strip of this silver is scratched across with a diamond, making a fine transverse cut or gap. if the resistance of this divided strip of silver is measured, it will be found not to be infinite, but may have a resistance as low as forty or fifty ohms if the strip is thirty millimetres wide. on examining the cut in the strip with a microscope, it will be found that the edges are ragged and that there are little particles of silver lying about in the gap. if, then, an electromotive force of three volts or more is put on the two separated parts of the strip, these little particles of silver fly to and fro like the pith balls in a familiar electrical experiment, and they convey electricity across from side to side. hence a current passes having a magnitude of a few milliamperes. if, however, the strip is employed as a kumascope and connected at one end to the earth and at the other end to an aerial, when electric waves fall upon the aerial, the electrical oscillations thereby excited seem to have the property of stopping this dance of silver particles and the resistance of the gap is increased several times, but falls again when the wave ceases. if, therefore, a telephone and battery are connected between two portions of the strip, the variation of this battery current will affect the telephone in accordance with the waves which fall upon the aerial, and the arrangement becomes therefore a wave-detecting device. it is said to have been used in wireless telegraph experiments in germany up to a distance of ninety-five kilometres. we must next direct attention to those wave-detecting devices which depend upon magnetisation of iron, and here we are able to record recent and most interesting developments. more than seventy years ago joseph henry, in the united states, noticed the effect of an electric spark at a distance upon magnetised needles.[50] of recent times, the subject came back into notice through the researches of professor e. rutherford,[51] who carried out at cambridge, england, in 1896, a valuable series of experiments on this subject. he found that if a magnetised steel needle or a very small bundle of extremely thin iron wires is magnetised and placed in the interior of a small coil, the ends of which are connected to two long collecting wires, then an electric wave started from a hertz oscillator at a distance causes an immediate demagnetisation of the iron. this demagnetisation he detected by means of the movement of the needle of a magnetometer placed near one end of the iron wire. although rutherford's wave detector has been much used in scientific research, it was not, in the form in which he used it, a telegraphic instrument, and could not record alphabetic signals. not long ago mr. marconi invented, however, a telegraphic instrument based upon his discovery that the magnetic hysteresis of iron can be annulled by electric oscillations. in one form, mr. marconi's magnetic receiver is constructed as follows[52] (see fig. 18): an endless band of thin iron wire composed of several iron wires about no. 36 gauge, arranged in parallel, is made to move slowly round on two pulleys, like the driving belt of a machine. in one part of its path the wire passes through a glass tube, on which are found two coils of wire, one a rather short, thick coil, and the other a very fine, long one. the fine, long coil is connected with a telephone, and the shorter coil is connected at one end to the earth and the other to the aerial. two permanent horse-shoe magnets are placed as shown n fig. 18, with their similar poles together, and, as the iron band passes through their field, a certain length of it is magnetised, and owing to the hysteresis of the material, it retains this magnetism for a short time after it has passed out of the centre of the field. if then an electric oscillation, coming down from the aerial, is passed through the shorter coil, it changes the position of the magnetised portion of the iron and, so to speak, brings the magnetised portion of iron back into the position it would have occupied if the iron had had no hysteresis. this action, by varying the magnetic flux through the secondary coil, creates in it an electromotive force which causes a sound to be heard in the telephone connected to it. if at a distant place a single wave or train of waves is started and received by the aerial, this will express itself by making an audible tick in the telephone, and if several groups of closely adjacent wave trains are sent, these will indicate themselves by producing a rapid series of ticks in the telephone, heard as a short continuous noise and taken as equivalent to the morse _dash_. [illustration: fig. 18.--marconi magnetic receiver. w_{1}w_{2}, wheels; i, iron wire band; p, primary coil; s, secondary coil; t, telephone; a, aerial; e, earthplate.] it was by means of this remarkably ingenious instrument that mr. marconi was able, in the summer of 1902, to detect the waves sent out from poldhu on the coast of cornwall, and receive messages as far as cronstadt in the baltic, in one direction, and as far as spezzia in the mediterranean in another direction, and also to receive messages across the atlantic from the power stations situated in glace bay, nova scotia, and from one at cape cod in massachusetts, u.s.a., in december, 1902. there can be no question that this magnetic detector of mr. marconi's, used in connection with a good telephone and an acute human ear, is the most sensitive device yet invented for the detection of electric waves and their utilisation in telegraphy without continuous wires. it is marvellously simple, ingenious and yet effective, as a hertzian wave telegraphic receiver. whilst on the subject of magnetic wave detectors, the author may describe experiments that he has been recently making to construct a hertzian wave detector on the rutherford principle, which shall be strictly quantitative. all the receivers of the coherer type and electrolytic type give no indications that are at all proportional to the energy of the incident wave. their indications are more or less accidental and depend upon the manner in which the receiver was last left. there is a great need for a quantitative wave detector, the indications of which shall give us a measure of the energy of the arriving wave. it is only by the possession of such an instrument that we can hope to study properly the sending powers of various transmitters or the efficiency of different forms of aerial or devices by which the wave is produced. this magnetic receiver is constructed as follows: a coil of fine wire is constructed in sections like the secondary coil of an induction coil, and in the instrument already made, this coil contains thirty or forty thousand turns of wire. in the interior of this coil are placed a number of little bundles of fine iron wire wound round with two coils, a fine wire coil which is a magnetising coil, and a thicker wire coil which is a demagnetising coil. these sets of coils are joined up, respectively, in series or in parallel. then, associated with this form of induction coil is a commutator of a peculiar kind, which performs the following functions when a battery is connected to it and when it is made to revolve by a motor or by clockwork. first, during part of the revolution, the commutator closes the battery circuit and magnetises the iron cores, and whilst this is taking place the secondary circuit of the induction coil is short-circuited and the galvanometer is disconnected from it. secondly, the magnetising current is stopped, and soon after that the secondary coil is unshort-circuited and connected to the galvanometer, and remains in this condition during the remainder of the revolution. this cycle of operations is repeated at every revolution. if then an electrical oscillation is sent into the demagnetising coils, and if it continues longer than one revolution of the commutator, it will demagnetise the iron core during that period of time in which the battery is disconnected and the galvanometer connected. the demagnetisation of the iron which ensues produces an electromotive force in the secondary coil and causes a deflection of the galvanometer, and this deflection will continue and remain steady if the oscillation persists. moreover, since this deflection is due to the passage through the galvanometer of a rapid series of discharges, it is large when the oscillations continue for a long time and are powerful, and small when they continue for a short time or are weak. we can, therefore, with this arrangement, receive on the galvanometer, just as on the mirror galvanometer used in submarine cable work, a dot or dash, and, moreover, the magnitude of these deflections is a measure of the energy of the wave. it is probable that when this arrangement is perfected it will become exceedingly useful for making all kinds of tests and measurements in connection with hertzian telegraphy, even if it is not sensitive enough to use as a long distance receiver. of late years a variety of wave-detecting devices have been brought forward which depend upon electrolysis. one of the best known of these is that by de forest and smythe.[53] in this arrangement, a tube contains two small electrodes like plugs, which may be made of tin, silver or nickel, or other metal. the ends of these plugs are flat and separated from each other by about one two-hundredth of an inch. sometimes the end of one of these plugs is made cup shaped and the cup or recess is filled with a mass of peroxide of lead and glycerine. in the interval between the electrodes is placed an electrolyzable mixture, which consists of glycerine or vaseline mixed with water or alcohol, and a small quantity of litharge and metallic filings. these metallic filings act as secondary electrodes. when a small electromotive force is applied between the terminals of the electrodes of this tube through a very high resistance of twenty or thirty thousand ohms, an exceedingly small current passes through this mixture, and it causes an electrolytic action which results in the production of chains of metallic particles connecting the two electrodes together. if, in addition to this, one terminal or electrode of the arrangement is connected to an aerial wire and the other terminal to the earth, then on the arrival of an electric wave creating oscillations in the wire, these oscillations pass down into the electrolytic cell, where they break up the chains of metallic particles and thus interrupt the current passing through the telephone quite suddenly, which is heard as a slight tick by an ear applied to it. as soon as the wave ceases, the chain of metallic particles is re-established, so that the appliance is always in a condition to be affected by a wave. it is said that this breaking up and reformation of the chains of metallic particles is so rapid that a short spark made at the transmitting station is heard as a tick in the telephone, but a rapid succession of oscillatory sparks is heard as a short continuous sound; hence the two signals necessary for alphabetical conversation can be transmitted. another receiver which has some resemblance to the above, although different in principle, is that of neugschwender.[54] in this arrangement, which to a certain extent resembles the schã¤fer detector, a glass plate has upon it a deposit of silver in the form of a strip, which is cut across at one place, thus interrupting it. if the cut is breathed upon or placed in a moist atmosphere, a little dew is deposited upon the glass, which bridges over the cut in the metal and creates an electric continuity. hence a small current can be passed across the gap and through a telephone by one or two cells of a battery. if, however, an electric oscillation passes across the gap on its way from an aerial to the earth, then the continuity of the liquid film is destroyed, and the current is interrupted and a sound created in the telephone. the opinion has been expressed by sir oliver lodge that in this case the interruption of the circuit which occurs is really due to the coalescence of minute water particles into larger drops, as when vapour is condensed into rain, and hence the continuity of the material is interrupted. we must then make a brief reference to other kumascopes which depend upon the heating power of an electrical oscillation, which it possesses in common with every other form of electric current. professor r. a. fessenden[55] has constructed a very ingenious thermal receiver in the following manner: an extremely fine platinum wire, about 0â·003 of an inch in diameter, is embedded in the middle of a silver wire about one tenth of an inch in diameter, like the wick of a candle. this compound wire is then drawn down until the diameter of the silver wire is only 0â·002 of an inch, and hence the platinum wire in its interior, being reduced in the same ratio, will have been drawn to a diameter of 0â·00006 of an inch. a short piece of this drawn wire is then bent into a loop and the ends fixed to wires. the tip of the loop is then immersed in nitric acid and dissolved in the silver, leaving an exquisitely fine platinum wire a few hundredths of an inch in length and having a resistance of about thirty ohms. this little loop is sealed into a glass bulb like a very small incandescent lamp, or it may be enclosed in a small silver bulb and the air may be exhausted. if an electrical oscillation is sent through this exceedingly fine platinum wire it heats it and rapidly increases its resistance. the electrical oscillations produced in an aerial are sent through a number of these loops arranged in parallel, and the loops are short-circuited by a telephone, joined in series with a source of very small electromotive force produced by shunting a single cell or opposing to one another two cells of nearly equal electromotive force. any variation of resistance of the little platinum loops due to the heat produced by the oscillations, by suddenly altering the current flowing through the telephone, will cause a sound to be heard in it. the electrical oscillations when passing through the loops are therefore detected by the heat which they generate in these exquisitely fine platinum wires. finally, one word must be said on the subject of electrodynamic receivers, due to the same inventor. an exceedingly small silver ring is suspended by a quartz fibre and has a mirror attached to it in the manner of a galvanometer. this ring is suspended between two coils joined in series, which are placed either in the circuit of the aerial or in the secondary circuit of the small air core transformer inserted between the aerial and the earth. when electrical oscillations travel down the aerial they induce other electrical oscillations in the silver ring, and if the ring is so placed that its normal position is with its plane inclined at an angle of forty-five degrees to the plane of the fixed coils, then the ring will be slightly deflected every time an oscillation occurs in the aerial. omitting further mention of the details of the kumascopes in use and the receiving aerial, we must next proceed to consider the receiving arrangements taken as a whole. in the original marconi system, the sensitive tube or coherer was inserted between the bottom of the receiving aerial and the earth.[56] accordingly, when the incident electric wave strikes the receiving aerial and creates in it an oscillatory electromotive force, this last will, if of sufficient amplitude, cause the particles of the coherer to cohere and become conductive. this sudden change from a nearly perfect non-conductivity to a conductive condition is made to act as a switch or relay, closing or completing the circuit of a single cell, and so sending a current through an ordinary telegraphic relay, closing or completing the circuit of a single cell, which may in turn actuate another recording telegraphic instrument, such as a morse printer. to prevent the oscillations from passing into the relay circuit, small choking or inductance coils are inserted between the ends of the sensitive tube and the relay and cell and serve to confine the oscillations to the tube. it has already been pointed out that in the transmitting aerial the amplitude at the potential vibrations increases from the bottom to the top, and when vibrating in its fundamental manner there is a potential node at the earth connection and a potential loop or antinode at the top. the same is true of the receiving aerial. hence, if the kumascope employed is a branly metallic filings tube and is inserted near the base of the aerial, the difference of potential between its two ends will be small. it has also been mentioned that a receiver of this type acts in virtue of electromotive force or potential difference, and hence the proper place to insert the coherer is not at the base of the aerial, but between the top of the aerial and the earth. this, however, could not be done by running up another wire from the earth, as that would amount to putting the coherer between the tops of two identical aerials, and between its ends there would be no difference of potential. professor slaby, in conjunction with count von arco, has given an ingenious solution of this problem. if we take two equal lengths of wire, bent at right angles, and connect the point of intersection with the earth, placing one of these wires vertically and the other horizontally, we then have an arrangement which responds to the impact of electric waves, and has electrical oscillations set up in it in such fashion that the common point of the two wires has a very small amplitude of potential, but the two extremities have equal and large variations. if, then, we insert a coherer tube between the earth and the outer extremity of the horizontal wire, it is influenced in the same manner as it would be by the potential variations at the top of the vertical wire. in other words, it is acted upon by a large difference of potential instead of a small one. it is not found necessary to stretch the horizontal wire out straight; it may be coiled into a spiral with open turns, and the slight decrease in capacity and increase in inductance resulting from this can be compensated by cutting off a short piece of it. [illustration: fig. 19.--slaby receiver. a, aerial; e, earth plate; f, coherer; m, multiplier; c, condenser; r, relay; b, battery; e, earth plate.] in this way we have an arrangement (see fig. 19) in which the outer extremity of this open spiral experiences variations or potential which exactly correspond with those at the summit of the vertical aerial. the receiving arrangements are then completed as in fig. 19, one end of the coherer being attached to the outer end of the spiral and the other end through a condenser to the earth, a relay and a voltaic cell being arranged as shown in the diagram. the mode of operation of this receiver is as follows: when the wave strikes the aerial it sets up in it electrical oscillations with a potential antinode at the summit, and at the same time a potential antinode is created at the outer end of the spiral attached near the base of the aerial, this spiral being called by professor slaby a _multiplicator_. as long as the coherer tube remains non-conductive, the local cell cannot send a current through the relay, but, as soon as the resistance is broken down by the impact of a wave, the local cell sends a current through the coherer tube which, passing down to the earth through the base of the aerial and up through the earth connection to the condenser, completes its circuit through the relay. many variations of this arrangement have been made by slaby and von arco and by the allgemeine elektricitã¤ts gesellschaft of berlin. in 1898, mr. marconi made a great advance in the construction of his receiving apparatus by the insertion of his "jigger" or oscillation transformer in the aerial receiving circuit.[57] in this arrangement, the primary coil of an air core transformer wound in a particular way is inserted between the receiving aerial and the earth, and the secondary circuit is cut in the middle and connected to the two surfaces of a condenser, these surfaces being also connected through the circuit of an ordinary telegraphic relay and a single cell (see fig. 20). the ends of the secondary circuit of this oscillation transformer are also connected to the terminals of the coherer tube, and these again are short-circuited by a small condenser. [illustration: fig. 20.--marconi receiver. a, aerial; j, jigger; cc, condensers; f, filings tube; t, tapper; r, relay; b, battery; m, morse printer.] the operation of this receiver is as follows: the oscillations set up in the aerial pass through the primary circuit of the jigger, and these induce other oscillations in the secondary circuit; the electromotive force or difference of potential between the primary terminals being transformed up in any desired ratio. it is this exalted electromotive force which is made to act on the coherer tube, and, inasmuch as the jigger operates in virtue of a current passing through its primary circuit and this current is at a maximum at the lower end of the aerial, the arrangement is exceedingly effective, because it, so to speak, converts current into voltage. at the lower end of the aerial, although the amplitude of the potential oscillations is a minimum, the amplitude of the current oscillations is a maximum, and the jigger transforms these large current oscillations into large potential oscillations, _provided it is constructed in the right manner_. we can also transform up or increase the amplitude of the small potential variations near the bottom of the aerial by employing the principle of resonance. many devices of this kind, due to professor slaby and others, have been suggested and tried but the details are rather too technical to be fully described here. it will be noticed that the receiving aerial may be arranged in one of two ways--it may be either earthed at the lower end or it may be insulated. it has been claimed that there is a great advantage in earthing the receiving aerial directly in that it eliminates atmospheric disturbances. we shall allude to this point more particularly later on. meanwhile it may be mentioned that the receiving arrangements, as a whole, constitute a sensitive arrangement, as shown by popoff, tommasina and by all the large experience of mr. marconi himself for detecting changes in the electrical condition of the atmosphere, which are doubtless of the nature of electrical oscillations. on the other hand, the receiving arrangements may be perfectly insulated and some experimentalists have asserted that by this method the greatest freedom is secured from atmospheric disturbances. amongst the non-earthed arrangements the system invented by professor f. braun, of strassburg, and worked by messrs. siemens, of berlin, may be mentioned.[58] [illustration: fig. 21.--braun's non-earthed receiver. i, induction coil; cc, condensers; s, spark gap; j, transmitting jigger; k, receiving jigger; f, filings tube; r, relay; b, battery.] professor braun's arrangements are indicated in the diagram in fig. 21. in this case an induction coil is used to create a discharge between two spark balls, and to these two balls are connected the two outer coatings of two condensers, the inner coatings of which are connected together through the primary coil of an air core transformer. the secondary coil of this transformer is connected to two extension wires forming a hertz resonator, and the length of these wires is so adjusted with reference to the time period of the primary circuit that they resonate to it, the whole length from end to end of the secondary circuit being half a wave-length. the receiver, as shown in the diagram, consists of a pair of quarter wave-length receiving wires connected through two condensers, which are short-circuited by the primary coil of an oscillation transformer. the secondary circuit of this last oscillation transformer has two extension wires to it, turned in the same manner, to respond to the primary oscillator; and in the circuit of one of these extension wires is placed a coherer tube, short-circuited by a relay and a local battery. it will thus be seen that there is an entire abolition of ground connection, which, professor braun claims, practically avoids all atmospheric disturbances.[59] the details of the receiving arrangement are as follows:--the coherer tube consists of an ebonite tube containing hard steel particles of a uniform size, placed in the adjustable space between two polished steel electrodes. it is found that with this steel coherer, a small amount of magnetism in the particles increases its sensitiveness, and to obtain this, a ring magnet is employed in connection with a coherer tube. receiving apparatus arranged on this system is said to have been used for telegraphing between heligoland and cuxhaven, a distance of thirty-six miles. all the immense experience, however, gained by mr. marconi and those who have worked with his system, is in favour of using the earth connection. there is no doubt that hertzian wave telegraphy can be conducted over short distances by means of totally insulated aerials, but for long distances the earth connection is essential, for the reasons that have been explained previously. there are many of the details of the receiving arrangements which remain to be considered. if the communication is received by a telegraphic instrument like the morse printer, which requires a current of anything like ten milliamperes to work it, then an important element in the receiving arrangement is the relay. the relay that is generally used is a modified form of the siemens polarised relay, which is so adjusted as to make a single contact. for marine work on board ship, it is essential that this relay shall be balanced so that variations in position shall not affect it. sometimes the relay is hung in gimbals like a compass, and at other times suspended from a support by elastic bands, so as to avoid jolting. in any case, the relay must be so adjusted that no change of position will cause it to close the circuit of the telegraphic printer or recorder. its sensibility ought to be such that it is actuated by a tenth of a milliampere, and, if possible, even by less. the alteration of sensibility in the ordinary contact form of relay is the pressure that is necessary to bring the platinum points of the circuit closer together, so as to pass the minimum current which will work the telegraph printer. the important matter, however, in connection with the use of the relay in hertzian wave telegraphy, is that it should be capable of adjustment without extraordinary skill. it is no use to put into the hands of an operator a relay which requires abnormal dexterity to make it work at all. * * * * * it remains, then, to consider some of the questions connected with practical hertzian wave telegraphy and the problem of the limitation of communication. these matters at the present moment very much occupy the public attention, and many conflicting opinions are expressed concerning them. it may be observed at the outset that the difficulty of dealing with the subject as freely as many desire is that hertzian wave telegraphy is no longer merely a subject of scientific investigation, but has developed into a business and involves, therefore, other interests than the simple advancement of scientific knowledge. we can, however, discuss in a general manner some of the scientific problems which present themselves for solution. the first of these is the independence of communication between stations. it is desirable, at the outset, to clear up a little misunderstanding. there is a great difference between preventing the reception of communication when it is not desired by the recipient, and preventing it when it is the object of the latter to overhear if he can. it is, therefore, necessary to distinguish between isolation and overhearing. we may say that a station is _isolated_ when it is not affected by hertzian waves other than those it desires to receive; but that a station _overhears_ when it can, if it chooses, pick up communications not intended for it, or cannot help receiving them against its will. this distinction is a perfectly fair one. any telegraph or telephone wire can be tapped, if it is desired, but unless there is some fault on the line, no station will receive a message against its desires. moreover, it may be noted that there are penalties attached to tapping a telegraph wire, and at present there are none connected with the misappropriation of an ether wave. we shall, therefore, consider in the first place the methods so far proposed for preventing any given receiver from being affected by hertzian waves sent out from other stations, except that of those from which it is desired to receive them. the first method is that which has been called the method of _electrical syntony_, and consists in adjusting the electrical capacity and inductance of the various open and closed circuits of the receiving and transmitting stations to be put in communication so that they have the same electrical time-period.[60] in the cantor lectures before the society of arts in 1900, on electrical oscillations and electric waves, the author has discussed at length the conditions under which powerful electrical oscillations can be set up in a circuit. it was there shown that every electric circuit having capacity and inductance has a particular or natural time-period of electrical oscillation depending on the product of these qualities, and that, to accumulate powerful electrical oscillations in it, the electromotive impulses on it must be delivered at this rate. illustrations were drawn from mechanics, such as the examples furnished by vibrating pendulums and springs, and from acoustics, as illustrated by the phenomena of resonance, to show that small or feeble blows or impulses delivered at the proper time intervals have a cumulative effect in setting up vibrations in a body capable of oscillation. it is a familiar fact that if we time our blows, we can achieve that which no single blow, however powerful, can accomplish in throwing into vibration a body such as a pendulum, which is capable of oscillation under the action of a restoring force. precisely the same is true of an electric circuit. we have already seen that the receiving aerial has an alternating electromotive force set up in it by the impact of the successive electric waves sent out from the transmitter. it must, however, be remembered that the transmitter sends out a series of trains of waves, not by any means a continuous train, but one cut up into groups of probably ten to fifty waves, each separated by intervals of silence, long, compared with the duration of a single train of waves. [illustration: fig. 22.--seibt's apparatus for exhibiting electric resonance. i, induction coil; s, spark gap; cc, condensers; l, variable inductance; e, earth plate; ww, wire spirals; vv, vacuum tubes.] if, however, by a suitable adjustment of capacity and inductance, we make the natural time-period of oscillation of the receiving aerial circuits agree with those of the transmitting aerial, within certain limits the former will only be receptive for waves of the frequency sent out by the transmitter. it is quite easy to illustrate this principle by numerous experiments. it can be done by means of an apparatus devised by dr. georg seibt for showing in an interesting manner the syntonisation or tuning of two electric circuits. this consists of two bobbins, each consisting of one layer of insulated wire wound on a wooden rod (see fig. 22). each of these bobbins has a certain electrical capacity with respect to the earth, when considered as an insulated conductor, and it has also a certain inductance. if, therefore, electromotive impulses are applied to one end of the bobbin at regular intervals, electrical oscillations will be set up in it, and, as already explained, if these are timed at a certain rate, the bobbin will act like a closed organ-pipe to air impulses and oscillations of potential will be accumulated at the opposite end, which have much greater amplitude than the impressed oscillations at the end at which they are applied. we can make the existence of the amplitude oscillations of potential evident by attaching to one end of the bobbin a vacuum tube, which will be illuminated thereby, or by terminating it by a pointed piece of wire, so that an electrical brush can be formed at the point, if the potential variations have sufficient amplitude. we arrange also another closed oscillation circuit, consisting of two leyden jars and a variable inductance coil and a pair of spark balls which are connected to an induction coil. in this manner we can set up oscillations in the discharge circuit of these leyden jars, and we can vary the time period by altering the inductance and the capacity. if we denote the capacity of the jars in the microfarads by the letter c and the inductance in centimetres of the discharge circuit of the jars by the letter l, it can then be shown that the number of oscillations per second denoted by _n_ is given by the expression--[61] n = (5,000,000,000) / ([\sq]{cl}). if now we adjust the leyden jar circuit to a particular rate of oscillation, we have between the terminals of the jar or condenser an alternating difference of potential or electromotive force. if we connect one side of the jars to the earth and the other side to the foot of one of the spirals or bobbins above described, we shall find perhaps that the vacuum tube at the other end is not rendered luminous. when, however, we adjust the inductance in the discharge circuit of the jar to a certain value to make the frequency of the condenser oscillations agree with the natural time period of the bobbin terminated by the vacuum tube, this latter at once lights up brilliantly. again, if we connect both these bobbins at the same time to the discharge circuit of the leyden jar, we shall find that we can make an adjustment of the inductance of that circuit, such that either of the bobbins at pleasure can be made to respond and be set in electrical vibration, as shown by the illumination of the vacuum tube at its upper end or by an electrical brush being formed at the terminal. in making this adjustment of inductance, we are _tuning_, as it is called, the leyden jar discharge circuit to the resonating bobbin. a very small variation of the inductance of the jar circuit causes the vacuum tube to change in luminosity. if, however, the natural time periods of these bobbins do not lie very far apart, then a faint luminosity will make its appearance in both the vacuum tubes. supposing, therefore, that we connect to the oscillating circuit of the jar a number of bobbins having different time periods of oscillation, like organ-pipes, and supply them all with one common alternating electromotive force. these bobbins, whose natural time period is very different to that of the osciilating circuit or impressed electromotive force, will not respond, but those bobbins of which the natural time period lies near to, even if not quite exactly the same as, that of the impressed electromotive force will give evidence of being set in oscillation. a very violent electromotive force will cause them all to respond to some slight extent, no matter whether the period of that impluse is tuned to their common period precisely or not. at this point questions arise of great practical importance. a matter which has been in dispute in connection with practical hertzian wave telegraphy is how far this electrical tuning is a sufficient solution of the practical problem of isolation. it is not denied that experiments such as those made with seibt's apparatus can be shown on a small scale; and, on a still larger scale, mr. marconi gave to the author in september, 1900, a demonstration in practical telegraphic work of sending two independent hertzian wave messages and receiving them on two independent receivers attached to the same aerial. since that date much experience has been gained and large power stations erected, and a statement has been frequently made that syntony is no protection against interference when one of the stations is sending out very powerful waves. the contention has been raised that large power stations producing electric waves will therefore play havoc with hertzian wave telegraphy on a smaller scale, such as the ship to shore and intermarine communication. under these circumstances, it appeared to the author important to subject the matter to a special test, and mr. marconi, therefore, offered to give a demonstration, with this object, in support of the opinion that he has expressed positively that waves from his power stations do not interfere with the working of his ship installations. this matter is vital to the whole question of practical hertzian wave telegraphy, for the ship to shore communication is of stupendous importance; and if mr. marconi had done nothing else except to render this possible and effective, he would have earned, as he has done, the gratitude of humanity for all time. accordingly, the author embraced the opportunity of making some careful tests to settle the question whether the powerful waves sent out from a station such as poldhu did or did not affect the exchange of messages between ship and shore stations in proximity, equipped with marconi apparatus of a suitable type. these experiments were carried out on the eighteenth of march last, at poldhu, in cornwall, and a programme was arranged by the author of the following kind. close to the poldhu station is an isolated mast, which was equipped by mr. marconi with a hertzian wave apparatus, similar to that he places on ships. six miles from poldhu is the lizard receiving station, with which ships proceeding up or down the english channel communicate. it was arranged that a series of secret messages, some of them in cipher, should be delivered simultaneously at certain known times, both to the power station at poldhu and to the small adjacent ship station; and it was arranged that these messages should be sent off simultaneously, the operators being kept in ignorance up to the moment of sending as to the nature of the messages. at the lizard, mr. marconi connected two of his receiving instruments to the aerial, one of them tuned to the waves proceeding from the power station at poldhu, and the other to those proceeding from the small ship station. at the appointed time, these two sets of messages were received simultaneously in the presence of the author, each message being printed down independently on its own receiver; and mr. marconi read off and interpreted all these messages perfectly correctly, not having known before what was the message that was about to be sent. in addition to this, precautions were taken to prove that the power station at poldhu was really emitting waves sufficiently powerful to cross the atlantic and not being made to sing small for the occasion. to assist in proving this, the messages sent out from the power station were also received at a station at poole, two hundred miles away, and the assistant there was instructed to telegraph back these messages by wire as soon as he received them. these messages came back perfectly correctly, thus demonstrating that the power station was sending out power waves. the whole programme was carried out with the greatest care to avoid any mistakes on the part of the assistants, and provided an absolute demonstration of the truth of mr. marconi's assertion that the waves from one of his power stations, such as poldhu, do not in the least degree interfere with the transmission and reception of messages between ship and shore, effected by means of certain forms of marconi apparatus for producing and detecting waves of a different wave length.[62] this complete independence of transmission, however, is entirely due to the employment of a receiving circuit of a certain type in mr. marconi's receivers. it does not at all follow that a receiving circuit of any kind, even a marconi receiver not especially arranged, set up in proximity to a power station would not be affected. this, however, is not an important matter. far more important is it to show, as has been shown, that practically perfect isolation can be achieved if it is desired. it must be noted, however, that, although the fact that electric circuits have a natural time-period of oscillation of their own is a scientific principle which carries us a considerable way towards a solution of what is called syntonic hertzian wave telegraphy, it is not in itself alone in every respect an entire solution of the practical problem. the degree to which it is a solution depends to a considerable extent upon the nature of the detecting device, or kumascope, which we are employing. the coherer, or branly filings tube, has the peculiarity that its passage from a non-conductive to a conductive condition follows immediately when the difference of potential between its ends is made sufficiently great. in other words, if the tube is acted upon by a sufficient electromotive force, it is not necessary that electromotive force should be repeated at intervals to make this particular form of kumascope responsive. again, if we consider the nature of the oscillations which are sent out from any transmitting aerial, we find that each group of oscillations corresponding to a single spark consists of waves gradually decreasing in amplitude. in other words, the first wave of the group is the strongest, and the decay in amplitude is often very rapid. supposing, then, we construct a simple receiver consisting of an aerial having inserted in its circuit a sensitive branly filings tube. such a receiver is almost entirely non-syntonic; that is to say, it is affected by any wave passing over it which is sufficiently powerful. we may look upon it that if the first wave of the series is sufficiently powerful to affect the kumascope, the conductive change takes place whether or not the first wave is followed by others. accordingly, it is perfectly certain that if a transmitter is sending out trains of waves of any period, a simple combination of coherer and aerial will be influenced, if it is placed near enough to the transmitter. on the other hand, it is possible to combine a kumascope of a certain type with a receiving aerial and other circuits in such a manner that when the waves that reach it are feeble it shall not respond at all unless those waves have very nearly a time period of a certain value. at this stage, it may be perhaps well to explain a little in detail what is meant by an easily responsive circuit, and, on the other hand, by an irresponsive circuit, or, as we may call it, a _stiff_ circuit. supposing that we consider an aerial consisting of a simple straight wire having small capacity and small inductance, such a circuit admits of being sent into electrical oscillation, not only by waves of its own natural time-period, but by the sudden application of any violent electromotive impulse. if, on the other hand, we bestow upon the circuit in any way considerable inductance, we then obtain what may be called a stiff or irresponsive circuit, which is one in which electrical oscillations can be accumulated only by the prolonged action of impulses tuned to a particular period. a mechanical analogue of this difference may be found in considering the different behaviour of elastic bodies to mechanical blows. take, for instance, a piece of elastic steel and fix the bottom end in a vice. the steel strip may be thrown into vibration by deflecting the upper end. it has, however, a very small mass, and therefore any violent blow or blows, even although not repeated, will set it in oscillation. if, however, we add mass to it by fixing at the other end a heavy weight, such as a ball of lead, and at the same time make the spring stiffer, we have an arrangement which is capable of being sent into considerable oscillation only by the action of a series of impulses or blows which are timed at a particular rate. returning then to the electrical problem, we see that in order to preserve a kumascope or wave detector from being operated on by any vagrant wave or waves having a period very different to an assigned period, it must be associated with an electrical circuit of the kind above called a stiff circuit. we will now consider the manner in which the problem has been practically attacked by mr. marconi, dr. slaby, sir oliver lodge and others, who have invented forms of receiver and transmitter, which are syntonic or sympathetic to one another. some of the methods which mr. marconi has devised for the achievement of syntonic wireless telegraphy were fully described by him in a paper read before the society of arts on may, 17, 1901.[63] [illustration: fig. 23.--marconi transmitter and receiver. i, induction coil; a, aerial; e, earth plate; hh, choking coils; s, spark gap; j, transmitting jigger; k, receiving jigger; r, relay; c, condenser; f, filings tube; b, battery. many practical details are omitted.] on referring to his paper, it will be seen that in one form his transmitter consists of an aerial, near the base of which is inserted the secondary circuit of an oscillation transformer or transmitting jigger. one end of this secondary circuit is attached to the aerial and the other end is connected to the earth through a variable inductance coil. the primary circuit of this oscillation transformer is connected in series with a condenser, consisting of a battery of leyden jars, and the two together are connected across to the spark balls which close the secondary circuit of an induction coil, having the usual make and break key in the primary circuit. mr. marconi so adjusts the induction of the aerial and the capacity of the condenser, or battery of leyden jars, that the two circuits, consisting respectively of this battery of leyden jars and the primary circuit of the transformer, and on the other hand of the capacity of the aerial and the inductance in series with it, and that of the secondary circuit of the transformer have the same time period. in other words, these two inductive circuits are tuned together. at the receiving end, the aerial is connected in series with a variable inductance and with the primary circuit of another oscillation transformer, the second terminal of which is connected to the earth. the secondary circuit of this last oscillation transformer is cut in the middle and is connected to the terminals of a small condenser. the outer terminals of this secondary circuit are connected to the metallic filings tube or other sensitive receiver and to a small condenser in parallel with it (see fig. 23). the terminals of the condenser which is inserted in the middle of the secondary circuit of the oscillation transformer are connected through two small inductance coils with a relay and a single cell. this relay in turn actuates a morse printer by means of a local battery. the two circuits of the oscillation transformer are tuned or syntonised to one another, and also to the similar circuit of the transmitting arrangement. when this is the case, the transmitter affects the co-resonant receiving arrangement, but will not affect any other similar arrangement, unless it is within a certain minimum range of distance. owing to the inductance of the oscillation transformer forming part of the receiving arrangements, the receiving circuit is, as before stated, very stiff or irresponsive; the sensitive tube is therefore not acted upon in virtue merely of the impact of the single wave against the aerial, but it needs repeated or accumulated effects of a great many waves, coming in proper time, to break down the coherer and cause the recording mechanism to act. an inspection of the diagram will show that as soon as the secondary electromotive force in the small oscillation transformer or jigger of the receiving instrument is of sufficient amplitude to break down the resistance of the coherer, the local cell in circuit with the relay can send a current through it and cause the relay to act and in turn make the associated telegraphic instrument record or sound. mr. marconi described in the above-mentioned paper some other arrangements for achieving the same result, but those mentioned all depend for their operation upon the construction of a receiving circuit on which the time-period of electrical oscillations is identical with that of a transmitting arrangement. by this means he showed experiments during the reading of his paper, illustrating the fact that two pairs of transmitting and receiving arrangements could be so syntonised that each receiver responded only to its particular transmitter and not to the other. with arrangements of substantially the same nature, he made experiments in the autumn of 1900 between niton, in the isle of wight, and bournemouth, a distance of about thirty miles, in which independent messages were sent and received on the same aerial. dr. slaby and count von arco, working in germany, have followed very much on the same lines as mr. marconi, though with appliances of a somewhat different nature. as constructed by the general electric company, of berlin, the slaby-arco syntonic system of hertzian telegraphy is arranged in one form as follows:--the transmitter consists of a vertical rod like a lightning conductor, say, 100 or 150 feet in height. at a point six or nine feet above the ground, a connection is made to a spark ball (see fig. 24), and the corresponding ball is connected through a variable inductance with one terminal of a condenser, the other terminal of which is connected to the earth. the two spark balls are connected to an induction coil, or alternating current transformer, and by variation of the inductance and capacity the frequency is so arranged that the wave-length corresponding to it is equal to four times the length of that portion of the aerial which is above the spark ball connection. the method by which this tuning is achieved is to insert in the portion of the aerial below the spark balls, between it and the earth, a hot wire ammeter of some form. it has already been shown that in the case of such an earthed aerial, when electrical oscillations are set up in it, there is a potential node at the earth and a potential anti-node or loop at the summit, if it is vibrating in its fundamental manner; also, there is a node of current at the summit of the aerial and an anti-node at the base. this amounts to saying that the amplitude of the potential vibrations is greatest at the top end of the aerial, and the amplitude of the current vibrations is greatest at the bottom or earthed end. accordingly, the inductance and capacity of the lateral branch of the transmitter is altered until the hot wire ammeter in the base of the aerial shows the largest possible current. [illustration: fig. 24.--slaby-arco syntonic transmitter and receiver. i, induction coil; m, multiplier; b, battery; a, aerial; f, filings tube; r, relay; e, earth plate; c, condenser.] the corresponding receiver is constructed in a very similar manner. a lightning conductor or long vertical rod of the same height as the transmitting aerial is set up at the receiving station, and at a point six or nine feet from the ground a circuit is taken off, consisting of a wire loosely coiled in a spiral, the length of which is nearly equal to, although a little shorter than, the height of the vertical wire above the point of connection. the outer end of this loose spiral is connected to one terminal of the coherer tube, and the other terminal of the coherer is connected to the earth through a condenser of rather large capacity. the terminals of this last condenser are short-circuited by a relay and a single cell. when the adjustments are properly made, it is claimed that the receiver responds only to waves coming from its own syntonised or tuned transmitter. in this case the length of the receiving aerial above the point of junction with the coherer circuit is one quarter the length of the wave. a variation of the above arangements consists in making this lateral circuit equal in length to one-half of a wave, and connecting the coherer to its centre through a condenser to the earth. the outer end of this lateral circuit is also connected to the earth (see fig. 24).[64] dr. slaby claims that this arrangement is not affected by atmospheric electricity, and that the complete and direct earthing of the aerial and also in the second arrangement, of the receiver of the outer end of the lateral conductor, conduces to preserve the receiver immune from any electrical disturbances except those having a period to which it is tuned. [illustration: fig. 25.--lodge-muirhead syntonic receiver. i, induction coil; s, spark gap; a, aerial; cc, condensers; e, earth plate; r, relay; l, variable inductance; f, filings tube; b, battery.] a method has also been arranged by him for receiving on the same aerial two messages from different transmitting stations simultaneously. in this case, two lateral wires of different lengths are connected to the receiving aerial, and to the outer end of each of these is connected a coherer tube, the other end of which is earthed through a condenser. one of these lateral wires is made equal, or nearly equal, in length to the aerial, and the other is made longer to fulfil the following condition.[65] if we call h the height of the receiving aerial above point of junction of the lateral wires, then the length of one lateral wire is made equal to h, and the height of the aerial is adjusted to be equal to one-quarter of the wave length of one incident wave. the other lateral wire may then be made of a length equal to one-third of h, and it will then respond to the first odd harmonic of that wave, of which the fundamental is in syntony with the vertical wire. by suitably choosing the relation between the wave-lengths of the two transmitting stations, it is possible to receive in this manner two different messages at the same time on the same aerial. subsequently to the date of the above-mentioned demonstration of multiplex wireless telegraphy by mr. marconi an exhibition of a similar nature was given by professor slaby in a lecture given in berlin on december 22, 1900.[66] both the above-described syntonic systems of mr. marconi and dr. slaby are "earthed" systems, but arrangements for syntonic telegraphy have been devised by sir oliver lodge and professor braun which are "non-earthed." sir oliver lodge and dr. muirhead have devised also syntonic systems. according to their last methods, the systonic transmitting and receiving arrangements are as shown in fig. 25.[67] on examining the diagrams it will be seen that the secondary terminals of the induction coil are, as usual, connected to a pair of spark balls, and that these spark balls are connected by a condenser and by a variable inductance. one terminal of the condenser is earthed through another condenser of large capacity, and the remaining terminal of the first condenser is connected to an aerial. it should, therefore, be borne in mind in dealing with electrical oscillations that a condenser of sufficient capacity is practically a conductor, and an inductance coil of sufficient inductance is practically a non-conductor. hence the insertion of a large capacity in the path of the aerial wire is no advantage whatever and makes no essential difference in the arrangement. in order to obtain any powerful radiation, the length of the aerial, or sky wire, as they call it, must be so adjusted that its length is one-quarter the wave-length corresponding to the oscillation circuit, consisting of the condenser and variable inductance. the receiving arrangement consists of a similar sky wire or aerial earthed through a condenser of large capacity and having in the portion above this last condenser another condenser of similar capacity. at the earthed side of this last condenser a connection is made to a resonant circuit, consisting of a variable inductance, and another condenser and a sensitive metallic filings tube of the branly type; also a portion of this resonant circuit is shunted by another consisting of a battery and telegraphic relay, as shown in the diagram. the circuit, including the coherer, is tuned to its own aerial and also to that of the transmitting circuit, and under these circumstances trains of waves thrown off at the transmitting aerial will sympathetically affect the receiving aerial. there is nothing in the arrangement which specially calls for notice. it is simply a variation of other known forms of syntonic transmitter and receiver, and possesses all the advantages and disadvantages attaching to such electrical syntonic methods. professor braun's syntonic system, the receiver and transmitter of which have been described, is also in one form a non-earthed system. innumerable other patentees have taken out patents for devices which are modifications in small degree of the above arrangements. it may be well to note at this point the disadvantages that are possessed by any form of coherer as a telegraphic kumascope in connection with proposed arrangements for the isolation of hertzian wave stations. all the detectors of the coherer type really depend for their actuation upon electromotive force; that is to say, upon the application to the terminals of the detector of a certain electromotive force. although there may be no sharp and defined critical electromotive force, yet, nevertheless, as a matter of fact, if the electromotive force applied exceeds a certain value, then the detector passes suddenly from one state of conductivity to another. it may be of great conductivity, as in the case of the branly coherer, or of lesser conductivity, as in the case of the so-called anti-coherers, of which the schã¤fer kumascope may be taken as a type. accordingly, when these instruments are subjected to a train of waves, each individual group of which is damped, their operation is largely governed by the fact that if the first wave or oscillation set up in the receiving circuit is powerful enough to break down the coherer, then the receiving mechanism acts, no matter whether the first impulse is followed by others or not. in comparison with so-called coherers, those depending upon the changes in the magnetisation of iron by electrical oscillations certainly have an advantage, because this is a process which requires the application of alternating electric currents decreasing in strength for a certain time; and it is found, therefore, that the magnetic receivers do not require to be associated with such a stiff or irresponsive resonant circuit to confine their indications to oscillations or waves of one definite period, and that they lend themselves much more perfectly to the work of "tuning" or syntonising stations than do those kumascopes depending upon the contact or coherer principle. we may then glance at the alternative solutions of the problem offered by other investigators. m. blondel has proposed to effect the syntonisation of two stations, not by syntonising the receiver for the exceedingly high-frequency oscillations of the individual electric waves, but to syntonise it for the much lower frequency, corresponding to that of the intervals between the groups of waves. thus, for instance, if an ordinary simple transmitting aerial is set up, the production of sparks between the spark balls results in the emission of short trains of waves, each of which may consist of half a dozen or more individual waves, the time of production of the whole group being very small compared with the interval between the groups. m. blondel proposes, however, to syntonise the receiver, not for the high-frequency period of the waves themselves, which may be reckoned in millions per second, but for the low-frequency period between the groups of waves, which is reckoned in hundreds per second. thus, for instance, if sparks are made at the rate of fifty or a hundred per second, they can be made to actuate the telephone receiver and so produce in the telephone a sound corresponding to a frequency of 50 or 100; in other words, to make a low musical note or hum. this continuous sound can be cut up, by means of a key placed in the primary circuit of the transmitting arrangement, into long or short periods, and hence the letters of the alphabet signal. m. blondel's arrangements comprise a mercadier's monotone telephone and either a coherer or a particular form of vacuum tube as a kumascope. on august 16, 1898, m. blondel deposited with the academy of sciences in paris a sealed envelope containing a description of his improvements in syntonic wireless telegraphy, which was opened on may 19, 1900.[68] the arrangement of the receiving apparatus was as follows:--a single-battery cell keeps a condenser charged until the kumascope is rendered conductive by the oscillations coming down the aerial; and under these circumstances the condenser discharges through the telephone and causes a tick to be heard in it. if the trains of waves are at the rate of 50 or 100 per second, these small sounds run together into a musical note, and this continuous hum can be cut up into long and short spaces, in accordance with the morse alphabet signals. the telephone must not be an ordinary telephone, capable of being influenced by any frequency, but be one which responds only to a particular note, and under these conditions the receiving arrangement is receptive only when the trains of waves arrive at certain regular predetermined intervals, corresponding with the tone to which the telephone is sensitive. * * * * * a number of more or less imperfect arrangements, having the isolation of communications for their object, have been devised or patented, which are dependent upon the use of several aerials, each supposed to be responsive only to a particular frequency; and attempts have been made to solve the problem of isolation by mm. tommasi, tesla, jegon, tissot, ducretet and others. we may then pass on to notice the attempts that have been made to secure isolation by a plan which is not dependent on electrical syntony. one of these, which has the appearance of developing into a practical solution of the problem, is that due to anders bull.[69] in the first arrangements proposed by this inventor, a receiver is constructed which is not capable of being acted upon merely by a single wave or train of waves or even a regularly-spaced train of electric waves, but only by a group of wave trains which are separated from one another by certain unequal, predetermined intervals of time. thus, for instance, to take a simple instance, the transmitting arrangements are so devised as to send out groups of electric waves, these wave trains following one another at time intervals which may be represented by the numbers 1, 3 and 5; that is to say, the interval which elapses between the second and third is three times that between the first two, and the interval between the fourth and fifth is five times that between the first two. this is achieved by making five electric oscillatory sparks with a transmitter of the ordinary kind, the intervals between which are settled by the intervals between holes punched upon strips of paper, like that used in a wheatstone automatic telegraphic instrument. it will easily be understood that by a device of this kind, groups of sparks can be made, say, five sparks rapidly succeeding each other, but not at equal intervals of time. one such group constitutes the morse dot, and two or three such groups succeeding one another very quickly constitute the morse dash. these waves, on arriving at the receiving station, are caused to actuate a punching arrangement by the intermediation of a coherer or other kumascope, and to punch upon a uniformly moving strip of paper holes, which are at intervals of time corresponding to the intervals between the sparks at the transmitting station. this strip of paper then passes through another telegraphic instrument, which is so constructed that it prints upon another strip a dot or a dash, according to the disposition of the holes on the first strip. accordingly, taken as a whole, the receiving arrangement is not capable of being influenced so as to print a telegraphic sign except by the operation of a series of wave trains succeeding one another at certain assigned intervals of time. an improvement has been lately described by the same inventor,[70] in which the apparatus used, although more complicated, performs the same functions. at each station two instruments have to be employed; at the transmitting station one to effect the conversion of morse signals into the properly arranged series of wave trains, and at the receiving station an instrument to effect the re-conversion of the series of wave trains into the morse signals. these are called respectively the dispenser and the collector. the details of the arrangements are somewhat complicated, and can only be described by the aid of numerous detailed drawings, but the inventor states that he has been able to carry on hertzian wave telegraphy by means of these arrangements for short distances. moreover, the method lends itself to an arrangement of multiplex telegraphy, by sending out from different transmitters signals which are based upon different arrangements of time intervals between the electric wave trains. although this method may succeed in preventing a receiving arrangement from being influenced by vagrant waves or waves not intended for it, yet an objection which arises is that there is nothing to prevent any one from intercepting these wave trains, and with a little skill interpreting their meaning. thus, if the record were received in the ordinary way on a simple receiver, corresponding to a morse dot would be printed five dots at unequal intervals, and corresponding to a morse dash would be printed two such sets of five dots. a little skill would then enable an operator to interpret these arbitrary signals. on the other hand, the inventor asserts that he can overcome this difficulty by making intervals of time between the impulses in the series so long that the latter become longer than the intervals between each of the series of waves which are despatched in continuous succession when the key is pressed for a dash. in this case, when telegraphing, the series of dots would overlap and intermingle with each other in a way which would make the record unintelligible if received in the usual manner, but would be perfectly legible if received and interpreted by a receiver adapted for the purpose. another way of obliterating the record, as far as outsiders are concerned, is to interpolate between the groups of signals an irregular series of dots--_i.e._, of wave trains--which would affect an ordinary coherer, and so make an unintelligible record on an ordinary receiver, but these dots are not received or picked up by the appropriate selecting instrument used in the anders bull system. the matter most interesting to the public at the present time is the long-distance telegraphy by hertzian waves to the accomplishment of which mr. marconi has devoted himself with so much energy of late years. everyone, except perhaps those whose interests may be threatened by his achievements, must accord their hearty admiration of the indomitable perseverance and courage which he has shown in overcoming the immense difficulties which have presented themselves. five years ago he was engaged in sending signals from alum bay, in the isle of wight, to bournemouth, a distance of twelve or fourteen miles; and to-day he has conquered twice that number of hundred miles and succeeded in sending, not merely signals, but long messages of all descriptions over three thousand miles across the atlantic. critics there are in abundance, who declare that the process can never become a commercial one, that it will destroy short-distance hertzian telegraphy, or that the multiplication of long-distance stations will end in the annihilation of all hertzian wave telegraphy. no one, however, can contemplate the history of any development of applied science without seriously taking to heart the lesson that the obstacles which arise and which prove serious in any engineering undertaking are never those which occur to armchair critics. sometimes the seemingly impossible proves the most easy to accomplish, whilst difficulties of a formidable nature often spring up where least expected. the long-distance transmission is a matter of peculiar interest to the author of these articles, because he was at an early stage in connection with it invited to render mr. marconi assistance in the matter.[71] the particular work entrusted to him was that of planning the electrical engineering arrangements of the first power station erected for the production of electric waves for long-distance hertzian wave telegraphy at poldhu, in cornwall. when mr. marconi returned from the united states in the early part of 1900, he had arrived at the conclusion that the time had come for a serious attempt to accomplish wireless telegraphy across the atlantic. up to that date the project had been an inventor's dream, much discussed, long predicted, but never before practically taken in hand. the only appliances, moreover, which had been used for creating hertzian waves were induction coils or small transformers, and the greatest distance covered, even by mr. marconi himself, had been something like 150 miles over sea. accordingly, to grapple with the difficulty of creating an electric wave capable of making itself felt at a distance of 3,000 miles, even with the delicate receiving appliances invented by mr. marconi, seemed to require the means of producing at least four hundred times the wave-energy that had been previously employed. the author was, therefore, requested to prepare plans and specifications for an electric generating plant for this purpose, which would enable electrical oscillations to be set up in an aerial on a scale never before accomplished. this work involved, not merely the ordinary experience of an electrical engineer, but also the careful consideration of many new problems and the construction of devices not before used. every step had to be made secure by laboratory experiments before the responsibility could be incurred of advising on the nature of the machinery and appliances to be ordered. many months in the year 1901 were thus occupied by the author in making small-scale experiments in london and in superintendence of large-scale experiments at the site of the first power station at poldhu, near mullion, in cornwall, before the plant was erected and any attempt was made by mr. marconi to commence actual telegraphic experiments. as this work was of a highly confidential nature, it is obviously impossible to enter into the details of the arrangements, either as made by the writer in the first instance, or as they have been subsequently modified by mr. marconi. the design of the aerial and of the oscillation transformers and many of the details in the working appliances are entirely due to mr. marconi, but as a final result, a power plant was erected for the production of hertzian waves on a scale never before attempted. the utilisation of 50 h.p. or 100 h.p. for electric wave production has involved dealing with many difficult problems in electrical engineering, not so much in novelty of general arrangement as in details. it will easily be understood that leyden jars, spark balls and oscillators, which are quite suitable for use with an induction coil, would be destroyed immediately if employed with a large alternating-current plant and immensely powerful transformers. [illustration: fig. 26.--wooden towers supporting the marconi aerial at poldhu power station, cornwall, england.] in the initial experiments with this machinery and in its first working there was very considerable risk, owing to its novel and dangerous nature; but throughout the whole of the work from the very beginning, no accident of any kind has taken place, so great have been the precautions taken. the only thing in the nature of a mishap was the collapse of a ring of tall masts, erected in the first place to sustain the aerial wires, but which now have been replaced by four substantial timber towers, 215 feet in height, placed at the corners of a square, 200 feet in length. these four towers sustain a conical arrangement of insulated wires (see fig. 26) which can be used in sections and which constitute the transmitting radiator or receiver, as the case may be. each of these wires is 200 feet in length and formed of bare stranded wire. at the outset, there was much uncertainty as to the effect of the curvature of the earth on the propagation of a hertzian wave over a distance of many hundreds of miles. in the case of the atlantic transmission between the station at poldhu in cornwall and that at cape cod in massachusetts, u.s.a., we have two stations separated by about 45 degrees of longitude on a great circle, or one-eighth part of the circumference of the world. in this case, the versine of the arc or height of the sea at the half-way point above the straight line or chord joining the two places is 300 miles. the question has recently attracted the attention of several eminent mathematical physicists. the extent to which a free wave propagated in a medium bends round any object or is diffracted depends on the relation between the length of the wave and the size of the object. thus, for instance, an object the size of an orange held just in front of the mouth does not perceptibly interfere with the propagation of the waves produced by the speaking or singing voice, because these are from two to six feet in length: but if arrangements are made by means of a galton whistle to produce air waves half an inch in length, then an obstacle the size of an orange causes a very distinct acoustic shadow. the same thing is true of waves in the ether. the amount of bending of light waves round material objects is exceedingly small, because the average length of light waves is about one-fifty-thousandth part of an inch. in the case of hertzian wave telegraphy, we are, however, dealing with ether waves many hundreds of feet in length, and the waves sent out from poldhu have a wave-length of a thousand feet or more, say, one-fifth to one-quarter of a mile. the distance, therefore, between poldhu and cape cod is only at most about twelve thousand wave-lengths, and stands in the same relation to the length of the hertzian wave used as does a body the diameter of a pea to the wave-length of yellow light. there is unquestionably a large amount of diffraction or bending of the electric wave round the earth, and, proportionately speaking, it is larger than in the case of light waves incident on objects of the same relative size. quite recently mr. h. m. macdonald (see _proc._ roy. soc., london, vol. lxxi., p. 251) has submitted the problem to calculation, and has shown that the power required to send given electric waves 3,000 miles along a meridian of the earth is greater than would be required to send them over the same distance if the sea surface were flat in the ratio of 10 to 3. hence the rotundity of the earth does introduce a very important reduction factor, although it does not inhibit the transmission. mr. macdonald's mathematical argument has, however, been criticised by lord rayleigh and by m. h. poincarã© (see _proc._ roy. soc., vol. lxxii., p. 40, 1903). the accomplishment of very long distances by hertzian wave telegraphy is, however, not merely a question of power, it is also a question of wave-length. having regard, however, to the possibility that the propagation which takes place in hertzian wave telegraphy is not that simply of a free wave in space, but the transmission of a semi-loop of electric strain with its feet tethered to the earth, it is quite possible that if it were worth while to make the attempt, an ether disturbance could be made in england sufficiently powerful to be felt in new zealand. leaving, however, these hypothetical questions and matters of pure conjecture, we may consider some of the facts which have resulted from mr. marconi's long-distance experiments. one of the most interesting of these is the effect of daylight upon the wave propagation. in one of his voyages across the atlantic, when receiving signals from poldhu on board the s.s. _philadelphia_, he noticed that the signals were received by night when they could not be detected by day.[72] in these experiments mr. marconi instructed his assistants at poldhu to send signals at a certain rate from 12 to 1 a.m., from 6 to 7 a.m., from 12 to 1 p.m., and from 6 to 7 p.m., greenwich mean time, every day for a week. he has stated that on board the _philadelphia_ he did not notice any apparent difference between the signals received in the day and those received at night until after the vessel had reached a distance of 500 statute miles from poldhu. at distances of over 700 miles, the signals transmitted during the day failed entirely, while those sent at night remained quite strong up to 1,551 miles, and were clearly decipherable up to a distance of 2,099 miles from poldhu. mr. marconi also noted that at distances of over 700 miles, the signals at 6 a.m., in the week between february 23 and march 1, were quite clear and distinct, whereas by 7 a.m. they had become weak almost to total disappearance. this fact led him at first to conclude that the cause of the weakening was due to the action of the daylight upon the transmitting aerial, and that as the sun rose over poldhu, so the wave energy radiated, diminished, and he suggested as an explanation the known fact of the dissipating action of light upon a negative charge. although the facts seem to support this view, another explanation may be suggested. it has been shown by professor j. j. thomson that gaseous ions or electrons can absorb the energy of an electric wave, if present in a space through which waves are being transmitted.[73] if it be a fact, as suggested by professor j. j. thomson, that the sun is projecting into space streams of electrons, and if these are continually falling in a shower upon the earth, in accordance with the fascinating hypothesis of professor arrhenius, then that portion of the earth's atmosphere which is facing the sun will have present in it more electrons or gaseous ions than that portion which is turned towards the dark space, and it will therefore be less transparent to long hertzian waves.[74] in other words, clear sunlit air, though extremely transparent to light waves, acts as if it were a slightly turbid medium for long hertzian waves. the dividing line between that portion of the earth's atmosphere which is impregnated with gaseous ions or electrons is not sharply delimited from the part not so illuminated, and there may be, therefore, a considerable penetration of these ions into the regions which i may call the twilight areas. accordingly, as the earth rotates, a district in which hertzian waves are being propagated is brought, towards the time of sunrise, into a position in which the atmosphere begins to be ionised, although far from as freely as is the case during the hours of bright sunshine. mr. marconi states that he has found a similar effect between inland stations, signals having been received by him during the night between poldhu and poole with an aerial the height of which was not sufficient to receive them by day. it has been found, however, that the effect simply amounts to this, that rather more power is required by day than by night to send signals by hertzian waves over long distances. some interesting observations have also been made by captain h. b. jackson, r.n.,[75] on the influence of various states of the atmosphere upon hertzian wave telegraphy. these experiments were all made between ships of the british royal navy, furnished with hertzian wave telegraphy apparatus on the marconi system. some of his observations concerned the effect of the interpositon of land between two ships. he found that the interposition of land containing iron ores reduced the signalling distances, compared with the maximum distance at open sea, to about 30 per cent. of the latter; whilst hard limestone reduced it to nearly 60 per cent. and soft sandstone or shale to 70 per cent. these results show that there is a considerable absorption effect when waves of certain wave-length pass through or over hard rocks containing iron ores. it would be interesting to know, however, whether this reduction was in any degree proportional to the dryness or moisture of the soil. earth conductivity is far more dependent upon the presence or absence of moisture than upon the particular nature of the material which composes it other than water. the observations of captain jackson, however, only confirm the already well-known fact that hertzian waves, as employed in the marconi system of wireless telegraphy, within a certain range of wave-length, are considerably weakened by their passage through land, over land or round land. in some cases he noticed that quite sharp electric shadows were produced by rocky promontories projecting into the line of transmission. his attention was also directed (_loc. cit._) to the more important matter of the effect of atmospheric electrical conditions upon the transmission. the effect of all lightning discharges, whether visible or invisible, is to make a record on the telegraphic receiver. on the approach of an atmospheric electrical disturbance towards the receiving station on a ship, the first visible indications generally are the recording of dots at intervals from a few minutes to a few seconds on the telegraphic tape. captain jackson states that the most frequent record is that of three dots, the first being separated from the other two by a slight interval like the letters e i on the morse code, and this is the sign most frequently recorded by distant lightning. but in addition to this, dashes are recorded and irregular signs, which, however, sometimes spell out words in the morse code. he noted that these disturbances are more frequent in summer and autumn than in winter and spring, and in the neighbourhood of high mountains more than in the open sea. in settled weather, if present, they reach their maximum between 8 p.m. and 10 p.m., and frequently last during the whole of the night, with a minimum of disturbance between 9 a.m. and 1 p.m. another important matter noted by captain jackson is the shorter distance at which signals can usually be received when any electrical disturbances are present in the atmosphere, compared with the distance at which they can be received when none are present. this reduction in signalling distance may vary from 20 to 70 per cent, of that obtainable in fine weather. it does not in any way decrease with the number of lightning flashes, but rather the reverse, the loss in signalling distance generally preceding the first indications on the instrument of the approaching electrical disturbance. it is clear that these observations fit in very well with the theory outlined above, viz., that the atmosphere when impregnated with free electrons or negatively-charged gaseous ions is more opaque to hertzian waves than when they are absent. captain jackson gives an instance of ships whose normal signalling distance was 65 miles, failing to communicate at 22 miles when in the neighbourhood of a region of electrical disturbance. these effects in the case of wireless telegraphy have their parallel in the disturbances caused to telegraphy with wires by earth currents and magnetic storms. another effect which he states reduces the usual maximum signaling distance is the presence of material particles held in suspension by the water spherules in moist atmosphere. the effect has been noticed in the mediterranean sea when the sirocco wind is blowing. this is a moist wind conveying dust and salt particles from the african coast. a considerable reduction in signalling distance is produced by its advent. another interesting observation due to captain jackson is the existence of certain zones of weak signals. thus, for instance, two ships at a certain distance may be communicating well; if their distance increases, the signalling falls off, but is improved again at a still greater distance. he advances an ingenious theory to show that this fact may be due to the interference between two sets of waves sent out by the transmitter having different wave-lengths. finally, in the paper referred to, he emphasises the well-known fact that long-distance signalling can only be accomplished by the aid of an aerial wire and a "good earth." summing up his results, he concludes: (1) that intervening land of any kind reduces the practical signalling distance between two ships or stations, compared with that which would be obtainable over the open sea, and that this loss in distance varies with the height, thickness, contour, and nature of the land; (2) material particles, such as dust and salt, held in suspension in a moist atmosphere also reduce the signalling distance, probably by dissipating and absorbing the waves; (3) that electrical disturbances in the atmosphere also act most adversely in addition to affecting the receiving instrument and making false signals or _strays_, as they are called; (4) that with certain forms of transmitting arrangement, interference effects may take place which have the result of creating certain areas of silence very similar to those which are observed in connection with sound signals from a siren. it is clear, therefore, from all the above observations, that hertzian-wave telegraphy taking place through the terrestrial atmosphere is not by any means equivalent to the propagation of a wave in free or empty space; and that just as the atmosphere varies in its opacity to rays of light, sometimes being clear and sometimes clouded, so it varies from time to time in transparency to hertzian waves, the cause of this variation in transparency probably being the presence in the atmosphere of negatively-charged corpuscles or electrons. if there are present in the atmosphere at certain times "clouds of electrons" or "electronic fogs," these may have the effect of producing a certain opacity, or rather diminution in transparency to hertzian waves, just as water particles do in the case of sunlight. we may, therefore, in conclusion, review a few of the outstanding problems awaiting solution in connection with hertzian wave wireless telegraphy. in spite of the fact that this new telegraphy has not been accorded a very hearty welcome by the representatives of official or established telegraphy in great britain, it has reached a point, unquestionably owing to mr. marconi's energy and inventive power, at which it is bound to continue its progress. but that progress will not be assisted by shutting our eyes to facts. many problems of great importance remain to be solved. we have not yet reached a complete solution of all the difficulties connected with isolation of stations. in the next place, the question of localising the source of the signals and waves is most important. our kumascopes and receiving appliances at present are like the rudimentary eyes of the lower organisms, which are probably sensitive to mere differences in light and darkness, but which are not able to _see_ or _visualise_, in the sense of locating the direction and distance of a radiating or luminous body. just as we have, as little children, to learn to see, so a similar process has to be accomplished in connection with hertzian telegraphy, and the accomplishment of this does not seem by any means impossible or even distant. we are dealing with hemispherical waves of electric and magnetic force, which are sent out from a certain radiating centre, and in order to localise that centre we have to determine the position of the plane of the wave and also the curvature of the surface at the receiving point. something, therefore, equivalent to a range finder in connection with light is necessary to enable us to locate the distance and the direction of the radiant point. lastly, there are important improvements possible in connection with the generation of the waves themselves. at the present moment, our mode of generating hertzian waves involves a dissipation of energy in the form of the light and heat of the spark. just as in the case of ordinary artificial illuminants, such as lamps of various kinds, we have to manufacture a large amount of ether radiation of long wave length, which is of no use to us for visual purposes--in fact, creating ninety-five per cent, of dark and useless waves for every five per cent. of luminous or useful waves--so in connection with present methods of generating hertzian waves, we are bound to manufacture by the discharge spark a large amount of light and heat rays which are not wanted, in order to create the hertzian waves we desire. it is impossible yet to state precisely what is the efficiency, in the ordinary sense of the word, of a hertzian wave radiator; how much of the energy imparted to the aerial falls back upon it and contributes to the production of the spark, and how much is discharged into the ether in the form of a wave. nothing is more remarkable, however, than the small amount of energy which, if properly utilised in electric wave making, will suffice to influence a sensitive receiver at a distance of even one or two hundred miles. suppose, for instance, that we charge a condenser consisting of a battery of leyden jars, having a capacity of one seventy-fifth of a microfarad, to a potential of 15,000 volts; the energy stored up in this condenser is then equal to 1â·5 joules, or a little more than one foot-pound. if this energy is discharged in the form of a spark five millimetres in length through the primary coil of an oscillation transformer, associated with an aerial 150 feet in height, the circuits being properly tuned by mr. marconi's method, then such an aerial will affect, as he has shown, one of mr. marconi's receivers, including a nickel silver filings coherer tube, at a distance of over two hundred miles over sea. consider what this means. the energy stored up in the leyden jars cannot all be radiated as wave energy by the aerial, probably only half of it is thus radiated. hence the impartation to the ether at any one locality of about half a foot-pound of energy in the form of a long hertzian wave is sufficient to affect sensitive receivers situated at any point on the circumference of a circle of 200 miles radius described on the open sea. hertzian wave telegraphy is sometimes described as being extravagant in power, but, as a matter of fact, the most remarkable thing about it is the small amount of power really involved in conducting it. on the other hand, hertzian wave manufacture is not altogether a matter of power. it is much more dependent upon the manner in which the ether is struck. just as half an ounce of dynamite in exploding may make more noise than a ton of gunpowder, because it hits the air more suddenly, so the formation of an effective wave in the ether is better achieved by the right application of a small energy than by the wrong mode of application of a much larger amount. if we translate this fact into the language of electronic theory, it amounts simply to this. it is the electron alone which has a grip of the ether. to create an ether wave, we have to start or stop crowds of electrons very suddenly. if in motion, their motion implies energy, but it is not only their energy which is concerned in the wave making, but the acceleration, positive or negative--_i.e._, the quickness with which they are started or stopped. it is possible we may discover in time a way of manufacturing long ether waves without the use of an electric spark, but at present we know only one way of doing this--viz., by the discharge of a condenser, and in the discharge of large condensers of very high potentials it is difficult to secure that extreme suddenness of starting the discharge which we can do in the case of smaller capacities and voltages. how strange it is that the discharge of a leyden jar studied so profoundly by franklin, henry, faraday, maxwell, kelvin and lodge should have become an electrical engineering appliance of great importance! whilst there are many matters connected with the commercial aspect of hertzian wave telegraphy with which we are not here concerned, there is one on which a word may properly be said. the ability to communicate over long distances by hertzian waves is now demonstrated beyond question, and even if all difficulties are not overcome at once, it has a field of very practical utility, and may even become of national importance. under these circumstances, we may consider whether it is absolutely necessary to place the signalling stations so near the coast. the greater facility of transmission over sea has already been discussed and explained, but in time of war, the masts and towers which are essential at present in connection with transmitting stations could be wrecked by shot or shell from an enemy's battleship at a distance of five or six miles out at sea, and would certainly be done within territorial waters. should not this question receive attention in choosing the location of important signalling stations? for if they can, without prejudice to their use, be placed inland by a distance sufficient to conceal them from sight, their value as a national asset in time of war might be greatly increased. it has been often contended that whilst cables could be cut in time of war no one can cut the ether; but wireless telegraph stations in exposed situations on high promontories, where they are visible for ten to fifteen miles out at sea and undefended by any forts, could easily be destroyed. the great towers which are essential to carry large aerials are a conspicuous object for ten miles out at sea; and a single well-placed shell from a six-inch gun would wreck the place and put the station completely out of use for many months. hence if oceanic telegraphy is ever to be conducted in a manner in which the communication will be inviolable or, at any rate, not be capable of interruption by acts of war, the careful selection of the sites for stations is a matter of importance. a small station consisting of a single 150-foot mast and a wooden hut can easily be removed or replaced, but an expensive power station, the mere aerial of which may cost several thousand pounds, is not to be put up in a short time.[76] meanwhile, whatever may be the future achievements of this new _supermarine_ wireless telegraphy conducted over long distances, there can be no question as to its enormous utility and present value for intercommunication between ships on the ocean and ships and the shore. at the present time, there are some forty or more of the transatlantic ocean liners and many other ships equipped with this hertzian wave wireless telegraph apparatus on the marconi system. provided with this latest weapon of applied science, they are able to chat with one another, though a hundred miles apart on the ocean, with the ease of guests round a dinner table, to exchange news or make demands for assistance. ships that pass in the night, and speak each other in passing- only a signal shown, and a distant voice in the darkness; so, on the ocean of life, we pass and speak one another, only a look and a voice, then darkness again, and a silence. abundant experience has been gathered to show the inexpressible value of this means of communication in case of accident, and it can hardly be doubted that before long the possession of this apparatus on board every passenger vessel will be demanded by the public, even if not made compulsory. although the privacy of an ocean voyage may have been somewhat diminished by this utilisation of ether waves, there is a vast compensation in the security that is thereby gained to human life and property by this latest application of the great energies of nature for the use and benefit of mankind. geo. tueker, printer, salisbury court, fleet street, london. [1] this series of articles is based on the cantor lectures delivered before the society of arts, london, in march, 1903. the lectures were attended by many of the leading british scientific men and electrical engineers, and attracted wide attention as the most complete and authoritative statement hitherto made of wireless telegraphy. in writing the articles for the "popular science monthly," the author has omitted advanced technicalities in order that the substance may be suitable for the general reader.--editor. [2] for a more detailed account of this hypothesis, the reader is referred to an article by the present writer, entitled "the electronic theory of electricity," published in the "popular science monthly" for may, 1902. [3] see j. j. thomson, "recent researches in electricity and magnetism," chap. i., p. 16. [4] see o. heaviside, "electromagnetic theory," vol. i., p. 54. [5] wiedemann's _annalen_, 36, p. 1, 1889; or in his republished papers, "electric waves," p. 137, english translation by d. e. jones. [6] the fraction 7/22 here denotes a stranded wire formed of seven strands, each single wire having a diameter expressed by the number 22 on the british standard wire gauge. [7] g. marconi, "syntonic wireless telegraphy," _journal_ of the society of arts, vol. xlix., p. 501, 1901. [8] instruction for the manufacture of large induction coils may be obtained from a "treatise on the construction of large induction coils," by a. t. hare. (methuen & co., london.) also see vol. ii. of "the alternate-current transformer," by j. a. fleming, chap. i. ("the electrician" printing and publishing co., 1, 2 and 3, salisbury-court, fleet-street, london, e.c.) [9] see "the alternate-current transformer," by j. a. fleming. vol. i., p. 184. [10] du moncel states that macgauley of dublin independently invented the form of hammer break as now used. see "the alternate-current transformer," vol. ii. chap. i. j. a. fleming. [11] see professor j. trowbridge, "on the induction coil" _phil. mag._, april, 1902 vol. iii., series 6, p. 393. [12] see dr. wehnelt's article in the _elektrotechnische zeitschrift_, january, 1899. [13] see _the electrician_, vol. xlii., 1899, pp. 721, 728, 731, 732 and 841; communications from mr. campbell swinton, professor s. p. thompson, dr. marchant, the author and others; also p. 864, same volume, for a leader on the subject; also p. 870, letters by m. blondel and professor e. thomson. see also _the electrician_, vol. xliii., p. 5, 1899, extracts from a paper by p. barry; _comptes rendus_, april, 1899. see also the _electrical review_, vol. xliv., p. 235, 1899, february 17. [14] see _the electrician_, vol. xlii., 1899. [15] for a discussion of the function of the condenser in an ordinary induction coil, see "the alternate-current transformer," by j. a. fleming. vol. ii., p. 51. [16] see lord rayleigh, _phil. mag._, december, 1901. [17] it has sometimes been stated that the spark balls must be _solid_ metal and no hollow, but this is a fallacy, and has been disproved by mr. c. a. chant. see "an experimental investigation into the skin effect in electrical oscillators," _phil. mag._, vol. iii., sec. 6, p. 425, 1902. [18] see _proc._ roy. soc., london, february 23 and april 12, 1860; or reprint of papers on electrostatics and magnetism, p. 247. [19] see _phil. mag._, august, 1902, vol. iv., p. 224, 6th series. mr. jervis-smith has also described an experiment to show how much the use of compressed air round a spark gap is of advantage in working an ordinary tesla coil. in his british specification, no. 12,039 of 1896, mr. marconi had long previously mentioned the use of compressed air round the spark gap. [20] this energy storage is at the rate of 44 foot-pounds per cubic foot of glass. this figure shows what a relatively small amount of energy is capable of being stored up in the form of electric strain in glass. in the case of an air condenser, it is only stored at the rate of 1 foot-pound per cubic foot. [21] see british specification no. 7,777 of 1900.--g. marconi. "improvements in apparatus for wireless telegraphy." [22] that this number really does represent the order of this oscillation frequency in an aerial has been shown by c. tissot, _comptes rendus_, 132, p. 763, march 25, 1901, by photographs taken of the oscillatory spark of a hertzian wave telegraphic transmitter. (see _science abstracts_, vol. iv., abs. 1,518.) he found frequencies from 0â·5 million to 1â·6 million. [23] the term "jigger" is one of those slang terms which contrive to effect a permanent attachment to various arts and crafts. similarly, the word "booster" is now used for a step-up or voltage-raising transformer or dynamo, inserted in series with an electric supply main. the word "boost" is a slang term signifying to raise or lift up. "to give a real good boost" is an expression for lending a helping hand. the term "jigger," in the same manner, is an adaptation of a seaman's term for hoisting tackle or lift. [24] the "earth" itself probably only conducts electrolytically. all such materials as sand, clay, chalk, etc., and most surface soils are fairly good insulators when very dry, but conduct in virtue of moisture present in them. [25] _the electrician_, vol. xl., p. 86 (leader). [26] british patent specification, c. and s. a. varley, no. 165, 1866. [27] see also _journal de physique_, vol. v., p. 573, 1886. [28] see _comptes rendus_, vol. cxi., p. 785; vol. cxii., p. 112, 1891; or _la lumiã¨re electrique_, vol. xl., pp. 301, 506, 1891; or _the electrician_, vol. xxvii., 1891, pp. 221, 448. [29] see _the electrician_, vol. xxix., 1892, pp. 397 and 432. [30] mr. w. b. croft, _proc._ phys. soc., vol. xii., p. 421. report of meeting on october 27, 1893. [31] see professor minchin, _proc._ phys. soc., november 24, 1893; or _the electrician_, vol. xxxii., 1893, p. 123. see also professor minchin, _phil mag._, january, 1894, vol. xxxvii., p. 90, "on the action of electromagnetic radiation on films containing metallic powders." [32] this lecture was afterwards published as a book, the first edition bearing the same title as the lecture--viz., "the work of hertz and some of his successors." in the second edition, published in 1898, an appendix was added (p. 59) containing "the history of the coherer principle," and the original title of the work had prefixed to it "signalling without wires." [33] see _the electrician_, vol. xxvii., p. 222, 1891. e. branly, "variations of conductivity under electrical influence." [34] see _the electrician_, vol. xl., p. 90. sir oliver lodge, "the history of the coherer principle." [35] see professor e. branly, "a sensitive coherer," _comptes rendus_, vol. cxxxiv., p. 1,187, 1902; or _science abstracts_, vol. v., p. 852, 1902. [36] this device of making the inter-electrode gap in a tubular filings coherer wedge-shaped has been patented again and again by various inventors. see german patent no. 116,113, class 21a, 1900. it has also been claimed by m. tissot. [37] see _the electrician_, vol. xxvii., 1891, p. 448. [38] _journal_ of the russian physical and chemical society, vol. xxviii., division of physics, part i., january, 1896. [39] see british patent specification no. 12,039, june 2, 1896. [40] british patent specification no. 19,710 of 1899. [41] _comptes rendus._, vol. cxxviii., p. 1,225, 1889; _science abstracts_, vol. ii., p. 521. [42] _il nuovo cimento_, vol. x., p. 279, 1899. [43] _wied ann._, vol. lxviii., p. 594, 1899; _science abstracts_, vol. ii., p. 757. [44] _comptes rendus_, vol. cxxx., p. 902, 1900; _science abstracts_, vol. iii., p. 615. [45] see _proc._ roy. soc., london, vol. lxxi., p. 402. [46] see report by capt. quintino bonomo, "telegrafia senza fili," rome, 1902; _l'elettricista_, ser. ii., vol. i., pp. 118, 173. [47] see royal institution, friday evening discourse, by mr. marconi, june 13, 1902; also _the electrician_, vol. xlix., p. 490; also a letter to _the times_ of july 3, 1902, by the marchese luigi solari. [48] see u.s.a. patent specification no. 700,161, may 24, 1900. [49] see e. marx, _phys. zeitschrift_, vol. ii., p. 249; _science abstracts_, vol. iv., p. 471. see also german patent specification no. 121,663, class 21a. [50] see "the scientific writings of professor joseph henry." [51] _phil. trans._ roy. soc., london, 1897, vol. clxxxix.a, p. 1. [52] see _proc._ roy. soc., london, june 12, 1902. "note on a magnetic detector for electric waves which can be employed as a receiver for space telegraphy," by g. marconi. [53] see u.s.a. patent specification no. 716,000, application of july 5, 1901. [54] see the _electrical review_, vol. xliv., 1899, may 26; _wied ann._, vol. lxviii., p. 92; or german patent specification no. 107,843. [55] u.s.a. patent specification no. 706,742, 1902. [56] see british patent specification, g. marconi, no. 12,039, june 2, 1896. [57] see g. marconi, british patent specification no. 12,326, of june 1, 1898. [58] see the _electrical review_, september 26, 1902, vol. li., p. 543. [59] there is a good deal of contradiction between various inventors on this point, some saying that "earthed" aerials obviate atmospheric electrical disturbances, and others that insulated aerials are in this respect superior. the truth appears to be that, neither form is absolutely free from risk of disturbance by this cause. [60] the capacity of an electrical circuit corresponds to the elastic pliability, or what is commonly called the elasticity, of a material substance, and the inductance to mass or inertia. hence capacity and inductance are qualities of an electric circuit which are analogous to the elasticity and inertia of such a body as a heavy spring. [61] see cantor lectures, on "electrical oscillations and electric waves," delivered before the society of arts, london, november 26, december 4, 10, 17, 1900. lecture i., p. 12, of reprint. [62] a fuller account of these experiments was given by the author in a letter to the london _times_ published on april 14, 1903. [63] see _journal_ of the society of arts, vol. xlix., p. 505. "syntonic wireless telegraphy," by g. marconi. [64] see german patent specifications, class 21a, no. 7,452 of 1900, and also no. 8,087 of 1901. [65] see german patent specification, class 21a, no. 7,498 of 1900, applied for november 9, 1900. the above-mentioned patent is subsequent in date to mr. marconi's experiments on the same subject. [66] see _the electrician_, january 18, 1900, vol. xlvi., p. 475. also reprint of a paper of professor a. slaby, "abgestimmte und mehrfache funkentelegraphie." [67] see british specification no. 11,348 of 1901. [68] see _comptes rendus_, may 21, 1900; rapports du congrã¨s international d'electricitã©, paris, 1900, p. 341. [69] see _the electrician_, vol. xlvi., p. 573, february 8, 1901. [70] see _the electrician_, vol. l., p. 418, january 2, 1903. [71] see mr. marconi's friday evening discourse at the royal institution, june 13, 1902; also _the electrician_, vol. xlix., p. 390. [72] see _proc._ roy. soc., june 12, 1902. "a note on the effect of daylight upon the propagation of electromagnetic impulses over long distances," by g. marconi. [73] see _phil. mag._, vol. iv., p. 253, series 6, august, 1902. j. j. thomson, "on some consequences of the emission of negatively-electrified corpuscles by hot bodies." [74] the opinion that ionisation of the air by sunlight is a cause of obstruction to hertzian waves propagated over long distances has also been expressed by mr. j. e. taylor. see _proc._ roy. soc., vol. lxxi., p. 225, 1903. "characteristics of earth current disturbances and their origin." [75] see _proc._ roy. soc., may 15, 1902. "on some phenomena affecting the transmission of electric waves over the surface of the sea and earth," by captain h. b. jackson, r.n., f.r.s. [76] mr. marconi has informed the writer that these strategic questions have received attention in selecting the sites for large marconi power stations in italy. * * * * * [detailed transcriber's notes the text has been made to match the original text as much as possible retaining all apparent printer's errors and inconsistencies. the following, detail the apparent printer's errors etc. identified in the original text. variation in spelling, strasburg and strassburg for strasbourg. there are a number of inconsistencies in hyphenation present in the original text. those concerned with the variation between one word or a hyphenated word are detailed below. those concerned with the variation between multiple words and hyphenated words are too numerous to detail individually. inconsistent hyphenation of word, 'anti-node' and 'antinode' both present in original text. inconsistent hyphenation of word, 'electro-dynamic' and 'electrodynamic' both present in original text. inconsistent hyphenation of word, 'horse-shoe' and 'horseshoe' both present in original text. inconsistent hyphenation of word, 'over-blowing' and 'overblowing' both present in original text. page 5, possible printer's error, a for at, 'consisting when a rest'. page 6, printer's error, comma rather than full stop at end of sentence, 'ether constituting electric radiation,'. page 10, printer's error, millmetre for millimetre, 'three thousand volts per millmetre,'. page 13, possible printer's error, set for sets, 'there are three set of phenomena'. page 13, printer's error, duplicate word, 'detached and and travel away.'. page 13, brackets added to in-line equation to aid clarity, 'f = (3/8)cv^{2}/10^{6}.'. page 13, both equations originally multi-line fraction, rendered into one line for clarity. page 15, both equations originally multi-line fraction, rendered into one line for clarity. page 22, printer's error, correponding for corresponding, 'correponding to this frequency'. page 22, printer's error, consist for consists, 'due to braun, consist of attaching'. page 24, printer's error, one-hundreth for one-hundredth, 'capacity of one-hundreth of a microfarad,'. page 28, printer's error, missing full stop at end of sentence added, 'in the case of the hammer break.'. page 33, printer's error, supppse for suppose, 'let us supppse'. page 44, equation originally multi-line fraction, rendered into one line for clarity. page 46, printer's error, comma rather than full stop at end of sentence, 'to the transmitting aerial,'. page 48, possible printer's error, alterations for alternations, 'alterations of electric strain'. page 54, printer's error, banly for branly, 'proved that in a banly tube,'. page 56, variation in spelling, unsensitive for insensitive, 'wounded and unsensitive.'. page 59, possible printer's error, sensive for sensitive 'to work a sensive recording apparatus'. page 59, possible printer's error, arragement for arrangement, 'most interesting arragement'. page 61, printer's error, missing letter i, 'as shown n fig. 18,'. page 70, equation originally multi-line fraction, rendered into one line for clarity. page 71, printer's error, osciilating for oscillating, 'to that of the osciilating circuit'. page 71, printer's error, impluse for impulse, 'the period of that impluse'. page 74, possible printer's error, extra comma in date, 'on may, 17, 1901.'. page 76, printer's error, arangements for arrangements, 'variation of the above arangements'. page 77, printer's error, systonic for syntonic, 'the systonic transmitting'. page 86, printer's error, interpositon for interposition, 'effect of the interpositon of land'. page 87, printer's error, signaling for signalling, 'the usual maximum signaling'. footnote 17, printer's error, missing letter t, 'must be _solid_ metal and no hollow,'. footnote 31, printer's error, missing full stop after abbreviation, '_phil mag._'. footnote 41, printer's error, extra full stop after reference, '_comptes rendus._'. ] courtesy of the digital library@villanova university (http://digital.library.villanova.edu/)) [illustration: "thank heaven you came before it was too late."--page 108] ----------------------------------------------------------------------- the ocean wireless boys on war swept seas by captain wilbur lawton author of "the boy aviators' series," "the dreadnought boys' series," "the ocean wireless boys on the atlantic," "the ocean wireless boys and the lost liner," "the ocean wireless boys on the pacific" with illustrations by arthur o. scott new york hurst & company, inc. publishers ----------------------------------------------------------------------- copyright, 1917, by hurst & company ----------------------------------------------------------------------- contents chapter page i the gold ship 5 ii war is declared! 15 iii on deck once more 23 iv icebergs ahead! 32 v a close shave 38 vi smoke on the horizon 49 vii a shot at the rudder 55 viii land ho! 61 ix a strange quest 69 x under old glory 78 xi the "herr professor" again 84 xii the armed cruiser 90 xiii a message in code 96 xiv the cattle ship 103 xv jack's brave leap 113 xvi awaiting orders 120 xvii what befell in the after cabin 128 xviii a rascal brought to book 135 xix the "barley rig" 147 xx the hidden mine 154 xxi the north sea 160 xxii a night of alarms 167 xxiii meeting an old friend 173 xxiv the sky slayer 179 xxv in the glare of the flames 187 xxvi two young heroes 194 xxvii "the germans are coming!" 201 xxviii fast traveling 207 xxix the uhlans! 215 xxx "you are a spy!" 221 xxxi court-martialed 227 xxxii the long night 233 xxxiii through bullet-racked air 243 xxxiv a flight of terror 248 xxxv the bully of the clouds 254 xxxvi a mysterious capture 260 xxxvii the might of militarism 266 xxxviii military cross-examination 272 xxxix shattering the shackles 278 xl old glory again 285 xli war in times of peace 292 ----------------------------------------------------------------------- the ocean wireless boys on war swept seas chapter i. the gold ship. the newspapers announced in large type that the _kronprinzessin emilie_, the crack flyer of the bremen-american line, was to carry from the united states to germany the vast sum of $6,000,000 in bullion. on her sailing day the dock, from which she was to start on what destined to prove the most eventful voyage ever made since men first went down to the sea in ships, was jammed with gaping crowds. they interfered with the passengers, and employees of the company had to jostle their way among them as best they could. the thought of the vast fortune stowed within the tall, steel sides of the liner had attracted them, although what they expected to see of it was difficult to imagine. but just as a crowd will gather outside a prison where some notorious malefactor is confined, feasting their eyes on its gray walls without hope of seeing the lawbreaker himself, so the throngs on the _kronprinzessin emilie's_ pier indulged their curiosity by staring at the colossal casket that held such an enormous fortune. among those who had to win their way through the crowd almost by main force, were two tanned, broad-shouldered youths carrying suitcases and handbags. "my, what a mob, jack!" exclaimed one of them, elbowing himself between a stout man who was gazing fixedly at the vessel's side--and showed no disposition to move--and an equally corpulent woman whose mouth was wide open and whose eyes bulged as if she almost expected to see the ship gold-plated instead of black. "yes, gold's a great magnet even if it is stowed away inside the specie room of a steamer," replied jack ready. "we ought to feel like millionaires ourselves, bill, sailing on such a ship." "a sort of vacation _de luxe_," laughed bill raynor. "what a chance for the buccaneers of the old days if they could only come to life again. then there would be real adventure in sailing on the _kronprinzessin_." "i guess we've had about all the adventure we want for a time, bill," replied jack, as they finally gained the gang-plank and two white-coated, gilt-buttoned stewards grabbed their hand baggage. "the pacific and new guinea provided what you might call 'an ample sufficiency' for me in that line." "we earned this holiday, that's one thing sure," agreed bill, "and the best part of it is that the sale of those pearls gave us enough funds for a holiday abroad without putting too much of a crimp in our bank accounts." he referred to the pearls the boys' native chums in the pamatou islands in the south pacific had presented them with, after their narrow escape from death in the sea-cave and the subsequent wreck on a coral reef, during the memorable pacific voyage and adventures, which were described in detail in the volume of this series which immediately preceded the present book. this volume was called, "the ocean wireless boys on the pacific." in the first book of this series, which was called "the ocean wireless boys on the atlantic," we were introduced to jack ready, then the young wireless operator of the big tank steamer _ajax_. his chum, bill raynor, was a junior engineer of that craft. a strong friendship sprang up between the two lads, which their subsequent adventures on that voyage cemented into a lasting affection. jack also won the approval of jacob jukes, head of the great shipping combine that owned the _ajax_ and a vast fleet of craft, both passenger and freight, besides, by his masterly handling of a difficult situation when the millionaire shipping-man's yacht burned in mid-atlantic. this incident, and others which proved that the young wireless man was level-headed and cool, even in the worst emergency, resulted in his being transferred to the passenger service on board the west indian service craft, the _tropic queen_. the thrilling events that accompanied the vessel's last voyage were set forth in the second volume of the ocean wireless boys series, entitled, "the ocean wireless boys and the lost liner." still another book related how jack and his chum took to the seas again on different vessels, only to be reunited in the strangest manner. "the ocean wireless boys of the iceberg patrol," as this was named, told something of the work of the craft detailed by uncle sam to the duty of patrolling northern seas, sending wireless warnings of icebergs to trans-atlantic liners--a work of infinite usefulness which, had it been instituted earlier, might have averted the loss of the _titanic_, the greatest marine disaster in the history of the world. this was followed by an account of the exciting pacific adventures already referred to. the boys, and their employer, mr. jukes, agreed with them, and felt that after their experiences in the south seas with the millionaire's expedition in search of his lost brother, they had earned a holiday; and their determination to tour europe was the outcome. but even as they stepped on board the "gold ship," the machinery of war was beginning to rumble in europe, and before many hours had passed, the storm of well-nigh universal war was destined to begin. of this, of course, they had no inkling, as they busied themselves in establishing their belongings in their main-deck cabin. these preparations had hardly been completed when the siren boomed warningly, and a tremor ran through the big vessel. as she backed out of her pier, the brass band began to play and the crowds on the decks, and on the docks, waved wildly, cheered and shouted last messages which, by no possibility, could have been heard above the din. "well, off at last, jack," said raynor, entwining jack's elbow in his own as the two leaned, side by side, on the railing, bidding good-bye to new york's wonderful skyscraper skyline as it slid past. "how does it feel to be a passenger?" jack's eyes sought the lofty wireless aerials swung far above them between the two masts. "it feels mighty odd to think of somebody else sending out the t. r." he said slowly, naming the wireless method of saying "good-bye," on sailing. "well, i never saw such a fellow!" exclaimed raynor. "for goodness' sake forget your everlasting coherers and keys and converters and the rest of them and enjoy taking life easy. but--hullo!" he broke off, "there's someone we know." approaching them was a dapper little man, with a neat black moustache and dressed in a careful, almost dignified manner. "why, it's raymond de garros, that french aviator we saved from the sea off florida when we were on the old _tropic queen_!" exclaimed jack. "that's the man. but what in the world is he doing here? i thought he was in france organizing an aeroplane corps for the army." "so did i. the newspapers have had several despatches about his work. but we shall soon find out about the reason for his being on board." a minute later they were warmly shaking hands with the little frenchman, who, with many gesticulations and twirlings of his moustache, assured them how glad he was to "greet zee two brave boys zat save my life from zee sea." "you're the last person we expected to see," said jack, when first greetings were over. "we didn't even know you were in america." the little frenchman shrugged his shoulders and looked about him uneasily. then he buttonholed the boys confidentially. "no one know zat i am here but my government," he said in low tones. "you are on a secret mission of some kind?" asked jack. "can i trust you to keep somethings to yourselves if i tell you what i am do in amerique?" asked the aviator. "of course, but if you don't wish---i didn't mean to appear inquisitive," jack hastened to say. "zat is all right, my friend!" exclaimed de garros. "you save my life. i should be ungrateful if i seemed secretive wiz you. i have been in amerique buying and shipping aeroplanes to france from one of your manufacturers." "but i thought france already had a powerful air fleet," said bill. the little aviator's next words were astonishing to the boys, who shared the common impression about the french strength in the air. "before many days are past we shall need all and more aeroplanes than we have," he said. "i wish we had twice as many. but i can say no more now. but my advice to you is to watch zee wireless closely. you are going abroad on pleasure?" "yes, we thought we'd earned a vacation," said jack. the little frenchman's rejoinder was a shrug and a smile. "your vacation may be what you americans call a 'strenuous one,'" he said meaningly, and with an emphasis the boys could not fathom. "by the way, on board this ship i am jules campion. there are reasons for my real name being unknown for the present. _au revoir_, i go to arrange my luggage. we shall meet again." and he was gone, leaving the boys to exchange puzzled glances. chapter ii. war is declared! "vell, yack retty, you yust like to hang aroundt undt see me vurk, hein?" hans poffer, the yellow-haired, red-cheeked wireless operator of the _kronprinzessin emilie_ asked the question, on the afternoon of the third day out. jack had discovered in young poffer an acquaintance he had made in antwerp when he was on board the _ajax_, and had renewed the friendship, to poffer's great delight, for the german wireless man had had trouble with his instruments the first day out which jack had adjusted for him. since that time jack, to bill raynor's amusement, had spent most of his time in the wireless room enjoying, as poffer put it, "watching me work." but there was another reason beside his deep-seated interest in everything appertaining to his profession that made jack haunt the _kronprinzessin's_ wireless coop. de garros, with whom he had had several conversations since their meeting on board, had repeatedly told him to be on the lookout for something "that would before long come over the wires." once, in discussing the boys' plans for amusing themselves in europe, the aviator had said meaningly, "if you ever get there." but what he meant by these words he had steadfastly refused to explain, telling jack that he would find out in good time. "me, if i gedt idt a holliday," said poffer, after greeting jack a day later, "i go by as far avay from der vireless as i couldt gedt idt. i gedt sick undt tired hearing idt all day 'tick-tick' undt sending idt all day der same 'tick-tick' alretty. donner! i'm hungry again. holdt idt mein key a minute vile i gedt idt mineself a bite." the stout german slipped his wireless "ears" from his head and extended them to jack, who, good-naturedly, took them. then he made off for his cabin where he kept constantly a stock of provisions to satisfy his appetite between meals. "well, i'm a fine chump," smiled jack, as he slipped into hans' vacant chair. "no wonder bill says i'm crazy. off for a holiday and the first thing i know i find myself back on the job. hullo, here's a message coming. k. p. e., that's our call. funny sort of sending, too. doesn't sound like a commercial operator." jack crackled out a reply. "this is the _kronprinzessin emilie_," he flashed back; "what do you want?" "tell your captain to lie to in his present position till further orders," came the reply. "well, i like your nerve," flashed back jack, thinking somebody was trying to play a wireless joke on him. "don't you know we are carrying the european mails from new york? you stick around where you are and we may bump into you on the way back again." "never mind about that. obey orders at once," came back bruskly. "say, never mind that comedy," implored jack. "i'm busy. ring off." "no trifling there, young man," was flashed back. "this is the british cruiser _essex_. we want to overhaul you." "but you can't stop a mail steamer." "in this case we can. war has been declared by england upon germany and austria. lay to or it will be the worse for you." a step sounded behind jack. he turned quickly, thinking it was someone who wanted to send a message, in which case he was anxious to "cut out" the man he thought was playing a senseless joke on him. the newcomer was de garros. "ah, sitting at zee wire, eh? i suppose our always hungry teutonic friend iz taking ze light lunch somewhere. ah, any news? i saw you working ze key as i came in." "no news since i came on," said jack, carelessly. "i was just trying to convince some deep sea joker that he couldn't fool me." "what do you mean?" "why, somebody just flashed a message to the ship that they were the british cruiser _essex_ and that war had been declared between england and germany and----" he got no further. de garros's hands flew out and seized his shoulders. "zat was no joke, _mon ami_," he exclaimed; "it was zee truth." "the truth? how do you know?" asked the naturally astonished jack. "it has been in zee air for months in diplomatic circles. i thought zee declaration would have come before this. it was for that that i was in amerique buying aeroplanes." "what, is france in this, too?" demanded the astonished jack. "yes, and russia also. russia declared war two days ago. then came france, zee second member of zee triple entente, as zee is called, and now, as was expected, comes england to help against the german barbarians." "but how did you know all this?" demanded jack. "there was nothing in the papers when we left new york, but something about a row between austria and servia." "which caused all the trouble," came the reply; "or, rather, zee match to zee powder. but zee ask me how i know zee declaration of war of russia and france. i am not the only man on zee ship zat does. captain rollok, he knows, zee officers know, like me zey have been getting wireless messages in code. zey have been warned to look out for english cruisers in case england joined france and russia. zis gerrman ship with six million dollars in gold on board would be a fine prize for great britain. my friend, before many hours have passed, you are going to have some excitement." "great gracious, then that message wasn't a joke and that british cruiser may overhaul us and take all that bullion?" "if she can catch us,--yes. she will also make prisoners of the germans on board and take the ship to an english port." "what had i better do?" "here comes young poffer now. tell him of zee message and get it to zee captain at once. if we are caught we may be delayed indefinitely and zee haste is imperative with me at zee present time." the german wireless man entered the cabin, gnawing at a huge pretzel. at jack's information of the message that had come, he dropped it to the floor in his astonishment and stood staring for a moment. "himmel!" he exclaimed, when he found his voice. "englandt is go var midt yarmany! undt a bridish sheep chase us. _ach du lieber_, if they catch us, hans poffer goes by a prison yet midt nudding to eat but bread undt vater----" "never mind about that now," interrupted jack quickly; "take that information to captain rollok at once. take it yourself. don't give it to a steward. if the passengers knew of this, there'd be a panic in a jiffy." poffer, still with his mouth and eyes wide open, hurried off on his errand. "captain rollok will probably come back himself," declared de garros, "and vee will be ordered out of the cabin. ve had better go now. but vee must not say a word of zees till zee time comes. vee have more as two thousand passengers on board and if zey zink a warship chase us,--_sacre!_" chapter iii. on deck once more. jack was lolling in a deck chair fifteen minutes later, still digesting the astonishing news that had come out of space, when a deck steward approached him and, with an air of caution, leant over the lad and said: "captain rollok would like to see you in the wireless room at once, please." "now what's up?" wondered jack, as greatly astonished by this message, he made his way to the radio cabin. "i guess i'm in for a call down for sitting in at the key. poor poffer, i'll see that he doesn't get into trouble if i can help it, and as for me--i'm a passenger now and captains have no terrors for me." these thoughts occupied him as far as his destination. within the cabin were captain rollok, a giant of a man, with a fresh complexion and huge blond beard, one of his officers and hans pollak, the latter looking in fear of his life as the big captain berated him, in german, with force and vigor. as jack entered the cabin, the great bulk of the captain swung round on him. "so you are de young mans who sits in at der vireless vile dis cabbage-head goes stuffing himself midt pretzels, is it?" he demanded, with what appeared great severity, but with an underlying twinkle in his eyes. jack contented himself with nodding and a brief admission that he had taken poffer's place at the key while the latter refreshed himself. he half-expected an outburst from the big german but, to his astonishment, the captain clapped him on the back with a force that almost knocked him off his feet. "_ach, du lieber!_" he exclaimed; "it was goot dot you vod dere, uddervise dis foolish poffer would haf left der key anyvay undt dot british cruiser would have overhauled us. now i got a proposition to make to you. you are a vireless man. our second operator is sick undt idt is necessary dot dere is someones at der vireless all of der time. vill you take der chob?" jack hardly knew what to say. the proposal had come so abruptly that he found it hard to make up his mind. "you would want me to help out all the way to europe?" he asked. "we are not going to europe," was the reply. "i am going to run back for der american coast undt try to dodge capture. six million dollars is a big enough prize to make der search for us pretty active. i don't believe dere would be a chance for us to reach der udder side." "well," said jack, after some consideration, "i guess my holiday is off anyhow, and i might as well get down to work now as later on. all right, captain, you can count on me." "goot for you. i vill see dot you are no loser by idt," said the big german, and so jack, by a strange combination of undreamt-of circumstances, became the wireless man of the "gold ship," whose subsequent adventures were destined to fill the world with wonder. poffer's hours of duty ended at dinner time that evening, and by the time jack sat down at the key, it was dark. no more word had come from the british cruiser, and so far the _kronprinzessin's_ course had not been altered. a hasty message in cipher had been sent to the offices of the line in new york, but so far no orders to turn back had come through the air. however, jack had not been on duty an hour before the expected command came. the passengers strolling and sitting about the decks were suddenly aware that the big ship was slowing up and being turned about. the incredulous ones among them were speedily convinced that this was actually the case when it was pointed out that the moon, which had been on the starboard side of the ship in the early evening, was now to be seen off the port quarter. rumors ran rife throughout the great steel vessel. there had been an accident to the machinery, there were icebergs ahead, some plot against the security of the gold in the specie room had been discovered--these, and even wilder reports, were circulated. the captain and the other officers were besieged for explanations, but none were forthcoming, for the time being. shortly before midnight, however, the captain in person entered the smoking room with a telegram in his hand. "gentlemen," he announced to those assembled there, "i am sorry to say that var has been declared bedween england and germany, great britain siding against my vaterland mit france and russia." he held up his hand to quell the hub-bub that instantly broke loose. when a measure of quiet was restored, he resumed: "id is therefore imbossible for the voyage of this ship to continue. as you haf observed, her course has been altered. ve are on our way back to america." "to new york?" demanded a score of voices. the captain shook his head. "new york vill be vatched more carefully than any udeer port on der atlantic coast," he said. "i haf not yet decided for vere i vill make; but i ask you all to take der situation philisophically and try to quiet any alarm among der lady passengers." the turmoil of questions and answers and excited conversation broke out again, and in the midst of it the captain's broad form disappeared through the doorway. a few moments later, raynor was in the wireless room after a fruitless search for his chum in other parts of the ship. "say, what are you doing sitting at that key?" he demanded. "have you gone to work for the ship?" "looks that way, doesn't it?" smiled jack. "did you know that we are running away from british cruisers?" asked raynor, breathlessly. "knew it before the ship was turned around," said jack, calmly. "but i couldn't have told even you about it at the time. it was confidential. but there's no reason why you shouldn't hear it all now," and he launched into a narration of the events just passed which had had such a strange culmination. he was in the midst of it, when one of the junior officers of the ship appeared. he told the boys they would have to close the door of the wireless room and cover the ports. not a ray of light must be visible about the ship, he informed them. in the darkness even the glow of a single port-light might give a clue as to the whereabouts of their quarry to the lurking british cruisers. in the passengers' quarters of the great ship, similar orders were issued. stewards went about blanketing portholes and turning out all unnecessary lights. by ten o'clock, except in the "working" quarters of the ship,--and there, they were carefully concealed, as in the wireless room,--there was not a light on board. in order to insure obedience to his orders, the captain had had the cabin lights disconnected from the dynamos at that hour. on the darkened decks, little groups of timid passengers, who refused to go to bed, huddled and talked in low tones, constantly gazing seaward to catch sight of a tell-tale searchlight which would tell of pursuit or interception. through the darkness, the great ship was driven at top speed without warning lights of any description. watches were doubled, and on the bridge, the unsleeping captain kept vigil with his anxious officers. through the long hours, jack sat unwinkingly at his key. but it was not till the sky was graying the next morning that anything disturbed the silence of the air. then came a break in the monotony. the british cruiser _essex_ was speaking to the _suffolk_. but the messages were in code and told nothing except that jack caught the name of the liner and knew the radio talk between the warships concerned her. at breakfast time the passengers assembled in the saloon, for the most part anxious and haggard after sleepless nights. the captain spoke encouragingly, but even his words had little effect. every one on board felt and showed the strain of this blind racing over the ocean with watchful naval bull-dogs lying in wait ready to pounce on the richest prize afloat on the seven seas. chapter iv. icebergs ahead! that night a dense fog fell. but the pace of the fleeing liner was not slackened by a fraction of a knot. without running lights, and with darkened decks and cabins, she raced blindly onward through the smother, facing disaster if she struck an obstacle. the passengers, already nerve-racked for the most part, almost beyond endurance, named a committee which was sent to the captain to protest against the reckless risk he was taking in ploughing ahead at top speed through the blinding mist. they returned with a report that the captain had refused to slacken speed. with reckless fatalism, it appeared, he was prepared to lose his ship in a disaster rather than run the chance of its capture by cruisers of the country with which his ruler was at war. a new feeling, one of indignation, began to spread through the big ship. little knots gathered and angrily censured the captain's action. some even visited him in person, but while he was polite to all, he firmly refused to reduce speed or display lights. this was the condition of affairs when jack came on duty accompanied by bill raynor, who had agreed to share his lonely vigil, for, from being one of the most sought out places on the ship, the wireless room was now deserted by the passengers, for strict orders had been given against the sending or receiving of any wireless messages lest the watching cruisers should get definite information of the liner's whereabouts and pounce upon her. there was little for jack to do under this "ukase" but to lean back restfully in his chair, with the receivers over his ears on the lookout for what might be coming through the air. he and raynor chatted, discussing the wild flight of the "gold ship," intermittently, as the hours passed. but suddenly jack became alert. out in the dark, fog-ridden night, two ships were talking through the air. they were, as he learned after a moment of listening, the _caledonian_ of the english anchor line and the _mersey_, which also flew the british flag. the young wireless man listened for a time and then "grounded" with a grave face. "what's up now?" asked raynor, noticing this. "if it's the cruisers, i don't mind, for only the germans and austrians would be held as prisoners. i'd kind of like to be 'captured,' as a novelty." "this trouble's worse than cruisers," rejoined jack, in sober tones. "what is it then?" "icebergs," said jack, sententiously. "icebergs at this time of the year?" asked bill, incredulously, for bergs are rare in august on the usual steamer lanes, though occasionally seen. "that's what," rejoined jack; "the _caledonian_ was telling the _mersey_. she says they are sown thick to the northwest of us. you've got to remember that we're a long way to the north of the usual steamer tracks now, so it's not surprising that the 'growlers' are about." "no, but it's mighty unpleasant," said raynor. "what are you going to do?" "tell the captain about it at once," said jack, decisively, rising and putting on his cap. "i hope he puts on the brakes when he hears about it," commented bill. "i'm not particularly nervous, but going full speed ahead through the fog into a field of bergs doesn't just exactly feel good." "i'm only glad that the passengers don't know about it," said jack. "they're scary enough now. if they knew about the bergs, i firmly believe some of them would have to be put in strait jackets." "yes, about the only cool ones on board are the americans and the english," declared bill. "i heard to-day that a party of american millionaires got together in the smoking room and laid plans to make an offer to buy the ship and run her across anyhow." "that sounds like the american spirit all right," chuckled jack. "what became of the idea?" "the captain told them the ship was not for sale," said bill, "even if they offered to throw in the millions in the specie room." jack found captain rollok and his officers in anxious consultation in the former's cabin. "ha, so you haf the news, is it?" demanded the captain, as jack entered. "yes, and not very good news, i'm sorry to say," said jack. "the _caledonian_ has just been telling the _mersey_ that there are icebergs ahead." the officers exchanged glances. they all looked at the captain. evidently some orders were expected, with the greatest peril the sea holds lying ahead of the racing vessel. one of them,--second officer muller, who had the watch,--put his anxiety into words. "is it that you will change the course or reduce speed, captain?" he inquired. the big, bearded captain turned on him like a flash. he raised his massive fist and brought it down on the table with a crash that bade fair to split the wood. "we keep on as we are going!" he exclaimed. "rather than let this ship get into the hands of the english, i'll send her to the bottom." "but the passengers!" exclaimed jack; "surely----" "herr ready," said the captain, "i am in command of this ship. the orders are full speed ahead." chapter v. a close shave. bill raynor received jack's news with a shrug. "i'm not surprised, to tell you the truth," he said. "i've met a good many germans in the course of my sea-going years, and that's usually their idea,--rather sink the ship than give it up." "but the fearful danger, bill," protested jack. "at any moment there may come a crash and----" "we've got iceberg detectors," said bill, "and maybe they'll sound the whistle and locate a big berg by the echo." "they won't sound any whistle to-night," declared jack. "that skipper is determined not to give any cruiser the least inkling of his whereabouts. i'm going to take a run on the deck, the wireless bell will call me if something comes. want to join me?" "all right. but it's not much of a night for a stroll outside." "anything's better than sitting in that cabin waiting for you-don't-know-what to happen." "you're getting nervous, jack." "not so much for my own sake as at the thought of all these thousands of tons of steel being raced through this fog at a twenty-four knot clip and icebergs ahead. it's sheer madness." "well, the captain's word is law at sea, so it's no use protesting. we must hope for the best." the upper decks were deserted except for the boys. on the lower deck the passengers huddled in the darkness behind canvas screens erected to prevent any chance ray of light from filtering out. it was an uncanny feeling this, of speeding through an impenetrable pall of blackness with the thought of the iceberg warning ever and anon recurring to both lads, though they tried to talk of indifferent subjects. the hours wore on and the fog did not lighten. chilled to the bone, although it was august, jack and bill had about decided to turn in when there came a sudden sharp cry from the lookout forward. involuntarily, bill clutched jack's arm. the strain had affected them both more than they cared to admit. suddenly, dead ahead of them, as it seemed, there reared, seen white through the mist, a monstrous spectral form. it towered above the steamer's masts and appeared to their alarmed imaginations to hang like an impending cliff above the ship. from the bridge came quick shouts. orders were given and harshly echoed. somewhere down on the passenger decks, a woman screamed. then came cries of consternation. the next moment there was a slight shock and a long, shuddering grind passed along the vessel's side. the mountainous ice mass appeared to sheer off, but in reality the ship was swinging clear of it. by a miracle she had escaped with a mere graze of her side. at diminished speed, she continued on her course. "phew, what a narrow escape!" exclaimed jack, as the fog shut in about the monster berg they had sheered. "i thought we were goners, sure," declared bill, soberly. "a little of that sort of thing goes a long way. i---hark!" from the lower decks there now came the confused noise of a frightened crowd. now and then, above, could be heard the shrieks of an hysterical woman. sharp, authoritative voices belonging, as the boys guessed, to the officers, who were trying to quiet the panic-stricken throngs, occasionally sounded above the babel. "they're coming this way!" cried jack suddenly, as a rush of feet could be heard making for the ascents to the boat deck, where the wireless coop was situated. "bill, we'll be in the middle of a first-class panic in a minute." "yes, if that crowd gets up here among the boats, there's going to be the dickens popping," agreed bill. "what will we do?" "run into the wireless room. in the drawer of the desk by the safe there are two revolvers. one's mine and the other belongs to poffer. get them on the jump." it did not take bill long to carry out his errand, but in even the short time that he had been absent, the forefront of the terrified crowd from below was almost at the head of the companionway leading from the promenade to the boat deck. jack had stationed himself at the head of it. "keep cool, everybody," he was shouting; "there is no danger." "the _titanic_!" shrieked somebody. "we've hit an iceberg. we'll sink like her." "the boats!" shouted a man. "we'll lower 'em ourselves. we're sinking!" in the gloom jack could see the man's face, round and white, with a big yellow mustache. [illustration: "keep cool, everybody," he was shouting; "there is no danger."--page 42] the fellow shoved two women, wedged in the throng, aside, and addressed himself to jack, who stood at the head of the companionway. "let me pass, you!" he bellowed, seemingly mad with fear. "i want a place in the first boat. i----" jack felt bill slip a revolver into his pocket. but he did not remove the weapon, the time had not yet come for its use. "stop that noise," he told the yellow-mustached man bluntly. "ladies and gentlemen," he went on, "there's no danger. we merely grazed the berg. thank heaven the ship was swung in time to save her." "don't believe him," shrieked the terrified man. "stand to one side there. the boats!" he made a rush for jack and struck heavily at the young wireless operator. but before his blow landed, jack had crouched and the next instant his fist shot out like a piston rod. the fellow staggered back, but could not fall because of the pressure of humanity behind him. it is difficult to say what might have happened had there not been cooler heads in the crowd. reassured by jack's cool manner, these began quieting the more timid ones. just then, too, captain rollok and some of his officers appeared. all carried drawn revolvers, for a disorganized rush on the boats would have meant that scores of women would have been trampled and many lives lost in the confusion. the captain's firm, stern tones completed the work jack and bill had begun. he assured the passengers that an examination had been made and that no damage had been done. he also promised thereafter to run at a more moderate speed. gradually, the excited crowd calmed down, and some sought their cabins. the greater part, however, elected to remain on deck throughout the night. the next morning the fog had somewhat cleared and the break-neck speed of the ship was resumed. jack was just resigning the key to young poffer when the doorway was darkened by a bulky figure. it was that of a big, yellow-mustached man, whom jack recognized instantly as the man who had led the panic of the night before, and whom he had been forced to deal with summarily. he furiously glared at jack, and the boy noticed that under his left eye was a dark bruise, a memento of the previous night. "what did you mean by striking me last night?" he began angrily. "i demand your name. i will have you discharged." "my name is ready," answered jack calmly, "and as far as having me discharged is concerned, i'm afraid that will be impossible. you see i'm here in what you might call an extra-official capacity." "bah! don't be impudent with me, boy. i am herr professor." "oh, a barber," smiled jack, amiably. the yellow-mustached man fairly growled. his light blue eyes snapped viciously. "i am herr----" "oh, yes, i see you're here," responded jack calmly. "you seem to be in rather a bad temper, too." "boy, i will see that you are punished for this. i am a gentleman." "really, it would be as hard to tell it on you this morning as it was last night," responded jack, in quite unruffled tones. "be very careful, young man. i have already told you i am herr professor." "oh, don't hang out the barber pole again," begged jack. the other shot a glance full of venom at the perfectly cool youth before him. then, apparently realizing that there was nothing to be gained from indulging in tirades, he turned abruptly on his heel and strode to the door. on the threshold he paused. "i am going to report your conduct to the captain at once," he said. "you will find out before long what such gross impertinence to a passenger means." "i shouldn't advise you to tell him about your behavior last night, though," observed jack. "why not?" "because from what i've observed of him, he is a rather hot-tempered man and he might feel inclined to throw you out of his cabin--and it's quite a drop from there to the promenade deck." "you will hear more of this," snarled the infuriated man; but at jack's parting shot he made off, looking very uncomfortable. poffer regarded jack with a look in which admiration and awe were oddly blended. "i dink you haf for yourself made idt troubles," he remarked. "trouble! in what way?" demanded jack. "the fellow is an arrant coward. he----" "ah yah, dot is so, but den he is herr----" "gracious, have you got hair on your brain, too?" "yah," was the innocent response. "he is a big professor at a cherman war college. he is a great man in germany, der herr professor radwig." "well, mr. earwig, or whatever his name is, may be a great man as you say, hans, my boy, but he is also a great coward. as for his threat to make trouble with the captain, that does not bother me in the least. to begin with, i'm only a volunteer, as it were, and in the second place, i'll bet you a cookie or one of those big red apples you're so fond of, that mr. earwig will avoid discussing the events of last night as much as he can. i've heard the last of him." but in this jack was wrong. in days that lay ahead of the boys, they were to find that herr professor radwig was ordained to play no unimportant part in their lives. chapter vi. smoke on the horizon. late that afternoon jack, who had just come on deck, was in time to notice an unusual thrill of excitement among the already overwrought passengers. on the northern horizon was a smudge of smoke, and a dark hull bearing down on them. those who had glasses had already announced the other craft to be a warship, although, of what nation, it was as yet impossible to say. jack hurried to the wireless room. young poffer declared that he had received no wireless, nor intercepted any message which might have any bearing on the identity of the strange ship. on the bridge, the ship's officers were in excited consultation. the warship was drawing closer every moment. she was black and squat, with two fat funnels from which volumes of dark smoke rolled. at her bow was a smother of white foam showing the speed at which she was being pushed. "ach, now comes it!" exclaimed poffer the next instant. he wrote rapidly and then handed the message to jack. the wireless boy read: "heave to at once. "dutton, commanding his majesty's ship _berwick_." "i'll take it forward right away!" exclaimed jack. "you listen with all your ears for any more messages, hans." "you bet you my life i will undt den some," hans promised. "vot you dink, dey shood us up, jack?" "i don't know. i suppose if we don't heave to, they will," said the wireless boy as he hurried off. "chust as i thought," declared captain rollok, after he had read the message. "shall i tell hans to send back word we'll stop?" asked jack. "stop! i vouldn't stop for der whole british navy," declared captain rollok vehemently. he stepped to the engine room telegraph and set it violently over to "full speed ahead." then he picked up the engine-room telephone and gave orders to pile on every ounce of steam possible. the great ship quivered and then sprang forward like a grayhound from a leash. clouds of black smoke rose from her funnels, deluging the decks with ashes as force draught was applied to the furnaces. jack hastened back to the wireless room. he found poffer, pop-eyed and frightened looking. "there's another cruiser coming up on the other side!" he exclaimed. "i just heard her talking to the _berwick_." "that's nice," commented jack, as bill raynor and de garros appeared in the doorway. "hullo, bill," he continued. "you'll have a chance to be under fire now." "what do you mean?" demanded young raynor. "surely it is that the captain will stop?" asked the french aviator. "stop nothing," rejoined jack. "he doesn't appear to care what he risks, so long as he saves his ship." "i thought i felt her speeding up," said bill. "so he's going to cut and run for it?" "that's the size of it," responded jack, while the frenchman shrugged his shoulders. "they are not understandable, these germans," he commented. "here comes it anudder message," struck in hans, holding up his hand to enjoin silence. they all looked over his shoulder as he wrote rapidly. "your last warning. heave to or take the consequences." it was signed as before by the commander of the _berwick_. "my friends, this captain had better heed that warning," said de garros. "englishmen are not in zee habit of what zee call 'bluffing.'" but when jack came back from the bridge, whither he had sped at once with the message, it was to report the captain as obdurate as ever. his only comment had been to call for more speed. "i guess he thinks we can show that cruiser a clean pair of heels," said raynor. "that looks to be the size of it," agreed jack, "but he is taking desperate chances. let's go outside and see the fun." the cruiser was coming toward them on an oblique line now. from her stern flowed the red cross of st. george on a white field, the naval flag of england. they watched her narrowly for some minutes and then jack exclaimed: "jove! i believe that with luck we can outrun her. the _kronprinzessin_ is the fastest ship of this line, and if her boilers don't blow up we may be able to beat that cruiser out." "i hope so," declared raynor, fervently. "i'm not exactly a coward but i must say the idea of being made a target without having the chance to hit back is not exactly pleasant." "as i shall be in zee thick fighting not before very long, i might as well receive my baptism of fire now as any other time," said the frenchman. "i expect to be placed in charge of zee aviation corps, and i am told zee germans have some very good aeroplane guns." "look," cried bill, suddenly, "they are going to----" a white mushroom of smoke broke from the forward turret of the cruiser, followed by a screeching above their heads. then came an ear-splitting report. "great guns! where is this going to end?" gasped bill, involuntarily crouching. chapter vii. a shot at the rudder. "_ach himmel!_" groaned hans poffer. "suppose dey hit us vee----" he got no further. there was another burst of smoke, a quick, lightning-like flash and the same screech of a projectile. but this time, accompanying the sound of the report, was a sound of tearing metal and the ship shook as if she had struck on the rocks. "the after funnel," cried jack, pointing to a jagged hole in the smoke stack. "the next one may come closer," choked out bill rather shakily. on the lower decks there was the wildest confusion. women were fainting and the stewards and petty officers had all they could do to handle the frightened throngs. the striking of the funnel was the occasion for an angry and badly scared deputation to wait upon the captain and demand that he stop the ship at once. but the deputation did not reach the bridge. they were met at the foot of the stairway leading to it by a polite but firm officer who informed them that under no circumstances would the captain tolerate any interference with his method of running the ship. a third shot, which went wide, closely followed the one that had struck the after funnel. it flew high above them and caused jack to observe: "i don't believe they mean to hit the hull, but only to scare the captain into heaving the boat to." "looks that way," agreed bill, "and as for the scare part of it, i guess they've succeeded, so far as everybody is concerned but captain rollok and his officers." "we are gaining on zee cruiser without a doubt," asserted de garros, whose eyes had been fixed on the pursuing sea fighter for some minutes. "yes, but look, there comes another," cried jack, suddenly, pointing astern. "that must be the one poffer heard signaling to the _berwick_." "we're in for it now," said bill. "i wish that pig-headed captain would heave to and let them take the gold and the germans, if that's all they are after." "hullo!" exclaimed jack, suddenly, as they all stood waiting nervously to see the next flash and puff from the cruiser's turret. "i can see a gleam of hope for us. see what's ahead!" ahead of them the sea appeared to be giving off clouds of steam as if it was boiling. as yet this vapor had not risen high, but it was rapidly making a curtain above the sunny waters. "fog!" cried bill, delightedly. "it cannot be too thick for me," said de garros. "perhaps captain rollok foresaw this and that was why he refused to halt," said jack. "certainly, if we can gain that mist bank before we get badly injured, we'll be all right." it was now a race for the thickening fog curtains. the cruisers appeared to realize that if the _kronprinzessin_ could gain the shelter of the mist, there would be but small chance of their capturing her. increased smoke tumbling from their funnels showed that they were under forced draught. but as their speed increased so did that of the "gold ship." the gun boomed again on the _berwick_, the foremost of the pursuers. the projectile struck the stern of the liner and knocked the elaborate gilt work wreathing, her name and port, into smithereens. "aiming at the rudder," commented jack. "that's a good idea from their point of view." "but a mighty bad one from ours if they succeed in hitting it," said raynor, with a rather sickly laugh. two more shots, one of them from the second cruiser, flew above the fugitive liner and then the mist began to settle round her swiftly-driven hull in soft, cottony wreaths. in five minutes more the fog had shut in all about her. then ensued a game of marine blind-man's buff. captain rollok, having steamed at full speed some miles through the fog,--and this time there were no protests from passengers,--altered his course and deliberately steamed in circles. "hark!" exclaimed jack, during one of these manoeuvers. "what was that?" out in the fog somewhere they could hear a sound like the soft beating of a huge heart. it was the throbbing of another vessel's engines. to the fear of the chase now was added the peril of collision, for in the fog, dense as it was, the captain would not permit the siren to be sounded. it was almost impossible to tell from which direction the sound was proceeding. it seemed to be everywhere. was it another peaceful vessel like themselves, or a man-of-war? much depended on the answer to this question. all at once, with startling distinctness, a huge black bulk loomed up alongside them. through the fog they caught a sudden glimpse of crowded decks and great guns projecting from grim-looking turrets. it was one of the british cruisers. by grim irony, the fog had delivered them into the hands of their pursuers. "great scott, it's all off now!" cried bill, as they simultaneously sensed the identity of the other craft. chapter viii. land ho! but the strange cruise of the _kronprinzessin emilie_ was not destined to come to an end then, although, for an instant, it appeared so. whether the britisher was mutually astonished, and in the confusion the right orders were not given, or whatever the cause was, before they had more than glimpsed her grim, dogged outlines, she faded away in the fog and was blotted out. "phew! a few more close shaves like that and i'd be looking in the mirror to see if my hair hasn't turned gray," said jack. "i wonder they didn't take some action," commented bill, "although i'm glad they didn't." "perhaps zey was so astonished zey forgot to fire zee gun," suggested de garros. "i guess that was it," agreed jack, "but just the same it was a mighty lucky thing for us they didn't come to their senses sooner." "yes, this thing of playing tag in the fog gets on my nerves," muttered bill. by nightfall, they had steamed through the fog belt, but every eye was anxiously turned astern as if their owners expected at any moment to see the ram-shaped bows of the black british sea bulldogs come poking put of the mist. but nothing of the sort happened, however, though late that night, far to the eastward of their course, they could see the glowing fingers of the cruisers' searchlights pointing in every direction across the sea. the next day passed without any untoward happenings, and when, the morning following, jack gazed from the wireless coop he saw, in the first faint light of dawn, that they were steaming along a strange, unfamiliar, rugged coast. by the time the passengers were astir, the outlines of the coast had become dotted with cottages and houses, and in the midst of breakfast they steamed into a harbor, and the anchor was dropped with a roar and a rumble. like a flash, the tables in the saloon were deserted. there was a general rush for the deck. "why, that house over there looks just like my home at bar harbor," cried one woman. ten minutes later her words were confirmed. it _was_ bar harbor, maine, into which the sorely-harried liner had taken refuge under the neutral protection of the stars and stripes. not daring to run into new york or boston, the captain had selected the world-famous summer resort as a harbor that the english cruisers would be the least likely to watch, and his judgment proved sound. and so ended the cruise of the "gold ship," in whose strange adventures the boys were ever proud of having participated. an hour after the great liner's arrival, she was almost deserted by her passengers who were choking the telegraph wires with messages. the wireless disseminated far and wide the news of her safe arrival, and they learned, ashore, that for days the fate of the "gold ship" had been the puzzle of the country. all sorts of wild guesses had been printed as to her whereabouts. she had been reported off the coast of scotland and again in the english channel. one rumor had it that she had been captured, another that she had been sunk and most of those on board lost. not one of these guesses, however wild or probable, came within striking distance of the extraordinary truth of the "gold ship's" flight across the war-swept seas. the day after their arrival, and while the town was still seething with excitement over the great liner's presence in the harbor, jack received a telegram at the hotel where he, raynor and de garros had taken up temporary quarters. the message was from mr. jukes and read as follows: "learned by the papers of your safe return. kindly call at my office as soon as possible after your arrival in new york. important." "what's in the wind now?" exclaimed jack to bill raynor, who was with him when he got the message. "i haven't the slightest idea," said raynor; "but i have a sort of notion in the back of my head that your vacation is over." "if you can call it a vacation," laughed jack. "well then, perhaps experience would be a better word," substituted bill, also laughing. that evening, arrangements having been made about the shipment of their baggage to new york, the boys and the young french aviator obtained their tickets from an agent of the steamship company, for the line was bearing all expenses, and took a night train for home. almost as soon as they reached the city, jack visited mr. jukes' office. "thank goodness you've come, ready!" he exclaimed as soon as he had shaken hands with the lad, upon whom, since their adventures in the south seas, he strangely came to rely; "the _st. mark_ sails to-morrow for europe. i don't know yet, in the middle of this european muddle, just what ports she will touch at. that must be settled by her captain later on." "but mullen is on the _st. mark_," began jack. "i wouldn't wish to usurp his job and----" "and anyhow, it's your vacation," interpolated the magnate. "i know all that, ready, and depend upon it, you won't suffer by it if you agree to my wishes. it isn't exactly as wireless operator i want you to sail on the _st. mark_, it's on a personal mission in part. my son, tom, is among the refugees somewhere in france. i don't know where. i haven't heard a word since this war started, but the last i know he was auto touring north of paris. he may even have gone into belgium, for that was a part of his plan." "and you want me to try to find him?" demanded jack slowly. "yes, i know it's a big job, but i know that if anyone can carry it through, you can. expense is no object, spend all you like but find the boy. this suspense is simply killing his mother and worrying me sick." "i'm willing and glad to take the job, mr. jukes," said the young wireless man, "but, as you say, it's a big undertaking and has about one chance in a hundred of being successful. besides, you may have heard of him and his whereabouts even before the _st. mark_ reaches europe." "i'll take my chances of that," declared the millionaire. "it's action that i want. the feeling that something has actually been done to find him." "on these conditions, i'll go and do my best," said jack. "thank you, ready, thank you. i knew you wouldn't fail me. now about funds. they tell me finances are all topsy-turvy over there now. nobody can get any american paper money or travelers' checks cashed. that may be tom's fix. you'd better take gold. here." he drew a check book out of a drawer and wrote out a check of a size that made jack gasp. "get gold for that," he said, as he handed it over, "and when that's gone, linwood and harding, of london, are my agents. draw on them for what you need. and, by the way, is there anybody you want to take with you?" "i was going to say, sir," said jack, "that for a task like this, bill raynor----" "the very fellow. i'll never forget him in new guinea. a splendid lad. but will he go with you?" "i rather think he will," rejoined jack with a twinkle in his eye. chapter ix. a strange quest. readers of earlier volumes of this series will recall tom jukes, who, after being cast away when his father's yacht burned at sea, was found by jack's clever wireless work. this was the youth,--he was about jack's own age,--whom the wireless boy had been commissioned to find. although the task appeared, as jack had said, one almost impossible of accomplishment, still jack was boy enough to be delighted at the prospect of traversing war-ridden europe and possibly playing a part in the mightiest struggle of all time. as for bill raynor, he was wild with excitement at the idea. uncle toby ready, when he was told of the intended trip, shook his head and muttered something about "playing with fire," but he was eventually won over and presented jack with a dozen bottles of the golden embrocation and universal remedy for man and beast. "if so be as you meet up with the kaiser, or the king of england, or the czar, just give 'em a bottle with my compliments," he said in bestowing the gift. "by the flying jib, it might be the means of building me up a big european trade. think of it, cap'n toby ready, p. o. h. r. h.--physician in ordinary to his royal highness. if you don't run acrost any of them skippers of state you can just distribute it around careless like, and draw special attention to the directions and to my address in case the prescription should require to be refilled." jack promised, but it is to be feared that the golden embrocation never got nearer europe than the cabin of the square rigger _jane harding_, of halifax, nova scotia, which happened to be in the erie basin unloading lumber. captain podsnap, of the _jane harding_, was an ardent admirer of, and believer in, captain toby's concoctions which, as the compounder boasted, never were known to do harm even where they didn't do good. to captain podsnap, therefore, jack hied himself perfidiously and made over to him the gifts intended for ailing royalty. the _st. mark_ was what is known as a "popular" ship. that is, she usually crossed with full cabins. but on the present trip there were a bare score of passengers in the first cabin, not many more in the second, while in the steerage were a couple of hundred travelers, mostly reservists of the various countries at war, returning to europe to take up arms. as they steamed down the harbor, the docks on each side of the river could be observed to be crowded with idle steamers of all sizes, from small freighters to huge four-funnelled liners. with smokeless stacks and empty decks, they lay moored to their piers, offering an eloquent testimonial to the almost complete paralysis of ocean traffic that marked the earlier days of the war. off tompkinsville, staten island, the dreadnought, _florida_, swung at anchor, grim in her gray war paint,--uncle sam's guardian of neutrality. it was her duty to keep watch and ward over the port to see that no contraband went out of the harbor on the ships flying the flags of combatting nations and in other ways to enforce president wilson's policy of "hands off." with dipping ensign, the _st. mark_ slipped by, after a brief scrutiny by a brisk young officer. then, down the bay she steamed, which the boys had traversed only a few days before on the hunted _kronprinzessin_. "well, jack, old fellow," observed raynor, as jack leaned back after sending a few routine messages of farewell and business of the ship, "off again on our travels." "yes, and this time, thank goodness, we're under uncle sam's flag, and that means a whole lot in these days." "it does, indeed," agreed the other fervently, "but have you any idea what port we are bound for?" "not as yet. we are to get instructions by wireless, either from the new york or london offices." "this a queer job we've embarked on, jack," resumed raynor, after a pause in which jack had "picked up" _nantucket_ and exchanged greetings. "it is indeed. i only hope we can carry it through successfully. at any rate, it will give us an opportunity to see something of the war for ourselves." "it's a great chance, but as to finding tom jukes, i must say i agree with you that a needle in a hay stack isn't one, two, three with it." a heavily built man, dark bearded and mustached, entered the wireless cabin. he had a despatch ready written in his hand. "send this as soon as possible, please," he said, handing it to jack. as his eyes met those of the young wireless man he gave a perceptible start which, however, was unnoticed by either of the boys. raynor was paying no particular attention to the matter in hand and jack was knitting his brows over the despatch. it was in code, to an address in new york and was signed martin johnson. "i'm sorry, mr. johnson," said jack, "but we can't handle this message." "can't? why not?" demanded the passenger indignantly. "because it is in code." "what's that got to do with it?" "while the war lasts we have instructions not to handle code messages or any despatches that are not expressed in english that is perfectly plain." "that's preposterous," sputtered the passenger angrily. "this is a message on a business matter i tell you." "if you'll write it out in english, i'll transmit it," said jack; "that's what i'm here for." the man suddenly leaped forward. he thrust a hand in his pocket and pulled out a roll of bills. "can i speak to you confidentially?" he asked, turning his eyes on raynor. "anything you've got to say you can say before my friend," said jack. "then, see here--there's a hundred dollars in that roll," as he threw it on the desk, "forget that code rule a while and it's yours." "look here, mr. johnson," said jack coldly, "i've already told you what my orders are. as for your money, if it was a million it would be just the same to me." "bah! you are a fool," snapped the other, angrily snatching up the money and flinging out of the cabin, crumpling the code message in his hand. "that infernal boy again," he muttered, as he gained the deck outside. "this only makes another score i have to settle with him. these americans, they are all fools. well, von gottberg in new york will have to go without information, that's all, if i can't find some way of getting at the wireless." "say, jack," asked raynor, as the bearded man left the cabin, "did that fellow remind you of anybody?" "who, johnson?" asked jack idly. "why yes, now that you come to mention it, there was something familiar about his voice and his eyes, but for the life of me i couldn't place him." "nor i, and yet i've a strong feeling that we've met him somewhere before." "johnsons are as thick as blackberries," commented jack. "yes, but i don't connect that name with this man. it was some other name altogether. oh, well, what's the use of trying to recall it--anyhow, mr. johnson, whoever he is, hasn't got a very amiable temper. i thought he was going to swell up and bust when you refused that message." but further comment on the irate passenger was cut short at that moment by a beating of dots and dashes against jack's ears, to which one of the "receivers" was adjusted. he hastily slipped the other into place and then turned to raynor with a grin. "it's our old friend, the _berwick_," he said. "she's outside waiting for us, but this time, glory be, we're flying old glory." chapter x. under old glory. sandy hook lay behind a dim blue line on the horizon, and the long atlantic heave was beginning to swing the _st. mark_ in a manner disconcerting to some of the passengers, before they came in sight of the cruiser that had led the _kronprinzessin_ such a harried chase. "looks familiar, doesn't she?" commented jack, as they slowed down and the _berwick_ steamed up alongside, about five hundred yards off. "if it hadn't been for that lucky fog, she'd have looked more familiar yet," declared bill. "look, they're lowering a boat." from the cruiser's side a small boat, crowded with uniformed sailors, and in the stern sheets of which sat a smart junior officer, dropped and, propelled by long, even strokes of the oars which rose and fell in perfect unison, was presently coming toward the liner. the _st. mark's_ accommodation ladder was lowered, and in a few minutes the young british officer was aboard. every passenger was lined up in the saloon and compelled to answer questions as to their nationality, etc. all passed satisfactorily. then came the turn of the second cabin and the steerage. from the second cabin, two admitted german reservists were taken as prisoners of war and in the steerage six more were found. they took their apprehensions stoically, although they knew that they would probably be confined at halifax or bermuda till the close of hostilities. jack and bill raynor watched these scenes with interest. "i suppose it will be months, maybe years, before some of those poor fellows see their homes again," said bill. "yes, but it's what you might call the fortune of war," responded jack briefly. so expeditiously was the work of culling out the reservists done that an hour after the _berwick's_ officers had boarded the liner, the last of the prisoners was off and the ship's papers had been inspected and o.k.'d. with mutual salutes, the two craft parted, the _berwick_ to lie "off and on," looking for commerce carriers of a hostile nation, the _st. mark_ to resume her voyage to a europe which was even then crowded with desperate, stranded american tourists unable to obtain money or passage home. at dinner time muller, the _st. mark's_ regular operator, relieved jack, and he was free for the evening. he elected to spend his leisure time reading up in a text-book, lately issued, an account of the workings of a new coherer that had recently been brought out. but the fatigues of the day had made him drowsy and he soon dropped off to sleep in the chair he had placed on the upper deck in the shelter of a big ventilator. despite the time of year there was a cool, almost a chilly breeze stirring, and most of the small number of first-class passengers were either in the smoking room or the saloon. how long he slept jack did not know, but he was awakened by the sound of voices proceeding from the other side of the ventilator, which masked him from the speakers' view. one of the voices, which jack recognized as belonging to martin johnson, grated harshly on his ears. "if it hadn't been for that cub of a wireless boy," johnson was saying, "that message would have been in the hands of von gottberg by this time." "and so you haven't been able to send word about the british cruiser?" inquired the other speaker. "no, and from the same cause. i shall have to see what i can do with the night operator. he may not be so absurdly scrupulous, unless that young whelp who was on day duty has been talking to him." "did you say, herr professor, that you had met him before?" asked the last speaker's companion. "yes, confound him, on the _kronprinzessin emilie_. i was--er--i was trying to organize an orderly retreat to the boats after the alarm had been spread that british cruisers were after us, when this young scoundrel attacked me brutally." "didn't you report him to the captain?" "well, you see there were--er--reasons which made it unwise to do so." "you bet there were, herr professor radwig,--for i know who you are now, mr. johnson," muttered jack to himself. "no wonder i thought i knew you in spite of your disguise." "what are your present plans?" asked mr. johnson's, or rather, herr professor radwig's companion. "i shall have to see. you understand wireless, schultz?" "intimately. why, you have some idea--?" "never mind now. it is getting chilly. let us go to our cabins. i will talk to you more about this to-morrow." the voices died away as the two left the upper deck. jack, wide awake now, sprang to his feet. clearly there was some mischief concerning the wireless in the air. but of the nature of the impending scheme he could not hazard a guess. "anyhow, i'll just put muller wise to what's going on," thought jack. "he's a decent, square fellow, who wouldn't stand for any monkey business. how to deal with herr radwig is another matter. i guess i'll sleep on it. if only those chaps on the _berwick_ knew who they had overlooked on their hunt for germans, wouldn't they be mad as hornets!" chapter xi. the "herr professor" again. it was not part of jack's plan to apprise muller of the identity of mr. johnson. he did not wish to act prematurely in any way till he had consulted raynor and a plan of campaign had been worked out. "that guy certainly won't try any monkey-shines with me," muller assured jack slangily, but with a sincere ring in his voice, and jack knew he could trust him. then he sought out bill, whom he found in the latter's cabin writing letters. "well, bill," he began. "i've solved the mystery of mr. johnson." bill's writing was instantly forgotten. "you mean that peppery chap?" "the same person. he's an old friend of yours. you were not mistaken when you said that you thought you recognized his voice." "the dickens you say?" bill was all attention now. "and who is he?" "why,--as the nickel novels say,--none other than our old college chum, herr professor radwig." "for gracious' sake!" bill's expression left no doubt as to the genuineness of his astonishment. "old earwig turned up again, eh?" "yes, and from some not very complimentary remarks he made about me, bill," continued jack, "i don't think he'd be averse to doing me some mischief, if he could." "he'd better not try." bill doubled his fists pugnaciously. "the trouble is, i didn't overhear enough to find out just what his little game is." "that's too bad. it's a shame we didn't know his identity earlier. we would have earned the thanks of that english cruiser." "we certainly would. de garros told me that radwig is accounted a very clever and dangerous man. he has invented explosives and is active in the entire german military movement." "by the way, where is de garros?" asked bill. "i don't know any more than you do. after we left him at the depot in new york on our return from bar harbor, i lost sight of him. in fact, things have gone on with such a rush since then, that i haven't had time to think of him till now. he told me, though, that he would take the first ship possible to france." "well, to get back to old earwig." "yes." "are you going to expose him?" "expose him to whom?" "the captain, for instance." "what would be the good? he has committed no crime. if he wants to travel under a false name that is not our business so long as he does not interfere with us." "that's true, but just the same, if we are boarded by another british cruiser, i'll have something to whisper in the boarding officer's ear," said bill, truculently. "i wish we knew who this schultz was," confessed jack. "does that name appear on the passenger lists?" "on none of them. besides, if it had, the man would have been questioned by that officer from the _berwick_. he quizzed everybody with a name that even sounded german." "that's so," admitted bill; "he certainly went through the ship with a rake. i guess old earwig's friend has some american sounding name that will carry him safe across the ocean no matter what happens." soon after, jack sought his berth in the wireless room. as he approached the opened door of the radio station, from which a flood of yellow light issued, he saw, or thought he saw, two lurking figures in the shadow of one of the boats. but even as he sighted them, they vanished. for an instant, jack assumed that they were two of the boat crew but, as they scurried past an open port, he saw they wore ordinary clothes and not the sailor uniforms of the crew. "odd," he mused. "those fellows were certainly hanging around the wireless room for no good purpose. if they had been, they wouldn't have sneaked the instant they saw me coming. i'm willing to bet a cookie one of them was earwig and the other his precious pal who understands wireless. jack, old boy, it's up to you to keep your eyes open." "anything doing?" he asked muller, as he entered the wireless room. "not a thing. deader than a baseball park on christmas day," rejoined muller. "you didn't see anything of our friend, for instance?" "who, johnson? no, he hasn't been near here." jack nodded good-night and then turned in. but as the ship bored on through the darkness his eyes refused, as they customarily did, to close in his usual sound sleep. his mind was busy with many things. it was clear that radwig was contemplating some use of the wireless which did not yet seem quite clear. that it was his duty to checkmate him jack was convinced, but as yet he had little to go upon except the conversation overheard behind the ventilator. "i guess watchful waiting will have to be the policy," he murmured to himself as he fell asleep. chapter xii. the armed cruiser. the next morning, when jack and bill turned out, there was quite a flutter among the passengers. a large ship had been sighted in the distance, coming rapidly westward. as she drew nearer it could be seen that she was a monster craft of four immense funnels painted a sombre black without colored bands to relieve the effect. her upper works were a dull brown and her hull, black. speculation was rife concerning her identity, but it soon became noised about that the craft was the _ruritania_ of the anglican line, which had, apparently, been converted into an auxiliary cruiser by the english government on the outbreak of the war. the sight of guns mounted on her fore and aft decks confirmed this. on she came, a fine, grim spectacle in her dull paint. an absorbed shipload watched her, leaning over the rails as she drew abreast. "lie to!" the signals fluttered from her halliards and the same order was flashed by wireless. for the second time the _st. mark's_ engines revolved more and more slowly. the two big vessels lay opposite each other on the swells, nodding solemnly. before long a boat came bobbing over the seas from the _ruritania_. "now's your chance to give that fellow earwig up," declared raynor to jack, as, leaning in the door of the wireless room, they watched the scene. "somehow it seems to me that would be a shabby trick," said jack, after a moment's thought. "i'll confess, though, that when the _ruritania_ hove in sight such a thought came into my mind. but--oh, well, i guess we'll let him get by this time." "maybe you'll be sorry for it later on," said raynor, little guessing that those words were prophetic. there was to come a time when jack was to bitterly regret having let radwig escape capture by the british. the inspection by the naval reserve officer of the _ruritania_ did not vary from that which the _st. mark_ had already undergone at the hands of the _berwick_. naturally, the german reservists having been already given up, there was little to do but to overhaul the ship's papers. this did not take long, and before half an hour had passed, the two steamships saluted each other and parted company. that afternoon jack had a visitor in the wireless room. it was mr. johnson. he opened the conversation ingratiatingly. "i'm afraid i rather lost my temper the other afternoon," he said. "i want to apologize." "that's all right," said jack briefly, choking back a longing to tell mr. johnson that he was perfectly aware of his identity. "i--er--perhaps what i offered was not enough," he continued. "i may tell you now that i will double or triple the amount if you will send a message for me,--using a code, of course." jack jumped to his feet, his eyes ablaze. "see here, sir," he shot out, "you might offer me all the money there is in germany but it would not be of the slightest interest to me. now if you have nothing more to say, i'll ask you to leave this cabin before i----" the angry boy checked himself with his hands clenched and his eyes flashing. a murderous look came into mr. johnson's bearded face, but he appeared to be determined to keep himself in check. "do not be foolish," he urged; "have an eye to your own interests. as for your reference to germany----" "you are going to say that you don't understand it," cut in jack. "well, i must say i----" "don't go any further," interrupted the angry young wireless boy, "and now 'mr. johnson,' or herr radwig, i'll ask you to leave." radwig looked for a moment as if he was about to choke. his face turned purple and his hands clenched and unclenched nervously. the sweat stood out in tiny beads on his forehead. "what do you mean----?" he began. jack leaned forward and looked at him significantly. "just this, herr professor, that in spite of that fake beard and your dyed mustache, i know you. your reason for being disguised and going under a false name is no business of mine _now_. see that you don't make it so." "you--you----" sputtered the man who was startled in the extreme. "and furthermore," continued jack, "we are likely to run across some more british ships. if you annoy me any more, i shall point you out for what you are. that will be all. now go." utterly bereft of words, radwig turned heavily and half fell out of the cabin. he collided with bill raynor, who was just coming in. he fairly snarled at jack's chum, who airily remarked: "don't slam the door when you're going out!" "you young whipper snapper, i--i----" choked out radwig, and being too discomfited to find words, ended the sentence by shaking his fist at the two boys. "well," said raynor, as radwig vanished, muttering angrily to himself, "it would appear as if you'd spilled the beans, jack." "it does look that way, doesn't it?" said jack with a smile. "i rather fancy our teutonic friend will be good for a while now." chapter xiii. a message in code. "what happened?" was raynor's next question. "oh, he came in here and offered me untold gold to send a code message for him. i fancy that it was about the _ruritania_, telling her whereabouts and so on." "so that was his game, eh?" "well, he didn't work it. i got mad and told him that he needn't bother to conceal his identity from me, and that if he bothered me any more i'd show him up to the first british officer that again boarded us." "phew! going some. how did he take it?" "i thought he was going up like a balloon for a minute," laughed jack. "now, if we only could identify schultz, we'd have both of them where we want them." "that's going to be a hard job," declared bill. "they don't go about together. at least, i've watched closely, but never saw radwig talking with anyone on board." "no, i guess they keep pretty well under cover for fear of accident. i wish i could have gotten a look at them that night i overheard them talking." "yes, it would have simplified matters a good deal," bill admitted, "but, as you say, i don't think either of them will try to bother us again." the day passed uneventfully. in the afternoon they sighted a small british freighter making her way west, and later on overtook a french oil ship bound for holland. jack flashed them the latest war news, for they had a small wireless outfit, and in return received the information that two german cruisers were somewhere in the vicinity and that the french ship was in fear of capture at any time. that evening the wind blew rather hard. a high sea was whipped up by the gale and the _st._ _mark_, big as she was, rolled and pitched violently. it was what sea-faring men would have called "a fresh breeze," but to the passengers, that is, such of them as were unseasoned travelers, it was a veritable storm. jack and bill rather enjoyed the rough weather, coming as it did after a monotonous calm. after dinner they ascended to the boat deck and paced up and down, chatting for some time. inside the wireless room muller was at the key. now and then, as they passed and repassed, they would exchange a word with him. it was on one of these occasions that muller hailed them excitedly. "there's a ship just wirelessed the s. o. s.!" he exclaimed. "great scott," cried jack, "and on a night like this. what's the trouble?"' "don't know yet. i'm trying to get them again. notify the captain, will you?" "on the jump," cried jack. he despatched his errand in a few minutes, and was back in the wireless room with instructions to "stand by" and get further information as soon as possible. "anything new?" he asked muller. the wireless man shook his head. "nothing but that first s. o. s.," he said. suddenly there came a shout from bill, who was standing in the door. "look, jack, what's that off there?" he exclaimed, pointing to the horizon. a dull glow was reflected against the night sky in the direction he indicated. now it flashed bright as a blown furnace, and again it sank to a faint glare. jack was not long in deciding what it was. "it's a ship on fire," he declared. at almost the same moment a hoarse shout from the forward lookout and a shouted reply from the bridge told that the glare had been observed from there, too. possibly there is nothing at sea that thrills like the sight of a vessel on fire. jack, it will be recalled, had witnessed such a spectacle before, but yet his heart bounded as he watched the distant glare now bright and glowing, now dull and flickering. "hullo, the old man has rung for full speed ahead!" exclaimed bill, as the next moment the _st. mark's_ speed was perceptibly quickened and her course changed. several seamen in charge of the third officer, a mr. smallwood, came trampling aft. they busied themselves loosening the fastenings of one of the boats and getting it ready for launching. presently they were joined, and three additional craft were made ready for the work of life saving. all this time the glow had been getting brighter as the _st. mark_ approached the burning ship. but the distance was as yet too great to make out what manner of vessel she was. "i'd give anything to get in one of those boats," observed jack to bill, as the two lads watched the preparations for lowering away. "so would i," agreed bill. "do you think there's a chance?" "i don't know. i 'deadheaded' a radio for mr. smallwood to his sick mother the day we sailed. that might have some influence with him. i'll ask him anyhow." jack vainly pleaded with the at first obdurate officer, but after a long interval, he returned to bill with a smile on his face. "it's all right," he announced. "it was a hard job to get him to consent. i won him over at last. we go." "hurray!" cried bill. "now for some oilskins! it's not the sort of night to be without them." "i've got mine in the cabin," said jack. "i'll borrow muller's for you." "good for you. gosh! look at those flames. seems to be a big steamer." both boys paused a moment to look at the awe-inspiring spectacle of the blazing ship. as they did so, something occurred which chilled the hot blood in their veins and caused them to exchange startled, bewildered looks. over the dark, heaving waters that divided them from the blazing vessel there was borne to their ears what sounded like an awful concerted groan of agony. again and again it came, rising and falling in a terrible rhythm. it was not human. it sounded like the sufferings of demons. "wow! but that's fearful!" exclaimed bill, paling. "what under the sun can it be?" chapter xiv. the cattle ship. the awesome sound continued while the boats were being lowered. the weird nature of the uproar and its mystery made even the rough seamen apprehensive. the more religious among them crossed themselves fervently. "bad cess to it, if it don't sound like the howling of poor sowls in purgathory," muttered one of them. as the boat in which he and bill were sitting beside mr. smallwood was lowered, jack glanced upward and had a view of the lighted decks, the rails being lined with the heads of curious and excited passengers. then came a sickening swing outward as the ship rolled. "let go all or we'll be smashed!" shouted mr. smallwood. for a moment, as the ship heaved back, it seemed indeed, as if the boat was doomed to be dashed against her steel sides and smashed into splinters. but in the nick of time the "falls" were let go "all standing." the boat rushed downward and struck the top of a great wave with a force that shook her. the next instant, the patent blocks opened and on the crest of the great comber mr. smallwood's boat, and the others, were swept off into the darkness. behind them arose a mighty cheer, but they hardly noticed it in the excitement and danger of the launching. "a bad night for this work," muttered mr. smallwood as the boat was lifted heavenward and then rushed down into a dark profundity from which it seemed impossible she could emerge. a blood red glow from the leaping flames enveloping the stern of the doomed craft, which was a large, single funneled steamer, lay on the roughened sea. "are there passengers on board, do you think?" asked jack, rather tremulously, as the blood-chilling uproar from the burning vessel continued. "looks to me more like a freighter--hard there on the bow-oars,--meet that sea,--she has no upper decks," replied the third officer. "i don't see anybody on board her, either," said bill, after an interval, during which the boat escaped swamping, as it seemed to the boys, by a miracle only. "let's hope they got away," said the third officer, "but that devil's concert on board beats me. it's not human, that's one sure thing. what in blazes is it?" "it gives me the shivers," confessed bill. the noise grew positively deafening as they got closer. the intense heat of the blaze and the shower of falling embers that enveloped them added to their discomfort. "row toward the bow," roared mr. smallwood, cupping his hands, "or we'll have the boats afire next." already several of the seamen had hastily extinguished portions of their clothing that had caught, and burns on hands and faces were plentiful. but as they pulled toward the blazing craft's bow, this annoyance was avoided, the wind blowing the heat and embers from them. all at once, as they swung upward on the crest of an immense comber, jack uttered a shout: "the mystery's solved." "what do you mean?" demanded mr. smallwood. "the mystery of that horrible noise. that's a cattle ship yonder, and the poor beasts are mad with fear." the next wave gave them a clear view of tossing horns and heads as the unfortunate cattle, penned on the burning craft, rushed madly about the decks, in vain seeking some means of relief. it was a piteous sight, for there was no way of saving them from being burned alive unless the ship sank first. "oh, but that's awful!" gasped jack, with a shudder. "look, look up on the bow!" cried bill suddenly. "there's a man. he's seen us." "he's waving," cried mr. smallwood. "hurrah! give way, men! there's a poor beggar roasting on that ship." but the boat's crew needed no urging. in the lee of the burning cattle ship the water was smoother and they could make better time. silhouetted against the glare, too, every man of them could see, by a twist of his head, that solitary marooned figure on the bow of the fire ship. as the first boat,--mr. smallwood's,--ranged in alongside the high steel prow, jack's quick eye caught sight of a rope dangling from the great steel anchor chains. by what impulse he did it he could not have explained, but as the boat ranged close alongside he poised for an instant on the heaving gunwale and then launched his body forward into space. "come back, boy!" shouted mr. smallwood. but by the time the words had left his mouth, jack was scrambling up the rope amidst the cheers of the men in the tossing boats now far below him. it was the work of a few moments only to gain the anchor chain, and to climb up them was, for a lad of jack's brawn and activity, an easy task. "thank heaven you came before it was too late," cried the solitary man on the fore deck, staggering toward the boy with outstretched arms. "are you the only man on board?" demanded the boy, deciding to leave explanations till later. "no, dick sanders is sick in his bunk below." "where, down this hatchway? in the forecastle?" asked jack quickly. "yes, i was too weak to carry him up, heaven help me," muttered the other reeling weakly. jack did not stop to listen. he knew that within a few minutes his shipmates would be on board and would rescue the half-crazed man on the bow. it was his duty to go after the sick man below. into the ill-smelling darkness of the forecastle of the cattle ship he plunged, clawing his way down an iron ladder. at the bottom he struck a match. as its light flared up he heard a groan, and looking in the direction from which it came he espied the emaciated form of a boy lying in a bunk. "have you come to save me?" gasped out the sick lad, who was almost a skeleton and whose eyes glowed with unnatural brightness in his parchment-like face. "yes, but you must do exactly what i tell you," instructed jack. "i will, oh, i will," choked out the other. "only save me. i was afraid i was going to be left here to die alone." "don't talk about dying now," ordered jack. "now clasp your arms round my neck and hold on tight. do you think you can keep your grip till we get to the top of that ladder?" "yes--that is, i think so," returned the sick lad, who had been cabin boy on the doomed ship. "then, hold on," ordered jack as, having carried his pitifully light burden across the forecastle to the foot of the ladder, he prepared to ascend the rounds. once or twice he had to stop on the way up, and holding on with one hand, grasp dick sanders with his other arm to allow the lad to recruit his strength. at last they reached the deck and jack, who was almost exhausted, laid his frail burden down with a sigh of relief. he looked about for his companions, who he fully expected to see on the forecastle. there was no sign of them. the lone man who had waved to them from the bow had also vanished. a rope ladder, one end of which was secured inboard, showed the way they had gone. "queer that they didn't wait for me," muttered jack. "they must have known i was below. i wonder----" there was a sudden warning shout from somewhere. "look out for your life!" came in mr. smallwood's voice. jack looked up, startled. the burning ship was a flush-decked craft. that is, her forecastle was not raised, but was on a level with the main deck where the cattle pens were. the terrified creatures, in their frenzy of fear, had broken loose from the flimsy timber structure, and now, urged on by the flames behind them, were charging down in a wild stampede upon jack and the half-conscious form of the sick boy at his feet. it was not possible to effect a retreat down the forecastle hatch, for his efforts to support himself on the journey up had been too much for dick sanders' strength. jack looked about him. it was imperative to act with desperate swiftness. now, not fifty feet from him was the advance guard of the maddened, fear-crazed steers. in a few seconds, if he did not act swiftly, both he and the lad he had rescued would be pounded by their sharp hoofs into an unrecognizable mass. suddenly he formed a resolution. with desperate eagerness he stripped off his oilskins and kicked off the light deck shoes he had not thought to change in the hurry of embarkment. then, picking up the fragile form of dick in his arms, he sped for the side of the forecastle. as the long-horned steers swept down so close to him that he could feel their breaths and see the whites of their frenzied eyes, the boy leaped up and outward into the night. chapter xv. jack's brave leap. what happened after the leap, jack never knew clearly. he felt a wild, half-suffocating rush through the air and then a sensation of choking and strangling as a cold, stifling weight of water pressed in on him. down, down, down he plunged. it seemed as if he would never rise. in his ears was an intolerable drumming. everything was blood-red before his eyes. then came a sudden blast of blessed air, following a swift upward rush, and he found himself struggling in the wild sea with dick sanders clinging desperately to him and almost making him go under again. luckily jack, without conscious thought, had chosen the lee side of the burning ship, where the boats hovered, for his leap for two lives. as his head appeared above the surface, the bright glare of the flames showed his form clearly to the anxious watchers who had witnessed his daring dive. "there he is! hurrah!" shouted bill raynor, who was the first to see him. "hold on, jack, old boy, we'll be with you in just a second." "keep up your heart! we'll get you!" bellowed mr. smallwood. jack essayed a feeble wave in response, with the result that he was once more engulfed. but in a few moments he was safe and a dozen pairs of strong arms had drawn him and dick sanders into mr. smallwood's boat. "heavens, lad, what a dive," cried the third mate admiringly, when jack was somewhat recovered and dick lay covered with seamen's coats on the floor of the boat. "gracious, we thought you were a goner!" exclaimed raynor, "when the cattle made the first charge. i guess you didn't hear it, being below. we all came close to being caught. the man on the forecastle, who was unconscious by the time we got on board, was reached in time to be lowered into one of the boats. in the confusion, we thought you were among us. it was not till we reached the boats again that we found our mistake." "in the meantime," said mr. smallwood, "those poor devils of steers had reached the rail and not liking the look of the water any better than the fire, charged back again. it was just as the second 'wave,' as you might call it, was coming for you that we saw you weren't with us. suddenly we sighted you with that poor kid there," he nodded to the bottom of the boat, "right in the line of their charge." "if it hadn't been for your warning shout, i might not have been here now," said jack. "i saw that and so i yelled with all my power," said the third officer, "but lad," he went on, slapping jack on the back, "when i saw what you were going to do, i regretted having warned you." "it was the only thing to do," said jack. "we wouldn't have stood a chance if we had remained where we were," and he explained that it was impossible to find shelter on the flush deck or to retreat back into the forecastle. "well, all's well that ends well," said mr. smallwood, "but it gave me a turn when i saw you come sky-hottling off that bow. but,--great christmas,--look yonder." he pointed back at the burning ship. by her own light they saw her pitch heavily forward, hesitate an instant and then, without further warning, and amidst a piteous bellowing that sounded like a death-wail, shoot downward to the depths of the ocean. in an instant the light she had spread across the rough sea had vanished, and by contrast, the night appeared to have suddenly solidified about them in velvety blackness. a moment later a blinding white light groped across the waste of tossing waters and enveloped them in its glow. it was the searchlight of the _st. mark_ and it accompanied them with its cheering light till they reached the ship's side. they were greeted amid acclamation, and dick sanders was at once taken charge of by the ship's doctor and some lady passengers. the man who had been rescued had, by this time, however, sufficiently recovered to accompany mr. smallwood, bill and jack to captain jameson's cabin, where that officer was eagerly waiting to hear the details of the rescue. the rescued sailor, whose name was mark cherry, soon told them the story of the disaster to the _buffalonian_, a british cattle ship which had left new york for london several days previously. early that evening the craft had been overtaken by a german cruiser and ordered to surrender. every one on board was made prisoner, and some of the cattle taken, when the british captain, seized by a sudden fit of anger, struck the german commander in the face. he was instantly ironed, as were his officers, mark cherry observing all this from under the cover of a boat where he had been working when the cruiser took the cattle craft, and in which he had remained hidden. in revenge, apparently, for the british captain's attack on him, the german commander had, on his return to his own ship, ordered the _buffalonian_ fired upon by the big guns. the hidden sailor crouched in terror in his place of concealment while the cannon boomed. he thought his last hour had come. the projectiles shrieked through the sternworks of the ship and one, he thought, had struck amidships (which accounted for the vessel's foundering). at length, appearing to tire of this, the german cruiser put about and steamed away. cherry crept from his hiding place where he had remained paralyzed with fright throughout the bombardment, and making for the wireless room sent out the only signal he knew, the s. o. s., which he had learned from a friendly wireless man, in case there ever came a time when it would be a matter of life and death to him to use it. this explained why no answer came to muller's frantic calls after the first distress signal. it was only a few moments after this call that flames burst from the shattered stern, and cherry knew that unless help came, his hours were numbered. so confused and terrified was he by his desperate situation, that it was not till jack's appearance on the scene, he remembered little dick sanders, the cabin boy, lying sick in his bunk below. (it may be said here that with care and good treatment the lad quickly recovered his health, and he and mark cherry were put to work with the crew of the _st. mark_.) thus, without further incident, the english channel was reached and jack began busily to try to communicate with the firm's london agents for instructions as to docking orders. chapter xvi. awaiting orders. while awaiting orders, which the wireless had told the _st. mark's_ captain were not ready for transmission, the big liner stood "off and on" at the mouth of the channel. it was wearing work, and all looked forward eagerly to the day when their destination would be settled and they could proceed. jack felt the monotony of it no less than anyone else on board, but he spent a good many busy hours perfecting an attachment for a wireless coherer which he hoped would prove of great value in the future, and possibly prove as profitable as the universal detector, to which allusion has already been made in "the ocean wireless boys" and "the naval code." one night, after working for some time at some rather abstruse calculations in this connection, he decided to abandon the work for the night and take a stroll on deck before turning in. raynor, he knew, was finishing up the last of a series of match games of checkers, so he did not bother to look up his friend. knowing that bill was busily engaged, jack was rather surprised when, at his fourth or fifth turn up and down the deck, which was almost deserted, a steward stepped up to him with a note. it proved to be from raynor and read as follows: "dear jack: "meet me at once in the stern where we can talk without being spied on. the steward will show you where. i have something important to tell you about radwig. "bill." "this is very peculiar," mused jack, and then, turning to the steward he asked: "did mr. raynor give you this?" "yes, sir, and he told me to bring you to where he was waiting, sir," was the obsequious response. "all right, lead on," said jack and then to himself he added: "i can't in the least make out why old bill should be so secretive. i might just as well have met him in his cabin. but maybe he is being watched, and thinks the place he has appointed would be better." the steward led the way aft through a maze of corridors and passages. at last they arrived far in the stern of the ship where the unlighted passages showed no cabins were occupied. the twenty first-class passengers had all been booked amidships, thus the hundreds of cabins opening on the stern passages were unoccupied and nobody went near them. "you've no idea why mr. raynor selected this part of the ship to meet me?" said jack, as he followed the man who lighted the way with an electric torch. "no, sir," he replied, with a shake of his head. "i suppose he had his reasons, sir." "no doubt, but this is an odd part of the ship to keep an appointment," said jack. "we must be far away from the occupied cabins." "oh, yes, sir. almost a tenth of a mile. wonderful, ain't it, sir, the size of these big ships? a fellow could yell his lungs out in this part of the vessel, sir, and things, being as they are, and the cabins empty and all, nobody could hear him." "i suppose not," said jack idly. "are we nearly there?" "yes, sir. just turn down this passage, sir. right to the left, sir, mind that step and--" crash! a great burst of light, as if a sudden explosion had occurred in front of him blinded jack, and at the same instant he felt a violent blow on the back of the head. then the bright light vanished with a loud report and he seemed to swim for an instant, in blackness. everything went out, as if a light had been switched off, and the lad pitched heavily forward on his face. "good, that will settle his hash for a while," muttered a voice, and radwig, a short, wicked-looking bludgeon in his hand, bent over the senseless boy. by the german's side was another man, a short, thick-set, clean-shaven fellow with a projecting jaw, known on the passenger list as mr. duncan ewing, of chicago. the light of the steward's torch illumined their faces as they stood above the recumbent young wireless boy. "i say, sir," muttered the man, "i know you've paid me well and all, sir, but i didn't bargain for no murdering business, sir. i----" "don't be an idiot," snapped radwig impatiently. "we haven't hurt him. see, he's beginning to stir. now then, schultz----" radwig bent and took up the limp body by the head while mr. duncan ewing, who answered with alacrity to the name of schultz, laid hold of poor jack by the feet. "now, steward," said radwig, as they carried their burden into an empty cabin, "keep a stiff upper lip till we dock, and then i don't care what happens. you'll be well taken care of. don't forget that." "yes, sir, i know, sir," said the man, whose hand was trembling as he held the torch; "but i don't like the business, sir. if it wasn't for my poor wife being sick and needing the money, and all---" "that will do. go get us the lamp you promised. in the meantime we'll revive this young fellow and show you that he's not dead." from a carafe of stale water that stood on the washstand, radwig dashed a liberal application in jack's face. he loosened the lad's collar and chafed his wrists. jack moaned, stirred, and opened his eyes. for a moment his swimming senses refused to rally to his call. then, with a flash, he realized what had happened. "radwig, you scoundrel!" he exclaimed, "what is the meaning of this outrage?" "just a delicate little way of reminding you that it is not well to thwart the wishes of herr professor radwig," was the reply. "schultz, my dear fellow, shut that door. no, wait a moment, here comes our man with the lamp. that's better." he took the lamp from the steward, and set it in a frame on the wall provided for it in case the electric light failed from any cause. the steward, still pale and shaky, hurried away after one glance at jack. "and now," said radwig, "we will leave you to your reflections, my young friend. it will do you no good to shout. under present conditions this part of the ship is uninhabited. no one comes near it. as for trying to force the door after we have gone, it would be wasted labor. i have taken the pains to affix bolts to the outside of it. bread you will find, and some water, under the bunk. i advise you to be sparing of it, for you will not get any more and now--_auf wiedersehn_." he opened the door, motioned schultz out, and turned a malevolent smile on the boy. with a shout, jack flung himself forward, but the door slammed in his face. he heard a laugh from outside, a laugh that made his blood boil and his fists clench. he fell against the door and wrenched at it furiously. but already the bolts outside had been shot into place and the portal held firmly. "now don't lose your temper," begged radwig mockingly from without; "it's very bad, very bad for the digestion. i would recommend you to spend your time mediating over the manifest advantages of being obliging. good-night." jack, listening at the bolted door, heard their footsteps die away down the deserted passageway. chapter xvii. what befell in the after cabin. "man overboard!" bill, making his way along the deck to the wireless room companionway, heard the thrilling cry and joined the rush of passengers to the stern rail from whence the shout had come. radwig and schultz stood there with every expression of alarm on their faces. the captain came hurrying up. "what is it? what's the matter?" he demanded. "somebody fell overboard," declared radwig; "we heard a splash and hastened here at once to cut loose a life belt." "lower a boat at once," commanded the captain; "slow down the engines." the petty officer to whom the command had been given, hurried off at top speed to the bridge while the captain asked more questions of radwig and his companion. but they could tell nothing more definite than that they had heard a splash and a cry and that was all. they had not seen who was the victim of the accident. the captain decided to call a roll of passengers and crew at once. while the boat was lowered, and was rowed to and fro, on the dark waters, this work went on. when it was over, there was only one person on board found to be missing. this was, of course, jack ready. the cunning of radwig had evolved this clever plan to obviate the search that would be surely made on the ship for the imprisoned young wireless lad when his absence from duty was discovered. if the lad was believed to be drowned, of course, no effort would be made to find him on board and he and schultz would be safe from the results of their rascality. it was a clever though simple scheme and it worked to perfection, for after an hour of investigation the captain was forced to conclude that jack had, in some inexplicable manner, fallen overboard and had perished. but there was one person on board who did not accept this theory, and that was bill raynor. by no figuring could he bring himself to believe that jack had fallen into the sea. in the first place, the rail was almost breast high, and in the second, jack was too good a sailor to have lost his head and toppled from the ship. "i am convinced he'll turn up," he told mullen in the wireless room. "yes, but a thorough search was made for him without result," objected the other. "never mind, something seems to tell me that he is all right," protested bill. "i'm afraid you are deluding yourself," said mullen, shaking his head. "when he fell overboard----" "you mean _if_ he fell overboard," interrupted bill. "why, you surely don't doubt that!" exclaimed mullen; "a splash is heard and following that a canvass of the ship shows that jack ready is missing. if he wasn't drowned, where is he?" "i admit that it sounds like a poser," said bill. "see here, i'm not absolutely certain that he did go overboard at all." "what?" mullen stared at raynor as if he thought he had suddenly been bereft of his senses. "i mean what i say," repeated bill slowly. "i'm not sure that he did go overboard." "in that case he must be on board the ship." "exactly." "but why should he be hiding?" "he's not hiding." "then why doesn't he show up?" "because he's been hidden," replied bill. "oh, that's too fantastic an idea," cried mullen. "i know it sounds wild--almost crazy, in fact, but i simply cannot help feeling it." "i wish i could think the same way," said mullen, and the tone of his voice left no room to doubt that he meant what he said. in the meantime, how was it with jack? confined in the stuffy cabin, lighted only by the smoky lamp, his head ached intolerably from the cruel blow that had been dealt him. in fact, it was not till the following morning that he felt himself again. neither of the men who had made him a prisoner came near the cabin in which he was confined, and although he tried shouting for aid till his throat was sore, nobody appeared to hear him. the boy began to be seriously alarmed over his predicament. radwig had told him in so many words, that neither he nor schultz intended to return to the cabin. the water and bread left him would not suffice for more than a few hours. by the time the cabin was entered by some employee of the ship, it was entirely probable that the aid would come too late. luckily for him, his mental anguish was not increased by knowledge of the story of his death by drowning that had circulated through the ship. had he known of this, it is likely that, plucky as the lad was, he would have given way entirely to despair. the cabin was an inside one, so that there was no porthole through which he could project his head and call for aid. examination of the small chamber, even to the length of pulling up the carpet, showed that there was no means of escape short of forcing open the door and that jack, strong as he was, was unable to accomplish, although he wore out his muscles trying it. the hours passed by with dragging feet until it seemed to the boy that he must have been in the bolted cabin for years instead of hours. the lamp guttered and went out, leaving him plunged in pitchy darkness. it was the last straw. jack flung himself on the bunk and buried his head in his hands. how long he lay thus he did not know, but he was aroused and his heart set suddenly in a wild flutter by the sound of approaching footsteps and voices. he shouted aloud: "help, for heaven's sake, help!" then he sat silent, hardly daring to believe that there was a possibility of his rescue. more probably the voices and footsteps were those of radwig and his rascally accomplice. in an agony of apprehension, jack sat in the darkness waiting for the answer to his cry for aid. chapter xviii. a rascal brought to book. we must now go back to an occurrence that happened earlier in the evening. the ship had finally received orders to dock at southampton and was proceeding at a fast clip up the channel when the telephone in the wireless room rang and a voice inquired for bill raynor. summoned to the wire by mullen, bill, who had just entered the station after a miserable day of anxiety for jack, replied and found that he had been called by the ship's surgeon, dr. moore. "there has been an accident," said the doctor; "one of the men has been badly injured. he says he wants to see you without delay." "but i know none of the crew," said bill. "this man evidently knows you, however," returned the doctor, "and i wish you would come as soon as possible. he appears to be worrying over something and says he cannot rest till he has seen you." greatly mystified, bill obeyed the summons. on entering the doctor's cabin he saw, stretched on the lower bunk, and swathed in bandages, the figure of a man who turned a pair of sunken eyes on him. "one of the stewards," whispered the doctor. "poor fellow. badly scalded in the galley." he turned to the sufferer. "this is mr. raynor, whom you wanted to see," he said. "let him come here," said the man feebly. bill approached the man's side. "what can i do for you?" he asked. "i want to ease my conscience of a great burden. bend low so that you can hear me. it hurts when i talk loud." bill bent over the pitiable, bandaged form. "what do you want to tell me?" he said. "that your friend, mr. ready, is a prisoner on this steamer," was the reply that brought an exclamation of amazement from bill. he was half-inclined to believe the man was delirious for an instant, but a moment later revised this opinion. "how do you know this?" he asked, when he had recovered from his astonishment. "i helped the plotters who put him there," moaned the man. "they were germans, like myself, and they told me that if he was not shut up he would betray them to the english authorities as soon as the ship docked. they gave me money and i let them have the key to a cabin far in the stern of the vessel. they forged a note to him and trapped him when, in answer to it, i led him to where they were waiting." "and he is there now?" cried bill. the man nodded slowly. "so far as i know. they had screwed bolts on the door." "he was not hurt?" demanded bill. "not seriously; but they struck him on the head." "the brutes," cried bill. "you know who they were, then?" "i can guess--a man named radwig and another named schultz." the bandaged man nodded again. "you have named them correctly." "doctor!" exclaimed bill, "you have heard what this man has said. can you leave him long enough to go with me to captain jameson?" "gladly, my boy. but of all extraordinary tales----" "it is true, upon my word of honor," groaned the injured man. "the number of the cabin is 14. the chief steward has the keys. i stole them from his desk to open the stateroom and placed them back again without his knowledge." "and just to think," muttered bill, as he and the doctor hastened from the injured man's side, "that if it had not been for that accident we'd never have known a thing about poor old jack's plight till too late. after all, that feeling i had was correct." captain jameson summoned the chief steward as soon as he had heard bill's story and together the commander, and the others, hastened through the maze of corridors leading to stateroom 14. theirs were the voices the boy had heard, and in ten minutes' time he was wringing bill's hand and telling, to an indignant group, the story of radwig's outrage. the captain's indignation knew no bounds. "i'll have those rascals in irons before we drop anchor!" he exclaimed. "we are nearing southampton now and if that man had not met with his accident they might have landed and escaped scot free." jack was weakened by his trying experience, but he was not too exhausted not to be able to accompany the officer to radwig's cabin. a knock on the door brought an immediate answer: "come in." "keep back," whispered the captain to jack, "i want to see how far these rascals will incriminate themselves." accordingly, jack and the others kept out of sight as the door was opened and captain jameson stepped inside, but as the portal was left ajar, they could hear what went on within. "you know my friend, mr. ewing," said radwig, in oily tones, indicating schultz, who, it will be recalled, had adopted that alias, and who was seated in radwig's cabin engaged over a valise full of papers. the captain bowed his acknowledgment of the introduction. "and to what am i to attribute the honor of this visit?" said radwig. "possibly something connected with the formalities of landing? i am informed we shall be in harbor in a short time now." "that is correct," said the captain bruskly, "and we shall land minus one of the ship's company." "you mean poor young ready, the wireless operator," said radwig. "it was too bad about that unfortunate lad. if my friend and myself had been a few seconds earlier we might have saved him before he went overboard." "well, of all the precious hypocrites," gasped bill under his breath. "he takes the grand trophy," breathed jack, who had been told of the cleverly arranged story of his death that had been circulated. "there is not a question but that he is drowned, i'm afraid," came from schultz the next minute. then was heard the captain's voice. "why, yes, gentlemen, there is," he said; "in fact, there is every question for _here he is_!" as if he had been an actor answering his "cue," jack stepped into the lighted doorway. at the sight of him, the two miscreants shrank back as if they had seen a ghost. "oh, i'm real enough, messrs. radwig and schultz," smiled jack, as the others crowded in behind him. "and it will be my duty to hand you both over to the british authorities," snapped the captain to the speechless pair. radwig made a sudden dart for the valise full of documents. his move was so unexpected that before they could stop him he had hurled it out through the open porthole. then, with a snarl of rage, he flung himself at jack. but the captain's erect figure interposed. "stand where you are," he ordered, and radwig found himself looking into the muzzle of a revolver. "hold out your hands," he ordered and cringing, the two miscreants obeyed. "jones," he added, addressing the chief steward, "oblige me by slipping those handcuffs on the men." the click of the steel bracelets appeared to arouse radwig to speech. "you--you--young whelp," he shouted, shaking his manacled fists at jack. "whatever may be my fate, i'll remember you and see that you are attended to if it takes every penny and every resource i have." "violence won't do you any good," commented the captain quietly, "and if i know anything of the english law you are apt to spend quite some time in great britain. jones, march the prisoners to the smoking room and detain them there till the ship docks." sullenly, the two prisoners shuffled out of the cabin and were marched past wondering passengers to their place of detention. three hours later, when the ship docked, the boys saw them being taken ashore by british officials. a thorough ransacking of their cabin had failed to reveal any incriminating documents, although the valise which radwig had hurled out of the porthole undoubtedly had contained such papers. at southampton they learned that the _st. mark_ was likely to be tied up for some time. rumors of mines and torpedoes made the owners unwilling to risk her loss. the two lads, therefore, left the vessel, and proceeded to london, where their instructions were to visit agents of the line and learn if anything had been heard of tom jukes. they found the city thronged with marching soldiers and territorials, while everywhere proclamations calling on the men of england to enlist were posted. otherwise, however, everything appeared to be going on as if there were no war. inquiry at the agents resulted in a meagre clue to the whereabouts of the lad of whom they were in search. he had wired for funds from malines, a belgian town, a few days before war was declared and the germans invaded belgium. since then nothing had been heard of him. the magnitude of their task appeared greater than ever to the two lads now that they had actually started the work. but jack was not the sort of lad to give up at the first difficulty. "we'll go to belgium," he announced, but right here a stumbling block appeared. there were no longer regular steamers running to belgian ports, and the small and infrequent craft that did venture had been warned by the admiralty that the north sea was thickly sown with mines. it was a journey full of peril but, nothing daunted, jack and bill journeyed to grimsby, a town on the east coast, where they were told they might be able to engage passage on a trawler, provided they could find a captain adventurous enough to take them across. all this took up valuable time, for in the confusion and turmoil of war time, business was harder to transact than in normal times. two days were consumed in london, but on the evening of the second they started for grimsby. as they took their seats in the train, a newsboy came along shouting "war extras." they bought some of his papers and settled back to read them. "well, here's an encouraging item," said bill ironically, as the train moved out. he pointed to a despatch headed: "trawler destroyed by mines in the north sea." "we'll have to take our chances," decided jack, "but, hullo--what's this?" he exclaimed suddenly; "listen here, bill." he read excitedly from his paper: "the two prisoners arrested as german military agents on the arrival of the american liner _st. mark_ at southampton two days ago have, in some mysterious manner, escaped. four of their guards are under arrest. it is hinted that bribery was used to effect the germans' liberty." chapter xix. the "barley rig." it was with captain hoeseason of the trawler _barley rig_ that the boys finally succeeded in striking a bargain to land them in antwerp. the captain of the craft, who was also her owner, was a giant of a man, more than six feet tall in his great sea boots and dressed in rough fisherman's garb. the boys found him in a small, waterfront inn, with a thatched roof and red window curtains which bore the sign of the magpie and shark, apparently, in the owner's estimation, a happy combination of land and sea. captain hoeseason declared that he knew the north sea like a book and that there would be no danger of encountering mines if they sailed with him. his craft would be ready at the long fish dock at six the next morning, he declared, and at that hour the boys presented themselves. the crew of the _barley rig_ were a rough, weather-beaten looking set of men, and almost immediately, upon the boy's arrival, they set to work, under the hoarsely bawled orders of captain hoeseason, setting the fisher craft's great red sails. at last all was ready. under a brisk breeze, that momentarily grew stronger, the trawler slipped out to sea. "they're a rough-looking lot on this craft," observed jack to bill, as the _barley rig_ began to toss about in a way that would have been trying to less experienced sailors. "yes, i'm glad you've got that money in your money-belt," said bill, referring to the american gold they carried. "they have none of them seen it, thank goodness, or we might have cause to worry." "oh, i don't know," declared jack. "they may be honest enough for all their rough looks. i imagine that the north sea fishery doesn't tend to make men very refined looking." "at all events it hasn't had that effect on this crew," laughed bill. at noon they were summoned, by the cook's beating on a tin pan, to a dinner of fried fish and boiled potatoes. the little cabin where they ate it reeked of the fish that for years had formed the _barley rig's_ cargo, and was lighted, for it had no openings but the companionway above, by a swinging, smoking lamp of what was known among the fishermen as the "pot" variety. but it would have taken more than this to dull the keen edges of the boys' appetites, whet to razor sharpness by the freshening wind. the cook, an old, bent man, with a wild blue eye, stood by his rusty stove watching as they devoured what was set before them. overhead they could hear the trample of feet and the occasional impact of a big wave as it broke in spray over the bow. "it's getting rougher," remarked jack. "seems to be," agreed bill; "this is a small boat to be out in a storm." "they say that the trawlers are fine sea boats," declared jack. there was no doubt that it was getting rougher. by mid-afternoon the green seas with breaking, white tops, were leaping mountainously under a scudding gray sky. still, the captain of the _barley rig_ did not take in a reef of his sails. he stood beside the tiller, which was gripped by a young giant of a fisher in jersey and boots, giving an occasional order and puffing vigorously at his stubby clay pipe. beside an occasional gruff word, captain hoeseason did not have much to say to his passengers, but they noticed that his eyes followed them constantly. "i can't shake off an idea that the fellow has some mischief in mind," declared bill, after he had noticed the furtive scrutiny the skipper of the _barley rig_ was bestowing on them. "nonsense," declared jack. "i made a few inquiries about him and he appears to bear a good character. anyhow, we are going among dangers beside which this trip won't appear as anything, so don't get nervous at the start off." as dusk began to settle down, it showed a wild scene. the trawler appeared to be alone on the troubled ocean; at least, no other craft was within sight. the wind howled dismally through the cordage, and the reefed sails tore at their ropes as if they would part at any moment. "bad weather, captain," said jack, as he and bill stood bracing themselves against a back stay. "oh, aye," rejoined the captain, taking out his pipe like a stopper to permit himself speech, "but she'll be worse afore she gits better." he was right. by nightfall, it was blowing a gale, and the big seas were breaking over the _barley rig_, drenching everything. water fell in cataracts down the cabin companionway every time the hatch was opened. cooking was impossible, and the boys made their supper on hard ship biscuit and water while a small flood washed about their feet. "this is awful, jack," remarked bill after a lurch that had sent him sliding across the cabin. "cheer up, old fellow, it might be worse," retorted jack cheerily. bill gave a groan. "i don't see how it could be, unless we go to the bottom," bill grumbled dismally. "you don't think there's any danger of that, jack, do you?" "not a bit of it. this craft has weathered many a storm as bad or worse than this, i don't doubt," declared jack stoutly, although the laboring of the storm-stricken _barley rig_ was beginning to get on his nerves. not long after the completion of their scanty meal, the captain came below and snatched a bite. he was dripping from head to foot and reported the gale as increasing in violence. "my advice to you younkers is to turn in," he said. "you can have my bunk--that one yonder. i'll be on deck all night and so will 'tother lads." the bunk in question was not much more than a shelf with some very dubious-looking blankets piled untidily on it. but the boys were tired, and so they clambered up and composed themselves to rest with the deck within a foot of their faces, so low was the cabin ceiling. for a time sleep was impossible. the buffeting blows that the big waves struck the laboring trawler made her shake and creak as if she would go to pieces at any moment. on deck the heavy trampling of sea boots kept up without intermission. the smoky lamp swung drearily. the motion grew so violent at times that they were almost pitched out of the bunk. in some corner into which he had dragged himself, they could hear the old cook snoring and mumbling in his sleep. but at last, despite all this, tired nature asserted herself and they dozed off, while outside, the storm howled and shrieked like a furious and sentient creature aroused to frenzy and extermination. chapter xx. the hidden mine. about midnight, jack awakened with a start and a vague feeling that all was not well. the _barley rig_ was still tossing violently and for a few moments after he opened his eyes, the lad who had slept on the outside of the bunk felt dazed. then he became aware that captain hoeseason was standing near to him, feeling about under the mattress. "he's trying to rob us," thought jack. "what shall i do?" the thought flashed across him that he had no weapon, and that hoeseason was probably armed. he was undecided whether to feign sleep or not, for the captain of the _barley rig_ was apparently not yet aware that the boy was awake, when he was saved the trouble of making a decision. he was grasped roughly by the shoulder and violently shaken. the giant captain, with an evil look in his eyes, stood above him, a huge seaman's knife glimmering in his hand under the light of the guttering lamp. "now, younker," he said, in his hoarse tones, with a ferocious look, "i ain't goin' ter beat about the bush. i've come after that money of yourn." "what money?" demanded jack, deeming it wisest to "spar for time," and see if he could not devise some way out of the dilemma. "now, don't play foxey, mister yankee kid," snarled the huge fisherman; "you know as well as i do. the money in that belt i heard you talking to your chum about." "i know nothing about it," declared jack. "when i paid you i gave you almost all the money i had. i am looking to get fresh funds in antwerp." the man tightened his grip on the boy's shoulder and fairly yanked him out of the bunk. he placed his knife between his teeth and compelling jack to hold his arms above his head he searched him. jack's heart sank. he knew the money belt was in the bunk under the pillow. beyond doubt this desperate ruffian would search the sleeping place before very long and discover its hiding place. "so it ain't on you," snarled hoeseason, when he had finished his search, "but i'll bet a guinea it ain't far away. stand where you are and don't move as you value your life while i overhaul the bunk." a moment later an exclamation of savage delight burst from his bearded lips. "ah! here it is. see, younker, i was bound to find it and---what the----?" as the giant of a man stood half-facing him, jack gathered himself for a crouching leap. he sprang straight at the man's legs and, catching him entirely by surprise, brought him to the floor with a crash that could be heard above the raging of the storm. [illustration: jack gathered himself for a crouching leap and sprang straight at the man's legs.--page 156] "bill! bill!" he shouted. there was a stir in the bunk above. "help me, quick. he'll be too much for me alone." "what in the world, jack ready----?" "don't ask questions. come, quick!" bill clambered out of his bunk with alacrity as soon as he saw what was going forward. hoeseason, who had been, luckily for jack, slightly stunned by the fall, lay still. in his fall the knife had flown from his hand and lay half-way across the cabin. "the knife, bill," panted jack, "the knife before he comes to. i dare not take chances with him." bill quickly fetched the weapon. "so he did try to rob us after all," he said. "the precious ruffian, i didn't like his looks from the start." "never mind about that now, bill, but hustle and get some rope. we must tie him, for when he comes out of this he'll be a match for the two of us." there were plenty of odd bits of rope lying about the cabin on lockers that ran down one side of it. bill procured several lengths, and in a few moments, the semi-conscious giant was bound hand and foot. in the meantime, jack fastened the money belt round his waist once more. "i wish we had pistols," he said, as they stood watching the slow return of consciousness to the bound captain's face. "why, this fellow is harmless now," rejoined bill. "yes, but you have forgotten the rest of the crew, haven't you?" "great scott, i had for a moment. do you think they are in league with him?" "i don't know, but they are bound to find out his plight sooner or later and we shall have to reckon with them. we're in a tight place, bill." captain hoeseason began to stir. he rolled his eyes uneasily, and the next moment discovered that he was tied fast. "you young imps," he roared in stentorian tones, "cut me loose instantly, or when i do get free i'll have such a vengeance on you as will----" "it won't do you any good to rave like that, captain," declared jack, "and, moreover, we----" the sentence was never finished. the fabric of the _barley rig_ seemed to heave suddenly upwards and then rush apart. there was a burst of blinding flame, and a report that drove the ear drums in. the next instant, as it seemed to them, there was an inrush of water on the tide of which the boys were swept out into the darkness of the raging seas. the trawler vanished almost as quickly as the terrific flash of flame from the mine that she had struck, and which had ended her career for all time. chapter xxi. the north sea. the moments that followed were the most terrible that jack had ever known in his adventurous life at sea. cast adrift in the dark night and wild sea, he was at first completely bewildered. the very suddenness with which the end of the _barley rig_ had come had benumbed him. but ere long, the blind instinct of life asserted itself. he struck out, hoping to find some wreckage with which to sustain himself, for in that rolling, breaking sea, he could not have hoped to remain afloat long without some support. wave after wave swept over the bravely battling lad, half choking him in spite of the fact that he was an experienced and powerful swimmer. "great scott!" he thought with dismay. "if i can't find some support to cling to before long, i'm a goner. this is the worst ever." in addition to the difficulty of fighting the baffling waves, jack now began to experience a fresh obstacle to keeping afloat. the weight of the heavy money belt at his waist seemed to be drawing him remorselessly down toward the depths. at first, he had difficulty in accounting for the leaden feeling that possessed him after being a short time in the water. but suddenly he recalled the money belt with its weight of gold. "i'll stick it out as long as i can," resolved the boy, "and then unfasten the buckle and let the money sink." a section of wreckage came within his grasp at that moment. he made a wild grab for it, but a great wave swept it beyond his reach. he began to feel numb and chilled and utterly incapable of battling for his life much longer. an odd, reckless feeling of indifference came over him. his movements became automatic, no longer consciously directed. suddenly he recollected the money belt that dragged at his body like a leaden weight. he fumbled with the buckle with one hand while he trod water. but the strap proved obdurate. his chilled fingers could not undo it. "it is the end," murmured the exhausted boy. "i'm all in, and can't keep up the fight any longer." a strange, dreamy sort of feeling crept over him. he felt the water closing over his head. then, suddenly he seemed to be dragged skyward. his senses swam and he knew nothing more. when he opened his eyes, it was daylight. he lay in the bottom of a small boat that was being tossed about like a chip on the rough sea which, although it had moderated to some extent, was still running high. "where on earth am i and what has happened?" he wondered in the first few seconds of returning consciousness. "i remember that terrible feeling that all was over, that i was drowning and----" "thank goodness you're all right again, old fellow." "bill!" cried the young wireless man wildly, as he recognized the voice, "is that really you or your ghost? am i dreaming or drowned?" "neither, i hope," rejoined bill, helping his chum to raise himself in the bottom of the boat, "but you came mighty near being the latter if i hadn't providentially come within reach of you just in time." "thank heaven you did," replied jack fervently, "but tell me, how did it all happen? i don't understand. the last i can recollect is going under and thinking that all was over." "which must have been just about the time i grabbed you by the hair and got you on board somehow," continued bill. "i don't know how i did it, but i succeeded." "but how did you come to be in the boat?" jack wanted to know. "well, you see when we were both swept out of that cabin--i guess the trawler must have been broken in half by the explosion,--when we were both swept out, i didn't know what was happening and just struck out blindly." "same here," observed jack. "i was looking for a bit of wreckage to float on, but none came my way." "i don't know, though i guess i answer that description," chuckled bill, regarding himself with critical eyes. he was only half dressed, and the few garments he had on, for it will be recalled that neither of the boys had had time to dress, had been almost ripped from him. nor was jack in any better plight. "anyhow," went on bill, "the first thing i struck was this boat. it's the small one that hung astern of the trawler. the explosion, which struck about midships, i guess, hadn't harmed it and it must have torn loose from its fastenings when the _barley rig_ sank. i clambered into it and found it was half full of water. i managed, with an old tin bucket, which luckily, hadn't been washed overboard, to bale it to some extent, and--and then i heard you yell----" "i don't remember crying out," interrupted jack. "well, anyhow, you gave a good husky yowl and i glimpsed your head just alongside. i hauled you aboard and laid you in the bottom of the boat but i had not the least idea that it was you that i had the good fortune to rescue till daylight. you can imagine how glad i was." "but what are we going to do now? have we oars?" "no." "water?" "no." "nor food?" bill shook his head. "if we're not sighted and picked up we'll be in a bad fix, old fellow." "i'm afraid so. i guess we're the sole survivors." "yes, poor fellows. one can't help feeling sorry even for that rascal hoeseason." the boat, a small, not over tight ship's yawl, swung on the top of a high wave. the boys eagerly took advantage of this to gaze out over the crests of the tossing water-mountains. but the heaving, steel-gray sea was vacant of life. all they could see was a vast expanse of mighty rollers, desolate and cold under a leaden sky. they exchanged blank looks. "bill, old fellow, we're up against it," came from jack. "well, i've known times when things looked considerably brighter," admitted bill dolefully. chapter xxii. a night of alarms. castaways on the open sea in a boat without water, food or oars! it was a situation to frighten the bravest. to add to the peril of the boys' position, they had too appalling evidence of the fact that the north sea was strewn with floating mines which, even the impact of a small craft, like the one in which they were drifting at the mercy of the winds and waves, would serve to detonate. small wonder, then, that after a while conversation grew more and more desultory until at length they each sat silent, gloomily surveying their predicament. fortunately, there was no hot sun to beat down on them and aggravate the thirst both were already beginning to feel. but even with cool weather they could not hope to fight off the agonies of thirst for long. food, so far, was a secondary consideration. then, too, the frail nature of their craft gave them cause for anxiety. the gale showed as yet no signs of breaking up. from time to time the ragged tops of great waves were ripped off by the fury of the wind, deluging the boat in spray. it was necessary to keep bailing constantly if they hoped to remain afloat. the constant buffeting to which they were subjected was dizzying and nauseating. both lads ached in every limb. in a way they were glad to have the exercise afforded by bailing, for it went a long way to keeping their minds employed and their limbs from stiffening in the cramped, wet boat. yet their nerves showed no outward sign of a breakdown. from time to time they exchanged sentences intended to be cheerful; but it was a ghastly sort of merriment of which they soon tired. thus the hours wore away and darkness set in with a slight dimunition of the violence of the wind and signs, by the clearing of the sky, that the break of the gale was at hand. but they dared not sleep through the hours of darkness, except in hasty snatches. had the bailing pail been left alone for even an hour, the boat inevitably would have been swamped. by midnight, though, the sea was much smoother. their dizzied heads, racked by the incessant tossing, became clearer. they looked about them. suddenly jack gave a shout. "look! look yonder!" a short distance off, and apparently bearing down on them, were the red and green sidelights and the bright white mast-head signal of a steamer! bill broke into a shout. "hurray, jack, we're saved!" "not so fast, bill. they may not see us in the dark." "that's so. i'd give a million dollars, if i had it, for a box of matches and some good dry stuff to burn for a signal." "not having those things, there's no use worrying about them," returned jack quietly, "but say, bill, see here." his voice was anxious. he gazed nervously at the approaching lights. "that steamer's coming right down on us. we can see both her sidelights." "well, so much the better. she's bound to see us." "haven't you thought of another possibility?" "what do you mean?" "of a great danger?" "i don't understand you." "she's headed straight for us and we can't get out of the way. if she doesn't change her course, it will be a miracle if she doesn't run us down." "i hadn't thought of that," said bill in sobered tones. "what can we do?" "nothing but to sit tight and trust to luck." both lads now sat with anxious eyes fixed on the approaching lights. nearer and nearer they came, traveling fast. "shout, bill, shout with all your might," enjoined jack. they began yelling at the top of their lungs. but those inexorable lights, like the eyes of some savage monster, still bore down menacingly on them. already, in anticipation, they felt the impact of the sharp bow, the crash of smashed timbers and the suction of the propellers drawing them down to death. "they don't hear us," said jack. "if the lookout doesn't sight us, we're lost." the steamer was very close now. by straining their eyes they thought they could make out the dark outlines of her hull and spars against the clearing sky. bill hid his face in his hands. he could not bear to look at the juggernaut of the seas advancing to crush them. jack, with more fortitude, sat erect with a thousand thoughts whirring through his brain. the mighty bow loomed above the tiny chip of a boat, throwing off a great wave. the comber caught the light craft and flung it aside. what seemed like a black cliff, with here and there a gleaming light piercing its face, raced past them, and the boat, with two white-faced, shaken boys in it, was left in the wake of the fast-moving steamer, safe, but being madly tossed about by the wash of her propellers. the danger had passed, almost by a hand's breadth, but it was some time before they were sufficiently masters of themselves to discuss their escape. chapter xxiii. meeting an old friend. morning broke on a comparatively smooth sea, and two utterly exhausted, sunken-cheeked lads, weak from exposure and lack of nourishment. "this thing has got to end one way or another before long," declared bill, his voice coming in a sort of croak from his parched throat. "yes, i'm afraid we can't stick it out much longer, bill," assented jack languidly. "i'm beginning to see things," muttered bill; "black objects dancing about in the sun. over there on the horizon, for instance, i can see a dark cloud that looks like a tower. i know it isn't there, of course, but----" "but, bill, by hookey, it is!" cried jack. "what, are you going crazy, too?" "that's not a tower, but a steamer's smoke, bill," declared jack, after prolonged scrutiny. in a few minutes bill became convinced that his chum was right. "but will she pass near enough to see us?" it was a question upon which much, indeed, their very existence, might depend. on came the cloud of smoke, and now they could see the funnel and then the hull, of the steamer that was making it. "bill, i--i believe she'll pass near us." jack's voice trembled and his eyes shone as if he were a victim of fever. bill did not answer, but he clutched the gunwale with hands that shook, and fixed his gaze on the oncoming vessel. neither boy dared to speak, but both of them felt that if the steamer did not sight them, it would be more than they could bear. they stood up in the boat when they thought the craft was near enough to see and waved frantically, at the risk of upsetting the cranky little affair. "bill, she's changing her course," came from jack's parched and fevered lips. "i believe she is. yes, see there!" three white puffs of steam burst from the ship's whistle. then came the booming sound of her siren thrice repeated. the sweetest music produced by the finest musicians of both hemispheres could not have sounded as good to the boys at that moment as did the harsh roar of the steam whistle that showed them they had been sighted and that rescue was at hand. from the steamer's stern flag-staff fluttered the dutch ensign, proclaiming that she was a ship of a neutral power. this was an additional cause of congratulation to the boys, for had they been picked up by a craft flying a belligerent flag, they might have become involved in fresh difficulties. in half an hour the steamer, a small freighter, was lying to not far off the drifting yawl, and a boat had been lowered and was rapidly pulled toward the castaways. in a short time they were on board, and after being refreshed and provided with clothes, were able to tell their stories to captain van der hagueen, the stout, red-faced little captain to whom they owed their safety. the _zuyder zee_, the name of the little steamer, was bound, to the boys' great joy, for antwerp. she carried salt fish and herrings from scotland and scented her entire vicinity with the aroma of her cargo. but the boys, as bill expressed it, would have thought "a limburger cheese ship a paradise" after all they had gone through. the next morning they steamed up the river scheldt and came once more in sight of the towers and spires of the historic city which, it will be recalled, they had visited some time before on jack's first voyage. captain van der hagueen told them that after discharging his cargo he meant to lay up his ship, in which he was part owner, at antwerp till the war was over. the risk of floating mines in the north sea was too great to encounter, he declared. it was in the earlier days of the war and antwerp, a city strongly fortified, had not been threatened, although every preparation was being made to receive the enemy if they did come. barricades were being thrown up in the streets and the suburbs, and the thoroughfares were full of the queerly uniformed belgian soldiers the boys had been so much amused at on their previous visit. their amusement at belgian soldiers had given way, by now, however, to admiration and respect for the sturdy little country of fighters that had managed to give a good account of itself against the most formidable army ever assembled. the boys decided to seek out their good friend m. la farge, the minister of government railroads, who, it will be recalled, they had served on their first visit, and whose appreciation in the form of two handsomely engraved and inscribed gold watches were at that moment in jack's money belt, where he had luckily placed them for fear of robbery before they embarked on the _barley rig_. it was fortunate that he had done so, otherwise it is doubtful if they would have obtained access to his offices, where they found him overwhelmed with work. the sight of the watches, however, proved an "open sesame" to the minister's presence, and the boys--who had in the meantime provided themselves with new outfits,--presently found themselves warmly shaking hands with their old friend who was unfeignedly glad to see them. chapter xxiv. the sky slayer. after the first greetings were over, jack plunged into an explanation of their presence in belgium in such stormy times. m. la farge looked grave, but promised to do what he could through diplomatic and other sources to locate tom jukes. "if, as you say, he has been traveling in state in a large auto, he ought to be easy to locate," he assured them. "i will let you know what i have been able to discover to-morrow morning. every auto entering the country is registered and its occupants kept track of. rest assured i shall do my best for the two young friends to whom i can never be sufficiently grateful." jack thanked him warmly for them both, and explained that while in london they had communicated with the american consuls in paris and berlin, but that nothing had been heard at either place of tom jukes being among the refugees beseiging the american representatives. "possibly i shall have better success. at least, we must hope so," said m. la farge. "much of the telegraph system is still intact, fortunately. at least rest on my promise that i will do all i can." as they had already visited the american consulate in antwerp, where they had obtained no news, the two boys found themselves without anything to do but kill time as best they could till the next day. as they had spent much of their time on the dutch steamer in sleep, they did not feel like turning in early and so, at jack's suggestion, they visited a theatre. but it was a gloomy manner of spending the evening, as it transpired. the inhabitants of antwerp were more interested in the bulletin boards announcing the inroads of the german troops than in entertainments. there was an air of anxiety and depression abroad that could not help but be contagious, and oppressed by the general atmosphere, the boys decided before the end of the performance to return to their hotel. but jack could not sleep. he lay awake tossing and turning for an hour or more. in the street he could hear the regular step and quick challenge of sentries. occasionally, far off, came the sound of bugle calls. all at once he became aware of another sound. it was one that was strange to him. he could liken it to nothing but the droning buzz of a giant bumblebee. it was at first faint; hardly audible in fact, except to strained ears, but it rapidly grew in volume, filling the whole air with the steady vibrating buzz. the sound irritated jack, sleepless as he was. "it sounds for all the world as if there was a big buzz saw or a threshing machine at work," he mused. "where on earth does the racket come from?" he lay awake listening for a few moments longer. then he got out of bed and tiptoed across the room where bill lay snoring violently. the lad looked out of the window. the street and a public square lay far below him. only a few lights shone on the thoroughfare. it appeared deserted but for the sentries marching up and down unceasingly. "nothing there," said the boy to himself. "i guess i'll turn in again." the buzzing sound had grown fainter now. it was hardly audible in fact. but for some reason it lingered in jack's mind. it was like half a dozen things he could think of and yet he could not recall ever having heard that precise sound before. at last he dozed off, and then sank into a dream in which it seemed to him that he was somewhere far out in the country lying under a shady tree contentedly chewing on a bit of grass and gazing up through the leafy branches at the bright sky. but suddenly everything clouded over. the landscape grew dark and sinister, and the leaves of the tree above him began to toss and sway in a harsh wind. in his dream, jack arose and standing up looked about him. it appeared to him as if he was gazing down from a height over an immense battlefield. he could see the dust and smoke as cannon were wheeled into position and then the flashes of flame and the belching of fire from the rifle pits. men were mowed down like ripe grain in long windrows. it was horrible but fascinating. then, all at once, came again that strange buzzing sound. but now it seemed to have in it a menacing note. it was like a terrible voice. the boy shuddered as he heard it, harsh and inexorable, filling the air, which seemed to vibrate to the steady humming. it grew sharper and louder. above all, the noise of the dream cannon and rifles, the boy could hear it. he awakened with a start, his heart beating rather wildly. "that was a kind of a nightmare," he said to himself. "glad i woke up. i guess--what's that?" again that humming sound filled the air as if a pulsing chord, strung at high tension, had been twanged. "it's outside!" exclaimed jack, for the second time going to the window. "it's in the air!" he cried an instant later. he turned his face upward. high above the city, against the stars, he could trace the outline of a gigantic cigar-shaped body. it was moving slowly far above him. "an airship!" gasped the boy, and then the next instant: "a zeppelin!" something seemed to launch itself from the dark body of the immense aircraft and streak downward like a falling star. the next moment, from a part of the city some distance off, there was a brilliant flash of flame, and then an appalling report that shook the earth. but jack had no eyes for this at the moment. his gaze was fixed on the zeppelin. having dealt destruction in one part of the city it was now making directly toward the hotel! the boy watched it with a horrible fascination that held him speechless. the death-dealing craft was destined to pass directly above the building that sheltered them and how many others. craning his neck, jack watched its flight above the sleeping city. dark as death itself and, with no indication of its presence but the drone of its engines, the sky monster moved majestically toward him. it was then that jack suddenly found his tongue as the death in the air approached till it was almost above his staring eyes. "bill," he yelled, "bill, wake up!" he shook his chum's shoulder violently. "whazzermarrer?" inquired bill sleepily. "get up for your life. fling on any old clothes. let's get out of here quick." "what's up?" demanded bill, wide awake now, and hastily pulling on some clothes, for he knew jack would not have aroused him needlessly. "it's a zeppelin, a giant german airship. she's blown up a piece some blocks away and now she's headed over here." at almost the same instant, a roar of artillery burst forth. the defenses of antwerp had awakened and were concentrating their fire on the death-dealing monster of the sky. but as the first reports ripped the silence of the night, there came another and a mightier report. the hotel rocked to its foundations. a shower of plaster and debris crashed into the boys' room, half burying them. the sky slayer had struck again! chapter xxv. in the glare of flames. for a fragment of time,--while a man might have counted ten,--there was absolute silence following the shattering report of the bomb. then came a babel of cries, shouts and women's screams. hastily throwing on whatever clothes came first, the two boys rushed out of the wrecked room. but they did not do this without difficulty, for a mass of fallen plaster and debris blocked the door. in the corridor, an electric light still burned, and the force of the explosion appeared to have spent itself at the end of the passage where the boys' room was situated. "wha--what happened?" stammered bill, as they gained the corridor. "it was a bomb, a bomb dropped from a zeppelin," answered jack, equally moved. "what a fiendish bit of business." "i only hope they don't drop any more," bill cried, as they hurried to where the stairway should have been. but it was not there. a great section of it had been blown to kindling by the force of the explosion. it was at that moment that jack became aware of an acrid, sharp smell very different from the reek of the lyddite with which the shell had been loaded. it was a few minutes before he realized what it was,--fire! he looked behind them. a red glare lighted up the corridor, and even as he gazed, a sheet of flame burst from a doorway further down the passage. below them, there was bustle and shouting in plenty, but apparently they were the only guests quartered in that part of the hotel. jack looked grave. the position they occupied was a very dangerous one. the gap in the stairway was wide and they were trapped with that chasm in front and the flames behind them. "what are we going to do?" gasped bill, turning pale. "i don't know; we are in a bad fix, bill," confessed jack. "perhaps,--hello!" he broke off, as the tiny figure of a pretty little girl emerged from a room which adjoined the one they had just vacated. the tot held in her arms a doll and her eyes were wide with dismay. "oh, man, what has happened?" she gasped. "something very terrible, little girl," answered jack, "but are you alone?" "oh, no, my mamma's in the room. she's sick, i think." "great scott," groaned jack, "this is serious. it was bad enough before, but now----" he looked at bill desperately. "we've got to get that woman out of there," said bill. "yes, but how?" cried jack desperately. "there's no way of bridging that gap." "i've got a plan that might work," said bill. "are you going to save us?" asked the tot in a trembling voice. "yes, dear. don't be frightened. stay here while we bring mamma to you." "oh, i'm scared," wailed the child, but she obediently sat down on a chair to await the boys' return. inside the room they found a handsome, middle-aged woman lying half dressed on the floor, in a faint. apparently, she had risen and begun dressing hastily when the first shock of the bomb came, but the effort had been too much for her, and she had collapsed. the boys picked her up as gently as possible and tried to revive her, but their efforts met with no success. outside, the glare and roar of the flames were increasing. there was no time to be lost. "there's only one thing to do," said bill seriously. "and that is what? i'm stupid," confessed jack. "we must make a rope of bed clothes and lower her and the child down." "good. i believe we can get out of this." they hastily tore the clothes of the two beds in the room and made a long rope of them. when this had been done, they took a turn of their "rope" round the marble pillar at the head of the wrecked staircase. but then came a fresh difficulty. there was no one on the floor below, though they shouted to attract attention. obviously someone would have to be there to catch the woman and untie her when she was lowered. "you go," said jack. "i guess i'm strong enough to lower you." "and leave you here in danger of the flames?" protested bill, for it was getting uncomfortably hot now, and the smoke was blinding. "i'll be all right, if we hurry," said jack. "go ahead, bill, there's not a minute to be lost." "i know, but----" "never mind any 'buts'--it's a matter of life and death." so bill reluctantly looped the "rope" under his arms and then jack lowered the young engineer to the next floor. this done, jack had a hard task in front of him. he had to fasten the life-line round the woman and lift her to the edge of the gulf. this he accomplished by knotting the rope to the marble pillar, tying it securely at just such a length as would allow its unconscious burden to be suspended over the gap in the stairway. this was accomplished. she was lowered, and in a short time the woman was received by bill, who released her from the line with all speed. then came the little girl's turn. she was terrified at the idea, but at last jack, with the loss of much valuable time, succeeded in persuading her to make the attempt. but the delay had made his position terribly dangerous. the fire was so intensely hot now that its breath scorched him. the smoke was so dense, too, that breathing was difficult. "i'll have a close shave of it," thought jack, as he glanced behind him and prepared to lower the little girl. as before, the feat was successfully accomplished, and then came jack's turn. as he slid nimbly down the rope that had done them such good service, the flames actually singed his garments. he was none too soon in reaching the lower floor, for he had hardly landed when the fire reached the pillar to which the line was secured and burned through its fabric. "well, 'a miss is as good as a mile,'" said jack, "but that's about as close as i want to come to being roasted alive." chapter xxvi. two young heroes. the corridor was deserted, but a few lights burned dimly. no damage appeared to have been done there, and it was clear that the bomb had wrought havoc only on the top floor, which was the one occupied by the boys and those they had rescued. "i wonder if the elevator is running?" asked bill. the lift was at the upper end of the passage and they carried the woman to it, but there was no response to their rings. outside they could hear fire apparatus clanging wildly up and the confused roaring murmur of an immense crowd. in the distance, the guns of the forts boomed, filling the air with their sonorous thunder as they fired at the daring night raider of the enemy. with this sound was mingled the sharper crackle of light artillery and specially built "sky guns." but as they learned afterward, the perpetrator of destruction on the sleeping city escaped scot-free, to make subsequent attacks. the elevator apparently not running, they had to face the task of carrying the unconscious woman down to the lobby and securing medical aid. luckily for their tired muscles, antwerp hotels are not like our skyscrapers, and it was not long before they reached the ground. the scene was a wild one. hysterical women and white-faced, frightened men, in every stage of dress or undress, were huddled in the centre of the place while the hotel clerks and servants were doing their best to pacify them. in the confusion, the boys attracted hardly any attention, and they laid the woman down on a lounge while they summoned a doctor, of whom several were already busy attending to women who had swooned or become hysterical. the fear of the crowd was that another bomb might follow the first. already word had spread that a hospital had been struck and a dwelling house wrecked, two women and a man being killed outright in their sleep in the latter. "what an outrage!" exclaimed bill, looking about him at the wild scene while a doctor administered restoratives to the woman they had saved. "to attack women and children and harmless citizens from the sky." "i hope they get that old wind bag and blow it to bits," wished jack, with not less warmth. "well, this is our first taste of war, jack, and i can't say i like it." "nor i. it would do some of those jingoes in our own country, who were yelling for war with mexico, a lot of good to see this," returned the young wireless man. "let's go outside and see what's going on," suggested bill. "i guess our charge is all right, now she's beginning to recover." if the scene in the hotel had been wild, like a nightmare more than a reality, that outside was pandemonium itself. imagine a crowd of wild-eyed men and women, few of them wholly dressed, surging behind lines of policemen and the entire street lighted by the ghastly glare of flames upon which the engines were playing furious streams. "if that bomb-thrower sailed over here now he could wipe out half of antwerp, i should think," said jack, as they elbowed their way through the throng. oddly enough, although the lads had only been able to throw on a few garments hastily, they did not, till that moment, recollect that their new outfits had been destroyed. it was bill who called attention to this. "we ought to make the fortunes of a tailor," he commented. "we'll have to get a lot of new stuff to-morrow,--or rather to-day, for it's after three o'clock." "if this keeps up we'll be reduced to adam and eve garments before we get through," laughed jack. far in the distance, on the outskirts of the city and on the chain of forts, the white fingers of the searchlights were sweeping the sky questioningly, looking for the sky-destroyer to deal out death to him in his turn. the guns boomed and cracked incessantly, sending a rain of missiles upward. but flying high, and favored by a misty sky, the zeppelin escaped without injury, leaving a panic-stricken city in its wake. there was no more sleep for any one in antwerp that night. vigilance against spies increased ten-fold, and it was bruited about that the real object of the aviators had been to blow up the royal palace, and by destroying the king and queen to terrify the belgians into submission. naturally, sleep was out of the question for the boys. they spent the rest of the night wandering about the city and visiting the ruins of the house that had been struck just before the hotel. its entire front was torn out by the force of the explosion, and just as they arrived, three bodies had been found in the ruins. the sight of the shrouded, still forms brought home to them with still greater force the horror of it all. "tell you what, bill," said jack, as they returned to the hotel to breakfast, and found that the fire had been extinguished and the panic quieted down, "war is a pretty thing on paper, and uniforms, and bands, and fluttering flags, and all that to make a fellow feel martial and war-like, but it's little realities like these that make you feel the world would be a heap better off without soldiers or sailors whose places could be taken by a few wise diplomats in black tail coats. it wouldn't be so pretty but it would be a lot more like horse sense." "gracious, you're developing into a regular orator," laughed bill. "well, the sight of these poor dead folks and all this useless wreckage got under my skin," said jack, flushing a little, for he was not a boy much given to "chin music," as bill called oratorical flights. during the morning they secured new clothes for the second time since landing in the city, and then paid their appointed call on m. la farge. "i have good news for you, boys," he said as they came into his office. "your man was last heard from at louvain. i suspect he is rather given to adventure, for i understand that he has been quite active in aiding our people. it's strange that his people have not heard from him, though." "perhaps they have by this time," said jack; "but if he has been actively siding with the belgians, isn't his neutrality in grave danger, with all its serious consequences?" m. la farge nodded thoughtfully. "i have heard much of your wealthy young americans," he said, "and while their hearts are warm and it is good of this young man to be doing what he can, my advice to you is to get him to return home as soon as possible--the germans shoot first and listen to explanations afterward, as they say in your country." chapter xxvii. "the germans are coming!" it was in the early days of the war when the gallant defenders of liege were still undauntedly holding back the teuton thousands with their great "caterpillar" siege guns that were destined, ere long, to hammer down the stubborn defense of belgium's neutrality. trains were running and business, although seriously hampered, was still being carried on, though the foe was at the gate and the capital had been removed from brussels to antwerp. armed with passes signed by m. la farge, to which their photographs were attached for purposes of identification, the boys started for liege the next day. it was likely to prove an arduous and not unhazardous task that they had embarked upon. in the first place "spy fever" was at its height. anyone not in uniform was liable to be held up and questioned, and if satisfactory explanations were not forthcoming, they were liable to very unpleasant consequences. the word of any frightened peasant choosing to "denounce" anybody had led to riots and affrays in which men and women, suspected of espionage, had been rescued by troopers after being half beaten to death. above all, the boys were warned not to carry weapons of any kind, an injunction which they obeyed as they did all the rest of m. la farge's admonitions. the train journey proved exasperating. sometimes it would be halted for hours on a side track while trains, loaded with young-looking soldiers in a strange medley of gay belgian uniforms, went by, the men cheering and singing. again, much time was wasted by careful reconnaissances, for there was fear that bridges might have been dynamited or the right of way mined by the spies who were rife throughout the country. a whole day passed thus, with the train creeping like a snail and continually stopping and starting. the roads at the side of the track were alive with peasants flocking to different centres from their lonely houses in the country. some had their family possessions piled high in small carts drawn by dogs. others carried what they had been able hastily to collect. it was another sad picture of war and the desolation it had brought on an inoffensive, industrious little country. several aeroplanes soared above the train, reconnoitering the country. at first the boys were nervous lest there might be a repetition of the bomb-dropping at antwerp, but they were assured by the official on the train, who had examined their passes, that the aircraft were all friendly french and belgian aeroplanes, after which they watched them with less uncomfortable feelings. as bill put it: "if we were at war and shouldering rifles for the dear old u. s. a., we'd take the chances of war with the rest of them, but being a neutral, there's no sense in throwing away our bright young lives," a sentiment to which jack agreed heartily. it was dark when the train rolled into louvain. after innumerable challenges by armed sentries, they at last reached the hotel of the place where many of the soldiers were quartered. if antwerp had seemed like an armed fortress, signs of military activity were much more marked in the old cathedral town. lights were not allowed after eight o'clock. citizens were kept off the streets at night after certain hours. artillery rumbled through the city all night, going to the front, the boys were told. disquieting rumors of the fall of liege, and the advance of the germans, had already reached the town, and on the outskirts, barbed wire defenses were erected and trenches dug hastily. residents were warned, in the event of the germans entering the city, to behave themselves strictly as non-combatants, the magnificent cathedral was fitted up as a hospital in case of emergencies. the thrill of warfare was in the air. it was early the next morning that jack aroused bill from his sleep. "hark, bill!" he exclaimed, holding up one hand. from far off came the boom of cannon. the ground seemed to tremble under the thunder-like reverberations. down in the street a squadron of cavalry raced through the town. then came the rumbling of guns being rushed to the front. "it's a big battle," declared jack; "and what's more the sounds have been growing louder. it must be a retreat." bill looked grave. "in that case we are likely to be in the thick of it." "i'm afraid so, and it may be mighty difficult to get away. we'll have to find tom jukes as soon as we can, and then get back to the coast." an aeroplane buzzed by overhead, its powerful engines whirring, buzzing thunderously. by daylight the town was almost empty of soldiers; they had all, except a few detachments, been called to the front during the night. the landlord of the hotel was in a great state of perturbation. "ah, those terrible germans!" he exclaimed, "they will wreck our beautiful town and put us to death. i know them. oh, what unhappy times." "perhaps they may be beaten back," encouraged jack. "oh, no! no such good fortune," said the landlord, wringing his hands miserably. just after dawn, a mud-spattered courier arrived, and declared liege had fallen, "the germans are coming." everywhere that was the cry as, after a hasty breakfast in the disordered hotel, the boys hurried out. chapter xxviii. fast traveling. the sound of firing was now much closer. frightened faces were peering from behind shuttered windows. all traffic appeared to have stopped, and the only life beyond the few persons abroad, whose curiosity was stronger than their fear of the big german guns, was when an occasional body of troops would rush through the streets. the beautiful hotel de ville and the fine old cathedral, so soon destined to be damaged by fire and bullets, attracted the attention of the boys and gained a hearty expression of admiration from them both. all at once there was a whirr and the snort of a horn, and an armored war-automobile, carrying a machine gun, and painted a business-like gray, dashed around a corner and sped on. another car came close behind it. the second machine carried an american and a red cross flag. it was coming fast and contained two occupants. both were youths, and one carried a camera over his shoulder by a broad strap. but the other attracted jack's notice, for in him he recognized instantly the lad they were in search of, tom jukes, the millionaire's son. "hey, tom jukes!" he hailed. the car slowed up and the young driver turned questioningly in his seat. "well, by all that's wonderful, it's jack ready and bill raynor!" he exclaimed, as the two lads came up to the car. "what in the world are you doing here?" "we've been sent to ask you that same question," responded jack, who, it will be recalled, became well acquainted with tom jukes when the young wireless man was in the hospital in new york following his battle with the desperate tobacco smugglers he was instrumental in sending to prison. "what do you mean?" asked tom with wide-open eyes. "why, your father hadn't heard from you and----" "hadn't heard from me! why, i've written several letters," declared tom. "i'd have cabled, but they've stopped all that for the present, at least. i declare, that's too bad. and so the governor sent you on a searching expedition, eh?" "well, it was to be a combination of that and a vacation," laughed jack, and he told something of their adventures on board the "gold ship." "my word, you fellows are always having adventures," said tom, with a smile on his good-looking face. "the fact is, i guess reading of your exploits made me stay over here when this row started to see if i couldn't have some of my own. i'm staying with belgian friends, about half a mile from here, and so far i haven't done much but get ready to help in red cross work and so on. but now i guess it's up to me to get back to the u. s. a." "if we can," said jack. "i don't know where the ship we came over on, the _st. mark_, has been sent to. london and paris are overrun with american refugees. when we were there, hundreds of them were unable to get passage, or even change their money." "oh, the whole world seems to have been shuffled in this thing," frowned tom, "but let me introduce my friend, philander pottle. he's a photographer for a new york newspaper." the boys shook hands with pottle, a dark young fellow who talked as explosively as a machine gun. "glad to meet you--fine fight--be here soon--great pictures--snap! bang!--action--that's the stuff!" "we're going out toward the front, that is, if we can get by," declared tom; "want to come along?" the boys looked rather dubious. "i don't know what your father----" began jack doubtfully. tom interrupted him impulsively. "oh, there's no danger so long as we don't get in any of the scrimmages ourselves," he declared, "and then the american flag and the red cross emblem will keep us out of trouble." both boys were anxious to go, so that it did not take much more persuasion to make them get in. "now then off we go--bang! biff!--big guns!" outside the city lay an open country. far off they could see a great cloud-like mass of smoke which, no doubt, marked the place where the fight was taking place. "we'll make a detour to the north," declared tom. "there's rising ground there and we can look down without danger of getting hit." "not want to get hit--cannon ball--gee whizz, off goes your head--much better keep it on," said pottle, in his firecracker way. "he talks as fast as a photographic shutter moves," chuckled bill to jack in a low voice and the other could not but agree. as they rode on, they passed groups of soldiers and artillery. now and then a lumbering wagon, bringing back wounded men lying on piles of straw, jolted by, bearing mute testimony of the havoc going on at the front. the boys began to feel sick and queer and even tom sobered down at these sights. they were stopped several times by small skirmishing bands and made to show their papers, for a few days before german spies had been captured in a car flying an american flag. the car sped up a hill and then started swiftly down on the other side of the acclivity. at the foot of the hill, a long and steep one, was a wooden bridge. tom was driving fast, when suddenly there was a sharp, snapping sound and the car leaped forward. tom's foot was on the brake in a jiffy, but there was no diminution in the speed of the machine. instead, it appeared to gain momentum every moment. "bother it all," muttered tom; "brakes bust. i can't slow down till we get to the bottom of the hill." "i hope we don't meet anything," cried jack. "if we do grand bust--smash--crash--no chance--wow!" exploded the photographer. but there was nothing in sight, and beyond the bridge was another up grade where tom hoped to gain control of the runaway machine. but within a few hundred feet of the bridge some soldiers suddenly appeared, running from the bridge as if they were in haste to leave the vicinity. as the car came in sight they waved it frantically back. one even leveled a rifle. "can't stop," shouted tom jukes, "brakes bust." they flashed by the men who looked mere blurs at the pace the car was now going. bang! came a shot behind them, but the bullet whistled by, making them involuntarily crouch low in the madly racing car. behind them came shouts and yells. they could catch something about germans. "they think we're german spies," gasped bill, as the car thundered across the bridge. hardly had it flashed across than there came a terrific explosion and looking back they saw the whole bridge blown skyward. their lives had been saved by a miracle. "those soldiers must have mined that bridge and set the fuse just before we appeared," declared jack, looking rather white and dismayed. "we weren't a second too soon. if we'd been going slower we'd have been wiped off the map," added bill soberly. "i'm going to keep running at this speed till we're out of this neighborhood," cried tom jukes. "it's not healthy." chapter xxix. the uhlans! but clearly fate was against their seeing anything of the battle that morning. they were still going fast, traveling through a wooded country that alternated with open stretches, where they could catch a glimpse of the far-off fight, when there came a sudden ominous sound: bang! "there's a shot," cried bill, looking round with alarm on his face. "that was no shot," returned tom with a rueful grin, "it was one of the tires blowing out." "pop--bang--air all out--pump her up--hard work--too bad," exploded pottle. "fritz, i'll be jiggered if you don't talk like a tire going on the fritz yourself," laughed tom, as he succeeded in slowing the car down on a gentle grade by reversing the engine and then stopping at the bottom. "fritz--german name--don't use it in belgium--think you're a spy--then you'll be on the fritz," sputtered pottle. the car was brought to a standstill opposite a neat white farmhouse approached by an avenue of slender dark poplars. a big dog bayed as the car stopped, but there was no other sign of life about the place except some chickens pecking and scratching in the dooryard. in the background were yellow stacks, for the harvest had just been gathered. it made a pretty, contented scene in contrast with the turbulent experiences through which the boys had passed only recently. but they did not spend much time comparing the rural peace with the unrest of the cities in the war area. there was work for them all to do. first the brake was mended by replacing a broken bolt that had caused the trouble that almost ended tragically for them. then came the fitting of a new "shoe" and tube, at which they all helped by turns. the work took some time, and at its completion they were all dusty, hot, and very thirsty. "i'd give a lot for a good drink of cold water or milk right now," puffed tom, resting from his exertions with the tire pump. "what do you say if we go up to that farmhouse and see if we can buy something to drink?" "oh, for an ice cream soda," sighed bill. "you might as well wish for lemonade in the sahara desert," scoffed tom. "they wouldn't know an ice cream soda here if they met it." laughing and chatting, they approached the house, walking up the avenue. but as they neared it, their cheerfulness appeared to receive a check. no indication of life but those mentioned appeared about the place. it was silent and shuttered. the stable seemed to be empty. no farm wagons stood about. repeated knockings at the door failed to produce anyone. "there's a well yonder," said tom jukes. "what do you say if we help ourselves?" "we'll have to, i guess," agreed jack. "everyone about the place must have been scared away by the battle." "or more probably the men were called to arms and the women have gone to some place of safety," was bill's opinion. a great earthenware vessel stood by the well brink and they refreshed themselves from this with long draughts of cold, clear water. "that's better," declared tom, as he set down the pitcher after a second application from it. "now let's be getting on, for we've got to find another road back." "wait a minute--great chance--deserted farm--men at war--women flee in haste leaving faithful dog!" exclaimed pottle, unslinging his camera. "well, hurry up and get through with your old picture box," conceded tom, "and, by the way, you might let that dog loose. poor creature, he'll surely starve to death tied up like that." although the dog was a ferocious-looking animal, he seemed to know that the boys meant to give him his liberty, for he allowed them to take off his chain without any opposition and went to a small stream that flowed behind the house to slake his thirst. this had hardly been done, and pottle had taken a few snaps, when down the road came a furious galloping and a squadron of belgian cavalry appeared, spurring for their lives, while behind came hoarse shouts and shots. "great scott! we're in for it now!" exclaimed tom in a dismayed voice; "a flanking party must have attacked those fellows and driven them back." the squadron, a small one, and probably a scouting party, galloped past the house without even noticing the boys and the auto standing in the road. it was plain they were hard pressed. they had hardly gone when another body of horsemen appeared. they wore gray uniforms. their metal helmets were covered with canvas with the number of their troop stencilled on it in large figures. each man carried a lance with a gleaming point. like those they pursued they swept by without paying attention to anything but the pursuit. "uhlans!" exclaimed tom. "i hope we haven't blundered into the thick of this thing." they all stopped to listen. the noise of the pursuit had died out, but now more hoof beats could be heard approaching rapidly. chapter xxx. "you are a spy!" in another moment a smaller body of men swept up to the farmhouse, drawing rein at the sight of the stalled car. by their uniforms and the fluttering ensign held up by a big trooper, the boys guessed them to be officers. they paused for a moment and then, after a few words, turned and came galloping up the poplar-lined approach. the boys exchanged blank looks. "keep cool," urged tom, "there isn't anything they can do to hurt us." "i don't know, i've heard some queer tales of the germans," declared jack, rather apprehensively, "for one thing they've no great love for americans." "but they wouldn't dare to injure us," declared bill. the horsemen, of whom there were six, and they saw that two were slightly wounded, came galloping up and drew rein. the leader of the party was a fierce, hawk-nosed old man with an immense drooping mustache. the others were young officers, rather foppish-looking. two of them wore monocles. but it was the figure of the man who brought up the rear of the party that excited jack's attention to the exclusion of the others. "radwig!" he gasped to bill as he recognized the figure of the former herr professor of the german war college, in spite of his wearing a uniform. "wow! there'll be trouble sure now," muttered bill. "see, he's looking at us." "yes, he recognizes us and he doesn't look over amiable." radwig spurred his horse to the side of the hawk-nosed old colonel and spoke rapidly. the old man bent keen eyes on the party of boys. "herr radwig informs me that two of your party are spies," he said in a chilling voice; "is that the truth?" "of course not," declared jack, paling a trifle. "we are all americans." "unfortunately, a great many persons, including english spies, are protecting themselves under that banner nowadays," was the rejoinder. "i'll trouble you to show your papers." "why, mr. radwig knows me and my friend here," burst out jack. "i know nothing but what i suspect," snarled radwig, his eyes gleaming viciously. "colonel, will you allow me to search these boys?" the other nodded assent. "i would rather be searched by somebody else," protested jack, guessing what sort of treatment they would get from the man who hated him. "herr radwig will search you," was the rejoinder, and then, in german, he gave orders to a non-commissioned officer,--a sergeant,--to get a meal ready within the house. radwig compelled the indignant boys to turn out everything in their pockets and pottle's camera was ordered destroyed forthwith. radwig's search was rapid and thorough. when it was concluded, he turned to the colonel. "there is nothing incriminating on any of them, but on this one here," he declared. he pointed at jack as he spoke. "and he----?" "has two passes on the belgian railroads in his pocket." this was true, for jack had not given up both passes the last time they had to show them. "that seems to prove that he has some position of trust with the belgian government," declared radwig, "and as such is properly a prisoner of war." jack looked his dismay; but the colonel gave a sharp order. two soldiers laid hold of the boy. he started to shake them off indignantly while his friends looked on aghast. "i can explain all this," he cried; "this man radwig had trouble with me. he's trying to get even. he----" "take him away," came the cold order in unmoved tones. "you are responsible for him," added the colonel to jack's two captors. "see that he is carefully guarded till the court martial." "the court martial!" cried jack. "why, i--i'm an american citizen and----" "there is no more to be said," and jack, with an armed guard pressing a revolver to either side, was marched off without a chance to say more. as he went on, he could hear his friends protesting indignantly and then, they too, were taken in charge by the soldiers and escorted to the automobile. then came a sharp order to them to drive back to louvain on pain of death. there was nothing for them to do but to obey. the iron discipline of the german officers allowed no argument. and so, leaving jack to his fate, they were compelled to drive off with heavy hearts. "don't worry, we'll get the american consul and get him out all right," said tom, as cheerfully as he could. but bill, with the thought of a court martial in his mind, sat in a miserable state all the way back to the town which they reached only after making a long detour, necessitated by the blown-up bridge. his chum in the hands of the germans, and subject to court martial, bill had good cause to feel worried and oppressed as to the outcome when he realized the influence that radwig, jack's enemy, appeared to possess. to what terrible lengths might not his desire for vengeance lead him? chapter xxxi. court-martialed. poor jack, with feelings that may be imagined, was roughly thrust into a smoke house and the door slammed. outside the sentries paced up and down ceaselessly, showing him that to think of escaping would be useless. there he must stay at the mercy of radwig till his fate was decided. no wonder, as he sank on a rough stool, he felt for a moment sick and apprehensive. the glitter in radwig's eyes when he saw who it was he had made prisoner had warned jack to expect severe treatment. the hours dragged by and no one came near him. it was pitch dark in the smoke house, which, of course, had no openings and hardly any ventilation. the clank of the sentries' sabres, and their steady, monotonous tread, were the only sounds that disturbed the stillness except for an occasional, far-off rumble of cannonading. evidently the main tide of the battle had rolled back from the scene of the morning's engagement. if it had not been for the presence of the sentries, which showed that he was not forgotten, jack would have been inclined to think that his captors had ridden on and left him. but the steady tramp-tramp outside precluded all possibility of this. at last the door was flung open, and the two men guarding him entered the dark smoke house. jack saw then that it was late twilight, but a cloudy sunset, threatening a coming storm, made it appear later. "come," ordered one of the impassive, gray-uniformed germans, who seemingly possessed a knowledge of a little english. there was no resource but to obey. jack, with a beating heart, fell in between his two guardians. [illustration: "you have heard yourself accused of being a spy," began the colonel harshly.--page 229] "i've got to be cool and keep my head," he told himself as he was marched toward the house. "any false step now might be fatal." within the farmhouse, kitchen lights had been kindled. two yellow flaring lamps showed the group of officers about the table with their swords laid among the remains of a meal. wine spilled on the cloth and empty glasses showed that the farmhouse cellar had been raided for their entertainment. at the head of the table sat the hawk-nosed colonel. next him was radwig. one of the officers, a major, was tilted back in his chair snoring noisily. jack's heart sank. he saw no signs of a fair trial. "you have heard yourself accused of being a spy," began the colonel harshly. "what have you to say to the charge?" "simply that it's ridiculous. if you will give me time my friends will be back here with ample proof that i am an american citizen, a wireless operator and----" "ah, ha!" exclaimed the colonel, placing one finger to the side of his hawk-like beak and looking cunning. "so that is it. a wireless operator with belgian passes in his possession. it looks bad." radwig bent over and whispered something in the colonel's ear. "herr radwig tells me that you are a hater of germans. that you had him placed in custody in england and that he only escaped to join our army after surmounting great difficulties. what have you to say to that?" "as to being a hater of germans, no american is that," said jack. "we are all neutral in this struggle. so far as herr radwig being imprisoned in england, he was already in irons on the ship before she docked." "is that true?" demanded the colonel of radwig, who smiled and waved his hand with a gesture that signified "absurd." "you see herr radwig denies that you tell the truth," remarked the colonel. "surely my word is as good as his," protested jack, trying to keep cool, although he saw that things looked black indeed for him before such a prejudiced tribunal. "herr radwig is a german we all know and honor," retorted the colonel. "who you are we do not know. therefore, between you, we must believe him." "you don't mean that you believe i am a spy?" blurted out jack. "the evidence shows it," rejoined the colonel coldly. "you are aware of the rules of war?" the whole room suddenly swam before jack's eyes. a deadly chill passed through him. for an instant he could not assure himself that it was not a hideous dream from which he must soon awaken. but the next instant, the reality, the horrible fact that he was about to be sentenced to death as a spy, rushed back upon him. he tried to speak but his dry lips refused to deliver a word. the colonel and radwig whispered, and then the former announced in his harsh grating voice: "it will be at reveille to-morrow. remove the prisoner." "but you don't understand," he choked out, "surely you don't mean to execute me, an american citizen, without a chance to explain. i----" "i will assume full responsibility," was the cold reply. jack struggled with his captors, but a cruel blow in the small of the back with the butt of a rifle so dizzied him, that by the time he recovered his senses, he was back in the dark, foul-smelling smoke house once more. chapter xxxii. the long night. then followed the blackest hours of jack's life. outside the sentries kept up their eternal pacing. in the distance a dog barked, and there was still scattered firing. for a long time the unfortunate young wireless man sat huddled on the floor of his prison in a sort of torpor. all at once he recollected that one of his guards spoke english. perhaps he could get the loan of pen or pencil and paper to write some last words. but when hammering at the door for some moments brought a response, his request was gruffly refused. the sentry resumed his measured pacing. one--two! one--two! hour after hour the sound beat into jack's brain till he thought his head would burst. then came another sound. the sound of digging! the blows of a mattock! a cold perspiration broke out on jack's forehead as he realized the import of this. they were digging his grave, and by a refinement of cruelty, within earshot of his prison place. whether by accident or design, poor jack was being forced to hearken to the most grisly of the preparations for the next morning's reveille. so the hours crept by leaden-footed. sleep was out of the question as much as was possibility of escape. the sound of the digging, which jack had stopped his ears to keep out, had ceased. then came a sudden stir outside. the sound of hurrying feet and commands barked in sharp, quick voices. jack's heart gave a bound. could it be a detachment of belgians summoned by tom and bill coming to wipe out the small force occupying the farm? he flung himself against the door of the smoke house, listening intently. there was a tiny crack at one of the posts and through this he could command a limited view of the moonlit farmyard. then came an odd sound. like the dry whirring of insects in the fall. it grew in volume. the hurrying and the shouts increased, too. shots were heard, scattering one after the other and a yell that sounded like a shout of warning. then the world rocked and spurted flame. screams and groans filled the air. again there came an explosion that shattered the night and sickened the senses. jack, half stunned, fell to the floor of the smoke house as part of its roof was torn off. then came silence, broken an instant afterward by groans and moans and swift, alarmed orders. there was a rat-a-plan of hoofs. the queer whirring sound died out. only the moans still continued. dizzy and sick, jack got to his feet. as yet he could not quite realize what had happened. suddenly followed realization. a night raiding aircraft had spied the shifting lights of the encampment and, by the moonlight, caught the gleam of stacked arms, and had struck. the sound of the sentries' ceaseless pacing had stopped. jack shouted and pounded on the door of the partially wrecked smoke house, but there was no answer but the moans and cries that were now getting fainter and less frequent. the sides of the smoke house were of rough logs and without much difficulty jack clambered to the shattered roof. he raised himself and clambering over, gave a hasty glance about him. it was a terrible scene of wreckage that he surveyed. in the earth two immense holes, big enough to bury two horses, had been torn, and close by lay two men. over toward the house was a third figure stretched out. three horses, one of which died as jack was looking over the carnage, lay not far off. there was nobody else in sight. jack clambered over the edge of the gap the shell had torn in the roof and dropped lightly to the ground. "wasser!" moaned one of the wounded men, whom jack recognized as one of his guards. the boy sped to the well and hastened back with the big earthen pitcher from which they had refreshed themselves earlier that day. but he was too late. even as the boy held the cooling draught to the sentry's lips, the man died. the other was already dead when the boy dropped to the ground, his body frightfully shattered by the aerial bomb. there was still the third man lying by the house and jack, thinking he might be able to minister to him, hurried over. but here, too, the bomb had struck fatally. a shaft of moonlight fell through the poplars and illumined the man's face. it was radwig, struck down in death even as he had planned a cruel revenge for another. jack covered the dead professor's face with the man's huge blue cloak and then stood silent for a moment. the rapidity with which it had all happened almost stunned him. fifteen minutes before he had been a prisoner with the hideous sounds of spade and mattock in his ears. now he was, by nothing short of a miracle, free again. he raised his face to the sky and his lips moved silently. then, with a last look about the place, he prepared to leave, fervently hoping that before another day had passed he would be with his friends once more in louvain. all at once he heard a loud whinny. one of the dead troopers' horses had been left behind in the mad flight from the farmhouse. it was saddled and bridled, although the girth had been loosened. jack untied it, tightened the girths, and mounted. he did not know much about riding, but somehow he managed to stick to the animal's back as he directed it down the road. every now and then he drew rein and listened. he had no desire to encounter prowling bands of uhlans or to run into the small force that had evacuated the farmhouse, no doubt believing him to be dead. but dawn broke while he was still traveling, not at all certain that he was going in the right direction. jack decided to abandon his mount. taking off its bridle so that it could find forage along the roadside, he patted its neck and said: "thanks for the ride, old fellow." then bareheaded, and tired almost to exhaustion by all he had gone through, yet driven on by dire necessity of reaching the belgian lines, the lad struck off across a wheat field into a path of woodland. on the edge of the field he shrank suddenly back into the tall wheat. there lay a man's coat, a stone jug and a basket. no doubt the man was close at hand. but although he crouched there for a long time, nobody came, nor was there any sound of human life. birds twittered and once a rabbit cocked an inquisitive eye at the lad as he lay crouched in the wheat. cautiously jack raised himself and parting the stalks, peered out. he saw something he had not noticed before. the man, who doubtless owned the belongings which had alarmed jack, lay stretched out at the foot of a tree. he was on his face sleeping. but was he sleeping? an ugly, dark stain discolored the ground around him. his shirt was dyed crimson. jack saw, with a shudder, that he had nothing to fear here. the poor peasant was dead. shot down by wandering uhlans no doubt, as he was about to gather his harvest. "poor fellow, he'll never need these now," said jack, as driven by thirst and hunger he investigated the stone jug and the basket. one held cider, the other the man's dinner of black bread, onions and coarse bacon. too famished to mind the idea of eating the dead man's dinner, jack stuffed his pockets, took a long pull of the cider jug and then plunged into the wood. here he flung himself down to rest and eat. then, tired as he was, he forced himself to rise and travel on again. faint and far off the distant rumble of cannonading came to his ears, but here in the woods it was as calm and peaceful as if war, death and slaughter were forgotten things. at length he came to a place where the woods thinned out and there was a small clearing. he was about to advance across this when he saw something that caused his heart to give a quick leap and stopped him short in his tracks. at one side of the clearing was an aeroplane! it was a big monoplane with gauzy, yellow wings and a body painted the color of the sky on a gray day, no doubt to make it invisible at any considerable height. any doubt that it was a war machine was removed by the sight of a small but wicked-looking rapid-fire gun that was mounted on its forward part. jack was still looking at it, rooted to the spot as if he had been a figure of stone, when there was a sudden crackle on the floor of the wood behind him. then came an order sharp and crisp. "arrette!" jack was not a french scholar but there was something in the way the command was given that made him stand without moving a muscle. footsteps came behind him and then he felt rather than saw a man passing from the rear to face him. he worked round to the front of the boy and then jack saw that he was a small man with carefully waxed mustache in whose hand was a particularly serviceable-looking revolver, which he held unpleasantly level at jack's head. chapter xxxiii. through bullet-racked air. the man with the revolver gave a sudden cry: "_mon ami_ read-ee!" "great scott, de garros!" gasped jack, recognizing the french aviator. "what are you doing here?" "i might ask zee same question of you," smiled the other. "i leave you on zee sheep and now, voila! i find you in a belgian wood wizout zee hat, wiz your face scratched by zee bramble and looking--pardon me, please,--like zee tramp." "i guess i do," laughed jack, in his relief at finding that instead of falling again into the enemy's hands, he had met an old friend; "but i'm lucky that there's nobody to say 'how natural he looks'----" "pardon, i don't understand," said de garros in a puzzled tone. jack plunged into a recital of his adventures, interrupted frequently by a hail of "_sacres_," "_nom d'un noms_," and "_chiens_," from the frenchman. "and now it's up to you to explain how i find you here in the heart of a belgian wood with a war machine," said jack as he concluded. "zat is eezee to explain," said the frenchman. "after you leave me in new york i get passage on a french liner for havre. we arrive and i am at once placed in command of zee air forces of belgium. since zat time, pardon my conceit, monsieur, i think zat wizout bragging i can say i 'ave cause zee germans very much trouble. last night i fly over zee country and where i see germans i drop a little souvenir,--but what is zee matter, monsieur, you look excited." "no, no, go on," said jack; "i was just thinking that it's possible the day of miracles has come back." de garros stared at him but went on: "in zee course of my journey i see a farmhouse where gerrman cavalry horses and stacked arms show in zee moonlight," said the frenchman. "how did you know they were germans?" asked jack. "did you not know all zis territory is now overrun by zem? yesterday they advance. they are now near louvain. but nevaire fear, someway we drive zem back. but to continue. i drop one, two bomb wiz my compliments and----" "saved my life!" exploded jack. de garros looked concerned. "once more pardon, my dear readee, but you are well in zee head? zee sun----?" "no, no, don't you see?" cried jack; "those were your bombs that resulted in my being saved from a spy's death." "_sacre!_ ees zat possible? and yet it must 'ave been so! embrace me, my dear readee, nuzzing i 'ave done 'ave give me so much plaisair as zees." jack had to submit to being hugged by the enthusiastic little aviator to whom, as may be expected, he felt the deepest gratitude. "and now what are zee plan?" asked de garros, when his enthusiasm had subsided. "i want to join my friends in louvain," said jack. "_nom d'un chien!_ you are trying to walk zere through zees part of zee country!" "why, yes. i----" "_mon ami_, you might as well commit zee suicide. it is swarm wiz german. i hide in zees wood till night when i can travel wizout having zee bullet swarm like zee bee round what you call zee bonnet." "then what am i going to do?" he demanded. "i can't stay here and i've had one experience with the germans, and i assure you it was quite sufficient to last me for a lifetime." "i 'ave zee plan," said de garros. "yes." "my aeroplane hold three people." "go on." "you shall fly wiz me." "to louvain?" "if that is possible. if not, to some place where you can communicate wiz your friend. 'ow you like zat?" jack hesitated a moment. he was not a timid lad, nor did he fear ordinary danger. yet flying above the german troops, between the place where they were talking and louvain, was a risky business to say the least of it. yet there was no alternative that he could perceive. the mere idea of getting captured by uhlans again gave him goose flesh. as if he read his thoughts de garros said: "you run no more of zee reesk in zee flight than you do on zee ground. not so much. at night i fly high and i promise you i will not make any attacks." "you're on," said jack, extending his hand. chapter xxxiv. a flight of terror. "take zees. you need zem. we fly fast. _trã¨s vite._" de garros was speaking as he handed jack a pair of goggles. it was dusk and they, having finished an excellent meal from the aviator's provision pannier, were about to start on their flight across the war-smitten country. already the flying man, aided to the best of jack's ability, had gone over the aircraft, testing every part of it. everything was in perfect order, from the big gnome eight-cylindered, self-contained motor, mounted with the big propeller forward, to the last bolt on the dragonfly tail. just before full darkness fell, which might have involved them in an accident in rising, de garros gave the word to get on board. they clambered aboard, jack with a heart that beat and nerves that throbbed rather more than was comfortable. there are few people who do not feel a trifle "queer" before their first flight above the earth, and in jack's case the conditions of danger were multiplied a hundred-fold, for before they had cleared the woods and risen to a safe height they might be the target for german rifles and quick firers. de garros wore a metal helmet padded inside. jack had to be content with an old cap that happened to be in the aeroplane, left there by some machinist. but, as de garros said, the metal helmet would not be much protection against the projectile of a quick firer, or even a rifle. the fighting aircraft was fitted with a self-starter, obviating the necessity of swinging the great propeller. "all ready?" asked the frenchman of jack, who sat behind him, tandem wise, in the long, narrow body of the machine. "ready," said jack, in the steadiest voice just then at his command. "then up ve go." the self-starter purred, and then came the roar and a crackle of the exhausts as the propeller swung swiftly till it was a blur. blue smoke from the castor-oil lubricant spouted, mingled with flame, into the thickening air of the evening. the wholesome smell of the wood was drowned in the reek of gasoline and oil fumes. "gracious, if there are any germans within a mile, they'll hear this racket," thought jack, with a gulp. "it sounds like a battery of gatling guns." de garros took his foot from the brake lever and the machine darted forward. jack clutched the sides desperately till his knuckles showed white through the skin. then he gave a shout of alarm. the machine had suddenly reared up like a startled horse. the jolting and bumping of the "take-off" stopped. the boy realized with a thrill that they were flying. at that instant from the trees on one side of the clearing burst several uhlans. "germans!" cried jack. "maledictions!" exclaimed the frenchman. for a second or two the uhlans stood paralyzed as the machine shot upward. they had heard the staccato rattle of the engine from where they lay camped, not far off in the same woods that had sheltered de garros and jack. thinking it betokened a skirmish, they had hastily run toward the noise just in time to see the wasp-like machine whirr its way skyward. but the machine was not well above the trees when they recovered from their surprise. rifles were leveled. "look out!" cried jack, "they are going to fire on us." "hold tight now, i show you zee trick," rejoined the flying man quietly. the aeroplane was now above the wood which on that side was a mere belt of tall trees. suddenly the machine ceased its upward flight. it rocketed downward like a stone. above it bullets whistled harmlessly as the uhlans fired at the place where it had been and was not. the ground rushed up to meet them as the machine plummeted downward. jack's head swam dizzily. "we'll be killed sure!" he thought, but strangely enough, without much emotion, except a dull feeling that the end was at hand. then just as disaster seemed inevitable, the machine suddenly began to soar again as jack could have sworn it grazed the tall grass. up and up they shot, in a long series of circles, and then de garros turned and grinned at jack, showing his white teeth. "'ow you like?" he asked. "i--i guess. i'll tell you after a while" rejoined jack, with suspended judgment. the earth lay far below them now, although it was still light enough to see the fields marked off like the squares on a chess board and the countless fires of the germans that dotted the landscape almost as far as could be seen. at every one of them were men, who, if any accident befell the machine and it had to descend, would make things very interesting for the air travelers. jack could not help thinking of this as the aeroplane flew steadily along, her motor buzzing with an even sound that told all was going well. but he knew they were not out of danger yet. a hundred things might befall before they arrived safely in louvain. chapter xxxv. the bully of the clouds. and then all at once the danger came. ahead of them loomed, in the darkness, for the moon had not yet risen, a bulking dark form. an exclamation burst from the frenchman's lips. "a zeppelin. malediction!" "do you think she'll attack us?" asked jack. "i don't know. i can't tell yet which way she is coming. ah!" a long ray of light, like a radiant scimitar, glowed suddenly from the mighty aircraft, 400 feet long and capable of carrying many men and tons of explosives. hither and thither the ray was flung. "zey heard our engines. zey look for us!" exclaimed de garros. he shot up to a greater height. he was manoeuvering to get above the zeppelin, where her guns would be useless against the aeroplane, which was more mobile and swifter in the air than the kaiser's immense sky-ship. but suddenly the glowing light enveloped them in its full blaze. dazzlingly it showed them in its rays. it was the most peculiar sensation jack had ever experienced. it was like being stood up against a wall with a fiery sabre pressed to your breast. with a quick movement of the wheel, de garros sent the aeroplane out of range of the revealing light. the next moment came a sharp crackle and something screamed through the air. "missed!" exclaimed the aviator with satisfaction. again the questioning finger pointed its interrogating tip hither and yon across the night sky. others from below now joined it in its quest. the firing from above, and the sight of the searchlight had been rightly guessed by the germans encamped below. they knew that a hostile aircraft was above them and were helping in the search for it. a sharp exclamation broke from the frenchman. he bent and fumbled with some contrivance on the floor of the aeroplane. there was a sharp click. "what have you done?" asked jack. "i have released zee bomb." "the dickens!" "watch! now you see!" fascinated, even in the midst of the awful danger they were facing high above the earth in the upper air, jack leaned over and stared at a battery of searchlights sending out fan-shaped rays on every side. he guessed this was the objective of de garros' bombs. he was right. as he gazed there was what looked like the sudden opening of a flaming fire below, and the searchlights went out as if a giant had snuffed a monstrous candle. then came the report, booming upward through the air. "aha! zere are some germans below zere who will not do zee mischief more!" exclaimed the frenchman with vicious satisfaction. but his congratulations to himself were premature. again the light of the zeppelin enveloped them. the glare seemed like a warm bath of all-revealing light. there was a flash and then the shriek of a projectile as the aeroplane dipped under the glow of the light. then came the boom of the report. "zey ought to learn to shoot," muttered de garros. "thank heaven they can do no better than they are," rejoined jack. "now we show zem zee clean pair of heels and run away," said de garros. "i'm glad to hear that. i couldn't stand much more of this," thought jack. "if i was alone, or had an officer wiz me, we go above zat zeppelin high in zee air and blow him up," announced de garros cheerfully, after a minute or two. "ah! zey get us again. _peste!_" the whine of a machine gun sounded as the searchlight of the pursuing zeppelin again enveloped the bold little aeroplane. her great bulk, big as a steamship, was rushed at top speed through the air. they could catch the roar of her four motors being driven at top speed. de garros had dropped again, and thanks to his skill, the aeroplane was still unhit, although the projectiles from the quick firer had come close enough for the occupants of the monoplane to hear their whine. "we beat zem out!" exclaimed the frenchman. "then we are faster than they are." "oh, very much." "well, we can't be too fast for me," muttered jack. "i----" "_sacre!_" the searchlight had again caught them, and again there had come reports from her underbody. this time the sharp crackle of rifles. "are you hurt?" cried jack, as the frenchman gave a sharp exclamation recorded above. "malediction, yes. zey nick my hand. eet is not bad. but worse zey hit zee motor i think." the smooth-running machine was no longer firing regularly. its speed had decreased. "what are you going to do now?" cried jack. "we'll be mowed down by those machine guns if we slow up." "we must come down." "but the germans?" "there are no campfires below us now." "but can you make a good landing?" the frenchman shrugged his shoulders. "_parbleu!_ if i cannot zen all our troubles are over, _mon ami_." the aeroplane began to descend, slowly at first and then faster. the dark earth sky-rocketed up at them from below. chapter xxxvi. a mysterious capture but the disaster de garros had feared more than admitted did not happen. between two patches of wood lay an open field, readily distinguished even in the dark by its lighter color. in the stubble of a mown crop the aeroplane alighted, not without a considerable jolt to its occupants. their main anxiety now was the great zeppelin they could hear, but not see, above them. jack trusted they were equally invisible and that the searchlight would not reveal them, for high explosive bombs in a deadly rain from above would certainly follow. de garros, while wringing his wounded hand with pain, was helped out of the machine by jack. "malediction, and i not get zee chance to fire on zat _chien_ of a zeppelin," lamented the frenchman. "some day i pay zem back." "is your hand badly hurt?" asked jack anxiously. "i do not know and we dare not yet use zee electric torch i 'ave on zee machine." "why not?" "it would show zee zeppelin where we 'ide." "then you don't think they guess that we have descended?" "no, if they had zey would search zee ground wiz zeir light." "that's so." "but now they are point eet 'ere, zere, all over zee sky. if zey no find us zey think zat we are keel and zey go away." jack shuddered at the narrow escape they had from this being made literally true. for a long time, or so it seemed to the anxious watchers below, the zeppelin soared above them, her searchlight swinging in every direction. but at last the noise of her engines grew dimmer and the light vanished. "zey go away disgoost," said de garros, shrugging his shoulders. "now we see what are zee chances of patching up my hand and getting zee engine going again." the electric light, carried to locate engine trouble at night, was switched on and brought out by its long wires over the side of the craft. then began an anxious examination of the aviator's hand. it proved that the tip of his thumb, where it had laid on the edge of the wheel, had been badly nicked by a bullet, but luckily it was the left member. "if zee engine ees capable of being fixed i can drive wiz my right hand," declared the aviator. "thank the _bon dieu_ that it was not zee steering wheel zat was struck." with the first aid kit, carried by all soldiers in the field, they soon dressed and bound the injured member, and then came the examination of the engine, an investigation on which much depended. if it proved to have been too badly damaged to be repaired, they would not stand much chance for escape in a country so overrun with german troops. for all they knew some might be camped not far off. but they had to take their chance of that. "_ciel_, we are in zee luck!" exclaimed de garros, after a brief examination, "the _chiens_ only smashed a spark plug. i soon fix 'im and zen once more we start." the repair kit contained the necessary plug, which he quickly replaced. then the journey through the night, which had already proved so eventful, was renewed. but now jack felt a fresh alarm. how would they be able to tell at louvain that it was a french and not a german aeroplane hovering above them. he put the question to de garros. "zat is easy. i 'ave on zee side of zee machine a set of four electric lights. two are red, one is green, one is white. zat is zee secret night signal of zee french machines." "but suppose the germans should find out your code?" asked jack. "eet is changed every night. sometimes two green, one white, one red--many combinations are possible." "by jove, i never thought of that!" exclaimed jack, struck by the simplicity of the idea, and relieved at the thought that there would be no danger of being attacked by mistake. half an hour later they landed at a sort of fair ground in louvain after answering all challenges satisfactorily. the germans were not yet at the gate of the city. but they were near at hand and the place was wrapped in darkness. however, on account of de garros' rank, they obtained an escort to the hotel. tired from the excitement and nervous strain, jack went to bed, sighing with relief at the thought that all was so promising. in about an hour or so he awakened from a deep sleep. the night was sultry, and there was a strange calmness in the atmosphere seemingly weighed with grave and impending events. jack could not resist an impulse to leave his room and wander out into the deserted streets of louvain. he had not taken a dozen steps when a heavy hand fell on his shoulder. before he could turn to see his assailant, he was whisked from the ground and swept onward to a great height. still dead silence reigned. chapter xxxvii. the might of militarism. it was some time later that jack began to realize that he was a prisoner and borne on a giant aeroplane. how did he get there? try as he would he could not answer that question. he gazed about him. away in the distance he could distinguish small specks of light, which, were they not moving so rapidly about space, he would have mistaken for stars. below searchlights swept the horizon. here and there were the glimmerings of fast dying out camp-fires. suddenly a faint streamer of red light shot high into the air, held steadily for a moment, and then broke into a million colored globules. "a signal," thought jack. "i wonder if it will be answered." he then became aware of a movement on the part of the air pilot. till that moment he had not noticed the least sign of life from the wheel man. now there came a soft _blob_ and a red light shot into the air. almost instantly there again was darkness. "by jove!" whispered jack to himself, amazedly. "this certainly is marvelously fast work!" there was no repetition of the signals. for a while jack was content to gaze about him in idle wonder. he seemed indifferent to his plight. he drank in the scenes about him, gazed interestedly at other air-craft that passed them, and watched the sky begin to turn a dull slate color. it was the dawn of another day of carnage. others, too, were on the watch for these faint signs of day. from somewhere came the long, awful boom of a huge cannon. jack tried to get up, but fell back to his former position. he only then realized that he was chained to his seat. he had a certain amount of freedom, but beyond that he was a prisoner, helpless. "well," mused jack upon this discovery, "even if my hands and feet were free, i could not escape from this height. we must land some time, and then i'll have more need to use them." so jack settled back to watch developments. now everything was astir. a faint murmur was wafted to him on the morning breeze. he could see the soldiers moving about, the great cannons and howitzers beginning to lumber onward, the column of uhlans already in saddle, and the hundreds of air-craft rising to greet the early sun's rays. "it's wonderful!" whispered jack, fascinated. "yes, wonderful, but how terrible! this whole array is primed to create nothing but havoc, sorrow, destruction, and death! gee, but i'm glad the good old united states has no need for such military organization!" another sound came to his ears, and cut short his thoughts of america. in an astonishingly brief time, the army of the invasion had completed its formations and was on the march, the rank and file, all deep-throated men, singing _das fatherland_. "good god!" gasped jack. "they are going to their death with a song on their lips!" from somewhere in front of these columns came a roar of cannon. the air was filled with shrill, piercing shrieks as tons upon tons of metal, charged with fearful destructive powers, tried to stem the human flood. for a few minutes the smoke and steam hid the dreadful spectacle from jack. he gazed intently below him, anxious to see the victor of this clash. of course, it must not be forgotten that the human waves of men were supported by great artillery fire on their own side. unaided entirely these men would have been annihilated miles before the fortresses. the ranks were on the double run now. their bayonets glistened in the dull sunlight. on, on, ever on, they went, keeping perfect stride, never faltering. jack could not tear his eyes from the sight. even while storming the redoubt, the ranks held firm. another sheet of flame checked them for a moment. they tried to recover, and somehow couldn't. again came that destructive, raking fire. the lines faltered. jack trembled from excitement. was this magnificent effort to fail? he was not thinking of them as germans. he was only aware of brave, dauntless men trying to best steel and explosives. again came a sheet of flame. the ranks actually seemed to fall back. then once more, from the rear, rose the deep notes of _das fatherland_. it stiffened the thinned ranks. they rushed forward, the fierce cry of victory mingling with the strains of their national anthem. "that was great!" cried jack. "my sympathies are not very strongly with the germans, but i'm bound to give credit where credit is due. well, what now----?" jack became aware that the machine on which he was a prisoner was going to make a landing. silently, swiftly, the winged mechanism was guided toward earth behind the german lines. jack smiled with satisfaction. "i'll have a chance to stretch my legs," he said. "as long as radwig is dead, i have not so much to fear. i wonder what they want of me?" chapter xxxviii military cross-examination the machine came to a stop. the pilot never moved from his seat. instead, he motioned to a soldier to come to him. evidently a few words were exchanged. a sharp command was issued. two soldiers came up to jack. he held up his hands to show that he was chained. one of the soldiers leaned forward, and pressed a button at the side of the car. the chains fell from jack. without comment the two soldiers seized jack and flanked him. a detail of six additional men fell in step, a petty officer wheeled about,--a movement that acted as a signal for the soldiers to march. a five-minute walk brought them to a small cottage. here they halted. jack was blindfolded. when the bandage was removed, he found himself facing an elderly man seated at a desk. jack could not make out his features, as they were hidden in a gray mask. "_sprechen sie deutsch?_" he was asked. jack understood the question, and replied: "no." "what is your nationality?" came the question in english. "american." "what part of america?" "new york." "your occupation?" "wireless operator." "for your government?" "no, for the transatlantic shipping combine." there followed a short pause. jack was wondering what next to expect. the questions had been brief and propounded in a crisp, commanding way. there was no leeway for equivocation. "do you tell the truth?" "i do," replied jack quietly. "why do you tell the truth?" "because i believe in it," said jack simply. "under what circumstances did you first meet herr radwig?" jack, greatly surprised, hesitated. would it be wise to tell everything? how under the sun did this man in the gray mask know so much? "remember, the truth." jack thought quickly. the question implied that this officer had some knowledge of his dealings with radwig. possibly, also, the officer was about to test the value of his declaration that he told the truth. so jack figured. but was this not an amazing illustration of the wonderful efficiency and thoroughness of the german secret service. "speak!" came the imperative command. "very well," replied jack calmly. "it was on the _kronprinzessin emilie_. it seemed that we were about to be dashed to pieces on floating icebergs. some shrieked: "'the _titanic_!' "'the boats!' shouted a man. he violently pushed two women aside, wedged in the panic-stricken throng. i stood at the head of the companion way. the man told me to get out of the way. i tried to calm the people. but this man seemed to have lost his reason. he rushed at me, trying to strike me. i was too quick for him. i struck first. he staggered back, subdued. it was only later that i learned this man's name." "and then--how and when did you meet herr radwig?" so jack had to relate incident after incident. always, at the end of a recital, came the same question, asked in the same matter-of-fact tone of voice: "and then--when and where did you meet herr radwig?" everything must have its end. at last jack had modestly related every episode with which the reader has been made acquainted. the even tone of his questioner, his piercing eyes, and the unbroken silence was beginning to weary jack. he felt that he could hardly keep his wits about him. evidently the german officer noticed these signs and was patiently waiting for them. he leaned forward, and the steady monotone now gave place to a rasping, menacing gruffness. "who are you?" he suddenly snapped. "an american," came the tired reply. "an american!" jeered the officer. "yes, and i'm proud of it!" "why should you be proud of something you could not help?" "i don't understand you," replied jack, passing his hand over his brow as if to clear away the ever increasing drowsiness. "you don't understand me?" jack shook his head. "answer me!" jack opened his mouth to speak, his lips moved, but he could utter no sound. he stood still, staring stupidly at the man in front of him. his thoughts were befuddled. what did he--the man in the gray mask--want? "i wish those eyes wouldn't glare at me so," jack mumbled to himself. "i didn't do anything to them." but the eyes behind the gray mask became larger, rounder, more compelling. jack knew instinctively that they meant him harm. what power they held! something within him fought to arouse him. he tried to move and could not. larger, ever larger those eyes seemed to grow! the features of the man were lost; in fact, those eyes seemed to belong to no one; they seemed to have life and power, dreadful power, of their own. jack shrieked with terror! was he lost? chapter xxxix. shattering the shackles. did it ever occur to you that nature plays many pranks? from the many learned books and men--and from daily events--we are lead to assume that nature is grim, relentless. on the whole, this assumption is true. but one of the things that has made nature a harder problem for man to solve is that there are the most unexpected exceptions to the most carefully proved rules. sometimes these exceptions take place with things and sometimes with persons. nature had played a prank with jack. when he came to his senses he found de garros solicitously bending over him, his broken english running riot in his native french. "what's up?" questioned bewildered jack. de garros shrugged his shoulders. "i--er--_phew_! zee--la--_compron_--eh---i understand not! you make zee big cry, i in rush--excited much--_phew_!" jack sat up in bed. "are we still in louvain?" he demanded. "_we_, _we_, certainly!" de garros hastened to assure him. a big sigh of relief welled from jack. "de garros," he said, "i have had the most remarkable nightmare!" whereupon jack related to de garros, as well as he could recall the details, the dream that had seemed so real. de garros was thrilled. every now and then he broke into the recital with exclamations most expressive of the impressions they made upon him. "and now," jack said in conclusion, "i think it is best for us to dress. i have never dreamed before, and i never want to dream again, if all dreams are so terribly real." de garros laughingly agreed with him. when jack had dressed, he began to explore the corridors of the hotel. he felt that bill, tom jukes and pottle were guests of it. of course, the easiest way about it would have been to inquire at the office. as the hour was rather early he did not care to do this at once. a little later jack was joined by de garros, and together they walked into the dining room. even at this hour several tables were occupied. almost at once the two were espied by their friends. a more amazed and glad set of chaps would have been indeed difficult to find anywhere. "honest, jack," cried bill, tears of real joy in his eyes, "we had given up all hope of ever seeing you again." "man alive!" declared tom jukes, "you can't imagine how we felt, for we knew that there was no chance of getting through to save you." "blues--here--everybody!" exploded pottle. "funeral cheerful in comparison--no eat--no food--just blues!" "come, jack," invited bill, "and de garros, breakfast with us and tell us about it." so, between mouthfuls, jack related his experiences with radwig's party of uhlans. affectionately he placed his hand on de garros' arm, and soberly said: "i owe my life to you. if it hadn't been for you----" "it was sure luck, the greatest ever," declared tom jukes. "fine stuff--fooled the enemy--shot at sunrise--others get shot instead--up in the air--down again--all safe--at last--hurray!" cried pottle, capering about wildly. "i can't think it was luck," said jack gravely. "i think there was a higher power than that concerned in it." "you are right," agreed bill. "read--ee--_mon ami_, you 'ave not forget zee dream," slyly remarked de garros. jack turned scarlet. somehow he felt that it was not very manlike to have even bothered with nightmares. "what's this?" demanded bill. "come on, now," coaxed tom; "don't hold anything back." "dreams?" questioned pottle. "dreams? great stuff--big inventors--and columbus--dreamers!" so jack went over that adventure again. this time, however, he decided to tell it in the way it actually happened. the result was that when jack led them up to the climax he held even de garros spellbound. jack ceased to speak and looked at his friends. "how did you get away?" asked bill. "i didn't," was the smiling reply. "you didn't!" came the perplexed chorus. de garros was chuckling softly. he had to admire jack's cleverness. "battle--prisoner--great fight--man in gray mask--disappear--eyes bigger and bigger--what's this--fairy tale?" "no, pottle," replied jack, "it was only a dream." for a moment there was silence and then they all broke into peals of laughter, laughter that seemed so strange and out of place in these days frought with war's devastation. so they had the good sense to check their merriment, especially as they saw the eyes of many surprised men and women upon them. they soon left the dining room, and prepared to leave louvain. late that afternoon arrangements were completed. regretful good-byes were said to plucky little de garros, whose demonstrative eyes were wet as he clasped their hands in farewell. "we may nevaire meet again," he stammered, "but i nevaire forget you all." "nor will we forget you!" cried jack warmly. "you--you, if it hadn't been for you----" "read--ee, _mon ami_, you 'ave forget what you do for me long ago. a fair exchange. you save _my_ life." "you're fine," exploded pottle. "legion of honor cross for you--long war--much dead--much wounded--but you'll live!" a prediction, strangely enough, that came true. chapter xl. old glory again. before the fall of louvain, jack and his friends were across the border in france. ultimately they were lucky enough to rejoin the _st. mark_--sent for the accommodation of refugees--at marseilles. a cable was despatched to america, telling of tom juke's safety. pottle, the young photographer, cabled his paper, asking for permission to remain in the battle zone. this was granted. so the trio--jack, bill and tom--said farewell to pottle. "when i get back--possible--the paper will make--hurrah!--look me up--eh?" "we sure will, old top," promised tom. the voyage across was without incident, save that, as was expected, they were stopped by british warships. so, one fine morning, unannounced, jack called upon uncle toby ready. the old tar gave vent to a great cry of joy. though jack had often been away for long periods, uncle toby never fully knew the thrilling adventure jack had participated in. now there was no hiding of the truth. the war was at hand. the germans were sweeping everything before them. how had it fared with jack? this uncertainty had worried uncle toby. he felt that he would never be able to forgive himself, had anything happened to jack. when the first greetings were over, uncle toby could not help but ask about his golden embrocation and universal remedy for man and beast. "did you meet up with the king of england?" he queried. "no, uncle toby," laughed jack, "i did not." "be it so with the kaiser?" "no, not the kaiser, either." "how now--was it the czar?" jack shook his head. "but made a--use of 'em?" "yes," replied jack with a twinkle in his eye. "i did make----" at this moment there came a sharp rap on the door. jack opened it, and a messenger, upon ascertaining who he was, handed him a telegram. "what now?" demanded uncle toby. jack tore open the envelope. the inclosed sheet read: "congratulations and grateful appreciation. report immediately. "jacob jukes." "yeou ain't a-goin' back to europe!" declared uncle toby emphatically. "don't worry, uncle," replied jack. "i don't think it is for that mr. jukes wants me." "well, if he don't," replied the old captain, "give 'im a bottle of my golden embrocation and universal remedy for man and beast with my compliments." "all right," laughed jack as he put the bottle in his pocket, never intending, of course, to carry out the errand. jack found mr. jukes in earnest conversation with his son, tom. however, the moment jack entered, father and son arose. "jack," said mr. jukes, extending his hand, "let me thank you." it was said sincerely and simply. their handclasp was hearty and true. mr. jukes began to pace the office. tom looked at jack and winked. "young man," suddenly said mr. jukes, sternly addressing jack, "you are bound to succeed in life. you have the _makings_. you have your trade--or shall i call it profession? but operating wireless is not everything. you can be a wireless operator all your life and your salary will be your only means of keeping the wolf from the door. too many of our people have to depend on that means of support. some day i feel it will be different. at all events, i shall make a beginning with you. so tom and i have decided to give you a number of shares in our combine." thereupon mr. jukes went on to explain the value of the shares, instructing jack just what he should do with them. to tell the truth, jack had never troubled himself very much with the intricacies of stock values. finally jack left mr. jukes' office feeling like a millionaire. "strange," mused jack, "that this good fortune should come to me when thousands of others are losing their all in europe." feeling thus satisfied, jack decided to acquaint helen dennis with the good news. as he strolled down to the dock, he could not help but note that in so far as new york was concerned, the war did not exist. people went about their business in their accustomed way. beyond the usual set or serious expression characteristic of the average new yorker when he is engaged in earning his dividends or salary, as the case may be in different instances and walks of life, the average person seemed absolutely unconcerned of the world tragedy that was unfolding itself across the sea. at the docks, however, there was increased activity. the demand upon american ammunition and commodities had jumped by leaps and bounds. shippers were reaping a harvest. the _silver star_, captain dennis' ship, was in port. jack had little difficulty in getting aboard. captain dennis was delighted to see jack. he could spare but little time, so when jack had told him only briefly of his experiences, the wise tar, his eyes twinkling with mischief, said: "really, jack, don't you think helen would be more interested in your adventures?" jack blushed. "never mind, lad," laughed the captain, "we all have those days, you know." so jack made his way to the captain's cabin. but let us say nothing more of them; rather let us ask what became of bill raynor? chapter xli. war in times of peace. just before jack called upon his uncle toby, bill had expressed a desire to stroll about the great city. "you see," bill said in explanation, "the sight of old new york makes me glad to be back again. they say it's a selfish place. well, perhaps there are towns that make you feel more at home, but once you know manhattan's ways, you don't want to change!" "have it your way," agreeably laughed jack. so they parted for the time being. feeling hungry, bill decided to visit one of the select downtown restaurants his purse seldom allowed him to patronize. now, as the reader will remember, bill had no need to worry over funds--at any rate, not for the immediate future. bill thoroughly enjoyed his meal. he left the restaurant feeling like a prince. "those prices are steep," he reflected, "but the food and service are worth it." barely had he walked a block when he recognized tom jukes a few strides in front of him. bill's first impulse was to hail tom, but something about the latter made him hesitate. "something seems queer," muttered tom, puzzled. he was undecided. should he follow the millionaire's son? tom jukes seemed anxious to avoid being seen. every now and then he glanced about him hurriedly. he kept close to the building line, his cap pulled over his eyes. he turned into one of those ancient alleys down in the financial district of new york. bill raynor came to a quick decision. "i'll follow him!" he muttered. a moment later bill was also in the moldy alleyway. tom swung south, then west, and south again, and finally halted before a pair of ornamental iron gates of the most antique and peculiar design. bill, mystified that such places still existed in the great metropolis, dogged tom's footsteps, always careful to keep well out of sight. he saw tom pass through these iron gates. a moment later bill had followed tom through, though now he had to be far more careful, for every flagstone seemed to give up a hollow bellow. tom walked up an iron staircase clinging to a decaying bulk of a dirt-gray stone ramshackle building. he climbed one flight and then disappeared from view. bill, very carefully--every nerve alert--followed. a moment later he stepped into a long, dim, lofty corridor, walled with marble of a greenish tint, and smelling faintly of dry-rot. picking his steps with the greatest caution, bill felt his way forward. somewhere in front of him he saw the shadowy form of tom. bill saw tom pause before a door, which he opened very slowly. a faint light came from within. a moment later tom had disappeared from view. bill crept forward. should he open the door? "i wish jack were here," said bill to himself. jack, it was, who had won the approval of jacob jukes, head of the great shipping combine, and father of tom, for his masterly handling of many difficult situations. under the circumstances, bill did not flinch in his determination to learn _what was going on behind that door_! bill put his ear to the door--and at once heard a faint _tick-tick_, as well as a muffled voice. slowly bill felt the door for the knob and to his surprise he found there was none! "entrance by signal only!" instantly decided bill. but how was he to get in without it? his eyes were now more accustomed to the gloom. he looked about him, hoping to find a window or some outlet that might lead to the barred room. farther down the corridor, to his right, he saw a stairway--or what appeared to be a stairway. he walked toward it, always bearing in mind to be extremely careful. he climbed up one flight without mishap. on this floor, the feeling of desertion and forlorn desolation grew deeper. bill could barely suppress a shiver. suddenly a rat scampered across the floor. "phew!" ejaculated bill, "this is _some_ place!" he noticed a thin ray of daylight a short distance from him. bill at once decided to discover its origin. a moment later he saw that the light flowed from the cracks of a door. a brief investigation proved the door to be unlocked. as he quietly pulled the door open he saw that the room was absolutely bare, and that the light came from the mud-pasted windows facing a brick wall not five feet from them. bill tip-toed across the room, and raised one of the windows. to his satisfaction he at once noticed the drain pipe at arm's length. a moment later he had slid to the floor below. to his surprise he saw the window of that mysterious room wide open. he could see only part of it. there seemed many men listlessly sitting about, though the majority kept unseeing eyes on a blackboard. "a blind tiger!" breathed bill, amazed. bill meant that it was a fake racing broker's place. in years gone by there were many such dens of evil in new york, where congregated the broken-hearted, the reckless, the unscrupulous, all of whom tempted fate on this horse or that. as a rule the proprietor controlled the destinies of his victims, for he could "fake" any information he desired as to what horse won or lost. happily these dens are now more scarce than hen's teeth. it was these dens, the graves of dupes, that were called _blind tigers_. "does tom play the ponies?" wondered bill. he listened intently. somewhere a ticker droned, and a husky voice announced: "gas a half--five eighths; steel six--nine hundred at a quarter--a thousand--five-hundred--a quarter--an eighth--erie--an eighth--steam--an eighth----" "what does this mean?" questioned bill. "it sounds like stock quotations. can it be----?" he decided to risk glancing into the room. at some risk of losing his hold he balanced himself in order to accomplish his wish. he saw a room, unclean and unwholesome. the men seemed to be of the discarded of the street, the diseased and maimed of the financial district; here and there was a younger, smarter type, the kind that makes the gangster, the pickpocket and worse. he also saw tom sitting quietly yet alert. at his elbow was a young man, somewhat older than tom. on the wall facing the window was a great blackboard, and as the ticker spelled out its information, and the slovenly dressed clerk gave it voice, a second clerk chalked away without cessation. beyond this clerk's announcements everything was quiet. bill felt himself slipping, so he silently swung back to his former position. the light of understanding was in his eyes. "by jove, it's a bucket shop!" now a bucket shop is where people buy and sell stock on less margin or in smaller quantity than is accepted on the curb on broad street or on the stock exchange. these establishments, too, are fast disappearing, though as is always possible in new york, an exception--as in all directions of semi-organized crime--manages to keep from the sharp talons of the law for a longer period of time. the bucket shops were where messenger boys and clerks gamboled with dame fortune. sooner or later they lost--lost not only every cent to their names, but much of their self-respect and honesty. it was also the place for the men who had gone down to defeat in the great battle fought bitterly every minute of the day in the great financial arena. these men were unfit for everything else, so they turned to the bucket shops as a drowning man grasps at a straw. but we have digressed enough--though this was really necessary--and let us continue with the narrative. bill did not know what to make of it all. surely tom jukes had little need to play for stakes. his father was sufficiently wealthy and knew the great money game, and its pitfalls, not to have acquainted his son with them. the more bill thought, the more puzzled he became. suddenly he heard tom shout: "you robber, you thief!" "git out," bawled the voice, evidently that of the proprietor, "or i'll have you put out!" "you do, and i'll have you in the hands of the police within twenty-four hours!" "you will, will you?" came the snarling challenge, followed by a general commotion. "here's where i take a hand!" decided bill, and leaped into the room, now in fearful confusion. "stop!" cried bill, drawing his revolver, which he had a special permit to carry at any time he wished, "or i'll fire!" his command was obeyed. "stand where you are!" bill demanded, noting a suspicious movement on the part of several to escape. "bill, good old bill!" exclaimed tom, overjoyed. "yes, it's bill," was the reply. "call up headquarters while i hold them in line." "that's your tip, fred," said tom, turning to the young man bill had noticed before. "on the run now!" the young man called fred seemed to need no further invitation. tom now joined bill. from one of the drawers of the desk at which the proprietor had been seated, tom brought to light an ugly-looking colt. "let's move 'em toward the rear!" suggested tom. "some of 'em are showing signs of restlessness." "all right!" acquiesced bill. so, at the point of the revolvers, everyone in the room was lined up against the rear wall. the older men, who had seen better days, appeared indifferent to it all. to them life meant very little. spirit, youth, ambition, success had long passed them by. they still clung to the vain hope of winning something out of sheer habit. stock gambling, like opium, oftentimes urges on its victim until the sands of life slowly ebb away. the younger no-accounts scowled darkly. but what could they do? those two lads were too business-like to attempt anything rash. "say," growled the proprietor, addressing tom, "can't we call this quits?" "nothing doing!" was the curt reply, both boys at once becoming more alert that ever. "aw, take a joke," pleaded the man. "i'll square it with you. honest i will." both boys remained silent. "i'll tell you what," continued the owner, "just to square myself, i'll throw in one hundred dollars." silence. "five hundred!" "you're going out of business," announced tom. "save your breath!" "one thousand dollars!" "one more word," warned bill, "and i won't be responsible for my action. keep still." defeated, the man depicted his silent disdain. a moment later fred and the police arrived. the police captain in charge wanted the boys to go along to press the charge, but tom, upon quickly satisfying the officer of their intentions of doing so the next day--especially establishing that tom was the son of jacob jukes, the multimillionaire--were at liberty to proceed as they pleased. "explanations are now in order." "correct," replied tom. "let me first introduce fred strong, an old-time friend of mine. bill raynor, one of the finest boys in the world!" the introduction was acknowledged with appropriate remarks. tom then unfolded a most interesting story. fred was a wall street clerk--and, like many others, dabbled in stocks. he kept on losing. so, desperate, he attempted to court luck at the bucket shop a friend of his had told him of. for a time he won. his hopes rose. then the inevitable reverses began. the proprietor meanwhile had studied his victim. fred, without realizing it, became one of his dupes. he loaned money from every one. he began to tamper with his books. disgrace stared him in the face when he met tom. a few hours had straightened out all tangles. tom, however, insisted on bringing the bucket shop keeper to book. "well, that's all to it!" interspersed tom. "hold on," expostulated bill, "why did you sneak along the street as if wishing to be unrecognized?" "easy," replied tom. "saw dad, across the street, so had to--as you say--_sneak_." "_phew!_" whistled bill, astonished. "i never saw him. one other point, how did you know the revolver was in that desk?" "it seems," answered tom, "that the bucket shop proprietor made it a practice to show new customers that weapon. i suppose it was an effective reminder that all disagreements might be settled rather abruptly." "well," chimed in fred, "let us forget about it. i'll never play the market again. but, boys, i want you to come with me. i have to tell this story to the sweetest girl in town. you've got to meet her!" "if you insist, lead on," replied tom. "but suppose you tell her the truth of the matter, and then,--well--i guess bill and i will be honored, i'm sure!" bill laughed outright. "i never suspected," he said, "you had so much of the so-called 'society sass'." tom chuckled with glee. he was highly satisfied with the first day's adventure in america. in excellent spirits, the trio rode uptown. while en route bill briefly told, in turn, of catching sight of tom, and the consequences thereof. an hour later fred brought them to a neatly nestled house. there was a hand-ball court on the property, and fred saw to it that they were made to feel at home. then he entered the house. "elsie," said fred, when first greetings were over and they were comfortably settled, "i've something to tell you." "what is it, fred?" "i--i couldn't buy you the engagement ring--be--because i lost the money." "that is _too_ bad! but don't mind it, dear. i can wait." "it's nice of you to say it, but i lost the money on stocks." "tell me about it," she requested calmly, though there was a break in her voice. so fred related the facts already familiar to us. nor did he spare himself in the recital. at its conclusion, there was a moment's silence. then---"fred," said the girl softly, "i'm glad you told me of this. please, fred, don't gamble again--whether it be on cards or stocks--and if you were younger--i'd add buttons and marbles." "i've already promised not to do so--but elsie, i have something else to tell you. i have a new position at a higher salary--thirty dollars a week." "that's great!" "it'll be more--if i make good." "fred, i'm _so_ glad." a pause. "the cost of living is very high now," asked fred--"isn't it?" "i should say so! diamonds will soon be cheaper than onions or potatoes or cut sugar." "elsie!" "yes?" "would you like--could you--i mean--er--do you think two persons could live on thirty dollars a week?" "_certainly!_" "how about _us_?" "oh, george!" "elsie!" a blissful interval. then-"elsie--i've completely forgotten! those two boys i told you of are playing handball. they insisted that i confess my crimes before you met them!" a moment later fred was introducing tom and bill to elsie. the young lady's form of greeting was most unexpected and unconventional. before either of the boys could surmise her intention, she had kissed them! of course general laughter and banter followed. of this let us say no more. the reader, however, may rest assured that the boys whose adventures we have followed through six volumes were always true to american ideals and aspirations. they participated in many strange and thrilling adventures. we may write of these in the near future, but for the time being, with every good wish for the bright future that appears assured to them, we will bid farewell to the ocean wireless boys. the end. -----------------------------------------------------------------------transcriber's notes: 1. obvious typographical errors have been corrected. 2. inconsistent spelling and hyphenation in the original document have been preserved. 3. underscores indicate text originally in printed in italics. the ocean wireless boys and the naval code by captain wilbur lawton author of "the boy aviators' series," "the dreadnought boys' series," "the ocean wireless boys on the atlantic," "the ocean wireless boys and the lost liner," "the ocean wireless boys of the ice-berg patrol," etc. _with illustrations by charles l. wrenn_ new york hurst & company publishers copyright, 1915, by hurst & company [illustration: "huh, i don't think the idea's worth a cent," sniffed thurman.] contents i. vacation days ii. "speedway" vs. "curlew" iii. captain simms, of the "thespis" iv. on secret service v. night signals vi. in the dark vii. the naval code viii. a monkey interlude ix. noddy and the bear x. "what do you make of it?" xi. a swim with a memory xii. a tale from the frozen lands xiii. a night alarm xiv. jack's curiosity and its results xv. billy takes the trail xvi. a "ghostess" abroad xvii. one mystery solved xviii. bill sniggers decides xix. what a "hayseed" did xx. the "curlew" in trouble xxi. the end of jack's holiday xxii. "the gem of the ocean" xxiii. jack's big secret xxiv. the navy department "sits up" xxv. a mystery on board xxvi. a "flash" of distress xxvii. a strange wreck xxviii. cast away with a python xxix. captured by radio xxx. thurman plots xxxi. the "suitable reward" xxxii. the plotter's triumph xxxiii. in the power of the enemy xxxiv. the search for jack xxxv. the wireless makes good the ocean wireless boys and the naval code. chapter i. vacation days. "up with your helm there, noddy! luff her up or you'll have the _curlew_ on the rocks!" "that's right, luff!" cried billy raynor, adding his voice to jack ready's command. "that's what i _luff_ to do," grinned the red-headed, former bowery waif, noddy nipper, as, with a dexterous motion, he jerked over the tiller of the fine, speedy sloop in which the boys were enjoying a sail on alexandria bay, above the thousand islands. the mainsail and jib shivered, and the _curlew_ spun round like a top just as it seemed inevitable that she must end her career on some jagged rocks that had suddenly loomed up ahead. "neatly done, noddy," applauded jack. "we'll forgive you even that awful pun for that skillful bit of boat-handling." the freckled lad grinned in appreciation of the compliment paid him by the wireless boy. "much obliged," he said. "of course i haven't got sailing down as fine as you yet. how far do you reckon we are from home?" "from the pine island hotel, you mean?" rejoined billy raynor. "oh, not more than ten miles." "just about that," chimed in jack. "if this wind holds we'll be home in time for supper." "supper!" exclaimed bill; "i could eat an octogenarian doughnut, i'm so hungry." a groan came from noddy. although the bowery lad had polished up on his grammar and vocabulary considerably since jack ready first encountered him as second cook on the seal-poaching schooner _polly ann_, captain "terror" carson commanding, still, a word like "octogenarian" stumped him, as the saying is. "what's an octo-octo--what-you-may-call-'um doughnut, anyhow?" he demanded, for noddy always liked to acquire a new word, and not infrequently astonished his friends by coming out with a "whopper" culled out of the dictionary. "is it a doughnut with legs on it?" jack and billy broke into a roar of laughter. "a doughnut with legs on?" sputtered billy. "whatever put that idea into your head, noddy?" "well, don't octo-octo-thing-a-my-jigs have legs?" inquired noddy. "oh, you mean octopuses," cried jack, with another laugh. "billy meant an eighty-year-old doughnut." "i'll look it up when we get back," remarked noddy gravely; "it's a good word." "say, fellows, we are sure having a fine time out of this holiday," remarked billy presently, after an interval of silence. "yes, but just the same i shan't be sorry when mr. juke's new liner is completed and we can go to sea again," said jack, "but after our experiences up north, among the ice, i think we had a holiday coming to us." "that we did," agreed noddy. "some difference between skimming around here in a fine yacht and being cast away on that wretched island with nothing to eat and not much prospect of getting any." "yes, but if it hadn't been for that experience, and the ancient treasure we found, we couldn't have taken such a jolly vacation," argued jack. "it's made uncle toby a rich man and put all of us on easy street." "yes, it was certainly worth all the hardships we went through," agreed noddy. "i guess we are in for a long spell of quiet now, though," remarked jack, after a pause, during which each boy thought of their recent adventures. "not so sure of that," replied noddy. "you're the sort of fellow, judging from what you've told us, who is always tumbling up against something exciting." "yes, i feel it in my bones that we are not destined to lead an absolutely uneventful time----" began billy raynor. "i--hold hard there, noddy; watch yourself. here comes another yacht bearing down on us!" jack and billy leaped to their feet, steadying themselves by clutching a stay. billy was right. another yacht, a good deal larger than their own, was heading straight for them. "hi! put your helm over! we've got the right of way!" shouted jack, cupping his hands. "look out where you're going!" cried billy. but whoever was steering the other yacht made no motion to carry out the suggestions. instead, under a press of canvas, she kept directly on her course. "she'll run us down," cried noddy. "what'll i do, jack?" "throw her over to port lively now," sang out jack ready. "hurry up or we'll have a bad smash-up!" he leaped toward the stern to noddy's assistance, while billy raynor, the young engineer, did the same. in former volumes of this series the previous adventures of the lads have been described. in the first book, devoted to their doings and to describing the fascinating workings of sea-wireless aboard ocean-going craft, which was called "the ocean wireless boys on the atlantic," we learned how jack became a prime favorite with the irascible jacob jukes, head of the great transatlantic and pacific shipping combine. jack's daring rescue of millionaire jukes' little girl resulted in the lad's obtaining the position of wireless man on board a fine ship, after he had looked for such a job for months in vain. but because jack would not become the well-paid companion of mr. jukes' son tom, a rather sickly youth, the millionaire became angry with the young wireless man. however, jack was able, subsequently, to rescue mr. jukes from a drifting boat after the magnate's yacht had burned in mid-ocean and, following that, to reunite the almost frantic millionaire with his missing son. other exciting incidents were described, and jack gained rapidly in his chosen profession, as did his chum, billy raynor, who was third assistant engineer of the big vessel. the next volume, which was called "the ocean wireless boys and the lost liner," told of the loss of the splendid ship "tropic queen," on a volcanic island after she had become disabled and had drifted helplessly for days. by wireless jack managed to secure aid from u. s. vessels, and it came in the nick of time, for the island was destroyed by an eruption just after the last of the rescued passengers had been taken off. wireless, too, secured, as described in that book, the capture of a criminal much wanted by the government. the third volume related more of jack's doings and was called "the ocean wireless boys of the ice-berg patrol." this book told how jack, while serving aboard one of the revenue cutters that send out wireless warnings of ice-bergs to transatlantic liners, fell into the hands of a band of seal poachers. things looked black for the lad for a time, but he found two good friends among the rough crew in the persons of noddy nipper and pompey, an eccentric old colored cook, full of superstitions about ghosts. the _polly ann_, as the schooner was called, was wrecked and jack and his two friends cast away on a lonesome spot of land called skull island. they were rescued from this place by jack's eccentric, wooden-legged uncle, captain toby ready, who, when at home, lived on a stranded wooden schooner where he made patent medicines out of herbs for sailors. captain toby had got wind of an ancient treasure hidden by a forgotten race on an arctic island. after the strange reunion they all sailed north. but an unscrupulous financier (also on a hunt for the treasure) found a way to steal their schooner and left them destitute. for a time it appeared that they would leave their bones in the bleak northland. but the skillful resource and pluck of jack and noddy won the day. we now find them enjoying a holiday, with captain toby as host, at a fashionable hotel among the beautiful thousand islands. having made this necessary digression, let us again turn our attention to the situation which had suddenly confronted the happy three, and which appeared to be fraught with imminent danger. like their own craft, the other boat carried a single mast and was sloop-rigged. but the boat was larger in every respect than the _curlew_. she carried a great spread of snowy canvas and heeled over under its press till the white water raced along her gunwale. as she drew nearer the boys saw that there were two occupants on board her. one was a tall, well-dressed lad in yachting clothes, whose face, rather handsome otherwise, was marred by a supercilious sneer, as if he considered himself a great deal better than anyone else. the other was a somewhat elderly man whose hair appeared to be tinged with gray. his features were coarse, but he resembled the lad with him enough to make it certain he was his father. "sheer off there," roared jack at the top of his lungs, to the occupants of the other boat; "do you want to run us down?" "get out of the way then," cried the boy. "yes, sheer off yourselves, whipper-snappers!" came from the man. "we've got the right of way!" cried jack. "go chase yourselves," yelled noddy, reverting in this moment of excitement, as was his habit at such times, to his almost forgotten slang. "keep her on her course, donald; never mind those young jack-a-napes," said the man in the other sloop, addressing the boy, who was steering. "all right, pop," was the reply; "they'll get the worst of the smash if they don't clear out." "gracious, they really mean to run us down," cried jack, in a voice of alarm. "better sheer off, noddy, though i hate to do it." "by jinks, do you see who they are?" cried bill raynor, who had been studying the pair in the other boat, which was now only a few yards off. "it's that millionaire hiram judson and his son donald, the boy you had the run in with at the hotel the other day." but jack made no reply. the two boats were now almost bowsprit to bowsprit. as for noddy, the freckles stood out on his pale, frightened face like spots on the sun. chapter ii. "speedaway" vs. "curlew." but at the critical moment the lad at the helm of the other craft, which bore the name _speedaway_, appeared to lose his nerve. he sheered off and merely grazed the _curlew's_ side, scraping off a lot of paint. "hi, there! what do you mean by doing such a thing?" demanded jack, directly the danger of a head-on collision was seen to have been averted. the other lad broke into a laugh. it was echoed by the man with him, whom he had addressed as "pop." "just thought i'd see how much you fellows knew about handling a boat," he sneered. "it's just as i thought, you're a bunch of scare-cats. you needn't have been afraid that i couldn't keep the _speedaway_ out of danger." "you risked the lives of us all by running so close," cried billy indignantly. "never attempt such a thing again," said jack angrily, "or----" "or what, my nervous young friend?" taunted the elderly man. "yes," said the lad, with an unpleasant grin, "what will you do?" "i shall feel sorely tempted to come on board your boat and give you the same sort of a thrashing i gave you the other day when i found you tormenting that poor dog," said jack, referring to the incident billy raynor had already hinted at when he first recognized the occupants of the _speedaway_. "you'll never set foot on my boat," cried donald judson, with what he meant to be dangerous emphasis; but his face had suddenly become very pale. "you think you got the best of me the other day, but i'll fix you yet." the two craft were out of earshot almost by this time, and none of the three lads on the _curlew_ thought it worth while to answer donald judson. the millionaire and his son occupied an island not far from the pine island hotel. a few days before the incident we have just recorded, jack, who hated cruelty in any form, had found donald judson, who often visited the hotel to display his extensive assortment of clothes, amusing himself by torturing a dog. when jack told him to stop it the millionaire's son started to fight, and jack, finding a quarrel forced upon him, ended it in the quickest way--by knocking the boy flat. donald slunk off, swearing to be revenged. but jack had only laughed at him and advised him to forget the incident except as a lesson in kindness to animals. it appeared, however, that, far from forgetting his humiliation, donald judson was determined to avenge it even at the risk of placing his own life in danger. "i wonder if he followed us up to-day on purpose to try to ram us or force us on a sandbar?" mused noddy, as they sailed on. "looks like it," said billy. "i believe he is actually sore enough to sink our boat if he could, even if he damaged his own in doing it," said jack. "to my mind his father is as bad he is," said noddy; "he made no attempt to stop him. if i----look, they've put their boat about and are following us." "there's no doubt that they are," said jack, after a moment's scrutiny of the latest maneuver of the _speedaway_. the judsons' boat, which was larger, and carried more sail and was consequently faster than the _curlew_, gained rapidly on the boys. soon she was within hailing distance. "what are you following us for? want to have another collision?" cried jack. "do you own the water hereabouts?" asked donald. "i didn't know i was following you." "we've a right to sail where we please," shouted judson. "yes, if you don't imperil other folks' boats," agreed jack. "if you've got any scheme in mind to injure us i'd advise you to forget it," he added. "huh! what scheme would i have in mind? think i'd bother with insignificant chaps like you and your little toy boat?" "you keep out of our way," added the man. "yes, just do that little thing if you know what's healthy for you," chimed in donald judson. his insulting tone aroused jack's ire. "it'll be the worse for you if you try any of your tricks," he roared. "what tricks would i have, ready?" demanded the other. "some trick that may turn out badly for you!" "i guess i don't need you to tell me what i will or what i won't do." "all right, only keep clear of us. that's fair warning. you'll get the worst of it if you don't." "so, young man, you are going to play the part of bully, are you?" shouted donald's father. "that fits in with what i've heard of you from him. you've been prying around our boat for several days. i don't like it." "well, keep away from us," cried billy. "yes, your room's a lot better than your company," sputtered noddy. "we don't care if you never come back." "really, what nice language," sneered donald. "i congratulate you on your gentlemanly friend, ready. he----" "look out there," warned jack, for noddy, in his indignation, had sprung to his feet, entirely forgetting the tiller. the _curlew_ broached to and heeled over, losing "way." the _speedaway_ came swiftly on. in an instant there was a ripping, tearing sound and a concerted shout of dismay from the boys as the sharp bow of judson's larger, heavier craft cut deep into the _curlew's_ quarter. "now you've done it!" cried billy raynor. "i--er--it was an accident," cried donald, as the two boats swung apart, and there was some justification for this plea, as the _speedaway_ was also damaged, though not badly. "it was no accident," cried jack, but he said no more just then. he was too busy examining the rent in the _curlew's_ side. still shivering, like a wounded creature, from the shock of the impact, the _curlew_, with the water pouring into the jagged rip in her side, began slowly to sink! chapter iii. captain simms of the "thespis." silence, except for the inrush of water into the damaged side of the _curlew_, followed the collision. the three lads on the sinking craft gazed helplessly at each other for a few seconds. "get away as quick as you can," whispered donald's father to the boy who had wrought the damage, and now looked rather scared. the _speedaway_ swung out and her big mainsail began to fill. "we are going to the bottom," choked out billy, the first of the party to recover the use of his vocal organs. "i'm afraid there's no doubt of that," said jack. "donald judson," he shouted, raising his voice and throwing it across the appreciable distance that now separated the two craft, "you'll pay for this." "it was an accident, i tell you," yelled back the other lad, but in a rather shaky voice. "you'll do no good by abusing us," chimed in his father. "what'll we do, jack?" demanded noddy, tugging at jack's sleeve. "steer for the shore. there's just a chance we can make it, or at least shallow water," was the reply. "doesn't look much as if we could make it," said billy dubiously, shaking his head and regarding the big leak ruefully, "but i suppose we can try." the wounded _curlew_ began to struggle along with a motion very unlike her usual swift, smooth glide. she staggered and reeled heavily. "put her on the other tack," said jack. noddy followed his orders with the result that the _curlew_ heeled over on the side opposite to that which had been injured, and thus raised her wound above the water line. billy began bailing, frantically, with a bucket, at the water that had already come in. "shall we help you?" cried donald. "no, we don't want your help," answered jack shortly. "we'll thresh all this out in court later on," he added. "i'm a witness that it was an accident," shouted the elder judson. "you'll have a swell time proving i ran you down on purpose," added his son. seeing that it was useless to prolong such a fruitless argument at long distance, jack refrained from making a reply. besides, the _curlew_ required his entire attention now. he took the tiller himself and kept the injured craft inclined at such an angle that but little water entered the hole the _speedaway's_ sharp bow had punched in her. the shore, on which were a few small houses and a wharf hidden among trees and rocks, appeared to be a long distance off. but the _curlew_ staggered gamely onward with jack anticipating every puff of wind skillfully. "i believe that we'll make it, after all," said billy hopefully, as the water-logged craft was urged forward. "i wish that donald, with his sissy-boy clothes, was ashore when we land," grumbled noddy. "i'd give him what-for. i have not forgotten how to handle my dukes, and as for his old octo-octo----" "octogenarian," chuckled raynor. "octogenarian of a father,--i knew i'd get a chance to use that word----" said noddy triumphantly; "he's worse than his son. they're a fine pair,--i don't think." "well, abusing them will do no good," said jack. "we'll have to see what other steps can be taken. i'm afraid, though, that they were right; we'll have a hard time proving that it was not an accident, especially as noddy had dropped our tiller." "well, i just couldn't----" began noddy, rather shamefacedly, when there came a mighty bump and the _curlew_ came to a standstill. "now what?" cried raynor. "we've run on a shoal, fellows," declared jack. "this cruise is over for a time." "well, anyhow, we can't sink now," said noddy philosophically, "but although the _curlew's_ stuck on the shoal i'm not stuck on the situation." "better quit that stuff," ordered jack, "and help billy lower the mainsail and jib. they are no good to us now. in fact a puff of wind might send us bowling over." his advice was soon carried out and the _curlew_ lay under a bare pole on the muddy shoal. the boys began to express their disgust at their predicament. they had no tender, and would have to stay there till help came because of their lack of a small boat. "better set up some sort of a signal to attract the attention of those folks on shore," suggested billy. "that's a good idea," agreed jack, "but hullo! look yonder, there's a motor boat coming out from the shore. let's hail that." "hullo, there! motor boat ahoy!" they all began to yell at the top of their lungs. but they might have saved their voices, for the motor boat swung about in a channel that existed among the shoals and began making straight for them. its single occupant waved an encouraging hand as he drew closer. "in trouble, eh?" he hailed; "well, maybe i can get you off. i saw that other boat run you down. it was a rascally bit of business." "gracious!" cried jack suddenly, as the motor boat drew closer and they saw its occupant was a bronzed, middle-aged man with a pleasant face; "it's captain simms of the revenue cutter _thespis_! what in the world is he doing up here?" "if it isn't jack ready!" came in hearty tones from the other, almost simultaneously. chapter iv. on secret service. there was no question about it. astonishing as it appeared, the bluff, sunburned man in the motor boat which was winding its way toward the _curlew_, in serpentine fashion, among the tortuous channels, was captain simms, the commander of the revenue cutter on which jack ready had served as "ice-patrol" operator. the greetings between his late commander and himself were, as might be imagined, cordial, but, owing to the circumstances under which they were exchanged, somewhat hurried. "so you've been in a smash-up," cried the captain, as he reduced speed on nearing the stern of the _curlew_, which was still afloat. "nobody hurt, i hope?" "except the boat," smiled jack with grim humor. "so i see. a nasty hole," was the captain's comment. "lucky that i happen to be camping ashore or you might have stayed out here for some time. rivermen hereabouts aren't over-obliging, unless they see big money in it for their services." "we'd have been content to pay a good salvage to get off here," jack assured him. "well, that other craft certainly sheered off in short order after she hit you," was captain simms' comment, as he shut off power and came in under the _curlew's_ stern, which projected, as has been said, over fairly deep water, only the bow being in the mud. "then you can tell who was to blame?" asked billy eagerly. "i certainly can and will, if i am called upon to do so." "thank you," said jack. "i mean to make them settle for the damage, even if i have to go to court to do it." "that's right. it was a bad bit of business. she followed you right up. i'd be willing to swear to that in any tribunal in the land. i hope you bring them to justice. who were the rascals?" "a millionaire named judson, who owns an island near here, and his son, who is a fearful snob." the boys saw a look of surprise flit across the naval officer's face. but it was gone in an instant. "surely not hiram judson?" he demanded. "the same man," replied jack. "why, do you know him, sir?" "i--er--that is, i think we had better change the subject," said captain simms with odd hesitation. jack saw that there was something behind the sea officer's hesitancy, but of course he did not ask any more questions. "i can give you a tow to the shore where there is a man who makes a business of repairing boats," volunteered captain simms. "but will your craft keep afloat that long?" "i think so," said jack. "we can all sit on one side and so raise the leak above water. but can you pull us off?" "we shall soon see that," was the rejoinder. "it looks as if it would be an easy task. throw me a line and i'll make it fast to my stern bitts." this was soon done, and then the little launch set to work with might and main to tug off the injured yacht. "hurray, she's moving!" cried billy presently. this was followed by a joyous shout from all the boys. "she's off!" they moved down the channel with the boys hanging over one side in order to keep the _curlew_ heeled over at an angle that would assure safety from the leak. they landed at a rickety old dock with a big gasoline tank perched at one end of it. attached to it was a crudely painted sign: "charles hansen, boats built and repaired. all work promptly exicutid." hansen himself came toddling down the wharf. he was an old man with a rheumatic walk and a stubbly, unshaven chin stained with tobacco juice. a goodly sized "chaw" bulged in his withered cheek. "can you repair our boat quickly?" asked jack, pointing to the hole. old hansen shot a jet of tobacco juice in the direction of the injury. "bustitupconsiderable," he remarked. "what's that?" demanded billy. "doesn't he talk english?" and he turned an inquiring glance at captain simms, who laughed. "that's just his way of talking when he's got a mouthful of what he calls 'eatin' tobacco.' he said, 'he is of the opinion that your boat is bust up considerable.'" "well, we don't need an expert to tell us that," laughed jack. "doyouwantmetofixit?" inquired the eccentric old man, still running his words together in the same odd way. "yes," replied jack, "can we have her by to-morrow?" "haveterseehowbadlyshesbusted," muttered the old man. "he'll have to see how badly she's busted," translated jack. "suppose you take a look at her," he added to the boatman. "maybeagoodidee," agreed old hansen, and he scrambled down into the boat. "i'llfixherbyto-morrow," he said at last. the charges, it appeared, would not be more than ten or twelve dollars, which the boys thought reasonable. "especially as they won't come out of our pockets," commented billy. "not if i can help it," promised jack decisively. "and now," said captain simms, "as i happen to have some business at the pine island hotel, i'll run you down there in the _skipjack_, as i call my boat." "that's awfully good of you," said jack gratefully. "i began to think that we would have to stay ashore here all night." before many minutes had passed they were off, leaving old hansen, with working jaws, examining the hole in the _curlew's_ side. the _skipjack_ proved speedy and they made the run back to the hotel in good time, arriving there before sundown. captain toby had met captain simms after the latter had found the treasure party at the spot where they had unearthed the rich trove. but he proved equally reticent as to the object of his presence at alexandria as he had been with the boys. he was doing some "special work" for the government, was all that captain toby could ascertain. "there's considerable mystery to all this," said captain toby to the boys after captain simms had left them to write some letters which, he said, he wished to send ashore by the hotel motor boat that evening. "it's some sort of secret work for uncle sam, i guess," hazarded jack, "but what it is i've no idea. anyhow it's none of our business." the boys little guessed, when jack made that remark, how very much their business captain simms' secret mission was to become in the near future. chapter v. night signals. after supper captain simms suddenly announced that he wished to make a trip to the mainland to the town of clayton. he wished to send an important telegram to washington, he explained. "how are you going?" asked jack. "the hotel boat has stopped running for the day." "i know that, but i'll go on the _skipjack_. you lads want to come?" "do we? i should say we do." "you lads must be full of springs from the way you're always jumping about," remarked uncle toby, with a smile, "but i suppose it's boy nature." the run to the shore was made quickly. it seemed almost no time at all before they made out the string of lights that marked the pier and the radiance of the brilliantly lit hotel behind them. but as they were landing an unforeseen accident occurred. mistaking his distance in the darkness, the captain neglected to shut off power soon enough, and the nose of the _skipjack_ bumped into the pier with great force. at the same time a splintering of wood was heard. "gracious, another wreck," exclaimed jack. "wow! what a bump!" cried noddy. "is it a bad smash?" asked billy anxiously. the captain was bending over the broken prow of the boat examining it by the white lantern. "bad enough to keep us here all night, i'm afraid," he said. "do you boys mind? it looks to me as if it could soon be repaired in the morning, and the boat will be safe here to-night at any rate." "it's too bad," exclaimed jack. "we seem to be regular hoodoos on a boat." "it was my own fault," said the captain, "but the lights on the pier dazzled me so that i miscalculated my distance." "well, it's a good thing no other harm was done," was billy's comment. the boat was tied up and the watchman on the dock given some money to keep an eye on it. they engaged rooms at the hotel, and while captain simms composed his telegram, the boys took a stroll about the grounds of the hostelry, which sloped down to the bay. they had about passed beyond the radiance of the lights of the hotel when jack suddenly drew his companions' attention to a figure that was stealing through the darkness hugging a grove of trees. there was something indescribably furtive in the way the man crept along, half crouched and glanced behind him from time to time. "a burglar?" questioned billy. "some sort of crook i'll bet," exclaimed noddy. "he's up to some mischief or i'm much mistaken," said jack, as he drew his companions back further into a patch of black shadow cast by some ornamental shrubs. "let's trail him and see what he's up to," said noddy. "gracious, you're a regular sherlock holmes at the drop of the hat," laughed billy. "what do you think, jack?" "i don't know. he's going toward the wharf and i don't see just what he could steal there." "look at him stop and glance all around him as if he was afraid of being followed," whispered billy. "that doesn't look like an honest man's action, certainly," agreed jack. "come on, boys; we'll see what's in the wind. do you know, somehow i've got an idea that we've seen that fellow somewhere before." "what gives you that impression?" asked billy. "i can't say--it's just a feeling i've got. an instinct i guess you might call it." the three boys moved forward as stealthily as did the man whose actions had aroused their suspicions. presently they saw him cut across a small patch of lawn and strike into a narrow path which led among some trees. with every care to avoid making any noise, the three boys followed. the path led to the edge of a cliff, down the face of which a flight of stone steps ran down to the water's edge. the man descended these. "what can he be? a smuggler," suggested billy. "i don't see any boat down there, if he is," rejoined jack in low tones. suddenly a sharp, low exclamation came from noddy, who had been looking out over the lake. he caught jack's arm and pointed. "look, boys, a yacht!" he breathed. "heading in this way, too," rejoined jack. "it looks like--but no, it cannot be." "cannot be what?" asked billy, caught by something in his companion's voice. "cannot be the _speedaway_." "judson's craft, the one that ran us down? nonsense, you've got judson on the brain, jack." "have i? well, it's an odd coincidence, then, that the yacht yonder has a tear in her foresail exactly where our bowsprit tore the _speedaway's_ jib this afternoon." "by hookey, you're right, jack!" cried noddy. "there may be more to this than we think." billy was peering from behind a bush over the edge of the cliff, which was not very high. he could see below, the dark figure of a man making a black patch in the gloom upon the white beach. he was moving about and pacing nervously to and fro on the shingle as if awaiting something or somebody. suddenly he made a swift move. "he's waving his handkerchief," whispered billy to the others, as he saw the man make a signal with a square of white linen. "to that yacht, i'll bet a cookie," exclaimed noddy. as if in answer to his words there suddenly showed, on the yacht, a red lantern, as if a scarlet eye had suddenly opened across the dark water. chapter vi. in the dark. "something's in the wind sure enough," said jack. "hark, there's the plash of oars. they must be going to land here." from below there came a man's voice. "right here, judson; here's the landing place. are you alone?" "no, my son is with me," came the reply, "but for heaven's sake, man, not so loud." "there's no one within half a mile of this place. i came down through the grounds and they were deserted." "humph, but still it's as well to be careful. one never knows what spies are about," came the reply. the boys, nudging each other with excitement, heard the bow of the boat scrape on the shingly beach and then came the crunch of footsteps. "they are coming up the steps," whispered jack in low, excited tones. "that's right, so they are," breathed billy cautiously. "let's get behind the trees and learn what is going on." "it's something crooked, that's sure," whispered noddy. "i begin to think so myself," agreed jack, "but that man's voice, as well as his figure, seemed familiar to me when he hailed judson, but i can't, for the life of me, think where i heard his voice before." the three lads lost no time in concealing themselves behind some ornamental bushes in the immediate vicinity. they were none too soon, for hardly had they done so when the figures of two men and a boy appeared at the top of the steps. "phew," panted judson, "i'm not as young as i was. that climb has made me feel my age. let's sit down here." "very well, that bench yonder will be just the place," agreed the man the boys had followed, and who had seemed so oddly familiar to jack. the seat they had selected could hardly have been a better one for the boys' purpose. it was placed right against the bush behind which they were hiding. the voices came to them clearly, although the speakers took pains to modify them. "well, i've been waiting for you," came in the voice of the man the boys had instinctively followed. "we'd have got here sooner, but were delayed by an accident, or rather a sort of accident on purpose that occurred this afternoon. i was glad to see that you hadn't forgotten our night signal code," said judson. "what was the accident?" asked the man, who was a stranger to the boys, who were listening intently. "oh, just three brats who are summering here," scoffed donald judson. "they appeared to think they owned the bay, and i guess it was up to me to show them they didn't. i guess jack ready will be on the market for another boat before long and----" "hold on, hold on," exclaimed the strange man. "what was that name?" "ready, jack ready. he thinks he's a wizard at wireless. why, do you know him, jarrow?" jarrow, at the sound of the name there, brought into jack's mind the recollections of the rascally partner of terrill & co., who had financed his uncle's treasure hunt and had then tried to steal the hoard from him. it was jack who had overthrown the rascal's schemes and made him seek refuge in the west to escape prosecution. yet he had apparently returned and in some way become associated with judson. noddy, too, as had bill, had started at the name. both nudged jack, who returned the gesture to show that he had heard and understood. "so ready is here, eh?" growled jarrow. "confounded young milksop." "you appear not to be very fond of him," interjected the elder judson. "fond of him! i should think not! i hate him like poison." "what did he ever do to you?" "he--er--er--he upset an--er--er--business deal i was in with his uncle." "the one-legged old sea captain?" "that's the fellow. he trusted me in everything till jack ready came nosing in and spoilt his uncle's chance of becoming a rich man through his association in business with me." "i've no use for him either," exclaimed donald vindictively. "i'll give him a good licking when i see him." "well, well, let's get down to business," said the elder judson decisively. "you have been to washington, jarrow?" "yes, and found out something, but not much. the new naval wireless code is not yet completed. i found out that by bribing a clerk in the navy department and----" "this business is proving pretty expensive," grumbled judson. "we're playing for a big stake," was the reply. "i found out that the code has been placed in the hands of a captain simms, recently attached to the revenue service, for revision. i believe that it is the same captain simms against whom i have a grudge, for it was on his ship that i was insulted by aspersions on my business honesty, and that, also, was the work of this jack ready." "pity he didn't tell them that he was in irons at the time," thought jack to himself. "where is this captain simms?" asked judson, not noticing, or appearing not to, his companion's outbreak. "that's just it," was the rejoinder. "nobody knows. his whereabouts are being kept a profound secret. since it has become rumored that the navy wireless code was being revised, washington fairly swarms with secret agents of different governments. simms is either abroad or in some mighty safe place." "our hands are tied without him," muttered judson, "and if i don't get that code i don't stand a chance of landing that big steel contract with the foreign power i have been dealing with." "i'm afraid not," rejoined jarrow. "i saw their representative in washington and told him what i had learned. his answer was, 'no code, no contract.' i'm afraid you were foolish in using that promise as a means to try to land the deal." "i had my thumb on the man who would have stolen it for me at the time," rejoined judson, "but he was discharged for some minor dishonesty before i had a chance to use him." "the thing to do is to locate this captain simms." "evidently, you must do your best. the wind has died down and i guess we'll stop at the hotel till to-morrow. anyhow, it's too long a sail back to-night. come on, donald; come, jarrow." the bench creaked as they rose and made off, turning their footsteps toward the hotel. not till they had gone some distance did the boys dare to speak, and even then they did not say much for a minute or two. the first expression came from jack. it was a long, drawn-out: "we-e-l!" "and so that is the work that captain simms has been doing in that isolated retreat of his," exclaimed billy. "and these crooks have just had the blind luck to tumble over him," exploded noddy. "just wait till they take a look at the hotel register." "maybe by the time they enter their names the page will have turned," suggested billy. "no," rejoined jack, "our names were at the top of the page and there would hardly have been enough new arrivals after us at this time of night to have filled it since." "we must find captain simms at once and tell what is in the wind," decided the young wireless man a moment later. "i guess the instinct that made us follow jarrow was a right one." "i wonder how the rascal became acquainted with judson?" pondered billy. "mixed up with him in some crooked deal or other before this," said noddy. "i shouldn't wonder," said jack. they began to walk back to the hotel. they did not enter the lobby by the main entrance, for the path they followed had brought them to a side door. they were glad of this, for, screened by some palms, they saw, bending intently over the register, the forms of the three individuals whose conversation they had overheard. chapter vii. the naval code. "now that you boys know the nature of the work i have been engaged on, i may as well tell you that confidential reports from washington have warned me to be on my guard," said captain simms. "it was in reply to one of these that i sent a code dispatch to-night." it was half an hour later, and they were all seated in the captain's room, having told their story. "but i should have imagined making up a code was a very simple matter," said billy. "that is just where you are wrong, my boy," smiled captain simms. "a commercial code, perhaps, can be jumbled together in any sort of fashion, but a practical naval code is a different matter. besides dealing in technicalities it must be absolutely invulnerable to even the cleverest reader of puzzles. the new code was necessitated by the fact that secret agents discovered that an expert in the employ of a foreign power had succeeded in solving a part of our old one. it was only a very small part, but in case of trouble with that country it might have meant defeat if the enemy knew even a fragment of the wireless code that was being flashed through the air." "have you nearly completed your work?" asked jack. "almost," was the reply, "but the fact that these men are here rather complicates matters. at musky bay, the name of the little settlement where i am stopping, they think i am just a city man up for the fishing. i do not use my right name there. by an inadvertence, i suppose it was habit, i wrote it on the hotel register to-night. that was a sad blunder, for it is practically certain that these men will not rest till they have found out where i am working." "at any rate i'm mighty glad we followed that jarrow," said jack. "and caught enough of their plans to put you on guard," chimed in billy. "yes, and i am deeply grateful to you boys," was the rejoinder. "'forewarned is forearmed.' if judson and his crowd attempt any foul tactics they will find me ready for them." "judson apparently wishes now that he had not been so anxious to secure that contract as to promise the naval code as a sort of bonus," said jack. "i don't doubt it," answered captain simms. "now that i recall it, i heard rumors that judson, who once had a steel contract with our government, is not so sound financially as he seems. i judge he would go to great lengths to assure a large contract that would get him out of his difficulties." "i should imagine so," replied jack. "what was the reason he never did any more work for the government?" "the inferior quality of his product, i heard. there were ugly rumors concerning graft at the time. some of the newspapers even went so far as to urge his prosecution." "then we are dealing with bad men?" commented jack. "unquestionably so. but i think we had better break up this council of war and get to bed. i want to get an early start in the morning." but when morning came, it was found that the repairs to the _skipjack_ would take longer than had been anticipated. while captain simms remained at the boat yard to superintend the work, the lads returned to the hotel and addressed some post cards. this done they sauntered out on the porch. almost the first person they encountered chanced to be jarrow. he started and turned a sickly yellow at the sight of them, although he knew, from an inspection of the register the night before, that they were there. "why--er--ahem, so it is you once more. where did you spring from?" "we came out of that door," murmured jack, while noddy snickered. "where did you come from?" "i might say from the same place," was the rejoinder, with a look of malice at noddy. "we thought you were in the west," said billy. "great place, the west. they say the climate out there is healthier than the east--for some folks." "boy, you are impudent," snarled jarrow. "not at all. i was merely making a meteorological remark," smiled billy. "wait till i get that word," implored noddy, pulling out a notebook and a stub of pencil. "splendid grounds they have here for taking strolls at night," jack could not help observing. from yellow jarrow's face turned ashen pale. muttering something about a telephone call, he hurried into the hotel. "goodness, that shot brought down a bird, with a vengeance," chuckled billy. jarrow's head was suddenly thrust out of an open window. he glared at the boys balefully. his face was black as a thundercloud. "you boys have been playing the sneak on me," he cried angrily. "if you take my advice, you will not do so in the future." he withdrew his head as quickly as a turtle draws its headpiece into its shell. "he's a corker," cried noddy. "i'll bet if he had a chance, he'd like to half kill us." "shouldn't wonder," laughed jack, "but he isn't going to get that chance. but hullo! what's all this coming up the driveway?" the others looked in the same direction and beheld a curious spectacle. chapter viii. a monkey interlude. "well, here's something new, and no mistake," cried billy. "good, it will help pass our morning," declared noddy, who was beginning to find time hang heavily on his hands now that he had nobody to play pranks on, like those he used to torment poor pompey with. an italian was coming up the road toward the hotel. strapped across his shoulders was a small hand-organ. he led a trained bear, and two monkeys squatted on the big creature's back. he came to a halt near the grinning boys. "hurray! this is going to be as good as a circus!" declared noddy. "start up your performance, professor." "they're off!" cried billy. summer residents of the hotel, anxious for any diversion out of the ordinary, came flocking to the scene as the strains of the barrel organ reached their ears, and the bear, in a clumsy fashion, began to dance to the music of the ear-piercing instrument. "where are you going, noddy?" asked jack, as the red-headed lad tried to get quietly out of the crowd. "i just saw a chance for a little fun," rejoined noddy innocently. "well, be careful," warned jack. "this is no place for such jokes as you used to play on pompey." "oh, nothing like that," noddy assured him as he hurried off. "just the same i'm afraid of noddy when he starts getting humorous," thought jack. he would have been still more afraid if he could have seen noddy make his way to the hotel kitchen and bribe a kitchen maid to get him three large sugar cakes. then he made his way to the dining-room, and boring tiny holes in the buns filled each of them with red pepper from the casters. "now for some fun," he chuckled. "i just know that boy is up to some mischief by the look on his face," remarked an old lady as he hurried by. quite a big crowd was round the italian when noddy got back. almost as soon as he arrived the man began passing the hat, and taking advantage of this, noddy proffered his buns to the animals. they accepted them greedily. "peep! peep!" chattered the monkeys. "you mean 'pep,' 'pep'," chuckled noddy to himself. both bear and monkeys tore into their buns as if they were half starved. in their hunger they got a few mouthfuls down without appearing to notice that anything was wrong. then suddenly one of the monkeys hurled his bun at the bear and the other leaped on the big hairy creature's head. apparently they thought the innocent bear had something to do with the trick that had been played on them. "da monk! da monk!" howled the italian, "da monk go a da craz'." "he says they are mad," exclaimed an old gentleman, and hurried away. just as he did so, the bear discovered something was wrong. he set up a roar of rage and broke loose from his keeper. the monkeys leaped away from the angry beast and sought refuge. one jumped on the head of an elderly damsel who was very much excited. the other made a dive for a fashionably dressed youth who was none other than donald judson. "help!" screamed the old maid. "help! will no one help me?" "i will, madam," volunteered an old gentleman, coming forward. he seized the monkey and tugged at its hind legs, but it only clung the tighter to the elderly damsel's hair. suddenly there came a piercing scream. "gracious, her hair's come off!" cried a woman. "she's been scalped, poor creature!" declared another. "oh, you wretch, how dare you!" shrieked the monkey's victim, rushing at the gallant old gentleman. she raised her parasol and brought it down on his head with a resounding crack. in the meantime the italian was howling to "garibaldi," as he called the monkey, to come to him. but this the monkey had no intention of doing. clutching the old maid's wig in its hands, it leaped away in bounds and joined its brother on the person of donald judson. "ouch, take them off. they'll bite me!" donald was yelling. the monkeys tore off his straw hat with its fancy ribbon and tore it to bits and flung them in the faces of the crowd. then, suddenly, they both darted swiftly off and climbed a tree, where they sat chattering. it was at that moment that the confused throng recollected the bear, which had not remained in the vicinity but had gone charging off across the lawn looking for water to drown the burning sensation within him. now, however, an angry roar reminded them of him. the beast was coming back across the lawn, roaring and showing his teeth. "look out for the bear!" "get a gun, quick." "oh, he'll hug me," this last from the old maid, were some of the cries which the crowd sent up. "he's mad, shoot him!" cried somebody. the italian set up a howl of protest. "no, no, no shoota heem. mika da gooda da bear. no shoota heem." "if you don't want him shot, catch him and get out of here. you'll have my hotel turned into a sanitarium for nervous wrecks the first thing you know," cried the proprietor of the place. "somebody playa da treeck," protested the italian. "mika da nica da bear, da gooda da bear." "i guess he's like an indian, only good when he's dead," said the hotel man. "i'm off to get my gun." noddy watched the results of his joke with mixed feelings. he had not meant it to go as far as this. he looked about him apprehensively, but everybody was too frightened to notice him. suddenly the bear headed straight for noddy. perhaps his red head was a shining mark or perhaps the creature recollected the prank-playing youth as the one who had given him the peppered bun. at any rate he charged straight after the lad, who fled for his life. "help!" he called as he ran. "help, help!" "noddy's getting a dose of his own medicine," cried jack to billy. "but we don't want to let the bear get him," protested billy. "of course not, but he'll beat the bear into the hotel, see if he doesn't." the hotel front door was evidently noddy's objective point. it appeared he would reach it first, but suddenly he tripped on a croquet hoop and went sprawling. he was up in a minute, but the bear had gained on him. as he rushed up the steps it was only a few inches behind him. noddy gave a wild yell and took the steps in three jumps. the next second he was at the door and swinging it shut with all his might. but just then an astonishing thing happened. just as noddy swung the door shut the bear made a leap. the result surprised noddy as much as bruin. the edge of the door caught the big creature's neck and held him as fast as if he had been caught in a dead-fall. he was gripped as in a vise between the door and the frame. but poor noddy was in the position of the man who caught the wild cat. he didn't know how to let go! chapter ix. noddy and the bear. "i've got him!" yelled noddy. "help me, somebody!" "goodness, noddy's caught the bear," cried jack, as he and billy streaked across the lawn, followed by the less timid of the guests. "hold him tight," shouted some in the crowd. "let him go," bawled others. perspiring from his efforts, noddy braced his feet and kept the door tightly closed on the bear's neck. but the creature's struggles made the portal groan and creak as if it would be shoved off its hinges. "gracious, i can't hold it much longer. can't somebody hit him on the head with a club?" the negro bell boys and clerk, together with several of the guests who had been in the lobby, began to come back, now that they saw there was no immediate chance of the bear rushing in. "ah reckon ah knows a way ter fix dat b'ar widout hurting him," cried one of the negro boys. he snatched a fire extinguisher off the wall of the office and squirted its contents full in the bear's face. the animal gave one roar of dismay and a mighty struggle that burst the door open and threw noddy off his feet. he set up a yell of fright. but he need not have been afraid. the ugliness had all gone out of the bear, and besides being half choked he was temporarily blinded by the contents of the fire extinguisher. the italian came running up, carrying a chain and a muzzle. "gooda da boy! gooda da mika!" he cried ingratiatingly. the bear was as mild as a kitten, but nevertheless the muzzle was buckled on and the italian departed in search of his monkeys just as the manager appeared with his gun. it had taken him a long time to find, he explained, whereat noddy, who had recovered his spirits, snickered. "i'm going to pay the bill and get out of here," whispered jack in noddy's ear. "you'd better get away as quietly as you can. several people saw you give those buns to the animals. if they find you here, they'll mob you." "being chased by a bear is quite enough excitement for one day," rejoined noddy, "but my! it was good fun while it lasted. did you see that old maid's hair, did you see donald judson, did you----" "get out of here quickly," warned jack, and this time noddy took his advice without waiting. it was just as well he did, for the elderly gentleman, whose shining bald head had been belabored by the old maid's parasol, came in, accompanied by the damsel. she had recovered her hair when the monkeys were caught and had tendered handsome apologies to the would-be gallant. "where is that boy who started all this?" demanded the old gentleman. "it was one of that gang there," cried donald judson, who had followed them and whose face showed plenty of scratches where the monkeys had clambered up to demolish his hat. "oh, what a terrible boy he must be," cried the old maid. "he ought to go to prison. where is he?" "ask them, they'll know," cried donald, pointing to jack and billy. "no, it wasn't either of them. they were back in the crowd," cried the old maid; "it was another boy, a red-headed one." "i'm glad i told noddy to get out," whispered jack to his friends. "look, they are whispering to each other. i told you they knew all about it," cried donald, who saw a chance of avenging himself for his treatment by the monkeys. "say, young man," said the manager, coming up to jack, "i think your friend was responsible for this rumpus." "what rumpus?" "why, that trouble with the bear, of course. you boys are at the bottom of it all." "why, the bear chased my friend harder than anyone else," said jack, with assumed indignation. "i guess we'll pay our bill and leave," struck in billy. "think you'd better, eh?" sneered the manager. "if you want your money you'd better be civil," said jack. "yes, but--your bill is eight dollars." "here it is. now don't bother us any more or i'll report you to the proprietor." "i know, but look here." "i can't see in that direction." "i don't know if that man has caught his monkeys yet." "no use of your worrying about that unless you're afraid one of them will get your job." there was a loud laugh at this and in the midst of it the boys passed out of the hotel, leaving the clerk very red about the ears. "i hope that will teach noddy a lesson," said jack, as they hurried down to the boat yard where noddy had been instructed to precede them. "it ought to. being chased by a bear is no joke." but when they reached the yard they were just in time to see the man who was working on the boat clap his hand to the back of his neck and yell: "ouch! a bee stung me." not far off, looking perfectly innocent, stood noddy, but jack detected him in the act of slipping into his pocket a magnifying glass, by which he focused the sun's rays on the workman's neck. chapter x. "what do you make of it?" the _skipjack_ was all ready for them and no delay was had in making a start back to musky bay, where, it will be remembered, the boys had left their boat to be repaired. a brief stop was made at the pine island hotel and then the trip was resumed. "wonder where judson and his crowd have gone to?" pondered jack, as they moved rapidly over the water. "one thing sure, they never started back home in the _speedaway this_ morning," said billy. "the water is like glass, and there's not a breath of wind." "look, there's a handsome motor boat off yonder," exclaimed jack presently. he pointed to a low, black craft, some distance behind them and closer in to the shore. "she's making fast time," said bill. "maybe she wants to give us a race," suggested noddy. "i'm afraid we wouldn't stand much chance with her," laughed captain simms. they watched the black boat for a time, but she appeared to slacken speed as she drew closer, as if those in charge of her had no desire to come any nearer to the _skipjack_ than they were. "that's odd," remarked jack. "there is evidently nothing the matter with her engine, but for all that they don't seem to want to pass us. that's the first fast boat i ever saw act that way." "it does seem queer," said captain simms, and suddenly his brow clouded. "could it be possible----" he exclaimed, and stopped short. jack looked at him in a questioning way. "could what be possible, sir?" he asked. "why, that judson and the others are on board that black craft?" "ginger! that never occurred to me!" cried jack; "and yet, if they were following us to find out where you are located that would be just the sort of way in which they would behave." "so i was thinking," said captain simms thoughtfully. "however, we can soon find out." he opened a locker and took out his binoculars. then he focused them on the black craft. "well?" questioned jack, as the captain laid them down again. "there's a man at the wheel, but he isn't the least like your descriptions of your men," said the captain. "what does he look like?" questioned billy. "he's rather tall and has a full black beard," was the answer. "then it's not one of judson's crowd," said jack with conviction. "i guess we are all the victims of nerves to-day," smiled the captain. they swung round a point and threaded the channel that led among the shoaly waters of musky bay. the point shut out any rearward view of the black motor boat and they saw no more of it. captain simms invited them up to the house he occupied, which was isolated from the half dozen or so small habitations that made up the settlement. it was plainly furnished and the living room was littered with papers and documents. "what made you select musky bay as a retreat?" asked jack. "i come from up in this part of the country," rejoined captain simms, "and i thought this would be a good quiet place to hide myself till my work was complete. but it seems," he added, with a smile, "that i may have been mistaken." "oh, i don't know," replied jack. "those fellows would never think of trailing you here. i guess they think you are still in clayton." "let us hope so, anyway," said the captain, and here the discussion ended. soon after they said good-by, promising to run over again before long. their boat was all ready for them. a good job had been done with it. "it looks as good as new," commented jack. "she's a fine boat," said billy. "a regular pippin," agreed noddy. "well, young men, your-craft-will-carry-you-through many a blow yet. she's as nice a little-ship-as-i-ever-saw." "i guess he says that of every boat that brings him a job," grinned noddy, as jack paid the man, and they got ready to get under way. a light breeze had risen, and they were soon skimming along, taking great care to avoid shoals and sand-banks. by standing up to steer, jack was easily able to trace the deeper water by its darker color and they got out of the bay without trouble. as they glided round the point, which had shrouded the black motor boat from their view when they entered the bay, billy, who was in the bow, uttered a sharp cry and pointed. the others looked in the direction he indicated, realizing that something unusual was up. "well, look at that, will you?" exclaimed jack. the black motor-boat was anchored close in to the shore. her dinghy lay on the beach, showing that somebody had just landed. clambering up the steep and rocky sides of the point were three figures. when the boys caught sight of them the trio had just gained the summit of the rocky escarpment. they crouched behind rocks, as if fearing that they would be seen, and one of them drew from his pocket a pair of field glasses. he gazed through these down at the settlement of musky bay, which lay below. then he turned to his companions and made some remark and each in turn took up the glasses. "what do you make of it?" asked billy, turning to jack. the wireless boy shook his head dubiously. "i'll tell you what _i_ make of it," he said. "just this. those three figures up yonder are judson, donald and jarrow. they trailed us here in that motor boat but were too foxy to round the point. when they saw us turn into the bay, they knew they could land and sneak over the point without being seen. they are spying on the settlement and watching for captain simms. at any rate, they will see his boat tied up there and realize that they have struck a home trail." "what will we do?" asked billy, rather helplessly. "there's only one thing to do," said jack with decision, "and that is to turn back and warn captain simms of what is going on." the _curlew_ was headed about and a few moments later was in sight of musky bay again. chapter xi. a swim with a memory. "so they did find me out, after all?" said captain simms grimly, after he had heard the boys' story. "well, it will not do them much good. i am well armed and the government is at my back. if i get the chance i will deal with those rascals with no uncertain hand." "why don't you have them arrested right now?" asked noddy. "because it would be premature to do so at the present moment. the agents of several nations are keen on getting a copy of the code. if these men were arrested, it would reveal, directly, the whereabouts of the code and its author." "it seems too bad such rascals can carry on their intrigues without being punished," said jack. as it was noon by that time, and the appetites of all were sharp set, captain simms invited the boys to have lunch with him. it was a simple meal, consisting mainly of fish; but the boys did ample justice to it, and finished up with some pie, which the captain had brought from clayton to replenish his larder. after dinner the capricious breeze died out entirely. the heat was intense, and the water glittered like a sheet of molten glass. the boys looked longingly at the bay, however. the idea of a cool swim seemed very attractive just then. captain simms had left them to their own devices while he took a nap. "tell you what," said billy, "let's take a swim, eh, fellows?" "suits me down to the ground," said jack. "suits me down to the water," grinned noddy. they had bathing trunks on their boat, and, having found what looked like a good spot, a little cove with a sandy beach, they disrobed and were soon sporting in the water. "ouch! it's colder than i thought it was," cried noddy. "you'll soon warm up," encouraged jack. "i'll race you out to that anchored boat." "bully for you," cried billy. "you're on," echoed noddy, not to be outdone. but, as a matter of fact, the red-headed lad, who had eaten far more than the others, wasn't feeling very well. however, he did not wish to spoil the fun, so he didn't say anything. jack and billy struck out with long, strong strokes. "come on," cried jack, looking back at noddy, who was left behind, and who began to feel worse and worse. "what's the trouble--want a tow-rope?" "i'll beat you yet, jack ready," cried noddy, fighting off a feeling of nausea. "i guess i went in the water too soon after eating," he thought. "it will wear off." "help!" the single, half-choked cry for aid reached the ears of jack and billy when they were almost at the anchored boat, which was the objective point of the race. "great cã¦sar!" burst from jack. "what's up now?" he turned round just in time to see noddy's arms go up in the air. then the red-headed lad sank out of sight like a stone. "he can't be fooling, can he?" exclaimed billy nervously. "he wouldn't be so silly as to do that," rejoined jack, who was already striking out for the spot where noddy had vanished. billy followed him closely. they were still some yards off when noddy suddenly reappeared. he was struggling desperately, and his eyes seemed to be popping out of his head. his arms circled wildly, splashing the water helplessly. then he disappeared once more. "heavens, he is drowning," choked out jack. "we must save him, billy." "of course we will, old boy," panted billy, upon whom the pace was beginning to tell. jack reached the spot where the disturbed water showed that noddy had gone down for the second time. just as he gained the place noddy shot up again. he was totally unconscious and sank again almost instantly. like a flash jack was after him, diving down powerfully. he grasped noddy round the chest under the arms. "noddy! noddy!" he exclaimed, as they shot to the surface. but the lad's eyes were closed, his face was deadly white, and his matted hair lay over his eyes. a terrible thought invaded jack's mind. what if noddy were dead and had been rescued too late? "here, give me one of his arms. we must get him ashore as quickly as we can," cried billy. "that's right; he's a dead weight. oh, billy, i hope that he isn't----" a moan came from noddy. suddenly he opened his eyes and grasped at jack wildly, with five times his normal strength. the movement was so unexpected that jack was dragged under water. but the next moment noddy's drowning grip relaxed and they rose to the surface. "he's unconscious again," panted jack. "he'll be all right, now. take hold, billy, and we'll make for the shore." it was an exhausting swim, but at last they reached shallow water, and, ceasing swimming, carried noddy to the beach. they anxiously bent over him. "we must get that water out of his lungs," declared jack, who knew something of how to treat the half-drowned. luckily, an old barrel had drifted ashore not far off, and over this poor noddy was rolled and pounded and then hoisted up by the ankles till most of the water was out of his lungs and he began to take deep, gasping breaths. but it was a long time before he was strong enough to get on his feet, and even then his two chums had to support him back to captain simms' house, where they received a severe lecture for going in the water so soon after eating. "it was an awful sensation," declared noddy. "it just hit me like an electric shock. i couldn't move a limb. then i don't remember much of anything more till i found myself on the beach." noddy's deep gratitude to his friends may be imagined, but it was too painful a subject to be talked about. it was a long while, however, before any of them got over the recollection of noddy's peril. chapter xii. a tale from the frozen lands. although noddy had recovered remarkably quick, thanks to his rugged constitution, from the effects of his immersion, captain simms ordered him on the sick-list and he was, much against his will, sent to bed. "he'd better stay there all night," said the captain. "we don't want to run any risks of pneumonia. i don't suppose your uncle will worry about you?" "he's got over that long ago," laughed jack; "besides, there's a professor stopping at the hotel who is on the lookout for funny plants and herbs. that's uncle toby's long suit, you know." "so i have heard," smiled the captain. "well, you boys may as well make yourselves at home." "thank you, we will," said billy. whereat there was a general laugh. there was a phonograph and a good selection of records in the cottage, so they managed to while away a pleasant afternoon. jack cooked supper, "just by way of paying for our board," he said. after the meal they sat up for a time listening to captain simms' tales of seal poachers in the arctic and the trouble they give the patrol assigned to see that they do not violate the international boundary, and other laws. before he had taken command of the _thespis_, of the ice-berg patrol, captain simms had been detailed to command of the _bear_ revenue cutter, and had chased and captured many a sealer who was plying his trade illicitly. the boys listened attentively as he told them of the rough hardships of such a life, and how, sometimes, a whole fleet of sealers, if frozen in by an early formation of ice, must face hunger and sometimes death till the spring came to release them from their imprisonment. "it must take a lot of nerve and courage to be a sealer," said jack. "it certainly does," agreed the captain. "yet i heard from one sealing captain the story of a young fellow whom it turned from a weak coward into a brave man. this lad, who was regarded as a weakling, saved himself and two companions from a terrible death simply by an act of almost sublime courage. would you like to hear the story?" "if you don't mind spinning the yarn," said jack. "well, then," began the captain, "to start with, the name of my hero is shavings. of course he had another name, but that's the one he was always known by, and i've forgotten the right one. he was a long-legged, lanky vermont farmer, with dank strings of yellow hair hanging about his mild face. this hair gave him his nickname aboard the sealing schooner, _janet barry_, on which he signed as a boat man. how shavings came to st. johns, from which port the _janet barry_ sailed, or why he picked out such a job, nobody ever knew. he had, as sailors say, 'hayseed in his hair' and knew nothing about a ship. "but what he didn't know he soon learned under the rough method of tuition they employed on the _barry_. a mate with a rope's end sent him aloft for the first time and kept sending him there till shavings learned how to clamber up the ratlines with the best of them. he learned boat-work in much the same way, although he passed through a lot of experiences while chasing seals, that scared him badly. he told the captain long afterward that, although he was afraid of storms and gales, still he sometimes welcomed them, because he knew the boats would not have to go out. "one day, far to the north, they ran into an exceptionally fine school of seals. all the boats were sent away, and among them the one to which shavings belonged. in command of this boat was olaf olsen, the mate who had taught shavings the rudiments of his profession by means of hard knocks. dark clouds were scurrying across the sky, and the sea looked angry, but that made no difference to the sealers. lives or no lives, women in the states had to have their sealskin coats. "so the boats pursued the seals for a long distance, and in the excitement nobody noticed what the weather was doing. nobody, that is, but shavings, and he didn't dare to say that it was growing worse, for fear of angering the mate. the hunters harpooned a goodly catch before the gale was upon the little fleet almost without warning. "then the storm broke with a screech and a massing of angry water. the boats had been under sail, and in a flash two of them were over-turned. shavings saw all this with terror in his eyes and a cold clutch at his heart. he knew the men in those boats would never go sealing again. "then his eyes fell on the mate, olaf olsen. the man appeared to be petrified with fright. he made no move to do anything. then something in shavings seemed to wake up. "perhaps that yellow hair of his was a survival of some old viking strain, or perhaps all those months of rough sea life had made him over without his knowing it. but he seized the mate and shook him by the shoulder: "'give an order, man!' he shouted. 'order the sail reefed.' "but the sight of the death of his shipmates had so unnerved the mate that he could no nothing. shavings kicked him disgustedly, and went about the job himself. clouds of spray burst over him. time and again he was within an inch of being swept overboard, but at last he had the sail reefed down. then he took the tiller and headed back for the schooner across the immense seas through the screeching gale. "he handled that boat skillfully, meeting the big seas and riding their summits, only to be buried the next instant in the watery valley between the giant combers. but always he rose. he had the cheering sight of the schooner before him and it grew closer. the boat sailed more on her beam than on her keel, but at last shavings, more dead than alive, ran her in under the lee of the schooner's hull, and willing hands got the survivors out of the boat. "the skipper of that craft was a rough man. he drove olaf olsen forward with blows and curses and the strong swede whimpered like a whipped cur. then he came aft to where the cook was giving shavings and the rest hot coffee. "'shavings,' he said, 'after this you're mate in that coward olsen's place. you're a man.' "'no, sirree,' rejoined shavings, 'i'm a farmer. no mate's job for me. when we gets back ter home i'm goin' ter take my share uv ther catch and buy a farm.' "but he was finally persuaded to take the job of mate when his canny new england mind grasped the fact that the mate's share of the profits is much bigger than a foremast hand's. he was as good as his word, however, and, when the _janet barry_, with her flag at half mast but her hold full of fine skins, docked at st. johns after the season was over, shavings drew his money and vanished. i suppose he is farming it somewhere in vermont now, but i agree with his captain, who told me the story, that there was a fine sailor lost in shavings." chapter xiii. a night alarm. jack sat bolt upright in bed and listened with all his might. outside the window of the little room he occupied that night in the captain's cottage he was almost certain he had heard the sound of a furtive footfall and whisperings. his blood beat in his ear-drums as he sat tense and rigid, waiting a repetition of the noise. suddenly, there came a low whisper from outside. "if only we knew if the captain was alone. for all we know those bothersome boys may be with him, and, if they are, we are likely to get the worst of it." "donald judson!" exclaimed jack to himself. "what ought i to do?" he pondered a moment and then recollected that there was a door to his room which let directly out on a back porch without the occupant of the room having to traverse any other chamber. jack at once formed a bold resolve. he did not wish to arouse the others unnecessarily, but he did want, with all his power, to find out what was going on. he rose from the bed as cautiously as he could, and made his way to the door. it was a ticklish task, in the dark, to accomplish without noise, but he succeeded in doing it. outside it was very dark, with a velvety sort of blackness. the boy was glad of this, for it afforded him protection from the men he felt sure were reconnoitering the house for no good purpose. suddenly he saw, not far off, the gleam of a light of some sort. if it belonged to the judsons, they must have presumed that nobody was about, or not have realized that the place where they had left it was visible from the cottage. "now i wonder what they've got up there?" mused jack. "maybe it would be a good scheme to go up and see." anything that looked like an adventure aroused jack's animation, and a few seconds after the idea had first taken hold of him he was making his way up a rather steep hillside, covered with rocks and bushes, toward the light. at last he reached a place where he could get a good look at the shining beacon. he hardly knew what he had expected to see, but somehow he felt a sort of sense of disappointment. the lantern stood by itself on a rock and the idea suggested itself to jack that it might have been placed there as a beacon to guide the midnight visitors back when they had accomplished whatever they purposed doing. "i've a good mind to carry off their lantern," said jack to himself; "if they put it there to guide them that would leave them in a fine fix and we could easily capture them." once more, half involuntarily, his feet appeared to draw him toward the lantern. the next instant he had it in his grasp. "now to turn it out," he muttered, when he felt himself seized from behind in a powerful grip and a harsh voice growled in his ear: "yer would, would yer, you precious young scallywag." the lantern was wrested from his grasp, and jack felt a noose slipped over his head. "who are you?" he demanded indignantly of his unknown captor. "bill smiggers, of the motor boat _black beauty_," was the gruff reply. "they left me up here to watch by the light, and i guess they'll be glad they did when they see who i've caught. i reckon you're one of those snoopy kids i've heard them talking about." "i don't know what you mean," replied jack, "but you'd better let me go at once." "huh, i'd be a fine softy to do that, wouldn't i? no, young man, here you are, and here you stay. i'm getting well paid for this job, and i'm going to do a good one." just then footsteps were heard coming up the hillside. then a low, cautious voice whispered out of the darkness: "what's the matter, bill? we saw the light waved, and came right back. is there any danger?" "not right now, i reckon," rejoined bill, with grim humor. "any of you gents know this young bantam i've got triced up here?" "jack ready, by all that's wonderful!" cried judson, stepping forward. he was followed by young judson and jarrow. "dear me, what an--er--what a pleasant encounter," grinned jarrow. "so you thought you'd spy on us, did you?" snarled donald, vindictively; "well, this is the time that we've got you and got you right." jack's heart, stout as it was, sank like lead within him. he was in the hands of his enemies and that, largely, by his own foolishness. "so this is that ready kid i hearn you talkin' about?" asked bill. "that's the boy, confound him! he's always meddling in my schemes," growled jarrow. "bright looking lad, ain't he?" "too bright for his own good. he's so sharp he'll cut himself." "no, his brightness won't help him now," chuckled donald maliciously. "i'll bet you're scared to death," he went on, coming close to jack. "not particularly. it takes more than a parcel of cowards and crooks to frighten me." "don't you put on airs with me. you're in our power now," jeered donald. "i'll make you suffer for the way you've treated me." "it would be like you to take advantage of the fact that my arms are tied," retorted jack. donald came a step closer and stuck his fist under jack's nose. "you be careful, or i'll crack you one," he snarled. "you're a nice sort of an individual, i must say. why don't you try fair dealing for a change?" "i do deal fair. it's you that don't. i----" "that will do," interrupted his father; "i've been talking with bill and he says he knows a place where we can take this young bantam and leave him till he cools off." "you mean that you are going to imprison me?" demanded jack indignantly. "you may call it that, if you like," said judson imperturbably; "you are quite too clever a lad to have at large." "where are you taking me to?" "you'll find that out soon enough. now then, forward march and, if you attempt to make an outcry, you'll feel this on your head." judson, with a wicked smile, flourished a stout club under the captive boy's nose. chapter xiv. jack's curiosity and its results. "what do you intend to do with me?" repeated jack, as they hurried over the rough ground, following bill, who trudged ahead with the lantern. "you'll find out quick enough, i told you before," said donald. "don't you know that my friends are in the neighborhood? they will invoke the law against you for this outrage." "we know all about that," was the elder judson's reply, "but we're not worrying. we'll have them prisoners, too, before long." jack made no reply to this, but he judged it was an empty threat made to scare him. he knew that nothing would have delighted donald judson more than to see him breaking down. so he kept up a brave front, which he was in reality far from feeling at heart. from the bold manner in which bill displayed the lantern as he led the party on, jack knew that the rascal must be familiar with the country, and know it to be sparsely inhabited. so far as jack could judge they were retreating from the river and going up hill. about an hour after they had started, bill paused in front of an ancient stone dwelling--or rather what had been a dwelling, for it was now dilapidated and deserted. "this is the place, boss," he grated, holding up his lantern so that its rays fell on the old place, which looked as grim as a fortress. "it's haunted, too, isn't it, bill?" asked donald meaningly. "well, they do say there was a terrible murder done here some years ago and that's the reason it's been deserted ever since, but i really could not say as to the truth of that, master judson," rejoined bill, falling into donald's plan to tease jack. inside the place was one large room. a few broken bits of furniture stood about. bill set the lantern down on a rickety table and then went to guard the door, while the others retreated to a corner and held a parley. at its conclusion judson came over to jack. "well, ready," he said, "you've caused us a lot of trouble, but still i might come to terms with you." "are you ready to release me?" demanded jack. "yes, under certain conditions. first, you must tell us all you know about that naval code of captain simms." "and the truth, too," snarled jarrow. "we'll find out quick enough if you're lying, and we'll make it hot for you." "you bet we will," chimed in donald. "donald, be quiet a minute," ordered his father. "well, ready, what have you to say?" "suppose i tell you i know nothing about the naval code?" said jack quietly. "then i should say you were not telling the truth." "nevertheless i am." "what, you know nothing about the code?" "nothing except that captain simms was ordered to get up something of the sort." "you don't know if it's finished or not?" "i have no idea." "is your life worth anything to you?" struck in jarrow. "what do you mean?" asked jack. "just what i say. if it is, you had better make terms to save it." "impossible. you are fooling with me, jarrow. even a man as base as you wouldn't dare----" "i wouldn't, eh? well, you'll find out before long if i'm in earnest or not." jack was a brave lad, as we know, and carried himself well through many dangerous situations. but he was not the dauntless hero of a nickel novel whom nothing could scare. he knew jarrow for a desperado and, although he could not bring himself to believe the man would actually carry out any such threat as he had made, still he realized to the full the peril of his situation. "well, what do you say?" demanded jarrow, after a pause. "i don't know just what to say," said jack. "my head is all in a whirl. give me time to think the thing over. i can hardly collect my thoughts at present." the men made some further attempts to get something out of him, but, finding him obdurate, they ordered bill to see that his bonds were tight and then to put him in the "inner room" he had spoken of. bill gave the ropes a savage yank, found they were tight and then led jack to a green door at the farther end of the large room. jack had a glimpse of a square room with a broad fireplace at one end and a small window. it appeared to be used as a storehouse of some kind, for it was half filled with bags, apparently containing potatoes. in one corner stood a grindstone operated by a treadle. then the door was shut with a bang, and he was left to his own, none-too-pleasant reflections. outside he could hear the buzz of voices. but he couldn't catch much of what was being said. once he heard jarrow say: "you're too soft with the boy. a good lashing with a black-snake would bring him to his senses quick enough." "i'd like to lay it on," he heard donald chime in. at last they appeared to grow sleepy. jack heard a key turned in the lock of the inner room that he occupied and not long thereafter came the sound of snores. evidently nobody was on guard, the men who had captured him thinking that there was no chance of the boy's escape. "now's my chance," thought jack. "if only i could get my hands free, i might be able to do something. but, as it is, i'm helpless." his heart sank once more, as he thought bitterly of the predicament into which his own foolhardiness had drawn him. chapter xv. billy takes the trail. "what's the matter?" just as jack stole out of the house billy raynor sat bolt upright in bed and asked himself that question. he was on the other side of the cottage, and, like jack a few minutes before, he too heard the cautious footsteps of the marauders, as they crept round the cottage, reconnoitering. "somebody's up to mischief," thought the boy. "it may only be common thieves, or it may be that rascally outfit. i'll go and rouse jack. perhaps we can get after them." he tiptoed across the main room of the cottage to jack's door. inside the room he struck a match. he almost cried out aloud when he saw that the bed was empty and that there was no sign of his chum. "where can he be?" thought the lad. "surely he has not gone after that gang single-handed." raynor hastened to his own room, slipped on some clothes, and went to the door. far up on the hillside a lantern was twinkling like some fallen star. "that's mighty odd," reflected the lad. "i guess i'll take a look up there and see what's coming off." he picked his way cautiously up the rough hillside. but the lantern retreated as he went forward. as we know, judson and his gang, led by bill, were carrying off jack. without realizing how far he had gone, raynor kept on and on. some instinct told him that the dodging will-o'-the-wisp of light ahead of him had something to do with jack, and he wanted to find out what that something was. but, not knowing the trail bill was following, and having no light but the spark ahead of him, raynor found it pretty hard traveling. at last he was so tired that he sat down to snatch a moment's rest, leaning his back against a bush. as his weight came against the bush, however, a strange thing happened. the shrub gave way altogether under the pressure. raynor struggled for an instant to save himself, and then felt himself tumbling backward down an unknown height. he gave a shout of alarm, but his progress down what appeared to be a steep wall of rock, was over almost as soon as it had begun. "what happened?" gasped the lad, as, shaken by his adventure, he picked himself up and tried to collect his wits. "oh, yes, i know, that bush gave way and i toppled over backward. i must be in some sort of hole in the ground. well, the first thing to do is to get a light." luckily raynor's pockets held several matches, and he struck one of them and looked about him. his eyes fell on the bush which lay at his feet. "no wonder it gave way," he muttered. "the thing is dead and withered. but"--as a sudden thought struck him--"it will make a dandy torch and help save matches." he lit the dead bush, which blazed up bravely, illumining his surroundings with a ruddy glow. above him was a dark hole, presumably the one through which he had fallen. but there was no way of escape in that direction. he turned his gaze another way. the cave appeared to recede beyond the light of the blazing branch. looking down, he saw that the floor of the cave was thickly littered with leaves and small branches. this encouraged him a good deal. "they couldn't have been blown in by the hole i fell through," he mused, "for the dead bush covered that. their being here must mean that there is another entrance to this place." carrying his torch aloft, he struck off into the cave. its floor sloped gently upward as he progressed and the walls began to grow narrower. the air, too, rapidly lost its musty odor, and blew fresh and sweet on his perspiring head. "this will be quite an adventure to tell about if i ever get out of here," muttered raynor, and the thought of jack, whom he had almost forgotten in his fright at his fall into the cave, occurred to him. what could have happened to his chum? surely he had not been foolhardy enough to face the marauders alone? raynor did not know what to make of it. "somehow," he pondered, "i am sure that lantern had something to do with jack. i wonder if they would have dared to carry him off? i wish to goodness i'd kept on, instead of leaning against that bush. even if i do get out of here, the light must be far out of sight by this time, and i'll have to wait till daylight, anyhow, for i must have walked almost a mile from the other entrance to the cave by this time." his thoughts ran along in this strain as he walked. the thought of captain simms' alarm, too, when he found both boys missing, gave him a good deal of worry. he was thinking over this phase of the situation when he was startled by a low growl, coming from a pile of rocks just ahead of him. what could it be? holding his breath painfully, while a cold chill ran down his spine, raynor came to a dead pause and listened. his improvised torch had almost burned out and it was appalling to think that he faced the possibility of being in darkness ere long, with a wild beast close at hand. again came the growl. it echoed and re-echoed hollowly in the cave till the frightened lad appeared to be menaced from all directions. "it must be a bear, or some wild beast just as bad," thought raynor. the growling was repeated, but now it appeared to be retreating from him. plucking up courage, after a while, raynor, waving his torch, pushed forward again. he came to a place where it was necessary to scramble up to a sort of platform considerably higher than the path he had been traversing. as he gained this, he saw several tiny bright lights in front of him. "hurrah! it's the stars!" he cried aloud. "the--s-t-a-r-s!" the echoes boomed back. at almost the same instant raynor saw, in front of him, what looked like two balls of livid green flame. but the boy knew that they were the eyes of whatever beast it was that had sent its growls echoing fearfully through the cave. chapter xvi. a "ghostess" abroad. suddenly, like an inspiration, jack thought of a way in which he might free his captive hands. naturally quick-witted, the emergency he found himself facing had made his mind more active than usual. "that grindstone," he thought. "i can work the treadle with my foot, while i stand backward to it. if i hold the rope against the sharp edge of the stone it ought to cut through in a very short time." it was quite a task to locate the grindstone in the darkness without making a noise. but at last jack, by dint of feeling softly along the walls, located it. then he turned his back to the machine and put his foot on the treadle. as the wheel began to turn he pressed the rope that bound his hands against the rough stone. in ten minutes he was free. "now for the next move," counseled the boy. "i've got to do whatever i decide upon quickly. if i don't escape, and that gang finds how i've freed my wrists, they'll shackle me hand and foot, and i'll not get another chance to get away. if it was only daylight i'd stand a much better opportunity of getting out." there was the door, but to try that was out of the question. jack had heard it locked and the key turned. the window? it was too small for a big, well-grown boy like jack to creep through. he had noted that during the time the door was open and his prison was lighted by the rays of the lantern. "there's that fireplace," thought the boy, "that's about the last resort. i wonder----" he located the big, old-fashioned chimney, built of rough stones and full of nooks and crannies, without trouble. getting inside it on the hearthstone he looked upward; it was open to the sky and at the top he could see a faint glow. "it's getting daylight," he exclaimed to himself. the next moment he noticed that right across the top of the chimney was the stout branch of a tree. "if i could get up the chimney that branch would afford me a way of getting to the ground," he thought. "by jove! i believe i could do it," he muttered, as the light grew stronger and he saw how roughly the interior of the chimney was built. "it's not very high, and those rough stones make a regular ladder." as time was pressing, jack began the ascent at once. for a lad as active as he was, it proved even more easy than he had anticipated. but long before he reached the top he was covered from head to foot with soot, although, oddly enough, that thought never occurred to him. at length, black as a negro in mourning, he reached the top of the chimney and grasped the tree branch he had noticed from below. he swung into it and made his way to the main trunk of the tree, an ancient elm. it was no trick at all then for him to slide to the ground. then, silently as a cat, he tiptoed his way from the old stone house, with its occupants sleeping and snoring, blissfully unaware that jack had stolen a march on them. "well, things have gone finely so far," he mused. "now, what shall be the next step?" he looked about him. the country was a wild one. there was no sign of a house, and, as far as he could see, there was nothing but an expanse of timber and rocks. "this is a tough problem," thought the boy. "i've no idea where i am, or the points of the compass. if i go one way, i might come out all right, but then again i might find myself lost in the forest. hanged if i know what to do." but, realizing that it would not do to waste any time around the old house, jack at length struck off down what appeared to have been, in bygone days, some sort of a wood road. it wound for quite a distance among the trees, but suddenly, to his huge delight, the boy beheld in front of him the broad white ribbon of a dusty highway. suddenly, too, he heard the sound of wheels and the rattle of a horse's hoofs coming along at a smart rate. "good; now i can soon find out where i am," thought the boy, and he hurried forward to meet the approaching vehicle. it contained a pretty young woman, wearing a sunbonnet. jack had no hat to lift, but he made his best bow as the fair driver came abreast of him. "i beg your pardon," he began, "but could you tell me----" the young woman gave one piercing scream. "oh-h-h-h-h-h!" she cried, and gave her horse a lash with the whip that made it leap forward like an arrow. in a flash she was out of sight in a cloud of dust. "well, what do you know about that?" exclaimed jack. "she must be crazy, or something, or else she's the most bashful girl i ever saw." he sat down on a rock at the side of the road to rest and waited for another rig or a foot passenger to come by. before long he heard a sprightly whistle, and a barefooted boy, carrying a tin pail, and with a fish pole over his shoulder, appeared round a curve in the road. "now, i'll get sailing directions," said jack to himself, and then, as the boy drew near: "hullo, sonny! can you tell me----" the boy gave one look and then, dropping his can of bait, and his pole, fled with a howl of dismay. "hi! stop, can't you? what's the matter with you?" shouted jack. he ran after the boy at top speed. but the faster he ran the faster the youngster sped along the road. "oh-h-h-h-h! help! mum-muh!" he yelled, as he ran, in terrified tones. at length jack gave up the chase. he leaned against a fence and gave way to his indignation. "bother it all," he said. "what can be the matter with these people? everyone i speak to runs away from me, as if i had the plague or something. anyhow, that youngster can't be very far down this road. i guess i'll keep right on after him, and then i'm bound to come to some place where there are some sensible folks." as he assumed, it was not long before he came in sight of a neat little farm-house, standing back from the road in a grove of fine trees. he made his way toward it. in the front yard an old man was trimming rose-bushes. "can you tell me----" began jack. the old man looked up. then uttering an appalling screech, he ran for his life into the house. "mandy! mandy! thar be a ghostess in the yard!" he yelled, as he ran. jack looked after him blankly. what could be the matter? chapter xvii. one mystery solved. "well, i'll be jiggered!" exclaimed jack. "what _can_ be the matter? it beats me. i----" "hey you, git out of thar. i don't know what of critter ye be, but you scared my old man nigh ter death. scat now, er i'll shoot!" jack looked up toward an upper window of the farm-house, from which the voice, a high-pitched, feminine one, had proceeded. an old lady, with a determined face, stood framed in the embrasure. in her hands, and pointed straight at the mystified jack, she held an ancient but murderous looking blunderbuss. "it's loaded with slugs an' screws, an' brass tacks," pleasantly observed the old lady. "jerushiah!" this to someone within the room, "stop that whimperin'. i'm goin' ter send it on its way, ghost or no ghost." "but, madam----" stammered jack. "don't madam me," was the angry reply. "git now, and git quick!" "this is like a bad dream," murmured jack, but there was no choice for him but to turn and go; "maybe it is a dream. if it is i wish i could wake up." he turned into the hot, dusty road once more. he felt faint and hungry. his mouth was dry, and he suffered from thirst, too. before long he found a chance to slake this latter. a cool, clear stream, spanned by a rustic bridge, appeared as he trudged round a bend in the road. "ah, that looks good to me," thought jack, and he hurried down the bank as fast as he could. he bent over the stream at a place where an eddy made an almost still pool, as clear as crystal. but no sooner did his face approach the water than he gave a violent start. a hideous black countenance gazed up at him. then, suddenly, jack broke into a roar of laughter. "jerusalem! no wonder everybody was scared at me when i scare myself!" he exclaimed. "it's the soot from that chimney. just think, it never occurred to me why they were all so alarmed at my appearance. why, i'd make a locomotive shy off the track if it saw me coming along." it did not take jack long to clean up, and, while his face was still grimy when he had finished, it was not, at least, such a startling looking countenance as he had presented to those from whom he sought to find his way back to musky bay. "now that i look more presentable i guess i'll try and get some breakfast," thought the boy as, his thirst appeased, he scrambled up the bank again. about half a mile farther along the road was the queerest-looking house jack had ever seen. it was circular in form, and looked like three giant cheese-boxes, perched one on the top of the other, with the smallest at the top. "well, whoever lives there must be a crank," thought jack; "but still, since i've money to pay for my breakfast, even a crank won't drive me away, i guess." a man was sawing wood in the back yard and to him jack addressed himself. "i'd like to know if i can buy a meal here?" he said. "no, you can't fry no eel here," said the man, and went on sawing. "i didn't say anything about frying eels. i said 'can i get a meal?'" shouted jack, who now saw that the man was somewhat deaf. "don't see it makes no difference to you how i feel," rejoined the man. "i'm hungry. i want to eat. i can pay," bellowed jack. "what's that about yer feet?" asked the deaf man. "not feet--eat--e-a-t. i want to eat," fairly yelled jack. "what do you mean by calling me a beat?" angrily rejoined the deaf man. "i didn't. oh, great scott, everything is going wrong to-day," cried jack. then he cupped his hands and fairly screeched in the man's ear. "can i buy a meal here?" a light of understanding broke over the other's face. "surely you can," he said. "araminta--that's my wife--'ull fix up a bite fer yer. why didn't you say what you wanted in the fust place?" "i did," howled jack, crimson in the face by this time; "but you didn't hear me. you are deaf." "wa'al, i may be a _little_ hard o' hearing, young feller," admitted the man, "but i hain't deef by a dum sight." jack didn't argue the point, but followed him to the house, where a pleasant-faced woman soon prepared a piping hot breakfast. as he ate and drank, jack inquired the way to musky bay. "it ain't far," the woman told him, "five miles or so." "can i get anyone to drive me back there?" asked jack, who was pretty well tired out by this time. "oh, yes; abner will drive you over fer a couple of dollars." she hurried out to tell her husband to hitch up. jack could hear her shouting her directions in the yard. "all right. no need uv speaking so loud. i kin hear ye," jack could hear the deaf man shouting back. "i kin hear ye." "just think," said the woman when she came back into the kitchen, where jack had eaten, "abner won't admit he's deef one bit. at church on sundays he listens to the sermon just as if he understood it. if anyone asks him what it was about, he'll tell 'um that he doesn't care to discuss the new minister, but he's not such a powerful exhorter as the old one. he's mighty artful, is abner." the rig was soon ready and jack was on his homeward way. to his annoyance, abner proved very talkative and required answers to all his remarks. "gracious, i'll have no lungs left if i have to shout this way all the way home," thought jack. "it'll be husky bay. if ever i drive with abner again, i'll bring along some cough lozenges." "must be pretty tough to be really, down-right deef," remarked abner, after jack had roared out answers to him for a mile and a half. "it must be," yelled jack. "yes, sir-ee," rejoined abner, wagging his head. "i'm just a trifle that er-way, and it bothers me quite a bit sometimes, 'specially in damp weather. gid-ap!" chapter xviii. bill sniggers decides. we left billy raynor in a most unpleasant position. with escape from the cave within his grasp the way was blocked, it will be recalled, by some wild beast, the nature of which billy did not know. his torch, made from the withered bush that was responsible for his dilemma, was burning low. just in front of him glowed two luminous green eyes. while billy stood there hesitating, the creature gave another of its alarming growls. hardly thinking what he was doing, billy, startled by a shrill caterwaul, which followed the growl, flung his lighted torch full at the eyes, and heard a screech that sounded as if his blazing missile had struck its mark. [illustration: while billy stood there hesitating, the creature gave another of its alarming growls.] there was a swift patter of feet and the eyes vanished. "great christmas, i've scared the creature off," said billy to himself, with a sigh of relief; "a lucky thing i had that torch." he walked forward more boldly. the evident alarm of the animal that had scared him, when the torch struck, convinced the boy that there was no more danger to be feared from it. in a few seconds more he was out in the open air and on a hillside. it was still pitch dark, but the stars seemed to be growing fainter. billy drew out his watch and, striking a match, looked at it. the hands pointed to three-thirty. "it will be daylight before long," thought billy. "if i start walking now i will only lose myself. i'll wait till it gets light and then try to get my bearings." never had dawn come so slowly as did that one, in the opinion of the tired and impatient lad. but at last the eastern sky grew faintly gray and then flushed red, and another day was born. in the growing light, billy stood up and looked about him. the bay or any familiar landmarks were not in sight. billy was in a quandary. but before long he came to a decision. "i'll strike out for a main road," he decided; "if i can find one, that will bring me to where i can get some information, at any rate." with this end in view, he scrambled down the hillside and found himself in some fields. after a half-hour's walk across these, he saw, with delight, that he had not miscalculated his direction. a road lay just beyond a brush hedge. billy made his way through a gap and struck off, in what he was tolerably sure was the way to musky bay. if he had but known it, however, he was proceeding in an exactly opposite direction. he had walked about a mile when another foot passenger hove in sight. the lad was glad of this at first, for, although he had walked some distance, he had not passed a house, nor had any vehicles come by. but a second glance at the man who was coming toward him made him by no means so pleased at his appearance. the other foot passenger was a heavily built man with a lowering brow. he wore clothes that savored of a nautical character. "hullo, there, young feller," he said, as he halted to allow billy to come up to him. "good morning," said billy. "i am trying to find my way to musky bay. can you direct me?" the other looked at the boy with a glance of quick suspicion. "livin' there?" he asked. "yes, that is to say, i'm staying there with friends." "umph! i know a crowd of folks there. who you stopping with?" before billy realized what he was saying he had made a fatal slip. "with captain simms--that is," he hurried on, in an effort to correct his blunder, "i----" "know a kid named ready--jack ready?" "why, yes, he's my best friend. he--here, what's the matter?" the other had suddenly drawn a pistol and held it pointed unwaveringly at billy. "jerk up yer hands, boy, and get 'em up quick!" he snarled. billy had no recourse but to obey. the man facing him was a hard-looking enough character to commit any crime. with a sudden pang billy recalled that he was wearing the handsome watch--one of which had been given both to jack and himself for services they had performed for a high official in holland, when they rescued the latter's wife and daughter from robbers who had held up the ladies' automobile. he saw the man's eyes fixed on the chain with a greedy glare. "hand over that watch," he ordered. billy did as he was told. then came another order while the pistol was pointed unwaveringly at him. "now come across with your cash." billy handed over what money he possessed--about fifteen dollars. the rest was in a new york bank, and some in a safe at the hotel. the man looked at the inscription on the watch. "william raynor, eh? your friend was talking about you just before we had to----" all his fear was forgotten as the man spoke. his tones were sinister. billy realized, like a flash, that this man was an ally of the judsons, and must have had a hand in jack's disappearance. "had to what?" billy demanded. "you don't mean that you committed any act of violence?" "well, i'm not sayin' as to that," rejoined the other, who, as our readers will have guessed, was bill sniggers, "you'll find out soon enough." the man was deliberately torturing billy. soon after jack's escape, judson had awakened, and had been the first to discover that the boy had got away. a hasty and angry consultation followed, and it had been decided to send bill, who was not known by sight in the vicinity, out to scout and see if the hunt for the missing boy was up. his astonishment at running into billy was great. at first, till the boy spoke of musky bay, bill, who was an all-around scoundrel, merely regarded him as a favorable object of robbery when he spied his gold watch chain. now, however, the boy was a source of danger. "come over here, and i'll tell you all about it," said bill. "oh, you needn't be scared. i won't hurt you. i got all i wanted off of you. you see your friend got a little uppish after we carried him off, and so we had--_to hit him this way_!" the last words were spoken quickly and were accompanied by a terrific blow aimed at billy's chin. the boy sank in the roadway without a moan. he lay white and apparently lifeless, while bill, with a satirical grin on his face, regarded him. "well, you won't come to life this little while, young feller," he muttered. "i'll just put you over this hedge for safekeeping, so as you won't attract undue attention, and then be on my way." he picked the unconscious boy up as if he had been a feather and placed him behind the hedge. then, with unconcern written on his brutal face, the rascal walked on. he was bound for a neighboring village to get provisions; for, till they knew how the land lay, none of the judson gang dared to leave the deserted house. bill, in his rough clothes, would attract little or no attention. but the others were smartly dressed and wore jewelry, and donald had on yachting clothes. had they been seen they could not have failed to be noticed in that simple community. "this must be my lucky day," muttered bill, as he walked along. "i got my pay for that job last night, and now i've got a gold watch and chain and fifteen dollars beside. tell you what, bill, old-timer, i won't go back to that old house again. i'll just leave that bunch up there, and beat it out of these parts in my motor-boat. that's what i'll do--go, while the goin's good, because i kin smell trouble coming sure as next election." chapter xix. what a "hayseed" did. billy opened his eyes. his head swam dizzily, and he felt sick and faint. the hot sun was beating down on him, but at first he thought he was at home and in bed. then he began to remember. he sat up, and then, not without an effort, rose to his feet dizzily. "where on earth am i?" he thought. "and what happened? let's see what time it is." but his watch pocket was empty, and then full recollection of what had occurred came back to him. he was still rather painfully trying to regain the road when he heard the sound of a voice. it was a very loud voice, even though the owner of it was not yet in sight. "looks like we might have rain. i said it looks like we might have a shower." then another voice--a boyish one--shouted back: "yes--it--does." "gid-ap," came in the first voice, and then came hoof-beats and the rumble of wheels. the next minute a ramshackle, two-seated rig, with a man and a boy on the front seat, came into sight. billy gave one long stare, as one who doubted the evidence of his own eyes. then he broke into a glad shout: "jack!" "billy, old fellow, what in the world? why, you're white as a sheet." with alarm on his face, jack sprang out, as abner stopped the rig, and rushed toward billy. "how did you get here? what has happened?" demanded jack. billy told his story in as few words as possible. "oh, the rascal," broke out jack, when billy described the hold-up. "that was bill sniggers. he's the man who led the way to the stone house--but get in and i'll tell you my story as we go along." "where are you going?" "back to musky bay; but a few hours ago i didn't think i'd ever see it again." jack had to shout both his story and billy's for abner's benefit. but he gave them in highly condensed versions, as his sorely taxed vocal organs had almost reached the limit of their strength. he had just reached the conclusion, having been interrupted several times by abner's exclamations, when, ahead of them, on the road, they spied a figure shuffling along in the dust. the two boys were on the rear seat of the rig, so that the man, when he saw the rig approaching, having turned his head at the sound of hoofs, did not see the boys. "reckon that feller means ter ask fer a ride," remarked abner, as a bend in the road ahead screened the man from view for a few minutes. a sudden idea had come into jack's head. "let him have it," he said; "and then drive to the nearest village and up to the police station. i'll pay you well for it." "but--but--who is he?" demanded abner, stopping his horse. "bill sniggers, the rascal who is in league with judson." "great hemlock! you bet i'll pick him up right smart. but he'll see you boys and scare." "no, we'll hide in here," and jack raised a leather flap that hung from the back seat. "it will be a tight fit, but there'll be room." "wa'al, if that don't beat all," said abner. "git in thar, then, and then the show kin go on." as jack had said, it was a "tight fit" in the recess under the seat, but, as abner's rig had been made to take produce to market, there was a sort of extension at the back, which gave far more room than would ordinarily have been the case. pretty soon the boys, in their hiding-place, felt the rig come to a stop. then came a voice both recognized as bill's. "say, gimme a ride, will yer?" "did ye say my harness was untied?" "no, i said gimme a ride," roared bill, at the top of his powerful lungs. "oh, all right. git in. whoa thar', consarn yer (this to the horse). whar yer goin'?" "nearest village. i'm campin' up the bay. i want to get some grub," shouted bill. "yer a long ways frum ther river," remarked abner. "maybe; but i reckon that ain't your business," growled bill. "not ef you don't want ter tell it, 'tain't," said abner apologetically. he had heard enough of bill's character not to argue with him. "that's a nice-looking watch you've got there," the boys heard abner say pleasantly. there was a pause and then bill roared out: "what's that to you if it is?" "oh, nothing, only i jest saw that printing on it, and calkilated it might have bin a present to yer." jack could almost see bill hurriedly thrusting the watch back into his pocket. then, after a little while, he spoke again. "didn't see nothing of a kid back there in the road, did yer?" "he means you, billy," whispered jack. "no, i didn't see nothing of nobody," was abner's comprehensive rejoinder. there was a long silence, during which the boys sweltered in their close confinement. but they would have gone through more than that for the sake of what they hoped to bring about--the apprehension of at least one of judson's aides. "getting near a village?" asked bill presently. "yep; 'bout half a mile more," rejoined abner. in a short time the rig began to slacken its pace. then it stopped. "here, what's this?" the boys heard bill exclaim. "you're stopping in front of a police station." "sure. the chief is araminta's--that's my wife--cousin. i'm goin' in ter see him a minit. hold the horse, will yer, he's a bit skittish." the boys heard abner get out, and then an eternity seemed to elapse. then a door banged and a sharp voice snapped out: "throw up your hands, gol ding yer. i'm the chief uv perlice, an' i arrest ye fer ther robbery of one gold watch and assault and batt'ry." "confound it, the old hayseed led me into a trap!" exclaimed bill. he threw himself out of the rig and started to run. but, as he did so, jack and billy, who had crawled out from the back, suddenly appeared. bill gave a wild shout, and the next instant he was sprawling headlong in the dusty street, while a crowd came rushing from all directions. jack had tripped him by an old football trick. with an oath the desperado reached for his revolver. but, before he could reach it, he was pinioned by a dozen pairs of hands, and marched, struggling and swearing, into the police station. he was searched, and billy's watch found on him, as well as the money. then he was locked up. he refused to give any information about the judsons, in which he showed his astuteness, for, if they had been caught, his plight would have been worse than it was, for they would have been certain to implicate him deeply. so he contented himself by saying that he knew nothing about them. they had hired him to help the elder judson recover his nephew from another uncle, who had treated him badly. he knew nothing more about the case, he declared, except that, after jack's escape, the judsons had left for new york. (it may be said here that he was eventually found guilty of the theft and the assault and received a jail sentence.) abner was well rewarded for the clever way he had brought about bill's capture; and, well pleased with the way everything had come out, the boys resumed their journey. "i hope abner will invest part of what i gave him in an ear-trumpet," said jack, as they entered musky bay. "i hope so," laughed billy. he was going to add something, but a shout stopped him. "there's captain simms and noddy," shouted jack, as the two came running toward the vehicle. there is no need to go into the details of the reunion, or to relate what anxious hours the captain and noddy had gone through after their discovery that the boys had vanished. if they had not reappeared when they did, captain simms was preparing to organize posses and make a wide search for them, as well as enlisting the aid of the authorities. in the vague hope that the judsons and jarrow might have remained in the stone house, waiting bill's return, a party searched it next day, under the guidance of a native who knew the trail to it. but it was empty. a search for the black motor boat, too, resulted in nothing being found of her. as a matter of fact, not many minutes after bill, from whom they wished to be separated, had left the house, the judsons--father and son--and jarrow, had made all speed to the point where the motor craft had been left and had hastily made off in her. they knew that the search for jack would be hot and wished to get as far away from bill as he treacherously wished to get from them. in their case there was certainly none of the proverbial honor among thieves. the black motor boat was left at clayton and afterward claimed by a relative of bill, who, by reason of "circumstances over which he had no control," was unable to claim her himself. as for the judsons, they vanished, leaving no trace behind them. the same was the case with jarrow. a message had been sent to uncle toby, telling him of the reason for the boys' delay at musky bay, _via_ a small mail steamer that plied those waters. his reply was characteristic: "them buoys is as hard to hurt as gotes, and as tuff as ship's biskit on a cape horner. best wishes to awl. awl well here at eight bells. "cap'n toby ready, "_inventor and patentee of the universal herb medicine, guaranteed to cure all ills, both of man and quadruped._" chapter xx. the "curlew" in trouble. "looks as if we might have a blow, jack." the _curlew_ was lazily moving along, with all sail set, carrying the boys back to pine island from their adventurous visit to musky bay. but, although every bit of canvas was stretched on her spars, she hardly moved. her form was reflected in the smooth water with almost mirror-like accuracy. "a blow? pshaw," scoffed noddy, "there isn't a breath of wind. i wish we could get a blow and cool off." "well, your wish is likely to come true before very long," said jack, who was at the tiller. "how's that?" "see that cloud bank over yonder, that ragged one?" "yes, what's that got to do with it?" "well, that's as full of wind as an auto tire," said jack. "i've been watching it for some time. it'll be a nasty storm when it hits us." "hadn't we better run in for shelter somewhere?" asked billy. "there's so little wind now that i doubt if we could get inshore before the squall hits us," replied jack. "i'll try to, though." he headed for the distant shore, where the outlines of some sort of a wooden structure could be seen. "if it gets very bad we can take refuge there," he said. "that's so. i've no great fancy for getting wet," said billy. "nor have i. we've had enough experiences of late to last us a long time," laughed jack. "and i was left out of every one of them," grumbled noddy. "for which you ought to be duly thankful," said billy. "yes, i didn't enjoy that stone house much, or the soot," declared jack. "that cave didn't make much of a hit with me, either," said billy. "my, those green eyes gave me a scare. i thought it was a bear or a mountain lion, sure; but they say there aren't any such animals in this part of the country." "abner said it must have been a lynx," said jack. "that being the case, you should have cuffed it," chuckled noddy. for the time being he escaped punishment for perpetrating this alleged pun, for the wind began to freshen and the _curlew_ slid through the water like a thing of life. the shore drew rapidly nearer. but the cloud curtain spread with astonishing rapidity, till the whole sky was covered. the water turned from green to a dull leaden hue. puffs of wind came with great velocity, heeling over the _curlew_ till the foam creamed in her lee scuppers. the wind moaned in a queer, eerie sort of way, that bespoke the coming of a storm of more than ordinary severity. jack was a prey to some anxiety as he held the _curlew_ on her course. if they could not make the dock he was aiming for before the storm struck, there might be serious consequences. but, to his great relief, they reached the wharf, a tumble-down affair, before the tempest broke. the _curlew_ was made "snug," and this had hardly been done before a mighty gust of wind, followed by a blanket of rain, tore through the air. "just in time, boys," said jack, as they set out on the run for the structure which they had observed from the water. on closer view it turned out to be nothing more than a barn, not in any too good repair, but still it offered a shelter. the boys reached it just as a terrific blast of wind swept across the bay, roughening it with multitudinous whitecaps. a torrent of rain blotted out distances at the same time and turned all the world in their vicinity into a driving white cloud. the barn proved to be even more rickety than its outside had indicated. the door was gone and its windows were broken out. but at least it was pleasanter under a roof than it would have been out in the open. the rain, driven by the furious wind, penetrated the rotten, sun-dried shingles and pattered on the earthen floor, but the boys found a dry place in one corner, where there was a pile of hay. as the storm increased in fury the clouds began to blot out the daylight. it grew as dark as night almost. the roar of the rain was like the voice of a giant cataract. "we may have to stay here all night," said billy, after a long silence. "that's true," rejoined jack. "it would be foolhardy to take a boat like the _curlew_ out in such a storm." suddenly there came a terrific flash of lightning, followed by a sharp clap of thunder. it was succeeded by flash after flash, in blinding succession. "my, this is certainly a snorter," exclaimed billy, and the others agreed with him. "we won't forget it in a hurry," said jack. "i can't recall when i've heard the wind make such a noise." to add to their alarm, as the fury of the wind increased, the old barn visibly quavered. it seemed to rock back and forth on its foundations. the noise of the wind grew so loud that conversation was presently impossible. suddenly there came a fiercer blast than any that had gone before. there was a ripping and rending sound. "great scott! boys, run for your lives, the old shack is tumbling down," cried jack. he had scarcely spoken when what he had anticipated happened. beams, boards and shingles flew in every direction. there was no time even to think. acting instinctively, each boy threw himself flat upon the pile of moldy hay. noddy, in his terror, burrowed deep into it. the noise that accompanied the dissolution of the old barn was terrific. each boy felt as if at any moment a huge beam might fall on him and crush his life out. above it all the wind howled with a note of triumph at its work of destruction. the boys felt as if the end of the world had come. chapter xxi. the end of jack's holiday. fortunately, otherwise this story might have had a different ending, the barn was lifted almost entirely from its foundations and hurled over on its side. the roof was ripped off like an old hat and hurtled through the tempest to the water's edge. none of the wreckage and dã©bris struck the crouching boys. but the mere sound was terrifying enough. even jack was cowed by the tremendous force of the elements. each lad felt as if the next moment would be his last. but at last jack mustered up courage and looked up. the beating rain, which had already soaked them all through, stung his face like hailstones. "hullo, fellows," he exclaimed, "is--is anybody hurt?" "all right here," rejoined billy. "but say, wasn't that the limit?" "it sure was," agreed jack. "at one time i thought we were goners, and----" "goo-oof-g-r-r-r-r-r!" an extraordinary sound, which can only be typographically rendered in this manner, suddenly interrupted him. "heavens, what's that?" gasped billy, looking about him in a rather alarmed manner. "ugh-ugh-groof-f-f-f-f-f-f!" "it's noddy!" cried jack. "gracious, he must be dying," gasped billy. in his eagerness to escape the full fury of the storm and the flying wreckage of the barn, noddy had plunged into the hay with his mouth open, and now his throat was full of the dry stuff. he was almost choked. "pull him out," directed jack, and he and billy laid hold of noddy's heels and dragged him out of the hay-pile. the lad was almost black in the face. "ug-gug-groo-o-o-o-o-o!" he mumbled, making frantic gestures with his arms. "goodness, this is as bad as the time he was almost drowned," cried jack. "clap him on the back good and hard. that's it." there were several gulps and struggles, and then noddy began to cough. but all danger from strangulation had passed, thanks to the heroic efforts of jack and billy. "phew! i thought i was choked," sputtered noddy, as soon as he found his voice. "i'd hate to be a horse and have to eat that stuff." "you are a kind of a horse," said billy slyly. "how do you make that out?" demanded noddy, falling into the trap. "a donkey," laughed billy teasingly, but poor noddy felt too badly after his experience in the hay to retaliate in kind. after the restoration of noddy, they began to survey the situation. all were soaked through, and the rain beat about them unmercifully. but they were thankful to have escaped with their lives. through the white curtain of rain they could make out the outlines of the _curlew_, riding at the dock. "i'm glad to see that," observed jack. "i was half afraid that she might have broken away." "then we _would_ have been in a fine fix," said billy. "what will we do next?" asked noddy, removing some fragments of hay from his ears. "wait till the clouds roll by," laughed billy. "i guess that's about the program, isn't it, jack?" "seems to be about all that there is to do," replied jack; "but it seems to me that the storm is beginning to let up even now. look in the northwest--it's beginning to get lighter." "so it is," agreed billy. "let's get under that clump of trees yonder till it blows over altogether." "say, fellows, if we had a fire now, it would feel pretty good," observed noddy. "well, what's the matter with having one?" asked jack. "we can get some of those old shingles and tarred posts. they're pretty wet, but we can start the blaze going with dried hay from the bottom of the pile." "good for you. volunteer firemen, get to work," cried billy. soon the boys were carrying the dry hay and such wood as seemed suitable for their purpose to the clump of trees. jack took some matches from his safe and struck a lucifer after the wood had been properly piled. it blazed up cheerily. each lad stripped to his underclothes and their drenched garments were hung in front of the hot fire. the dripping clothes sent up clouds of steam, but it was not long before they were dry enough to put on. by the time this was done the storm had abated. presently the rain, which did not bother the boys under the thick clump of trees, ceased altogether. only in the distance a dull muttering of thunder still went on. a rainbow appeared, delighting them with its brilliant colors. "well, that's over," observed jack, as he dressed. "now we'll go down and pump out the _curlew_. i'll bet she's half full of water." his conjecture proved correct. on their return to their trim little craft they found a foot or more of water in her hull. but this was soon disposed of and, with a brisk breeze favoring them, they set out once more for pine island. on their return they found captain toby, who had spied them from a distance, awaiting them on the dock. in his hand he held a yellow envelope. it was a telegram for jack. the boy eagerly tore it open, and for a moment, as he scanned its contents, his face fell. but almost instantly he brightened. "well, what's the news?" demanded his uncle. "good and bad," rejoined jack. "i guess our holiday is over. billy and i are ordered to join the _columbia_ as soon as we can." "hurrah! i was beginning to long for the sea again," declared billy raynor. "i must confess i was, too," said jack. "it's a great life for lads--makes men out of them," said captain toby. "i must see if i've got two bottles of the universal remedy for you boys to take to sea with you," and he hurried off. noddy looked rather blue. "you are lucky fellows--off for more adventures and fun," he said, "while i just stick around." "nonsense, you've got your business in new york to attend to, and, as for adventures, i've had plenty of them for a time, haven't you, billy?" "a jugful," declared raynor. "enough to last me for the rest of my life-time, and, anyhow, life at sea is mostly hard work." "that's what makes it worth living," said jack. "i'll be glad to get down to work again after our long holiday." "and i really believe i will, too," said billy; "and on a crack liner like the _columbia_ we may be able to make our marks." "i hope we will. i mean to work mighty hard, anyhow," said the young wireless man, "but hark, there goes the bell for supper. hurry up, fellows, i'll race you to the house." the next day was devoted to saying good-by to the scenes and the people who had helped make up a happy vacation for the lads. noddy, it was decided, would stay on with captain toby for the present, as his presence was not required in new york. of course the lads visited captain simms. he told them that his holiday also was almost over. the naval code was nearly completed, and he must get back to washington within a week or so. "well, here's to our next meeting," he said, as he heartily clasped the hands of both lads in farewell. under what circumstances that meeting was to occur none of them just then guessed. chapter xxii. "the gem of the ocean." the _columbia_, a magnificent and imposing vessel of more than 20,000 tons burden, lay at her new york dock two weeks later. within her steel sides, besides the usual cabin accommodations, she had swimming pools, roman courts, palm gardens and even a theater. elevators conveyed her passengers from deck to deck. the new vessel of the jukes shipping interests was the last word in shipbuilding, and from her stern flew the stars and stripes. it was sailing day. from the three immense black funnels smoke was rolling. steam issued, roaring from the escape pipes. the dock buzzed and fermented with a great crowd assembled to see their friends off on the first voyage of the great ship. wagons, taxicabs and autos blocked the street in front of the docks. photographers and reporters swarmed everywhere. the confusion was tremendous, yet, promptly at the hour set for sailing, the booming siren began to sound, last farewells were shouted, and the invariable late stayer on board made his wild leap for the gang-plank before it was drawn in. a perceptible vibration ran through the monster ship. her propellers began to churn the water white. a small fleet of tugs helped to swing her against the tide as she slowly backed into the stream. majestically her monster bulk swung round, her bow pointing seaward. her maiden voyage had begun. it is doubtful if among her delighted passengers and proud officers, however, there were any more enthusiastic about the great vessel than two lads who were seated in the wireless operators' cabin on the topmost deck. "well, billy, this is different from the old _ajax_, eh?" "is it? well, i should say so," responded billy. "you ought to see the engine-room. you could have put the _ajax_ in it, almost." "we ought to be proud of our jobs," continued jack. "i know i am. it's a great thing to be part of the human machinery of a huge vessel like this, and the best part of it is that she flies the american flag," added billy enthusiastically. "i heard that the _gigantia_, of the london line, sails to-day, too. by jove, there she comes now." he pointed out of the open door back up the river. the great british steamer, till then the biggest thing on the ocean, was backing out. her four red-and-black funnels loomed up imposingly above her black hull. "then we'll have a race for certain," said billy, his eyes dilating with excitement; "good for us, but my money goes on the _columbia_." "that britisher can travel, though," said jack. "oh, we won't have an easy time of it, but i'll bet my shirt we'll win the blue ribbon of the ocean." "i hope so," rejoined jack with a smile at the other's enthusiasm. "but what do you think of my quarters, billy?" "why, they're fit for a king or a millionaire," laughed raynor. "i'll bet you never thought, when you were in that little rabbit hutch of a wireless room on the old _ajax_, that some day you'd be traveling in such style?" raynor's eyes wandered to the instrument table, with its array of the most up-to-date wireless apparatus. "hullo! what's that thing?" he asked suddenly, pointing to a device that looked unfamiliar. it was a box-shaped arrangement, metal, with complicated wires strung to it and had a "telephone" receiver attached to it with a band to hold it securely to the operator's head. "oh, that's an invention of my own that i'm trying out," said jack. "i don't just know what success i'll have with it. i haven't really put it to the test yet." "what do you call it?" "the universal detector," replied jack. "just what is that?" "well, at present you know a ship can only receive wireless messages from a ship that is 'in tune' with her own radio apparatus. the universal detector should make it possible to catch every wireless sound. i am very anxious, if i perfect it, to get it adopted in the navy. it would be of great value in time of war, for by its use every message sent by an enemy, even if they were purposely put 'out of tune,' could be caught." "by the way, speaking of the navy, did you hear from captain simms?" "yes; he is still up at musky bay. some difficulties in the code have arisen, and he will not be through with his work for two weeks or more yet, he says." "no more attempts to steal his work, or to spy on him?" "he doesn't mention any. i guess we're through with the judson crowd." "looks that way. what a gang of thorough-paced rascals they were." "i guess judson's business must be in a bad way to make him take such desperate chances to recoup by landing that contract." "i suppose that's it." raynor lifted his eyes to the ship's clock above jack's operating instruments. "by jove, almost eight bells! i've got to go on watch. this is my first job as second engineer, and i mean to keep things on the jump. well, so long, old fellow." "see you this evening," said jack, as raynor hurried off. jack soon became very busy. the air was full of all sorts of messages. besides that, his cabin was crowded with men and women who wished to file last messages to those they left behind them. he worked steadily through the afternoon, catching meteorological radios as well as information from other steamers scattered along the atlantic lane. he knew that he might expect hard work and plenty of it all that day. there would be no chance for him to experiment with his universal detector. about dusk, harvey thurman, his assistant, came into the wireless room to relieve him while he went to dinner. thurman was a short, thick-set young man, with a flabby, pallid face and shifty eyes. he had got his job on the new liner through a "pull" that he possessed through a distant relationship with mr. jukes. jack had not met him before, and, since they had been on board, they had exchanged only a few words, but he instinctively felt that he and thurman were not going to make very good shipmates. as jack relinquished the head-receivers and the key to his "relief," thurman's gaze rested on the universal detector. "what's that?" he demanded. "oh, just a little idea i'm working on," said jack, "a new invention. if i can perfect it, it may be valuable." "yes, but what is it? what's it for?" persisted thurman. jack explained what he hoped to accomplish with the instrument, and an instant later was sorry he had done so, for he noticed an expression of cupidity creep into thurman's eyes. the youth persisted in asking a host of questions, and jack, having started to explain, could not very well refuse to answer. besides, inventors are notoriously garrulous about their brain children, and jack, even though he did not like thurman, soon found himself talking away at a great rate. "huh, i don't think the idea's worth a cent," sniffed thurman contemptuously, when jack had finished. "i guess that's where you and i differ," said jack, controlling his temper with some difficulty, for the sneer in thurman's voice had been marked. "i'm going to make it a success, and then we shall see." he left the wireless room, and the instant he was gone thurman, with a crafty look on his flabby face, eagerly began examining the detector. as he was doing so jack, who had forgotten his cap, suddenly reã«ntered the wireless room. thurman had been so intent on his scrutiny of the detector that he did not hear him. "you appear to be taking great interest in that useless invention," said jack in a quiet voice. thurman started and spun round. his face turned red and he had an almost guilty look. "i didn't think you were coming creeping back like that," he exclaimed, "a fellow would almost think you were spying on him." "have you any reason to fear being spied upon?" asked jack. "me? no, not the least. that's a funny question." "i want to tell you, thurman, that my invention is not yet completed and therefore, of course, is not patented. i was pretty free with you in describing it, and i shall trust to your honor not to talk about it to anyone." "certainly not," blustered thurman. "i'm not that sort of a chap." but, after jack had gone out, he resumed his study of the detector a second time, desisting every time he heard a step outside. "so it's not patented, eh?" he muttered to himself. "that will help. it's an idea there that ought to be worth a pot of money." chapter xxiii. jack's big secret. the next day jack found an opportunity to sandwich in some work on his invention between his regular work. the thing fascinated him, and he tried and tested it in a hundred different combinations. suddenly, just after he had altered two important units of the device, a new note came to his ears through the "watch-case" receivers that were clamped to his head. "it's code--somebody sending code!" exclaimed jack, and then the next instant, "it's some ship of the navy! hurrah! the detector is working, for they use different wave lengths from the commercial workers, and, if it hadn't been for the universal detector, i'd never have been able to listen in at their little talk-fest." he waited till the code message, a long one from washington to the _idaho_, of the north atlantic fleet at guantanamo, cuba, was finished, and then he could not refrain from "butting in." "hello, navy," he chattered with the wireless key, "that was a nice little message you had. how's the weather up your way?" "who is this?" demanded the navy wireless in imperious tones. "oh, just a fellow who was listening," responded jack. "butting in, you mean. but say, how did you ever get on to our sending? we were using eccentric wave-lengths to keep our talk a secret." "i'll have to keep how i caught your talk a secret, too, for the present, old man." "great scott! it isn't possible that you've solved the problem of a universal detector. why, that's a thing the navy sharps have been working on for years." "i can't say how i caught your message," shot back jack's radio through space. "you'll have to tell if the government gets after you," was the reply. "uncle sam isn't going to have a fellow running round loose with anything like that." "what do you mean?" "that you will be forbidden to use it." "is that so?" "yes, that's so. i'm going to make out a report for my superiors about it right now. you're pretty fresh." "put that in the report, too," chuckled the _columbia's_ wireless disdainfully. "you'll find it's no joke to monkey with the government," snapped back the naval man. jack didn't answer. a message from the _taurus_, of the bull line, was coming in. she had sighted an iceberg, something very unusual at that time of year. jack hurried the message, which gave latitude and longitude of the menace, to captain turner. "well, that won't bother us," said that dignitary. "we're far to the south of that. those bull fellows run to quebec. send a radio to captain spencer, of the _taurus_, thanking him for his information." the great man, the captain of a liner, who has literally more power than a king, lit a cigar, and bent his head once more over the problem in navigation he was wrestling with. jack saluted and hurried back to his quarters. he was highly elated over the success of his universal detector. the threats of the government man did not alarm him, for he did not propose to place his invention on the general market, but to sell it outright to the government, whose secret it would then remain. he resolved to test it again. a moment after he had put the receivers to his ears, a broad grin came over his face. the air was literally vibrant with the calls of the navy men, flinging their high-powered currents through space. "... he's a cheeky beggar, whoever he is, but he's got the goods," was the first he heard. "hum, that's mr. washington," thought jack. then, from some other point came another message. "great scott! uncle sam won't let him get away with anything like that." "i should say not. the secret service department is already at work trying to find out who the dickens he is." "that will be a sweet job," came the naval station at point judith. "talk about a needle in a haystack," sputtered the u. s. s. _alabama_. "not a patch on it," agreed the great dreadnought _florida_. then came washington again. "i'll tell you it's stirred up a fuss here," he said. "i wonder who it can be." "maybe that italian fellow who invented the sliding sounder," suggested the _florida_. "or pederson, out in chicago," came from a land station. all the navy men appeared to be joining in the confab. "gracious, what a fuss i've stirred up," thought jack, with a quiet smile. "they'd never guess in a million years that it's a kid of an operator who's causing all the trouble." "no; both the men you mentioned are in europe," declared washington. "the department's been trailing them since they got my news." "well, the wireless men are going to be a happy hunting ground for the secret service fellows for this one little while," chuckled the _florida_. "wonder if he's listening now?" struck in the _north dakota_, which had not yet talked. "shouldn't wonder," remarked the _idaho_. jack pressed down his key and the spark began to flash and crackle. "you fellows are having a grand old pow-wow," he said. "sorry i can't give you any information. i know you're dying of curiosity." "you've got your nerve, i must say," sputtered washington indignantly. "have you been listening right along?" "yes; that secret service hunt is going to be very interesting." "it won't be very interesting for you, whoever you are, when they get you," thundered the mighty _florida_. "it's bad business monkeying with uncle sam." "maybe they won't get me," suggested jack's spark. "oh, yes, they will," came from washington, "and you'll find it doesn't pay to be as sassy as you've been." "m-m-m," sent out jack mischievously. the three letters mean, in telegraphers' and wireless men's language, "laughter." washington's dignity took fire at this gross insult. they must have sizzled as from the national capital an angry message shot out to the other ships to talk in code. jack's fun was over, but he had thoroughly enjoyed all the excitement he had stirred up. as he laid down the receivers raynor came in. "you look tickled to death over something," he exclaimed. "what's up?" jack sprang to his feet. his eyes were shining. he clasped raynor's hand and wrung it pump-handle fashion. raynor looked at the usually quiet, rather self-contained lad, in blank astonishment. "what's happened--somebody wirelessed you that you're heir to a million?" he demanded. "no, better than that, billy." "great scott! tell me." "billy, old boy, it works. it works like a charm. i've got half the navy all snarled up about it now. by to-morrow they'll be after me with secret service men." "gee whillakers. you've done the trick! good for you, old boy." a sudden shadow in the open door made them both look round. thurman stood in the embrasure. "may i add my congratulations?" he said, holding out his hand. chapter xxiv. the navy department "sits up." jack could not refuse the proffered hand. but he took it with an uneasy air. there was something not quite "straight" about thurman, it seemed to jack, but as the former offered his congratulations he appeared sincere enough. "after all, it may be just his misfortune that he can't look you in the eyes," jack told himself. but if he had been in the wireless room that night he would have deemed his suspicions only too well founded. thurman busied himself with routine matters till he was sure jack was asleep. then he began calling washington with monotonous regularity. an irritable operator answered him. by the wave length the washington man knew that it was not a naval station or vessel calling. "yes--yes--what--is--it?" he snapped. "i know the fellow who has that universal detector." "what!" the other man, hundreds of miles away, almost fell out of his chair. recovering himself, he shot out another message: "who is this?" "never mind that, just for the present." "say, you're not that fresh fellow himself talking just to kid us, are you?" "no, i'm far from joking. i expect to make some money out of this." "a reward?" "that's the idea." "well, there's no doubt but you would get it if you really have the information. the department's been all up in the air ever since that fellow butted in." "are you going to report this conversation?" "most assuredly." "don't forget that i demand a substantial reward for the information." "i won't. when will you call me again?" "about this time to-morrow night." "all right, then. good-by." thurman took the receiver from his head with a slow smile of satisfaction. "i guess that will cook that fresh kid's goose," he said. "it's a mean thing to do, maybe, but i need the money, and i'm glad to get a chance to set him down a peg or two." thurman could hardly wait for the next night to come. during the day jack had been having some more fun with the navy men, driving them almost wild. when thurman finally got washington, therefore, everything in the government's big wireless station was at fever heat. a high official of the navy sat by the operator, waiting for thurman's promised call to come out of space. men of the secret service were scattered about the room as well as department officials. the air was tense with expectancy. at last thurman's message came. his first question was about the reward. "tell him he will be liberally rewarded," ordered the naval official. "tell him to give us the information at once. that fellow has been playing with us all day, and we've been powerless to outwit the universal detector, or whatever device it is he uses. the man must be a wizard to have solved a problem that has baffled the keenest minds in the navy bureau." "reward is assured you," flashed back the naval operator. "now give us your information. time is precious." but thurman's answer proved disappointing to those in the room. "impossible to do so now. inventor is on the high seas. will wireless you later when he will return." "confound it," grumbled the naval official. "i thought we would have had our hands on the fellow before daylight. now it seems we shall have to play a waiting game." "if the man is on the high seas, it is not unlikely that he is the wireless man on one of the liners," put in burns, a spare, grizzled man and chief of the secret service. "that's probable, burns," rejoined the navy official. "more than likely, i think," put in another member of the group, "but it's impossible to find out which one." "yes, we are at the mercy of our unknown informant," said burns. "why the deuce was he so mysterious about it?" he tugged at his gray mustache as a sudden thought struck him. "jove!" he exclaimed. "you don't think it's a put-up job to get money out of the government? put up, i mean, by an agent of the inventor himself." "i don't know, burns," was the official's reply. "it's all mighty mysterious. i confess i can't hazard a guess as to the man's identity. we've looked up all the most prominent wireless sharps all over the country. i am satisfied this fellow is not one of their number." "some obscure fellow, i guess," said a secret service man. "well, he won't remain obscure long," remarked burns, "if he has brains enough to turn the navy department topsy-turvy for forty-eight hours." chapter xxv. a mystery on board. two days later the monotony of the voyage, which was broken only by the radiograms which were posted daily concerning the race between the american and british liners--the _columbia_ being in the lead--was rudely shattered by an incident in which jack was destined to play an important part. jack had been on a visit to raynor during the young engineer's night watch in the engine-room. they had stayed chatting and talking over old times till jack suddenly realized that it was long after midnight and time for him to be in his bunk. hastily saying good-night, he made his way through the deserted corridors of the great ship, which stretched empty and dimly lit before him. as he traversed them the young wireless man could not but think of the contrast to the busy life of the day when stewards swarmed and passengers hurried to and fro. now everything was silent and deserted, except for the still figures up on the bridge and below in the engine and fire rooms, guiding and powering the great vessel onward through the night at a twenty-four-knot clip. the lad had just reached the end of one corridor, and was about to turn into another which led to a companionway, which would bring him to his own domain, when he stopped short, startled by the sound of a single sharp outcry. it came from the corridor he was about to turn into. jack darted round the corner and almost instantly stumbled over the huddled body of a man lying outside one of the cabin doors. a dark stain was under his head, and jack saw at once that the man had been the victim of an attack. at almost the same moment, by the dim light, he recognized the unconscious form as being that of joseph rosenstein, a diamond merchant, so wealthy and famous that he had been pointed out to jack by the purser as a celebrity. "queer fellow," the purser had said. "won't put his jewels in the safe, although i understand he is carrying three magnificent diamonds with him. likely to get into trouble if anyone on board knows about it." "he's taking big chances," agreed jack, and now here was the proof of his words lying at the boy's feet. suddenly he recalled having received a message a few days before from new york for the injured man. "be very careful. f. is on board," it had read, and jack interpreted this to be meant as a warning to the diamond merchant. but he did not devote much attention to it just then, except to rouse the sleepy stewards. within a few minutes the captain and the doctor were on the scene. "a nasty cut, done with a blackjack or a club," opined dr. browning, as he raised the man. "is it a mortal wound?" asked the captain. "this is a terrible thing to have happen on my ship." "i think he'll pull through if no complications set in," said the doctor, and ordered the man removed to his cabin. suddenly jack recollected what the purser had said about the diamonds. "i beg your pardon, sir," said he to the captain, "but i heard that this man carried about valuable diamonds with him. he was probably attacked for purposes of robbery." "that's right," answered the captain, with a quick look of approval at jack. "browning, we'd better examine the contents of his pockets." they did so, but no traces of precious stones could be found. "whoever did this, robbed him," declared the captain, with a somber brow, "and the deuce of it is that, unless we can detect him, he will walk ashore at southampton or cherbourg a free man." the door of the stateroom opposite to which the injured man lay opened suddenly, and a little, wizen-faced man, wearing spectacles, looked out. he appeared startled and shocked as he saw the limp form. "good gracious! this is terrible, terrible, captain," he sputtered. "is--is the man dead?" "no, professor dusenberry, although that does not appear to be the fault of whoever attacked him," was the rejoinder. "he was attacked, then, for purposes of robbery, do you think?" "i suspect so." "oh, dear, this has so upset me that i shan't sleep the rest of the night," protested the little man, and withdrew into his stateroom. the next day, naturally, the whole ship buzzed with the news of the night's happenings, and speculation ran rife as to who could have attacked the diamond merchant, who had recovered consciousness and was able to talk. he himself had not the slightest idea of his assailant. he had sat up till late in the smoking saloon, he said, and was coming along the corridor to his stateroom when he was struck down from behind. a black leather wallet, containing three diamonds, which were destined to be sold to the scion of a european royal house, was missing from his pocket, and the loss nearly drove the unfortunate diamond man frantic. he valued the stones at $150,000, so that perhaps his frenzy at losing them was not unnatural. in the afternoon, professor dusenberry, dressed in a frock coat and top hat, although he was at sea and the weather was warm, came into the wireless room. he wanted to send a message, he said, a wireless to london. he was very cautious about inquiring the price and all the details before he sat down to write out his dispatch. when it was completed he handed it to jack with his thin fingers, and asked that it be dispatched at once. then he retreated, or rather faded, from the wireless room. jack scanned the message with thoughtful eyes. it seemed an odd radiogram for a college professor, such as he had heard prof. dusenberry was, to be sending. it read as follows: "meet me at three on the granite paving-stones. the weather is fine, but got no specimens. there is no suspicion as you have directed, but i'm afraid wrong." f. "well, that's a fine muddle for somebody to make out when they get it," mused jack, as he sent out a call for the fowey station. "must be some sort of a cipher the old fellow is using. he's a dry sort of old stick. goodness! how scared he was when he saw that man lying outside his door. i thought he was going to faint or something." "wonder what sort of a cipher that is," mused jack, as he waited for an answer to his call. "looks to me as if it's one of those numerical ciphers where every second or third or fourth or fifth word is taken from the context and composes a message. guess i'll try and work it out some time. it'll be something to do. and, hullo, he signs himself 'f'." jack looked up at the printed passenger-list that hung before him. "professor f. dusenberry" was the last of the "d's" "his initial," thought jack, "but it's a funny coincidence that it should be the same as that of the man the diamond merchant was warned to watch out for, and that it should have been the professor's door outside of which he was struck down." chapter xxvi. a "flash" of distress. having dispatched the message, jack sat back in his chair and mused over the future of the universal detector. it was a fascinating subject to day-dream over, but his reverie was rudely interrupted by a sharp summons from space. "yes--yes--yes," he shot back, "who--is--it?" "this is the _oriana_," came back the reply, "hamburg for new york. we are in distress." "what's the trouble?" the spark crackled and writhed, as jack's rapid fingers spelled out the message. "we struck a half submerged derelict and our bow is stove in. we believe we are sinking. this is an s. o. s." then followed the position of the craft and another earnest appeal to rush to her aid. jack roughly figured out the distances that separated the two ships. "will be there in about two hours," he flashed, and then hurried to captain turner's cabin with his message. the captain scanned the message with contracted brow. "the _oriana_," he muttered, "i know her well. rotten old tramp. we must have full speed ahead. stand by your wireless, ready, and tell them we are rushing at top speed to their aid. confound it, though," he went on, half to himself, "this will lose us the race with the britisher, but still if we can save the lives of those poor devils i shall be just as well satisfied." the captain hastened to the bridge to issue his orders and change the big ship's course. jack went quickly back to his cabin and began flashing out messages of good cheer. about half an hour later captain turner came along. "any more news, ready?" he asked. "no, sir. their current is getting weak. the last time i had them the operator said that the ship was slowly settling, but that they had the steam pumps going and would keep them working till the water reached the fires. the officers were keeping the firemen at their work with revolvers." "i've been through such scenes," remarked the captain. "it's part of a seaman's life, but it's an inferno while it lasts." "notify me if you hear anything further," said captain turner a few moments later. "yes, sir. hullo, here's something coming now. it's the _borovian_, of the black star line. she got that s. o. s. too, and is hurrying to the rescue. but she's far to the south of us." "yes, we shall reach the _oriana_ long before she does," said the captain. "by the way, ready, i've heard that you have quite a reputation for loving adventure." jack colored. he did not quite make out what the captain was "driving at," as the saying is. "i do like action, yes, sir," he replied. "well, then," said captain turner, "you've got a little excitement due to you for your prompt action last night in the case of the assault on that diamond merchant. if you want to go on the boats to the _oriana_, you may do so. get thurman to stand by the wireless while you're gone. you can make the time up to him on some other occasion." jack's eyes danced. he could hardly express his thanks at the opportunity for a break in the rather monotonous life on shipboard. but the captain had turned on his heel as he finished his speech and left the grateful lad alone. thurman was sleeping when jack roused him. when he learned that jack was to make one of the boat parties and that he (thurman) was to remain on duty, the second wireless man's temper flared up. "that's a fine thing, i must say," he growled. "you're to go on a junket while i do your work. i won't stand for it." "pshaw, thurman," said jack pacifically. "i'll do the same for you at any time you say. besides, i heard you say once you wouldn't like to go in the small boats." "think i'm afraid, eh?" "i said no such thing," retorted jack, "i----" "i don't care, you thought it. i'll complain to captain turner." "i would not advise you to." "keep your advice to yourself. i've got pull enough to have you fired." "this line treats its employees too fairly for any such claim as a 'pull' to be advanced." "you think so, eh? well, i'll show you. you've been acting like a swelled head all the way over, ready," said thurman, forgetting all bounds in his anger. "i'll find a way to fix you----" "say, you talk like an angry kid who's been put out of a ball game," said jack. "i hope you get over it by the time you come on duty." an angry snarl was thurman's only rejoinder as jack left the wireless operator's sleeping quarters. but the next instant all thought of thurman was put out of his mind. the lookout had reported from the crow's-nest. on the far horizon a mighty cloud of dark smoke was rising and spreading. before many moments had passed it was known that fire--that greatest of sea perils--had been added to the sinking _oriana's_ troubles. as the news spread through the ship the passengers thronged to the rails. suppressed excitement ran wild among them. even jack found himself unable to stay still as he thought of the lives in peril under that far-off smoke pall. all communication with the stricken ship had ceased, and jack knew that things must have reached a crisis for her crew. then came an order to cast loose four boats, two on the port and two on the starboard side. officers and men obeyed with a will. by the time they were ready to be dropped overside, the outlines of the burning steamer were plainly visible. she looked very low in the water. from her midships section smoke, in immense black clouds, was pouring. but to jack's surprise no boats surrounded her, as he had expected would be the case. instead, on her stern, an old-fashioned, high-raised one, he could make out, through his glasses, a huddled mass of human figures. suddenly one figure detached itself from the rest and jack saw a pistol raised and aimed at the lower deck. spurts of smoke from the weapon followed. thrilled, jack was about to report what he had seen to the bridge when the third officer, a young man named billings, came up to him. "you're in my boat," he said. "cut along." chapter xxvii. a strange wreck. "well, boys, we got here just in time," observed mr. billings, as the boat cut through the water. "i'm not so sure that we have arrived in time to avert a tragedy," said jack, and he told of the shooting that he had witnessed. "probably a mutiny," said mr. billings, with the voice of experience. "the crews on those old tramps are the riff-raff of a hundred ports. bad men to handle in an emergency." he had hardly finished speaking when, borne toward them on the wind, which was setting from the burning, sinking ship, came a most appalling uproar. it sounded like the shrieks of hundreds of passing souls mingled with deep roars and screeches. even mr. billings turned a shade paler under his tan. "in the name of heaven what was that?" he exclaimed. as he spoke a huge tawny form was seen to climb upon the rail of the rusty old steamer and then launch itself into the sea with a mighty roar. "a lion!" exclaimed jack, "by all that's wonderful, a lion." "that explains the mystery of those noises and the predicament of those poor fellows crowded on the stern away from the boats," said mr. billings, who had quite regained his self-possession. "but--but i don't understand," said jack. "that ship has a cargo of wild animals on board," explained mr. billings. "such shipments are regularly made from hamburg, her hailing port, to america. most probably she had lions, tigers, leopards, great serpents and other animals on board. when her bow was stove in a number of cages were smashed and the wild beasts escaped." "that accounts for the shooting i saw, then," exclaimed jack; "they must have been firing from the raised stern at the animals which menaced them on the main deck." "unquestionably. i am glad i brought my own shooting iron," said mr. billings. "i packed it along in case we had trouble with a mutinous crew." they were now close to the blazing ship. the heat and odor of the flames were clearly felt. "we'll have to pull around on the weather side," decided mr. brown. "if we come up under the wind, we'd all be scorched before we could effect any rescues. "pull round the stern, my lads," he ordered. "aye, aye, sir," came in a deep-throated chorus from the crew. as the four boats made under the stern, white, anxious faces looked down on them. "thank heaven you've come!" exclaimed the captain, whose haggard countenance showed all that he had been through. "we're just about at our last ditch. the animals we were taking from jamrachs, in hamburg, for an american circus, broke loose after the collision with the derelict. they've killed two of my men and maimed another." "all right, my hearties, just hold on a minute and we'll have you out of that," exclaimed mr. billings cheerfully. more roars and screeches from the loosened animals checked him. then came more shots, telling of an attack on the stern, the only cool part of the ship left, which had been repulsed. the flames shot up, seeming to reach to the sky, and the smoke blotted out the sun, enveloping everything in the burning ship's vicinity in a sort of twilight. "do you think we'll be able to get all of them off?" asked jack eagerly. "i'm in hopes that we will," said mr. billings, "if nothing untoward happens." there was, jack noticed, a shade of anxiety in the young officer's tone. there was, then, some peril, of which he knew nothing as yet, attached to the enterprise, thought jack. but of the nature of the danger he had no guess till later. as the first boat, mr. billings' craft, drew alongside the blistering side of the burning ship, a jacob's ladder came snaking down from the stern. at almost the same moment jack, who had been looking upward, uttered a shout of alarm. the fierce face of a wild beast had suddenly appeared above the rail of the blazing _oriana_. the next instant a great lithe, striped body streaked through the air straight for the boat. instinctively jack, who saw the huge form of the tiger, for that was the desperate flame-maddened creature that had made the jump, sprang for the side of the boat and dived overboard. [illustration: the next instant a great lithe, striped body streaked through the air.--] he was not a second too soon. the tiger struck the side of the boat in the stern just where jack had been sitting a fragment of a minute before. the boat heeled over as the great beast, mad with terror, clawed at its sides with its fore-paws and endeavored to climb in. mr. billings, pale but firm, whipped out his revolver with an untrembling hand while the men, utterly unnerved, dropped their oars and shouted with alarm. bang! the tiger gave a struggle that almost capsized the boat. then, suddenly, its claws relaxed their hold and it slid into the water, limp and lifeless, shot between the eyes. but where was jack? the question just occurred to mr. billings when, looking up suddenly, he saw something that made him yell a swift order at the top of his lungs. "row for your lives, men, row. she's going to blow up!" chapter xxviii. cast away with a python. when jack dived overboard he was so unnerved by the sudden apparition of the fear-frenzied tiger that he rose some distance back of the boat. he came to the surface just in time to see the slaying of the animal and hear mr. billings' sharp cry of warning. before he could attract attention the boats were all pulling at top speed from the burning ship. "she's going to blow up!" the words etched themselves on jack's brain with the rapidity of a photographic plate. he saw a convulsive tremor shake the big steel fabric and the despairing shouts of the men in the stern rang in his ears. at the same moment he dived and began swimming with all his strength away from the doomed ship. suddenly came a shock that even under water seemed to drive his ear-drums in. then he felt himself seized as if in a giant's grip and dragged down, down, down. his vision grew scarlet. his heart beat as if it must burst from his frame and his entire body felt as if it was being cruelly compressed in a monster vise. jack knew what had occurred: the boilers of the _oriana_ had blown up and he was being carried down by the suction of the hull as it sank. just as he felt that he could no longer endure the strain, the dragging sensation ceased. like a stone from a catapult jack was projected up again to the surface of the sea. the sky, the ocean, everything burned red as flame as he regained the blessed air and sucked it in in great lungfulls. for a moment or so he was actually unconscious. then, as his normal functions returned, and his sight grew less blurred, he made out a hatch floating not far from him. he struck out for this and clambered upon it. the sea was strewn with the wreckage of the explosion. beams, skylights, even charred and blistered metal liferafts floated all about him. but these did not engross jack's attention for long after he had cast his gaze in the direction where the _oriana_ last lay. there he encountered an extraordinary sight. on the surface of the ocean floated the stern section of the sunken steamer. to it still clung the occupants that he had last seen there. jack rubbed his eyes and looked and looked again. yes, there was no doubt about it, the after part of the _oriana_ was still afloat, although how long it would remain so it was impossible to say. jack guessed, and as it afterward transpired, guessed correctly, that the watertight bulkhead doors, which had automatically been closed all over the ship when the collision occurred, were sustaining the stern fragment of the ship on the surface. this part of the _oriana_, unharmed by the explosion or the collision, was now floating much as a corked bottle might be expected to do, excepting, of course, that there was a marked list to the drifting fragment.[1] [footnote 1: the after part of the ill-fated tank steamer _oregon_, sunk 100 miles off sandy hook, in 1913, when, during a severe storm, she broke in two, floated with the survivors in exactly the manner described in the _oriana's_ case.--author's note.] jack now saw the scattered boats returning to the scene. the man in command of each was urging the crews on with voice and gesture. not one had been harmed, but it was a narrow escape. jack set up a shout, but apparently, in the excitement of racing for the floating stern part of the _oriana_, he was unnoticed. however, this did not alarm him, for he was sure of being able to attract attention before long. a sudden lurch of the hatchway on which he was drifting, and the sound of a slithering motion as of some heavy body being dragged along some rough surface, made him turn his head. what he saw made him almost lose his grip on the hatchway. [illustration: what he saw made him almost lose his grip on the hatchway.] the hideous flat head and wicked eyes of a huge python faced him. the great snake, escaping somehow from the catastrophe to the menagerie ship, had swum for the same refuge jack had chosen. now it was dragging its brilliantly mottled body, as thick as a man's thigh, up upon the hatchway. the floating "raft" dipped under the great snake's weight, while jack, literally petrified with horror, watched without motion or outcry. but apparently the snake was too badly stunned by the explosion to be inclined for mischief. it coiled its great body compactly in gay-colored folds on the hatch and lay still. but jack noticed that its mottled eyes never left his figure. "gracious, i can't stand this much longer," thought jack. he looked about him for another bit of wreckage to which he might swim and be free of his unpleasant neighbor. but the dã©bris had all drifted far apart by this time and his limbs felt too stiffened by his involuntary dive to the depths of the ocean for him to attempt a long swim. not far off he could see the boats busily transferring the castaways of the _oriana_ on board. supposing they pulled away from the scene without seeing him? undoubtedly, they deemed him lost and would not make a search for him. warmly as the sun beat down, jack felt a chill that turned his blood to ice-water run over him at the thought. left to drift on the broad atlantic with a serpent for a companion and without a weapon with which to defend himself. the thought was maddening and he resolutely put it from him. so far the great snake had lain somnolently, but now, as the sun began to warm its body, jack saw the brilliantly colored folds begin to writhe and move. it suddenly appeared to become aware of him and raised its flat, spade-shaped head above its coils. its tongue darted in and out of its red mouth viciously. jack became conscious of a strong smell of musk, the characteristic odor of serpents. his mouth went dry with fear, although he was naturally a brave lad, as we know. a dreadful fascination seemed to hold him in thrall. he could not have moved a muscle if his life, as he believed it did, depended on his escape. the hideous head began to sway rhythmically in a sort of dance. still jack could not take his eyes from that swaying head and darting red tongue. a species of hypnotic spell fell over him. he heard nothing and saw nothing but the swaying snake. all at once the head shot forward. with a wild yell jack, out of his trance at last, fell backward off the hatch into the water. at the same instant mr. billings' pistol spoke. again and again he fired it till the great snake's threshing form lay still in death. unwilling to give jack up for lost, although he feared in his heart that this was the case, the third officer would not leave the scene till all hope was exhausted. sweeping the vicinity with his glasses, he had spied the impending tragedy on the hatch. full speed had been made to the rescue at once and, as we know, aid arrived in the nick of time. as jack rose sputtering to the surface strong hands pulled him into the boat. he was told what had happened. "a narrow escape," said mr. billings, beside whom sat captain sanders of the lost steamer. he looked the picture of woe. "i owe my life to you, mr. billings," burst out jack, holding out his hand. the seaman took it in his rough brown palm. "that's all right, my lad," he said. "maybe you'll do as much for me some day." and then, as if ashamed even of this display of emotion, he bawled out in his roughest voice: "give way there, bullies! don't sit dreaming! bend your backs!" as the boats flew back toward where the great bulk of the _columbia_, her rails lined with eager passengers, rested immobile on the surface of the ocean, the castaway captain turned a glance backward to the stern of his ship, which was still floating but settling and sinking fast. it was easy to guess what his thoughts were. "that's one of the tragedies of the sea," thought jack. chapter xxix. captured by radio. it was two days later and they were nearing southampton, but the stop they had made to aid the _oriana's_ crew had given the britisher a big lead on them. the passengers eagerly clustered to read jack's wireless bulletin from the other ship which was posted every day. excitement ran high. jack had seen no more of professor dusenberry, but he had spent a good deal of leisure time pondering over the code message the queer little dried up man had sent. raynor, who had quite a genius for such things, and spent much time solving the puzzles in magazines and periodicals, helped him. but they did not make much progress. suddenly, however, the night before they were due to reach southampton, jack was sitting staring at the message when, without warning, as such things sometimes will, the real sense of the message leaped at him from the page. "meet me at _three_ on the paving _stones_, the weather is _fine_ but got no _specimens_, there is no _suspicion_ as you have _directed_ but i'm afraid _wrong_." taking every fourth word from the dispatch then, it read as follows: "three stones. fine specimens. suspicion directed wrong." jack sat staring like one bewitched as the amazingly simple cipher revealed itself in a flash after his hours of study. granted he had struck the right solution, the message was illuminating enough. professor dusenberry was a dangerous crook, instead of the harmless old "crank" the passengers had taken him for, and his cipher message was to a confederate. but on second thought jack was inclined to believe that it was merely a coincidence that placing together every fourth word of the jumbled message made a dispatch having a perfectly understandable bearing on the jewel theft. it was impossible to believe that professor dusenberry, mild and self-effacing, could have had a hand in the attack on the diamond merchant. jack was sorely perplexed. he was still puzzling over the matter when the object of his thoughts appeared in his usual timid manner. he wished to send another dispatch, he said. while he wrote it out jack studied the mild, almost benevolent features of the man known as prof. dusenberry. "but there's one test," he thought to himself. "if the 'fourth word' test applies to this dispatch also, the professor is a criminal, of a dangerous type, in disguise. but he contrived to glance carelessly over the dispatch when the professor handed it to him and fumbled in his pocket for a wallet with which to pay for it. not till the seemingly mild old man had shuffled out did jack apply his test to it. the message read as follows: "_columbia_ fast as motor-boat, watch her in southampton. am well and will no more time throw away on fake life-preserver." f. with fingers that actually trembled, jack wrote down every fourth word. here is the result he obtained: "motorboat southampton. will throw life-preserver." "by the great horn-spoon," exclaimed jack to himself, "it worked out like a charm. but still, what am i going to do? i can't go to the captain with no more evidence than this. he would not order the man detained. i have it!" he cried, after a moment of deep reflection. "the southampton detectives have been already wirelessed about the crime and are going to board the ship. i'll flash them another message, telling them of the plan to drop the jewels overboard in a life-preserver so that they will float till the motor-boat picks them up." jack first, however, sent the supposed prof. dusenberry's message through to london, with which he was now in touch. he noted it was to the same address as before, that of a mr. jeremy pottler, 38 south totting road, w. then he summoned the southampton station, and, before long, a messenger brought to the police authorities there a dispatch that caused a great deal of excitement. he had just finished doing this when jack's attention was attracted by the re-entrance of the professor. he wanted to look over the dispatch he had sent again, he said, but jack noticed that his eyes, singularly keen behind his spectacles, swept the table swiftly as if in search of something. the abstract that jack had made of the cipher dispatch lay in plain view. jack hastily swept it out of sight by an apparently careless movement. but he felt the professor's eyes fixed on him keenly. but if prof. dusenberry had observed anything he said nothing. he merely remarked that the dispatch appeared to be all right and walked out again in his peculiar shambling way. "the old fox suspects something," thought jack. "i wonder if he saw that little translation i took the liberty of making of his dispatch. if he did, he must have known that i smelled a rat." just then raynor dropped in on his way on watch. "well, we're in to-morrow, jack," he said, "but i'm afraid the britisher will beat us out." "i'm afraid so, too," responded jack. "their operator has been crowing over me all day. but at any rate it was in a good cause." "yes, and they're taking up a subscription for the shipwrecked men at the concert to-night, i hear, so that they won't land destitute." "that's good; but say, bill, you're off watch to-morrow and i want you to do something for me." "anything you say." "this may involve danger." "great scott, you talk like sherlock holmes or a dime novel. what's up?" "i've got the man who stole those diamonds." "what!" "don't talk so loud. i mean what i say. listen." and jack related everything that had occurred. "now, what i want you to do is to watch prof. dusenberry, as he calls himself, to-morrow when we get into the harbor. his is an inside stateroom so that he can't throw it out of a porthole from there. he'll most likely go to one at the end of a passage." "yes, and then what?" "i'd do it myself but the old fox suspects me, i half fancy, and if he saw me in the vicinity he'd change his plans. you'd better take two of your huskiest firemen with you, billy. he's an ugly customer, i fancy, and might put up a bad fight." "u-m-m-m, some job," mused billy. "why don't you put the whole thing up to the captain?" "it would do no good the way things are now, and he might get wind of it and hide the jewels so that they couldn't be found. anyhow, we've no proof against him till he is actually caught throwing the jewels out in that life-preserver to his confederates in the motor-boat." "i see, you want to catch him red-handed, but what about those cipher radios?" "there's no way of proving that i read the cipher right," said jack. "our only way is to do as i suggested." "i hear that rosenstein has offered a big reward for the recovery of the diamonds," said billy. "he's up and about again, you know." "well, billy, i think he'll have his diamonds back by to-morrow noon if we follow out my plan." and so it was arranged. the next morning jack received a message from southampton: "all ready. does our man suspect anything?" this was jack's answer: "not so far as i know. have a plan to catch him red-handed. you watch the motor-boat." saluted by the whistles of a hundred water craft, the _columbia_ made stately progress into southampton harbor. as her leviathan bulk moved majestically along under reduced speed, her whistles blowing and her flag dipping in acknowledgment of the greeting, jack with a beating heart, stood on the upper deck watching earnestly for developments. he knew that billy and the two firemen he had selected to help him, on what might prove a dangerous job, were below watching prof. dusenberry. they all wore stewards' uniforms so that the man who jack believed struck down the diamond merchant and stole the stones might not get suspicious at seeing them about in the corridors. "i believe they must have changed their plans, after all," jack was thinking when, from the shore, there shot out, at tremendous speed, a sharp-bowed, swift motor-boat. it headed straight for the _columbia_. as it drew closer, jack saw it held two men. both were blowing a whistle, waving flags and pointing at the big ship as if they, like many other small water craft, were just out to get a glimpse of the triumph of american shipbuilders. they maneuvered close alongside, while jack's fingers grasped the rail till the paint flaked off under the pressure he exerted in his excitement. what was happening below? he wondered. could billy and his companions carry out their part of the program? not far from the boy the diamond merchant, unconscious of the drama being enacted on his account, stood, with bandaged head, explaining for the hundredth time the beauty and the value of the gems he had lost. "five thousand thalers i give if i get them back," he declared. suddenly jack's heart gave a bound. from a port far down on the side of the ship, and almost directly under him, a white object was hurled. it struck the water with a splash and spread out, floating buoyantly. instantly the black motor-boat darted forward, one of the men on board holding a boat hook extended to grasp the floating life-preserver, hidden in which was a king's fortune in gems. jack stood still just one instant. then, driven by an impulse he could not explain, he threw off his coat, kicked off the loose slippers he wore when at work, and the next moment he had mounted the rail and made a clean, swift dive for the life-preserver. billy rushed on deck, excitement written on his face, just as jack dived overboard. "jack! jack!" he shouted. but he was too late. "great neptune, has the boy gone mad?" exclaimed captain turner, who had passed along the deck just in time to see jack's dive. regardless of sea etiquette, billy grasped the skipper's arm and rushed into a narrative of the plan he and jack had hoped to carry out. "but dusenberry was too quick for us, sir," he concluded. "never mind that, now," cried the captain, "that boy may be in danger." he looked over the rail, which, owing to most of the passengers being busy below with their preparations for landing, was almost deserted. billy was at his side. in the black motor-boat two men stood with their hands up. alongside was a speedy-looking launch full of strapping big men with firm jaws and the unmistakable stamp of detectives the world over. some of them were hauling on board the police launch jack's dripping figure, which clung fast to the life-preserver. others kept the men in the black launch covered with their pistols. half an hour later, when the passengers--all that is but mr. rosenstein--had gone ashore (the diamond merchant had been asked by the captain to remain), a little group was assembled in captain turner's cabin. in the center of it stood professor dusenberry, alias foxy fred, looking ever more meek and mild than usual. he had been seized and bound by the two disguised firemen as he threw the life-preserver, but not in time to prevent his getting it out of the port. beside him, also manacled, were the two men who had been in the motor-boat and who, according to the southampton police, formed a trio of the most daring diamond thieves who ever operated. "i think we may send for mr. rosenstein now," said captain turner with a smile. "only i hope that he is not subject to attacks of heart failure. ready," he said, turning to jack, who stood side by side with billy, "take these and give them to mr. rosenstein with your compliments." jack blushed and hesitated. "i'd,--i'd rather--sir--if you--don't mind----" he stammered. "you may regard what i just said as an order if you like," said captain turner, trying to look grim, while everybody else, but jack and the prisoners, smiled. "you wanted to see me on important business, captain?" asked mr. rosenstein, as he entered. "you will keep me as short a time as possible, please. i must get to scotland yard, my diamonds----" "are right here in this boy's hand," said the captain, pushing jack forward. "what! this is the fellow who took them?" thundered the diamond merchant. "no; this is the lad you have to thank for recovering them for you from those three men yonder," said the captain. "professor dusenberry!" exclaimed the diamond expert, throwing up his hand. "or foxy fred," grinned one of the english detectives. "oh, my head, it goes round," exclaimed mr. rosenstein. "this lad, with wonderful ingenuity, and finally courage, when he leaped overboard to save your property, traced the guilty parties," went on the captain, "and by wireless arranged for their capture." "it's a bit of work to be proud of," said the head of the english contingent. "it is that," said the captain. "it has cleared away a cloud that might have hung over this ship till the mystery was dispelled, which probably would have been never." mr. rosenstein, who had taken the diamonds from jack, stood apparently stupefied, holding them on his palm. suddenly, however, to jack's great embarrassment, he threw both arms round the boy's neck and saluted him on both cheeks. then he rushed at billy and finally the two firemen, who dodged out of the way. then he drew out a check book and began writing rapidly. he handed a pink slip of paper to jack. it was a check for $5,000. "a souvenir," he said. "but--but----" began jack, "we didn't do it for money. it was our duty to the company and----" "it's your duty to the company to take that check, then," laughed captain turner, and in the end jack did. the two firemen, who had helped the boys, received a good share of it and later were promoted by the company for their good work. as for prof. dusenberry and his companions, they vanish from our story when, in custody of the detectives, they went over the side a few minutes later. but jack and billy to-day have two very handsome diamond and emerald scarf-pins, the gifts of the grateful mr. rosenstein. "looks as if we are always having adventures of some kind or another," said billy to jack that evening as they strolled about the town, for the ship would not sail for cherbourg, her last port before the homeward voyage, till the next day. "it certainly does look that way," agreed jack and then, with a laugh, he added: "but they don't all turn out so profitably as this one." with which billy agreed. chapter xxx. thurman plots. it was two nights before the _columbia_, on her homeward voyage, entered new york harbor. on the trip across she had once more had the big british greyhound of the seas for a rival. but this time there was a different tale to tell. the _columbia_ was coming home, as billy raynor put it, "with a broom at the main-mast head." all day the wireless snapped out congratulations from the shore. jack was kept busy transmitting shore greetings and messages from returning voyagers who had chosen the finest ship under the stars and stripes on which to return to the united states. patriotism ran riot as every bulletin showed the _columbia_ reeling over two or three knots more an hour than her rival. one enthusiastic millionaire offered a twenty-dollar gold piece to every fireman, and five dollars each to all the other members of the crew, if the _columbia_ beat her fleet rival by a five-hour margin. the money was as good as won. thurman sat in the wireless room. his head was in his hands and he was thinking deeply. should he or should he not send that message to washington which, he was sure, would cause jack's arrest the instant the ship docked. he had struggled with his conscience for some time. but then the thought of the reward and the fancied grudge he owed jack overtopped every other consideration. he seized the key and began calling the big naval station. it was not long before he got a reply, for when not talking to warships the land stations of the department use normal wave-lengths. "who is this?" came the question from the government man. "it's x. y. z," rapped out thurman. this was the signature he had appended to his other messages. "the thunder you say," spelled out the other; "we thought we'd never hear from you again." "well, here i am." "so it appears. well, are you ready to tell us who this chap is who's been mystifying us so?" "i am." "great ginger, wait till i get rear-admiral ---and secretary ---on the 'phone. it's late but they'll get out of bed to hear this news." but it transpired that both the officials were at a reception and thurman was asked to wait till they could be rushed at top speed to the wireless station in automobiles. at last everything was ready and thurman, while drops of sweat rolled down his face, rapped out his treachery and sent it flashing from the antennã¦ across the sea. "thank you," came the reply when he had finished, "the secretary also wishes me to thank you and assure you of your reward. secret service men will meet the ship at the pier." "and jack ready, what about him?" "he will be taken care of. you had better proceed to washington as soon as possible after you land." "how much will the reward be?" greedily demanded thurman. "the secretary directs me to say that it will be suitable," was the rejoinder. the next morning, when jack came on duty, he sent a personal message to uncle toby via siasconset. this was it: "universal detector a success. will you wire washington of my intention to proceed there with all speed when i arrive? "jack." late that day he got back an answer that appeared to astonish him a good deal, for he sat knitting his brows over it for some moments. "washington says some ding-gasted sneak has been cutting up funny tricks. looks like you have been talking. "toby ready." this characteristic message occupied jack for some moments till he thought of a reply to its rather vaguely worded contents. then he got siasconset and shot this through the air: "have talked to no one who could have seen washington. my last letter to the secretary of the navy was that i thought i was on the road to success. "jack." no reply came to this and jack went off watch with the matter as much of a mystery as ever. but as thurman came in to relieve him a sudden suspicion shot across jack's mind. could thurman have----? he recalled the night he had caught him examining the device with such care! jack had since removed it, but in searching in the waste basket for a message discarded by mistake he had since come across what appeared to be crude sketches of the universal detector. if thurman had not drawn them, jack was at a loss to know who had. but for some mysterious reason he only smiled as he left the wireless room. "if you've been up to any hocus-pocus business, mr. thurman," he said to himself, as he descended to dinner, "you are going to get the surprise of your life within a very short time." after dinner he came back to the upper deck again, but as he gained it his attention was arrested by the scream of the wireless spark. it was a warm night and the door of the cabin was open. jack stopped instinctively to listen to the roaring succession of dots and dashes. "he's calling washington," said jack to himself as he listened. "he's got them," he exclaimed a minute later. "hullo! hullo! i guess i was right in my guess, then, after all. oh, thurman, what a young rascal you are." he listened attentively as thurman shot out his message to the national capital. jack repeated it in an undertone as the spark crackled and squealed. "do--i--get--my--reward--right--away?" jack actually burst, for some inexplicable reason, into a hearty laugh. "oh, thurman! thurman!" he exploded to himself. "what a badly fooled young man you are going to be." chapter xxxi. the "suitable reward." the arrival of the _columbia_ at her dock the next day was in the nature of an ovation. a band played "hail columbia," and a dense crowd blocked the docks and adjacent points of vantage to view the great liner which had taken the blue ribbon of the seas from england's crack ship. news of the dramatic rescue of the crew of the _oriana_, wirelessed at the time of the occurrence to the newspapers, had inflamed public interest in the big ship too, and her subsequent doings had been eagerly followed in the dailies. "great to be home again, isn't it, old fellow?" asked raynor, coming up to jack as a dozen puffing tugs nosed the towering _columbia_ into her dock. "it is, indeed," said jack, looking over the rail. "i'm going to----" he broke off suddenly and began waving frantically to two persons in the crowd. one was an old man, rather bent, but hale and hearty and sunburned. beside him was a pretty girl. it was helen dennis and her father, captain dennis, who had been rescued from a sinking sailing ship during jack's first voyage, as told in the "ocean wireless boys on the atlantic." captain dennis, since the disaster, had been unable to get another ship to command and had been forced to accept a position as watchman on one of the docks, but jack had been working all he knew how to get the captain another craft, so far, however, without success. "there's one reason why you're glad to be home," said raynor slyly, waving to helen. "you're a lucky fellow." the gang-plank was down, but before any passengers were allowed ashore, way was made for four stalwart, clean-shaven men who hurried on board. "wonder who those fellows are?" said raynor; "must be some sort of big-wigs." "yes, they certainly got the right of way," responded jack without much interest. thurman joined them. "i hear that the secret service men are on board," he said. "must be looking for someone." "i suppose so," said jack. "they usually are." somebody tapped jack on the shoulder. it was one of the men who had boarded the ship. an evil leer passed over thurman's face as he saw this. "are you jack ready?" asked the man. "that's my name," replied jack. the man threw back his coat, displaying a gold badge. his three companions stood beside him. "i want you to come to washington with us at once," said the man. "i am operative thomas of the united states secret service." "why what's the matter? what's he done?" demanded raynor. "that's for the navy department to decide," said the man sternly. thurman had slipped away after the man had displayed his badge. his envious mind was now sure of its revenge. he, too, meant to get the first train to washington. "don't worry, old fellow," said jack. "just slip ashore and make my excuses to helen and her father, will you, and then meet me in washington at the willard. i think i shall have some news that will surprise you." greatly mystified, raynor obeyed, while jack and the four men, two on each side of him, left the ship. thurman followed them closely. his flabby face wore a look of satisfaction. "two birds with one stone," he muttered to himself. "i've got even with jack ready and i get a reward for doing it. slick work." the trip to washington was uneventful. on their arrival there jack and the secret service men went straight to the navy department. they passed through a room filled with waiting persons having business there, and were at once admitted to the office of the secretary of the navy, a dignified looking man with gray hair and mustache, who sat ensconced behind a large desk littered with papers and documents. there were several other gentlemen in the room. some of them were in naval uniforms and all had an official appearance that was rather overawing. "so, this is our young man," said the secretary, as jack removed his hat. "sit down, mr. ready, these gentlemen and myself wish to talk to you." then, for an hour or more, jack described the universal detector and answered scores of questions. after the first few minutes his sense of embarrassment wore off and he talked easily and naturally. when he had finished, and everybody's curiosity was satisfied, the secretary turned to him. "and you are prepared to turn this instrument over to the united states navy?" "that was the main object i had in designing it," said jack, "but i am at a loss to know how you discovered that i was on board the _columbia_." "that will soon be explained," said the secretary, with a smile that was rather enigmatic. "you recollect having a little fun with our navy operators?" jack colored and stammered something while everybody in the room smiled. "don't worry about that," laughed the secretary. "it just upset the dignity of some of our navy operators. well, following that somebody offered, for a consideration, to tell us who it was that had discovered the secret of a universal detector. it turned out, as i had expected from our previous correspondence, that it was you. but not till two nights ago, when our informant again wirelessed, did we know that you were at sea." "but--but, sir," stuttered jack, greatly mystified, "who did this?" the secretary pressed a button on his desk. a uniformed orderly instantly answered. "tell mr. thurman to come in," said the secretary. there was a brief silence, then the door opened and thurman, with an expectant look and an assured manner, stepped into the room. "mr. thurman?" asked the secretary. "yes, sir," said thurman in a loud, confident voice, "i thought i'd hurry over here as soon as the ship docked and talk to you about my work in discovering for you the fellow who invented the universal detector. i----" he suddenly caught sight of jack and turned a sickly yellow. jack looked steadily at the fellow who, he had guessed for some time, had been evilly interested in the detector. "well, go on, mr. thurman," said the secretary, encouragingly, but with a peculiar look at the corners of his mouth. thurman shuffled miserably. "i'd prefer not to talk with--with him in the room," he said, nodding his head sideways at jack. "why not? mr. ready has just sold his invention to the united states government." "sold it, sir----" began jack, flushing, "why i----" the secretary held up a hand to enjoin silence. then he turned to the thoroughly uncomfortable thurman. "we feel, mr. thurman," he said, "that you really tried to do us a great service." thurman recovered some of his self-assurance. could he have had the skill to read the faces about him, though, he must have known that a bomb was about to burst. "thank you, sir," he said, "i did what i could, what i thought was my duty. and now, sir, about that reward." "'suitable reward,' was what was said, i think, mr. thurman," said the secretary. "well, yes, sir, 'suitable reward,'" responded thurman, his eyes glistening with cupidity. "mr. thurman," and the secretary's voice was serious and impressive, "these gentlemen and i have decided that the most suitable reward for a young man as treacherous and mean as you have shown yourself to be, would be to be kicked downstairs. instead i shall indicate to you the door and ask you to take your leave." "but--but--i told you who the fellow was that had discovered the detector. why, i even made drawings of it for you." "i don't doubt that," said the secretary dryly. "there was only one weak point in your whole scheme, mr. thurman, and that was that mr. ready wrote us some time ago when he first began his experiments about his work and asked some advice. at that time he informed us that if he succeeded in producing a universal detector that it would be at the service of this government. so you see that you were kind enough to inform us of something we knew already. but for a time we were at a loss to know whether it was not some other inventor working on similar lines who had discovered such a detector. to find out definitely we fine-combed the country." "and--and i get no reward?" stuttered thurman. "except the one i mentioned and the possible lesson you may have learned from your experience. good-afternoon, mr. thurman." thurman was so thunderstruck by the collapse of his hopes of reaping a fortune by his treachery that he appeared for a moment to be deprived of the power of locomotion. the secretary nodded to the orderly, who came forward and took the wretched youth, for whom jack could not help feeling sorry, by the arm and led him to the door. this was the last that was seen of thurman for a long time, but jack was destined to meet him again, thousands of miles away and under strange circumstances. when jack left the navy department he felt as if he was walking on air. in his pocket was a check, intended as a sort of retaining fee by the government, till tests should have established beyond a doubt the value of his invention. his eyes were dancing and all he felt that he needed was a friend to share his pleasure with. this need was supplied on his return to the hotel, for there was a telegram from billy raynor, telling jack to meet him on an evening train. it wound up with these words: "helen dennis and myself badly worried. hope everything is all right." "all right," smiled jack, "yes, all right, and then some." chapter xxxii. the plotter's triumph. the face of one of the first of the passengers to disembark from the train as it rolled into the depot was a familiar one to jack. with a thrill of pleasure he darted through the crowd to clasp the hand of his old friend, captain simms. "here's a coincidence," he exclaimed. "i'm here to meet billy raynor. he must have come on the same train. but are you ill, sir? is anything the matter?" "jack, my boy," said the captain, who was pale and drawn, "a terrible thing has happened. the code has been stolen." "stolen! by whom?" "undoubtedly by judson and his gang. i thought i saw them on the train between clayton and new york. i was on my way here with the completed code. i had it under my pillow in my berth on the sleeper. when i awakened it had gone." "didn't you have a hunt made for judson when you reached new york?" "yes, but we had made two stops in the night. undoubtedly, they got off at one of them. unless that code is found i'm a ruined and a disgraced man." at that moment billy raynor came hurrying up. but there was not much warmth in jack's welcome to him. his mind was busy with other things. "what's the matter?" said billy in a low voice, for he too had noticed captain simms' dejection. "never mind now," whispered jack, "i'll tell you later. if i may suggest it, sir," he said, addressing the captain, who appeared completely broken by the loss of the code, "hadn't we better get into a cab and drive to the willard? you are not going to the department to-night?" "no, i couldn't face them to-night," said the captain. "we'll do as you say." "there may be a way of catching the rascals," said jack as the taxicab bumped off. the captain shook his head. "the code is in the hands of the ambassador of the foreign power that wanted it as the price of a contract by this time," he said. "it is gone beyond recovery. i am disgraced." on their arrival at the hotel, the captain retired at once to his room. the boys had dinner without much appetite for the meal and then set out for a stroll to talk things over. "this is a terrible off-set to my good news," said jack. "don't you think there's a chance of getting the code back?" asked billy. jack shook his head. "i think it is as captain simms said, the code is in the hands of that ambassador by this time." "jack ready, by all that's good, and billy too, shake!" the cry came from up the street and a tall, good-looking lad of their own age came hurrying toward them. it was ned rivers, a youth who was interested in wireless and in that way had become acquainted with jack and billy on board the _tropic queen_ while he was accompanying his father on a cruise on that ill-fated ship. "ned!" cried jack. "you're a sight for sore eyes," exclaimed billy, and a general handshaking followed. "what are you doing here, ned?" asked jack, after a few more words had been exchanged. "yes, i thought you lived in nebraska," said billy. "so we did, but we've moved here. father's in the senate now. i thought you knew." "congratulations," said jack. "i guess we'll have to call you mr. senator, jr., now and tip our hats to you." "avast with that nonsense, as they don't say at sea," laughed ned. "there's our house yonder," and he pointed to a handsome stone residence. "hullo, what's that i see on the roof?" asked jack. "that's my wireless outfit. mother made an awful kick about having it there, but at last she gave in." "so you're still a wireless boy?" said billy. "yes, and i've got a dandy outfit too. come on over. i want to introduce you to the folks." "thanks, we will some other time, but not to-night. we don't feel fit for company. you see quite a disaster has happened to a friend of ours," and under a pledge of secrecy from ned, who he knew he could rely on, jack told the lad part of the story of the theft of the code. "by jove, that is a loss," said ned sympathetically. "i've heard dad talking about the new code. it was a very important matter." "we were going for a walk to discuss the whole question," said billy. "can i join you?" asked ned. "glad to have you," was the rejoinder. talking and laughing merrily over old times on the _tropic queen_, the boys walked on, not noticing much where they were going till they found themselves on an ill-lighted street of rather shabby-looking dwellings. "hullo," said ned, "i don't think much of this part of town. let's get back to a main street." "it's a regular slum," said billy, and the three boys started to retrace their steps. but suddenly jack stopped and jerked his companions into a doorway. two figures had just come in sight round the corner. they were headed down the street on the opposite sidewalk. "it's judson and his son," whispered jack. "what can they be doing here?" "hiding, most probably," returned billy. "yes, they--hullo! look, they're going into that alley-way." the boys darted across the street. looking down the alley-way, they saw the figures of judson and his son, by the light of a sickly gas lamp, ascending the steps of a rickety-looking tenement house. "jove, this is worth knowing," exclaimed jack. "if they are really hiding here we can get the police on their track. how lucky that we just let ourselves roam into this part of town." "we ought to have them arrested at once," said billy. "yes, that's a good idea. but they may have just sneaked through the hallway and out by a rear way. you fellows wait here till i go and see." "oh, jack, you may get in trouble." "yes, we'll go with you," said ned. "no, you stay here," jack insisted. "one of us won't be noticed. three would. besides, that house is full of other tenants. nothing much could happen to me." in spite of their further protests he walked rapidly, but cautiously, down the alley-way. noiselessly he entered the hallway and walked to the door of a rear room, where he heard voices. but it was a laboring man and his wife quarreling over something. jack heard a door open on an upper floor. then came a voice that thrilled him. it was jarrow's. "hullo, judson, back again? well, how did things go?" then jack heard the door closed and locked. "so, they are really here," he muttered. "what a piece of luck. but the question is, have they got the code? if it is out of their hands it will be well nigh impossible to recover it, for it is a serious matter to charge an ambassador with wrong-doing." jack began to ascend the rickety stairs with great caution. they creaked dismally under his tread. at a door on the second floor he caught the sound of judson's voice. with a beating heart he crept as close as he dared and listened. "the plans have all been changed," he heard judson saying. "we are to take the code to crotona (the capital of the power represented by the ambassador) ourselves. there's a steamer that leaves baltimore for naples to-morrow. we are to take that and proceed from naples to our destination." "what a bother," came in donald's voice. "i don't see why the ambassador didn't take them." "he said it was too dangerous. he was being watched by the secret service men." "well, it's just as dangerous for us, if it comes to that," grumbled jarrow. "i've got another piece of news for you," said judson. "as i was passing the willard to-night i saw simms, and who do you think was with him?" "i don't know, i'm sure." "those two brats who made trouble for us at alexandria bay. it was a good thing i was disguised, for i passed close to them before i recognized them." "confound it all," burst out jarrow, "do you think they know we are here?" "not a ghost of a chance of it," said judson confidently; "anyhow, we've picked a hiding place where no one would ever dream of looking for us." "that's so. i'll be glad when we get out of the horrid hole," grumbled donald. a footstep sounded behind jack on the creaking boards. it startled him. he had not heard a door open. but now he was confronted by a portly italian. the man grabbed him by the shoulder. "whadda you do-a here?" demanded the man, "me thinka you one-a da sneak-a da tief." "let me go," demanded jack, striving to wrench himself free. "i no leta you go justa yet. i tinka you here steala da tings," cried the man in a loud voice. the talk inside judson's room broke off suddenly. "hullo, what's up outside?" exclaimed donald. "somebody's collared a thief. let's see what it's all about." he flung the door open and the lamplight streamed out full on jack's face. donald fell back a pace with astonishment. "great scott! it's jack ready," he exclaimed. "what in the world are you doing here?" "you knowa desa boy?" asked the italian, still holding jack fast. "yes, i do. he's no good," replied donald. "dena i throwa him out or calla da police." "yes--no, for goodness' sake, not the police," exclaimed donald. "dad, jarrow, here's that ready kid spying on us. he was caught in the hall by that italian next door, who thought he was a sneak thief." "ha! ready, you are the most unlucky lad i know," cried judson, coming to the door, "we've got you just where we want you this time. there are no chimneys here. bring him inside." "not much! help!" jack began to shout, but jarrow clapped a hand over his mouth. "help us run him in here," he ordered the italian, "i'll pay you for it." "whatsa da mat'?" asked the italian suspiciously. "he no lika you." "no wonder. he robbed us once. i guess he was here to do it again. we want to settle accounts with him." "oh-ho, datsa eet ees it?" said the italian. "all righta, i no make da troub'." he gave jack a forward shove into the room of the wireless boy's enemies. chapter xxxiii. in the power of the enemy. as soon as the door was shut and locked, judson faced jack. "now you keep quiet if you don't want a rap over the head with this," he said, exhibiting a heavy bludgeon. "don't dare touch me," spoke jack boldly. "that will depend. i want to ask you some questions. will you answer them?" "i shall see." "you followed donald and me here and were spying on us when that italian caught you." "a good thing he did," interjected donald. "you heard us planning--er--er something?" "possibly i did." "boy, i know you did." "then what's the sense of asking me?" "none of your impudence, young man! you've always been too much of a busy-body for your own good," snarled jarrow. "what's the use of questioning him, dad?" said donald. "he'll only lie." "that's probably correct. i guess he heard everything. what shall we do with him?" "make him a prisoner," said jarrow. "but we can't stay here to guard him and he'd be out of this room in a jiffy." "i'll tell you where we'll take him," said donald. he whispered in his father's ear. judson's face brightened and he nodded approvingly. "just the place. it will serve him right. he got himself into this mess." "are you going to let me go?" demanded jack. "certainly not. you've made your bed--you can lie on it." jack made a leap for the door. the key was in the lock, but he didn't have a chance to turn it before all three threw themselves on him. a scuffle followed which judson brought to a quick stop by striking jack a stunning blow on the head with his bludgeon. with a million stars dancing before him in a void of blackness, jack went down. "now come on quick before anyone spots us," said jarrow. jack's limp form was rolled up in a dirty old blanket so as to look like some kind of a bundle. then jarrow and judson lifted him by the head and feet, while donald preceded them with the lamp. the younger judson led the way out of a rear door to a side hallway. from here two flights of stairs led down to an ill-ventilated, low cellar which was seldom visited and was used mostly for old rubbish and rags. jack was carried to a high-sided wooden coal bin and his form dropped on a pile of dirty old newspapers and decaying straw. there was a heavy door with an iron bolt on the outside leading into the place. as judson closed this, leaving jack to his fate, he muttered: "this is the time we don't need to bother about his getting out. he'll stay there till to-morrow, anyhow, and by that time we'll be at sea." "what time will that auto be at the corner?" asked donald. "it should be there in a few minutes. we must get ready right away," replied his father. "come on, we've no time to lose." in the meantime billy and ned waited on the corner. as the minutes flew by they began to get worried. "jack is certainly taking his time," said ned. "perhaps he is scouting about," suggested billy. "perhaps he has fallen into a trap," exclaimed ned. "i've a good mind to go for the police." "well, we'll wait a little longer," said billy. almost an hour passed and there was no sign of jack. "i won't wait any longer," declared ned, when suddenly three figures emerged from the house. their hats were pulled over their eyes and they glanced about suspiciously. "it's the two judsons and jarrow," exclaimed billy. as he spoke a big touring car came down the street and stopped at the mouth of the alley-way. the three persons who had just emerged from the tenement house began to hasten to it, but billy intercepted them. "what have you done with jack?" he demanded. "yes, where is he?" cried ned. "out of our way," said jarrow, giving billy a shove. "we don't know any jack," growled judson. before the boys could stop them they had reached the car and sprung in. "drive off at full speed," judson ordered the chauffeur, and, leaving the boys standing rooted to the spot, the car dashed off with a roar. borne back to them they could hear the mocking laughter of its occupants. "those rascals have played some trick on jack and they've got away scot-free," groaned billy. "we must hunt for him at once," exclaimed ned. the two boys set out for the tenement. it was pitch dark in the hallway. ned struck a match. "jack! jack! where are you?" he called softly. chapter xxxiv. the search for jack. the two boys, with their hearts heavy as lead, ascended the stairs calling for jack. on the second floor, as they reached it, a door was suddenly flung open. "be jabers, stop that racket. can't yez be lettin' a dacent family slape in pace?" another door flew open and a black, woolly head was poked out. "what fo' you alls come makin' such a cumsturbance at dis yar hour ob de night?" "we're looking for a boy who we think has been trapped in this building. have you seen anything of him?" asked ned. "sure and i haven't. this is a dacent house and dacent folks. go along wid yer now and let us slape." "by gollys we don't kidsnap no boys," came from the negro. another door was opened and the italian who had caught jack in the hall came out. "whatsa da mat'?" he asked. "we're looking for a boy, our chum. he came into this house two hours ago. we're afraid he----" burst out billy desperately. "i see-a da boy in deesa hall," said the italian. "i teenka heem sneaka teef. i catcha heem but two men and a boy in data rooma dere dey taka heem. dey say dat he robba heem and they getta even." "did they take him into the room?" burst out ned. the italian nodded. "yes, dey takea heem in. i geeva heem to them," said the man indifferently. "great heavens, they invented that story about his robbing them," cried billy. "they've made him a prisoner. we must get him out. jack! jack!" no answer came and then billy, regardless of consequences, flung himself against the door of the room the italian had indicated. by this time quite a crowd of tenement dwellers had assembled, attracted by the loud voices. at first the door stood firm, but when ned joined billy it gave way with a bang, precipitating them into the room. but now a new voice was added to the uproar. hans pumpernickel, a sour old german who owned the tenements and lived there to save rent in a better quarter, put in an appearance. "vos is los?" he demanded, "ach himmel, de door vos busted py der outside. who did dis?" "we did," said billy boldly. "my chum was decoyed into this house by some bad characters. this was the room they occupied. but he isn't here." "ach du liebe! vos iss idt i care aboupt your droubles? i haf mein own." "we'll find jack if we go through this house from cellar to attic," declared ned. "i dond pelief dot boy vos harmed by der men dot hadt idt dis room," declared the crabbed old man. "dey vos very respectable. now you pay me for dot door undt den go aboudt your pusiness." "if you interfere with us we'll call in the police," said billy. "yes, if you want to keep out of trouble, you'll help us," said ned boldly. "is dot so? undt who iss you?" "i'm the son of senator rivers of nebraska." the landlord's jaw dropped. he grew more respectful. "vell, vot am i to do?" he asked. "don't interfere with us. we'll pay for this door. hullo, what's that on the floor?" exclaimed billy. "why, it's jack's knife. but where is he?" "den dose nice mens, mr. jenkins undt mister thompson are kidsnabbers," exclaimed the landlord. "are those the names they gave?" asked billy. "ches. dey pay idt me a month in advance. dey vost nice gentlemen." "yes, very nice," exclaimed billy bitterly. "however, knowing those names may give a clew later on." they searched for several hours but found no further trace of jack. at last, tired out and sick at heart, they returned home. billy accepted ned's invitation to stay at the latter's house that night and to lay the matter before the senator in the morning. * * * * * half stunned, jack lay still for some time on the moldy straw and the old newspapers in the coal bin in the cellar. but at length he mustered his strength and rose, rather giddily, to his feet. "well, this is the limit of tough luck," he complained. "if i don't get out of here before to-morrow, when that steamer sails, the code will have gone for good. if only i'd cut away sooner. confound that italian. he spoiled it all with his stupidity." besides being pitch dark, the place was full of cobwebs. to add to jack's discomfort, a spider occasionally dropped on him. suddenly overhead sounded footsteps and voices. "somebody lives up there," he thought. "if i could only attract their attention." he shouted but nobody answered, although he tried it at intervals for some hours. at last he gave up and sat down on the pile of straw to think. he was very thirsty and his mouth and eyes were full of coal dust and dirt. the roof of the cellar was so low, too, that in moving about he bumped his head-against the beams. suddenly he remembered that he had some matches. to strike a light was the work of a moment. then he located the door. but all his efforts failed to make it budge. he struck another light and this time he made a discovery. "gee whiz, that looks like a trap-door just above me," he decided. he raised his hands and the cut-out square in the flooring came up with ease. jack scrambled up into a kitchen. in one corner was a ladder, no doubt used when the occupants wished to enter the cellar. through one of the windows daylight was streaming, the gray light of early dawn. "great scott! i've been down there all night," ejaculated the boy. he was considering his next step when a large woman, with stout red arms, came into the kitchen. her husband had to be at work early and she was about to prepare his breakfast. she had a florid, disagreeable face. "what are you after doing here?" she demanded, picking up a heavy rolling pin. "i'm trying to get out of this house. will you show me the way?" "indade and i will not. i'll hand yez over ter the perlice." she raised her voice. "pat! pat! come here at onct." "phwat's the mather?" came from another room. "thare's a thafe forninst the kitchen. get ther perlice. i'll hold him--he's only a gossoon." "are you crazy?" demanded jack. "i was locked in that cellar by some rascals and got out through your trap-door." "tell that to the marines," sneered the woman, as she made a grab for him. jack wrenched himself away and dodged a blow from the rolling-pin. the window was open and it was a short drop to the yard. he darted for the window and made the jump. "pat! pat!" yelled the woman. jack leaped over a fence at the back of the yard and found himself in an alley. he ran for his life. behind him came cries of pursuit but they soon died away. he ran for several blocks, however, and then came to a standstill. "i guess ned and billy went home," he mused. "i'd better hunt up ned. if his father is a senator he may be able to use some influence to catch these rascals before they get away for good. i wonder what time that ship sails? by the way, i don't know her name." at the hotel, to which he went first, he slipped up to his room without attracting much attention and washed off the dirt of the cellar. then he inquired for billy and learned that raynor had telephoned the night before that he was going to stop at senator rivers' house and for jack to come straight over there, if he came in. jack procured a copy of a commercial newspaper which he knew listed sailings of ships from all important ports. he turned to the baltimore section. half way down the column he found this entry: "italian-american line. s.s. _southern star_,--balto., for naples, italy. sails--a.m. (hour indefinite). mixed cargo. ten passengers." "hurrah! that's the ship, all right," thought jack, "there's a chance yet that we can stop them." chapter xxxv. the wireless makes good. he lost no time in hastening to senator rivers' house. just as he turned into the gate billy and ned emerged. they had spent a sleepless night and were on their way to police headquarters to report jack's absence. as they saw their missing comrade, they set up a glad shout. "gracious, where have you been?" demanded billy. "we were on our way to the police about you," put in ned. "do you know anything about the judsons and jarrow?" asked jack eagerly. "why, yes, they came out of the house some time after you went in. we chased them but they jumped into a high-powered car and escaped." "i know; they've gone to baltimore." "how in the world do you know that?" asked billy wonderingly. "i'll tell you it all in a few minutes. ned, is your father up yet?" "gracious, no. but if it's important i can tell him to hurry up." "i wish you would; there's a chance that we can get back the naval code if you do." "i'll tell him that, and he'll be dressed and down in record time," cried ned, running off. jack waited to tell his adventures till they were all at breakfast. then billy and ned had to tell their stories. "well, you boys certainly have your share of adventures," remarked the senator, "but the most important thing now is to secure the apprehension of those rascals without delay. we had better call up the steamship company at baltimore and find out if anyone called jenkins or thompson, i think those are the aliases they gave at the tenement house, are among the passengers." this was done at once, but to the intense chagrin of all concerned, the telephone company had seized that early hour of the day to repair some wires which had been knocked down in a thunderstorm near baltimore the night before. it was impossible to communicate with that city till some hours later. "we might telegraph," suggested jack. "yes, i'll call a messenger at once. but i doubt even then that we'll be in time," said the senator. the telegram was sent, but before a reply came they were able to use the telephone. "hullo, is this the italian-american steamship company?--all right--are three passengers, two men and a boy, booked on the _southern star_ as jenkins and thompson,--they are,--good, this is senator rivers talking, from washington,--those men are criminals,--they have robbed the government of valuable documents--summon the police and have them arrested and held--i'll take full responsibility--what!--the _southern star_ sailed two hours ago!" the senator dropped the receiver from his hand in his disappointment. "too late! the code is lost to the united states for good, and those rascals have escaped!" but jack suddenly sprang forward. his cheeks were aflame with excitement. "senator," he cried. "there is still a chance." "i fail to see it," said mr. rivers. "get the line on the wire again, sir, and find out if the _southern star_ has a wireless." "but what--jove, boy! i see your plan now." eagerly the senator snatched up the receiver again. before long connection was again established. "the _southern star_ has a wireless," he exclaimed. "her call is s. x. a., and now for your plan, my boy." "show me to your wireless room, will you, ned?" said jack, subduing the excitement in his voice with a struggle. "oh, jack, i see what you're going to do now," cried ned. "come on. we don't want to lose a minute." the boys dashed up the stairs three at a time. the senator followed at a more discreet pace. they entered the wireless room with a bang and a shout. jack fairly flung himself at the key and began pounding out the _southern star's_ call. in reality it was only ten minutes, but to those in that room it seemed hours before he got a reply. when he did, he summoned the captain through the operator. "have i got authority to use your name, senator?" asked the boy while he waited for the announcement that the captain was in the wireless room. "you have authority to use the name of the most powerful institution in the world, my boy, the united states government," said the senator solemnly. then, as if he had suddenly thought of something, he hurriedly left the room. downstairs he once more applied himself to the telephone, but this time he talked to the secretary of the navy. fifteen minutes after jack had spoken to the captain of the _southern star_ that craft was anchored in the chesapeake river waiting the arrival of a gunboat hastily detailed by government wireless to proceed at once up that river and take three prisoners off the _southern star_. this latter order was the result of senator rivers' call to the navy department. jack's happy task was then to break the good news to captain simms, which he lost no time in doing, and the captain's deep gratitude, which was none the less because he expressed it in few words, may be imagined. "i declare," he said, "you boys have been my good angels all through. you have helped me as if your own interests had been at stake. i don't know how to thank you." the code was yielded up by judson without a struggle, which procured him some leniency later on. but both he and jarrow met with heavy punishment for their misdeeds. donald was allowed to go free on account of his youth and the government's disability to prove that he had actually anything to do with the theft of the code. after the news of his arrest spread, the long threatened disaster to judson's company happened and it went into bankruptcy. donald, the pampered and selfish, had to go to work for a living. the boys heard that he had gone west. they were destined to meet him again, however, as they were thurman. one of jack's proudest possessions is a framed letter from the secretary of the navy thanking him for his great aid and that of his friends in the matter of the navy code, but he values the friendship of captain simms as highly. not long after the successful tests of the detector, there was a joyous gathering on board the old _venus_, to which queer home uncle toby had returned. all our friends were there and jack was able to announce a joyous surprise. he had been able to secure, through captain simms' influence, the command of a fine new sailing ship for captain dennis. she was a full-rigged bark, plying between new york and mediterranean ports. tears stood in the veteran captain's eyes, as he thanked jack, and helen cried openly. "oh, jack, i--i'd like to hug you!" she exclaimed, whereupon everybody laughed, and the emotional strain was over. after a while, captain dennis began to tell of some of his adventures. not only had he gone through many experiences on the sea, but also on land, and especially during the great civil war. "one time," said captain dennis, "while on a foraging expedition, our men were surprised, and before i knew what had happened i was a prisoner. i was taken to an old building and put in the upper story of it. "of course, i wanted to escape. so, after a while, i began to try my luck with the rope tied around my wrists. to my joy i found that i could move them. half an hour later my wrists were free. "i peered out of the window. it was a very dark night, and the guard set around the building was close and vigilant. i felt that my chances to escape were very small. "still, i determined to try. after listening many hours, i thought i learned the exact position of the sentries. the spaces between them were very short, but it would be quite possible, i thought, to pass by them noiselessly and without being perceived. i may as well state that the watch would have been even more strict had not the confederates regarded the struggle as virtually at an end, and were, therefore, less careful as to their prisoners than they would otherwise have been. "i prepared for escape by tearing up the sheet on the bed, and knotting the strips into a rope. i opened the window, threw out this rope, and slipped down to the ground. so far i was safe. "it was dark and foggy, and very difficult to see two feet in advance. i soon found that my observations as to the places of the sentries had been useless. still, in the darkness and thickness of the night, i thought that the chance of detection was small. "creeping quietly and noiselessly along, i could hear the constant challenges of the sentries around me. these, excited by the unusual darkness of the night, were unusually vigilant. "i approached until i was within a few yards of the line, and the voices of the men as they challenged enabled me to ascertain exactly the position of the sentries on the right and left of me. passing between these, i could see neither, although they were but a few paces on either hand. suddenly i fell into a stream running across my path. "of course, in the darkness i had not observed it. at the sound of my falling there was an instant challenge. then a shot was fired!" "oh! how thrilling!" exclaimed helen. jack and ned laughed. "well," resumed captain dennis, "i struggled across the stream, and clambered out on the opposite side. as i did so, a number of muskets were fired in my direction by soldiers who had rushed up to the point of alarm. i felt a sharp, twitching pain in my shoulder, and i knew that i had been hit. but fortunately the other shots fired whizzed harmlessly by. at top speed i ran forward. "i was safe from pursuit, for in the darkness it would have been absolutely impossible to follow me. so, in a few moments, i ceased running. what was the use of taking chances? all was quiet behind me, but i could no longer tell in what direction i was advancing. "so long as i heard the shouts of the sentries, though the sounds seemed far off, i continued my way; and then, all guidance being lost, i lay down under a hedge and waited for morning." "oh, dear!" helen cried sympathetically, "did you have to sleep in that cold, moist night?" "quite so," replied captain dennis, smiling good-humoredly; "and in the morning it was still foggy. after wandering aimlessly about for some time i at last succeeded in striking a road. i decided to take a westerly course. "my shoulder was stiff and somewhat swollen. but the bullet had passed through its fleshy part, missing the bone; and although it cost much pain i was able, by wrapping my arm tightly to my body, to proceed. more than once i had to withdraw from the road into the fields or bushes when i heard a straggling number of confederates coming along. "i came upon a house, and although i was hungry and tired, i was cautious. instead of going to the door i made for the window. but i had my trouble for nothing. i looked in and saw a number of confederate soldiers there, and knew that there was no safety for me. to add to my dismay, one of the soldiers happened to cast his eyes up as i glanced in the room and he at once gave a shout of warning. "instantly the others sprang to their feet and started out to pursue me. i fled down the road. a few shots were fired, but fortunately i was not hit again. "at last i came to a small village. i wondered why i had not reached my camp. but you must remember that i was attached to a small number of men only, and that we always were many miles ahead or in the rear of the army, as occasion called for. "the village was deserted, for it was late at night again. i made myself comfortable in a sort of stable warehouse, climbing over a number of bales of cotton, and laid myself down next to the wall, secure from casual observation. "when i awoke the next morning, i nearly uttered a cry of pain a sudden movement had given to my arm. i, however, suppressed it, and it was well that i did so, for i suddenly heard voices right near me. darkies were moving bales of cotton but, being well back, i had little fear of being discovered. "the hours passed wearily. i was parched and feverish from pain of my wound. yet i was afraid to move. so i sometimes dozed off into snatches of fitful sleep. perhaps i moaned, or i was accidentally discovered. at all events, when i awoke a mammy was bending over me, her voice fully of pity. and--well, to make a long story short, i had blundered again, for the village was being occupied by the federals, and the cotton the darkies had been taking away was going north. there is no need to add that i was well fed and well taken care of." captain dennis paused, and thoughtfully smoked his pipe. his little audience sat very quietly, their eager faces and shining eyes plainly showing their rapt interest in the modestly told story. "well, well," said captain dennis, at last breaking the silence, "some day you, jack and you ned will be able to tell very many far more thrilling stories." "yes" replied jack, "but none of them will be about so great a cause." "you are right, jack," captain dennis said fervently; "it was a good cause. but come, you are tired, so let us say 'good night,' my friends." a half hour later jack and ned were fast asleep, dreaming of those stirring times when the immortal abraham lincoln was president of this glorious nation. * * * * * the next week the _columbia_ sailed again. as she passed out of new york harbor, and past sandy hook, the passengers crowded to the rail to look at a beautiful sea picture. the sun was setting, and the radiance turned to gold the white sails of a beautiful bark outward bound. as she heeled over on the starboard tack, it was evident that she would pass close to the steamer. from the wireless room jack ready and billy raynor watched the pretty sight with more interest, perhaps--certainly it was so in jack's case--than anyone else on board. "it's the _silver star_, jack, captain dennis's ship," said billy. jack nodded. "i know it," he answered. "she sailed this morning. i've been on the lookout for her all the way down the bay." there was silence between the two chums. the _silver star_, gliding swiftly through the water, came steadily on. as the steamer passed her, she was quite close, looking like a beautiful toy from the towering decks of the _columbia_. "look!" exclaimed billy, half in a whisper, as her ensign fluttered down in salute and then climbed upward to the peak again. a booming roar from the _columbia's_ siren acknowledged the compliment. but jack had no eyes for this. his gaze was fixed on the stern deck of the _silver star_, where, by her steering-wheel, gripped by two stalwart seamen, stood an upright old man, with glasses bent on the _columbia_. a graceful girl was at his side. jack saw her wave, and was waving frantically back, when there came an insistent summons from the wireless room. when he came out on deck again twilight had fallen, but far back on the horizon was a tiny blur--the _silver star_. as jack gazed back at her, she vanished below the horizon as suddenly as an extinguished spark in a piece of tinder. "good-night," breathed jack, and he stood for a long time motionless, leaning on the rail. and here, for the time being, we, too, will say good-by to our young friends, to meet them all again in the next volume devoted to their doings, which will be called "the ocean wireless boys on the pacific." the end. hurst & company's books for young people kindergarten limericks by florence e. scott _pictures by arthur o. scott with a foreword by lucy wheelock_ _a volume of cheerfulness in rhyme and picture_ the book contains a rhyme for every letter of the alphabet, each illustrated by a full page picture in colors. the verses appeal to the child's sense of humor without being foolish or sensational, and will be welcomed by kindergartners for teaching rhythm in a most entertaining manner. * * * * * frank armstrong series by matthew m. colton _frank armstrong's vacation_ how frank's summer experiences with his boy friends make him into a sturdy young athlete through swimming, boating and baseball contests, and a tramp through the everglades, is the subject of this splendid story. _frank armstrong at queens_ we find among the jolly boys at queen's school, frank, the student-athlete, jimmy, the baseball enthusiast, and lewis, the unconsciously-funny youth who furnishes comedy for every page that bears his name. fall and winter sports between intensely rival school teams are expertly described. _frank armstrong's second term_ the gymnasium, the track and the field make the background for the stirring events of this volume, in which david, jimmy, lewis, the "wee one" and the "codfish" figure, while frank "saves the day." _frank armstrong, drop kicker_ with the same persistent determination that won him success in swimming, running and baseball playing, frank armstrong acquired the art of "drop-kicking," and the queen's football team profits thereby. _frank armstrong, captain of the nine_ exciting contests, unexpected emergencies, interesting incidents by land and water make this story of frank armstrong a strong tale of school-life, athletic success, and loyal friendships. _frank armstrong at college_ with the development of this series, the boy characters have developed until in this, the best story of all, they appear as typical college students, giving to each page the life and vigor of the true college spirit. six of the best books of college life stories published. they accurately describe athletics from start to finish. * * * * * oakdale academy series stories of modern school sports by morgan scott. ben stone at oakdale. under peculiarly trying circumstances ben stone wins his way at oakdale academy, and at the same time enlists our sympathy, interest and respect. through the enmity of bern hayden, the loyalty of roger eliot and the clever work of the "sleuth," ben is falsely accused, championed and vindicated. boys of oakdale academy. "one thing i will claim, and that is that all grants fight open and square and there never was a sneak among them." it was rodney grant, of texas, who made the claim to his friend, ben stone, and this story shows how he proved the truth of this statement in the face of apparent evidence to the contrary. rival pitchers of oakdale. baseball is the main theme of this interesting narrative, and that means not only clear and clever descriptions of thrilling games, but an intimate acquaintance with the members of the teams who played them. the oakdale boys were ambitious and loyal, and some were even disgruntled and jealous, but earnest, persistent work won out. oakdale boys in camp. the typical vacation is the one that means much freedom, little restriction, and immediate contact with "all outdoors." these conditions prevailed in the summer camp of the oakdale boys and made it a scene of lively interest. the great oakdale mystery. the "sleuth" scents a mystery! he "follows his nose." the plot thickens! he makes deductions. there are surprises for the reader--and for the "sleuth," as well. new boys at oakdale. a new element creeps into oakdale with another year's registration of students. the old and the new standards of conduct in and out of school meet, battle, and cause sweeping changes in the lives of several of the boys. * * * * * log cabin to white house series lives of celebrated americans from boyhood to manhood (the life of benjamin franklin). by _wm. m. thayer_. benjamin franklin was known in the scientific world for his inventions and discoveries, in the diplomatic world because of his statemanship, and everywhere, because of his sound judgment, plain speaking, and consistent living. from farm house to white house (the life of george washington). by _wm. m. thayer_. the story of the hatchet and other familiar incidents of the boyhood and young manhood of washington are included in this book, as well as many less well-known accounts of his experiences as surveyor, soldier, emissary, leader, and first president of the united states. from log cabin to white house (the life of james a. garfield). by _wm. m. thayer_. it was a long step from pioneer home in ohio where james a. garfield was born, to the white house in washington, and that it was an interesting life-journey one cannot doubt who reads mr. thayer's account of it. from pioneer home to white house (the life of abraham lincoln). by _wm. m. thayer_. no president was ever dearer to the hearts of his people than was homely, humorous "honest abe." to read of his mother, his early home, his efforts for an education, and his rise to prominence is to understand better his rare nature and practical wisdom. from ranch to white house (the life of theodore roosevelt). by _edward s. ellis. a. m._ every boy and girl is more or less familiar with the experiences of mr. roosevelt as colonel and president, but few of them know him as the boy and man of family and school circles and private citzenship. mr. ellis describes theodore roosevelt as a writer, a hunter, a fighter of "graft" at home and of spaniards in cuba, and a just and vigorous defender of right. from tannery to white house (the life of ulysses s. grant). by _wm. m. thayer_. perhaps general grant is best known to boys and girls as the hero of the famous declaration: "i will fight it out on this line if it takes all summer." * * * * * rex kingdon series by gordon braddock _rex kingdon of ridgewood high_ a new boy moves into town. who is he? what can he do? will he make one of the school teams? is his friendship worth having? these are the queries of the ridgewood high students. the story is the answer. _rex kingdon in the north woods_ rex and some of his ridgewood friends establish a camp fire in the north woods, and there mystery, jealousy, and rivalry enter to menace their safety, fire their interest and finally cement their friendship. _rex kingdon at walcott hall_ lively boarding school experiences make this the "best yet" of the rex kingdon series. _rex kingdon behind the bat_ the title tells you what this story is; it is a rattling good story about baseball. boys will like it. gordon braddock knows what boys want and how to write it. these stories make the best reading you can procure. * * * * * new books on the war great war series by major sherman crockett _two american boys with the allied armies_ _two american boys in the french war trenches_ _two american boys with the dardanelles battle fleet_ the disastrous battle raging in europe between germany and austria on one side and the allied countries on the other, has created demand for literature on the subject. the american public to a large extent is ignorant of the exact locations of the fighting zones with its small towns and villages. major crockett, who is familiar with the present battle-fields, has undertaken to place before the american boy an interesting series of war stories. * * * * * boy scout series _endorsed by boy scout organizations_ by lieut. howard payson boy scouts of the eagle patrol in this story, self-reliance and self-defense through organized athletics are emphasized. boy scouts on the range cow-punchers, indians, the arizona desert and the harkness ranch figure in this tale of the boy scouts. boy scouts and the army airship the cleverness of one of the scouts as an amateur inventor and the intrigues of his enemies to secure his inventions make a subject of breathless interest. boy scouts' mountain camp just so often as the reader draws a relieved breath at the escape of the scouts from imminent danger, he loses it again in the instinctive impression, which he shares with the boys, of impending peril. boy scouts for uncle sam patriotism is a vital principle in every boy scout organization, but few there are who have such an opportunity for its practical expression as comes to the members of the eagle patrol. boy scouts at the panama canal most timely is this authentic story of the "great ditch." it is illustrated by photographs of the canal in process of building. boy scouts under fire in mexico another tale appropriate to the unsettled conditions of the present is this account of recent conflict. boy scouts on belgian battlefields wonderfully interesting is the story of belgium as it figures in this tale of the great war. boy scouts with the allies in france on the firing line--or very near--we find the scouts in france. boy scouts at the panama-pacific exposition if you couldn't attend the exposition yourself, you can go even now in imagination with the boy scouts. boy scouts under sealed orders here the boy scouts have a secret mission to perform for the government. what is the nature of it? keen boys will find that out by reading the book. it's a dandy story. boy scouts' campaign for preparedness just as the scouts' motto is "be prepared," just for these reasons that they prepare for the country's defense. what they do and how they do it makes a volume well worth reading. you do not have to be a boy scout to enjoy these fascinating and well-written stories. any boy has the chance. next to the manual itself, the books give an accurate description of boy scout activities, for they are educational and instructive. * * * * * motor cycle series by lieut. howard payson you do not need to own either a motor-cycle or a bicycle to enjoy the thrilling experiences through which the motor cycle chums pass on their way to seek adventure and excitement. brimful of clever episodes. _the motor cycle chums around the world_ could jules verne have dreamed of encircling the globe with a motor cycle for emergencies, he would have deemed it an achievement greater than any he describes in his account of the amusing travels of philias fogg. this, however, is the purpose successfully carried out by the motor cycle chums, and the tale of their mishaps, hindrances and delays is one of intense interest, secret amusement, and incidental information to the reader. _the motor cycle chums of the northwest patrol_ the great northwest is a section of vast possibilities and in it the motor cycle chums meet adventures even more unusual and exciting than many of their experiences on their tour around the world. there is not a dull page in this lively narrative of clever boys and their attendant, "chinee." _the motor cycle chums in the gold fields_ how the motor cycle chums were caught by the lure of the gold and into what difficulties and novel experiences they were led, makes a tale of thrilling interest. _the motor cycle chums' whirlwind tour_ to right a wrong is the mission that leads the riding rovers over the border into mexico and gives the impulse to this story of amusing adventures and exciting episodes. _the motor cycle chums south of the equator_ new customs, strange peoples and unfamiliar surroundings add fresh zest to the interest of the motor cycle chums in travel, and the tour described in this volume is full of the tropical atmosphere. _the motor cycle chums through historic america_ the motor cycle chums explore the paths where american history was made, where interest centers to-day as never before. [illustration: samuel finley breese morse inventor of the telegraph] masters of space morse _and the telegraph_ thompson _and the cable_ bell _and the telephone_ marconi _and the wireless telegraph_ carty _and the wireless telephone_ by walter kellogg towers illustrated 1917 to my co-laborer and companion berenice laura towers whose encouragement and assistance were constant in the gathering and preparation of material for this volume. contents chap. preface i. communication among the ancients ii. signals past and present iii. forerunners of the telegraph iv. inventions of sir charles wheatstone v. the achievement of morse vi. "what hath god wrought?" vii. development of the telegraph system viii. telegraphing beneath the sea ix. the pioneer atlantic cable x. a successful cable attained xi. alexander graham bell, the youth xii. the birth of the telephone xiii. the telephone at the centennial xiv. improvement and expansion xv. telegraphing without wires xvi. an italian boy's work xvii. wireless telegraphy established xviii. the wireless serves the world xix. speaking across the continent xx. telephoning through space appendix a appendix b index illustrations samuel finley breese morse morse's first telegraph instrument cyrus w. field william thomson (lord kelvin) the "great eastern" laying the atlantic cable, 1866 alexander graham bell thomas a. watson professor bell's vibrating reed professor bell's first telephone the first telephone switchboard used in new haven, conn., for eight subscribers early new york exchange professor bell in salem, mass., and mr. watson in boston, demonstrating the telephone before audiences in 1877 doctor bell at the telephone opening the new york-chicago line, october 18, 1892 guglielmo marconi a remarkable photograph taken outside of the clifden station while messages were being sent across to cape race marconi station at clifden, ireland preface this is the story of talking at a distance, of sending messages through space. it is the story of great men--morse, thomson, bell, marconi, and others--and how, with the aid of men like field, vail, catty, pupin, the scientist, and others in both the technical and commercial fields, they succeeded in flashing both messages and speech around the world, with wires and without wires. it is the story of how the thought of the world has been linked together by those modern wonders of science and of industry--the telegraph, the submarine cable, the telephone, the wireless telegraph, and, most recently, the wireless telephone. the story opens with the primitive methods of message-sending by fire or smoke or other signals. the life and experiments of morse are then pictured and the dramatic story of the invention and development of the telegraph is set forth. the submarine cable followed with the struggles of field, the business executive, and thomson, the inventor and scientific expert, which finally culminated in success when the _great eastern_ landed a practical cable on the american coast. the early life of alexander graham bell was full of color, and i have told the story of his patient investigations of human speech and hearing, which, finally culminated in a practical telephone. there follows the fascinating story of marconi and the wireless telegraph. last comes the story of the wireless telephone, that newest wonder which has come among us so recently that we can scarcely realize that it is here. an inner view of the marvelous development of the telephone is added in an appendix. the part played by the great business leaders who have developed and extended the new inventions, placing them at the service of all, has not been forgotten. not only have means of communication been discovered, but they have been improved and put to the widest practical use with remarkable efficiency and celerity. the stories of these developments, in both the personal and executive sides, embody the true romance of the modern business world. the great scientists and engineers who have wrought these wonders which have had so profound an influence upon the life of the world lived, and are living, lives filled with patient effort, discouragement, accomplishment, and real romance. they are interesting men who have done interesting things. better still, they have done important, useful things. this book relates their life stories in a connected form, for they have all worked for a similar end. the story of these men, who, starting in early youth in the pursuit of a great idea, have achieved fame and success and have benefited civilization, cannot but be inspiring. they did not stumble upon their discoveries by any lucky accident. they knew what they sought, and they labored toward the goal with unflagging zeal. had they been easily discouraged we might still be dependent upon the semaphore and the pony express for the transmission of news. but they persevered until success was attained, and in the account of their struggle to success every one may find encouragement in facing his own tasks. one can scarce overestimate the value of modern methods of communication to the world. so much of our development has been more or less directly dependent upon it that it is difficult to fancy our situation without the telegraph and telephone. the diligence with which the ancients sought speedy methods for the sending of messages demonstrates the human need for them. the solution of this great problem, though long delayed, came swiftly, once it was begun. even the simple facts regarding "masters of space" and their lives of struggle and accomplishment in sending messages between distant points form an inspiring story of great achievement. w.k.t. #masters of space# i communication among the ancients signaling the fall of troy--marine signaling among the argonauts--couriers of the greeks, romans, and aztecs--sound-signaling--stentorophonic tube--the shouting sentinels--the clepsydra--signal columns--indian fire and smoke signals. it was very early in the history of the world that man began to feel the urgent need of communicating with man at a distance. when village came into friendly contact with village, when nations began to form and expand, the necessity of sending intelligence rapidly and effectively was clearly realized. and yet many centuries passed without the discovery of an effective system. those discoveries were to be reserved for the thinkers of our age. we can understand the difficulties that beset king agamemnon as he stood at the head of his armies before the walls of troy. many were the messages he would want to send to his native kingdom in greece during the progress of the siege. those at home would be eager for news of the great enterprise. many contingencies might arise which would make the need for aid urgent. certainly queen clytemnestra eagerly awaited word of the fall of the city. yet the slow progress of couriers must be depended upon. one device the king hit upon which was such as any boy might devise to meet the simplest need. "if i can go skating tonight," says johnny jones to his chum, "i'll put a light in my window." such is the simple device which has been used to bear the simplest message for ages. so king agamemnon ordered beacon fires laid on the tops of mount ida, mount athos, mount cithæron, and on intervening eminences. beside them he placed watchers who were always to have their faces toward troy. when troy fell a near-by fire was kindled, and beacon after beacon sprang into flame on the route toward greece. thus was the message of the fall of troy quickly borne to the waiting queen by this preconceived arrangement. yet neither king agamemnon nor his sagest counselors could devise an effective system for expediting their messages. prearranged signals were used to convey news in even earlier times. fire, smoke, and flags were used by the egyptians and the assyrians previous to the trojan war. the towers along the chinese wall were more than watch-towers; they were signal-towers. a flag or a light exhibited from tower to tower would quickly convey a certain message agreed upon in advance. human thought required a system which could convey more than one idea, and yet skill in conveying news grew slowly. perhaps the earliest example of marine signaling of which we know is recorded of the argonautic expedition. theseus devised the use of colored sails to convey messages from ship to ship of the fleet, and caused the death of his father by his failure to handle the signals properly. theseus sailed into conflict with the enemy with black sails set, a signal of battle and of death. with the battle over and himself the victor, he forgot to lower the black flag and set the red flag of victory. his father, the aged ægeus, seeing the black flag, believed it reported his son's death, and, flinging himself into the sea, was drowned. in time it occurred to the great monarchs as their domains extended to establish relays of couriers to bear the messages which must be carried. such systems were established by the greeks, the romans, and the aztecs. each courier would run the length of his own route and would then shout or pass the message to the next runner, who would speed it away in turn. such was the method employed by our own pony-express riders. an ancient persian king thought of having the messages shouted from sentinel to sentinel, instead of being carried more slowly by relays of couriers. so he established sentinels at regular intervals within hearing of one another, and messages were shouted from one to the other. just fancy the number of sentinels required to establish a line between distant cities, and the opportunities for misunderstanding and mistake! the ancient gauls also employed this method of communication. cæsar records that the news of the massacre of the romans at orleans was sent to auvergne, a distance of nearly one hundred and fifty miles, by the same evening. though signaling by flashes of light occurred to the ancients, we have no knowledge that they devised a way of using the light-flashes for any but the simplest prearranged messages. the mirrors of the pharaohs were probably used to flash light for signal purposes. we know that the persians applied them to signaling in time of war. it is reported that flashes from the shields were used to convey news at the battle of marathon. these seem to be the forerunners of the heliograph. but the heliograph using the dot-and-dash system of the morse code can be used to transmit any message whatever. the ancients had evolved systems by which any word could be spelled, but they did not seem to be able to apply them practically to their primitive heliographs. an application of sound-signaling was worked out for alexander the great, which was considered one of the scientific wonders of antiquity. this was called a stentorophonic tube, and seems to have been a sort of gigantic megaphone or speaking-trumpet. it is recorded that it sent the voice for a dozen miles. a drawing of this strange instrument is preserved in the vatican. another queer signaling device, built and operated upon a novel principle, was an even greater wonder among the early peoples. this was known as a clepsydra. fancy a tall glass tube with an opening at the bottom in which a sort of faucet was fixed. at varying heights sentences were inscribed about the tube. the tube, being filled with water, with, a float at the top, all was ready for signaling any of the messages inscribed on the tube to a station within sight and similarly equipped. the other station could be located as far away as a light could be seen. the station desiring to send a message to another exhibited its light. when the receiving station showed its light in answer, the tap was opened at the bottom of the tube in each station. when the float dropped until it was opposite the sentence which it was desired to transmit, the sending station withdrew its light and closed the tap. this was a signal for the receiving station to stop the flow of water from its tube. as the tubes were just alike, and the water had flowed out during the same period at equal speed, the float at the receiving station then rested opposite the message to be conveyed. many crude systems of using lights for signaling were employed. lines of watch-towers were arranged which served as signal-stations. the ruins of the old roman and gallic towers may still be found in france. hannibal erected them in africa and spain. colored tunics and spears were also used for military signals in the daytime. for instance, a red tunic displayed meant prepare for battle; while a red spear conveyed the order to sack and devastate. an ancient system of camp signals from columns is especially interesting as showing a development away from the prearranged signals of limited application. for these camp signals the alphabet was divided into five or six parts, and a like number of columns erected at each signal-station. each column represented one group of letters. suppose that we should agree to get along without the q and the z and reduce our own alphabet to twenty-four letters for use in such a system. with six columns we would then have four letters for each column. the first column would be used to signal a, b, c, and d. one light or flag shown from column one would represent a, two flags or lights b, and so on. thus any word could be spelled out and any message sent. without doubt the system was slow and cumbersome, but it was a step in the right direction. the american indians developed methods of transmitting news which compare very favorably with the means employed by the ancients. smoke-rings and puffs for the daytime, and fire-arrows at night, were used by them for the sending of messages. smoke signals are obtained by building a fire of moist materials. the indian obtains his smoke-puffs by placing a blanket or robe over the fire, withdrawing it for an instant, and then replacing it quickly. in this way puffs of smoke may be sent aloft as frequently as desired. a column of smoke-puffs was used as a warning signal, its meaning being: look out, the enemy is near. one smoke-puff was a signal for attention; two puffs indicated that the sender would camp at that place. three puffs showed that the sender was in danger, as the enemy was near. fire-arrows shot across the sky at night had a similar meaning. the head of the arrow was dipped in some highly inflammable substance and then set on fire at the instant before it was discharged from the bow. one fire-arrow shot into the sky meant that the enemy were near; two signaled danger, and three great danger. when the indian shot many fire-arrows up in rapid succession he was signaling to his friends that his enemies were too many for him. two arrows discharged into the air at the same time indicated that the party sending them was about to attack. three indicated an immediate attack. a fire-arrow discharged diagonally across the sky indicated the direction in which the sender would travel. such were the methods which the indians used, working out different meanings for the signals in the various tribes. very slight progress was made in message-sending in medieval times, and it was the middle of the seventeenth century before even signal systems were attained which were in any sense an improvement. for many centuries the people of the world existed, devising nothing better than the primitive methods outlined above. ii signals past and present marine and military signals--code flags--wig-wag--semaphore telegraphs--heliographs--ardois signals--submarine signals. in naval affairs some kind of an effective signal system is imperative. even in the ordinary evolutions of a fleet the commander needs some better way of communicating with the ship captains than despatching a messenger in a small boat. the necessity of quick and sure signals in time of battle is obvious. yet for many centuries naval signals were of the crudest. the first distinct advance over the primitive methods by which the commander of one roman galley communicated with another came with the introduction of cannon as a naval arm. the use of signal-guns was soon thought of, and war-ships used their guns for signal purposes as early as the sixteenth century. not long after came the square-rigged ship, and it soon occurred to some one that signals could be made by dropping a sail from the yard-arm a certain number of times. up to the middle of the seventeenth century the possibilities of the naval signal systems were limited indeed. only a few prearranged orders and messages could be conveyed. unlimited communication at a distance was still impossible, and there were no means of sending a message to meet an unforeseen emergency. so cumbersome were the signal systems in use that even though they would convey the intelligence desired, the speaking-trumpet or a courier was employed wherever possible. to the officers of the british navy of the seventeenth century belongs the credit for the first serious attempt to create a system of communication which would convey any and all messages. it is not clear whether admiral sir william penn or james ii. established the code. it was while he was duke of york and the commander of britain's navy, that the james who was later to be king took this part in the advancement of means of communication. messages were sent by varying the position of a single signal flag. in 1780 admiral kempenfeldt thought of adding other signal flags instead of depending upon the varied positions of a single signal. from his plan the flag signals now in use by the navies of the world were developed. the basis of his system was the combining of distinct flags in pairs. the work of admiral philip colomb marked another long step forward in signaling between ships. while a young officer he developed a night-signal system of flashing lights, still in use to some extent, and which bears his name. colomb's most important contribution to the art of signaling was his realization of the utility of the code which morse had developed in connection with the telegraph. code flags, which are largely used between ships, have not been entirely displaced by the wireless. the usual naval code set consists of a set of alphabet flags and pennants, ten numeral flags, and additional special flags. this of course provides for spelling out any conceivable message by simply hoisting letter after letter. so slow a method is seldom used, however. various combinations of letters and figures are used to indicate set terms or sentences set forth in the code-book. thus the flags representing a and e, hoisted together, may be found on reference to the code-book to mean, "weigh anchor." each navy has its own secret code, which is carefully guarded lest it be discovered by a possible enemy. naval code-books are bound with metal covers so that they may be thrown overboard in case a ship is forced to surrender. the international code is used by ships of all nations. it is the universal language of the sea, and by it sailors of different tongues may communicate through this common medium. any message may be conveyed by a very few of the flags in combination. the wig-wag system, a favorite and familiar method of communication with every boy scout troop, is in use by both army and navy. the various letters of the alphabet are indicated by the positions in which the signaler holds his arms. keeping the arms always forty-five degrees apart, it is possible to read the signals at a considerable distance. navy signalers have become very efficient with this form of communication, attaining a speed of over fifteen words a minute. a semaphore is frequently substituted for the wig-wag flags both on land and on sea. navy semaphores on big war-ships consist of arms ten or twelve feet long mounted at the masthead. the semaphore as a means of communication was extensively used on land commercially as well as by the army. a regular semaphore telegraph system, working in relays over considerable distances was in operation in france a century ago. other semaphore telegraphs were developed in england. the introduction of the morse code and its adaptation to signaling by sight and sound did much to simplify these means of communication. the development of signaling after the adoption of the morse code, though it occurred subsequent to the introduction of the telegraph, may properly be spoken of here, since the systems dependent upon sight and sound grow from origins more primitive than those which depend upon electricity. up to the middle of the nineteenth century armies had made slight progress in perfecting means of communication. the british army had no regular signal service until after the recommendations of colomb proved their worth in naval affairs. the german army, whose systems of communication have now reached such perfection, did not establish an army signal service until 1902. the simplicity of the dot and dash of the morse code makes it readily available for almost any form of signaling under all possible conditions. two persons within sight of each other, who understand the code, may establish communication by waving the most conspicuous object at hand, using a short swing for a dot and a long swing for a dash. two different shapes may also be exhibited, one representing a dot and the other a dash. the dot-and-dash system is also admirably adapted for night signaling. a search-light beam may be swung across the sky through short and long arcs, a light may be exhibited and hidden for short and long periods, and so on. where the search-light may be played upon a cloud it may be seen for very considerable distances, messages having been sent forty miles by this means. fog-horns, whistles, etc., may be similarly employed during fogs or amid thick smoke. a short blast represents a dot, and a long one a dash. the heliograph, which established communication by means of short and long light-flashes, is another important means of signaling to which the morse code has been applied. this instrument catches the rays of the sun upon a mirror, and thence casts them to a distant receiving station. a small key which throws the mirror out of alignment serves to obscure the flashes for a space at the will of the sender, and so produces short or long flashes. the british army has made wide use of the heliograph in india and africa. during the british-boer war it formed the sole means of communication between besieged garrisons and the relief forces. where no mountain ranges intervene and a bright sun is available, heliographic messages may be read at a distance of one hundred and fifty miles. while the british navy used flashing lights for night signals, the united states and most other navies adopted a system of fixed colored lights. the system in use in the united states navy is known as the ardois system. in this system the messages are sent by four lights, usually electric, which are suspended from a mast or yard-arm. the lights are manipulated by a keyboard situated at a convenient point on the deck. a red lamp is flashed to indicate a dot in the morse code, while a white lamp indicates a dash. the ardois system is also used by the army. the perfection of wireless telegraphy has caused the ardois and other signal systems depending upon sight or sound to be discarded in all but exceptional cases. the wig-wag and similar systems will probably never be entirely displaced by even such superior systems as wireless telegraphy. the advantage of the wig-wag lies in the fact that no apparatus is necessary and communication may thus be established for short distances almost instantly. its disadvantages are lack of speed, impenetrability to dust, smoke, and fog, and the short ranges over which it may be operated. there is another form of sound-signaling which, though it has been developed in recent years, may properly be mentioned in connection with earlier signal systems of similar nature. this is the submarine signal. we have noted that much attention was paid to communication by sound-waves through the medium of the air from the earliest times. it was not until the closing years of the past century, however, that the superior possibilities of water as a conveyer of sound were recognized. arthur j. mundy, of boston, happened to be on an american steamer on the mississippi river in the vicinity of new orleans. it was rumored that a spanish torpedo-boat had evaded the united states war vessels and made its way up the great river. the general alarm and the impossibility of detecting the approach of another vessel set mundy thinking. it seemed to him that there should be some way of communicating through the water and of listening for sounds underwater. he recalled his boyhood experiments in the old swimming-hole. he remembered how distinctly the sound of stones cracked together carried to one whose ears were beneath the surface. thus the idea of underwater signaling was born. mundy communicated this idea to elisha gray, and the two, working together, evolved a successful submarine signal system. it was on the last day of the nineteenth century that they were able to put their experiments into practical working form. through a well in the center of the ship they suspended an eight-hundred-pound bell twenty feet beneath the surface of the sea. a receiving apparatus was located three miles distant, which consisted simply of an ear-trumpet connected to a gas-pipe lowered into the sea. the lower end of the pipe was sealed with a diaphragm of tin. when submerged six feet beneath the surface the strokes of the bell could be heard. then a special electrical receiver of extreme sensitiveness, known as a microphone, was substituted and connected at the receiving station with an ordinary telephone receiver. with this receiving apparatus the strokes of the bell could be heard at a distance of over ten miles. this system has had a wide practical application for communication both between ship and ship and between ship and shore. most transatlantic ships are now equipped with such a system. the transmitter consists of a large bell which is actuated either by compressed air or by an electro-magnetic system. this is so arranged that it may be suspended over the side of the ship and lowered well beneath the surface of the water. the receivers consist of microphones, one on each side of the ship. the telephone receivers connected to the two microphones are mounted close together on an instrument board on the bridge of the ship. the two instruments are used when it is desired to determine the direction from which the signals come. if the sound is stronger in the 'phone on the right-hand side of the ship the commander knows that the signals are coming from that direction. if the signals are from a ship in distress he may proceed toward it by turning his vessel until the sound of the signal-bell is equal in the two receivers. the ability to determine the direction from which the signal comes is especially valuable in navigating difficult channels in foggy weather. signal-bells are located near lighthouses and dangerous reefs. each calls its own number, and the vessel's commander may thus avoid obstructions and guide the ship safely into the harbor. the submarine signal is equally useful in enabling vessels to avoid collision in fogs. because water conducts sound much better than air, submarine signals are far better than the fog-horn or whistles. the submarine signal system has also been applied to submarine war-ships. by this means alone may a submarine communicate with another, with a vessel on the surface, or with a shore station. an important and interesting adaptation of the marine signal was made to meet the submarine warfare of the great european conflict. at first it seemed that battle-ship and merchantman could find no way to locate the approach of an enemy submarine. but it was found that by means of the receiving apparatus of the submarine telephone an approaching submarine could be heard and located. while the sounds of the submarine's machinery are not audible above the water, the delicate microphone located beneath the water can detect them. hearing a submarine approaching beneath the surface, the merchantman may avoid her and the destroyers and patrol-boats may take means to effect her capture. iii forerunners of the telegraph from lodestone to leyden jar--the mysterious "c.m."--spark and frictional telegraphs--the electro-magnet--davy and the relay system. the thought and effort directed toward improving the means of communication brought but small results until man discovered and harnessed for himself a new servant--electricity. the story of the growth of modern means of communication is the story of the application of electricity to this particular one of man's needs. the stories of the masters of space are the stories of the men who so applied electricity that man might communicate with man. some manifestations of electricity had been known since long before the christian era. a greek legend relates how a shepherd named magnes found that his crook was attracted by a strange rock. thus was the lodestone, the natural magnetic iron ore, discovered, and the legend would lead us to believe that the words magnet and magnetism were derived from the name of the shepherd who chanced upon this natural magnet and the strange property of magnetism. the ability of amber, when rubbed, to attract straws, was also known to the early peoples. how early this property was found, or how, we do not know. the name electricity is derived from _elektron_, the greek name for amber. the early chinese and persians knew of the lodestone, and of the magnetic properties of amber after it has been rubbed briskly. the romans were familiar with these and other electrical effects. the romans had discovered that the lodestone would attract iron, though a stone wall intervened. they were fond of mounting a bit of iron on a cork floating in a basin of water and watch it follow the lodestone held in the hand. it is related that the early magicians used it as a means of transmitting intelligence. if a needle were placed upon a bit of cork and the whole floated in a circular vessel with the alphabet inscribed about the circle, one outside the room could cause the needle to point toward any desired letters in turn by stepping to the proper position with the lodestone. thus a message could be sent to the magician inside and various feats of magic performed. our own modern magicians are reported as availing themselves of the more modern applications of electricity in somewhat similar fashion and using small, easily concealed wireless telegraph or telephone sets for communication with their confederates off the stage. the idea of encircling a floating needle with the alphabet was developed into the sympathetic telegraph of the sixteenth century, which was based on a curious error. it was supposed that needles which had been touched by the same lodestone were sympathetic, and that if both were free to move one would imitate the movements of another, though they were at a distance. thus, if one needle were attracted toward one letter after the other, and the second similarly mounted should follow its movements, a message might readily be spelled out. of course the second needle would not follow the movements of the first, and so the sympathetic telegraph never worked, but much effort was expended upon it. in the mean time others had learned that many substances besides amber, on being rubbed, possessed magnetic properties. machines by which electricity could be produced in greater quantities by friction were produced and something was learned of conductors. benjamin franklin sent aloft his historic kite and found that electricity came down the silken cord. he demonstrated that frictional and atmospheric electricity are the same. franklin and others sent the electric charge along a wire, but it did not occur to them to endeavor to apply this to sending messages. credit for the first suggestion of an electric telegraph must be given to an unknown writer of the middle eighteenth century. in the _scots magazine_ for february 17, 1755, there appeared an article signed simply, "c.m.," which suggested an electric telegraph. the writer's idea was to lay an insulated wire for each letter of the alphabet. the wires could be charged from an electrical machine in any desired order, and at the receiving end would attract disks of paper marked with the letter which that wire represented, and so any message could be spelled out. the identity of "c.m." has never been established, but he was probably charles morrison, a scotch surgeon with a reputation for electrical experimentation, who later emigrated to virginia. of course "c.m.'s" telegraph was not practical, because of the many wires required, but it proved to be a fertile suggestion which was followed by many other thinkers. one experimenter after another added an improvement or devised a new application. a french scientist devised a telegraph which it is suspected might have been practical, but he kept his device secret, and, as napoleon refused to consider it, it never was put to a test. an englishman devised a frictional telegraph early in the last century and endeavored to interest the admiralty. he was told that the semaphore was all that was required for communication. another submitted a similar system to the same authorities in 1816, and was told that "telegraphs of any kind are now wholly unnecessary." an american inventor fared no better, for one harrison gray dyar, of new york, was compelled to abandon his experiments on long island and flee because he was accused of conspiracy to carry on secret communication, which sounded very like witchcraft to our forefathers. his telegraph sent signals by having the electric spark transmitted by the wire decompose nitric acid and so record the signals on moist litmus paper. it seems altogether probable that had not the discovery of electro-magnetism offered improved facilities to those seeking a practical telegraph, this very chemical telegraph might have been put to practical use. in the early days of the nineteenth century the battery had come into being, and thus a new source of electric current was available for the experimenters. coupled with this important discovery in its effect upon the development of the telegraph was the discovery of electro-magnetism. this was the work of hans christian oersted, a native of denmark. he first noticed that a current flowing through a wire would deflect a compass, and thus discovered the magnetic properties of the electric current. a frenchman named ampère, experimenting further, discovered that when the electric current is sent through coils of wire the magnetism is increased. the possibility of using the deflection of a magnetic needle by an electric current passing through a wire as a means of conveying intelligence was quickly grasped by those who were striving for a telegraph. experiments with spark and chemical telegraphs were superseded by efforts with this new discovery. ampère, acting upon the suggestion of la place, an eminent mathematician, published a plan for a feasible telegraph. this was later improved upon by others, and it was still early in the nineteenth century that a model telegraph was exhibited in london. about this time two professors at the university of göttingen were experimenting with telegraphy. they established an experimental line between their laboratories, using at first a battery. then faraday discovered that an electric current could be generated in a wire by the motion of a magnet, thus laying the basis for the modern dynamo. professors gauss and weber, who were operating the telegraph line at göttingen, adapted this new discovery to their needs. they sent the message by moving a magnetic key. a current was thus generated in the line, and, passing over the wire and through a coil at the farther end, moved a magnet suspended there. the magnet moved to the right or left, depending on the direction of the current sent through the wire. a tiny mirror was mounted on the receiving magnet to magnify its movement and so render it more readily visible. one steinheil, of munich, simplified it and added a call-bell. he also devised a recording telegraph in which the moving needle at the receiving station marked down its message in dots and dashes on a ribbon of paper. he was the first to utilize the earth for the return circuit, using a single wire for despatching the electric current used in signaling and allowing it to return through the ground. in 1837, the same year in which wheatstone and morse were busy perfecting their telegraphs, as we shall see, edward davy exhibited a needle telegraph in london. davy also realized that the discoveries of arago could be used in improving the telegraph and making it practical. arago discovered that the current passing through a coil of wire served to magnetize temporarily a piece of soft iron within it. it was this principle upon which morse was working at this time. davy did not carry his suggestions into effect, however. he emigrated to australia, and the interruption in his experiments left the field open for those who were finally to bring the telegraph into usable form. davy's greatest contribution to telegraphy was the relay system by which very weak currents could call into play strong currents from a local battery, and so make the signals apparent at the receiving station. iv inventions of sir charles wheatstone wheatstone and his enchanted lyre--wheatstone and cooke--first electric telegraph line installed--the capture of the "kwaker"--the automatic transmitter. before we come to the story of samuel f.b. morse and the telegraph which actually proved a commercial success as the first practical carrier of intelligence which had been created for the service of man, we should pause to consider the achievements of charles wheatstone. together with william fothergill cooke, another englishman, he developed a telegraph line that, while it did not attain commercial success, was the first working telegraph placed at the service of the public. charles wheatstone was born near gloucester in 1802. having completed his primary schooling, charles was apprenticed to his uncle, who was a maker and seller of musical instruments. he showed little aptitude either in the workshop or in the store, and much preferred to continue the study of books. his father eventually took him from his uncle's charge and allowed him to follow his bent. he translated poetry from the french at the age of fifteen, and wrote some verse of his own. he spent all the money he could secure on books. becoming interested in a book on volta's experiments with electricity, he saved up his coppers until he could purchase it. it was in french, and he found the technical descriptions rather too difficult for his comprehension, so that he was forced to save again to buy a french-english dictionary. with the aid of this he mastered the volume. immediately his attention was turned toward the wonders of the infant science of electricity, and he eagerly endeavored to perform the experiments described. aided by his older brother, he set to work on a battery as a source of current. running short of funds with which to purchase copper plates, he again began to save his pennies. then the idea occurred to him to use the pennies themselves, and his first battery was soon complete. he continued his experiments in various fields until, at the age of nineteen, he first brought himself to public notice with his enchanted lyre. this he placed on exhibition in music-shops in london. it consisted of a small lyre suspended from the ceiling which gave forth, in turn, the sounds of various musical instruments. really the lyre was merely a sounding-box, and the vibrations of the music were conveyed from instruments, played in the next room, to the lyre through a steel rod. the young man spent much time experimenting with the transmission of sound. having conveyed music through the steel rod to his enchanted lyre, much to the mystification of the londoners, he proposed to transmit sounds over a considerable distance by this method. he estimated that sound could be sent through steel rods at the rate of two hundred miles a second and suggested the use of such a rod as a telegraph between london and edinburgh. he called his arrangement a telephone. a scientific writer of the day, commenting in a scientific journal on the enchanted lyre which wheatstone had devised, suggested that it might be used to render musical concerts audible at a distance. thus an opera performed in a theater might be conveyed through rods to other buildings in the vicinity and there reproduced. this was never accomplished, and it remained for our own times to accomplish this and even greater wonders. wheatstone also devised an instrument for increasing feeble sound, which he called a microphone. this consisted of a pair of rods to convey the sound vibrations to the ears, and does not at all resemble the modern electrical microphone. other inventions in the transmission and reproduction of sound followed, and he devoted no little attention to the construction of improved musical instruments. he even made some efforts to produce a practical talking-machine, and was convinced that one would be attained. at thirty-two he was widely famed as a scientist and had been made a professor of experimental physics in king's college, london. his most notable work at this time was measuring the speed of the electric current, which up to that time had been supposed to be instantaneous. by 1835 wheatstone had abandoned his plans for transmitting sounds through long rods of metal and was studying the telegraph. he experimented with instruments of his own and proposed a line across the thames. it was in 1836 that mr. cooke, an army officer home on leave, became interested in the telegraph and devoted himself to putting it on a working basis. he had already exhibited a crude set when he came to wheatstone, realizing his own lack of scientific knowledge. the two men finally entered into partnership, wheatstone contributing the scientific and cooke the business ability to the new enterprise. the partnership was arranged late in 1837, and a patent taken out on wheatstone's five-needle telegraph. in this telegraph a magnetic needle was located within a loop formed by the telegraph circuit at the receiving end. when the circuit was closed the needle was deflected to one side or the other, according to the direction of the current. five separate circuits and needles were used, and a variety of signals could thus be sent. five wires, with a sixth return wire, were used in the first experimental line erected in london in 1837. so in the year when morse was constructing his models wheatstone and cooke were operating an experimental line, crude and impracticable though it was, and enjoying the sensations of communicating with each other at a distance. in 1841 the telegraph was placed on public exhibition at so much a head, but it was viewed as an entertaining novelty without utility by the public at large. after many disappointments the inventors secured the cooperation of the great western railroad, and a line was erected for a distance of thirteen miles. but the public would not patronise the line until its utility was strikingly demonstrated by the capture of the "kwaker." early one morning a woman was found dead in her home in the suburbs of london. a man had been observed leaving the house, and his appearance had been noted. inquiries revealed that a man answering his description had left on the slow train for london. without the telegraph he could not have been apprehended. but the telegraph was available at this point, and his description was telegraphed ahead and the police in london were instructed to arrest him upon his arrival. "he is dressed as a quaker," ran the message. there was no q in the alphabet of-the five-needle instrument, and so the sender spelled quaker, kwaker. the clerk at the receiving end could not-understand the strange word, and asked to have it repeated again and again. finally some one suggested that the message be completed and the whole was then deciphered. when the man dressed as a quaker stepped from the slow train on his arrival at london the police were awaiting him; he was arrested and eventually confessed the murder. the news of this capture and the part the telegraph played gave striking proof of the utility of the new invention, and public skepticism and indifference were overcome. by 1845 wheatstone had so improved his apparatus that but one wire was required. the single-needle instrument pointed out the letters on the dial around it by successive deflections in which it was arranged to move, step by step, at the will of the sending station. the single-needle instrument, though generally displaced by morse's telegraph, remained in use for a long time on some english lines. wheatstone had also invented a type-printing telegraph, which he patented in 1841. this required two circuits. with a working telegraph attained, the partners became involved in an altercation as to which deserved the honor of inventing the same. the quarrel was finally submitted to two famous scientists for arbitration. they reported that the telegraph was the result of their joint labors. to wheatstone belongs the credit for devising the apparatus; to cooke for introducing it and placing it before the public in working form. here we see the combination of the man of science and the man of business, each contributing needed talents for the establishment of a great invention on a working basis. wheatstone's researches in the field of electricity were constant. in 1840 he devised a magnetic clock and proposed a plan by which many clocks, located at different points, could be set at regular intervals with the aid of electricity. such a system was the forerunner of the electrically wound and regulated clocks with which we are now so familiar. he also devised a method for measuring the resistance which wires offer to the passage of an electric current. this is known as wheatstone's bridge and is still in use in every electrical and physical laboratory. he also invented a sound telegraph by which signals were transmitted by the strokes of a bell operated by the current at the receiving end of the circuit. the invention of wheatstone's which proved to be of greatest lasting importance in connection with the telegraph was the automatic transmitter. by this system the message is first punched in a strip of paper which, when passed through the sending instrument, transmits the message. by this means he was able to send messages at the rate of one hundred words a minute. this automatic transmitter is much used for press telegrams where duplicate messages are to be sent to various points. the automatic transmitter brought knighthood to its inventor, wheatstone receiving this honor in 1868. wheatstone took an active part in the development of the telegraph and the submarine cable up to the time of his death in 1875. wheatstone's telegraph would have served the purposes of humanity and probably have been universally adopted, had not a better one been invented almost before it was established. and it is because morse, taking up the work where others had left off, was able to invent an instrument which so fully satisfied the requirements of man for so long a period that he is known to all of us as the inventor of the telegraph. and yet, without belittling the part played by morse, we must recognize the important work accomplished by sir charles wheatstone. v the achievement of morse morse's early life--artistic aspirations--studies in paris--his paintings--beginnings of his invention--the first instrument--the morse code--the first written message. when we consider the youth and immaturity of america in the first half of the nineteenth century, it seems the more remarkable that the honor of making the first great practical application of electricity should have been reserved for an american. with the exception of the isolated work of franklin, the development of the new science of electrical learning was the work of europeans. this was natural, for it was europe which was possessed of the accumulated wealth and learning which are usually attained only by older civilizations. yet, with all these advantages, electricity remained largely a scientific plaything. it was an american who fully recognized the possibilities of this new force as a servant of man, and who was possessed of the practical genius and the business ability to devise and introduce a thoroughly workable system of rapid and certain communication. we have seen that wheatstone was early trained as a musician. samuel morse began life as an artist. but while wheatstone early indicated his lack of interest in music and devoted himself to scientific studies while yet a youth, morse's artistic career was of his own choosing, and he devoted himself to it for many years. this explains the fact that wheatstone attained much scientific success before morse, though he was eleven years his junior. it was in 1791 that samuel morse was born. samuel finley breese morse was the entire name with which he was endowed by his parents. he came from the sturdiest of puritan stock, his father being of english and his mother of scotch descent. his father was an eminent divine, and also notable as a geographer, being the author of the first american geography of importance. his mother also was possessed of unusual talent and force. it is interesting to note that samuel morse first saw the light in charlestown, massachusetts, at the foot of breed's hill, but little more than a mile from the birthplace of benjamin franklin. he came into the world about a year after franklin died. it is interesting to believe that some of the practical talent of america's first great electrician in some way descended to samuel morse. he received an unusual education. at the age of seven he was sent to a school at andover, massachusetts, to prepare him for phillips academy. at the academy he was prepared for yale college, which he entered when fifteen years of age. with the knowledge of science so small at the time, collegiate instruction in such subjects was naturally meager in the extreme. jeremiah day was then professor of natural philosophy at yale, and was probably america's ablest teacher of the subject. his lectures upon electricity and the experiments with which he illustrated them aroused the interest of morse, as we learn from the letters he wrote to his parents at this time. one principle in particular impressed morse. this was that "if the electric circuit be interrupted at any place the fluid will become visible, and when it passes it will leave an impression upon any intermediate body." thus was it stated in the text-book in use at yale at that time. more than a score of years after the telegraph had been achieved morse wrote: the fact that the presence of electricity can be made visible in any desired part of the circuit was the crude seed which took root in my mind, and grew into form, and ripened into the invention of the telegraph. we shall later hear of the occasion which recalled this bit of information to morse's mind. but though yale college was at that time a center of scientific activity, and morse showed more than a little interest in electricity and chemistry, his major interest remained art. he eagerly looked forward to graduation that he might devote his entire time to the study of painting. it is significant of the tolerance and breadth of vision of his parents that they apparently put no bars in the path of this ambition, though they had sacrificed to give him the best of collegiate trainings that he might fit himself for the ministry, medicine, or the law. as a boy of fifteen samuel morse had painted water-colors that attracted attention, and he was possessed of enough talent to paint miniatures while at yale which were salable at five dollars apiece, and so aided in defraying his college expenses. after his graduation from yale in 1810, morse devoted himself entirely to the study of art, still being dependent upon his parents for support. he secured the friendship and became the pupil of washington allston, then a foremost american painter. in the summer of 1811 allston sailed for england, and morse accompanied him. in london he came to the attention of benjamin west, then at the height of his career, and benefited by his advice and encouragement. that he had no ambition other than his art at this period we may learn from a letter he wrote to his mother in 1812. my passion for my art [he wrote] is so firmly rooted that i am confident no human power could destroy it. the more i study the greater i think is its claim to the appellation divine. i am now going to begin a picture of the death of hercules, the figure to be large as life. when he had completed this picture to his own satisfaction, he showed it to west. "go on and finish it," was west's comment. "but it is finished," said morse. "no, no. see here, and here, and here are places you can improve it." morse went to work upon his painting again, only to meet the same comment when he again showed it to west. this happened again and again. when the youth had finally brought it to a point where west was convinced it was the very best morse could do he had learned a lesson in thoroughness and painstaking attention to detail that he never forgot. that he might have a model for his painting morse had molded a figure of hercules in clay. at the advice of west he entered the cast in a competition for a prize in sculpture, with the result that he received the prize and a gold medal for his work. he then plunged into the competition for a prize and medal offered by the royal academy for the best historical painting. his subject was, "the judgment of jupiter in the case of apollo, marpessa, and idas." though he completed the picture to the satisfaction of west, morse was not able to remain in london and enter it in the competition. the rules required that the artist be present in person if he was to receive the prize, but morse was forced to return to america. he had been in england for four years--a year longer than had originally been planned for him--and he was out of funds, and his parents could support him no longer. morse lived in london during the war of 1812, but seems to have suffered no annoyance other than that of poverty, which the war intensified by raising the prices of food as well as his necessary artist's materials to an almost prohibitive figure. the last of the napoleonic wars was also in progress. news of the battle of waterloo reached london but a short time before morse sailed for america. it required two days for the news to reach the english capital. the young american, whose inability to sell his paintings was driving him from london, was destined to devise a system which would have carried the great news to its destination within a few seconds. but while he gained fame in america and secured praise and attention as he had in london, he found art no more profitable. he contrived to eke out an existence by painting an occasional portrait, going from town to town in new england for this purpose. he turned from art to invention for a time, joining with his brother in devising a fire-engine pump of an improved pattern. they secured a patent upon it, but could not sell it. he turned again to the life of a wandering painter of portraits. in 1818 he went to charleston, south carolina, at the invitation of his uncle. his portraits proved very popular and he was soon occupied with work at good prices. this prosperity enabled him to take unto himself a wife, and the same year he married lucretia walker, of concord, new hampshire. after four years in the south morse returned to the north, hoping that larger opportunities would now be ready for him. the result was again failure. he devoted his time to huge historical paintings, and the public would neither buy them nor pay to see them when they were exhibited. another blow fell upon him in 1825 when his wife died. at last he began to secure more sitters for his portraits, though his larger works still failed. he assisted in the organization of the national academy of design and became its first president. in 1829 he again sailed for europe to spend three years in study in the galleries of paris and rome. still he failed to attain any real success in his chosen work. he had made many friends and done much worthy work, yet there is little probability that he would have attained lasting fame as an artist even though his energies had not been turned to other interests. it was on the packet ship _sully_, crossing the atlantic from france, that morse conceived the telegraph which was to prove the first great practical application of electricity. one noon as the passengers were gathered about the luncheon-table, a dr. charles t. jackson, of boston, exhibited an electro-magnet he had secured in europe, and described certain electrical experiments he had seen while in paris. he was asked concerning the speed of electricity through a wire, and replied that, according to faraday, it was practically instantaneous. the discussion recalled to morse his own collegiate studies in electricity, and he remarked that if the circuit were interrupted the current became visible, and that it occurred to him that these flashes might be used as a means of communication. the idea of using the current to carry messages became fixed in his mind, and he pondered, over it during the remaining weeks of the long, slow voyage. doctor jackson claimed, after morse had perfected and established his telegraph, that the idea had been his own, and that morse had secured it from him on board the _sully_. but doctor jackson was not a practical man who either could or did put any ideas he may have had to practical use. at the most he seems to have simply started morse's mind along a new train of thought. the idea of using the current as a carrier of messages, though it was new to morse, had occurred to others earlier, as we have seen. but at the very outset morse set himself to find a means by which he might make the current not only signal the message, but actually record it. before he landed from the _sully_ he had worked out sketches of a printing telegraph. in this the current actuated an electro-magnet on the end of which was a rod. this rod was to mark down dots and dashes on a moving tape of paper. thus was the idea born. of course the telegraph was still far from an accomplished fact. without the improved electro-magnets and the relay of professor henry, morse had not yet even the basic ideas upon which a telegraph to operate over considerable distances could be constructed. but morse was possessed of yankee imagination and practical ability. he was possessed of a fair technical education for that day, and he eagerly set himself to attaining the means to accomplish his end. that he realized just what he sought is shown by his remark to the captain of the _sully_ when he landed at new york. "well, captain," he remarked, "should you hear of the telegraph one of these days as the wonder of the world, remember that the discovery was made on board the good ship _sully_." with the notion of using an electro-magnet as a receiver, an alphabet consisting of dots and dashes, and a complete faith in the practical possibilities of the whole, morse went to work in deadly earnest. but poverty still beset him and it was necessary for him to devote most of his time to his paintings, that he might have food, shelter, and the means to buy materials with which to experiment. from 1832 to 1835 he was able to make but small progress. in the latter year he secured an appointment as professor of the literature of the arts of design in the newly established university of the city of new york. he soon had his crude apparatus set up in a room at the college and in 1835 was able to transmit messages. he now had a little more leisure and a little more money, but his opportunities were still far from what he would have desired. the principal aid which came to him at the university was from professor gale, a teacher of chemistry. gale became greatly interested in morse's apparatus, and was able to give him much practical assistance, becoming a partner in the enterprise. morse knew little of the work of other experimenters in the field of electricity and gale was able to tell morse what had been learned by others. particularly he brought to morse's attention the discoveries of another american, prof. joseph henry. the electro-magnet which actuated the receiving instrument in the crude set in use by morse in 1835 had but a few turns of thick wire. professor henry, by his experiments five years earlier, had demonstrated that many turns of small wire made the electro-magnet far more sensitive. morse made this improvement in his own apparatus. in 1832 henry had devised a telegraph very similar to that of morse by which he signaled through a mile of wire. his receiving apparatus was an electro-magnet, the armature of which struck a bell. thus the messages were read by sound, instead of being recorded on a moving strip of paper as by morse's system. while henry was possibly the ablest of american electricians at that time, he devoted himself entirely to science and made no effort to put his devices to practical use. neither did he endeavor to profit by his inventions, for he secured no patents upon them. professor henry realized, in common with morse and others, that if the current were to be conducted over long wires for considerable distances it would become so weak that it would not operate a receiver. henry avoided this difficulty by the invention of what is known as the relay. at a distance where the current has become weak because of the resistance of the wire and losses due to faulty insulation, it will still operate a delicate electro-magnet with a very light armature so arranged as to open and close a local circuit provided with suitable batteries. thus the recording instrument may be placed on the local circuit and as the local circuit an opened and closed in unison with the main circuit, the receiver can be operated. it was the relay which made it possible to extend telegraph lines to a considerable distance. it is not altogether clear whether morse adopted henry's relay or devised it for himself. it is believed, however, that professor henry explained the relay to professor gale, who in turn placed it before his partner, morse. by 1837 morse had completed a model, had improved his apparatus, had secured stronger batteries and longer wires, and mastered the use of the relay. it was in this year that the house of representatives ordered the secretary of the treasury to investigate the feasibility of establishing a system of telegraphs. this action urged morse to complete his apparatus and place it before the government. he was still handicapped by lack of money, lack of scientific knowledge, and the difficulty of securing necessary materials and devices. to-day the experimenter may buy wire, springs, insulators, batteries, and almost anything that might be useful. morse, with scanty funds and limited time, had to search for his materials and puzzle out the way to make each part for himself with such crude tools as he had available. need we wonder that his progress was slow? instead we should wonder that, despite all discouragements and handicaps, he clung to his great idea and labored on. but assistance was to come to him in this same eventful year of 1837, and that quite unexpectedly. on a saturday in september a young man named alfred vail wandered into professor gale's laboratory. morse was there engaged in exhibiting his model to an english professor then visiting in new york. the youth was deeply impressed with what he saw. he realized that here were possibilities of an instrument that would be of untold service to mankind. asking professor morse whether he intended to experiment with a longer line, he was informed that such was his intention as soon as he could secure the means. young vail replied that he thought he could secure the money if morse would admit him as a partner. to this morse assented. vail plunged into the enterprise with all the enthusiasm of youth. that very evening he studied over the commercial possibilities, and before he retired had marked out on the maps in his atlas the routes for the most needed lines of communication. the young man applied to his father for support. the senior vail was the head of the speedwell iron works at morristown, new jersey, and was a man of unusual enterprise and ability. he determined to back his son in the enterprise, and morse was invited to come and exhibit his model. two thousand dollars was needed to make the necessary instruments and secure the patents. on september 23, 1837, the agreement was drawn up by the terms of which alfred vail was, at his own expense, to construct apparatus suitable for exhibition to congress and to secure a patent. in return he was to receive a one-fourth interest. very shortly afterward they filed a caveat in the patent office, which is a notice serving to protect an impending invention. alfred vail immediately set to work on the apparatus, his only helper being a fifteen-year-old apprentice boy named william baxter. the two worked early and late for many months in a secret room in the iron-works, being forced to fashion every part for themselves. the first machine was a copy of morse's model, but vail's native ability as a mechanic and his own ingenuity enabled him to make many improvements. the pencil fastened to the armature which had marked zigzag lines on the moving paper was replaced by a fountain-pen which inscribed long and short lines, and thus the dashes and dots of the morse code were put into their present form. morse had worked out an elaborate telegraphic code or dictionary, but a simpler code by which combinations of dots and dashes were used to represent letters instead of numbers in a code was now devised. vail recognized the importance of having the simplest combinations of dots and dashes stand for the most used letters, as this would increase the speed of sending. he began to figure out for himself the frequency with which the various letters occur in the english language. then he thought of the combination of types in a type-case, and, going to a local newspaper office, found the result all worked out for him. in each case of type such common letters as _e_ and _t_ have many more types than little used letters such as _q_ and _z_. by observing the number of types of each letter provided, vail was enabled to arrange them in the order of their importance in assigning them symbols in the code. thus the morse code was arranged as it stands to-day. alfred vail played a very important part in the arrangement of the code as well as in the construction of the apparatus, and there are many who believe that the code should have been called the vail code instead of the morse code. [illustration: morse's first telegraph instrument a pen was attached to the pendulum and drawn across the strip of paper by the action of the electro-magnet. the lead type shown in the lower right-hand corner was used in making electrical contact when sending a message. the modern instrument shown in the lower left-hand corner is the one that sent a message around the world in 1896.] morse came down to speedwell when he could to assist vail with the work, and yet it progressed slowly. but at last, early in january of 1838 they had the telegraph at work, and william baxter, the apprentice boy, was sent to call the senior vail. within a few moments he was in the work-room studying the apparatus. alfred vail was at the sending key, and morse was at the receiver. the father wrote on a piece of paper these words: "a patient waiter is no loser." handing it to his son, he stated that if he could transmit the message to morse by the telegraph he would be convinced. the message was sent and recorded and instantly read by morse. the first test had been completed successfully. vi "what hath god wrought?" congress becomes interested--washington to baltimore line proposed--failure to secure foreign patents--later indifference of congress--lean years--success at last--the line is built--the first public message--popularity. morse and his associates now had a telegraph which they were confident would prove a genuine success. but the great work of introducing this new wonder to the public, of overcoming indifference and skepticism, of securing financial support sufficient to erect a real line, still remained to be done. we shall see that this burden remained very largely upon morse himself. had morse not been a forceful and able man of affairs as well as an inventor, the introduction of the telegraph might have been even longer delayed. the new telegraph was exhibited in new york and philadelphia without arousing popular appreciation. it was viewed as a scientific toy; few saw in it practical possibilities. morse then took it to washington and set up his instruments in the room of the committee on commerce of the house of representatives in the capitol. here, as in earlier exhibitions, a majority of those who saw the apparatus in operation remained unconvinced of its ability to serve mankind. but morse finally made a convert of the hon. francis o.j. smith, chairman of the committee on commerce. smith had previously been in correspondence with the inventor, and morse had explained to him at length his belief that the government should own the telegraph and control and operate it for the public good. he believed that the government should be sufficiently interested to provide funds for an experimental line a hundred miles long. in return he was willing to promise the government the first rights to purchase the invention at a reasonable price. later he changed his request to a line of fifty miles, and estimated the cost of erection at $26,000. smith aided in educating the other members of his committee, and one day in february of 1838 he secured the attendance of the entire body at a test of the telegraph over ten miles of wire. the demonstration convinced them, and many were their expressions of wonder and amazement. one member remarked, "time and space are now annihilated." as a result the committee reported a bill appropriating $30,000 for the erection of an experimental line between washington and baltimore. smith's report was most enthusiastic in his praise of the invention. in fact, the congressman became so much interested that he sought a share in the enterprise, and, securing it, resigned from congress that he might devote his efforts to securing the passage of the bill and to acting as legal adviser. at this time the enterprise was divided into sixteen shares: morse held nine; smith, four; alfred vail, two; and professor gale, one. we see that morse was a good enough business man to retain the control. wheatstone and others were developing their telegraphs in europe, and morse felt that it was high time to endeavor to secure foreign patents on his invention. accompanied by smith, he sailed for england in may, taking with him a new instrument provided by vail. arriving in london, they made application for a patent. they were opposed by wheatstone and his associates, and could not secure even a hearing from the patent authorities. morse strenuously insisted that his telegraph was radically different from wheatstone's, laying especial emphasis on the fact that his recording instrument printed the message in permanent form, while wheatstone's did not. morse always placed great emphasis on the recording features of his apparatus, yet these features were destined to be discarded in america when his telegraph at last came into use. with no recourse open to him but an appeal to parliament, a long and expensive proceeding with little apparent possibility of success, morse went to france, hoping for a more favorable reception. he found the french cordial and appreciative. french experts watched his tests and examined his apparatus, pronouncing his telegraph the best of all that had been devised. he received a patent, only to learn that to be effective the invention must be put in operation in france within two years, under the french patent law. morse sought to establish his line in connection with a railway, as wheatstone had established his in england, but was told that the telegraph must be a government monopoly, and that no private parties could construct or operate. the government would not act, and morse found himself again defeated. faring no better with other european governments, morse decided to return to america to push the bill for an appropriation before congress. while morse was in europe gaining publicity for the telegraph, but no patents, his former fellow-passenger on the _sully_, dr. charles jackson, had laid claim to a share in the invention. he insisted that the idea had been his and that he had given it to morse on the trip across the atlantic. this morse indignantly denied. congress would now take no action upon the invention. a heated political campaign was in progress, and no interest could be aroused in an invention, no matter what were its possibilities in the advancement of the work and development of the nation. smith was in politics, the vails were suffering from a financial depression, professor gale was a man of very limited means, and so morse found himself without funds or support. in paris he had met m. daguerre, who had just discovered photography. morse had learned the process and, in connection with doctor draper, he fitted up a studio on the roof of the university. here they took the first daguerreotypes made in america. morse's work in art had been so much interrupted that he had but few pupils. the fees that these brought to him were small and irregular, and he was brought to the very verge of starvation. we are told of the call morse made upon one pupil whose tuition was overdue because of a delay in the arrival of funds from his home. "well, my boy," said the professor, "how are we off for money?" the student explained the situation, adding that he hoped to have the money the following week. "next week!" exclaimed morse. "i shall be dead by next week--dead of starvation." "would ten dollars be of any service?" asked the student, astonished and distressed. "ten dollars would save my life," was morse's reply. the student paid the money--all he had--and they dined together, morse remarking that it was his first meal for twenty-four hours. morse's situation and feelings at this time are also illustrated by a letter he wrote to smith late in 1841. i find myself [he wrote] without sympathy or help from any who are associated with me, whose interests, one would think, would impell them to at least inquire if they could render me some assistance. for nearly two years past i have devoted all my time and scanty means, living on a mere pittance, denying myself all pleasures and even necessary food, that i might have a sum, to put my telegraph into such a position before congress as to insure success to the common enterprise. i am crushed for want of means, and means of so trifling a character, too, that they who know how to ask (which i do not) could obtain in a few hours.... as it is, although everything is favorable, although i have no competition and no opposition--on the contrary, although every member of congress, so far as i can learn, is favorable--yet i fear all will fail because i am too poor to risk the trifling expense which my journey and residence in washington will occasion me. i will not run in debt, if i lose the whole matter. no one can tell the days and months of anxiety and labor i have had in perfecting my telegraphic apparatus. for want of means i have been compelled to make with my own hands (and to labor for weeks) a piece of mechanism which could be made much better, and in a tenth the time, by a good mechanician, thus wasting time--time which i cannot recall and which seems double-winged to me. "hope deferred maketh the heart sick." it is true, and i have known the full meaning of it. nothing but the consciousness that i have an invention which is to mark an era in human civilization, and which is to contribute to the happiness of millions, would have sustained me through so many and such lengthened trials of patience in perfecting it. a patent on the telegraph had been issued to morse in 1840. the issuance had been delayed at morse's request, as he desired to first secure foreign patents, his own american rights being protected by the caveat he had filed. although the commercial possibilities, and hence the money value of the telegraph had not been established, morse was already troubled with the rival claims of those who sought to secure a share in his invention. while working and waiting and saving, morse conceived the idea of laying telegraph wires beneath the water. he prepared a wire by wrapping it in hemp soaked in tar, and then covering the whole with rubber. choosing a moonlight night in the fall of 1842, he submerged his cable in new york harbor between castle garden and governors island. a few signals were transmitted and then the wire was carried away by a dragging anchor. truly, misfortune seemed to dog morse's footsteps. this seems to have been the first submarine cable, and in writing of it not long after morse hazarded the then astonishing prediction that europe and america would be linked by telegraphic cable. failing to secure effective aid from his associates, morse hung on grimly, fighting alone, and putting all of his strength and energy into the task of establishing an experimental line. it was during these years that he demonstrated his greatness to the full. his letters to the members of the congressional committee on commerce show marked ability. they outline the practical possibilities very clearly. morse realized not only the financial possibilities of his invention, but its benefit to humanity as well. he also presented very practical estimates of the cost of establishing the line under consideration. the committee again recommended that $30,000 be appropriated for the construction of a washington-baltimore line. the politicians had come to look upon morse as a crank, and it was extremely difficult for his adherents to secure favorable action in the house. many a congressman compared morse and his experiments to mesmerism and similar "isms," and insisted that if the government gave funds for this experiment it would be called upon to supply funds for senseless trials of weird schemes. the bill finally passed the house by the narrow margin of six votes, the vote being taken orally because so many congressmen feared to go on record as favoring an appropriation for such a purpose. the bill had still to pass the senate, and here there seemed little hope. morse, who had come to washington to press his plan, anxiously waited in the galleries. the bill came up for consideration late one evening just before the adjournment. a senator who noticed morse went up to him and said: "there is no use in your staying here. the senate is not in sympathy with your project. i advise you to give it up, return home, and think no more about it." the inventor went back to his room, with how heavy a heart we may well imagine. he paid his board bill, and found himself with but thirty-seven cents in the world. after many moments of earnest prayer he retired. early next morning there came to him miss annie ellsworth, daughter of his friend the commissioner of patents, and said, "professor, i have come to congratulate you." "congratulate me!" replied morse. "on what?" "why," she exclaimed, "on the passage of your bill by the senate!" the bill had been passed without debate in the closing moments of the session. as morse afterward stated, this was the turning-point in the history of the telegraph. his resources were reduced to the minimum, and there was little likelihood that he would have again been able to bring the matter to the attention of congress. so pleased was morse over the news of the appropriation, and so grateful to miss ellsworth for her interest in bringing him the good news, that he promised her that she should send the first message when the line was complete. with the government appropriation at his disposal, morse immediately set to work upon the washington-baltimore line. professors gale and fisher served as his assistants, and mr. vail was in direct charge of the construction work. another person active in the enterprise was ezra cornell, who was later to found cornell university. cornell had invented a machine for laying wires underground in a pipe. it was originally planned to place the wires underground, as this was thought necessary or their protection. after running the line some five miles out from baltimore it was found that this method of installing the line was to be a failure. the insulation was not adequate, and the line could not be operated to the first relay station. a large portion of the $30,000 voted by congress had been spent and the line was still far from completion. disaster seemed imminent. smith lost all faith in the enterprise, demanded most of the remaining money under a contract he had taken to lay the line, and a quarrel broke out between him and morse which further jeopardized the undertaking. morse and such of his lieutenants as remained faithful in this hour of trial, after a long consultation, decided to string the wire on poles. the method of attaching the wire to the poles was yet to be determined. they finally decided to simply bore a hole through each pole near the top and push the wire through it. stringing the wire in such fashion was no small task, but it was finally accomplished. it was later found necessary to insulate the wire with bottle necks where it passed through the poles. on may 23, 1844, the line was complete. remembering his promise to miss ellsworth, morse called upon her next morning to give him the first message. she chose, "what hath god wrought?" and early on the morning of the 24th morse sat at the transmitter in the supreme court room in the capitol and telegraphed these immortal words to vail at baltimore. the message was received without difficulty and repeated back to morse at washington. the magnetic telegraph was a reality. still the general public remained unconvinced. as in the case of wheatstone's needle telegraph a dramatic incident was needed to demonstrate the utility of this new servant. fortunately for morse, the telegraph's opportunity came quickly. the democratic national convention was in session at baltimore. after an exciting struggle they dropped van buren, then president, and nominated james k. polk. silas wright was named for the vice-presidency. at that time mr. wright was in washington. hearing of the nomination, alfred vail telegraphed it to morse in washington. morse communicated with wright, who stated that he could not accept the honor. the telegraph was ready to carry his message declining the nomination, and within a very few minutes vail had presented it to the convention at baltimore, to the intense surprise of the delegates there assembled. they refused to believe that wright had been communicated with, and sent a committee to washington to see wright and make inquiries. they found that the message was genuine, and the utility of the telegraph had been strikingly established. vii development of the telegraph system the magnetic telegraph company--the western union--crossing the continent--the improvements of alfred vail--honors awarded to morse--duplex telegraphy--edison's improvements. for some time the telegraph line between washington and baltimore remained on exhibition as a curiosity, no charge being made for demonstrating it. congress made an appropriation to keep the line in operation, vail acting as operator at the washington end. on april 1, 1845, the line was put in operation on a commercial basis, service being offered to the public at the rate of one cent for four characters. it was operated as a branch of the post-office department. on the 4th of april a visitor from virginia came into the washington office wishing to see a demonstration. up to this time not a paid message had been sent. the visitor, having no permit from the postmaster-general, was told that he could only see the telegraph in operation by sending a message. one cent being all the money he had other than twenty-dollar bills, he asked for one cent's worth. the washington operator asked of baltimore, "what time is it?" which in the code required but one character. the reply came, "one o'clock," another single character. thus but two characters had been used, or one-half cent's worth of telegraphy. the visitor expressed himself as satisfied, and waived the "change." this penny was the line's first earnings. under the terms of the agreement by which congress had made the appropriation for the experimental line, morse was bound to give the government the first right to purchase his invention. he accordingly offered it to the united states for the sum of $100,000. there followed a distressing example of official stupidity and lack of foresight. with the opportunity to own and control the nation's telegraph lines before it the government declined the offer. this action was taken at the recommendation of the hon. cave johnson, then postmaster-general, under whose direction the line had been operated. he had been a member of congress at the time the original appropriation was voted, and had ridiculed the project. the nation was now so unfortunate as to have him as its postmaster-general, and he reported "that the operation of the telegraph between washington and baltimore had not satisfied him that, under any rate of postage that could be adopted, its revenues could be made equal to its expenditures." and yet the telegraph, here offered to the government for $100,000, was developed under private management until it paid a profit on a capitalization of $100,000,000. morse seems to have had a really patriotic motive, as well as a desire for immediate return and the freedom from further worries, in his offer to the government. he was greatly disappointed at its refusal to purchase, a refusal that was destined to make morse a wealthy man. amos kendall, who had been postmaster-general under jackson, was now acting as morse's agent, and they decided to depend upon private capital. plans were made for a line between new york and philadelphia, and to arouse interest and secure capital the apparatus was exhibited in new york city at a charge of twenty-five cents a head. the public refused to patronize in sufficient numbers to even pay expenses, and the entire exhibition was so shabby, and the exhibitors so poverty-stricken, that the sleek capitalists who came departed without investing. some of the exhibitors slept on chairs or on the floor in the bare room, and it is related that the man who was later to give his name and a share of his fortune to cornell university was overjoyed at finding a quarter on the sidewalk, as it enabled him to buy a hearty breakfast. though men of larger means refused to take shares, some in humbler circumstances could recognize the great idea and the wonderful vision which morse had struggled so long to establish--a vision of a nation linked together by telegraphy. the magnetic telegraph company was formed and work started on the line. in august of 1845 morse sailed for europe in an endeavor to enlist foreign capital. the investors of europe proved no keener than those of america, and the inventor returned without funds, but imbued with increased patriotism. he had become convinced that the telegraph could and would succeed on american capital alone. in the next year a line was constructed from philadelphia to washington, thus extending the new york-philadelphia line to the capital. henry o'reilly, of rochester, new york, took an active part in this construction work and now took the contract to construct a line from philadelphia to st. louis. this line was finished by december of 1847. the path having been blazed, others sought to establish lines of their own without regard to morse's patents. one of these was o reilly, who, on the completion of the line to st. louis, began one to now orleans, without authority from morse or his company. o'reilly called his telegraph "the people's line," and when called to account in the courts insisted not only that his instruments were different from morse's, and so no infringement of his patents, but also that the morse system was a harmful monopoly and that "the people's line" should be encouraged. it was further urged that wheatstone in england and steinheil in germany had invented telegraphs before morse, and that professor henry had invented the relay which made it possible to operate the telegraph over long distances. the suits resulted in a legal victory for morse, and his patents were maintained. but still other rival companies built lines, using various forms of apparatus, and though the courts repeatedly upheld morse's patent rights, the pirating was not effectively checked. the telegraph had come to be a necessity and the original company lacked the capital to construct lines with sufficient rapidity to meet the need. within ten years after the first line had been put into operation the more thickly settled portions of the united states were served by scores of telegraph lines owned by a dozen different companies. hardly any of these were making any money, though the service was poor and the rates were high. they were all operating on too small a scale and business uses of the telegraph had not yet developed sufficiently. an amalgamation of the scattered, competing lines was needed, both to secure better service for the public and proper dividends for the investors. this amalgamation was effected by mr. hiram sibley, who organized the western union in 1856. the plan was ridiculed at the time, some one stating that "the western union seems very like collecting all the paupers in the state and arranging them into a union so as to make rich men of them." but these pauper companies did become rich once they were united under efficient management. the nation was just then stretching herself across to the pacific. the commercial importance of california was growing rapidly. by 1857 stage-coaches were crossing the plains and the pony-express riders were carrying the mail. the pioneers of the telegraph felt that a line should span the continent. this was then a tremendous undertaking, and when mr. sibley proposed that the western union should undertake the construction of such a line he was met with the strongest opposition. the explorations of frémont were not far in the past, and the vast extent of country west of the mississippi was regarded as a wilderness peopled with savages and almost impossible of development. but sibley had faith; he was possessed of morse's vision and morse's courage. the western union refusing to undertake the enterprise, he began it himself. the government, realizing the military and administrative value of a telegraph line to california, subsidized the work. additional funds were raised and a route selected was through omaha and salt lake city to san francisco. the undertaking proved less formidable than had been anticipated, for, instead of two years, less than five months were occupied in completing the line. sibley's tact and ability did much to avoid opposition by the indians. he made the red men his friends and impressed upon them the wonder of the telegraph. when the line was in operation between fort kearney and fort laramie he invited the chief of the arapahoes at fort kearney to communicate by telegraph with his friend the chief of the sioux at fort laramie. the two chiefs exchanged telegrams and were deeply impressed. they were told that the telegraph was the voice of the manitou or great spirit. to convince them it was suggested that they meet half-way and compare their experiences. though they were five hundred miles apart, they started out on horseback, and on meeting each other found that the line had carried their words truly. the story spread among the tribes, and so the telegraph line became almost sacred to the indians. they might raid the stations and kill the operators, but they seldom molested the wires. among many ignorant peoples the establishment of the telegraph has been attained with no small difficulty. the chinese showed a dread of the telegraph, frequently breaking down the early lines because they believed that they would take away the good luck of their district. the arabs, on the other hand, did not oppose the telegraph. this is partly because the name is one which they can understand, _tel_ meaning wire to them, and _araph_, to know. thus in arabic _tele-agraph_ means to know by wire. just as the indians of our own plains had difficulty in understanding the telegraph, so the primitive peoples in other parts of the world could scarce believe it possible. a story is told of the construction of an early line in british india. the natives inquired the purpose of the wire from the head man. "the wire is to carry messages to calcutta," he replied. "but how can words run along a wire?" they asked. the head man puzzled for a moment. "if there were a dog," he replied, "with a tail long enough to reach from here to calcutta, and you pinched his tail here, wouldn't he howl in calcutta?" once sibley and the other american telegraph pioneers had spanned the continent, they began plans for spanning the globe. their idea was to unite america and europe by a line stretched through british columbia, alaska, the aleutian islands, and siberia. siberia had been connected with european russia, and thus practically the entire line could be stretched on land, only short submarine cables being necessary. it was then seriously doubted that cables long enough to cross the atlantic were practicable. the expedition started in 1865, a fleet of thirty vessels carrying the men and supplies. tremendous difficulties had been overcome and a considerable part of the work accomplished when the successful completion of the atlantic cable made the work useless. nearly three million dollars had been expended by the western union in this attempt. yet, despite this loss, its affairs were so generally successful and the need for the telegraph so real that it continued to thrive until it reached its present remarkable development. while the line-builders were busy stretching telegraph wires into almost every city and town in the nation, others were perfecting the apparatus. alfred vail was a leading figure in this work. already he had played a large part in designing and constructing the apparatus to carry out morse's ideas, and he continued to improve and perfect until practically nothing remained of morse's original apparatus. the original morse transmitter had consisted of a porte-rule and movable type. this was cumbersome, and vail substituted a simple key to make and break the circuit. vail had also constructed the apparatus to emboss the message upon the moving strip of paper, but this he now improved upon. the receiving apparatus was simplified and the pen was replaced by a disk smeared with ink which marked the dots and dashes upon the paper. as we have noticed, morse took particular pride in the fact that the receiving apparatus in his telegraph was self-recording, and considered this as one of the most important parts of his system. but when the telegraph began to come into commercial use the operators at the receiving end noticed that they could read the messages from the long and short periods between the clicks of the receiving mechanism. thus they were taking the message by ear and the recording mechanism was superfluous. rules and fines failed to break them of the habit, and vail, recognizing the utility of the development, constructed a receiver which had no recording device, but from which the messages were read by listening to the clicks as the armature struck against the frame in which it was set. thus the telegraph returned in its elements to the form of professor henry's original bell telegraph. with his bell telegraph and his relay henry had the elements of a successful system. he failed, however, to develop them practically or to introduce them to the attention of the public. he was the man of science rather than the practical inventor. alfred vail, joining with morse after the latter had conceived the telegraph, but before his apparatus was in practical form, was a tireless and invaluable mechanical assistant. his inventions of apparatus were of the utmost practical value, and he played a very large part in bringing the telegraph to a form where it could serve man effectively. after success had been won morse did not extend to vail the credit which it seems was his due. yet, though morse made free use of the ideas and assistance of others, he was richly deserving of a major portion of the fame and the rewards that came to him as inventor of the telegraph. morse was the directing genius; he contributed the idea and the leadership, and bore the brunt of the burdens when all was most discouraging. honors were heaped upon morse both at home and abroad as his telegraph established itself in all parts of the world. orders of knighthood, medals, and decorations were conferred upon him. though he had failed to secure foreign patents, many of the foreign governments recognized the value of his invention, and france, austria, belgium, netherlands, russia, sweden, turkey, and some smaller nations joined in paying him a testimonial of four hundred thousand francs. it is to be noticed that great britain did not join in this testimonial, though morse's system had been adopted there in preference to the one developed by wheatstone. in 1871 a statue of morse was erected in central park, new york city. it was in the spring of the next year that another statue was unveiled, this time one of benjamin franklin, and morse presided at the ceremonies. the venerable man received a tremendous ovation on this occasion, but the cold of the day proved too great a strain upon him. he contracted a cold which eventually resulted in his death on april 2, 1872. while extended consideration cannot be given here to the telegraphic inventions of thomas a. edison, no discussion of the telegraph should close without at least some mention of his work in this field. edison started his career as a telegrapher, and his first inventions were improvements in the telegraph. his more recent and more wonderful inventions have thrown his telegraphic inventions into the shadow. on the telegraph as invented by morse but one message could be sent over a single wire at one time. it was later discovered that two messages' could be sent over the single wire in opposite directions at the same time. this was called duplex telegraphy. edison invented duplex telegraphy by which two messages could be sent over the same wire in the same direction at the same time. later he succeeded in combining the two, which resulted in the quadruplex, by which four messages may be sent over one wire at one time. though edison received comparatively little for this invention, its commercial value may be estimated from the statement by the president of the western union that it saved that company half a million dollars in a single year. edison's quadruplex system was also adopted by the british lines. before this he had perfected an automatic telegraph, work on which had been begun by george little, an englishman. little could make the apparatus effective only over a short line and attained no very great speed. edison improved the apparatus until it transmitted thirty-five hundred words a minute between new york and philadelphia. such is the perfection to which morse's marvel has been brought in the hands of the most able of modern inventors. viii telegraphing beneath the sea early efforts at underwater telegraphy--cable construction and experimentation--the first cables--the atlantic cable projected--cyrus w. field becomes interested--organizes atlantic telegraph company--professor thomson as scientific adviser--his early life and attainments. the idea of laying telegraph wires beneath the sea was discussed long before a practical telegraph for use on land had been attained. it is recorded that a spaniard suggested submarine telegraphy in 1795. experiments were conducted early in the nineteenth century with various materials in an effort to find a covering for the wires which would be both a non-conductor of electricity and impervious to water. an employee of the east india company made an effort to lay a cable across the river hugli as early as 1838. his method was to coat the wire with pitch inclose it in split rattan, and then wrap the whole with tarred yarn. wheatstone discussed a calais-dover cable in 1840, but it remained for morse to actually lay an experimental cable. we have already heard of his experiments in new york harbor in 1842. his insulation was tarred hemp and india rubber. wheatstone performed a similar experiment in the bay of swansea a few months later. perhaps the first practical submarine cable was laid by ezra cornell, one of morse's associates, in 1845. he laid twelve miles of cable in the hudson river, connecting fort lee with new york city. the cable consisted of two cotton-covered wires inclosed in rubber, and the whole incased in a lead pipe. this cable was in use for several months until it was carried away by the ice in the winter of 1846. these early experimenters found the greatest difficulty in incasing their wires in rubber, practical methods of working that substance being then unknown. the discovery of gutta-percha by a scotch surveyor of the east india company in 1842, and the invention of a machine for applying it to a wire, by dr. werner siemens, proved a great aid to the cable-makers. these gutta-percha-covered wires were used for underground telegraphy both in england and on the continent. tests were made with such a cable for submarine work off dover in 1849, and, proving successful, the first cable across the english channel was laid the next year by john watkins brett. the cable was weighted with pieces of lead fastened on every hundred yards. a few incoherent signals were exchanged and the communication ceased. a boulogne fisherman had caught the new cable in his trawl, and, raising it, had cut a section away. this he had borne to port as a great treasure, believing the copper to be gold in some new form of deposit. this experience taught the need of greater protection for a cable, and the next year another was laid across the channel, which was protected by hemp and wire wrappings. this proved successful. in 1852 england and ireland were joined by cable, and the next year a cable was laid across the north sea to holland. the success of these short cables might have promised success in an attempt to cross the atlantic had not failures in the deep water of the mediterranean made it seem an impossibility. we have noted that morse suggested the possibility of uniting europe and america by cable. the same thought had occurred to others, but the undertaking was so vast and the problems so little understood that for many years none were bold enough to undertake the project. a telegraph from new york to st. john's, newfoundland, was planned, however, which was to lessen the time of communication between the continents. news brought by boats from england could be landed at st. john's and telegraphed to new york, thus saving two days. f.n. gisborne secured the concession for such a line in 1852, and began the construction. cables were required to connect newfoundland with the continent, and to cross the gulf of st. lawrence, but the rest of the line was to be strung through the forests. before much had been accomplished, gisborne had run out of funds, and work was suspended. in 1854 gisborne met cyrus west field, of new york, a retired merchant of means. field became interested in gisborne's project, and as he examined the globe in his library the thought occurred to him that the line to st. john's was but a start on the way to england. the idea aroused his enthusiasm, and he determined to embark upon the gigantic enterprise. he knew nothing of telegraph cables or of the sea-bottom, and so sought expert information on the subject. one important question was as to the condition of the sea-bottom on which the cable must rest. lieutenant berryman of the united states navy had taken a series of soundings and stated that the sea-bottom between newfoundland and ireland was a comparatively level plateau covered with soft ooze, and at a depth of about two thousand fathoms. this seemed to the investigators to have been provided for the especial purpose of receiving a submarine cable, so admirably was it suited to this purpose. morse was consulted, and assured field that the project was entirely feasible, and that a submarine cable once laid between the continents could be operated successfully. field thereupon adopted the plans of gisborne as the first step in the larger undertaking. in 1855 an attempt was made to lay a cable across the gulf of st. lawrence, but a storm arose, and the cable had to be cut to save the ship from which it was being laid. another attempt was made the following summer with better equipment, and the cable was successfully completed. other parts of the line had been finished, the telegraph now stretched a thousand miles toward england, and new york was connected with st. john's. desiring more detailed information of the ocean-bed along the proposed route, field secured the assistance of the united states and british governments. lieutenant berryman, u.s.n., in the _arctic_, and lieutenant dayman, r.n., in the _cyclops_, made a careful survey. their soundings revealed a ridge near the irish coast, but the slope was gradual and the general conditions seemed especially favorable. the preliminary work had been done by an american company with field at the head and morse as electrician. now field went to england to secure capital sufficient for the larger enterprise. with the assistance of mr. j.w. brett he organized the atlantic telegraph company, field himself supplying a quarter of the capital. associated with field and brett in the leadership of the enterprise was charles tiltson bright, a young englishman who became engineer for the new company. besides the enormous engineering difficulties of producing a cable long enough and strong enough, and laying it at the bottom of the atlantic, there were electrical problems involved far greater than morse seems to have realized. it had been discovered that the passage of a current through a submarine cable is seriously retarded. the retarding of the current as it passes through the water is a difficulty that does not exist with the land telegraph stretched on poles. faraday had demonstrated that this retarding was caused by induction between the electricity in the wire and the water about the cable. the passage of the current through the wire induces currents in the water, and these moving in the opposite direction act as a drag on the passage of the message through the wire. what the effect of this phenomenon would be on a cable long enough to cross the atlantic wan a serious problem that required deep study by the company's engineers. it seemed entirely possible that the messages would move so slowly that the operation of the cable, once it was laid, would not pay. faraday failed to give any definite information on the subject, but professor william thomson worked out the law of retardation accurately and furnished to the cable-builders the accurate information which was required. doctor whitehouse, electrician for the atlantic company, conducted some experiments of his own and questioned the accuracy of thomson's statements. thomson maintained his position so ably, and proved himself so thoroughly a master of the subject that field and his associates decided to enlist him in the enterprise. this addition to the forces was one of the utmost importance. william thomson, later to become lord kelvin, was probably the ablest scientist of his generation, and was destined to prove his great abilities in his early work with the atlantic cable. william thomson was born in belfast, ireland, in 1824. his father was a teacher and took an especially keen interest in the affairs of his boys because their mother had died while william was very young. when william was eight years of age his father removed to glasgow, scotland, where he had secured the chair of mathematics in glasgow university. his early education he secured from his father, and this training, coupled with his natural brilliancy, enabled him to develop genuine precocity. at the age of eight he attended his father's university lectures as a visitor, and it is reported that on one occasion he answered his father's questions when all of the class had failed. at the age of ten he entered the university, together with his brother james, who was but two years older. the brothers displayed marked interest in science and invention, eagerly pursued their studies in these branches, and performed many electrical experiments together. [illustration: cyrus w. field] [illustration: william thomson (lord kelvin)] james took the degrees b.a. and m.a. in successive years. though william also passed the examinations, he did not take the degrees, because he had decided to go to cambridge, and it was thought best that he take all his degrees from that great school. in writing to his older brother at this time, william was accustomed to sign himself "b.a.t.a.i.a.p.," which signified "b.a. to all intents and purposes." after finishing their work at glasgow the boys traveled extensively on the continent. at seventeen william entered st. peter's college, cambridge university, taking courses in advanced mathematics and continuing to distinguish himself. he took an active part in the life of the university, making something of a record us an athlete, winning the silver sculls, and rowing on a 'varsity crew which took the measure of oxford in the great annual boat-race. he also interested himself in literature and music, but his real passion was science. already he had written many learned essays on mathematical electricity and was accomplishing valuable research work. on the completion of his work at cambridge he secured a fellowship which brought him an income of a thousand dollars a year and enabled him to pursue his studies in paris. when he was but twenty-two years of age he was made professor of natural philosophy at the university of glasgow. though young, he proved entirely successful, and wan immensely popular with his students. at that time the university had no experimental laboratory, and professor thomson and his pupils performed their experiments in the professor's room and in an abandoned coal-cellar, slowly developing a laboratory for themselves. his development continued until, when at the age of thirty-three he was called upon to assist with the work of laying an atlantic cable, he was possessed of scientific attainments which made him invaluable among the cable pioneers. ix the pioneer atlantic cable making the cable--the first attempt at laying--another effort checked by storm--the cable laid at last--messages cross the ocean--the cable fails--professor thomson's inventions and discoveries--their part in designing and constructing an improved cable and apparatus. field and his business associates were extremely anxious that the cable be laid with all possible speed, and little time was allowed the engineers and electricians for experimentation. the work of building the cable was begun early in 1857 by two english firms. it consisted of seven copper wires covered with gutta-percha and wound with tarred hemp. over this were wound heavy iron wires to give protection and added strength. the whole weighed about a ton to the mile, and was both strong and flexible. the distance from the west coast of ireland to newfoundland being 1,640 nautical miles, it was decided to supply 2,500 miles of cable, an extra length being, of course, necessary to allow for the inequalities at the bottom of the sea, and the possibility of accident. the british and american governments had already provided subsidies, and they now supplied war-ships for use in the work of laying the cable. the _agamemnon_, one of the largest of england's war-ships, and the _niagara_, giant of the united states navy, were to do the actual work of cable-laying, the cable being divided between them. they were accompanied by the united states frigate _susquehanna_ and the british war-ships _leopard_ and _cyclops_. in august of 1857 the fleet assembled on the irish coast for the start, and the american sailors landed the end of the cable amid great ceremony. the work of cable-laying was begun by the _niagara_, which steamed slowly away, accompanied by the fleet. the great cable payed out smoothly as the irish coast was left behind and the frigate increased her speed. the submarine hill with its dangerous slopes was safely passed, and it was felt that the greatest danger was past. the paying-out machinery seemed to be working perfectly. telegraphic communication was constantly maintained with the shore end. for six days all went well and nearly four hundred miles of cable had been laid. with the cable dropping to the bottom two miles down it was found that it was flowing out at the rate of six miles an hour while the _niagara_ was steaming but four. it was evident that the cable was being wasted, and to prevent its running out too fast at this great depth the brake controlling the flow of the cable was tightened. the stern of the vessel rising suddenly on a wave, the strain proved too great and the cable parted and was lost. instant grief swept over the ship and squadron, for the heart of every one was in the great enterprise. it was felt that it would be useless to attempt to grapple the cable at this great depth, and there seemed nothing to do but abandon it and return. the loss of the cable and of a year's time--since another attempt could not be made until the next season--resulted in a total loss to the company of half a million dollars. public realization of the magnitude of the task had been awakened by the failure of the first expedition and field found it far from easy to raise additional capital. it was finally accomplished, however, and a new supply of cable was constructed. professor thomson had been studying the problems of submarine telegraphy with growing enthusiasm, and had now arrived at the conclusion that the conductivity of the cable depended very largely upon the purity of the copper employed. he accordingly saw to it that in the construction of the new section all the wires were carefully tested and such as did not prove perfect were discarded. in the mean time the engineers were busy improving the paying-out machinery. they designed an automatic brake which would release the cable instantly upon the strain becoming too great. it was thus hoped to avoid a recurrence of the former accident. chief-engineer bright also arranged a trial trip for the purpose of drilling the staff in their various duties. the same vessels were provided to lay the cable on the second attempt and the fleet sailed in june of 1858, this time without celebration or public ceremony. on this occasion the recommendation of chief-engineer bright was followed, and it was arranged that the _niagara_ and _agamemnon_ should meet in mid-ocean, there splice the cable together and proceed in opposite directions, laying the cable simultaneously. on this expedition professor thomson was to assume the real scientific leadership, professor morse, though he retained his position with the company, taking no active part. the ships had not proceeded any great distance before they ran into a terrible gale. the _agamemnon_ had an especially difficult time of it, her great load of cable overbalancing the ship and threatening to break loose again and again and carry the great vessel and her precious cargo to the bottom. the storm continued for over a week, and when at last it had blown itself out the _agamemnon_ resembled a wreck and many of her crew had been seriously injured. but the cable had been saved and the expedition was enabled to proceed to the rendezvous. the _niagara_, a larger ship, had weathered the storm without mishap. the splice was effected on saturday, the 26th, but before three miles had been laid the cable caught in the paying-out machinery on the _niagara_ and was broken off. another splice was made that evening and the ships started again. the two vessels kept in communication with each other by telegraph as they proceeded, and anxious inquiries and many tests marked the progress of the work. when fifty miles were out, the cable parted again at some point between the vessels and they again sought the rendezvous in mid-atlantic. sufficient cable still remained and a third start was made. for a few days all went well and some four hundred miles of cable had been laid with success as the messages passing from ship to ship clearly demonstrated. field, thomson, and bright began to believe that their great enterprise was to be crowned with success when the cable broke again, this time about twenty feet astern of the _agamemnon_. this time there was no apparent reason for the mishap, the cable having parted without warning when under no unusual strain. the vessels returned to queenstown, and field and thomson went to london, where the directors of the company were assembled. many were in favor of abandoning the enterprise, selling the remaining cable for what it would bring, and saving as much of their investment as possible. but field and thomson were not of the sort who are easily discouraged, and they managed to rouse fresh courage in their associates. yet another attempt was decided upon, and with replenished stores the _agamemnon_ and _niagara_ once again proceeded to the rendezvous. the fourth start was made on the 29th of july. on several occasions as the work progressed communication failed, and professor thomson on the _agamemnon_ and the other electricians on the _niagara_ spent many anxious moments fearing that the line had again been severed. on each occasion, however, the current resumed. it was afterward determined that the difficulties were because of faulty batteries rather than leaks in the cable. on both ships bad spots were found in the cable as it was uncoiled and some quick work was necessary to repair them before they dropped into the sea, since it was practically impossible to stop the flow of the cable without breaking it. the _niagara_ had some narrow escapes from icebergs, and the _agamemnon_ had difficulties with ships which passed too close and a whale which swam close to the ship and grazed the precious cable. but this time there was no break and the ships approached their respective destinations with the cable still carrying messages between them. the _niagara_ reached the newfoundland coast on august 4th, and early the next morning landed the cable in the cable-house at trinity bay. the _agamemnon_ reached the irish coast but a few hours later, and her end of the cable was landed on the afternoon of the same day. the public, because of the repeated failures, had come to look upon the cable project as a sort of gigantic wild-goose chase. the news that a cable had at last been laid across the ocean was received with incredulity. becoming convinced at last, there was great rejoicing in england and america. queen victoria sent to president buchanan a congratulatory message in which she expressed the hope "that the electric cable which now connects great britain with the united states will prove an additional link between the two nations, whose friendship is founded upon their mutual interest and reciprocal esteem." the president responded in similar vein, and expressed the hope that the neutrality of the cable might be established. honors were showered upon the leaders in the enterprise. charles bright, the chief engineer, was knighted, though he was then but twenty-six years of age. banquet after banquet was held in england at which bright and thomson were the guests of honor. new york celebrated in similar fashion. a grand salute of one hundred guns was fired, the streets were decorated, and the city was illuminated at night. the festivities rose to the highest pitch in september with field receiving the plaudits of all new york. special services were held in trinity church, and a great celebration was held in crystal palace. the mayor presented to field a golden casket, and the ceremony was followed by a torchlight parade. that very day the last message went over the wire. the shock to the public was tremendous. many insisted that the cable had never been operated and that the entire affair was a hoax. this was quickly disproved. aside from the messages between queen and president many news messages had gone over the cable and it had proved of great value to the british government. the indian mutiny had been in progress and regiments in canada had received orders by mail to sail for india. news reached england that the mutiny was at an end, and the cable enabled the government to countermand the orders, thus saving a quarter of a million dollars that would have been expended in transporting the troops. the engineers to whom the operations of the cable had been intrusted had decided that very high voltages were necessary to its successful operation. they had accordingly installed huge induction coils and sent currents of two thousand volts over the line. even this voltage had failed to operate the morse instruments, the drag by induction proving too great. the strain of this high voltage had a very serious effect upon the insulation. abandoning the morse instruments and the high voltage, recourse was then had to professor thomson's instruments, which proved entirely effective with ordinary battery current. because of the effect of induction the current is much delayed in traveling through a long submarine cable and arrives in waves. professor thomson devised his mirror galvanometer to meet this difficulty. this device consists of a large coil of very fine wire, in the center of which, in a small air-chamber, is a tiny mirror. mounted on the back of the mirror are very small magnets. the mirror is suspended by a fiber of the finest silk. thus the weakest of currents coming in over the wire serve to deflect the mirror, and a beam of light being directed upon the mirror and reflected by it upon a screen, the slightest movement of the mirror is made visible. if the mirror swings too far its action is deadened by compressing the air in the chamber. the instrument is one of the greatest delicacy. such was the greatest contribution of professor thomson to submarine telegraphy. without it the cable could not have been operated even for a short period. had it been used from the first the line would not have been ruined and might have been used for a considerable period. professor thomson together with engineer bright made a careful investigation of the causes of failure. the professor pointed out that had the mirror galvanometer been used with a moderate current the cable could have been continued in successful operation. ha continued to improve this apparatus and at the same time busied himself with a recording instrument to be used for cable work. both thomson and bright had recommended a larger and stronger cable, and other failures in cable-laying in the red sea and elsewhere in the next few years bore out their contentions. but with each failure new experience was gained and methods were perfected. professor thomson continued his work with the utmost diligence and continued to add to the fund of scientific knowledge on the subject. so it was that he was prepared to take his place as scientific leader of the next great effort. x a successful cable attained field raises new capital--the _great eastern_ secured and equipped--staff organized with professor thomson as scientific director--cable parts and is lost--field perseveres--the cable recovered--the continents linked at last--a commercial success--public jubilation--modern cables. the early 'sixties were trying years for the cable pioneers. it required all of field's splendid genius and energy to keep the project alive. in the face of repeated failures, and doubt as to whether messages could be sent rapidly enough to make any cable a commercial success, it was extremely difficult to raise fresh capital. america continued to evince interest in the cable, but with, the civil war in progress it was not easy to raise funds. but no discouragement could deter field. though he suffered severely from seasickness, he crossed the atlantic sixty-four times in behalf of the great enterprise which he had begun. it was necessary to raise three million dollars to provide a cable of the improved type decided upon and to install it properly. the english firm of glass, eliot & company, which was to manufacture the cable, took a very large part of the stock. the new cable was designed in accordance with the principles enunciated by professor thomson. the conductor consisted of seven wires of pure copper, weighing three hundred pounds to the mile. this copper core was covered with chatterton's compound, which served as water-proofing. this was surrounded by four layers of gutta-percha, cemented together by the compound, and about this hemp was wound. the outer layer consisted of eighteen steel wires wound spirally, each being covered with a wrapping of hemp impregnated with a preservative solution. the new cable was twice as heavy as the old and more than twice as strong, a great advance having been made in the methods of manufacturing steel wire. it was decided that the cable should, be laid by one vessel, instead of endeavoring to work from two as in the past. happily, a boat was available which was fitted to carry this enormous burden. this was the _great eastern_, a mammoth vessel far in advance of her time. this great ship of 22,500 tons had been completed in 1857, but had not proved a commercial success. the docks of that day were not adequate, the harbors were not deep enough, and the cargoes were insufficient. she had long lain idle when she was secured by the cable company and fitted out for the purpose of laying the cable, which was the first useful work which had been found for the great ship. the 2,300 miles of heavy cable was coiled into the hull and paying-out machinery was installed upon the decks. huge quantities of coal and other supplies were added. capt. james anderson of the cunard line was placed in command of the ship for the expedition, with captain moriarty, r.n., as navigating officer. professor thomson and mr. c.f. varley represented the atlantic telegraph company as electricians and scientific advisers. mr. samuel canning was engineer in charge for the contractors. mr. field was also on board. it was on july 23, 1865, that the expedition started from the irish coast, where the eastern end of the cable had been landed. less than a hundred miles of cable had been laid when the electricians discovered a fault in the cable. the _great eastern_ was stopped, the course was retraced, and the cable picked up until the fault was reached. it was found that a piece of iron wire had in some way pierced the cable so that the insulation was ruined. this was repaired and the work of laying was again commenced. five days later, when some seven hundred miles of cable had been laid, communication was again interrupted, and once again they turned back, laboriously lifting the heavy cable from the depths, searching for the break. again a wire was found thrust through the cable, and this occasioned no little worry, as it was feared that this was being done maliciously. it was on august 2d that the next fault was discovered. nearly two-thirds of the cable was now in place and the depth was here over one mile. raising the cable was particularly difficult, and just at this juncture the _great eastern's_ machinery broke down, leaving her without power and at the mercy of the waves. subjected to an enormous strain, the precious cable parted and was lost. despite the great depth, efforts were made to grapple the lost cable. twice the cable was hooked, but on both occasions the rope parted and after days of tedious work the supply of rope was exhausted and it was necessary to return to england. still another cable expedition had ended in failure. field, the indomitable, began all over again, raising additional funds for a new start. the _great eastern_ had proved entirely satisfactory, and it was hoped that with improvements in the grappling-gear the cable might be recovered. the old company gave way before a new organization known as the anglo-american telegraph company. it was decided to lay an entirely new cable, and then to endeavor to complete the one partially laid in 1865. with no services other than private prayers at the station on the irish shore, the _great eastern_ steamed away for the new effort on july 13, 1866. this time the principal difficulties arose within the ship. twice the cable became tangled in the tanks and it was necessary to stop the ship while the mass was straightened out. most of the time the "coffee-mill," as the seamen called the paying-out machinery, ground steadily away and the cable sank into the sea. as the work progressed field and thomson, who had suffered so many failures in their great enterprise, watched with increasing anxiety. they were almost afraid to hope that the good fortune would continue. just two weeks after the irish coast had been left behind the _great eastern_ approached newfoundland just as the shadows of night were added to those of a thick fog. on the next morning, july 28th, she steamed into trinity bay, where flags were flying in the little town in honor of the great accomplishment. amid salutes and cheers the cable was landed and communication between the continents was established. almost the first news that came over the wire was that of the signing of the treaty of peace which ended the war between prussia and austria. early in august the _great eastern_ again steamed away to search for the cable broken the year before. arriving on the spot, the grapples were thrown out and the tedious work of dragging the sea-bottom was begun. after many efforts the cable was finally secured and raised to the surface. a new section was spliced on and the ship again turned toward america. on september 7th the second cable was successfully landed, and two wires were now in operation between the continents. thus was the great task doubly fulfilled. once again there were public celebrations in england and america. field received the deserved plaudits of his countrymen and thomson was knighted in recognition of his achievements. [illustration: the "great eastern" laying the atlantic cable. 1866] the new cables proved a success and were kept in operation for many years. thomson's mirror receiver had been improved until it displayed remarkable sensitiveness. using the current from a battery placed in a lady's thimble, a message was sent across the atlantic through one cable and back through the other. professor thomson was to give to submarine telegraphy an even more remarkable instrument. the mirror instrument did not give a permanent record of the messages. the problem of devising a means of recording the messages delicate enough so that it could be operated with rapidity by the faint currents coming over a long cable was extremely difficult. but thomson solved it with his siphon recorder. in this a small coil is suspended between the poles of a large magnet; the coil being free to turn upon its axis. when the current from the cable passes through the coil it moves, and so varies the position of the ink-siphon which is attached to it. the friction of a pen on paper would have proved too great a drag on so delicate an instrument, and so a tiny jet of ink from the siphon was substituted. the ink is made to pass through the siphon with sufficient force to mark down the message by a delightfully ingenious method. thomson simply arranged to electrify the ink, and it rushes through the tiny opening on to the paper just as lightning leaps from cloud to earth. professor, now sir, thomson continued to take an active part in the work of designing and laying new cables. not only did he contribute the apparatus and the scientific information which made cables possible, but he attained renown as a physicist and a scientist in many other fields. in 1892 he was given the title of lord kelvin, and it was by this name that he was known as the leading physicist of his day. he survived until 1907. to cyrus w. field must be assigned a very large share of the credit for the establishment of telegraphic communication between the continents. he gave his fortune and all of his tremendous energy and ability to the enterprise and kept it alive through failure after failure. he was a promoter of the highest type, the business man who recognized a great human need and a great opportunity for service. without his efforts the scientific discoveries of thomson could scarcely have been put to practical use. the success of the first cable inspired others. in 1869 a cable from france to the united states was laid from the _great eastern_. in 1875 the direct united states cable company laid another cable to england, which was followed by another cable to france. one cable after another was laid until there are now a score. this second great development in communication served to bring the two continents much closer together in business and in thought and has proved of untold benefit. xi alexander graham bell, the youth the family's interest in speech improvement--early life-influence of sir charles wheatstone--he comes to america--visible speech and the mohawks--the boston school for deaf mutes--the personality of bell. the men of the bell family, for three generations, have interested themselves in human speech. the grandfather, the father, and the uncle of alexander graham bell were all elocutionists of note. the grandfather achieved fame in london; the uncle, in dublin; and the father, in edinburgh. the father applied himself particularly to devising means of instructing the deaf in speech. his book on _visible speech_ explained his method of instructing deaf mutes in speech by the aid of their sight, and of teaching them to understand the speech of others by watching their lips as the words are spoken. alexander graham bell was born in edinburgh in 1847, and received his early education in the schools of that city. he later studied at warzburg, germany, where he received the degree of doctor of philosophy. he followed very naturally in the footsteps of his father, taking an early interest in the study of speech. he was especially anxious to aid his mother, who was deaf. as a boy he exhibited a genius for invention, as well as for acoustics. much of this was duo to the wise encouragement of his father. he himself has told of a boyhood invention. my father once asked my brother melville and myself to try to make a speaking-machine, i don't suppose he thought we could produce anything of value, in itself. but he knew we could not even experiment and manufacture anything which even tried to speak, without learning something of the voice and the throat; and the mouth--all that wonderful mechanism of sound production in which he was so interested. so my brother and i went to work. we divided the task--he was to make the lungs and the vocal cords, i was to make the mouth and the tongue. he made a bellows for the lungs and a very good vocal apparatus out of rubber. i procured a skull and molded a tongue with rubber stuffed with cotton wool, and supplied the soft parts of the throat with the same material then i arranged joints, so the jaw and the tongue could move. it was a great day for us when we fitted the two parts of the device together. did it speak? it squeaked and squawked a good deal, but it made a very passable imitation of "mam-ma--mam-ma." it sounded very much like a baby. my father wanted us to go on and try to get other sounds, but we were so interested in what we had done we wanted to try it out. so we proceeded to use it to make people think there was a baby in the house, and when we made it cry "mam-ma," and heard doors opening and people coming, we were quite happy. what has become of it? well, that was across the ocean, in scotland, but i believe the mouth and tongue part that i made is in georgetown somewhere; i saw it not long ago. the inventor tells of another boyhood invention that, though it had no connection with sound or speech, shows his native ingenuity. again we will tell it in his own words. i remember my first invention very well. there were several of us boys, and we were fond of playing around a mill where they ground wheat into flour. the miller's son was one of the boys, and i am afraid he showed us how to be a good deal of a nuisance to his father. one day the miller called us into the mill and said, "why don't you do something useful instead of just playing all the time?" i wasn't afraid of the miller as much as his son was, so i said, "well, what can we do that is useful?" he took up a handful of wheat, ran it over in his hand and said: "look at that! if you could manage to get the husks off that wheat, that would be doing something useful!" so i took some wheat home with me and experimented. i found the husks came off without much difficulty. i tried brushing them off and they came off beautifully. then it occurred to me that brushing was nothing but applying friction to them. if i could brush the husks off, why couldn't the husks be rubbed off? there was in the mill a machine--i don't know what it was for--but it whirled its contents, whatever it was, around in a drum. i thought, "why wouldn't the husks come off if the raw wheat was whirled around in that drum?" so back i went to the miller and suggested the idea to him. "why," he said, "that's a good idea." so he called his foreman and they tried it, and the husks came off beautifully, and they've been taking husks off that way ever since. that was my very first invention, and it led me to thinking for myself, and really had quite an influence on my way and methods of thought. up to his sixteenth year young bell's reading consisted largely of novels, poetry, and romantic tales of scotch heroes. but in addition he was picking up some knowledge of anatomy, music, electricity, and telegraphy. when he was but sixteen years of age his father secured for him a position as teacher of elocution and this necessarily turned his thought into more serious channels. he now spent his leisure studying sound. during this period he made several discoveries in sound which were of some small importance. when he was twenty-one years of age he went to london and there had the good fortune to come to the attention of charles wheatstone and alex j. ellis. ellis was at that time president of the london philological society, and had translated helmholtz's _the sensation of tone_ into english. he had made no little progress with sound, and demonstrated to bell the methods by which german scientists had caused tuning-forks to vibrate by means of electro-magnets and had combined the tones of several tuning-forks in an effort to reproduce the sound of the human voice. helmholtz had performed this experiment simply to demonstrate the physical basis of sound, and seems to have had no idea of its possible use in telephony. that an electro-magnet could vibrate a tuning-fork and so produce sound was an entirely new and fascinating idea to the youth. it appealed to his imagination, quickened by his knowledge of speech. "why not an electrical telegraph?" he asked himself. his idea seems to have been that the electric current could carry different notes over the wire and reproduce them by means of the electro-magnet. although bell did not know it, many others were struggling with the same problem, the answer to which proved most elusive. it gave bell a starting-point, and the search for the telephone began. sir charles wheatstone was then england's leading man of science, and so bell sought his counsel. wheatstone received the young man and listened to his statement of his ideas and ambitions and gave him every encouragement. he showed him a talking-machine which had recently been invented by baron de kempelin, and gave him the opportunity to study it closely. thus bell, the eager student, the unknown youth of twenty-two, came under the influence of wheatstone, the famous scientist and inventor of sixty-seven. this influence played a great part in shaping bell's career, arousing as it did his passion for science. this decided him to devote himself to the problem of reproducing sounds by mechanical means. thus a new improvement in the means of human communication was being sought and another pioneer of science was at work. the death of the two brothers of the young scientist from tuberculosis, and the physician's report that he himself was threatened by the dread malady, forced a change in his plans and withdrew him from an atmosphere which was so favorable to the development of his great ideas. he was told that he must seek a new climate and lead a more vigorous life in the open. accompanied by his father, he removed to america and at the age of twenty-six took up the struggle for health in the little canadian town of brantford. he occupied himself by teaching his father's system of visible speech among the mohawk indians. in this work he met with no little success. at the same time he was gaining in bodily vigor and throwing off the tendency to consumption which had threatened his life. he did not forget the great idea which filled his imagination and eagerly sought the telephone with such crude means as were at hand. he succeeded in designing a piano which, with the aid of the electric current, could transmit its music over a wire and reproduce it. while lecturing in boston on his system of teaching visible speech, the elder bell received a request to locate in that city and take up his work in its schools. he declined the offer, but recommended his son as one entirely competent for the position. alexander graham bell received the offer, which he accepted, and he was soon at work teaching the deaf mutes in the school which boston had opened for those thus afflicted. he met with the greatest success in his work, and ere long achieved a national reputation. during the first year of his work, 1871, he was the sensation of the educational world. boston university offered him a professorship, in which position he taught others his system of teaching, with increased success. the demand for his services led him to open a school of vocal physiology. he had made some improvements in his father's system for teaching the deaf and dumb to speak and to understand spoken words, and displayed great ability as a teacher. his experiments with telegraphy and telephony had been laid aside, and there seemed little chance that he would turn from the work in which he was accomplishing so much for so many sufferers, and which was bringing a comfortable financial return, and again undertake the tedious work in search for a telephone. fortunately, bell was to establish close relationships with those who understood and appreciated his abilities and gave him encouragement in his search for a new means of communication. thomas sanders, a resident of salem, had a five-year-old son named georgie who was a deaf mute. mr. sanders sought bell's tutelage for his son, and it was agreed that bell should give georgie private lessons for the sum of three hundred and fifty dollars a year. it was also arranged that bell was to reside at the sanders home in salem. he made arrangements to conduct his future experiments there. another pupil who came to him about this time was mabel hubbard, a fifteen-year-old girl who had lost her hearing and consequently her powers of speech, through an attack of scarlet fever when an infant. she was a gentle and lovable girl, and bell fell completely in love with his pupil. four years later he was to marry her and she was to prove a large influence in helping him to success. she took the liveliest interest in all of his experiments and encouraged him to new endeavor after each failure. she kept his records and notes and wrote his letters. through her bell secured the support of her father, gardiner g. hubbard, who was widely known as one of boston's ablest lawyers. he was destined to become bell's chief spokesman and defender. hubbard first became aware of bell's inventive genius when the latter was calling one evening at the hubbard home in cambridge. bell was illustrating some mysteries of acoustics with the aid of the piano. "do you know," he remarked, "that if i sing the note g close to the strings of the piano, the g string will answer me?" this did not impress the lawyer, who asked its significance. "it is a fact of tremendous importance," answered bell. "it is evidence that we may some day have a musical telegraph which will enable us to send as many messages simultaneously over one wire as there are notes on that piano." from that time forward hubbard took every occasion to encourage bell to carry forward his experiments in musical telegraphy. as a young man bell was tall and slender, with jet-black eyes and hair, the latter being pushed back into a curly tangle. he was sensitive and high-strung, very much the artist and the man of science. his enthusiasms were intense, and, once his mind was filled with an idea, he followed it devotedly. he was very little the practical business man and paid scant attention to the small, practical details of life. he was so interested in visible speech, and so keenly alert to the pathos of the lives of the deaf mutes, that he many times seriously considered giving over all experiments with the musical telegraph and devoting his entire life and energies to the amelioration of their condition. xii the birth of the telephone the cellar at sanderses'--experimental beginnings--magic revived in salem town--the dead man's ear--the right path--trouble and discouragement--the trip to washington--professor joseph henry--the boston workshop--the first faint twang of the telephone--early development. alexander graham bell had not resided at the sanderses' home very long before he had fitted the basement up as a workshop. for three years he haunted it, spending all of his leisure time in his experiments. here he had his apparatus, and the basement was littered with a curious combination of electrical and acoustical devices--magnets, batteries, coils of wire, tuning-forks, speaking-trumpets, etc. bell had a great horror that his ideas might be stolen and was very nervous over any possible intrusion into his precious workshop. only the members of the sanders family were allowed to enter the basement. he was equally cautious in purchasing supplies and equipment lest his very purchases reveal the nature of his experiments. he would go to a half-dozen different stores for as many articles. he usually selected the night for his experiments, and pounded and scraped away indefatigably, oblivious of the fact that the family, as well as himself, was sorely in need of rest. "bell would often awaken me in the middle of the night," says mr. sanders, "his black eyes blazing with excitement. leaving me to go down to the cellar, he would rush wildly to the barn and begin to send me signals along his experimental wires. if i noticed any improvement in his apparatus he would be delighted. he would leap and whirl around in one of his 'war-dances,' and then go contentedly to bed. but if the experiment was a failure he would go back to his work-bench to try some different plan." in common with other experimenters who were searching for the telephone, bell was experimenting with a sort of musical telegraph. eagerly and persistently he sought the means that would replace the telegraph with its cumbersome signals by a new device which would enable the human voice itself to be transmitted. the longer he worked the greater did the difficulties appear. his work with the deaf and dumb was alluring, and on many occasions he seriously considered giving over his other experiments and devoting himself entirely to the instruction of the deaf and dumb and to the development of his system of making speech visible by making the sound-vibrations visible to the eye. but as he mused over the difficulties in enabling a deaf mute to achieve speech nothing else seemed impossible. "if i can make a deaf mute talk," said bell, "i can make iron talk." one of his early ideas was to install a harp at one end of the wire and a speaking-trumpet at the other. his plan was to transmit the vibrations over the wire and have the voice reproduced by the vibrations of the strings of the harp. by attaching a light pencil or marker to a cord or membrane and causing the latter to vibrate by talking against it, he could secure tracings of the sound-vibrations. different tracings were secured from different sounds. he thus sought to teach the deaf to speak by sight. at this time bell enjoyed the friendship of dr. clarence j. blake, an eminent boston aurist, who suggested that the experiments be conducted with a human ear instead of with a mechanical apparatus in imitation of the ear. bell eagerly accepted the idea, and doctor blake provided him with an ear and connecting organs cut from a dead man's head. bell soon had the ghastly specimen set up in his workshop. he moistened the drum with glycerine and water and, substituting a stylus of hay for the stapes bone, he obtained a wonderful series of curves which showed the vibrations of the human voice as recorded by the ear. one can scarce imagine a stranger picture than bell must have presented in the conduct of those experiments. we can almost see him with his face the paler in contrast with his black hair and flashing black eyes as he shouted and whispered by turns into the ghastly ear. surely he must have looked the madman, and it is perhaps fortunate that he was not observed by impressionable members of the public else they would have been convinced that the witches had again visited old salem town to ply their magic anew. but it was a new and very real and practical sort of magic which was being worked there. his experiments with the dead man's ear brought to bell at least one important idea. he noted that, though the ear-drum was thin and light, it was capable of sending vibrations through the heavy bones that lay back of it. and so he thought of using iron disks or membranes to serve the purpose of the drum in the ear and arrange them so that they would vibrate an iron rod. he thought of connecting two such instruments with an electrified wire, one of which would receive the sound-vibrations and the other of which would reproduce them after they had been transmitted along the wire. at last the experimenter was on the right track, with a conception of a practicable method of transmitting sound. he now possessed a theoretical knowledge of what the telephone he sought should be, but there yet remained before him the enormous task of devising and constructing the apparatus which would carry out the idea, and find the best way of utilizing the electrical current for this work. bell was now at a critical point in his career and was confronted by the same difficulty which assails so many inventors. in his constant efforts to achieve a telephone he had entirely neglected his school of vocal physiology, which was now abandoned. georgie sanders and mabel hubbard were his only pupils. though sanders and hubbard were genuinely interested in bell and his work, they felt that he was impractical, and were especially convinced that his experiments with the ear and its imitations were entirely useless. they believed that the electrical telegraph alone presented possibilities, and they told bell that unless he would devote himself entirely to the improvement of this instrument and cease wasting time and money over ear toys that had no commercial value they would no longer give him financial support. hubbard went even further, and insisted that if bell did not abandon his foolish notions he could not marry his daughter. bell was almost without funds, his closest friends now seemed to turn upon him, and altogether he was in a sorry plight. of course sanders and hubbard meant the best, yet in reality they were seeking to drive their protégé in exactly the wrong direction. as far back as 1860 a german scientist named philipp reis produced a musical telephone that even transmitted a few imperfect words. but it would not talk successfully. others had followed in his footsteps, using the musical telephone to transmit messages with the morse code by means of long and short hums. elisha gray, of chicago, also experimented with the musical telegraph. at the transmitting end a vibrating steel tongue served to interrupt the electric current which passed over the wire in waves, and, passing through the coils of an electro-magnet at the receiving end, caused another strip of steel located near the magnet to vibrate and so produce a tone which varied with the current. all of these developments depended upon the interruption of the current by some kind of a vibrating contact. the limitations which sanders and hubbard sought to impose upon bell, had they been obeyed to the letter, must have prevented his ultimate success. in a letter to his mother at this time, he said: i am now beginning to realize the cares and anxieties of being an inventor. i have had to put off all pupils and classes, for flesh and blood could not stand much longer such a strain as i have had upon me. but good fortune was destined to come to bell along with the bad. on an enforced trip to washington to consult his patent attorney--a trip he could scarce raise funds to make--bell met prof. joseph henry. we have seen the part which this eminent scientist had played in the development of the telegraph. now he was destined to aid bell, as he had aided morse a generation earlier. the two men spent a day over the apparatus which bell had with him. though professor henry was fifty years his senior and the leading scientist in america, the youth was able to demonstrate that he had made a real discovery. "you are in possession of the germ of a great invention," said henry, "and i would advise you to work at it until you have made it complete." "but," replied bell, "i have not got the electrical knowledge that is necessary." "get it," was henry's reply. this proved just the stimulus bell needed, and he returned to boston with a new determination to perfect his great idea. bell was no longer experimenting in the sanderses' cellar, having rented a room in boston in which to carry on his work. he had also secured the services of an assistant, one thomas watson, who received nine dollars a week for his services in bell's behalf. the funds for this work were supplied by sanders and hubbard jointly, but they insisted that bell should continue his experiments with the musical telegraph. though he was convinced that the opportunities lay in the field of telephony, bell labored faithfully for regular periods with the devices in which his patrons were interested. the remainder of his time and energy he put upon the telephone. the basis of his telephone was still the disk or diaphragm which would vibrate when the sound-waves of the voice were thrown against it. behind this were mounted various kinds of electro-magnets in series with the electrified wire over which the inventor hoped to send his messages. for three years they labored with this apparatus, trying every conceivable sort of disk. it is easy to pass over those three years, filled as they were with unceasing toil and patient effort, because they were drab years when little of interest occurred. but these were the years when bell and watson were "going to school," learning how to apply electricity to this new use, striving to make their apparatus talk. how dreary and trying these years must have been for the experimenters we may well imagine. it requires no slight force of will to hold oneself to such a task in the face of failure after failure. by june of 1875 bell had completed a new instrument. in this the diaphragm was a piece of gold-beater's skin, which bell had selected as most closely resembling the drum in the human ear. this was stretched tight to form a sort of drum, and an armature of magnetized iron was fastened to its middle. thus the bit of iron was free to vibrate, and opposite it was an electro-magnet through which flowed the current that passed over the line. this acted as the receiver. at the other end of the wire was a sort of crude harmonica with a clock spring, reed, and magnet. bell and watson had been working upon their crude apparatus for months, and finally, on june 2d, sounds were actually transmitted. bell was afire with enthusiasm; the first great step had been taken. the electric current had carried sound-vibrations along the wire and had reproduced them. if this could be done a telephone which would reproduce whole words and sentences could be attained. [illustration: alexander graham bell] [illustration: thomas a. watson] so great was bell's enthusiasm over this achievement that he succeeded in convincing sanders and hubbard that his idea was practical, and they at last agreed to finance him in his further experiments with the telephone. a second membrane receiver was constructed, and for many more weeks the experiments continued. it was found that sounds were carried from instrument to instrument, but as a telephone they were still far from perfection. it was not until march of 1876 that bell, speaking into the instrument in the workroom, was heard and understood by watson at the other instrument in the basement. the telephone had carried and delivered an intelligible message. the telephone which bell had invented, and on which he received a patent on his twenty-ninth birthday, consisted of two instruments similar in principle to what we would now call receivers. if you will experiment with the receiver of a modern telephone you will find that it will transmit as well as receive sound. the heart of the transmitter was an electro-magnet in front of which was a drum-like membrane with a piece of iron cemented to its center opposite the magnet. a mouthpiece was arranged to throw the sounds of the voice against the diaphragm, and as the membrane vibrated the bit of iron upon it--acting as an armature--induced currents corresponding to the sound-waves, in the coils of the electro-magnet. passing over the line the current entered the coils of the tubular electro-magnet in the receiver. a thin disk of soft iron was fastened at the end of this. when the current-waves passed through the coils of the magnet the iron disk was thrown into vibration, thus producing sound. as it vibrated with the current produced by the iron on the vibrating membrane in the transmitter acting as an armature, transmitter and receiver vibrated in unison and so the same sound was given off by the receiver and made audible to the human ear as was thrown against the membrane of the transmitter by the voice. the patent issued to bell has been described as "the most valuable single patent ever issued." certainly it was destined to be of tremendous service to civilization. it was so entirely new and original that bell found difficulty in finding terms in which to describe his invention to the patent officials. he called it "an improvement on the telegraph," in order that it might be identified as an improvement in transmitting intelligence by electricity. in reality the telephone was very far from being a telegraph or anything in the nature of a telegraph. as bell himself stated, his success was in large part due to the fact that he had approached the problem from the viewpoint of an expert in sound rather than as an electrician. "had i known more about electricity and less about sound," he said, "i would never have invented the telephone." as we have seen, those electricians who worked from the viewpoint of the telegraph never got beyond the limitations of the instrument and found that with it they could transmit signals but not sounds. bell, with his knowledge of the laws of speech and sound, started with the principles of the transmission of sound as a basis and set electricity to carrying the sound-vibrations. xiii the telephone at the centennial boll's impromptu trip to the exposition--the table under the stairs--indifference of the judges--enter don pedro, emperor of brazil--attention and amazement--skepticism of the public--the aid of gardiner hubbard--publicity campaign. the philadelphia centennial exposition--america's first great exposition--opened within a month after the completion of the first telephone. the public knew nothing of the telephone, and before it could be made a commercial success and placed in general service the interest of investors and possible users had to be aroused. the centennial seemed to offer an unusual opportunity to place the telephone before the public. but bell, like morse, had no money with which to push his invention. hubbard was one of the commissioners of the exposition, and exerted his influence sufficiently so that a small table was placed in an odd corner in the department of education for the exhibition of the apparatus. the space assigned was a narrow strip between the stairway and the wall. but no provision was made to allow bell himself to be present. the young inventor was almost entirely without funds. sanders and hubbard had paid nothing but his room rent and the cost of his experiments. he had devoted himself to his inventions so entirely that he had lost all of his professional income. so it was that he was forced to face the prospect of staying in boston and allowing this opportunity of opportunities to pass unimproved. his fiancée, miss hubbard, expected to attend the exposition, and had heard nothing of bell's inability to go. he went with her to the station, and as the train was leaving she learned for the first time that he was not to accompany her. she burst into tears at the disappointment. seeing this, bell dashed madly after the train and succeeded in boarding it. without money or baggage, he nevertheless succeeded in arriving in philadelphia. bell arrived at the exposition but a few days before the judges were to make their tour of inspection. with considerable difficulty hubbard had secured their promise that they would stop and examine the telephone. they seemed to regard it as a toy not worth their attention, and the public generally had displayed no interest in the device. when the day for the inspection arrived bell waited eagerly. as the day passed his hope began to fall, as there seemed little possibility that the judges would reach his exhibit. the western union's exhibit of recording telegraphs, the self-binding harvester, the first electric light, gray's musical telegraph, and other prominently displayed wonders had occupied the attention of the scientists. it was well past supper-time when they came to bell's table behind the stairs, and most of the judges were tired out and loudly announced their intention of quitting then and there. at this critical moment, while they were fingering bell's apparatus indifferently and preparing for their departure, a strange and fortunate thing occurred. followed by a group of brilliantly attired courtiers, the emperor of brazil appeared. he rushed up to bell and greeted him with a warmth of affection that electrified the indifferent judges. they watched the scene in astonishment, wondering who this young bell was that he could attract the attention and the friendship of the emperor. the emperor had attended bell's school for deaf mutes in boston when it was at the height of its success, and had conceived a warm admiration for the young man and taken a deep interest in his work. the emperor was ready to examine bell's invention, though the judges were not. bell showed him how to place his ear to the receiver, and he then went to the transmitter which had been placed at the other end of the wire strung along the room. the emperor waited expectantly, the judges watched curiously. bell, at a distance, spoke into the transmitter. in utter wonderment the emperor raised his head from the receiver. "my god," he cried, "it talks!" skepticism and indifference were at an end among the judges, and they eagerly followed the example of the emperor. joseph henry, the most venerable savant of them all, took his place at the receiver. though his previous talk with bell, when the telephone was no more than an idea, should perhaps have prepared him, he showed equal astonishment, and instantly expressed his admiration. next followed sir william thomson, the hero of the cable and england's greatest scientist. after his return to england thomson described his sensations. "i heard," he said, "'to be or not to be ... there's the rub,' through an electric wire; but, scorning monosyllables, the electric articulation rose to higher flights, and gave me passages from the new york newspapers. all this my own ears heard spoken to me with unmistakable distinctness by the then circular-disk armature of just such another little electro-magnet as this i hold in my hand." thomson pronounced bell's telephone "the most wonderful thing he had seen in america." the judges had forgotten that they were hungry and tired, and remained grouped about the telephone, talking and listening in turn until far into the evening. with the coming of the next morning bell's exhibit was moved from its obscure corner and given the most prominent place that could be found. from that time forward it was the wonder of the centennial. [illustration: professor bell's vibrating reed] [illustration: professor bell's first telephone] [illustration: the first telephone switchboard used in new haven, conn, for eight subscribers] [illustration: early new york exchange boys were employed as operators at first, but they were not adapted to the work so well as girls.] [illustration: professor bell in salem, mass., and mr. watson in boston, demonstrating the telephone before audiences in 1877] [illustration: dr bell at the telephone opening the new york-chicago line, october 18, 1892] yet but a small part of the public could attend the exposition and actually test the telephone for themselves. many of these believed that it was a hoax, and general skepticism still prevailed. business men, though they were convinced that the telephone would carry spoken messages, nevertheless insisted that it presented no business possibilities. hubbard, however, had faith in the invention, and as bell was not a business man, he took upon himself the work of promotion--the necessary, valuable work which must be accomplished before any big idea or invention may be put at the service of the public. hubbard's first move was to plan a publicity campaign which should bring the new invention favorably to the attention of all, prove its claims, and silence the skeptics. they were too poor to set up an experimental line of their own, and so telegraph lines were borrowed for short periods wherever possible, demonstrations were given and tests made. the assistance of the newspapers was invoked and news stories of the tests did much to popularize the new idea. an opportunity then came to bell to lecture and demonstrate the telephone before a scientific body in essex. he secured the use of a telegraph line and connected the hall with the laboratory in boston. the equipment consisted of old-fashioned box 'phones over a foot long and eight inches square, built about an immense horseshoe magnet. watson was stationed in the boston laboratory. bell started his lecture, with watson constantly listening over the telephone. bell would stop from time to time and ask that the ability of the telephone to transmit certain kinds of sounds be illustrated. musical instruments were played in boston and heard in essex; then watson talked, and finally he was instructed to sing. he insisted that he was not a singer, but the voices of others less experienced in speaking over the crude instruments often failed to carry sufficiently well for demonstration purposes. so watson sang, as best he could, "yankee doodle," "auld lang syne," and other favorites. after the lecture had been completed members of the audience were invited to talk over the telephone. a few of them mustered confidence to talk with watson in boston, and the newspaper reporters carefully noted down all the details of the conversation. the lecture aroused so much interest that others were arranged. the first one had been free, but admission was charged for the later lectures and this income was the first revenue bell had received for his invention. the arrangements were generally the same for each of the lectures about boston. the names of longfellow, of holmes, and of other famous american men of letters are found among the patrons of some of the lectures in boston. bell desired to give lectures in new york city, but was not certain that his apparatus would operate at that distance over the lines available. the laboratory was on the third floor of a rooming-house, and watson shouted so loud in his efforts to make his voice carry that the roomers complained. so he took blankets and erected a sort of tent over the instruments to muffle the sound. when the signal came from bell that he was ready for the test, watson crawled into the tent and began his shoutings. the day was a hot one, and by the time that the test had been completed watson was completely wilted. but the complaints of the roomers had been avoided. for one of the new york demonstrations the services of a negro singer with a rich barytone voice had been secured. watson had no little difficulty in rehearsing him for the part, as he objected to placing his lips close to the transmitter. when the time for the test arrived he persisted in backing away from the mouthpiece when he sang, and, though watson endeavored to hold the transmitter closer to him, his efforts were of no avail. finally bell told watson that as the negro could not be heard he would have to sing himself. the girl operator in the laboratory had assembled a number of her girl friends to watch the test, and watson, who did not consider himself a vocalist, did not fancy the prospect. but there was no one else to sing, the demonstration must proceed, and finally watson struck up "yankee doodle" in a quavering voice. the negro looked on in disgust. "is that what you wanted me to do, boss?" "yes," replied the embarrassed watson. "well, boss, i couldn't sing like that." the telegraph wires which were borrowed to demonstrate the utility of the telephone proved far from perfect for the work at hand. many of the wires were rusted and the insulation was poor. the stations along the line were likely to cut in their relays when the test was in progress, and bell's instruments were not arranged to overcome this retardation. however, the lectures were a success from the popular viewpoint. the public flocked to them and the fame of the telephone grew. so many cities desired the lecture that it finally became necessary for bell to employ an assistant to give the lecture for him. frederick gower, a providence newspaper man, was selected for this task, and soon mastered bell's lecture. it was then possible to give two lectures on the same evening, bell delivering one, gower the other, and watson handling the laboratory end for both. gower secured a contract for the exclusive use of the telephone in new england, but failed to demonstrate much ability in establishing the new device on a business basis. how little the possibilities of the telephone were then appreciated we may understand from the fact that gower exchanged his immensely valuable new england rights for the exclusive right to lecture on the telephone throughout the country. the success of these lectures made it possible for bell to marry, and he started for england on a wedding-trip. the lectures also aroused the necessary interest and made it possible to secure capital for the establishment of telephone lines. it also determined hubbard in his plan of leasing the telephones instead of selling them. this was especially important, as it made possible the uniformity of the efficient bell system of the present day. xiv improvement and expansion the first telephone exchange--the bell telephone association--theodore n. vail--the fight with the western union--edison and blake invent transmitters--last effort of the western union--mushroom companies and would-be inventors--the controversy with gray--dolbear's claims--the drawbaugh case--on a firm footing. through public interest had been aroused in the telephone, it was still very far from being at the service of the nation. the telephone increases in usefulness just in proportion to the number of your acquaintances and business associates who have telephones in their homes or offices. instruments had to be manufactured on a commercial scale, telephone systems had to be built up. while the struggles of the inventor who seeks to apply a new idea are often romantic, the efforts of the business executives who place the invention, once it is achieved, at the service of people everywhere, are not less praiseworthy and interesting. a very few telephones had been leased to those who desired to establish private lines, but it was not until may of 1877 that the first telephone system was established with an exchange by means of which those having telephones might talk with one another. there was a burglar-alarm system in boston which had wires running from six banks to a central station. the owner of this suggested that telephones be installed in the banks using the burglar-alarm wires. hubbard gladly loaned the instruments for the purpose. instruments were installed in the banks without saying anything to the bankers, or making any charge for the service. one banker demanded that his telephone be removed, insisting that it was a foolish toy. but even with the crude little exchange the first system proved its worth. others were established in new york, philadelphia, and other cities on a commercial basis. a man from michigan appeared and secured the perpetual rights for his state, and for his foresight and enterprise he was later to be rewarded by the sale of these rights for a quarter of a million dollars. the free service to the boston bankers was withdrawn and a commercial system installed there. but these exchanges served but a few people, and were poorly equipped. there was, of course, no provision for communication between cities. with the telephone over a year old, less than a thousand instruments were in use. but hubbard, who was directing the destinies of the enterprise during bell's absence in europe, decided that the time had come to organize. accordingly the bell telephone association was formed, with bell, hubbard, sanders, and watson as the shareholders. sanders was the only one of the four with any considerable sum of money, and his resources were limited. he staked his entire credit in the enterprise, and managed to furnish funds with which the fight for existence could be carried on. but a business depression was upon the land and it was not easy to secure support for the telephone. the entrance of the western union telegraph company into the telephone field brought the affairs of the bell company to a crisis. as we have seen, the telegraph company had developed into a great and powerful corporation with wires stretching across the length and breadth of the land and agents and offices established in every city and town of importance. once the telephone began to be used as a substitute for the telegraph in conveying messages, the telegraph officials awoke to the fact that here, possibly, was a dangerous rival, and dropped the viewpoint that bell's telephone was a mere plaything. they acquired the inventions of edison, gray, and dolbear, and entered the telephone field, announcing that they were prepared to furnish the very best in telephonic communication. this sudden assault by the most powerful corporation in america, while it served to arouse public confidence in the telephone, made it necessary for hubbard to reorganize his forces and find a general capable of doing battle against such a foe. hubbard's political activities had brought to him a presidential appointment as head of a commission on mail transportation. in the course of the work for the government he had come much in contact with a young man named theodore n. vail, who was head of the government mail service. he had been impressed by vail's ability and had in turn introduced vail to the telephone and aroused his enthusiasm in its possibilities. this vail was a cousin of the alfred vail who was morse's co-worker, and who played so prominent a part in the development of the telegraph. his experience in the post-office department had given him an understanding of the problems of communication in the united states, and had developed his executive ability. realizing the possibilities of the telephone, he relinquished his governmental post and cast his fortunes with the telephone pioneers, becoming general manager of the bell company. the western union strengthened its position by the introduction of a new and improved transmitter. this was the work of thomas edison, and was so much better than bell's transmitter that it enabled the western union to offer much better telephonic equipment. as we have seen, bell's transmitter and receiver were very similar, being about the same as the receiver now in common use. in his transmitter edison placed tiny bits of carbon in contact with the diaphragm. as the diaphragm vibrated under the sound-impulses the pressure upon the carbon granules was varied. an electric current was passed through the carbon particles, whose electrical resistance was varied by the changing pressure from the diaphragm. thus the current was thrown into undulations corresponding to the sound-waves, and passed over the line and produced corresponding sounds in the receiver. much stronger currents could be utilized than those generated by bell's instrument, and thus the transmitter was much more effective for longer distances. bell returned from europe to find the affairs of his company in a sorry plight. only the courage and generalship of vail kept it in the field at all. bell was penniless, having failed to establish the telephone abroad, even as morse before him had failed to secure foreign revenue from his invention. bell's health failed him, and as he lay helpless in the hospital his affairs were indeed at a low ebb. at this juncture francis blake, of boston, came forward with an improved transmitter which he offered to the bell company in exchange for stock. the instrument proved a success and was gladly adopted, proving just what was needed to make possible successful competition with the western union. prolonged patent litigation followed, and after a bitter legal struggle the western union officials became convinced of two things: one, that the bell company, under vail's leadership, would not surrender; second, that bell was the original inventor of the telephone and that his patent was valid. the western union, however, seemed to have strong basis for its claim that the new transmitter of the bell people was an infringement of edison's patent. a compromise was arranged between the contestants by which the two companies divided the business of furnishing communication by wire in the united states. this agreement proved of the greatest benefit to both organizations, and did much to make possible the present development and universal service of both the telephone and telegraph. by the terms of the agreement the western union recognized bell's patent and agreed to withdraw from the telephone business. the bell company agreed not to engage in the telegraph business and to take over the western union telephone system and apparatus, paying a royalty on all telephone rentals. experience has demonstrated that the two businesses are not competitive, but supplement each other. it is therefore proper that they should work side by side with mutual understanding. success had come at last to the telephone pioneers. other battles were still to be fought before their position was to be made secure, but from the moment when the western union admitted defeat the bell company was the leader. the stock of the company advanced to a point where bell, hubbard, sanders, and watson found themselves in the possession of wealth as a reward for their pioneering. the western union had no sooner withdrawn as a competitor of the bell organization than scores of small, local companies sprang up, all ready to pirate the bell patent and push the claims of some rival inventor. a very few of them really tried to establish telephone systems, but the majority were organized simply to sell stock to a gullible public. they stirred up a continuous turmoil, and made much trouble for the larger company, though their patent claims were persistently defeated in the courts. most of the rival claimants who sprang up, once the telephone had become an established fact and had proved its value, were men of neither prominence nor scientific attainments. of a very different type was elisha gray, whose work we have before noticed, and who now came forward with the claim that he had invented a telephone in advance of bell. gray was a practical man of real scientific attainments, but, as we have noticed, his efforts in search of a telephone were from the viewpoint of a musical telegraph and so destined to failure. it has frequently been stated that gray filed his application for a patent on a telephone of his invention but a few minutes after bell, and so bell wrested the honor from him by the scantiest of margins. a careful reading of the testimony brought out in gray's suit against bell does not support such a statement. while bell filed an application for a patent on a completed, invention, gray filed, a few moments later, a caveat. this was a document, stating that he hoped to invent a telephone of a certain kind therein stated, and would serve to protect his rights until he should have time to perfect it. thus gray did not have a completed invention, and he later failed to perfect a telephone along the lines described in his caveat. the decision of the court supported bell's claims in full. another of the western union's telephone experts, professor dolbear, of tufts college, also sought to make capital of his knowledge of the telephone. he based his claims upon an improvement of the reis musical telegraph, which had formed the starting-point for so many experimenters. the case fell flat, however, for when the apparatus was brought into court no one could make it talk. none of the attacks upon bell's claim to be the original inventor of the telephone aroused more popular interest at the time than the famous drawbaugh case. daniel drawbaugh was a country mechanic with a habit of reading of the new inventions in the scientific journals. he would work out models of many of these for himself, and, showing them very proudly, often claim them as his own devices. drawbaugh was now put forward by the opponents of the bell organization as having invented a telephone before bell. it was claimed that he had been too poor to secure a patent or to bring his invention to popular notice. much sympathy was thus aroused for him and the legal battle was waged to interminable length, with the usual result. bell's patent was again sustained, and drawbaugh's claims were pronounced without merit. many other legal battles followed, but the dominance of the bell organization, resting upon the indisputable fact that bell was the first man to conceive and execute a practical telephone, could not be shaken. the telephone business was on a firm footing: it had demonstrated its real service to the public; it had become a necessity; and, under the able leadership of vail, was fast extending its field of usefulness. xv telegraphing without wires the first suggestion--morse sends messages through the water--trowbridge telegraphs through the earth--experiments of preece and heaviside in england--edison telegraphs from moving trains--researches of hertz disclose the hertzian waves. great as are the possibilities of the telegraph and the telephone in the service of man, these instruments are still limited to the wires over which they must operate. communication was not possible until wires had been strung; where wires could not be strung communication was impossible. much yet remained to be done before perfection in communication was attained, and, though the public generally considered the telegraph, and the telephone the final achievement, men of science were already searching for an even better way. the first suggestion that electric currents carrying messages might some day travel without wires seems to have come from k.a. steinheil, of munich. in 1838 he discovered that if the two ends of a single wire carrying the electric current be connected with the ground a complete circuit is formed, the earth acting as the return. thus he was able to dispense with one wire, and he suggested that some day it might be possible to eliminate the wire altogether. the fact that the current bearing messages could be sent through the water was demonstrated by morse as early as 1842. he placed plates at the termini of a circuit and submerged them in water some distance apart on one side of a canal. other plates were placed on the opposite side of the waterway and were connected by a wire with a sensitive galvanometer in series to act as a receiver. currents sent from the opposite side were recorded by the galvanometer and the possibility of communication through the water was established. others carried these experiments further, it being even suggested that messages might be sent across the atlantic by this method. but bell's greatest contribution to the search for wireless telegraphy was not his direct work in this field, but the telephone itself. his telephone receiver provided the wireless experimenters with an instrument of extreme sensitiveness by which they were able to detect currents which the mirror galvanometer could not receive. while experimenting with a telephone along a telegraph line a curious phenomenon was noticed. the telephone experimenters heard music very clearly. they investigated and found that another telegraph wire, strung along the same poles, but at the usual distance and with the usual insulation, was being used for a test of edison's musical telephone. many other similar tests were made and the effect was always noted. in some way the message on one line had been conveyed across the air-gap and had been recorded by the telephones on the other line. it was decided that this had been caused by induction. prof. john trowbridge, of harvard university, might well be termed the grandfather of wireless telegraphy. he made the first extensive investigation of the subject, and his experiments in sending messages without wires and his discoveries furnished information and inspiration for those who were to follow. his early experiments tested the possibility of using the earth as a conductor. he demonstrated that when an electric current is sent into the earth it spreads from that point in waves in all directions, just as when a stone is cast into a pond the ripples widen out from that point, becoming fainter and fainter until they reach the shore. he further found that these currents could be detected by grounding the terminals of a telephone circuit. telegraphy through the earth was thus possible. however, the farther the receiving station was from the sending station the wider must be the distance between the telephone terminals and the smaller the current received. professor trowbridge did not find it possible to operate his system at a sufficient distance to make it of value, but he did demonstrate that the currents do travel through the earth and that they can be set to carrying messages. professor trowbridge also revived the idea of telegraphing across the atlantic by utilizing the conductivity of the sea-water to carry the currents. in working out the plan theoretically he discovered that the terminals on the american side would have to be widely separated--one in nova scotia and the other in florida--and that they would have to be connected by an insulated cable. two widely separated points on the coast of france were suggested for the other terminals. he also calculated that very high voltages would be necessary, and the practical difficulties involved made it seem certain that such a system would cost far too much to construct and to operate to be profitable. trowbridge suggested the possibility of using such a system for establishing communication between ships at sea. ship could communicate with ship, over short distances, during a fog. a trailing wire was to be used to increase the sending and receiving power, and trowbridge believed that with a dynamo capable of supplying current for a hundred lights, communication could be established at a distance of half a mile. not satisfied with the earth or the sea as a medium for carrying the current, trowbridge essayed to use the air. he believed that this was possible, and that it would be accomplished at no distant date. he believed, however, that such a system could not be operated over considerable distances because of the curvature of the earth. he endeavored to establish communication through the air by induction. he demonstrated that if one coil of wire be set up and a current sent through it, a similar coil facing it will have like currents induced within it, which may be detected with a telephone receiver. he also determined that the currents were strongest in the receiving coil when it was placed in a plane parallel with the sending coil. by turning the receiving coil about until the sound was strongest in the telephone receiver, it was thus possible to determine the direction from which the messages were coming. trowbridge recognized the great value of this feature to a ship at sea. but these induced currents could only be detected at a distance by the use of enormous coils. to receive at a half-mile a coil of eight hundred feet radius would have been necessary, and this was obviously impossible for use on shipboard. so these experiments also developed no practical improvement in the existing means of communication. but professor trowbridge had demonstrated new possibilities, and had set men thinking along new lines. he was the pioneer who pointed the way to a great invention, though he himself failed to attain it. bell followed up trowbridge's suggestions of using the water as a medium of communication, and in a series of experiments conducted on the potomac river established communication between moving ships. professor dolbear also turned from telephone experimentation to the search for the wireless. he grounded his wires and sent high currents into the earth, but improved his system and took another step toward the final achievement by adding a large induction coil to his sending equipment. he suggested that the spoken word might be sent as well as dots and dashes, and so sought the wireless telephone as well as the wireless telegraph. like his predecessors, his experiments were successful only at short distances. the next application of the induction telegraph was to establish communication with moving trains. several experimenters had suggested it, but it remained for thomas a. edison to actually accomplish it. he set up a plate of tin-foil on the engine or cars, opposite the telegraph wires. currents could be induced across the gap, no matter what the speed of the train, and, traveling along the wires to the station, communication was thus established. had edison continued his investigation further, instead of turning to other pursuits, he might have achieved the means of communicating through the air at considerable distances. these experiments by americans in the early 'eighties seemed to promise that america was to produce the wireless telegraph, as it had produced the telegraph and the telephone. but the greatest activity now shifted to europe and the american men of science failed to push their researches to a successful conclusion. sir w.h. preece, an englishman, brought himself to public notice by establishing communication with the isle of wight by morse's method. messages were sent and received during a period when the cable to the island was out of commission, and thus telegraphing without wires was put to practical use. preece carried his experiments much further. in 1885 he laid out two great squares of insulated wire, a quarter of a mile to the side, and at a distance of a quarter of a mile from each other. telephonic communication was established between them, and thus he had attained wireless telephony by induction. in 1887, another englishman, a.w. heaviside, laid circuits over two miles long on the surface and other circuits in the galleries of a coal-mine three hundred and fifty feet below, and established communication between the circuits. working together, preece and heaviside extended the distances over which they could communicate. preece finally decided that a combination of conduction and induction was the best means of wireless communication. he grounded the wire of his circuit at two points and raised it to a considerable height between these points. preece's work was to put the theories of professor trowbridge to practical use and thus bring the final achievement a step nearer. but conduction and induction combined would not carry messages to a distance that would enable extensive communication. a new medium had yet to be found, and this was the work of heinrich hertz, a young german scientist. he was experimenting with two flat coils of wire, as had many others before him, but one of the coils had a small gap in it. passing the discharge from a condenser into this coil, hertz discovered that the spark caused when the current jumped the gap set up electrical vibrations that excited powerful currents in the other coil. these currents were noticeable, though the coils were a very considerable distance apart. thus hertz had found out how to send out electrical waves that would travel to a considerable distance. what was the medium that carried these waves? this was the question that hertz asked himself, and the answer was, the ether. we know that light will pass through a vacuum, and these electric waves would do likewise. it was evident that they did not pass through the air. the answer, as evolved by hertz and approved by other scientists, is that they travel through the ether, a strange substance which pervades all space. hertz discovered that light and his electrical waves traveled at the same speed, and so deduced that light consists of electrical vibrations in the ether. with the knowledge that this all-pervading ether would carry electric waves at the speed of light, that the waves could be set up by the discharge of a spark across a spark-gap in a coil, and that they could be received in another coil in resonance with the first, the establishment of a practical wireless telegraph was not far away. xvi an italian boy's work the italian youth who dreamed wonderful dreams--his studies--early detectors--marconi seeks an efficient detector--devises new sending methods--the wireless telegraph takes form--experimental success. with the nineteenth century approaching its close, man had discovered that the electric waves would travel through the ether; he had learned something of how to propagate those waves, and something of how to receive them. but no one had yet been able to combine these discoveries in practical form, to apply them to the task of carrying messages, to make the improvements necessary to make them available for use at considerable distances. though many mature scientists had devoted themselves to the problem, it remained for a youth to solve it. the youth was guglielmo marconi, an italian. we have noticed that the telegraph, the cable, and the telephone were the work of those of the anglo-saxon race--englishmen or americans--so it came as a distinct surprise that an italian youth should make the next great application of electricity to communication. but anglo-saxon blood flows in marconi's veins. though his father was an italian, his mother was an irishwoman. he was born at villa griffone near bologna, italy, on april 25, 1874. he studied in the schools of bologna and of florence, and early showed his interest in scientific affairs. from his mother he learned english, which he speaks as fluently as he does his native tongue. as a boy he was allowed to attend english schools for short periods, spending some time at bedford and at rugby. one of his italian teachers was professor righi, who had made a close study of the hertzian waves, and who was himself making no small contributions to the advancement of the science. from him young marconi learned of the work which had been accomplished, and of the apparatus which was then available. marconi was a quiet boy--almost shy. he did not display the aggressive energy so common with many promising youths. but though he was quiet, he was not slothful. he entered into his studies with a determination and an application that brought to him great results. he was a student and a thinker. any scientific book or paper which came before him was eagerly devoured. it was this habit of careful and persistent study that made it possible for marconi to accomplish such wonderful things at an early age. marconi had learned of the hertzian waves. it occurred to him that by their aid wireless telegraphy might be accomplished. the boy saw the wonderful possibilities; he dreamed dreams of how these waves might carry messages from city to city, from ship to shore, and from continent to continent without wires. he realized his own youth and inexperience, and it seemed certain to him that many able scientists had had the same vision and must be struggling toward its attainment. for a year marconi dreamed those dreams, studying the books and papers which would tell him more of these wonderful waves. each week he expected the news that wireless telegraphy had been established, but the news never came. finally he concluded that others, despite their greater opportunities, had not been so far-seeing as he had thought. marconi attacked the problem himself with the dogged persistence and the studious care so characteristic of him. he began his experiments upon his father's farm, the elder marconi encouraging the youth and providing him with funds with which to purchase apparatus. he set up poles at the opposite sides of the garden and on them mounted the simple sending and receiving instruments which were then available, using plates of tin for his aerials. he set up a simple spark-gap, as had hertz, and used a receiving device little more elaborate. a morse telegraph-key was placed in circuit with the spark-gap. when the key was held down for a longer period a long spark passed between the brass knobs of the spark-gap and a dash was thus transmitted. when the key was depressed for a shorter period a dot in the morse code was sent forth. after much work and adjustment marconi was able to send a message across the garden. others had accomplished this for similar distances, but they lacked marconi's imagination and persistence, and failed to carry their experiments further. to the young irish-italian this was but a starting-point. [illustration: guglielmo marconi photographed in the uniform of an officer in the italian army] marconi quickly found that the receiver was the least effective part of the existing apparatus. the waves spread in all directions from the sending station and become feebler and feebler as the distance increases. to make wireless telegraphy effective over any considerable distance a highly efficient and extremely sensitive receiving device is necessary. some special means of detecting the feeble currents was necessary. the coherer was the solution. as early as 1870 a mr. s.a. varley, an englishman, had discovered that when he endeavored to send a current through a mass of carbon granules the tiny particles arranged themselves in order under the influence of the electric current, and offered a free path for the passage of the current. when shaken apart they again resisted the flow of current until it became powerful enough to cause them to again arrange themselves into a sort of bridge for its passage. thus was the principle of the coherer discovered. an italian scientist, professor calzecchi-onesti, carried these experiments still further. he used various substances in place of the carbon granules and showed that some of them will arrange themselves so as to allow the passage of a current under the influence of the spark setting up the hertzian waves. professor e. branly, of the catholic university of paris, took up this work in 1890. he arranged metal filings in a small glass tube six inches long and arranged a tapper to disarrange the filings after they had been brought together under the influence of the spark. with the branly coherer as the basis marconi sought to make improvements which would result in the detector he was seeking. for his powder he used nickel, mixed with a small proportion of fine silver filings. this he placed between silver plugs in a small glass tube. platinum wires were connected to the silver plugs and brought out at the opposite ends of the tube. it required long study to determine just how to adjust the plugs between which the powder was loosely arranged. if the particles were pressed together too tightly they would not fall apart readily enough under the influence of the tapper. if too much space was allowed they would not cohere readily enough. marconi also discovered that a larger proportion of silver in the powder and a smaller amount between the plugs increased the sensitiveness of the receiver. yet he found it well not to have it too sensitive lest it cohere for every stray current and so give false signals. under the influence of the electric waves set up from the spark-gap those tiny particles so arranged themselves that they would readily carry a current between the plugs. by placing these plugs with their platinum terminals in circuit with a local battery the current from this local battery was given a passage through the coherer by the action of the electric waves coming through the ether. while these waves themselves were too feeble to operate a receiving mechanism, they were strong enough to arrange the particles of the sensitive metal in the tube in order, so that the current from the local battery could pass through them. this current operated a telegraph relay which in turn operated a morse receiving instrument. an electrical tapper was also arranged in this circuit so that it would strike the tube a light blow after each long or short wave representing a dot or a dash had been received. thus the particles were disarranged, ready to array themselves when the next wave came through the ether and so form the bridge over which the stronger local circuit could convey the signal. marconi further discovered that the most effective arrangement was to run a wire from one terminal of the coherer into the ground, and from the other to an elevated metal plate or wire. the waves coming through the ether were received by the elevated wire and were conducted down to the coherer. experimenting with his apparatus on the posts in the garden, he discovered that an increase in the height of the wire greatly increased the receiving distance. at his sending station he used the exciter of his teacher, professor righi. this, too, he modified and perfected for his practical purpose. as he used the device it consisted of two brass spheres a millimeter apart. an envelope was provided so that the sides of the spheres toward each other and the space between was occupied by vaseline oil which served to keep the faces of the spheres clean and produce a more uniform spark. outside the two spheres, but in line with them, were placed two smaller spheres at a distance of about two-fifths of a centimeter. the terminals of the sending circuit were attached to these. the secondary coil of a large induction coil was placed in series with them, and batteries were wired in series with the primary of the coil with a sending key to make and break the circuit. when the key was closed a series of sparks sprang across the spark-gap, and the waves were thus set up in the ether and carried the message to the receiving station. as in the case of his receiving station, marconi found that results were much improved when he wired his sending apparatus so that one terminal was grounded and the other connected with an elevated wire or aerial, which is now called the antenna. by 1896 marconi had brought this apparatus to a state of perfection where he could transmit messages to a distance of several miles. this irish-italian youth of twenty-two had mastered the problem which had baffled veteran scientists and was ready to place a new wonder at the service of the world. the devices which marconi thus assembled and put to practical use had been, in the hands of others, little more than scientific toys. others had studied the hertzian waves and the methods of sending and detecting them from a purely scientific viewpoint. marconi had the vision to realize the practical possibilities, and, though little more than a boy, had assembled the whole into a workable system of communication. he richly deserves the laurels and the rewards as the inventor of the wireless telegraph. xvii wireless telegraphy established marconi goes to england--he confounds the skeptics--a message to france without wires--the attempt to span the ocean--marconi in america receives the first message from europe--fame and recognition achieved. the time had now come for marconi to introduce himself and his discoveries to the attention of the world. he went to england, and on june 2, 1896, applied for a patent on his system of wireless telegraphy. soon afterward his plans were submitted to the postal-telegraph authorities. fortunately for marconi and for the world, w.h. preece was then in authority in this department. he himself had experimented with some little success with wireless messages. he was able enough to see the merit in marconi's discoveries and generous enough to give him full recognition and every encouragement. the apparatus was first set up in the general post-office in london, another station being located on the roof but a hundred yards away. though several walls intervened, the hertzian waves traversed them without difficulty, and messages were sent and received. stations were then set up on salisbury plain, some two miles apart, and communication was established between them. though the postal-telegraph authorities received marconi's statements of his discoveries with open mind and put his apparatus to fair tests, the public at large was much less tolerant. the skepticism which met morse and bell faced marconi. men of science doubted his statements and scoffed at his claims. the hertzian waves might be all right to operate scientific playthings, they thought, but they were far too uncertain to furnish a medium for carrying messages in any practical way. then, as progress was made and marconi began to prove his system, the inevitable jealousies arose. experimenters who might have invented the wireless telegraph, but who did not, came forward to contest marconi's claims and to seek to snatch his laurels from him. the young inventor forged steadily ahead, studying and experimenting, devising improved apparatus, meeting the difficulties one by one as they arose. in most of his early experiments he had used a modification of the little tin boxes which had been set up in his father's garden as his original aerials. having discovered that the height of the aerials increased the range of the stations, he covered a large kite with tin-foil and, sending it up with a wire, used this as an aerial. balloons were similarly employed. he soon recognized, however, that a practical commercial system, which should be capable of sending and receiving messages day and night, regardless of the weather, could not be operated with kites or balloons. the height of masts was limited, so he sought to increase the range by increasing the electrical power of the current sending forth the sparks from the sending station. here he was on the right path, and another long step forward had been taken. in the fall of 1897 he set up a mast on the isle of wight, one hundred and twenty feet high. from the top of this was strung a single wire and a new series of experiments was begun. marconi had spent the summer in italy demonstrating his apparatus, and had established communication between a station on the shore and a war-ship of the italian navy equipped with his apparatus. he now secured a small steamer for his experiments from his station on the isle of wight and equipped it with a sixty-foot mast. communication was maintained with the boat day after day, regardless of weather conditions. the distance at which communication could be maintained was steadily increased until communication was established with the mainland. in july of 1898 the wireless demonstrated its utility as a conveyer of news. an enterprising dublin newspaper desired to cover the kingstown regatta with the aid of the wireless. in order to do this a land station was erected at kingstown, and another on board a steamer which followed the yachts. a telephone wire connected the kingstown station with the newspaper office, and as the messages came by wireless from the ship they were telephoned to dublin and published in successive editions of the evening papers. this feat attracted so much attention that queen victoria sought the aid of the wireless for her own necessities. her son, the prince of wales, lay ill on his yacht, and the aged queen desired to keep in constant communication with him. marconi accordingly placed one station on the prince's yacht and another at osborne house, the queen's residence. communication was readily maintained, and one hundred and fifty messages passed by wireless between the prince and the royal mother. while the electric waves bearing the messages were found to pass through wood, stone, or earth, it was soon noticed in practical operation that when many buildings, or a hill, or any other solid object of size intervened between the stations the waves were greatly retarded and the messages seriously interfered with. when the apparatus was placed on board steel vessels it was found that any part of the vessel coming between the stations checked the communication. marconi sought to avoid these difficulties by erecting high aerials at every point, so that the waves might pass through the clear air over solid obstructions. marconi's next effort was to connect france with england. he went to france to demonstrate his apparatus to the french government and set up a station near boulogne. the aerial was raised to a height of one hundred and fifty feet. another station was erected near folkestone on the english coast, across the channel. a group of french officials gathered in the little station near folkestone for the test, which was made on the 27th of march, 1899. marconi sent the messages, which were received by the station on the french shore without difficulty. other messages were received from france, and wireless communication between the nations was an accomplished fact. the use of the wireless for ships and lighthouses sprang into favor, and wireless stations were established all around the british coasts so that ships equipped with wireless might keep in communication with the land. the british admiralty quickly recognized the value of wireless telegraphy to war vessels. while field telegraphs and telephones had served the armies, the navies were still dependent upon primitive signals, since a wire cannot be strung from ship to ship nor from ship to shore. so the british battle-ships were equipped with wireless apparatus and a thorough test was made. a sham battle was held in which all of the orders were sent by wireless, and communication was constantly maintained both between the flag-ships and the vessels of their fleets and between the flag-ships and the shore. marconi's invention had again proved itself. the wireless early demonstrated its great value as a means of saving life at sea. lightships off the english coast were equipped with the wireless and were thus enabled to warn ships of impending storms, and on several occasions the wireless was used to summon aid from the shore when ships were sinking because of accidents near the lightship. following the establishment of communication with france, marconi increased the range of his apparatus until he was able to cover most of eastern europe. in one of his demonstrations he sent messages to italy. his ambition, however, was to send messages across the atlantic, and he now attacked this stupendous task. on the coast of cornwall, england, he began the construction of a station which should have sufficient power to send a message to america. instead of using a single wire for his aerial, he erected many tall poles and strung a number of wires from pole to pole. the comparatively feeble batteries which had furnished the currents used in the earlier efforts were replaced with great power-driven dynamos, and converters were used instead of the induction coil. thus was the great poldhu station established. late in 1901 marconi crossed to america to superintend the preparations there, and that he himself might be ready to receive the first message, should it prove possible to span the ocean. signal hill, near st. john's, newfoundland was selected as the place for the american station. the expense of building a great aerial for the test was too great, and so dependence was had upon kites to send the wires aloft. for many days marconi's assistants struggled with the great kites in an effort to get them aloft. at last they flew, carrying the wire to a great height. the wire was carried into a small government building near by in which marconi stationed himself. at his ear was a telephone receiver, this having been substituted for the relay and the morse instrument because of its far greater sensitiveness. marconi had instructed his operator at poldhu to send simply the letter "s" at an hour corresponding to 12.30 a.m. in newfoundland. great was the excitement and suspense in cornwall when the hour for the test arrived. forgetting that they were sleepy, the staff crowded about the sending key, and the little building at the foot of the ring of great masts supporting the aerial shook with the crash of the blinding sparks as the three, dots which form the letter "s" were sent forth. even greater was the tension on the newfoundland coast, where marconi sat eagerly waiting for the signal. finally it came, three faint ticks in the telephone receiver. the wireless had crossed the atlantic. marconi had no sending apparatus, so that it was not until the cable had carried the news that those in england knew that the message had been received. because marconi had never made a statement or a claim he had not been able to prove, he had attained a reputation for veracity which made his statement that he had received a signal across the atlantic carry weight with the scientists. many, of course, were skeptical, and insisted that the simple signal had come by chance from some ship not far away. but the inventor pushed quietly and steadily ahead, making arrangements to perfect the system and establish it so that it would be of commercial use. marconi returned to england, but two months later set out for america again on the liner _philadelphia_ with improved apparatus. he kept in constant communication with his station at poldhu until the ship was a hundred and fifty miles from shore. beyond that point he could not send messages, as the sending apparatus on the ship lacked sufficient power. messages were received, however, until the sending station was over two thousand miles away. this seemed miraculous to those on shipboard, but marconi accepted it as a matter of course. he had equipped the poldhu station to send twenty-one hundred miles, and he knew that it should accomplish the feat. a large station was set up at cape breton, nova scotia, and regular communication was established between there and poldhu. with the establishment of regular transatlantic communication the utility of marconi's invention, even for work at great distances, was no longer open to question. by quiet, unassuming, conscientious work he had put another great carrier of messages at the service of the world, and he now reaped the fame and fortune which he so richly deserved. xviii the wireless serves the world marconi organized wireless telegraphy commercially--the new wonder at the service of the world--marine disasters prevented--the extension of the wireless on shipboard--improved apparatus--the wireless in the world war--the boy and the wireless. with his clear understanding of the possibilities of his invention, marconi was not long in establishing the wireless upon a commercial basis. he is a man of keen business judgment, and as he brought his invention forward and clearly demonstrated its worth at a time when commercial enterprise was alert he found no great difficulty in establishing his company. the first marconi company was organized as early as 1897 under the name of the wireless telegraph and signal company, limited. this was later displaced by the marconi telegraph company, which operates a regular system of stations on a commercial basis, carrying messages in competition with the cable and telegraph companies. it also erects stations for other companies which are operated under the marconi patents. with the telegraph and the telephone so well established and serving the needs of ordinary communication on land, it was natural that the wireless should make headway but slowly as a commercial proposition between points on land. for communication at sea, however, it had no competition, and merchant-ships as well as war vessels were rapidly equipped with wireless apparatus. when the great liner _republic_ was sinking as a result of a collision off the port of new york in 1903 her wireless brought aid. her passengers and crew were taken off in safety, and what otherwise would have been a terrible disaster was avoided by the use of the wireless. the utility of the wireless was again brought sharply to the attention of the world. it was realized that a wireless set on a passenger-ship was necessary if the lives of the passengers were to be safeguarded. the united states government by its laws now requires that passenger-ships shall be equipped with wireless apparatus in charge of a competent operator. one of the early objections made to the wireless was its apparent lack of secrecy, since any other receiving apparatus within range of the waves sent forth by the sending station can receive the signals. it was also realized that as soon as any considerable number of stations were established about the world, and began sending messages to and fro, there would be a perfect jumble of waves flying about in all directions through the ether, so that no messages could be sent or received. marconi's answer to these difficulties was the tuning apparatus. the electric waves carrying the messages may be sent out at widely varying lengths. marconi found that it was possible to adjust a receiving station so that it would receive only waves of a certain length. thus stations which desired to communicate could select a certain wave-length, and they could send and receive messages without interfering with others using different wave-lengths, or without the receiving station being confused by messages coming in from other stations using different wave-lengths. you know that when a tuning-fork is set in vibration another of the same pitch near it will vibrate with it, but others of different pitch will not be affected. the operation of wireless stations in tune with each other is similar. [illustration: a remarkable photograph taken outside of the clifden station while messages were being sent across to cape race the camera was exposed for two hours, and the white bars show the sparks leaving the wires for their journey through the air for seventeen hundred miles.] [illustration: marconi station at clifden, ireland these dynamos send a message straight across the ocean.] an example of the value of tuning is afforded by the manner in which press reports are sent from the great marconi station at poldhu. each night at a certain hour this station sends out news reports of the events of the day, using a certain set wave-length. each ship on the atlantic and every land station within range which is to receive the reports at that hour adjusts its receiving set to receive waves of that length. in this way they hear nothing but the poldhu news reports which they desire to receive, and are not troubled by messages from other stations within range. secrecy is also attained by the use of tuning. it is possible that another station may discover the wave-length being used for a secret message and "listen in," but there are so many possible wave-lengths that this is difficult. secrecy may also be secured by the use of code messages. many of the advantages of tuning were lost by the international agreement which provided that but two wave-lengths should be used for commercial work. this, however, enables ships to get in touch with other ships in time of need. with his telephone receivers the operator can hear the passage of the waves as they are brought to him by his aerial and the dots and dashes sound as buzzes of greater or less length. out of the confusion of currents passing through the air he can select the messages he wishes to read by sound. you may wonder how one wireless operator gets into communication with another. he first listens in to determine whether messages are coming through the ether within range in the wave-length he is to use. hearing nothing, he adjusts his sending apparatus to the desired wave-length and switches this in with the signal aerial which serves both his sending and his receiving set. this at the same time disconnects his receiving set. he sends out the call letters of the station to which he wishes to send a message, following them with his own call letters, as a signature to show who is calling. after repeating these signals several times he switches out his sending set and listens in with his receiving set. if he then gets an answer from the other station he can begin sending the message. marconi was not allowed to hold the wireless field unmolested. many others set up wireless stations, some of them infringing upon marconi's patents. others have devised wireless systems along more original lines. particularly we should mention two american experimenters, dr. de forest and professor fessenden. both have established wireless systems with no little promise. the system of professor fessenden is especially unique and original and may be destined to work a revolution in the methods of wireless telegraphy. with an increase in the number of wireless stations and varieties of apparatus came a wide increase in the uses to which wireless telegraphy was applied. we have already noticed the press service from poldhu. the british government makes use of this same station to furnish daily news to its representatives in all parts of the world. the wireless is also used to transmit the time from the great observatories. some of the railroads in the united states have equipped their trails as well as their stations with wireless sets. it has proved its worth in communicating between stations, taking the place in time of need of either the telegraph or the telephone. in equipping the trains with sets a difficulty was met in arranging the aerials. it is, of course, impossible to arrange the wires at any height above the cars, since they would be swept away in passing under bridges. even with very low aerials, however, communication has been successfully maintained at a distance of over a hundred miles. the speed of the fastest train affects the sending and receiving of messages not at all. it was also found that messages passed without hindrance, even though the train was passing through a tunnel. another interesting application of wireless telegraphy is to the needs of the fire-fighters. fire stations in new york city have been equipped with wireless telegraph sets, and they have proved so useful in spreading alarms and transmitting news of fires that they seem destined to come into universal use. the outbreak of the world war gave a tremendous impetus to the development of wireless telegraphy. the german cable to the united states was cut in the early days of the conflict. the sending power of wireless stations had been sufficiently increased, however, so that the great german stations could communicate with those in the united states. communication was readily maintained between the allies by means of wireless, the great stations at poldhu and at the eiffel tower in paris being in constant communication with each other and with the stations in italy and in russia. portable field sets had been used with some slight success even in the boer war, and had definitely proved their worth in the balkans. the outbreak of the greater war found all of the nations equipped with portable apparatus for the use of their armies. these proved of great use. the field sets of the united states army also proved their utility in the campaign into mexico in pursuit of villa. by their means it was possible for general pershing's forces to keep in constant touch with the headquarters in the united states. the wireless proved as valuable to the navies as had been anticipated. the germans in particular made great improvements in light wireless sets designed for use on aircraft. the problem of placing an aerial on an aeroplane is difficult, but no little headway has been made in this direction. it is the american boy who has done the most interesting work with the wireless in the united states. while the commercial development has been comparatively slow, the boys have set up stations by the thousands. most of these stations were constructed by the boys themselves, who have learned and are learning how best to apply this modern wonder to the service of man. so many amateurs set up stations that the government found it necessary to regulate them by law. the law now requires that amateur experimenters use only short wave-lengths in their sending, which will not interfere with messages from government or commercial stations. it also provides for the licensing of amateurs who prove competent. the stations owned and operated by boys have already proved of great use. in times of storm and flood when wire communication failed they have proved the only means of communicating with many districts. in time of war these amateur stations, scattered in all parts of the country, might prove immensely valuable. means have now been taken to so organize the amateurs that they can communicate with one another, and by this means messages may be sent to any part of the country. one young american, john hays hammond, jr., has applied the wireless in novel and interesting ways. by means of special apparatus mounted on a small boat he can by the means of a wireless station on shore start or stop the vessel, or steer it in any direction by his wireless control. he has applied the same system to the control of torpedoes. by this means a torpedo may be controlled after it has left the shore and may be directed in any direction as long as it is within sight. this invention may prove of incalculable benefit should america be attacked by a foreign power. what startling developments of wireless telegraphy lie still in the future we do not know. marconi has predicted that wireless messages will circle the globe. "i believe," he has said, "that in the near future a wireless message will be sent from new york completely around the world without relaying, and will be received by an instrument in the same office with the transmitter, in perhaps less time than shakespeare's forty minutes." not long ago the united states battle-ship _wyoming_, lying off cape henry on the atlantic coast, communicated with the _san diego_ at guaymas, on the pacific coast of mexico. this distance, twenty-five hundred miles across land, shows that marconi's prediction may be realized in the not distant future. xix speaking across the continent a new "hello boy" in boston--why the boy sought the job--the useful things the boy found to do--young carty and the multiple switchboard--called to new york city--he quiets the roaring wires--carty made engineer-in-chief--extending the range of the human voice--new york talks to san francisco over a wire. it seemed to many that the wireless telegraph was to be the final word in the development of communication, but two striking achievements coming in 1915 proved this to be far from the case. while one group of scientists had given themselves to experimentation with the hertzian waves which led to wireless telegraphy, other scientists and engineers were busily engaged in bringing the telephone to a perfection which would enable it to accomplish even more striking feats. these electrical pioneers did not work as individuals, but were grouped together as the engineering staff of the american telephone and telegraph company. at their head was john j. carty, and it was under his guiding genius that the great work was accomplished. john carty is the american son of irish parents. he was born in cambridge, massachusetts, on april 14, 1861. his father was a gun-maker and an expert mechanic of marked intelligence and ingenuity who numbered among his friends howe, the creator of the sewing-machine. as a boy john carty displayed the liveliest interest in things electrical. when the time came for him to go to school, physics was his favorite study. he showed himself to be possessed of a keen mind and an infinite capacity for work. to these advantages was added a good elementary education. he was graduated from cambridge latin school, where he prepared for harvard university. before he could enter the university his eyesight failed, and the doctor forbade continuance of study. many a boy would have been discouraged by this physical handicap which denied him complete scholastic preparation. but this boy was not the kind that gives up. he had been supplementing his school work in physics with experimentations upon his own behalf. let us let mr. carty tell in his own words how he next occupied himself. i had often visited the shop of thomas hall, at 19 bromfield street, and looked in the window. i went in from time to time, not to make large purchases, but mostly to make inquiries and to buy some blue vitriol, wire, or something of the kind. it was a store where apparatus was sold for experimentation in schools, and on saturdays a number of harvard and institute of technology professors could be found there. it was quite a rendezvous for the scientific men in those days, just the same as the old corner bookstore at the corner of school and washington streets was a place where the literary men used to congregate. don't think that i was an associate of these great scientists, but i was very much attracted to the atmosphere of that store. i wanted to get in and handle the apparatus. finally it occurred to me that i would like to get into the business, somehow. but i did not have the courage to go in and ask them for a job. one day i was going by and saw a sign hanging out, "boy wanted." i was about nineteen, and really thought i was something of a scientist, not exactly a boy. i was a boy, however. i walked by on one side of the street and then on the other, looking in, and finally the idea possessed me to go in and strike for that job. so i took down the sign, which was outside the window, put it under my arm, and went in and persuaded tom hall that i was the boy he wanted. he said, "when can you begin?" i said, "now." there was no talk of wages or duties. he said, "take this package around to earle & prew's express and hurry back, as i have another errand for you to do." so i had to take a great, heavy box around to the express-office and get a receipt for it. i found, when saturday night came around, that i had been engaged at the rate of fifty cents a day. i would have been glad to work for nothing. well, i did not get near that apparatus in a hurry, not until the time came for fixing up the window. my first talk in regard to it had no reference to services in a scientific capacity on my part. i had rather hoped that the boss would come around and consult with, me as to how to adjust the apparatus. but that was not it. he said: "john, clean out that window. everything is full of dust, and be careful and don't break anything!" so i cleaned it out. i swept out the place, cleaned about there, did errands, mixed battery solutions, and got a great deal of experience there in one way or another. i did whatever there was to do and got a good deal of fun out of it, while becoming acquainted with the state of the art of that day. i got to know intimately all the different sorts of philosophical apparatus there were, and how to mix the various battery solutions. in fact, i became really quite experienced for those times in such matters. it was not long before young carty lost his job. being a regular boy, he had been guilty of too much skylarking. this experience steadied him, and he forthwith sought a new job. he had met some of the employees of the telephone company and was naturally interested in their work. at that time "hello boys" held sway in the crude telephone exchanges, the "hello girl" having not yet appeared. so john carty at the age of nineteen went to work in the boston telephone exchange. the switchboard at which they placed him had been good enough for the other boys who had been called upon to operate it, and indeed it represented the best thought and effort of the leaders in the telephone world. but it did not satisfy carty, who, not content with simply-operating the board, studied its construction and began planning improvements. as mr. carty himself puts it: the little switchboards of that day were a good deal like the automobiles of some years ago--one was likely to spend more time under the switchboard than, sitting at it! in that way i learned a great deal about the arrangement and construction of switchboards. encountering the trouble first, i had an advantage over others in being able to suggest a remedy. so i have always thought it was a good thing to have troubles, as long as they are not too serious or too numerous. troubles are certainly a great advantage, if we manage them correctly. certainly carty made these switchboard troubles the first stepping-stone in his climb to the top in the field of telephone engineering. the improvements which the youngster suggested were so valuable that they were soon being made under his direction, and ere long he installed in the boston exchange the first multiple switchboard, the fundamental features of which are in the switchboards of to-day. in his work with the switchboards young carty early got in touch with charles e. scribner, another youngster who was doing notable work in this field. the young men became fast friends and worked much together. scribner devoted himself almost exclusively to switchboards and came to be known as the father of the modern switchboard. boston had her peculiar problems and an "express" service was needed. how to handle this in the exchange was another problem, and this, too, carty solved. for this purpose he designed and installed the first metallic circuit, multiple switchboard to go into service. the problems of the exchange were among the most serious of the many which troubled the early telephone companies. of course every telephone-user desired to be able to converse with any other who had a telephone in his office or residence. the development of the switchboards had been comparatively slow in the past, and the service rendered by the boys proved far from satisfactory. the average boy proved himself too little amenable to discipline, too inclined to "sass" the telephone-users, and too careless. but the early use of "hello boys" was at least a success for the telephone in that it brought to its service john j. carty. this boy pointed the way to the great improvements that made it possible to handle the constantly growing volume of calls expeditiously and effectively. the early telephones were operated with a single wire grounded at either end, the earth return being used to complete the circuit as with the telegraph. but while the currents used to operate the telegraph are fairly strong and so can dominate the earth currents, the tiny currents which represented the vibrations of the human voice were all too often drowned by the earth currents which strayed on to the lines. telephone engineers were not then agreed that this caused the difficulty; but they did know there was difficulty. many weird noises played over the lines and as often as not the spoken word was twisted into the strangest gibberish and rendered unintelligible. if the telephone was to satisfy its patrons and prove of real service to the world, the difficulty had to be overcome. some of the more progressive engineers insisted that a double-wire system without a ground was necessary. this, of course, involved tremendous expenses in rebuilding every line and duplicating every wire. the more conservative hesitated, but carty forged ahead. in 1880 he was engaged in operating a new line out of boston. he was convinced that the double-wire system alone could be successful, and he arranged to operate a line on this plan. taking two single lines, he instructed the operator at the other end to join them, forming a two-wire circuit. the results justified him. at last a line had been attained which could be depended upon to carry the conversation. no sooner was one problem solved than another presented itself. what to do with the constantly increasing number of wires was a pressing difficulty. all telephone circuits had been strung overhead, and with the demand for telephones for office and residence rapidly increasing, the streets of the great cities were becoming a perfect forest of telephone poles, with the sky obscured by a maze of wires. poles were constantly increased in height until a line was strung along wall street in new york city at a height of ninety feet. from the poles the wires overflowed to the housetops, increasing the difficulty of the engineers. how to protect the wires so that they could be placed underground was the problem. we have noticed that theodore vail had been brought to the head of the bell system in its infancy and had led the fight against the rival companies until it was thoroughly established. now he was directing his genius and executive ability to so improving the telephone that it should serve every need of communication. while the engineers discussed theories vail began actual tests. a trench five miles long was dug beside a railway track by the simple expedient of hitching a plow to a locomotive. in this trench were laid a number of wires, each with a different covering. the gutta-percha and the rubber coverings which had been used in cable construction predominated. it was found that these wires would carry the telephone currents, not as well as might be desired, but well enough to assure vail that he was on the right track. the companies began to place their wires underground, and vail saw to it that the experiments with coverings for telephone wires were continued. the result was the successful underground cables in use to-day. at the same time vail and his engineers were seeking to improve the wires themselves. iron and steel wires had been used, but they proved unsatisfactory, as they rusted and were poor conductors. copper was an excellent conductor, but the metal in the pure state is soft and no one then knew how to make a copper wire that would sustain its own weight. but vail kept his men at the problem and the hard-drawn copper wire was at length evolved. this proved just what was needed for the telephone circuits. the copper wire was four times as expensive as the iron, but as it was four times as good vail adopted it. john carty had rather more than kept pace with these improvements. he was but twenty-six years of age when union n. bethell, head of the new york company, picked carty to take charge of the telephone engineering work in the metropolis. bethell was vail's chief executive officer, and under him carty received an invaluable training in executive work. carty's largest task was putting the wires underground, and here again he was a tremendous success. he found ways to make cables cheaper and better, and devised means of laying them at half the former cost. having solved the most pressing problems in this field, his employers, who had come to recognize his marked genius, set him to work again on the switchboard. he was placed in charge of the switchboard department of the western electric company, the concern which manufactures the apparatus for the telephone company. the switchboard, as we have seen, was carty's first love, and again he pointed the way to great improvements. most of the large switchboards of that time were installed under his direction, and they were better switchboards than had ever been known before. up to this time it had been thought necessary to have individual batteries supplying current to each line. these were a constant source of difficulty, and carty directed his own attention, and that of his associate engineers, to finding a satisfactory solution. he sought a method of utilizing one common battery at the central station and the way was found and the improvement accomplished. though the telephone circuits were now protected from the earth, telephone-users, at times when the lines were busy, were still troubled with roarings and strange cross-talk. though busy with the many engineering problems which the telephone heads had assigned to him, carty found time for some original research. he showed that the roarings in the wires were largely caused by electro-static induction. in 1889 he read a paper before the electric club that startled the engineers of that day. he demonstrated that in every telephone circuit there is a particular point at which, if a telephone is inserted, no cross-talk can be heard. he had worked out the rules for determining this point. thus he had at once discovered the trouble and prescribed the cure. of course it could not be expected that the sage experts would all agree with young carty right away; but they were forced to in the end, for again he was proved right. by 1901 carty was ready with another invention which was to place the telephone in the homes of hundreds of thousands who, without it, could scarcely have afforded this modern necessity. this was the "bridging bell" which made possible the party line. by its use four telephones could be placed on a single line, each with its own signal, so that any one could be rung without ringing the others. its introduction inaugurated a new boom in the use of the telephone. theodore vail had resigned from his positions with the telephone companies in 1890 with the determination to retire from business. but when the panic of 1907 came the directors of the company went to him on his vermont farm and pleaded with him to return and again resume the leadership. other and younger men would not do in this business crisis. they also pointed out that the nation's telephones had not yet been molded into the national system which had been his dream--a system of universal service in which any one at any point in the country might talk by telephone with any other. so vail re-entered the telephone field and again took the presidency of the american telephone and telegraph company. one of his first official acts was to appoint john j. carty his chief engineer. vail had selected the right man to make his dreams come true; carty now had the executive who would make it possible for him to accomplish even larger things. he set about building up the engineering organization which was to accomplish the work, selecting the most brilliant graduates of american technical schools. he set this organization to work upon the extension and development of the long-distance telephone lines. as a "hello boy" carty had believed in the possibility of the long-distance telephone when others had scoffed. he has told of an early experience while in the boston exchange: one hot day an old lady toiled up the inevitable flights of stairs which led to the telephone-office of those times. out of breath, she sat down, and when she had recovered sufficiently to speak she said she wanted to talk to chicago. my colleagues of that time were all what the ethnologists would rank a little bit lower than the wild indian. these youngsters set up a great laugh; and, indeed, the absurdity of the old lady's project could hardly be overstated, because at that time salem was a long-distance line, lowell sometimes worked, and worcester was the limit--that is, in every sense of the word. the lowell line was so unreliable that we had a telegraph operator there, and when the talk was not possible, he pushed the message through by morse. it is no wonder that the absurdity of the old lady's proposal was the cause of poorly suppressed merriment. but i can remember that i explained to her that our wires had not yet been extended to chicago, and that, after she had departed, i turned to the other operators and said that the day would come when we could talk to chicago. my prophecy was received with what might be called--putting it mildly--vociferous discourtesy. nevertheless, i remember very well the impression which that old lady's request made upon me; and i really did believe that, some day or other, in some way, we would be able to talk to chicago. by 1912 it was possible to talk from new york to denver, a distance of 2,100 miles. no european engineers had achieved any such results, and this feat brought to carty and his wonderful staff the admiration of foreign experts. but for the american engineers this was only a starting-point. the next step was to link new york and california. this was more than a matter of setting poles and stringing wires, stupendous though this task was. the line crosses thirteen states, and is carried on 130,000 poles. three thousand tons of wire are used in the line. the panama canal took nine years to complete, and cost over three hundred million dollars; but within that time the telephone company spent twice that amount in engineering construction work alone, extending the scope of the telephone. the technical problems were even more difficult. carty and his engineers had to find a way to send something three thousand miles with the breath as its motive power. it was a problem of the conservation of the tiny electric current which carried the speech. the power could not be augmented or speech would not result at the destination. added to the efforts of these able engineers was the work of prof. michael i. pupin, of columbia university, whose brilliant invention of the loading coil some ten years before had startled the scientific world and had increased the range of telephonic transmission through underground cables and through overhead wires far beyond what had formerly been possible. professor pupin applied his masterful knowledge of physics and his profound mathematical attainments so successfully to the practical problems of the transmission of telephone speech that he has been called "the telephone scientist." it is impossible to talk over long-distance lines anywhere in america without speaking through pupin coils, which are distributed throughout the hundreds of thousands of miles of wire covering the north american continent. in the transcontinental telephone line pupin coils play a most important part, and they are distributed at eight-mile intervals throughout its entire length from the atlantic to the pacific. in speaking at a dinner of eminent scientists, mr. carty once said that on account of his distinguished scientific attainments and wonderful telephonic inventions, professor pupin would rank in history alongside of bell himself. we have seen how alexander graham bell, standing in the little room in boston, spoke through the crude telephone he had constructed the first words ever carried over a wire, and how these words were heard and understood by his associate, thomas watson. this was in 1876, and it was in january of 1915--less than forty years later--that these two men talked across the continent. the transcontinental line was complete. bell in the offices of the company in new york talked freely with watson in san francisco, and all in the most conversational tone, without a trace of the difficulty that had attended their first conversation over the short line. thus, within the span of a single life the telephone had been developed from a crude instrument which transmitted speech with difficulty over a wire a hundred feet long, until one could be heard perfectly, though over three thousand miles of wire intervened. the spoken word travels across the continent almost instantaneously, far faster than the speed of sound. if it were possible for one to be heard in san francisco as he shouted from new york through the air, four hours would be required before the sound would arrive. thus the telephone has been brought to a point of perfection where it carries sound by electricity and reproduces it again far more rapidly and efficiently than sound can be transmitted through its natural medium. xx telephoning through space the search for the wireless telephone--early successes--carty and his assistants seek the wireless telephone--the task before them--de forest's amplifier--experimental success achieved--the test--honolulu and paris hear arlington--the future. no sooner had marconi placed the wireless telegraph at the service of the world than men of science of all nations began the search for the wireless telephone. but the vibrations necessary to reproduce the sound of the human voice are so infinitely more complex than those which will suffice to carry signals representing the dots and dashes of the telegraph code that the problem long defied solution. scientists attacked the problem with vigor, and various means of wireless telephony were developed, without any being produced which were effective over sufficient ranges to make them really useful. probably the earliest medium chosen to carry wireless speech was light rays. a microphone transmitter was arranged so that the vibrations of the voice would affect the stream of gas flowing in a sensitive burner. the flame was thus thrown into vibrations corresponding to the vibrations of sound. the rays from this flame were then directed by mirrors to a distant receiving station and there concentrated on a photo-electric selenium cell, which has the strange property of varying its resistance according to the illumination. thus a telephone receiver arranged in series with it was made to reproduce the sounds. this strange, wireless telephone was so arranged that a search-light beam could be used for the light path, and distances up to three miles were covered. even with this limited range the search-light telephone had certain advantages. its message could be received only by those in the direct line of the light. neither did it require aerial masts or wires and a trained telegrapher who could send and receive the telegraph code. it was put to some use between battle-ships and smaller craft lying within a radius of a few miles. the sensitive selenium cell proved unreliable, however, and this means of communication was destined to failure. the experimenters realized that future success lay in making the ether carry telephonic currents as it carried telegraphic currents. they succeeded in establishing communication without wires, using the same antenna as in wireless telegraphy, and the principles determined are those used in the wireless telephone of to-day. the sending apparatus was so arranged that continuous oscillations are set up in the ether, either by a high-frequency machine or from an electric arc. where set up by spark discharges the spark frequency must be above twenty thousand per second. this unbroken wave train does not affect the telephone and is not audible in a telephone receiver inserted in the radio receiving circuit. but when a microphone transmitter is inserted in the sending circuit, instead of the make-and-break key used for telegraphy, the waves of the voice, thrown against the transmitter in speaking, break up the waves so that the telephone receiver in the receiving circuit will reproduce sound. here was and is the wireless telephone. marconi and many other scientists were able to operate it successfully over comparatively short distances, and were busily engaged in extending its range and improving the apparatus. one great difficulty involved was in increasing the power of the sending apparatus. greater range has been secured in wireless telegraphy by using stronger sending currents. but the delicate microphone would not carry these stronger currents. increased sensitiveness in the receiving apparatus was also necessary. not content with their accomplishments in increasing the scope of the wire telephone, the engineers of the bell organization, headed by john j. carty, turned their attention to the wireless transmission of speech. determined that the existing telephone system should be extended and supplemented in every useful way, they attacked the problem with vigor. it was a problem that had long baffled the keenest of european scientists, including marconi himself, but that did not deter carty and his associates. they were determined that the glory of spanning the atlantic by wireless telephone should come to america and american engineers. they wanted history to record the wireless telephone as an american achievement along with the telegraph and the telephone. the methods used in achieving the wireless telephone were widely different from those which brought forth the telegraph and the telephone. times had changed. men had found that it was more effective to work together through organizations than to struggle along as individuals. the very physical scope of the undertakings made the old methods impracticable. one cannot perfect a transcontinental telephone line nor a transatlantic wireless telephone in a garret. and with a powerful organization behind them it was not necessary for carty and his associates to starve and skimp through interminable years, handicapped by the inadequate equipment, while they slowly achieved results. this great organization, working with modern methods, produced the most wonderful results with startling rapidity. important work had already been done by marconi, fessenden, de forest, and others. but their results were still incomplete; they could not talk for any considerable distance. carty organized his staff with care, bancroft gerhardi, doctor jewett, h.d. arnold, and colpitts being prominent among the group of brilliant american scientists who joined with carty in his great undertaking. while much had been accomplished, much still remained to be done, and the various contributions had to be co-ordinated into a unified, workable whole. in large part it was carty's task to direct the work of this staff and to see that all moved smoothly and in the right direction. just as the telephone was more complex than the telegraph, and the wireless telegraph than the telephone, so the apparatus used in wireless telephony is even more complex and technical. working with the intricate mechanisms and delicate apparatus, one part after another was improved and adapted to the task at hand. to the devices of carty and his associates was added the extremely delicate detector that was needed. this was the invention of dr. lee de forest, an american inventor and a graduate of the sheffield technical school of yale university. de forest's contribution was a lamp instrument, a three-step audion amplifier. this is to the wireless telephone what the coherer is to the wireless telegraph. it is so delicate that the faintest currents coming through the ether will stimulate it and serve to set in motion local sources of electrical energy so that the waves received are magnified to a point where they will produce sound. by the spring of 1915, but a few months after the transcontinental telephone line had been put in operation, carty had his wireless telephone apparatus ready for extended tests. a small experimental tower was set up at montauk point, long island, and another was borrowed at wilmington, delaware. the tests were successful, and the experimenters found that they could talk freely with each other. soon they talked over a thousand miles, from the tower at montauk point to another at st. simon's island, georgia. this in itself was a great achievement, but the world was not told of it. "do it first and then talk about it" is the maxim with theodore vail and his telephone men. this was but a beginning, and carty had far more wonderful things in mind. it was on the 29th of september, 1915, that carty conducted the demonstrations which thrilled the world and showed that wireless telephony was an accomplished fact. sitting in his office in new york, president theodore vail spoke into his desk telephone of the familiar type. the wires carried his words to the towers of the navy wireless station at arlington, virginia, where they were delivered to the sending apparatus of the wireless telephone. leaping into space, they traveled in every direction through the ether. the antenna of the wireless station at mare island, california, caught part of the waves and they were amplified so that john carty, sitting with his ear to the receiver, could hear the voice of his chief. carty and his associates had not only developed a system which made it possible to talk across the continent without wires, but they had made it possible to combine wire and wireless telegraphy. he and vail talked with each other freely and easily, while the naval officers who verified the tests marveled. but even more wonderful things were to come. early in the morning of the next day other messages were sent from the arlington tower, and these messages were heard by lloyd espenschied, one of carty's engineers, who was stationed at the wireless station at pearl harbor, near honolulu, hawaii. the distance covered was nearly five thousand miles, and half of it was across land, which is the more remarkable as the wireless does not operate so readily over land as over water. the distance covered in this test was greater than the distance from washington to london, paris, berlin, vienna, or petrograd. the successful completion of this test meant that the capitals of the great nations of the world might communicate, might talk with one another, by wireless telephone. only a receiving set had been installed at hawaii, so that it was not possible for espenschied to reply to the message from arlington, and it was not until his message came by cable that those at arlington knew that the words they had spoken had traveled five thousand miles. other receiving sets had been located at san diego and at darien on the isthmus of panama, and at these points also the words were distinctly heard. by the latter part of october all was in readiness for a transatlantic test, and on the 20th of october american engineers, with american apparatus installed at the great french station at the eiffel tower, paris, heard the words spoken at arlington, virginia. carty and his engineers had bridged the atlantic for the spoken word. because of war-time conditions it was not possible to secure the use of the french station for an extended test, but the fact was established that once the apparatus is in place telephonic communication between europe and america may he carried on regularly. the apparatus used as developed by the engineers of the bell system was in a measure an outgrowth of their work with the long-distance telephone. wireless telephony, despite the wonders it has already accomplished, is still in its infancy. with more perfect apparatus and the knowledge that comes with experience we may expect that speech will girdle the earth. it is natural that one should wonder whether the wireless telephone is destined to displace our present apparatus. this does not seem at all probable. in the first place, wireless telephony is now, and probably always will be, very expensive. where the wire will do it is the more economical. there are many limitations to the use of the other for talking purposes, and it cannot be drawn upon too strongly by the man of science. it will accomplish miracles, but must not be overtaxed. millions of messages going in all directions, crossing and recrossing one another, as is done every day by wire, are probably an impossibility by wireless telephony. weird and little-understood conditions of the ether, static electricity, radio disturbances, make wireless work uncertain, and such a thing as twenty-four-hour service, seven days in the week, can probably never be guaranteed. in radio communication all must use a common medium, and as its use increases, so also do the difficulties. the privacy of the wire is also lacking with the wireless telephone. but because a way was found to couple the wireless telephone with the wire telephone, the new wonder has great possibilities as a supplement to our existing system. before so very long it may be possible for an american business man sitting in his office to call up and converse with a friend on a liner crossing the atlantic. the advantages of speaking between ship and ship as an improvement over wireless telegraphy in time of need are obvious. a demonstration of the part this great national telephone system would play in the country's defense in case of attack was held in may of 1916. the navy department at washington was placed in communication with every navy-yard and post in the united states, so that the executive officers could instantly talk with those in charge of the posts throughout the country. the wireless telephone was used in addition to the long distance, and secretary of the navy daniels, sitting at his desk at washington, talked with captain chandler, who was at his station on the bridge of the u.s.s. _new hampshire_ at hampton roads. whatever the future limitations of wireless telephony, there is no doubt as to the place it will take among the scientific accomplishments of the age. merely as a scientific discovery or invention, it ranks among the wonders of civilization. much as the tremendous leap of human voice across the line from new york to san francisco appealed to the mind, there is something infinitely more fascinating in this new triumph of the engineer. the human mind can grasp the idea of the spoken word being carried along wires, though that is difficult enough, but when we try to understand its flight through space we are faced with something beyond the comprehension of the layman and almost past belief. we have seen how communication has developed, very slowly at first, and then, as electricity was discovered, with great rapidity until man may converse with man at a distance of five thousand miles. what the future will bring forth we do not know. the ether may be made to accomplish even more wonderful things as a bearer of intelligence. though we cannot now see how it would be possible, the day may come when every automobile and aeroplane will be equipped with its wireless telephone, and the motorist and aviator, wherever they go, may talk with anyone anywhere. the transmission of power by wireless is confidently predicted. pictures have been transmitted by telegraph. it may be possible to transmit them by wireless. then some one may find out how to transmit moving pictures through the ether. then one might sit and see before him on a screen a representation of what was then happening thousands of miles away, and, listening through a telephone, hear all the sounds at the same place. wonders that we cannot even now imagine may lie before us. appendix a new developments of the telegraph _by f.w. lienan, superintendent tariff bureau, western union telegraph company_ the invention of samuel f.b. morse is unique in this, that the methods and instruments of telegraph operation as he evolved them from his first experimental apparatus were so simple, and yet so completely met the requirements, that they have continued in use to the present day in practically their original form. but this does not mean that there has not been the same constant striving for betterment in this as in every other art. many minds have, since the birth of the telegraph, occupied themselves with the problem of devising improved means of telegraphic transmission. the results have varied according to the point of view from which the subject was approached, but all, directly or indirectly, sought the same goal (the obvious one, since speed is the essence of telegraphy), to find the best means of sending more messages over the wire in a given time. it will readily suggest itself that the solution of this problem lies either in an arrangement enabling the wire to carry more than one message at once, or in some apparatus capable of transmitting messages over the wire more rapidly than can be done by hand, or in a combination of both these principles. duplex and quadruples operations are perhaps the most generally known methods by which increased utilization of the capacity of the line has been achieved. duplex operation permits of the sending of two messages over one wire in opposite directions at the same time; and quadruples, the simultaneous transmission of four messages, two going in each direction. truly a remarkable accomplishment; but, like many other things that have found their permanent place in daily use, become so familiar that we no longer pause to marvel at it. these expedients constitute a direct and very effective attack on the problem how to get more work out of the wire with the existing means of operation, and on account of their fundamental character and the important place which by reason thereof they have taken in the telegraphic art, are entitled to first mention. the problem of increasing the rapidity of transmission has been met by various automatic systems of telegraphy, so called because they embody the idea of mechanical transmission with resulting gain in speed and other advantages. the number of these which have from time to time been devised is considerable. not all have proven to be practicable, but those which have failed to prove in under actual operating conditions none the less display evidence of ingenuity which may well excite our admiration. to mention one or two which may be interesting on account of the oddity of their method--there was, for instance, an early device, similar in principle to the calling apparatus of the automatic telephone, which involved the turning of a movable disk so that a projection on its circumference pointed successively to the letters to be transmitted. experiments were made with ordinary metal type set up in a composing-stick, a series of brushes passing over the type faces and producing similar characters on a tape at the other end of the line. in another more recent ingenious device a pivoted mirror at the receiving end was so manipulated by the electrical impulses that a ray of light reflected from the surface of the mirror actually wrote the message upon sensitized paper, like a pencil, in a fair handwriting. in another the receiving apparatus printed vertical, horizontal, and slanting lines in such manner that they combined to make letters, rather angular, it is true, but legible. these and other kindred devices are interesting as efforts to accomplish the direct production of legible messages. in experimental tests they performed their function successfully, and in some cases with considerable speed, but some of them required more than one line wire, some were too sensitive to disturbance by inductive currents and some developed other weaknesses which have prevented their incorporation in the actual operating machinery of to-day. in the general development of the so-called automatic telegraph devices which have been or now are in practical operation, two lines have been pursued. one involves direct keyboard transmission; the other, the use at the sending end of a perforated tape capable of being run through a transmitting machine at high speed. one type of the former is the so-called step-by-step process, in which a revolving body in the transmitting apparatus, as, for instance, a cylinder provided with pegs placed at intervals around its circumference in spiral fashion, is arrested by the depression of the keys of the keyboard in such a way that a type wheel in the receiving apparatus at the distant end of the line prints the corresponding letter. this method was employed in the house and phelps printing telegraphs operated by the western union telegraph company in its earlier days, and is to-day used in the operation of the familiar ticker. in another type of direct keyboard operation the manipulation of the keys transmits the impulses directly to the line and the receiving apparatus translates them by electrically controlled mechanical devices into printed characters in message form. the systems best adapted to rapid telegraph work are predicated on the use of a perforated tape on which, by means of a suitable perforating apparatus, little round holes are produced in various groupings, each group, when the tape is passed through the transmitter, causing a certain combination of electrical impulses to pass over the wire. the transmitter as a rule consists of a mechanically or motor driven mechanism which causes the telegraph impulses to be transmitted to the line, and the combination and character of the impulses are determined by the tape perforations. the rapidity with which the tape may be driven through the transmitter makes very high speed operation possible. of course it is necessary that there should be at the other end of the wire apparatus capable of receiving and recording the signals as speedily as they are sent. as early as 1848 alexander bain perfected a system involving the use of the perforated transmitting tape; at the receiving station the messages were recorded in dots and dashes upon a chemically prepared strip of paper by means of iron pens, the metal of which was, through the combined action of the electrical current and the chemical preparation, decomposed, producing black marks in the form of dots and dashes upon the paper. the bain apparatus was in actual operation in the younger days of the telegraph. various systems, based on similar principles, involving tape transmission and the production of dots and dashes on a receiving tape, have from time to time been devised, but have generally not succeeded in establishing any permanent usefulness in competition with more effective instrumentalities which have been perfected. the hardiest survivor of them is the wheatstone apparatus, which has been in successful operation for years. originally the perforating--or, to use the commonly current term, the punching--of the wheatstone sending tape was accomplished by a mechanism equipped with three keys--one for the dot, one for the dash, and one for the space. the keys were struck with rubber-tipped mallets held in the hands of the operator and brought down with considerable force. later this rather primitive perforator was supplanted by one equipped with a full keyboard on the order of a typewriter keyboard. at the receiving end of the line the messages are produced on a tape in dots and dashes of the morse alphabet, and hence a further process of translation is necessary. this system has proven very useful, particularly in times of wire trouble and scarcity of facilities, when it is essential to move as many messages as possible over the available lines. the schemes devised for combining automatic transmission by the perforated-tape method with direct production of the message at its destination in ordinary letters and figures, eliminating the intervening step of translation from morse characters, have been many. their individual enumeration is beyond the scope of the present discussion, and would in any event involve a wearisome exposition of their distinguishing technical features. several of these systems are at present in practical and very effective operation. one of the forerunners of the printing telegraph systems now in use was the buckingham system, for many years employed by the western union telegraph company, but now for some time obsolete. the receiving mechanism of this system printed the messages on telegraph blanks placed upon a cylinder of just the right circumference to accommodate two telegraph blanks. the blanks were arranged in pairs, rolled into the form of a tube and placed around the cylinder. when two messages had been written a new pair of blanks had to be substituted. this was a rather awkward arrangement, but at a time when more highly developed apparatus had not been perfected it served its purpose to good advantage. the printing telegraphs of to-day produce their messages by the direct operation of typewriting machines or mechanisms operating substantially in the same manner as the ordinary typewriting machine. the methods by which the electrical impulses coming over the line are transformed into mechanical operation of the typewriter keys, or what corresponds to the typewriter keys, vary. it would be difficult to describe how this function is performed without entering upon much detail of a highly technical character. suffice it to say that means have been devised by which each combination of electrical impulses coming over the line wire causes a channel to be opened for the motor operation of the typewriting key-bar operating the corresponding letter upon the typewriter apparatus. these machines write the messages with proper arrangement of the date line, address, text, and signature, operating not only the type, but also the carriage shift and the line spacing as required. a further step in advance has been made by feeding the blanks into the receiving typewriter from a continuous roll, an attendant tearing the messages off as they are completed. the entire operation is automatic from beginning to end and capable of considerable speed. there remained the problem of devising some means by which a number of automatic units could be operated over the same line at the same time. this is not by any means a new proposition. here again various solutions have been offered by the scientists both of europe and of this country, and different systems designed to accomplish the desired object have been placed in operation. one of the most recent, and we believe the most efficient so far developed, is the so-called multiplex printer system, devised by the engineers of the western union telegraph company and now being extensively used by that company. perhaps the best picture of what is accomplished by this system can be given by an illustration. let us assume a single wire between new york and chicago. at the new york end there are connected with this wire four combined perforators and transmitters, and four receiving machines operating on the typewriter principle. at the chicago end the wire is connected with a like number of sending and receiving machines. all these machines are in simultaneous operation; that is to say, four messages are being sent from new york to chicago, and four messages are being sent from chicago to new york, all at the same time and over a single wire, and the entire process is automatic. the method by which eight messages can be sent over a single wire at the same time without interfering with one another cannot readily be described in simple terms. it may give some comprehension of the underlying principle to say that the heart of the mechanism is in two disks at each end of the line, which are divided into groups of segments insulated from each other, each group being connected to one of the sending or receiving machines, respectively. a rotating contact brush connected to the line wire passes over the disk, so that, as it comes into contact with each segment, the line wire is connected in turn with the channel leading to the corresponding operating unit. the brushes revolve in absolute unison of time and position. to use the same illustration as before, the brush on the chicago disk and the brush on the new york disk not only move at exactly the same speed, but at any given moment the two brushes are in exactly the same position with regard to the respective group of segments of both disks. if we now conceive of these brushes passing over the successive segments of the disks at a very great rate of speed, it may be understood that the effect is that the electrical impulses are distributed, each receiving machine receiving only those produced by the corresponding sending machine at the other end. in other words, each of the sets of receiving and sending apparatus really gets the use of the line for a fraction of the time during each revolution of the brushes of the distributer or disk mechanism. the multiplex automatic circuits are being extended all over the country and are proving extremely valuable in handling the constantly growing volume of telegraph traffic. what has thus been achieved in developing the technical side of telegraph operation must be attributed in part to that impulse toward improvement which is constantly at work everywhere and is the most potent factor in the progress of all industries, but in large measure it is the reflex of the growing--and recently very rapidly growing--demands which are made upon the telegraph service. emphasis is placed on the larger ratio of growth in this demand in recent years because it is peculiarly symptomatic of a noticeably wider realization of the advantages which the telegraph offers as an effective medium for business and social correspondence than has heretofore been in evidence. it means that we have graduated from that state of mind which saw in the telegraph something to be resorted to only under the stress of emergency, which caused many good people to associate a telegram with trouble and bad news and sudden calamity. there are still some dear old ladies who, on receipt of a telegram, make a rapid mental survey of the entire roster of their near and distant relatives and wonder whose death or illness the message may announce before they open the fateful envelope, only to find that up-to-date cousin mary, who has learned that the telegraph is as readily used as the mail and many times more rapid and efficient, wants to know whether they can come out for the week-end. when cousin mary of to-day wants to know, she wants to know right away--not only that she has her arrangements to make, but also because she just does not propose to wait a day or two to get a simple answer to a simple question. therein she embodies the spirit of the times. our ancestors were content to jog along for days in a stuffy stage-coach; we complain that the train which accomplishes the same distance in a few hours is too slow. we act more quickly; we think more quickly. we have to if we want to keep within earshot of the band. this speeding up makes itself quite obviously most apparent in our business processes. no body of business men need be told how much keener competition is becoming daily, how much narrower the margin by which success must be won. familiar phrases, these. but behind them lies a wealth of tragedy. how many have fallen by the way? it is estimated that something less than ten per cent. of those who engage in business on their own account succeed. how terrible the percentage of those who fail! the race has become too swift for them. driven by the lash of competition, business must perforce move faster and faster. time is becoming ever more precious. negotiations must be rapidly conducted, decisions arrived at quickly, transactions closed on the moment. what wonder that all this makes for a vastly increased use of the quickest method of communication? that is but one of the conditions which accounts for the growing use of the telegraph. another is to be found in the recognition of the convenience of the night letter and day letter. this has brought about a considerable increase in the volume of family and social correspondence by telegraph, which will grow to very much greater proportions as experience demonstrates its value. in business life the night letter and day letter have likewise established a distinct place for themselves. here also the present development of this traffic can be regarded as only rudimentary in comparison with the possibilities of its future development, indications of which are already apparent. it has been discovered that the telegram, on account of its peculiar attention-compelling quality, is an effective medium not only for the individual appeal, but for placing business propositions before a number of people at once, the night letters and day letters being particularly adapted to this purpose by reason of the greater scope of expression which they offer. again, business men are developing the habit of using the telegram in keeping in touch with their field forces and their salesmen and encouraging their activities, in cultivating closer contact with their customers, in placing their orders, in replenishing their stocks, and in any number of other ways calculated to further the profitable conduct of their enterprises. all this means that the telegraph is increasingly being utilized as a means of correspondence of every conceivable sort. it means also that with the growing appreciation of its adaptability to the every-day needs of social and business communication a very much larger public demand upon it must be anticipated, and it is to meet this demand with prompt and satisfactory service that the telegraph company has been bending its efforts to the perfection of a highly developed organization and of operating appliances of the most modern and efficient type. appendix b through the courtesy of j.j. carty, esq., chief engineer of the american telephone and telegraph company, there follows the clean-cut survey of the evolution of the telephone presented in his address before the franklin institute in philadelphia, may 17, 1916, when he received the gold medal of the institute. more than any other, the telephone art is a product of american institutions and reflects the genius of our people. the story of its wonderful development is a story of our own country. it is a story exclusively of american enterprise and american progress, for, although the most powerful governments of europe have devoted their energies to the development and operation of telephone systems, great contributions to the art have not been made by any of them. with very few exceptions, the best that is used in telephony everywhere in the world to-day has been contributed by workers here in america. it is of peculiar interest to recall the fact that the first words ever transmitted by the electric telephone were spoken in a building at boston, not far from where benjamin franklin first saw the light. the telephone, as well as franklin, was born at boston, and, like franklin, its first journey into the world brought it to philadelphia, where it was exhibited by its inventor, alexander graham bell, at the centennial exhibition in 1876, held here to commemorate the first hundred years of our existence as a free and independent nation. it was a fitting contribution to american progress, representing the highest product of american inventive genius, and a worthy continuance of the labors of franklin, one of the founders of the science of electricity as well as of the republic. nothing could appeal more to the genius of franklin than the telephone, for not only have his countrymen built upon it an electrical system of communication of transcendent magnitude and usefulness, but they have made it into a powerful agency for the advancement of civilization, eliminating barriers to speech, binding together our people into one nation, and now reaching out to the uttermost limits of the earth, with the grand aim of some day bringing together the people of all the nations of the earth into one common brotherhood. on the tenth day of march, 1876, the telephone art was born, when, over a wire extending between two rooms on the top floor of a building in boston, alexander graham bell spoke to his associate, thomas a. watson, saying: "mr. watson, please come here. i want you." these words, then heard by mr. watson in the instrument at his ear, constitute the first sentence ever received by the electric telephone. the instrument into which doctor bell spoke was a crude apparatus, and the current which it generated was so feeble that, although the line was about a hundred feet in length, the voice heard in the receiver was so faint as to be audible only to such a trained and sensitive ear as that of the young mr. watson, and then only when all surrounding noises were excluded. following the instructions given by doctor bell, mr. watson with his own hands had constructed the first telephone instruments and ran the first telephone wire. at that time all the knowledge of the telephone art was possessed exclusively by those two men. there was no experience to guide and no tradition to follow. the founders of the telephone, with remarkable foresight, recognized that success depended upon the highest scientific knowledge and technical skill, and at once organized an experimental and research department. they also sought the aid of university professors eminent for their scientific attainments, although at that time there was no university giving the degree of electrical engineer or teaching electrical engineering. from this small beginning there has been developed the present engineering, experimental and research department which is under my charge. from only two men in 1876 this staff has, in 1915, grown to more than six hundred engineers and scientists, including former professors, post-graduate students, and scientific investigators, graduates of nearly a hundred american colleges and universities, thus emphasizing in a special way the american character of the art. the above number includes only those devoted to experimental and research work and engineering development and standardization, and does not include the very much larger body of engineers engaged in manufacturing and in practical field work throughout the united states. not even the largest and most powerful government telephone and telegraph administration of europe has a staff to be compared with this. it is in our great universities that anything like it is to be found, but even here we find that it exceeds in number the entire teaching staff of even our largest technical institutions. a good idea may spring up in the mind of man anywhere, but as applied to such a complex entity as a telephone system, the countless parts of which cover a continent, no individual unaided can bring the idea to a successful conclusion. a comprehensive and effective engineering and scientific and development organization such as this is necessary, and years of expensive work are required before the idea can be rendered useful to the public. but, vital as they are to its success, the, telephone art requires more than engineers and scientists. so we find that in the building and operation and maintenance of that vast continental telephone system which bears the name of bell, in honor of the great inventor, there are at work each day more than 170,000 employees, of which nearly 20,000 are engaged in the manufacture of telephones, switchboards, cables, and all of the thousands and tens of thousands of parts required for the operation of the telephone system of america. the remaining 150,000 are distributed throughout all of the states of the union. about 80,000 of these are women, largely telephone operators; 50,000 are linemen, installers, cable splicers, and the like, engaged in the building and maintaining of the continental plant. there are thousands of other employees in the accounting, legal, commercial and other departments. there are 2,100 engineers located in different parts of the country. the majority of these engineers have received technical training in american technical schools, colleges, and universities. this number does not include by any means all of those in the other departments who have received technical or college training. in view of the technical and scientific nature of the telephone art, an unusually high-grade personnel is required in all departments, and the amount of unskilled labor employed is relatively very small. no other art calls forth in a higher degree those qualities of initiative, judgment, skill, enterprise, and high character which have in all times distinguished the great achievements of america. in 1876 the telephone plant of the whole world could be carried away in the arms of one man. it consisted of two crude telephones like the one now before you, connected together by a wire of about one hundred feet in length. a piece cut from this wire by mr. watson himself is here in this little glass case. at this time there was no practical telephone transmitter, no hard-drawn copper wire, no transposed and balanced metallic circuits, no multiple telephone switchboard, or telephone switchboard of any kind, no telephone cable that would work satisfactorily; in fact, there were none of the multitude of parts which now constitute the telephone system. the first practical telephone line was a copy of the best telegraph line of the day. a line wire was strung on the poles and housetops, using the ground for the return circuit. electrical disturbances, coming from no one knows where, were picked up by this line. frequently the disturbances were so loud in the telephone as to destroy conversation. when a second telephone line was strung alongside the first, even though perfectly insulated, another surprise awaited the telephone pioneers. conversation carried on over one of these wires could plainly be heard on the other. another strange thing was discovered. iron wire was not so good a conductor for the telephone current as it was for the telegraph current. the talking distance, therefore, was limited by the imperfect carrying power of the conductor and by the confusing effect of all sorts of disturbing currents from the atmosphere and from neighboring telephone and telegraph wires. these and a multitude of other difficulties, constituting problems of the most intricate nature, impeded the progress of the telephone art, but american engineers, by persistent study, incessant experimentation, and the expenditure of immense sums of money, have overcome these difficulties. they have created a new art, inventing, developing, and perfecting, making improvements great and small in telephone, transmitter, line, cable, switchboard, and every other piece of apparatus and plant required for the transmission of speech. as the result of nearly forty years of this unceasing, organized effort, on the 25th of january, 1915, there was dedicated to the service of the american public a transcontinental telephone line, 3,600 miles long, joining the atlantic and the pacific, and carrying the human voice instantly and distinctly between san francisco and new york and philadelphia and boston. on that day over this line doctor bell again talked to mr. watson, who was now 3,400 miles away. it was a day of romantic triumph for these two men and for their associates and their thousands of successors who have built up the great american telephone art. the 11th of february following was another day of triumph for the telephone art as a product of american institutions, for, in the presence of dignitaries of the city and state here at philadelphia and at san francisco, the sound of the liberty bell, which had not been heard since it tolled for the death of chief-justice marshall, was transmitted by telephone over the transcontinental line to san francisco, where it was plainly heard by all those there assembled. immediately after this the stirring tones of the "star-spangled banner" played on the bugle at san francisco were sent like lightning back across the continent to salute the old bell in philadelphia. it had often been pointed out that the words of the tenth verse of the twenty-fifth chapter of leviticus, added when the bell was recast in 1753, were peculiarly applicable to the part played by the old bell in 1776. but the words were still more prophetic. the old bell had been silent for nearly eighty years, and it was thought forever, but by the use of the telephone a gentle tap, which could be heard through the air only a few feet away, was enough to transmit the tones of the historic relic all the way across the continent from the atlantic to the pacific. thus, by the aid of the telephone art, the liberty bell was enabled literally to fulfil its destiny and "proclaim liberty throughout all the land, unto all the inhabitants thereof." the two telephone instruments of 1876 had become many millions by 1916, and the first telephone line, a hundred feet long, had grown to one of more than three thousand miles in length. this line is but part of the american telephone system of twenty-one million miles of wire, connecting more than nine million telephone stations located everywhere throughout the united states, and giving telephone service to one hundred million people. universal telephone service throughout the length and breadth of our land, that grand objective of theodore n. vail, has been attained. while alexander graham bell was the first to transmit the tones of the human voice over a wire by electricity, he was also the first to transmit the tones of the human voice by the wireless telephone, for in 1880 he spoke along a beam of light to a point a considerable distance away. while the method then used is different from that now in vogue, the medium employed for the transmission is the same--the ether, that mysterious, invisible, imponderable wave-conductor which permeates all creation. while many great advances in the wireless art were made by marconi and many other scientists in america and elsewhere, it remained for that distinguished group of american scientists and engineers working under my charge to be the first to transmit the tones of the human voice in the form of intelligible speech across the atlantic ocean. this great event and those immediately preceding it are so fresh in the public mind that i will make but a brief reference to them here. on april 4, 1915, we were successful in transmitting speech without the use of wires from our radio station at montauk point on long island to wilmington, delaware. on may 18th we talked by radio telephone from our station on long island to st. simon island in the atlantic ocean, off the coast of georgia. on the 27th of august, with our apparatus installed by permission of the navy department at the arlington, virginia, radio station, speech was successfully transmitted from that station to the navy wireless station equipped with our receiving apparatus at the isthmus of panama. on september 29th, speech was successfully transmitted by wire from new york city to the radio station at arlington, virginia, and thence by wireless telephone across the continent to the radio station at mare island navy-yard, california, where i heard and understood the words of mr. theodore n. vail speaking to me from the telephone on his desk at new york. on the next morning at about one o'clock, washington time, we established wireless telephone communication between arlington, virginia, and pearl harbor in the hawaiian islands, where an engineer of our staff, together with united states naval officers, distinctly heard words spoken into the telephone at arlington, virginia. on october 22d, from the arlington tower in virginia, we successfully transmitted speech across the atlantic ocean to the eiffel tower at paris, where two of our engineers, in company with french military officers, heard and understood the words spoken at arlington. on the same day when speech was being transmitted by the apparatus at arlington to our engineers and to the french military officers at the eiffel tower in paris, our telephone engineer at pearl harbor, hawaii, together with an officer of the united states navy, heard the words spoken from arlington to paris and recognized the voice of the speaker. as a result of exhaustive researches, too extensive to describe here, it has been ascertained that the function of the wireless telephone is not to do away with the use of wires, but rather to be employed in situations where wires are not available or practicable, such as between ship and ship, and ship and shore, and across large bodies of water. the ether is a universal conductor for wireless telephone and telegraph impulses and must be used in common by all who wish to employ those agencies of communication. in the case of the wireless telegraph the number of messages which may be sent simultaneously is much restricted. in the case of the wireless telephone, owing to the thousands of separate wave-lengths required for the transmission of speech, the number of telephone conversations which may be carried on at the same time is still further restricted and is so small that all who can employ wires will find it necessary to do so, leaving the ether available for those who have no other means of communication. this quality of the ether which thus restricts its use is really a characteristic of the greatest value to mankind, for it forms a universal party line, so to speak, connecting together all creation, so that anybody anywhere, who connects with it in the proper manner, may be heard by every one else so connected. thus, a sinking ship or a human being anywhere can send forth a cry for help which may be heard and answered. no one can tell how far away are the limits of the telephone art, i am certain that they are not to be found here upon the earth, for i firmly believe in the fulfilment of that prophetic aspiration expressed by theodore n. vail at a great gathering in washington, that some day we will build up a world telephone system, making necessary to all peoples the use of a common language or a common understanding of languages which will join all of the people of the earth into one brotherhood. i believe that the time will come when the historic bell which now rests in independence hall will again be sounded, and that by means of the telephone art, which to-day has received such distinguished recognition at your hands, it will proclaim liberty once more, but this time throughout the whole world unto all the inhabitants thereof. and, when this world is ready for the message, i believe the telephone art will provide the means for transmitting to all mankind a great voice saying, "peace on earth, good will toward men." index a ampere's telegraph, 42. anglo-american telegraph co., 134. ardois signal system, 30. atlantic cable projected, 109; attempted, 117, 121, 123, 133; completed, 124, 136. audion amplifier, 256. automatic telegraphy, 53, 105, 266. b baltimore-washington telegraph line, 86. bell, alexander graham, parentage, 140; youth, 141; teaches elocution, 146; experiments with speech, 151, 161; meets henry, 158; invents telephone, 162; at centennial exposition, 165; demonstrates telephone, 170; bell telephone association, 178; bell-western union settlement; bell and wireless telegraphy, 189; transcontinental telephone, 248. bethell, union n., 241. blake, clarence j., 154. blake, francis, invents telephone transmitter, 182. branly coherer, 204. brett, j.w., 112. bright, charles tiltson, 112, 120, 125, 128. c cable laid across channel, 108. carty, j.j., youth, 232; enters telephone field, 234; carty and the switchboard, 235, 242; uses metallic circuit, 238; in new york city, 241; invents bridging bell, 243; chief engineer, 244; extends long-distance telephone, 246; seeks wireless telephone, 253; talks across continent by wireless, 257. clepsydra, 18. code flags at sea, 24. coherer, 203. colomb's flashing lights, 25. congress votes funds for telegraph, 84. cooke, william p., 49, 52. cornell, ezra, 86, 93, 107. d davy's needle telegraph, 44. de forest, dr. lee, 225, 256. dolbear and telephone, 185; wireless telegraphy, 194. drawbaugh case, 186. duplex telegraphy, 104, 265. dyar, harrison gray, 41. e edison, and the telegraph, 104; telephone transmitter 180; wireless telegraphy, 195. ellsworth, annie, 85. f field, cyrus w., plans transatlantic cable, 110; honors, 125, 136; develops cable, 130, 134. g gale, professor, 67, 86. gauss and weber's telegraph, 43. gisborne, f.n., 109. gray, elisha, 157, 184. _great eastern_, 132, 135, 139. guns as marine signals, 23. h hammond, john hays, 229. heaviside, a.w., 196. heliograph, 29. henry, joseph, 65, 67, 158, 169. hertz and the hertzian waves, 197. hubbard, gardiner g., 149, 159, 170, 178. hubbard, mabel, 148, 166. i indian smoke signals, 20. j jackson, dr. charles t., 64, 79. k kelvin, lord (see thomson), 138. "kwaker" captured, 50. l long-distance telephone, 245. m magnetic telegraph co., 93. marconi, boyhood, 199; accomplished wireless telegraphy, 202; demonstration in england, 209; transatlantic telegraphy, 217; marconi telegraph company, 220. marine signals on argonautic expedition, 15. mirror galvanometer, 127. mirrors of pharaoh, 17. morse at university of new york, 66. morse, code in signals, 27; parentage, 56; at yale, 57; art student, 59; artist, 62; conceives the telegraph, 63; exhibits telegraph, 75; offers telegraph to congress, 76, 91; patents telegraph, 82; submarine cable, 83, 107; erects first line, 86; dies, 104. multiplex printer telegraph, 274. mundy, arthur j., 31. o o'reilly, henry, 94. p preece, w.h., 196, 209. printing telegraph, 271. pupin, michael i., 247. q quadruplex telegraphy, 104, 265. r reis's musical telegraph, 157. s sanders, thomas, 148, 159, 178. scribner, charles e., 236. searchlight telephone, 251. semaphore signals, 27. shouting sentinels, 16. sibley, hiram, 96, 99. signal columns, 19. siphon recorder, 137. smith, francis o.j., 76. stentorophonic tube, 18. submarine signals, 31. t telegraph, first suggestion, 39; patented, 82; development, 264. telephone invented and patented, 162; at centennial, 165; exchange, 177. thomson, youth, 144; cable adviser, 121; invents mirror galvanometer, 126; knighted, 136; invents siphon recorder, 137; connection with telephone, 169. transatlantic cable (see atlantic cable). transatlantic wireless telegraphy, 216. transatlantic wireless telephone, 259. transcontinental telegraph, 96. transcontinental telephone, 246. transcontinental wireless telephone, 257. trowbridge, john, 190. troy, signaling fall of, 14. tuning the wireless telegraph, 222. v vail, alfred, arranges morse code, joins morse, 70; makes telephone apparatus, 72; operates first line, 90; improves telegraph, 100. vail, theodore, joins telephone forces, 180; puts wires underground, 239; adopts copper circuits, 240; resumes telephone leadership, 244; talks across continent without wires, 257. w watson, aids bell with telephone, 159; telephone partner, 175; helps demonstrate telephone, 175; telephones across continent, 248. western union, organized, 96; enters telephone field, 178. wheatstone, 1; boyhood, 45; five-needle telegraph, 49; single-needle telegraph, 52; wheatstone-cooke controversy, 52; automatic transmitter, 53; bridge, 53; opposes morse, 78; encourages bell, 145. wig-wag system, 26. wireless telegraphy suggested, 188; invented, 202; on shipboard, 221; in the future, 230. wireless telephone, conceived, 250; future, 260; in navy, 261. [transcriber's note: the illustrations have been included with another version of this work. the image files have been named in a straightforward manner that corresponds to the numbering in the text; thus, illustration 7 is included as file "fig007.png", while illustration (a) 22 is included as file "fig022a.png".] the radio amateur's hand book [illustration: a. frederick collins, inventor of the wireless telephone, 1899. awarded gold medal for same, alaska yukon pacific exposition, 1909.] the radio amateur's hand book a complete, authentic and informative work on wireless telegraphy and telephony by a. frederick collins inventor of the wireless telephone 1899; historian of wireless 1901-1910; author of "wireless telegraphy" 1905 to william marconi inventor of the wireless telegraph introduction before delving into the mysteries of receiving and sending messages without wires, a word as to the history of the art and its present day applications may be of service. while popular interest in the subject has gone forward by leaps and bounds within the last two or three years, it has been a matter of scientific experiment for more than a quarter of a century. the wireless telegraph was invented by william marconi, at bologna, italy, in 1896, and in his first experiments he sent dot and dash signals to a distance of 200 or 300 feet. the wireless telephone was invented by the author of this book at narberth, penn., in 1899, and in his first experiments the human voice was transmitted to a distance of three blocks. the first vital experiments that led up to the invention of the wireless telegraph were made by heinrich hertz, of germany, in 1888 when he showed that the spark of an induction coil set up electric oscillations in an open circuit, and that the energy of these waves was, in turn, sent out in the form of electric waves. he also showed how they could be received at a distance by means of a ring detector, which he called a _resonator_ in 1890, edward branly, of france, showed that metal filings in a tube cohered when electric waves acted on them, and this device he termed a _radio conductor_; this was improved upon by sir oliver lodge, who called it a coherer. in 1895, alexander popoff, of russia, constructed a receiving set for the study of atmospheric electricity, and this arrangement was the earliest on record of the use of a detector connected with an aerial and the earth. marconi was the first to connect an aerial to one side of a spark gap and a ground to the other side of it. he used an induction coil to energize the spark gap, and a telegraph key in the primary circuit to break up the current into signals. adding a morse register, which printed the dot and dash messages on a tape, to the popoff receptor he produced the first system for sending and receiving wireless telegraph messages. [illustration: collins' wireless telephone exhibited at the madison square garden, october 1908.] after marconi had shown the world how to telegraph without connecting wires it would seem, on first thought, to be an easy matter to telephone without wires, but not so, for the electric spark sets up damped and periodic oscillations and these cannot be used for transmitting speech. instead, the oscillations must be of constant amplitude and continuous. that a direct current arc light transforms a part of its energy into electric oscillations was shown by firth and rogers, of england, in 1893. the author was the first to connect an arc lamp with an aerial and a ground, and to use a microphone transmitter to modulate the sustained oscillations so set up. the receiving apparatus consisted of a variable contact, known as a _pill-box_ detector, which sir oliver lodge had devised, and to this was connected an ericsson telephone receiver, then the most sensitive made. a later improvement for setting up sustained oscillations was the author's _rotating oscillation arc_. since those memorable days of more than two decades ago, wonderful advances have been made in both of these methods of transmitting intelligence, and the end is as yet nowhere in sight. twelve or fifteen years ago the boys began to get fun out of listening-in to what the ship and shore stations were sending and, further, they began to do a little sending on their own account. these youngsters, who caused the professional operators many a pang, were the first wireless amateurs, and among them experts were developed who are foremost in the practice of the art today. away back there, the spark coil and the arc lamp were the only known means for setting up oscillations at the sending end, while the electrolytic and crystal detectors were the only available means for the amateur to receive them. as it was next to impossible for a boy to get a current having a high enough voltage for operating an oscillation arc lamp, wireless telephony was out of the question for him, so he had to stick to the spark coil transmitter which needed only a battery current to energize it, and this, of course, limited him to sending morse signals. as the electrolytic detector was cumbersome and required a liquid, the crystal detector which came into being shortly after was just as sensitive and soon displaced the former, even as this had displaced the coherer. a few years ahead of these amateurs, that is to say in 1905, j. a. fleming, of england, invented the vacuum tube detector, but ten more years elapsed before it was perfected to a point where it could compete with the crystal detector. then its use became general and workers everywhere sought to, and did improve it. further, they found that the vacuum tube would not only act as a detector, but that if energized by a direct current of high voltage it would set up sustained oscillations like the arc lamp, and the value of sustained oscillations for wireless telegraphy as well as wireless telephony had already been discovered. the fact that the vacuum tube oscillator requires no adjustment of its elements, that its initial cost is much less than the oscillation arc, besides other considerations, is the reason that it popularized wireless telephony; and because continuous waves have many advantages over periodic oscillations is the reason the vacuum tube oscillator is replacing the spark coil as a wireless telegraph transmitter. moreover, by using a number of large tubes in parallel, powerful oscillations can be set up and, hence, the waves sent out are radiated to enormous distances. while oscillator tubes were being experimented with in the research laboratories of the general electric, the westinghouse, the radio corporation of america, and other big companies, all the youthful amateurs in the country had learned that by using a vacuum tube as a detector they could easily get messages 500 miles away. the use of these tubes as amplifiers also made it possible to employ a loud speaker, so that a room, a hall, or an out-of-door audience could hear clearly and distinctly everything that was being sent out. the boy amateur had only to let father or mother listen-in, and they were duly impressed when he told them they were getting it from kdka (the pittsburgh station of the westinghouse co.), for was not pittsburgh 500 miles away! and so they, too, became enthusiastic wireless amateurs. this new interest of the grown-ups was at once met not only by the manufacturers of apparatus with complete receiving and sending sets, but also by the big companies which began broadcasting regular programs consisting of music and talks on all sorts of interesting subjects. this is the wireless, or radio, as the average amateur knows it today. but it is by no means the limit of its possibilities. on the contrary, we are just beginning to realize what it may mean to the human race. the government is now utilizing it to send out weather, crop and market reports. foreign trade conditions are being reported. the naval observatory at arlington is wirelessing time signals. department stores are beginning to issue programs and advertise by radio! cities are also taking up such programs, and they will doubtless be included soon among the regular privileges of the tax-payers. politicians address their constituents. preachers reach the stay-at-homes. great singers thrill thousands instead of hundreds. soon it will be possible to hear the finest musical programs, entertainers, and orators, without budging from one's easy chair. in the world war wireless proved of inestimable value. airplanes, instead of flying aimlessly, kept in constant touch with headquarters. bodies of troops moved alertly and intelligently. ships at sea talked freely, over hundreds of miles. scouts reported. everywhere its invisible aid was invoked. in time of peace, however, it has proved and will prove the greatest servant of mankind. wireless messages now go daily from continent to continent, and soon will go around the world with the same facility. ships in distress at sea can summon aid. vessels everywhere get the day's news, even to baseball scores. daily new tasks are being assigned this tireless, wireless messenger. messages have been sent and received by moving trains, the lackawanna and the rock island railroads being pioneers in this field. messages have also been received by automobiles, and one inventor has successfully demonstrated a motor car controlled entirely by wireless. this method of communication is being employed more and more by newspapers. it is also of great service in reporting forest fires. colleges are beginning to take up the subject, some of the first being tufts college, hunter college, princeton, yale, harvard, and columbia, which have regularly organized departments for students in wireless. instead of the unwieldy and formidable looking apparatus of a short time ago, experimenters are now vying with each other in making small or novel equipment. portable sets of all sorts are being fashioned, from one which will go into an ordinary suitcase, to one so small it will easily slip into a brownie camera. one receiver depicted in a newspaper was one inch square! another was a ring for the finger, with a setting one inch by five-eighths of an inch, and an umbrella as a "ground." walking sets with receivers fastened to one's belt are also common. daily new novelties and marvels are announced. meanwhile, the radio amateur to whom this book is addressed may have his share in the joys of wireless. to get all of these good things out of the ether one does not need a rod or a gun--only a copper wire made fast at either end and a receiving set of some kind. if you are a sheer beginner, then you must be very careful in buying your apparatus, for since the great wave of popularity has washed wireless into the hearts of the people, numerous companies have sprung up and some of these are selling the veriest kinds of junk. and how, you may ask, are you going to be able to know the good from the indifferent and bad sets? by buying a make of a firm with an established reputation. i have given a few offhand at the end of this book. obviously there are many others of merit--so many, indeed, that it would be quite impossible to get them all in such a list, but these will serve as a guide until you can choose intelligently for yourself. a. f. c. contents chapter i. how to begin wireless kinds of wireless systems--parts of a wireless system--the easiest way to start--about aerial wire systems--about the receiving apparatus--about transmitting stations--kinds of transmitters--the spark gap wireless telegraph transmitter--the vacuum table telegraph transmitter--the wireless telephone transmitter. ii. putting up your aerial kinds of aerial wire systems--how to put up a cheap receiving aerial--a two-wire aerial--connecting in the ground--how to put up a good aerial--an inexpensive good aerial--the best aerial that can be made--assembling the aerial--making a good ground. iii. simple telegraph and telephone receiving sets assembled wireless receiving sets--assembling your own receiving set--the crystal detector--the tuning coil--the loose coupled tuning coil--fixed and variable condensers--about telephone receivers-connecting up the parts--receiving set no. 2--adjusting the no. 1 set--the tuning coil--adjusting the no. 2 set. iv. simple telegraph sending sets a cheap transmitting set (no. 1)--the spark coil--the battery--the telegraph key--the spark gap--the tuning coil--the high-tension condenser--a better transmitting set (no. 2)--the alternating current transformer--the wireless key--the spark gap--the high-tension condenser--the oscillation transformer--connecting up the apparatus--for direct current--how to adjust your transmitter. tuning with a hot wire ammeter--to send out a 200-meter wave length--the use of the aerial switch--aerial switch for a complete sending and receiving set--connecting in the lightning switch. v. electricity simply explained electricity at rest and in motion--the electric current and its circuit--current and the ampere--resistance and the ohm--what ohm's law is--what the watt and kilowatt are--electromagnetic induction--mutual induction--high-frequency currents--constants of an oscillation circuit--what capacitance is--what inductance is--what resistance is--the effect of capacitance. vi. how the transmitting and receiving sets work how transmitting set no. 1 works--the battery and spark coil circuit--changing the primary spark coil current into secondary currents--what ratio of transformation means--the secondary spark coil circuit--the closed oscillation circuit--how transmitting set no. 2 works--with alternating current--with direct current--the rotary spark gap--the quenched spark gap--the oscillation transformer--how receiving set no. 1 works--how receiving set no. 2 works. vii. mechanical and electrical tuning damped and sustained mechanical vibrations--damped and sustained oscillations--about mechanical tuning--about electric tuning. viii. a simple vacuum tube detector receiving set assembled vacuum tube receiving set--a simple vacuum tube receiving set--the vacuum tube detector--three electrode vacuum tube detector--the dry cell and storage batteries--the filament rheostat--assembling the parts--connecting up the parts--adjusting the vacuum tube detector receiving set. ix. vacuum tube amplifier receiving sets a grid leak amplifier receiving set. with crystal detector--the fixed resistance unit, or grid leak--assembling the parts for a crystal detector set--connecting up the parts for a crystal detector--a grid leak amplifying receiving set with vacuum tube detector--a radio frequency transformer amplifying receiving set--an audio frequency transformer amplifying receiving set--a six step amplifier receiving set with a loop aerial--how to prevent howling. x. regenerative amplification receiving sets the simplest type of regenerative receiving set--with loose coupled tuning coil--connecting up the parts--an efficient regenerative receiving set. with three coil loose coupler--the a battery potentiometer--the parts and how to connect them up--a regenerative audio frequency amplifier--the parts and how to connect them up. xi. short wave regenerative receiving sets a short wave regenerative receiver, with one variometer and three variable condensers--the variocoupler--the variometer--connecting up the parts--short wave regenerative receiver with two variometers and two variable condensers--the parts and how to connect them up. xii. intermediate and long wave regenerative receiving sets intermediate wave receiving sets--intermediate wave set with loading coils--the parts and how to connect them up--an intermediate wave set with variocoupler inductance coils--the parts and how to connect them up--a long wave receiving set--the parts and how to connect them up. xiii. heterodyne or beat long wave telegraph receiving set what the heterodyne or beat method is--the autodyne or self-heterodyne long wave receiving set--the parts and connections of an autodyne or self-heterodyne, receiving set--the separate heterodyne long wave receiving set--the parts and connections of a separate heterodyne long wave receiving set. xiv. headphones and loud speakers wireless headphones--how a bell telephone receiver is made--how a wireless headphone is made--about resistance, turns of wire and sensitivity of headphones--the impedance of headphones--how the headphones work--about loud speakers--the simplest type of loud speaker--another simple kind of loud speaker--a third kind of simple loud speaker--a super loud speaker. xv. operation of vacuum tube receptors what is meant by ionization--how electrons are separated from atoms--action of the two electrode vacuum tube--how the two electrode tube acts as a detector--how the three electrode tube acts as a detector--how the vacuum tube acts as an amplifier--the operation of a simple vacuum tube receiving set--operation of a regenerative vacuum tube receiving set--operation of autodyne and heterodyne receiving sets--the autodyne, or self-heterodyne receiving set--the separate heterodyne receiving set. xvi. continuous wave telegraph transmitting sets with direct current sources of current for telegraph transmitting sets--an experimental continuous wave telegraph transmitter--the apparatus you need--the tuning coil--the condensers--the aerial ammeter--the buzzer and dry cell--the telegraph key--the vacuum tube oscillator--the storage battery--the battery rheostat--the oscillation choke coil--transmitter connectors--the panel cutout--connecting up the transmitting apparatus--a 100-mile c. w. telegraph transmitter--the apparatus you need--the tuning coil--the aerial condenser--the aerial ammeter--the grid and blocking condensers--the key circuit apparatus--the 5 watt oscillator vacuum tube--the storage battery and rheostat--the filament voltmeter--the oscillation choke coil--the motor-generator set--the panel cut-out--the protective condenser--connecting up the transmitting apparatus--a 200-mile c. w. telegraph transmitter--a 500-mile c. w. telegraph transmitter--the apparatus and connections-the 50-watt vacuum tube oscillator--the aerial ammeter--the grid leak resistance--the oscillation choke coil--the filament rheostat--the filament storage battery--the protective condenser--the motor-generator--a 1000-mile c. w. telegraph transmitter. xvii. continuous wave telegraph transmitting sets with alternating current a 100-mile c. w. telegraph transmitting set--the apparatus required--the choke coils--the milli-ammeter--the a. c. power transformer--connecting up the apparatus--a 200to 500-mile c. w. telegraph transmitting set-a 500to 1000-mile c. w. telegraph transmitting set--the apparatus required--the alternating current power transformer-connecting up the apparatus. xviii. wireless telephone transmitting sets with direct and alternating currents a short distance wireless telephone transmitting set--with 110-volt direct lighting current--the apparatus you need--the microphone transmitter--connecting up the apparatus--a 25to 50-mile wireless telephone transmitter--with direct current motor generator--the apparatus you need--the telephone induction coil--the microphone transformer--the magnetic modulator--how the apparatus is connected up--a 50to 100-mile wireless telephone transmitter--with direct current motor generator--the oscillation choke coil--the plate and grid circuit reactance coils--connecting up the apparatus--a 100to 200-mile wireless telephone transmitter--with direct current motor generator--a 50to 100-mile wireless telephone transmitting set--with 100-volt alternating current--the apparatus you need--the vacuum tube rectifier--the filter condensers--the filter reactance coil-connecting up the apparatus--a 100to 200-mile wireless telephone transmitting set--with 110-volt alternating current--apparatus required. xix. the operation of vacuum tube transmitters the operation of the vacuum tube oscillator--the operation of c. w. telegraph transmitters with direct current--short distance c. w. transmitter--the operation of the key circuit--the operation of c. w. telegraph transmitting with direct current--the operation of c. w. telegraph transmitters with alternating current--with a single oscillator tube--heating the filament with alternating current--the operation of c. w. telegraph transmitters with alternating current-with two oscillator tubes--the operation of wireless telephone transmitters with direct current--short distance transmitter--the microphone transmitter--the operation of wireless telephone transmitters with direct current--long distance transmitters--the operation of microphone modulators--the induction coil--the microphone transformer--the magnetic modulator--operation of the vacuum tube as a modulator--the operation of wireless telephone transmitters with alternating current--the operation of rectifier vacuum tubes--the operation of reactors and condensers. xx. how to make a receiving set for $5.00 or less. the crystal detector--the tuning coil--the headphone--how to mount the parts--the condenser--how to connect up the receptor. appendix useful information--glossary--wireless don'ts. list of figures fig. 1.--simple receiving set fig. 2.--simple transmitting set (a) fig. 3.--flat top, or horizontal aerial (b) fig. 3.--inclined aerial (a) fig. 4.--inverted l aerial (b) fig. 4--t aerial fig. 5.--material for a simple aerial wire system (a) fig. 6.--single wire aerial for receiving (b) fig. 6.--receiving aerial with spark gap lightning arrester (c) fig. 6.--aerial with lightning switch fig. 7.--two-wire aerial (a) fig. 8.--part of a good aerial (b) fig. 8.--the spreaders (a) fig. 9.--the middle spreader (b) fig. 9.--one end of aerial complete (c) fig. 9.--the leading in spreader (a) fig. 10.--cross section of crystal detector (b) fig. 10.--the crystal detector complete (a) fig. 11.--schematic diagram of a double slide tuning coil (b) fig. 11.--double slide tuning coil complete (a) fig. 12.--schematic diagram of a loose coupler (b) fig. 12.--loose coupler complete (a) fig. 13.--how a fixed receiving condenser is built up (b) fig. 13.--the fixed condenser complete (c) and (d) fig. 13.--variable rotary condenser fig. 14.--pair of wireless headphones (a) fig. 15.--top view of apparatus layout for receiving set no. 1 (b) fig. 15.--wiring diagram for receiving set no. 1 (a) fig. 16.--top view of apparatus layout for receiving set no. 2 (b) fig. 16.--wiring diagram for receiving set no. 2 fig. 17.--adjusting the receiving set (a) and (b) fig. 18.--types of spark coils for set no. 1 (c) fig. 18.--wiring diagram of spark coil fig. 19.--other parts for transmitting set no. 1 (a) fig. 20.--top view of apparatus layout for sending set no. 1 (b) fig. 20.--wiring of diagram for sending set no. 1 fig. 21.--parts for transmitting set no. 2 (a) fig. 22.--top view of apparatus layout for sending set no. 2 (b) fig. 22.--wiring diagram for sending set no. 2 fig. 23.--using a 110-volt direct current with an alternating current transformer fig. 24.--principle of the hot wire ammeter fig. 25.--kinds of aerial switches fig. 26.--wiring diagram for a complete sending and receiving set no. 1 fig. 27.--wiring diagram for complete sending and receiving set no. 2 fig. 28.--water analogue for electric pressure fig. 29.--water analogues for direct and alternating currents fig. 30.--how the ammeter and voltmeter are used fig. 31.--water valve analogue of electric resistance (a) and (b) fig. 32.--how an electric current is changed into magnetic lines of force and these into an electric current (c) and (d) fig. 32.--how an electric current sets up a magnetic field fig. 33.--the effect of resistance on the discharge of an electric current fig. 34.--damped and sustained mechanical vibrations fig. 35.--damped and sustained electric oscillations fig. 36.--sound wave and electric wave tuned senders and receptors fig. 37.--two electrode vacuum tube detectors fig. 38.--three electrode vacuum tube detector and battery connections fig. 39.--a and b batteries for vacuum tube detectors fig. 40.--rheostat for the a or storage-battery current (a) fig. 41.--top view of apparatus layout for vacuum tube detector receiving set (b) fig. 41.--wiring diagram of a simple vacuum tube receiving set fig. 42.--grid leaks and how to connect them up fig. 43.--crystal detector receiving set with vacuum tube amplifier (resistance coupled) (a) fig. 44.--vacuum tube detector receiving set with one step amplifier (resistance coupled) (b) fig. 44.--wiring diagram for using one a or storage battery with an amplifier and a detector tube (a) fig. 45.--wiring diagram for radio frequency transformer amplifying receiving set (b) fig. 45.--radio frequency transformer (a) fig. 46.--audio frequency transformer (b) fig. 46.--wiring diagram for audio frequency transformer amplifying receiving set. (with vacuum tube detector and two step amplifier tubes) (a) fig. 47.--six step amplifier with loop aerial (b) fig. 47.--efficient regenerative receiving set (with three coil loose coupler tuner) fig. 48.--simple regenerative receiving set (with loose coupler tuner) (a) fig. 49.--diagram of three coil loose coupler (b) fig. 49.--three coil loose coupler tuner fig. 50.--honeycomb inductance coil fig. 51.--the use of the potentiometer fig. 52.--regenerative audio frequency amplifier receiving set fig. 53.--how the vario coupler is made and works fig. 54.--how the variometer is made and works fig. 55.--short wave regenerative receiving set (one variometer and three variable condensers) fig. 56.--short wave regenerative receiving set (two variometer and two variable condensers) fig. 57.--wiring diagram showing fixed loading coils for intermediate wave set fig. 58.--wiring digram of intermediate wave receptor with one vario coupler and 12 section bank-wound inductance coil fig. 59.--wiring diagram showing long wave receptor with vario couplers and 8 bank-wound inductance coils fig. 60.--wiring diagram of long wave autodyne, or self-heterodyne receptor (compare with fig. 77) fig. 61.--wiring diagram of long wave separate heterodyne receiving set fig. 62.--cross section of bell telephone receiver fig. 63.--cross section of wireless headphone fig. 64.--the wireless headphone fig. 65.--arkay loud speaker fig. 66.--amplitone loud speaker fig. 67.--amplitron loud speaker fig. 68.--magnavox loud speaker fig. 69.--schematic diagram of an atom fig. 70.--action of two-electrode vacuum tube (a) and (b) fig. 71.--how a two-electrode tube acts as relay or a detector (c) fig. 71--only the positive part of oscillations goes through the tube (a) and (b) fig. 72.--how the positive and negative voltages of the oscillations act on the electrons (c) fig. 72.--how the three-electrode tube acts as detector and amplifier (d) fig. 72.--how the oscillations control the flow of the battery current through the tube fig. 73.--how the heterodyne receptor works fig. 74.--separate heterodyne oscillator (a) fig. 75.--apparatus for experimental c. w. telegraph transmitter. (b) fig. 75.--apparatus for experimental c. w. telegraph transmitter. fig. 76.--experimental c. w. telegraph transmitter fig. 77--apparatus of 100-mile c. w. telegraph transmitter fig. 78.--5to 50-watt c. w. telegraph transmitter (with a single oscillation tube) fig. 79.--200-mile c. w. telegraph transmitter (with two tubes in parallel) fig. 80.--50-watt oscillator vacuum tube fig. 81.--alternating current power transformer (for c. w. telegraphy and wireless telephony) fig. 82.--wiring diagram for 200to 500-mile c. w. telegraph transmitting set. (with alternating current.) fig. 83--wiring diagram for 500to 1000-mile c. w. telegraph transmitter fig. 84.--standard microphone transmitter fig. 85.--wiring diagram of short distance wireless telephone set. (microphone in aerial wire.) fig. 86.--telephone induction coil (used with microphone transmitter). fig. 87.--microphone transformer used with microphone transmitter fig. 88.--magnetic modulator used with microphone transmitter (a) fig. 89.--wiring diagram of 25--to 50-mile wireless telephone. (microphone modulator shunted around grid-leak condenser) (b) fig. 89.--microphone modulator connected in aerial wire fig. 90.--wiring diagram of 50to 100-mile wireless telephone transmitting set fig. 91.--plate and grid circuit reactor fig. 92.--filter reactor for smoothing out rectified currents fig. 93.--100to 200-mile wireless telephone transmitter (a) and (b) fig. 94.--operation of vacuum tube oscillators (c) fig. 94.--how a direct current sets up oscillations fig. 95.--positive voltage only sets up oscillations fig. 96.--rasco baby crystal detector fig. 97.--how the tuning coil is made fig. 98.--mesco loop-ohm head set fig. 99.--schematic layout of the $5.00 receiving set fig. 100.--wiring diagram for the $5.00 receiving set list of illustrations a. frederick collins, inventor of the wireless telephone, 1899. awarded gold medal for same, alaska yukon pacific exposition, 1909 collins' wireless telephone exhibited at the madison square garden, october, 1908 general pershing "listening-in" the world's largest radio receiving station. owned by the radio corporation of america at rocky point near port jefferson, l. i. first wireless college in the world, at tufts college, mass alexander graham bell, inventor of the telephone, now an ardent radio enthusiast world's largest loud speaker ever made. installed in lytle park, cincinnati, ohio, to permit president harding's address at point pleasant, ohio, during the grant centenary celebration to be heard within a radius of one square united states naval high power station, arlington, va. general view of power room. at the left can be seen the control switchboards, and overhead, the great 30 k.w. arc transmitter with accessories the transformer and tuner of the world's largest radio station. owned by the radio corporation of america at rocky point near port jefferson, l. i. broadcasting government reports by wireless from washington. this shows mr. gale at work with his set in the post office department wireless receptor, the size of a safety match box. a youthful genius in the person of kenneth r. hinman, who is only twelve years old, has made a wireless receiving set that fits neatly into a safety match box. with this instrument and a pair of ordinary receivers, he is able to catch not only code messages but the regular broadcasting programs from stations twenty and thirty miles distant wireless set made into a ring, designed by alfred g. rinehart, of elizabeth, new jersey. this little receptor is a practical set; it will receive messages, concerts, etc., measures 1" by 5/8" by 7/8". an ordinary umbrella is used as an aerial chapter i how to begin wireless in writing this book it is taken for granted that you are: _first_, one of the several hundred thousand persons in the united states who are interested in wireless telegraphy and telephony; _second_, that you would like to install an apparatus in your home, and _third_, that it is all new to you. now if you live in a city or town large enough to support an electrical supply store, there you will find the necessary apparatus on sale, and someone who can tell you what you want to know about it and how it works. if you live away from the marts and hives of industry you can send to various makers of wireless apparatus [footnote: a list of makers of wireless apparatus will be found in the _appendix_.] for their catalogues and price-lists and these will give you much useful information. but in either case it is the better plan for you to know before you start in to buy an outfit exactly what apparatus you need to produce the result you have in mind, and this you can gain in easy steps by reading this book. kinds of wireless systems.--there are two distinct kinds of wireless systems and these are: the _wireless telegraph_ system, and the _wireless telephone_ system. the difference between the wireless telegraph and the wireless telephone is that the former transmits messages by means of a _telegraph key_, and the latter transmits conversation and music by means of a _microphone transmitter_. in other words, the same difference exists between them in this respect as between the morse telegraph and the bell telephone. parts of a wireless system.--every complete wireless station, whether telegraph or telephone, consists of three chief separate and distinct parts and these are: (a) the _aerial wire system_, or _antenna_ as it is often called, (b) the _transmitter_, or _sender_, and (c) the _receiver_, or, more properly, the _receptor_. the aerial wire is precisely the same for either wireless telegraphy or wireless telephony. the transmitter of a wireless telegraph set generally uses a _spark gap_ for setting up the electric oscillations, while usually for wireless telephony a _vacuum tube_ is employed for this purpose. the receptor for wireless telegraphy and telephony is the same and may include either a _crystal detector_ or a _vacuum tube detector_, as will be explained presently. the easiest way to start.--first of all you must obtain a government license to operate a sending set, but you do not need a license to put up and use a receiving set, though you are required by law to keep secret any messages which you may overhear. since no license is needed for a receiving set the easiest way to break into the wireless game is to put up an aerial and hook up a receiving set to it; you can then listen-in and hear what is going on in the all-pervading ether around you, and you will soon find enough to make things highly entertaining. nearly all the big wireless companies have great stations fitted with powerful telephone transmitters and at given hours of the day and night they send out songs by popular singers, dance music by jazz orchestras, fashion talks by and for the ladies, agricultural reports, government weather forecasts and other interesting features. then by simply shifting the slide on your tuning coil you can often tune-in someone who is sending _morse_, that is, messages in the dot and dash code, or, perhaps a friend who has a wireless telephone transmitter and is talking. of course, if you want to _talk back_ you must have a wireless transmitter, either telegraphic or telephonic, and this is a much more expensive part of the apparatus than the receptor, both in its initial cost and in its operation. a wireless telegraph transmitter is less costly than a wireless telephone transmitter and it is a very good scheme for you to learn to send and receive telegraphic messages. at the present time, however, there are fifteen amateur receiving stations in the united states to every sending station, so you can see that the majority of wireless folks care more for listening in to the broadcasting of news and music than to sending out messages on their own account. the easiest way to begin wireless, then, is to put up an aerial and hook up a receiving set to it. about aerial wire systems.--to the beginner who wants to install a wireless station the aerial wire system usually looms up as the biggest obstacle of all, and especially is this true if his house is without a flag pole, or other elevation from which the aerial wire can be conveniently suspended. if you live in the congested part of a big city where there are no yards and, particularly, if you live in a flat building or an apartment house, you will have to string your aerial wire on the roof, and to do this you should get the owner's, or agent's, permission. this is usually an easy thing to do where you only intend to receive messages, for one or two thin wires supported at either end of the building are all that are needed. if for any reason you cannot put your aerial on the roof then run a wire along the building outside of your apartment, and, finally, if this is not feasible, connect your receiver to a wire strung up in your room, or even to an iron or a brass bed, and you can still get the near-by stations. an important part of the aerial wire system is the _ground_, that is, your receiving set must not only be connected with the aerial wire, but with a wire that leads to and makes good contact with the moist earth of the ground. where a house or a building is piped for gas, water or steam, it is easy to make a ground connection, for all you have to do is to fasten the wire to one of the pipes with a clamp. [footnote: pipes are often insulated from the ground, which makes them useless for this purpose.] where the house is isolated then a lot of wires or a sheet of copper or of zinc must be buried in the ground at a sufficient depth to insure their being kept moist. about the receiving apparatus.--you can either buy the parts of the receiving apparatus separate and hook them up yourself, or you can buy the apparatus already assembled in a set which is, in the beginning, perhaps, the better way. the simplest receiving set consists of (1) a _detector_, (2) a _tuning coil_, and (3) a _telephone receiver_ and these three pieces of apparatus are, of course, connected together and are also connected to the aerial and ground as the diagram in fig. 1 clearly shows. there are two chief kinds of detectors used at the present time and these are: (a) the _crystal detector_, and (b) the _vacuum tube detector_. the crystal detector is the cheapest and simplest, but it is not as sensitive as the vacuum tube detector and it requires frequent adjustment. a crystal detector can be used with or without a battery while the vacuum tube detector requires two small batteries. [illustration: fig. 1.--simple receiving set.] a tuning coil of the simplest kind consists of a single layer of copper wire wound on a cylinder with an adjustable, or sliding, contact, but for sharp tuning you need a _loose coupled tuning coil_. where a single coil tuner is used a _fixed_ condenser should be connected around the telephone receivers. where a loose coupled tuner is employed you should have a variable condenser connected across the _closed oscillation circuit_ and a _fixed condenser_ across the telephone receivers. when listening-in to distant stations the energy of the received wireless waves is often so very feeble that in order to hear distinctly an _amplifier_ must be used. to amplify the incoming sounds a vacuum tube made like a detector is used and sometimes as many as half-a-dozen of these tubes are connected in the receiving circuit, or in _cascade_, as it is called, when the sounds are _amplified_, that is magnified, many hundreds of times. the telephone receiver of a receiving set is equally as important as the detector. a single receiver can be used but a pair of receivers connected with a head-band gives far better results. then again the higher the resistance of the receivers the more sensitive they often are and those wound to as high a resistance as 3,200 ohms are made for use with the best sets. to make the incoming signals, conversation or music, audible to a room full of people instead of to just yourself you must use what is called a _loud speaker_. in its simplest form this consists of a metal cone like a megaphone to which is fitted a telephone receiver. about transmitting stations--getting your license.--if you are going to install a wireless sending apparatus, either telegraphic or telephonic, you will have to secure a government license for which no fee or charge of any kind is made. there are three classes of licenses issued to amateurs who want to operate transmitting stations and these are: (1) the _restricted amateur license_, (2) the _general amateur license_, and (3) the _special amateur license_. if you are going to set up a transmitter within five nautical miles of any naval wireless station then you will have to get a _restricted amateur license_ which limits the current you use to half a _kilowatt_ [footnote: a _kilowatt_ is 1,000 _watts_. there are 746 watts in a horsepower.] and the wave length you send out to 200 _meters_. should you live outside of the five-mile range of a navy station then you can get a general amateur license and this permits you to use a current of 1 kilowatt, but you are likewise limited to a wave length of 200 meters. but if you can show that you are doing some special kind of wireless work and not using your sending station for the mere pleasure you are getting out of it you may be able to get a _special amateur license_ which gives you the right to send out wave lengths up to 375 meters. when you are ready to apply for your license write to the _radio inspector_ of whichever one of the following districts you live in: first district..............boston, mass. second " ..............new york city third " ..............baltimore, md. fourth " ..............norfolk, va. fifth " ..............new orleans, la. sixth " ............. san francisco, cal. seventh " ............. seattle, wash. eighth " ............. detroit, mich. ninth " ..............chicago, ill. kinds of transmitters.--there are two general types of transmitters used for sending out wireless messages and these are: (1) _wireless telegraph_ transmitters, and (2) _wireless telephone_ transmitters. telegraph transmitters may use either: (a) a _jump-spark_, (b) an _electric arc_, or (c) a _vacuum tube_ apparatus for sending out dot and dash messages, while telephone transmitters may use either, (a) an _electric arc_, or (b) a _vacuum tube_ for sending out vocal and musical sounds. amateurs generally use a _jump-spark_ for sending wireless telegraph messages and the _vacuum tube_ for sending wireless telephone messages. the spark gap wireless telegraph transmitter.--the simplest kind of a wireless telegraph transmitter consists of: (1) a _source of direct or alternating current_, (2) a _telegraph key_, (3) a _spark-coil_ or a _transformer_, (4) a _spark gap_, (5) an _adjustable condenser_ and (6) an _oscillation transformer_. where _dry cells_ or a _storage battery_ must be used to supply the current for energizing the transmitter a spark-coil can be employed and these may be had in various sizes from a little fellow which gives 1/4-inch spark up to a larger one which gives a 6-inch spark. where more energy is needed it is better practice to use a transformer and this can be worked on an alternating current of 110 volts, or if only a 110 volt direct current is available then an _electrolytic interrupter_ must be used to make and break the current. a simple transmitting set with an induction coil is shown in fig. 2. [illustration: fig 2.--simple transmitting set.] a wireless key is made like an ordinary telegraph key except that where large currents are to be used it is somewhat heavier and is provided with large silver contact points. spark gaps for amateur work are usually of: (1) the _plain_ or _stationary type_, (2) the _rotating type_, and (3) the _quenched gap_ type. the plain spark-gap is more suitable for small spark-coil sets, and it is not so apt to break down the transformer and condenser of the larger sets as the rotary gap. the rotary gap on the other hand tends to prevent _arcing_ and so the break is quicker and there is less dragging of the spark. the quenched gap is more efficient than either the plain or rotary gap and moreover it is noiseless. condensers for spark telegraph transmitters can be ordinary leyden jars or glass plates coated with tin or copper foil and set into a frame, or they can be built up of mica and sheet metal embedded in an insulating composition. the glass plate condensers are the cheapest and will serve your purpose well, especially if they are immersed in oil. tuning coils, sometimes called _transmitting inductances_ and _oscillation transformers_, are of various types. the simplest kind is a transmitting inductance which consists of 25 or 30 turns of copper wire wound on an insulating tube or frame. an oscillation transformer is a loose coupled tuning coil and it consists of a primary coil formed of a number of turns of copper wire wound on a fixed insulating support, and a secondary coil of about twice the number of turns of copper wire which is likewise fixed in an insulating support, but the coils are relatively movable. an _oscillation transformer_ (instead of a _tuning coil_), is required by government regulations unless _inductively coupled_. the vacuum tube telegraph transmitter.--this consists of: (1) a _source of direct or alternating current_, (2) a _telegraph key_, (3) a _vacuum tube oscillator_, (4) a _tuning coil_, and (5) a _condenser_. this kind of a transmitter sets up _sustained_ oscillations instead of _periodic_ oscillations which are produced by a spark gap set. the advantages of this kind of a system will be found explained in chapter xvi. the wireless telephone transmitter.--because a jump-spark sets up _periodic oscillations_, that is, the oscillations are discontinuous, it cannot be used for wireless telephony. an electric arc or a vacuum tube sets up _sustained_ oscillations, that is, oscillations which are continuous. as it is far easier to keep the oscillations going with a vacuum tube than it is with an arc the former means has all but supplanted the latter for wireless telephone transmitters. the apparatus required and the connections used for wireless telephone sets will be described in later chapters. useful information.--it would be wise for the reader to turn to the appendix, beginning with page 301 of this book, and familiarize himself with the information there set down in tabular and graphic form. for example, the first table gives abbreviations of electrical terms which are in general use in all works dealing with the subject. you will also find there brief definitions of electric and magnetic units, which it would be well to commit to memory; or, at least, to make so thoroughly your own that when any of these terms is mentioned, you will know instantly what is being talked about. chapter ii putting up your aerial as inferred in the first chapter, an aerial for receiving does not have to be nearly as well made or put up as one for sending. but this does not mean that you can slipshod the construction and installation of it, for however simple it is, the job must be done right and in this case it is as easy to do it right as wrong. to send wireless telegraph and telephone messages to the greatest distances and to receive them as distinctly as possible from the greatest distances you must use for your aerial (1) copper or aluminum wire, (2) two or more wires, (3) have them the proper length, (4) have them as high in the air as you can, (5) have them well apart from each other, and (6) have them well insulated from their supports. if you live in a flat building or an apartment house you can string your aerial wires from one edge of the roof to the other and support them by wooden stays as high above it as may be convenient. should you live in a detached house in the city you can usually get your next-door neighbor to let you fasten one end of the aerial to his house and this will give you a good stretch and a fairly high aerial. in the country you can stretch your wires between the house and barn or the windmill. from this you will see that no matter where you live you can nearly always find ways and means of putting up an aerial that will serve your needs without going to the expense of erecting a mast. kinds of aerial wire systems.--an amateur wireless aerial can be anywhere from 25 feet to 100 feet long and if you can get a stretch of the latter length and a height of from 30 to 75 feet you will have one with which you can receive a thousand miles or more and send out as much energy as the government will allow you to send. the kind of an aerial that gives the best results is one whose wire, or wires, are _horizontal_, that is, parallel with the earth under it as shown at a in fig. 3. if only one end can be fixed to some elevated support then you can secure the other end to a post in the ground, but the slope of the aerial should not be more than 30 or 35 degrees from the horizontal at most as shown at b. [illustration: (a) fig. 3.--flat top, or horizontal aerial.] [illustration: (b) fig. 3.--inclined aerial.] the _leading-in wire_, that is, the wire that leads from and joins the aerial wire with your sending and receiving set, can be connected to the aerial anywhere it is most convenient to do so, but the best results are had when it is connected to one end as shown at a in fig. 4, in which case it is called an _inverted l aerial_, or when it is connected to it at the middle as shown at b, when it is called a _t aerial_. the leading-in wire must be carefully insulated from the outside of the building and also where it passes through it to the inside. this is done by means of an insulating tube known as a _leading-in insulator_, or _bulkhead insulator_ as it is sometimes called. [illustration: (a) fig. 4.--inverted l aerial.] [illustration: (b) fig. 4.--t aerial.] as a protection against lightning burning out your instruments you can use either: (1) an _air-gap lightning arrester,_ (2) a _vacuum tube protector_, or (3) a _lightning switch_, which is better. whichever of these devices is used it is connected in between the aerial and an outside ground wire so that a direct circuit to the earth will be provided at all times except when you are sending or receiving. so your aerial instead of being a menace really acts during an electrical storm like a lightning rod and it is therefore a real protection. the air-gap and vacuum tube lightning arresters are little devices that can be used only where you are going to receive, while the lightning switch must be used where you are going to send; indeed, in some localities the _fire underwriters_ require a large lightning switch to be used for receiving sets as well as sending sets. how to put up a cheap receiving aerial.--the kind of an aerial wire system you put up will depend, chiefly, on two things, and these are: (1) your pocketbook, and (2) the place where you live. a single wire aerial.--this is the simplest and cheapest kind of a receiving aerial that can be put up. the first thing to do is to find out the length of wire you need by measuring the span between the two points of support; then add a sufficient length for the leading-in wire and enough more to connect your receiving set with the radiator or water pipe. you can use any size of copper or aluminum wire that is not smaller than _no. 16 brown and sharpe gauge._ when you buy the wire get also the following material: (1) two _porcelain insulators_ as shown at a in fig. 5; (2) three or four _porcelain knob insulators_, see b; (3) either (a) an _air gap lightning arrester,_ see c, or (b) a _lightning switch_ see d; (4) a _leading-in porcelain tube insulator,_ see e, and (5) a _ground clamp_, see f. [illustration: fig. 5.--material for a simple aerial wire system.] to make the aerial slip each end of the wire through a hole in each insulator and twist it fast; next cut off and slip two more pieces of wire through the other holes in the insulators and twist them fast and then secure these to the supports at the ends of the building. take the piece you are going to use for the leading-in wire, twist it around the aerial wire and solder it there when it will look like a in fig. 6. now if you intend to use the _air gap lightning arrester_ fasten it to the wall of the building outside of your window, and bring the leading-in wire from the aerial to the top binding post of your arrester and keep it clear of everything as shown at b. if your aerial is on the roof and you have to bring the leading-in wire over the cornice or around a corner fix a porcelain knob insulator to the one or the other and fasten the wire to it. [illustration: (a) fig. 6.--single wire aerial for receiving.] [illustration: (b) fig. 6.--receiving aerial with air gap lightning arrester.] [illustration: (c) fig. 6.--aerial with lightning switch.] next bore a hole through the frame of the window at a point nearest your receiving set and push a porcelain tube 5/8 inch in diameter and 5 or 6 inches long, through it. connect a length of wire to the top post of the arrester or just above it to the wire, run this through the leading-in insulator and connect it to the slider of your tuning coil. screw the end of a piece of heavy copper wire to the lower post of the arrester and run it to the ground, on porcelain knobs if necessary, and solder it to an iron rod or pipe which you have driven into the earth. finally connect the fixed terminal of your tuning coil with the water pipe or radiator inside of the house by means of the ground clamp as shown in the diagrammatic sketch at b in fig. 6 and you are ready to tune in. if you want to use a lightning switch instead of the air-gap arrester then fasten it to the outside wall instead of the latter and screw the free end of the leading-in wire from the aerial to the middle post of it as shown at c in fig. 6. run a wire from the top post through the leading-in insulator and connect it with the slider of your tuning coil. next screw one end of a length of heavy copper wire to the lower post of the aerial switch and run it to an iron pipe in the ground as described above in connection with the spark-gap lightning arrester; then connect the fixed terminal of your tuning coil with the radiator or water pipe and your aerial wire system will be complete as shown at c in fig. 6. a two-wire aerial.--an aerial with two wires will give better results than a single wire and three wires are better than two, but you must keep them well apart. to put up a two-wire aerial get (1) enough _no. 16_, or preferably _no. 14_, solid or stranded copper or aluminum wire, (2) four porcelain insulators, see b in fig. 5, and (3) two sticks about 1 inch thick, 3 inches wide and 3 or 4 feet long, for the _spreaders_, and bore 1/8-inch hole through each end of each one. now twist the ends of the wires to the insulators and then cut off four pieces of wire about 6 feet long and run them through the holes in the wood spreaders. finally twist the ends of each pair of short wires to the free ends of the insulators and then twist the free ends of the wires together. for the leading-in wire that goes to the lightning switch take two lengths of wire and twist one end of each one around the aerial wires and solder them there. twist the short wire around the long wire and solder this joint also when the aerial will look like fig. 7. bring the free end of the leading-in wire down to the middle post of the lightning switch and fasten it there and connect up the receiver to it and the ground as described under the caption of _a single wire aerial_. [illustration: fig. 7.--two wire aerial.] connecting in the ground.--if there is a gas or water system or a steam-heating plant in your house you can make your ground connection by clamping a ground clamp to the nearest pipe as has been previously described. connect a length of bare or insulated copper wire with it and bring this up to the table on which you have your receiving set. if there are no grounded pipes available then you will have to make a good ground which we shall describe presently and lead the ground wire from your receiving set out of the window and down to it. how to put up a good aerial.--while you can use the cheap aerial already described for a small spark-coil sending set you should have a better insulated one for a 1/2 or a 1 kilowatt transformer set. the cost for the materials for a good aerial is small and when properly made and well insulated it will give results that are all out of proportion to the cost of it. an inexpensive good aerial.--a far better aerial, because it is more highly insulated, can be made by using _midget insulators_ instead of the porcelain insulators described under the caption of _a single wire aerial_ and using a small _electrose leading-in insulator_ instead of the porcelain bushing. this makes a good sending aerial for small sets as well as a good receiving aerial. the best aerial that can be made.--to make this aerial get the following material together: (1) enough _stranded or braided wire_ for three or four lengths of parallel wires, according to the number you want to use (2) six or eight _electrose ball insulators_, see b, fig. 8; (3) two 5-inch or 10-inch _electrose strain insulators_, see c; (4) six or eight _s-hooks_, see d; one large _withe_ with one eye for middle of end spreader, see e; (6) two smaller _withes_ with one eye each for end spreader, see e; (7) two still smaller _withes_, with two eyes each for the ends of the end spreaders, see e (8) two _thimbles_, see f, for 1/4-inch wire cable; (9) six or eight _hard rubber tubes_ or _bushings_ as shown at g; and (10) two _end spreaders_, see h; one _middle spreader_, see i; and one _leading-in spreader_, see j. [illustration: (a) fig. 8--part of a good aerial.] [illustration: (b) fig. 8.--the spreaders.] for this aerial any one of a number of kinds of wire can be used and among these are (a) _stranded copper wire;_ (b) _braided copper wire;_ (c) _stranded silicon bronze wire,_ and (d) _stranded phosphor bronze wire_. stranded and braided copper wire is very flexible as it is formed of seven strands of fine wire twisted or braided together and it is very good for short and light aerials. silicon bronze wire is stronger than copper wire and should be used where aerials are more than 100 feet long, while phosphor bronze wire is the strongest aerial wire made and is used for high grade aerials by the commercial companies and the government for their high-power stations. the spreaders should be made of spruce, and should be 4 feet 10 inches long for a three-wire aerial and 7 feet 1 inch long for a four-wire aerial as the distance between the wires should be about 27 inches. the end spreaders can be turned cylindrically but it makes a better looking job if they taper from the middle to the ends. they should be 2-1/4 inches in diameter at the middle and 1-3/4 inches at the ends. the middle spreader can be cylindrical and 2 inches in diameter. it must have holes bored through it at equidistant points for the hard rubber tubes; each of these should be 5/8 inch in diameter and have a hole 5/32 inch in diameter through it for the aerial wire. the leading-in spreader is also made of spruce and is 1-1/2 inches square and 26 inches long. bore three or four 5/8-inch holes at equidistant points through this spreader and insert hard rubber tubes in them as with the middle spreader. assembling the aerial.--begin by measuring off the length of each wire to be used and see to it that all of them are of exactly the same length. now push the hard rubber insulators through the holes in the middle spreader and thread the wires through the holes in the insulators as shown at a in fig 9. next twist the ends of each wire to the rings of the ball insulators and then put the large withes on the middle of each of the end spreaders; fix the other withes on the spreaders so that they will be 27 inches apart and fasten the ball insulators to the eyes in the withes with the s-hooks. now slip a thimble through the eye of one of the long strain insulators, thread a length of stranded steel wire 1/4 inch in diameter through it and fasten the ends of it to the eyes in the withes on the ends of the spreaders. [illustration: (a) fig. 9.--middle spreader.] [illustration: (b) fig. 9.--one end of aerial complete.] [illustration: (c) fig. 9.--leading in spreader.] finally fasten a 40-inch length of steel stranded wire to each of the eyes of the withes on the middle of each of the spreaders, loop the other end over the thimble and then wrap the end around the wires that are fixed to the ends of the spreaders. one end of the aerial is shown complete at b in fig. 9, and from this you can see exactly how it is assembled. now cut off three or four pieces of wire 15 or 20 feet long and twist and solder each one to one of the aerial wires; then slip them through the hard rubber tubes in the leading-in spreader, bring their free ends together as at c and twist and solder them to a length of wire long enough to reach to your lightning switch or instruments. making a good ground.--where you have to make a _ground_ you can do so either by (1) burying sheets of zinc or copper in the moist earth; (2) burying a number of wires in the moist earth, or (3) using a _counterpoise_. to make a ground of the first kind take half a dozen large sheets of copper or zinc, cut them into strips a foot wide, solder them all together with other strips and bury them deeply in the ground. it is easier to make a wire ground, say of as many or more wires as you have in your aerial and connect them together with cross wires. to put such a ground in the earth you will have to use a plow to make the furrows deep enough to insure them always being moist. in the counterpoise ground you make up a system of wires exactly like your aerial, that is, you insulate them just as carefully; then you support them so that they will be as close to the ground as possible and yet not touch it or anything else. this and the other two grounds just described should be placed directly under the aerial wire if the best results are to be had. in using a counterpoise you must bring the wire from it up to and through another leading-in insulator to your instruments. chapter iii simple telegraph and telephone receiving sets with a crystal detector receiving set you can receive either telegraphic dots and dashes or telephonic speech and music. you can buy a receiving set already assembled or you can buy the different parts and assemble them yourself. an assembled set is less bother in the beginning but if you like to experiment you can _hook up_, that is, connect the separate parts together yourself and it is perhaps a little cheaper to do it this way. then again, by so doing you get a lot of valuable experience in wireless work and an understanding of the workings of wireless that you cannot get in any other way. assembled wireless receiving sets.--the cheapest assembled receiving set [footnote: the marvel, made by the radio mfg. co., new york city.] advertised is one in which the detector and tuning coil is mounted in a box. it costs $15.00, and can be bought of dealers in electric supplies generally. this price also includes a crystal detector, an adjustable tuning coil, a single telephone receiver with head-band and the wire, porcelain insulators, lightning switch and ground clamp for the aerial wire system. it will receive wireless telegraph and telephone messages over a range of from 10 to 25 miles. another cheap unit receptor, that is, a complete wireless receiving set already mounted which can be used with a single aerial is sold for $25.00. [footnote: the aeriola jr., made by the westinghouse company, pittsburgh, pa.] this set includes a crystal detector, a variable tuning coil, a fixed condenser and a pair of head telephone receivers. it can also be used to receive either telegraph or telephone messages from distances up to 25 miles. the aerial equipment is not included in this price, but it can be bought for about $2.50 extra. assembling your own receiving set.--in this chapter we shall go only into the apparatus used for two simple receiving sets, both of which have a _crystal detector_. the first set includes a _double-slide tuning coil_ and the second set employs a _loose-coupled tuning coil_, or _loose coupler_, as it is called for short. for either set you can use a pair of 2,000or 3,000-ohm head phones. [illustration: original â© underwood and underwood. general pershing listening in.] the crystal detector.--a crystal detector consists of: (1) _the frame_, (2) _the crystal_, and (3) _the wire point_. there are any number of different designs for frames, the idea being to provide a device that will (a) hold the sensitive crystal firmly in place, and yet permit of its removal, (b) to permit the _wire point_, or _electrode_, to be moved in any direction so that the free point of it can make contact with the most sensitive spot on the crystal and (c) to vary the pressure of the wire on the crystal. a simple detector frame is shown in the cross-section at a in fig. 10; the crystal, which may be _galena_, _silicon_ or _iron pyrites_, is held securely in a holder while the _phosphor-bronze wire point_ which makes contact with it, is fixed to one end of a threaded rod on the other end of which is a knob. this rod screws into and through a sleeve fixed to a ball that sets between two brass standards and this permits an up and down or a side to side adjustment of the metal point while the pressure of it on the crystal is regulated by the screw. [illustration: (a) fig. 10.--cross section of crystal detector.] [illustration: (b) fig. 10.--the crystal detector complete.] a crystal of this kind is often enclosed in a glass cylinder and this makes it retain its sensitiveness for a much longer time than if it were exposed to dust and moisture. an upright type of this detector can be bought for $2.25, while a horizontal type, as shown at b, can be bought for $2.75. galena is the crystal that is generally used, for, while it is not quite as sensitive as silicon and iron pyrites, it is easier to obtain a sensitive piece. the tuning coil.--it is with the tuning coil that you _tune in_ and _tune out_ different stations and this you do by sliding the contacts to and fro over the turns of wire; in this way you vary the _inductance_ and _capacitance_, that is, the _constants_ of the receiving circuits and so make them receive _electric waves_, that is, wireless waves, of different lengths. the double slide tuning coil.--with this tuning coil you can receive waves from any station up to 1,000 meters in length. one of the ends of the coil of wire connects with the binding post marked _a_ in fig. 11, and the other end connects with the other binding post marked _b_, while one of the sliding contacts is connected to the binding post _c_, and the _other sliding contact_ is connected with the binding post _d_. [illustration: (a) fig. 11.--schematic diagram of double slide tuning coil.] [illustration: (b) fig. 11.--double slide tuning coil complete.] when connecting in the tuning coil, only the post _a_ or the post _b_ is used as may be most convenient, but the other end of the wire which is connected to a post is left free; just bear this point in mind when you come to connect the tuning coil up with the other parts of your receiving set. the tuning coil is shown complete at b and it costs $3.00 or $4.00. a _triple slide_ tuning coil constructed like the double slide tuner just described, only with more turns of wire on it, makes it possible to receive wave lengths up to 1,500 meters. it costs about $6.00. the loose coupled tuning coil.--with a _loose coupler_, as this kind of a tuning coil is called for short, very _selective tuning_ is possible, which means that you can tune in a station very sharply, and it will receive any wave lengths according to size of coils. the primary coil is wound on a fixed cylinder and its inductance is varied by means of a sliding contact like the double slide tuning coil described above. the secondary coil is wound on a cylinder that slides in and out of the primary coil. the inductance of this coil is varied by means of a switch that makes contact with the fixed points, each of which is connected with every twentieth turn of wire as shown in the diagram a in fig. 12. the loose coupler, which is shown complete at b, costs in the neighborhood of $8.00 or $10.00. [illustration: (a) fig. 12.--schematic diagram of loose coupler.] [illustration: (b) fig. 12.--loose coupler complete.] fixed and variable condensers.--you do not require a condenser for a simple receiving set, but if you will connect a _fixed condenser_ across your headphones you will get better results, while a _variable condenser_ connected in the _closed circuit of a direct coupled receiving set_, that is, one where a double slide tuning coil is used, makes it easy to tune very much more sharply; a variable condenser is absolutely necessary where the circuits are _inductively coupled_, that is, where a loose coupled tuner is used. a fixed condenser consists of a number of sheets of paper with leaves of tin-foil in between them and so built up that one end of every other leaf of tin-foil projects from the opposite end of the paper as shown at a in fig. 13. the paper and tin-foil are then pressed together and impregnated with an insulating compound. a fixed condenser of the exact capacitance required for connecting across the head phones is mounted in a base fitted with binding posts, as shown at b, and costs 75 cents. (paper ones 25 cents.) [illustration: (a) fig. 13.--how a fixed receiving condenser is built up.] [illustration: (b) fig. 13.--the fixed condenser complete.] [illustration: (c) and (d) fig. 13.--the variable rotary condenser.] a variable condenser, see c, of the rotating type is formed of a set of fixed semi-circular metal plates which are slightly separated from each other and between these a similar set of movable semi-circular metal plates is made to interleave; the latter are secured to a shaft on the top end of which is a knob and by turning it the capacitance of the condenser, and, hence, of the circuit in which it is connected, is varied. this condenser, which is shown at d, is made in two sizes, the smaller one being large enough for all ordinary wave lengths while the larger one is for proportionately longer wave lengths. these condensers cost $4.00 and $5.00 respectively. about telephone receivers.--there are a number of makes of head telephone receivers on the market that are designed especially for wireless work. these phones are wound to _resistances_ of from 75 _ohms_ to 8,000 _ohms_, and cost from $1.25 for a receiver without a cord or headband to $15.00 for a pair of phones with a cord and head band. you can get a receiver wound to any resistance in between the above values but for either of the simple receiving sets such as described in this chapter you ought to have a pair wound to at least 2,000 ohms and these will cost you about $5.00. a pair of head phones of this type is shown in fig. 14. [illustration: fig. 14.--pair of wireless head phones.] connecting up the parts--receiving set no. 1.--for this set get (1) a _crystal detector_, (2) a _two-slide tuning coil_, (3) a _fixed condenser_, and (4) a pair of 2,000 ohm head phones. mount the detector on the right-hand side of a board and the tuning coil on the left-hand side. screw in two binding posts for the cord ends of the telephone receivers at _a_ and _b_ as shown at a in fig. 15. this done connect one of the end binding posts of the tuning coil with the ground wire and a post of one of the contact slides with the lightning arrester or switch which leads to the aerial wire. [illustration: fig. 15.--top view of apparatus layout for receiving set no. 1.] [illustration: (b) fig. 15.--wiring diagram for receiving set no. 1.] now connect the post of the other contact slide to one of the posts of the detector and the other post of the latter with the binding post _a_, then connect the binding post _b_ to the ground wire and solder the joint. next connect the ends of the telephone receiver cord to the posts _a_ and _b_ and connect a fixed condenser also with these posts, all of which are shown in the wiring diagram at b, and you are ready to adjust the set for receiving. receiving set no. 2.--use the same kind of a detector and pair of head phones as for _set no. 1_, but get (1) a _loose coupled tuning coil_, and (2) a _variable condenser_. mount the loose coupler at the back of a board on the left-hand side and the variable condenser on the right-hand side. then mount the detector in front of the variable condenser and screw two binding posts, _a_ and _b_, in front of the tuning coil as shown at a in fig. 16. [illustration: fig. 16.--top view of apparatus layout for receiving set no. 2.] [illustration: (b) fig. 16.--wiring diagram for receiving set no. 2.] now connect the post of the sliding contact of the loose coupler with the wire that runs to the lightning switch and thence to the aerial; connect the post of the primary coil, which is the outside coil, with the ground wire; then connect the binding post leading to the switch of the secondary coil, which is the inside coil, with one of the posts of the variable condenser, and finally, connect the post that is joined to one end of the secondary coil with the other post of the variable condenser. this done, connect one of the posts of the condenser with one of the posts of the detector, the other post of the detector with the binding post _a_, and the post _b_ to the other post of the variable condenser. next connect a fixed condenser to the binding posts _a_ and _b_ and then connect the telephone receivers to these same posts, all of which is shown in the wiring diagram at b. you are now ready to adjust the instruments. in making the connections use no. 16 or 18 insulated copper wire and scrape the ends clean where they go into the binding posts. see, also, that all of the connections are tight and where you have to cross the wires keep them apart by an inch or so and always cross them at right angles. adjusting the no. 1 set--the detector.--the first thing to do is to test the detector in order to find out if the point of the contact wire is on a sensitive spot of the crystal. to do this you need a _buzzer_, a _switch_ and a _dry cell_. an electric bell from which the gong has been removed will do for the buzzer, but you can get one that is made specially for the purpose, for 75 cents, which gives out a clear, high-pitched note that sounds like a high-power station. connect one of the binding posts of the buzzer with one post of the switch, the other post of the latter with the zinc post of the dry cell and the carbon post of this to the other post of the buzzer. then connect the post of the buzzer that is joined to the vibrator, to the ground wire as shown in the wiring diagram, fig. 17. now close the switch of the buzzer circuit, put on your head phones, and move the wire point of the detector to various spots on the crystal until you hear the sparks made by the buzzer in your phones. [illustration: fig. 17.--adjusting the receiving set.] then vary the pressure of the point on the crystal until you hear the sparks as loud as possible. after you have made the adjustment open the switch and disconnect the buzzer wire from the ground wire of your set. this done, be very careful not to jar the detector or you will throw it out of adjustment and then you will have to do it all over again. you are now ready to tune the set with the tuning coil and listen in. the tuning coil.--to tune this set move the slide a of the double-slide tuner, see b in fig. 15, over to the end of the coil that is connected with the ground wire and the slide b near the opposite end of the coil, that is, the one that has the free end. now move the slide a toward the b slide and when you hear the dots and dashes, or speech or music, that is coming in as loud as you can move the b slide toward the a slide until you hear still more loudly. a very few trials on your part and you will be able to tune in or tune out any station you can hear, if not too close or powerful. [illustration: original â© underwood and underwood. the world's largest radio receiving station. owned by the radio corporation of america at rocky point near point jefferson, l.i.] adjusting the no. 2 set.--first adjust the crystal detector with the buzzer set as described above with _set no. 1,_ then turn the knob of your variable condenser so that the movable plates are just half-way in, pull the secondary coil of your loose-coupled tuner half way out; turn the switch lever on it until it makes a contact with the middle contact point and set the slider of the primary coil half way between the ends. now listen in for telegraphic signals or telephonic speech or music; when you hear one or the other slide the secondary coil in and out of the primary coil until the sounds are loudest; now move the contact switch over the points forth and back until the sounds are still louder, then move the slider to and fro until the sounds are yet louder and, finally, turn the knob of the condenser until the sounds are clear and crisp. when you have done all of these things you have, in the parlance of the wireless operator, _tuned in_ and you are ready to receive whatever is being sent. chapter iv simple telegraph sending sets a wireless telegraph transmitting set can be installed for a very small amount of money provided you are content with one that has a limited range. larger and better instruments can, of course, be had for more money, but however much you are willing to spend still you are limited in your sending radius by the government's rules and regulations. the best way, and the cheapest in the end, to install a telegraph set is to buy the separate parts and hook them up yourself. the usual type of wireless telegraph transmitter employs a _disruptive discharge,_ or _spark,_ as it is called, for setting up the oscillating currents in the aerial wire system and this is the type of apparatus described in this chapter. there are two ways to set up the sparks and these are: (1) with an _induction coil,_ or _spark-coil,_ as it is commonly called, and (2) with an _alternating current transformer_, or _power transformer_, as it is sometimes called. where you have to generate the current with a battery you must use a spark coil, but if you have a 110-volt direct or alternating lighting current in your home you can use a transformer which will give you more power. a cheap transmitting set (no. 1).--for this set you will need: (1) a _spark-coil_, (2) a _battery_ of dry cells, (3) a _telegraph key_, (4) a _spark gap_, (5) a _high-tension condenser_, and (6) an _oscillation transformer_. there are many different makes and styles of these parts but in the last analysis all of them are built on the same underlying bases and work on the same fundamental principles. the spark-coil.--spark coils for wireless work are made to give sparks from 1/4 inch in length up to 6 inches in length, but as a spark coil that gives less than a 1-inch spark has a very limited output it is best to get a coil that gives at least a 1-inch spark, as this only costs about $8.00, and if you can get a 2or a 4-inch spark coil so much the better. there are two general styles of spark coils used for wireless and these are shown at a and b in fig. 18. [illustration: (a) and (b) fig. 18.--types of spark coils for set. no. 1.] [illustration: (c) fig. 18.--wiring diagram of spark coil] a spark coil of either style consists of (_a_) a soft _iron core_ on which is wound (_b_) a couple of layers of heavy insulated wire and this is called the _primary coil_, (_c_) while over this, but insulated from it, is wound a large number of turns of very fine insulated copper wire called the _secondary coil_; (d) an _interrupter_, or _vibrator_, as it is commonly called, and, finally, (e) a _condenser_. the core, primary and secondary coils form a unit and these are set in a box or mounted on top of a hollow wooden base. the condenser is placed in the bottom of the box, or on the base, while the vibrator is mounted on one end of the box or on top of the base, and it is the only part of the coil that needs adjusting. the vibrator consists of a stiff, flat spring fixed at one end to the box or base while it carries a piece of soft iron called an _armature_ on its free end and this sets close to one end of the soft iron core. insulated from this spring is a standard that carries an adjusting screw on the small end of which is a platinum point and this makes contact with a small platinum disk fixed to the spring. the condenser is formed of alternate sheets of paper and tinfoil built up in the same fashion as the receiving condenser described under the caption of _fixed and variable condensers_, in chapter iii. the wiring diagram c shows how the spark coil is wired up. one of the battery binding posts is connected with one end of the primary coil while the other end of the latter which is wound on the soft iron core connects with the spring of the vibrator. the other battery binding post connects with the standard that supports the adjusting screw. the condenser is shunted across the vibrator, that is, one end of the condenser is connected with the spring and the other end of the condenser is connected with the adjusting screw standard. the ends of the secondary coil lead to two binding posts, which are usually placed on top of the spark coil and it is to these that the spark gap is connected. the battery.--this can be formed of dry cells or you can use a storage battery to energize your coil. for all coils that give less than a 1-inch spark you should use 5 dry cells; for 1-and 2-inch spark coils use 6 or 8 dry cells, and for 3 to 4-inch spark coils use 8 to 10 dry cells. the way the dry cells are connected together to form a battery will be shown presently. a dry cell is shown at a in fig, 19. [illustration: fig. 19.--other parts for transmitting set no. 1] the telegraph key.--you can use an ordinary morse telegraph key for the sending set and you can get one with a japanned iron base for $1.50 (or better, one made of brass and which has 1/8-inch silver contact points for $3.00. a key of the latter kind is shown at b). the spark gap.--it is in the _spark gap_ that the high tension spark takes place. the apparatus in which the spark takes place is also called the _spark gap_. it consists of a pair of zinc plugs, called _electrodes_, fixed to the ends of a pair of threaded rods, with knobs on the other ends, and these screw into and through a pair of standards as shown at _c_. this is called a _fixed_, or _stationary spark gap_ and costs about $1.00. the tuning coil.--the _transmitting inductance_, or _sending tuning coil_, consists of 20 to 30 turns of _no. 8 or 9_ hard drawn copper wire wound on a slotted insulated form and mounted on a wooden base. it is provided with _clips_ so that you can cut in and cut out as many turns of wire as you wish and so tune the sending circuits to send out whatever wave length you desire. it is shown at _d_, and costs about $5.00. see also _oscillation transformer_, page 63 [chapter iv]. the high tension condenser.--high tension condensers, that is, condensers which will stand up under _high potentials_, or electric pressures, can be bought in units or sections. these condensers are made up of thin brass plates insulated with a special compound and pressed into a compact form. the _capacitance_ [footnote: this is the capacity of the condenser.] of one section is enough for a transmitting set using a spark coil that gives a 2 inch spark or less and two sections connected together should be used for coils giving from 2 to 4 inch sparks. it is shown at _e_. connecting up the apparatus.--your sending set should be mounted on a table, or a bench, where it need not be moved. place the key in about the middle of the table and down in front, and the spark coil to the left and well to the back but so that the vibrator end will be to the right, as this will enable you to adjust it easily. place the battery back of the spark coil and the tuning coil (oscillation transformer) to the right of the spark coil and back of the key, all of which is shown in the layout at a in fig. 20. [illustration: (a) fig. 20.--top view of apparatus layout for sending set no. 1.] [illustration: (b) fig. 20.--wiring of diagram for sending set no. 1.] for the _low voltage circuit_, that is the battery circuit, use _no. 12_ or _14_ insulated copper wire. connect all of the dry cells together in _series_, that is, connect the zinc of one cell with the carbon of the next and so on until all of them are connected up. then connect the carbon of the end cell with one of the posts of the key, the zinc of the other end cell with one of the primary posts of the spark coil and the other primary post of the spark coil with the other post of the key, when the primary circuit will be complete. for the _high tension circuits_, that is, the _oscillation circuits_, you may use either bare or insulated copper wire but you must be careful that they do not touch the table, each other, or any part of the apparatus, except, of course, the posts they are connected with. connect one of the posts of the secondary coil of the spark coil with one of the posts of the spark gap, and the other post with one of the posts of the condenser; then connect the other post of the condenser with the lower spring clip of the tuning coil and also connect this clip with the ground. this done, connect the middle spring clip with one of the posts of the spark gap, and, finally, connect the top clip with the aerial wire and your transmitting set is ready to be tuned. a wiring diagram of the connections is shown at b. as this set is tuned in the same way as _set no. 2_ which follows, you are referred to the end of this chapter. a better transmitting set (no. 2).--the apparatus for this set includes: (1) an _alternating current transformer_, (2) a _wireless telegraph key_, (3) a _fixed_, a _rotary_, or a _quenched spark gap_, (4) a _condenser_, and (5) an _oscillation transformer_. if you have a 110 volt direct lighting current in your home instead of 110 volt alternating current, then you will also need (6) an _electrolytic interrupter_, for in this case the primary circuit of the transformer must be made and broken rapidly in order to set up alternating currents in the secondary coil. the alternating current transformer.--an alternating current, or power, transformer is made on the same principle as a spark coil, that is, it has a soft iron core, a primary coil formed of a couple of layers of heavy wire, and a secondary coil wound up of a large number of turns of very fine wire. unlike the spark coil, however, which has an _open magnetic core_ and whose secondary coil is wound on the primary coil, the transformer has a _closed magnetic core_, with the primary coil wound on one of the legs of the core and the secondary wound on the other leg. it has neither a vibrator nor a condenser. a plain transformer is shown at a in fig. 21. [illustration: fig. 21.--parts for transmitting set no. 2.] a transformer of this kind can be bought either (a) _unmounted_, that is, just the bare transformer, or (b) _fully mounted_, that is, fitted with an iron stand, mounted on an insulating base on which are a pair of primary binding posts, while the secondary is provided with a _safety spark gap_. there are three sizes of transformers of this kind made and they are rated at 1/4, 1/2 and 1 kilowatt, respectively, they deliver a secondary current of 9,000, 11,000 and 25,000 volts, according to size, and cost $16.00, $22.00 and $33.00 when fully mounted; a reduction of $3.00, $4.00 and $5.00 is made when they are unmounted. all of these transformers operate on 110 volt, 60 cycle current and can be connected directly to the source of alternating current. the wireless key.--for this transmitting set a standard wireless key should be used as shown at b. it is made about the same as a regular telegraph key but it is much heavier, the contact points are larger and instead of the current being led through the bearings as in an ordinary key, it is carried by heavy conductors directly to the contact points. this key is made in three sizes and the first will carry a current of 5 _amperes_[footnote: see _appendix_ for definition.] and costs $4.00, the second will carry a current of 10 amperes and costs $6.50, while the third will carry a current of 20 amperes and costs $7.50. the spark gap.--either a fixed, a rotary, or a quenched spark gap can be used with this set, but the former is seldom used except with spark-coil sets, as it is very hard to keep the sparks from arcing when large currents are used. a rotary spark gap comprises a wheel, driven by a small electric motor, with projecting plugs, or electrodes, on it and a pair of stationary plugs on each side of the wheel as shown at c. the number of sparks per second can be varied by changing the speed of the wheel and when it is rotated rapidly it sends out signals of a high pitch which are easy to read at the receiving end. a rotary gap with a 110-volt motor costs about $25.00. a quenched spark gap not only eliminates the noise of the ordinary gap but, when properly designed, it increases the range of an induction coil set some 200 per cent. a 1/4 kilowatt quenched gap costs $10.00. [footnote: see appendix for definition.] the high tension condenser.--since, if you are an amateur, you can only send out waves that are 200 meters in length, you can only use a condenser that has a capacitance of .007 _microfarad_. [footnote: see appendix for definition.] a sectional high tension condenser like the one described in connection with _set no. 1_ can be used with this set but it must have a capacitance of not more than .007 microfarad. a condenser of this value for a 1/4-kilowatt transformer costs $7.00; for a 1/2-kilowatt transformer $14.00, and for a 1-kilowatt transformer $21.00. see e, fig. 19. the oscillation transformer.--with an oscillation transformer you can tune much more sharply than with a single inductance coil tuner. the primary coil is formed of 6 turns of copper strip, or no. 9 copper wire, and the secondary is formed of 9 turns of strip, or wire. the primary coil, which is the outside coil, is hinged to the base and can be raised or lowered like the lid of a box. when it is lowered the primary and secondary coils are in the same plane and when it is raised the coils set at an angle to each other. it is shown at d and costs $5.00. connecting up the apparatus. for alternating current.--screw the key to the table about the middle of it and near the front edge; place the high tension condenser back of it and the oscillation transformer back of the latter; set the alternating current transformer to the left of the oscillation transformer and place the rotary or quenched spark gap in front of it. now bring a pair of _no. 12_ or _14_ insulated wires from the 110 volt lighting leads and connect them with a single-throw, double-pole switch; connect one pole of the switch with one of the posts of the primary coil of the alternating power transformer and connect the other post of the latter with one of the posts of your key, and the other post of this with the other pole of the switch. now connect the motor of the rotary spark gap to the power circuit and put a single-pole, single-throw switch in the motor circuit, all of which is shown at a in fig. 22. [illustration: (a) fig. 22.--top view of apparatus layout for sending set no. 2.] [illustration: (b) fig. 22.--wiring diagram for sending set no. 2.] next connect the posts of the secondary coil to the posts of the rotary or quenched spark gap and connect one post of the latter to one post of the condenser, the other post of this to the post of the primary coil of the oscillation transformer, which is the inside coil, and the clip of the primary coil to the other spark gap post. this completes the closed oscillation circuit. finally connect the post of the secondary coil of the oscillation transformer to the ground and the clip of it to the wire leading to the aerial when you are ready to tune the set. a wiring diagram of the connections is shown at b. for direct current.--where you have 110 volt direct current you must connect in an electrolytic interrupter. this interrupter, which is shown at a and b in fig. 23, consists of (1) a jar filled with a solution of 1 part of sulphuric acid and 9 parts of water, (2) a lead electrode having a large surface fastened to the cover of surface that sets in a porcelain sleeve and whose end rests on the bottom of the jar. [illustration: fig. 23.--using 110 volt direct current with an alternating current transformer.] when these electrodes are connected in series with the primary of a large spark coil or an alternating current transformer, see c, and a direct current of from 40 to 110 volts is made to pass through it, the current is made and broken from 1,000 to 10,000 times a minute. by raising or lowering the sleeve, thus exposing more or less of the platinum, or alloy point, the number of interruptions per minute can be varied at will. as the electrolytic interrupter will only operate in one direction, you must connect it with its platinum, or alloy anode, to the + or _positive_ power lead and the lead cathode to the or _negative_ power lead. you can find out which is which by connecting in the interrupter and trying it, or you can use a polarity indicator. an electrolytic interrupter can be bought for as little as $3.00. how to adjust your transmitter. tuning with a hot wire ammeter.--a transmitter can be tuned in two different ways and these are: (1) by adjusting the length of the spark gap and the tuning coil so that the greatest amount of energy is set up in the oscillating circuits, and (2) by adjusting the apparatus so that it will send out waves of a given length. to adjust the transmitter so that the circuits will be in tune you should have a _hot wire ammeter_, or radiation ammeter, as it is called, which is shown in fig. 24. it consists of a thin platinum wire through which the high-frequency currents surge and these heat it; the expansion and contraction of the wire moves a needle over a scale marked off into fractions of an ampere. when the spark gap and tuning coil of your set are properly adjusted, the needle will swing farthest to the right over the scale and you will then know that the aerial wire system, or open oscillation circuit, and the closed oscillation circuit are in tune and radiating the greatest amount of energy. [illustration: fig. 24.--principle of the hot wire ammeter.] to send out a 200 meter wave length.--if you are using a condenser having a capacitance of .007 microfarad, which is the largest capacity value that the government will allow an amateur to use, then if you have a hot wire ammeter in your aerial and tune the inductance coil or coils until the ammeter shows the largest amount of energy flowing through it you will know that your transmitter is tuned and that the aerial is sending out waves whose length is 200 meters. to tune to different wave lengths you must have a _wave-meter_. the use of the aerial switch.--where you intend to install both a transmitter and a receptor you will need a throwover switch, or _aerial switch_, as it is called. an ordinary double-pole, double-throw switch, as shown at a in fig. 25, can be used, or a switch made especially for the purpose as at b is handier because the arc of the throw is much less. [illustration: fig. 25.--kinds of aerial switches.] aerial switch for a complete sending and receiving set.--you can buy a double-pole, double-throw switch mounted on a porcelain base for about 75 cents and this will serve for _set no. 1_. screw this switch on your table between the sending and receiving sets and then connect one of the middle posts of it with the ground wire and the other middle post with the lightning switch which connects with the aerial. connect the post of the tuning coil with one of the end posts of the switch and the clip of the tuning coil with the other and complementary post of the switch. this done, connect one of the opposite end posts of the switch to the post of the receiving tuning coil and connect the sliding contact of the latter with the other and complementary post of the switch as shown in fig. 26. [illustration: fig. 26.--wiring diagram for complete sending and receiving set no. 1.] connecting in the lightning switch.--the aerial wire connects with the middle post of the lightning switch, while one of the end posts lead to one of the middle posts of the aerial switch. the other end post of the lightning switch leads to a separate ground outside the building, as the wiring diagrams figs. 26 and 27 show. [illustration: fig. 27.--wiring diagram for complete sending and receiving set no. 2.] chapter v electricity simply explained it is easy to understand how electricity behaves and what it does if you get the right idea of it at the start. in the first place, if you will think of electricity as being a fluid like water its fundamental actions will be greatly simplified. both water and electricity may be at rest or in motion. when at rest, under certain conditions, either one will develop pressure, and this pressure when released will cause them to flow through their respective conductors and thus produce a current. electricity at rest and in motion.--any wire or a conductor of any kind can be charged with electricity, but a leyden jar, or other condenser, is generally used to hold an electric charge because it has a much larger _capacitance_, as its capacity is called, than a wire. as a simple analogue of a condenser, suppose you have a tank of water raised above a second tank and that these are connected together by means of a pipe with a valve in it, as shown at a in fig. 28. [illustration: fig. 28.--water analogue for electric pressure.] [illustration: original â© underwood and underwood. first wireless college in the world, at tufts college, mass.] now if you fill the upper tank with water and the valve is turned off, no water can flow into the lower tank but there is a difference of pressure between them, and the moment you turn the valve on a current of water will flow through the pipe. in very much the same way when you have a condenser charged with electricity the latter will be under _pressure,_ that is, a _difference of potential_ will be set up, for one of the sheets of metal will be charged positively and the other one, which is insulated from it, will be charged negatively, as shown at b. on closing the switch the opposite charges rush together and form a current which flows to and fro between the metal plates. [footnote: strictly speaking it is the difference of potential that sets up the electromotive force.] the electric current and its circuit.--just as water flowing through a pipe has _quantity_ and _pressure_ back of it and the pipe offers friction to it which tends to hold back the water, so, likewise, does electricity flowing in a circuit have: (1) _quantity_, or _current strength_, or just _current_, as it is called for short, or _amperage_, and (2) _pressure_, or _potential difference_, or _electromotive force_, or _voltage_, as it is variously called, and the wire, or circuit, in which the current is flowing has (3) _resistance_ which tends to hold back the current. a definite relation exists between the current and its electromotive force and also between the current, electromotive force and the resistance of the circuit; and if you will get this relationship clearly in your mind you will have a very good insight into how direct and alternating currents act. to keep a quantity of water flowing in a loop of pipe, which we will call the circuit, pressure must be applied to it and this may be done by a rotary pump as shown at a in fig. 29; in the same way, to keep a quantity of electricity flowing in a loop of wire, or circuit, a battery, or other means for generating electric pressure must be used, as shown at b. [illustration: fig. 29.--water analogues for direct and alternating currents.] if you have a closed pipe connected with a piston pump, as at c, as the piston moves to and fro the water in the pipe will move first one way and then the other. so also when an alternating current generator is connected to a wire circuit, as at d, the current will flow first in one direction and then in the other, and this is what is called an _alternating current_. current and the ampere.--the amount of water flowing in a closed pipe is the same at all parts of it and this is also true of an electric current, in that there is exactly the same quantity of electricity at one point of the circuit as there is at any other. the amount of electricity, or current, flowing in a circuit in a second is measured by a unit called the _ampere_, [footnote: for definition of _ampere_ see _appendix._] and it is expressed by the symbol i. [footnote: this is because the letter c is used for the symbol of _capacitance_] just to give you an idea of the quantity of current an _ampere_ is we will say that a dry cell when fresh gives a current of about 20 amperes. to measure the current in amperes an instrument called an _ammeter_ is used, as shown at a in fig. 30, and this is always connected in _series_ with the line, as shown at b. [illustration: fig. 30.--how the ammeter and voltmeter are used.] electromotive force and the volt.--when you have a pipe filled with water or a circuit charged with electricity and you want to make them flow you must use a pump in the first case and a battery or a dynamo in the second case. it is the battery or dynamo that sets up the electric pressure as the circuit itself is always charged with electricity. the more cells you connect together in _series_ the greater will be the electric pressure developed and the more current it will move along just as the amount of water flowing in a pipe can be increased by increasing the pressure of the pump. the unit of electromotive force is the _volt_, and this is the electric pressure which will force a current of _1 ampere_ through a resistance of _1 ohm_; it is expressed by the symbol _e_. a fresh dry cell will deliver a current of about 1.5 volts. to measure the pressure of a current in volts an instrument called a _voltmeter_ is used, as shown at c in fig. 30, and this is always connected across the circuit, as shown at d. resistance and the ohm.--just as a water pipe offers a certain amount of resistance to the flow of water through it, so a circuit opposes the flow of electricity in it and this is called _resistance_. further, in the same way that a small pipe will not allow a large amount of water to flow through it, so, too, a thin wire limits the flow of the current in it. if you connect a _resistance coil_ in a circuit it acts in the same way as partly closing the valve in a pipe, as shown at a and b in fig. 31. the resistance of a circuit is measured by a unit called the _ohm_, and it is expressed by the symbol _r_. a no. 10, brown and sharpe gauge soft copper wire, 1,000 feet long, has a resistance of about 1 ohm. to measure the resistance of a circuit an apparatus called a _resistance bridge is used_. the resistance of a circuit can, however, be easily calculated, as the following shows. [illustration: fig. 31.--water valve analogue of electric resistance. aa valve limits the flow of water. ba resistance limits the flow of current.] what ohm's law is.--if, now, (1) you know what the current flowing in a circuit is in _amperes_, and the electromotive force, or pressure, is in _volts_, you can then easily find what the resistance is in _ohms_ of the circuit in which the current is flowing by this formula: volts e --------= ohms, or --= r amperes i that is, if you divide the current in amperes by the electromotive force in volts the quotient will give you the resistance in ohms. or (2) if you know what the electromotive force of the current is in _volts_ and the resistance of the circuit is in _ohms_ then you can find what the current flowing in the circuit is in _amperes_, thus: volts e ----= amperes, or --= i ohms r that is, by dividing the resistance of the circuit in ohms, by the electromotive force of the current you will get the amperes flowing in the circuit. finally (3) if you know what the resistance of the circuit is in _ohms_ and the current is in _amperes_ then you can find what the electromotive force is in _volts_ since: ohms x amperes = volts, or r x i = e that is, if you multiply the resistance of the circuit in ohms by the current in amperes the result will give you the electromotive force in volts. from this you will see that if you know the value of any two of the constants you can find the value of the unknown constant by a simple arithmetical process. this relation between these three constants is known as _ohm's law_ and as they are very important you should memorize them. what the watt and kilowatt are.--just as _horsepower_ or _h.p._, is the unit of work that steam has done or can do, so the _watt_ is the unit of work that an electric current has done or can do. to find the _watts_ a current develops you need only to multiply the _amperes_ by the _volts_. there are _746 watts_ to _1 horsepower, and 1,000 watts are equal to 1 kilowatt_. electromagnetic induction.--to show that a current of electricity sets up a magnetic field around it you have only to hold a compass over a wire whose ends are connected with a battery when the needle will swing at right angles to the length of the wire. by winding an insulated wire into a coil and connecting the ends of the latter with a battery you will find, if you test it with a compass, that the coil is magnetic. this is due to the fact that the energy of an electric current flowing in the wire is partly changed into magnetic lines of force which rotate at right angles about it as shown at a in fig. 32. the magnetic field produced by the current flowing in the coil is precisely the same as that set up by a permanent steel magnet. conversely, when a magnetic line of force is set up a part of its energy goes to make up electric currents which whirl about in a like manner, as shown at b. [illustration: (a) and (b) fig. 32.--how an electric current is changed into magnetic lines of force and these into an electric current.] [illustration: (c) and (d) fig. 32.--how an electric current sets up a magnetic field.] self-induction or inductance.--when a current is made to flow in a coil of wire the magnetic lines of force produced are concentrated, as at c, just as a lens concentrates rays of light, and this forms an intense _magnetic field_, as it is called. now if a bar of soft iron is brought close to one end of the coil of wire, or, better still, if it is pushed into the coil, it will be magnetized by _electromagnetic induction,_ see d, and it will remain a magnet until the current is cut off. mutual induction.--when two loops of wire, or better, two coils of wire, are placed close together the electromagnetic induction between them is reactive, that is, when a current is made to flow through one of the coils closed magnetic lines of force are set up and when these cut the other loop or turns of wire of the other coil, they in turn produce electric currents in it. it is the mutual induction that takes place between two coils of wire which makes it possible to transform _low voltage currents_ from a battery or a 110 volt source of current into high pressure currents, or _high potential currents_, as they are called, by means of a spark coil or a transformer, as well as to _step up_ and _step down_ the potential of the high frequency currents that are set up in sending and receiving oscillation transformers. soft iron cores are not used in oscillation inductance coils and oscillation transformers for the reason that the frequency of the current is so high the iron would not have time to magnetize and demagnetize and so would not help along the mutual induction to any appreciable extent. high-frequency currents.--high frequency currents, or electric oscillations as they are called, are currents of electricity that surge to and fro in a circuit a million times, more or less, per second. currents of such high frequencies will _oscillate_, that is, surge to and fro, in an _open circuit_, such as an aerial wire system, as well as in a _closed circuit_. now there is only one method by which currents of high frequency, or _radio-frequency_, as they are termed, can be set up by spark transmitters, and this is by discharging a charged condenser through a circuit having a small resistance. to charge a condenser a spark coil or a transformer is used and the ends of the secondary coil, which delivers the high potential alternating current, are connected with the condenser. to discharge the condenser automatically a _spark,_ or an _arc,_ or the _flow of electrons_ in a vacuum tube, is employed. constants of an oscillation circuit.--an oscillation circuit, as pointed out before, is one in which high frequency currents surge or oscillate. now the number of times a high frequency current will surge forth and back in a circuit depends upon three factors of the latter and these are called the constants of the circuit, namely: (1) its _capacitance,_ (2) its _inductance_ and (3) its _resistance._ what capacitance is.--the word _capacitance_ means the _electrostatic capacity_ of a condenser or a circuit. the capacitance of a condenser or a circuit is the quantity of electricity which will raise its pressure, or potential, to a given amount. the capacitance of a condenser or a circuit depends on its size and form and the voltage of the current that is charging it. the capacitance of a condenser or a circuit is directly proportional to the quantity of electricity that will keep the charge at a given potential. the _farad,_ whose symbol is _m,_ is the unit of capacitance and a condenser or a circuit to have a capacitance of one farad must be of such size that one _coulomb,_ which is the unit of electrical quantity, will raise its charge to a potential of one volt. since the farad is far too large for practical purposes a millionth of a farad, or _microfarad_, whose symbol is _mfd._, is used. what inductance is.--under the sub-caption of _self-induction_ and _inductance_ in the beginning of this chapter it was shown that it was the inductance of a coil that makes a current flowing through it produce a strong magnetic field, and here, as one of the constants of an oscillation circuit, it makes a high-frequency current act as though it possessed _inertia_. inertia is that property of a material body that requires time and energy to set in motion, or stop. inductance is that property of an oscillation circuit that makes an electric current take time to start and time to stop. because of the inductance, when a current flows through a circuit it causes the electric energy to be absorbed and changes a large part of it into magnetic lines of force. where high frequency currents surge in a circuit the inductance of it becomes a powerful factor. the practical unit of inductance is the _henry_ and it is represented by the symbol _l_. what resistance is.--the resistance of a circuit to high-frequency currents is different from that for low voltage direct or alternating currents, as the former do not sink into the conductor to nearly so great an extent; in fact, they stick practically to the surface of it, and hence their flow is opposed to a very much greater extent. the resistance of a circuit to high frequency currents is generally found in the spark gap, arc gap, or the space between the electrodes of a vacuum tube. the unit of resistance is, as stated, the _ohm_, and its symbol is _r_. the effect of capacitance, inductance and resistance on electric oscillations.--if an oscillation circuit in which high frequency currents surge has a large resistance, it will so oppose the flow of the currents that they will be damped out and reach zero gradually, as shown at a in fig. 33. but if the resistance of the circuit is small, and in wireless circuits it is usually so small as to be negligible, the currents will oscillate, until their energy is damped out by radiation and other losses, as shown at b. [illustration: fig. 33.--the effect of resistance on the discharge of an electric current.] as the capacitance and the inductance of the circuit, which may be made of any value, that is amount, you wish, determines the _time period_, that is, the length of time for a current to make one complete oscillation, it must be clear that by varying the values of the condenser and the inductance coil you can make the high frequency current oscillate as fast or as slow as you wish within certain limits. where the electric oscillations that are set up are very fast, the waves sent out by the aerial will be short, and, conversely, where the oscillations are slow the waves emitted will be long. chapter vi how the transmitting and receiving sets work the easiest way to get a clear conception of how a wireless transmitter sends out electric waves and how a wireless receptor receives them is to take each one separately and follow: (1) in the case of the transmitter, the transformation of the low voltage direct, or alternating current into high potential alternating currents; then find out how these charge the condenser, how this is discharged by the spark gap and sets up high-frequency currents in the oscillation circuits; then (2) in the case of the receptor, to follow the high frequency currents that are set up in the aerial wire and learn how they are transformed into oscillations of lower potential when they have a larger current strength, how these are converted into intermittent direct currents by the detector and which then flow into and operate the telephone receiver. how transmitting set no. 1 works. the battery and spark coil circuit.--when you press down on the knob of the key the silver points of it make contact and this closes the circuit; the low voltage direct current from the battery now flows through the primary coil of the spark coil and this magnetizes the soft iron core. the instant it becomes magnetic it pulls the spring of the vibrator over to it and this breaks the circuit; when this takes place the current stops flowing through the primary coil; this causes the core to lose its magnetism when the vibrator spring flies back and again makes contact with the adjusting screw; then the cycle of operations is repeated. a condenser is connected across the contact points of the vibrator since this gives a much higher voltage at the ends of the secondary coil than where the coil is used without it; this is because: (1) the self-induction of the primary coil makes the pressure of the current rise and when the contact points close the circuit again it discharges through the primary coil, and (2) when the break takes place the current flows into the condenser instead of arcing across the contact points. changing the primary spark coil current into secondary currents.--now every time the vibrator contact points close the primary circuit the electric current in the primary coil is changed into closed magnetic lines of force and as these cut through the secondary coil they set up in it a _momentary current_ in one direction. then the instant the vibrator points break apart the primary circuit is opened and the closed magnetic lines of force contract and as they do so they cut the turns of wire in the secondary coil in the opposite direction and this sets up another momentary current in the secondary coil in the other direction. the result is that the low voltage direct current of the battery is changed into alternating currents whose frequency is precisely that of the spring vibrator, but while the frequency of the currents is low their potential, or voltage, is enormously increased. what ratio of transformation means.--to make a spark coil step up the low voltage direct current into high potential alternating current the primary coil is wound with a couple of layers of thick insulated copper wire and the secondary is wound with a thousand, more or less, number of turns with very fine insulated copper wire. if the primary and secondary coils were wound with the same number of turns of wire then the pressure, or voltage, of the secondary coil at its terminals would be the same as that of the current which flowed through the primary coil. under these conditions the _ratio of transformation_, as it is called, would be unity. the ratio of transformation is directly proportional to the number of turns of wire on the primary and secondary coils and, since this is the case, if you wind 10 turns of wire on the primary coil and 1,000 turns of wire on the secondary coil then you will get 100 times as high a pressure, or voltage, at the terminals of the secondary as that which you caused to flow through the primary coil, but, naturally, the current strength, or amperage, will be proportionately decreased. the secondary spark coil circuit.--this includes the secondary coil and the spark gap which are connected together. when the alternating, but high potential, currents which are developed by the secondary coil, reach the balls, or _electrodes_, of the spark gap the latter are alternately charged positively and negatively. now take a given instant when one electrode is charged positively and the other one is charged negatively, then when they are charged to a high enough potential the electric strain breaks down the air gap between them and the two charges rush together as described in the chapter before this one in connection with the discharge of a condenser. when the charges rush together they form a current which burns out the air in the gap and this gives rise to the spark, and as the heated gap between the two electrodes is a very good conductor the electric current surges forth and back with high frequency, perhaps a dozen times, before the air replaces that which has burned out. it is the inrushing air to fill the vacuum of the gap that makes the crackling noise which accompanies the discharge of the electric spark. in this way then electric oscillations of the order of a million, more or less, are produced and if an aerial and a ground wire are connected to the spark balls, or electrodes, the oscillations will surge up and down it and the energy of these in turn, are changed into electric waves which travel out into space. an open circuit transmitter of this kind will send out waves that are four times as long as the aerial itself, but as the waves it sends out are strongly damped the government will not permit it to be used. the closed oscillation circuit.--by using a closed oscillation circuit the transmitter can be tuned to send out waves of a given length and while the waves are not so strongly damped more current can be sent into the aerial wire system. the closed oscillation circuit consists of: (1) a _spark gap_, (2) a _condenser_ and (3) an _oscillation transformer_. the high potential alternating current delivered by the secondary coil not only charges the spark gap electrodes which necessarily have a very small capacitance, but it charges the condenser which has a large capacitance and the value of which can be changed at will. now when the condenser is fully charged it discharges through the spark gap and then the electric oscillations set up surge to and fro through the closed circuit. as a closed circuit is a very poor radiator of energy, that is, the electric oscillations are not freely converted into electric waves by it, they surge up to, and through the aerial wire; now as the aerial wire is a good radiator nearly all of the energy of the electric oscillations which surge through it are converted into electric waves. how transmitting set no. 2 works. with alternating current. the operation of a transmitting set that uses an alternating current transformer, or _power transformer,_ as it is sometimes called, is even more simple than one using a spark coil. the transformer needs no vibrator when used with alternating current. the current from a generator flows through the primary coil of the transformer and the alternations of the usual lighting current is 60 cycles per second. this current sets up an alternating magnetic field in the core of the transformer and as these magnetic lines of force expand and contract they set up alternating currents of the same frequency but of much higher voltage at the terminals of the secondary coil according to the ratio of the primary and secondary turns of wire as explained under the sub-caption of _ratio of transformation_. with direct current.--when a 110 volt direct current is used to energize the power transformer an _electrolytic_ interruptor is needed to make and break the primary circuit, just as a vibrator is needed for the same purpose with a spark coil. when the electrodes are connected in series with the primary coil of a transformer and a source of direct current having a potential of 40 to 110 volts, bubbles of gas are formed on the end of the platinum, or alloy anode, which prevent the current from flowing until the bubbles break and then the current flows again, in this way the current is rapidly made and broken and the break is very sharp. where this type of interrupter is employed the condenser that is usually shunted around the break is not necessary as the interrupter itself has a certain inherent capacitance, due to electrolytic action, and which is called its _electrolytic capacitance_, and this is large enough to balance the self-induction of the circuit since the greater the number of breaks per minute the smaller the capacitance required. the rotary spark gap.--in this type of spark gap the two fixed electrodes are connected with the terminals of the secondary coil of the power transformer and also with the condenser and primary of the oscillation transformer. now whenever any pair of electrodes on the rotating disk are in a line with the pair of fixed electrodes a spark will take place, hence the pitch of the note depends on the speed of the motor driving the disk. this kind of a rotary spark-gap is called _non-synchronous_ and it is generally used where a 60 cycle alternating current is available but it will work with other higher frequencies. the quenched spark gap.--if you strike a piano string a single quick blow it will continue to vibrate according to its natural period. this is very much the way in which a quenched spark gap sets up oscillations in a coupled closed and open circuit. the oscillations set up in the primary circuit by a quenched spark make only three or four sharp swings and in so doing transfer all of their energy over to the secondary circuit, where it will oscillate some fifty times or more before it is damped out, because the high frequency currents are not forced, but simply oscillate to the natural frequency of the circuit. for this reason the radiated waves approach somewhat the condition of continuous waves, and so sharper tuning is possible. the oscillation transformer.--in this set the condenser in the closed circuit is charged and discharged and sets up oscillations that surge through the closed circuit as in _set no. 1_. in this set, however, an oscillation transformer is used and as the primary coil of it is included in the closed circuit the oscillations set up in it produce strong oscillating magnetic lines of force. the magnetic field thus produced sets up in turn electric oscillations in the secondary coil of the oscillation transformer and these surge through the aerial wire system where their energy is radiated in the form of electric waves. the great advantage of using an oscillation transformer instead of a simple inductance coil is that the capacitance of the closed circuit can be very much larger than that of the aerial wire system. this permits more energy to be stored up by the condenser and this is impressed on the aerial when it is radiated as electric waves. how receiving set no. i works.--when the electric waves from a distant sending station impinge on the wire of a receiving aerial their energy is changed into electric oscillations that are of exactly the same frequency (assuming the receptor is tuned to the transmitter) but whose current strength (amperage) and potential (voltage) are very small. these electric waves surge through the closed circuit but when they reach the crystal detector the contact of the metal point on the crystal permits more current to flow through it in one direction than it will allow to pass in the other direction. for this reason a crystal detector is sometimes called a _rectifier_, which it really is. thus the high frequency currents which the steel magnet cores of the telephone receiver would choke off are changed by the detector into intermittent direct currents which can flow through the magnet coils of the telephone receiver. since the telephone receiver chokes off the oscillations, a small condenser can be shunted around it so that a complete closed oscillation circuit is formed and this gives better results. when the intermittent rectified current flows through the coils of the telephone receiver it energizes the magnet as long as it lasts, when it is de-energized; this causes the soft iron disk, or _diaphragm_ as it is called, which sets close to the ends of the poles of the magnet, to vibrate; and this in turn gives forth sounds such as dots and dashes, speech or music, according to the nature of the electric waves that sent them out at the distant station. how receiving set no. 2 works.--when the electric oscillations that are set up by the incoming electric waves on the aerial wire surge through the primary coil of the oscillation transformer they produce a magnetic field and as the lines of force of the latter cut the secondary coil, oscillations of the same frequency are set up in it. the potential (voltage) of these oscillations are, however, _stepped down_ in the secondary coil and, hence, their current strength (amperes) is increased. the oscillations then flow through the closed circuit where they are rectified by the crystal detector and transformed into sound waves by the telephone receiver as described in connection with _set no. 1_. the variable condenser shunted across the closed circuit permits finer secondary tuning to be done than is possible without it. where you are receiving continuous waves from a wireless telephone transmitter (speech or music) you have to tune sharper than is possible with the tuning coil alone and to do this a variable condenser connected in parallel with the secondary coil is necessary. chapter vii mechanical and electrical tuning there is a strikingly close resemblance between _sound waves_ and the way they are set up in _the air_ by a mechanically vibrating body, such as a steel spring or a tuning fork, and _electric waves_ and the way they are set up in _the ether_ by a current oscillating in a circuit. as it is easy to grasp the way that sound waves are produced and behave something will be told about them in this chapter and also an explanation of how electric waves are produced and behave and thus you will be able to get a clear understanding of them and of tuning in general. damped and sustained mechanical vibrations.--if you will place one end of a flat steel spring in a vice and screw it up tight as shown at a in fig. 34, and then pull the free end over and let it go it will vibrate to and fro with decreasing amplitude until it comes to rest as shown at b. when you pull the spring over you store up energy in it and when you let it go the stored up energy is changed into energy of motion and the spring moves forth and back, or _vibrates_ as we call it, until all of its stored up energy is spent. [illustration: fig. 34.--damped and sustained mechanical vibrations.] if it were not for the air surrounding it and other frictional losses, the spring would vibrate for a very long time as the stored up energy and the energy of motion would practically offset each other and so the energy would not be used up. but as the spring beats the air the latter is sent out in impulses and the conversion of the vibrations of the spring into waves in the air soon uses up the energy you have imparted to it and it comes to rest. in order to send out _continuous waves_ in the air instead of _damped waves_ as with a flat steel spring you can use an _electric driven tuning fork_, see c, in which an electromagnet is fixed on the inside of the prongs and when this is energized by a battery current the vibrations of the prongs of the fork are kept going, or are _sustained_, as shown in the diagram at d. damped and sustained electric oscillations.--the vibrating steel spring described above is a very good analogue of the way that damped electric oscillations which surge in a circuit set up and send out periodic electric waves in the ether while the electric driven tuning fork just described is likewise a good analogue of how sustained oscillations surge in a circuit and set up and send out continuous electric waves in the ether as the following shows. now the inductance and resistance of a circuit such as is shown at a in fig. 35, slows down, and finally damps out entirely, the electric oscillations of the high frequency currents, see b, where these are set up by the periodic discharge of a condenser, precisely as the vibrations of the spring are damped out by the friction of the air and other resistances that act upon it. as the electric oscillations surge to and fro in the circuit it is opposed by the action of the ether which surrounds it and electric waves are set up in and sent out through it and this transformation soon uses up the energy of the current that flows in the circuit. [illustration: fig. 35.--damped and sustained electric oscillations.] to send out _continuous waves_ in the ether such as are needed for wireless telephony instead of _damped waves_ which are, at the present writing, generally used for wireless telegraphy, an _electric oscillation arc_ or a _vacuum tube oscillator_ must be used, see c, instead of a spark gap. where a spark gap is used the condenser in the circuit is charged periodically and with considerable lapses of time between each of the charging processes, when, of course, the condenser discharges periodically and with the same time element between them. where an oscillation arc or a vacuum tube is used the condenser is charged as rapidly as it is discharged and the result is the oscillations are sustained as shown at d. about mechanical tuning.--a tuning fork is better than a spring or a straight steel bar for setting up mechanical vibrations. as a matter of fact a tuning fork is simply a steel bar bent in the middle so that the two ends are parallel. a handle is attached to middle point of the fork so that it can be held easily and which also allows it to vibrate freely, when the ends of the prongs alternately approach and recede from one another. when the prongs vibrate the handle vibrates up and down in unison with it, and imparts its motion to the _sounding box_, or _resonance case_ as it is sometimes called, where one is used. if, now, you will mount the fork on a sounding box which is tuned so that it will be in resonance with the vibrations of the fork there will be a direct reinforcement of the vibrations when the note emitted by it will be augmented in strength and quality. this is called _simple resonance_. further, if you mount a pair of forks, each on a separate sounding box, and have the forks of the same size, tone and pitch, and the boxes synchronized, that is, tuned to the same frequency of vibration, then set the two boxes a foot or so apart, as shown at a in fig. 36, when you strike one of the forks with a rubber hammer it will vibrate with a definite frequency and, hence, send out sound waves of a given length. when the latter strike the second fork the impact of the molecules of air of which the sound waves are formed will set its prongs to vibrating and it will, in turn, emit sound waves of the same length and this is called _sympathetic resonance_, or as we would say in wireless the forks are _in tune_. [illustration: fig. 36.--sound wave and electric wave tuned senders and receptors. a variable tuning forks for showing sound wave tuning. b variable oscillation circuits for showing electric wave tuning.] tuning forks are made with adjustable weights on their prongs and by fixing these to different parts of them the frequency with which the forks vibrate can be changed since the frequency varies inversely with the square of the length and directly with the thickness [footnote: this law is for forks having a rectangular cross-section. those having a round cross-section vary as the radius.] of the prongs. now by adjusting one of the forks so that it vibrates at a frequency of, say, 16 per second and adjusting the other fork so that it vibrates at a frequency of, say, 18 or 20 per second, then the forks will not be in tune with each other and, hence, if you strike one of them the other will not respond. but if you make the forks vibrate at the same frequency, say 16, 20 or 24 per second, when you strike one of them the other will vibrate in unison with it. about electric tuning.--electric resonance and electric tuning are very like those of acoustic resonance and acoustic tuning which i have just described. just as acoustic resonance may be simple or sympathetic so electric resonance may be simple or sympathetic. simple acoustic resonance is the direct reinforcement of a simple vibration and this condition is had when a tuning fork is mounted on a sounding box. in simple electric resonance an oscillating current of a given frequency flowing in a circuit having the proper inductance and capacitance may increase the voltage until it is several times greater than its normal value. tuning the receptor circuits to the transmitter circuits are examples of sympathetic electric resonance. as a demonstration if you have two leyden jars (capacitance) connected in circuit with two loops of wire (inductance) whose inductance can be varied as shown at b in fig. 36, when you make a spark pass between the knobs of one of them by means of a spark coil then a spark will pass in the gap of the other one provided the inductance of the two loops of wire is the same. but if you vary the inductance of the one loop so that it is larger or smaller than that of the other loop no spark will take place in the second circuit. when a tuning fork is made to vibrate it sends out waves in the air, or sound waves, in all directions and just so when high frequency currents surge in an oscillation circuit they send out waves in the ether, or electric waves, that travel in all directions. for this reason electric waves from a transmitting station cannot be sent to one particular station, though they do go further in one direction than in another, according to the way your aerial wire points. since the electric waves travel out in all directions any receiving set properly tuned to the wave length of the sending station will receive the waves and the only limit on your ability to receive from high-power stations throughout the world depends entirely on the wave length and sensitivity of your receiving set. as for tuning, just as changing the length and the thickness of the prongs of a tuning fork varies the frequency with which it vibrates and, hence, the length of the waves it sends out, so, too, by varying the capacitance of the condenser and the inductance of the tuning coil of the transmitter the frequency of the electric oscillations set up in the circuit may be changed and, consequently, the length of the electric waves they send out. likewise, by varying the capacitance and the inductance of the receptor the circuits can be tuned to receive incoming electric waves of whatever length within the limitation of the apparatus. chapter viii a simple vacuum tube detector receiving set while you can receive dots and dashes from spark wireless telegraph stations and hear spoken words and music from wireless telephone stations with a crystal detector receiving set such as described in chapter iii, you can get stations that are much farther away and hear them better with a _vacuum tube detector_ receiving set. though the vacuum tube detector requires two batteries to operate it and the receiving circuits are somewhat more complicated than where a crystal detector is used still the former does not have to be constantly adjusted as does the latter and this is another very great advantage. taken all in all the vacuum tube detector is the most sensitive and the most satisfactory of the detectors that are in use at the present time. not only is the vacuum tube a detector of electric wave signals and speech and music but it can also be used to _amplify_ them, that is, to make them stronger and, hence, louder in the telephone receiver and further its powers of amplification are so great that it will reproduce them by means of a _loud speaker_, just as a horn amplifies the sounds of a phonograph reproducer, until they can be heard by a room or an auditorium full of people. there are two general types of loud speakers, though both use the principle of the telephone receiver. the construction of these loud speakers will be fully described in a later chapter. assembled vacuum tube receiving sets.--you can buy a receiving set with a vacuum tube detector from the very simplest type, which is described in this chapter, to those that are provided with _regenerative circuits_ and _amplifying_ tubes or both, which we shall describe in later chapters, from dealers in electrical apparatus generally. while one of these sets costs more than you can assemble a set for yourself, still, especially in the beginning, it is a good plan to buy an assembled one for it is fitted with a _panel_ on which the adjusting knobs of the rheostat, tuning coil and condenser are mounted and this makes it possible to operate it as soon as you get it home and without the slightest trouble on your part. you can, however, buy all the various parts separately and mount them yourself. if you want the receptor simply for receiving then it is a good scheme to have all of the parts mounted in a box or enclosed case, but if you want it for experimental purposes then the parts should be mounted on a base or a panel so that all of the connections are in sight and accessible. a simple vacuum tube receiving set.--for this set you should use: (1) a _loose coupled tuning coil,_ (2) a _variable condenser,_ (3) a _vacuum tube detector,_ (4) an a or _storage battery_ giving 6 volts, (5) a b or _dry cell battery_ giving 22-1/2 volts, (6) a _rheostat_ for varying the storage battery current, and (7) a pair of 2,000-ohm _head telephone receivers_. the loose coupled tuning coil, the variable condenser and the telephone receivers are the same as those described in chapter iii. the vacuum tube detector. with two electrodes.--a vacuum tube in its simplest form consists of a glass bulb like an incandescent lamp in which a _wire filament_ and a _metal plate_ are sealed as shown in fig. 37, the air is then pumped out of the tube and a vacuum left or after it is exhausted it is filled with nitrogen, which cannot burn. [illustration: fig. 37.--two electrode vacuum tube detectors.] when the vacuum tube is used as a detector, the wire filament is heated red-hot and the metal plate is charged with positive electricity though it remains cold. the wire filament is formed into a loop like that of an incandescent lamp and its outside ends are connected with a 6-volt storage battery, which is called the a battery; then the + or _positive_ terminal of a 22-1/2 volt dry cell battery, called the b battery, is connected to the metal plate while the or _negative_ terminal of the battery is connected to one of the terminals of the wire filament. the diagram, fig. 37, simply shows how the two electrode vacuum tube, the a or dry battery, and the b or storage battery are connected up. three electrode vacuum tube detector.--the three electrode vacuum tube detector shown at a in fig. 38, is much more sensitive than the two electrode tube and has, in consequence, all but supplanted it. in this more recent type of vacuum tube the third electrode, or _grid_, as it is called, is placed between the wire filament and the metal plate and this allows the current to be increased or decreased at will to a very considerable extent. [illustration: fig. 38.--three electrode vacuum tube detector and battery connections.] the way the three electrode vacuum tube detector is connected with the batteries is shown at b. the plate, the a or dry cell battery and one terminal of the filament are connected in _series_--that is, one after the other, and the ends of the filament are connected to the b or storage battery. in assembling a receiving set you must, of course, have a socket for the vacuum tube. a vacuum tube detector costs from $5.00 to $6.00. the dry cell and storage batteries.--the reason that a storage battery is used for heating the filament of the vacuum tube detector is because the current delivered is constant, whereas when a dry cell battery is used the current soon falls off and, hence, the heat of the filament gradually grows less. the smallest a or 6 volt storage battery on the market has a capacity of 20 to 40 ampere hours, weighs 13 pounds and costs about $10.00. it is shown at a in fig. 39. the b or dry cell battery for the vacuum tube plate circuit that gives 22-1/2 volts can be bought already assembled in sealed boxes. the small size is fitted with a pair of terminals while the larger size is provided with _taps_ so that the voltage required by the plate can be adjusted as the proper operation of the tube requires careful regulation of the plate voltage. a dry cell battery for a plate circuit is shown at b. [illustration: fig. 39.--a and b batteries for vacuum tube detectors.] the filament rheostat.--an adjustable resistance, called a _rheostat_, must be used in the filament and storage battery circuit so that the current flowing through the filament can be controlled to a nicety. the rheostat consists of an insulating and a heat resisting form on which is wound a number of turns of resistance wire. a movable contact arm that slides over and presses on the turns of wire is fixed to the knob on top of the rheostat. a rheostat that has a resistance of 6 ohms and a current carrying capacity of 1.5 amperes which can be mounted on a panel board is the right kind to use. it is shown at a and b in fig. 40 and costs $1.25. [illustration: fig. 40.--rheostat for the a or storage battery current.] assembling the parts.--begin by placing all of the separate parts of the receiving set on a board or a base of other material and set the tuning coil on the left hand side with the adjustable switch end toward the right hand side so that you can reach it easily. then set the variable condenser in front of it, set the vacuum tube detector at the right hand end of the tuning coil and the rheostat in front of the detector. place the two sets of batteries back of the instruments and screw a couple of binding posts _a_ and _b_ to the right hand lower edge of the base for connecting in the head phones all of which is shown at a in fig. 41. [illustration: (a) fig. 41.--top view of apparatus layout for a vacuum tube detector receiving set.] [illustration: (b) fig. 41.--wiring diagram of a simple vacuum tube receiving set.] connecting up the parts.--to wire up the different parts begin by connecting the sliding contact of the primary coil of the loose coupled tuning coil (this you will remember is the outside one that is wound with fine wire) to the upper post of the lightning switch and connect one terminal of this coil with the water pipe. now connect the free end of the secondary coil of the tuning coil (this is the inside coil that is wound with heavy wire) to one of the binding posts of the variable condenser and connect the movable contact arm of the adjustable switch of the primary of the tuning coil with the other post of the variable condenser. next connect the grid of the vacuum tube to one of the posts of the condenser and then connect the plate of the tube to the _carbon terminal_ of the b or dry cell battery which is the + or _positive pole_ and connect the _zinc terminal_ of the or _negative_ pole to the binding post _a_, connect the post _b_ to the other side of the variable condenser and then connect the terminals of the head phones to the binding posts _a_ and _b_. whatever you do be careful not to get the plate connections of the battery reversed. now connect one of the posts of the rheostat to one terminal of the filament and the other terminal of the filament to the or _negative_ terminal of the a or storage battery and the + or _positive_ terminal of the a or storage battery to the other post of the rheostat. finally connect the + or positive terminal of the a or storage battery with the wire that runs from the head phones to the variable condenser, all of which is shown in the wiring diagram at b in fig. 41. adjusting the vacuum tube detector receiving set.--a vacuum tube detector is tuned exactly in the same way as the _crystal detector set no. 2_ described in chapter iii, in-so-far as the tuning coil and variable condenser are concerned. the sensitivity of the vacuum tube detector receiving set and, hence, the distance over which signals and other sounds can be heard depends very largely on the sensitivity of the vacuum tube itself and this in turn depends on: (1) the right amount of heat developed by the filament, or _filament brilliancy_ as it is called, (2) the right amount of voltage applied to the plate, and (3) the extent to which the tube is exhausted where this kind of a tube is used. to vary the current flowing from the a or storage battery through the filament so that it will be heated to the right degree you adjust the rheostat while you are listening in to the signals or other sounds. by carefully adjusting the rheostat you can easily find the point at which it makes the tube the most sensitive. a rheostat is also useful in that it keeps the filament from burning out when the current from the battery first flows through it. you can very often increase the sensitiveness of a vacuum tube after you have used it for a while by recharging the a or storage battery. the degree to which a vacuum tube has been exhausted has a very pronounced effect on its sensitivity. the longer the tube is used the lower its vacuum gets and generally the less sensitive it becomes. when this takes place (and you can only guess at it) you can very often make it more sensitive by warming it over the flame of a candle. vacuum tubes having a gas content (in which case they are, of course, no longer vacuum tubes in the strict sense) make better detectors than tubes from which the air has been exhausted and which are sealed off in this evacuated condition because their sensitiveness is not dependent on the degree of vacuum as in the latter tubes. moreover, a tube that is completely exhausted costs more than one that is filled with gas. chapter ix vacuum tube amplifier receiving sets the reason a vacuum tube detector is more sensitive than a crystal detector is because while the latter merely _rectifies_ the oscillating current that surges in the receiving circuits, the former acts as an _amplifier_ at the same time. the vacuum tube can be used as a separate amplifier in connection with either: (1) a _crystal detector_ or (2) a _vacuum tube detector_, and (_a_) it will amplify either the _radio frequency currents_, that is the high frequency oscillating currents which are set up in the oscillation circuits or (_b_) it will amplify the _audio frequency currents_, that is, the _low frequency alternating_ currents that flow through the head phone circuit. to use the amplified radio frequency oscillating currents or amplified audio frequency alternating currents that are set up by an amplifier tube either a high resistance, called a _grid leak_, or an _amplifying transformer_, with or without an iron core, must be connected with the plate circuit of the first amplifier tube and the grid circuit of the next amplifier tube or detector tube, or with the wire point of a crystal detector. where two or more amplifier tubes are coupled together in this way the scheme is known as _cascade amplification._ where either a _radio frequency transformer_, that is one without the iron core, or an _audio frequency transformer_, that is one with the iron core, is used to couple the amplifier tube circuits together better results are obtained than where a high resistance grid leak is used, but the amplifying tubes have to be more carefully shielded from each other or they will react and set up a _howling_ noise in the head phones. on the other hand grid leaks cost less but they are more troublesome to use as you have to find out for yourself the exact resistance value they must have and this you can do only by testing them out. a grid leak amplifier receiving set. with crystal detector.--the apparatus you need for this set includes: (1) a _loose coupled tuning coil_, (2) a _variable condenser_, (3) _two fixed condensers_, (4) a _crystal detector_, or better a _vacuum tube detector_, (5) an a or _6 volt storage battery_, (6) a _rheostat_, (7) a b or 22-1/2 _volt dry cell battery_, (8) a fixed resistance unit, or _leak grid_ as it is called, and (9) a pair of _head-phones_. the tuning coil, variable condenser, fixed condensers, crystal detectors and head-phones are exactly the same as those described in _set no. 2_ in chapter iii. the a and b batteries are exactly the same as those described in chapter viii. the _vacuum tube amplifier_ and the _grid leak_ are the only new pieces of apparatus you need and not described before. the vacuum tube amplifier.--this consists of a three electrode vacuum tube exactly like the vacuum tube detector described in chapter viii and pictured in fig. 38, except that instead of being filled with a non-combustible gas it is evacuated, that is, the air has been completely pumped out of it. the gas filled tube, however, can be used as an amplifier and either kind of tube can be used for either radio frequency or audio frequency amplification, though with the exhausted tube it is easier to obtain the right plate and filament voltages for good working. the fixed resistance unit, or grid leak.--grid leaks are made in different ways but all of them have an enormously high resistance. one way of making them consists of depositing a thin film of gold on a sheet of mica and placing another sheet of mica on top to protect it the whole being enclosed in a glass tube as shown at a in fig. 42. these grid leaks are made in units of from 50,000 ohms (.05 megohm) to 5,000,000 ohms (5 megohms) and cost from $1 to $2. [illustration: fig. 42.--grid leaks and how to connect them up.] as the _value_ of the grid leak you will need depends very largely upon the construction of the different parts of your receiving set and on the kind of aerial wire system you use with it you will have to try out various resistances until you hit the right one. the resistance that will give the best results, however, lies somewhere between 500,000 ohms (1/2 a megohm) and 3,000,000 ohms (3 megohms) and the only way for you to find this out is to buy 1/2, 1 and 2 megohm grid leak resistances and connect them up in different ways, as shown at b, until you find the right value. assembling the parts for a crystal detector set.--begin by laying the various parts out on a base or a panel with the loose coupled tuning coil on the left hand side, but with the adjustable switch of the secondary coil on the right hand end or in front according to the way it is made. then place the variable condenser, the rheostat, the crystal detector and the binding posts for the head phones in front of and in a line with each other. set the vacuum tube amplifier back of the rheostat and the a and b batteries back of the parts or in any other place that may be convenient. the fixed condensers and the grid leak can be placed anywhere so that it will be easy to connect them in and you are ready to wire up the set. connecting up the parts for a crystal detector.--first connect the sliding contact of the primary of the tuning coil to the leading-in wire and one of the end wires of the primary to the water pipe, as shown in fig. 43. now connect the adjustable arm that makes contact with one end of the secondary of the tuning coil to one of the posts of the variable condenser; then connect the other post of the latter with a post of the fixed condenser and the other post of this with the grid of the amplifying tube. [illustration: fig. 43.--crystal detector receiving set with vacuum tube amplifier (resistance coupled).] connect the first post of the variable condenser to the + or _positive electrode_ of the a battery and its or _negative electrode_ with the rotating contact arm of the rheostat. next connect one end of the resistance coil of the rheostat to one of the posts of the amplifier tube that leads to the filament and the other filament post to the + or _positive electrode_ of the a battery. this done connect the _negative_, that is, the _zinc pole_ of the b battery to the positive electrode of the a battery and connect the _positive_, or _carbon pole_ of the former with one end of the grid leak and connect the other end of this to the plate of the amplifier tube. to the end of the grid leak connected with the plate of the amplifier tube connect the metal point of your crystal detector, the crystal of the latter with one post of the head phones and the other post of them with the other end of the grid leak and, finally, connect a fixed condenser in _parallel_ with--that is across the ends of the grid leak, all of which is shown in the wiring diagram in fig. 43. a grid leak amplifying receiving set with vacuum tube detector.--a better amplifying receiving set can be made than the one just described by using a vacuum tube detector instead of the crystal detector. this set is built up exactly like the crystal detector described above and shown in fig. 43 up to and including the grid leak resistance, but shunted across the latter is a vacuum tube detector, which is made and wired up precisely like the one shown at a in fig. 41 in the chapter ahead of this one. the way a grid leak and vacuum tube detector with a one-step amplifier are connected up is shown at a in fig. 44. where you have a vacuum tube detector and one or more amplifying tubes connected up, or in _cascade_ as it is called, you can use an a, or storage battery of 6 volts for all of them as shown at b in fig. 44, but for every vacuum tube you use you must have a b or 22-1/2 volt dry battery to charge the plate with. [illustration: (a) fig. 44--vacuum tube detector set with one step amplifier (resistance coupled).] [illustration: (b) fig. 44.--wiring diagram for using one a or storage battery with an amplifier and a detector tube.] a radio frequency transformer amplifying receiving set.--instead of using a grid leak resistance to couple up the amplifier and detector tube circuits you can use a _radio frequency transformer_, that is, a transformer made like a loose coupled tuning coil, and without an iron core, as shown in the wiring diagram at a in fig. 45. in this set, which gives better results than where a grid leak is used, the amplifier tube is placed in the first oscillation circuit and the detector tube in the second circuit. [illustration: (a) fig. 45.--wiring diagram for a radio frequency transformer amplifying receiving set.] [illustration: (b) fig. 45.--radio frequency transformer.] since the radio frequency transformer has no iron core the high frequency, or _radio frequency_ oscillating currents, as they are called, surge through it and are not changed into low frequency, or _audio frequency_ pulsating currents, until they flow through the detector. since the diagram shows only one amplifier and one radio frequency transformer, it is consequently a _one step amplifier_; however, two, three or more, amplifying tubes can be connected up by means of an equal number of radio frequency transformers when you will get wonderful results. where a six step amplifier, that is, where six amplifying tubes are connected together, or in _cascade_, the first three are usually coupled up with radio frequency transformers and the last three with audio frequency transformers. a radio frequency transformer is shown at b and costs $6 to $7. an audio frequency transformer amplifying receiving set.--where audio frequency transformers are used for stepping up the voltage of the current of the detector and amplifier tubes, the radio frequency current does not get into the plate circuit of the detector at all for the reason that the iron core of the transformer chokes them off, hence, the succeeding amplifiers operate at audio frequencies. an audio frequency transformer is shown at a in fig. 46 and a wiring diagram showing how the tubes are connected in _cascade_ with the transformers is shown at b; it is therefore a two-step audio frequency receiving set. [illustration: (a) fig. 46.--audio frequency transformer.] [illustration: (b) fig. 46--wiring diagram for an audio frequency transformer amplifying receiving set. (with vacuum tube detector and two step amplifier tubes.)] a six step amplifier receiving set with a loop aerial.--by using a receiving set having a three step radio frequency and a three step audio frequency, that is, a set in which there are coupled three amplifying tubes with radio frequency transformers and three amplifying tubes with audio frequency transformers as described under the caption _a radio frequency transformer receiving set_, you can use a _loop aerial_ in your room thus getting around the difficulties--if such there be--in erecting an out-door aerial. you can easily make a loop aerial by winding 10 turns of _no. 14_ or _16_ copper wire about 1/16 inch apart on a wooden frame two feet on the side as shown in fig. 47. with this six step amplifier set and loop aerial you can receive wave lengths of 150 to 600 meters from various high power stations which are at considerable distances away. [illustration: (a) fig. 47.--six step amplifier with loop aerial.] [illustration: (b) fig. 47.--efficient regenerative receiving set. (with three coil loose coupler tuner.)] how to prevent howling.--where radio frequency or audio frequency amplifiers are used to couple your amplifier tubes in cascade you must take particular pains to shield them from one another in order to prevent the _feed back_ of the currents through them, which makes the head phones or loud speaker _howl_. to shield them from each other the tubes should be enclosed in metal boxes and placed at least 6 inches apart while the transformers should be set so that their cores are at right angles to each other and these also should be not less than six inches apart. chapter x regenerative amplification receiving sets while a vacuum tube detector has an amplifying action of its own, and this accounts for its great sensitiveness, its amplifying action can be further increased to an enormous extent by making the radio frequency currents that are set up in the oscillation circuits react on the detector. such currents are called _feed-back_ or _regenerative_ currents and when circuits are so arranged as to cause the currents to flow back through the detector tube the amplification keeps on increasing until the capacity of the tube itself is reached. it is like using steam over and over again in a steam turbine until there is no more energy left in it. a system of circuits which will cause this regenerative action to take place is known as the _armstrong circuits_ and is so called after the young man who discovered it. since the regenerative action of the radio frequency currents is produced by the detector tube itself and which sets up an amplifying effect without the addition of an amplifying tube, this type of receiving set has found great favor with amateurs, while in combination with amplifying tubes it multiplies their power proportionately and it is in consequence used in one form or another in all the better sets. there are many different kinds of circuits which can be used to produce the regenerative amplification effect while the various kinds of tuning coils will serve for coupling them; for instance a two or three slide single tuning coil will answer the purpose but as it does not give good results it is not advisable to spend either time or money on it. a better scheme is to use a loose coupler formed of two or three honeycomb or other compact coils, while a _variocoupler_ or a _variometer_ or two will produce the maximum regenerative action. the simplest type of regenerative receiving set. with loose coupled tuning coil.--while this regenerative set is the simplest that will give anything like fair results it is here described not on account of its desirability, but because it will serve to give you the fundamental idea of how the _feed-back_ circuit is formed. for this set you need: (1) a _loose-coupled tuning coil_ such as described in chapter iii, (2) a _variable condenser_ of _.001 mfd._ (microfarad) capacitance; (3) one _fixed condenser_ of _.001 mfd._; (4) one _fixed condenser_ for the grid leak circuit of _.00025 mfd._; (5) a _grid leak_ of 1/2 to 2 megohms resistance; (6) a _vacuum tube detector_; (7) an _a 6 volt battery_; (8) a _rheostat_; (9) a _b 22 1/2 volt battery_; and (10) a pair of _2000 ohm head phones_. connecting up the parts.--begin by connecting the leading-in wire of the aerial with the binding post end of the primary coil of the loose coupler as shown in the wiring diagram fig. 48 and then connect the sliding contact with the water pipe or other ground. connect the binding post end of the primary coil with one post of the variable condenser, connect the other post of this with one of the posts of the _.00025 mfd._ condenser and the other end of this with the grid of the detector tube; then around this condenser shunt the grid leak resistance. [illustration: fig. 48.--simple regenerative receiving set. (with loose coupler tuner.)] next connect the sliding contact of the primary coil with the other post of the variable condenser and from this lead a wire on over to one of the terminals of the filament of the vacuum tube; to the other terminal of the filament connect one of the posts of the rheostat and connect the other post to the or negative electrode of the a battery and then connect the + or positive electrode of it to the other terminal of the filament. connect the + or positive electrode of the a battery with one post of the .001 mfd. fixed condenser and connect the other post of this to one of the ends of the secondary coil of the tuning coil and which is now known as the _tickler coil_; then connect the other end of the secondary, or tickler coil to the plate of the vacuum tube. in the wiring diagram the secondary, or tickler coil is shown above and in a line with the primary coil but this is only for the sake of making the connections clear; in reality the secondary, or tickler coil slides to and fro in the primary coil as shown and described in chapter iii. finally connect the _negative_, or zinc pole of the _b battery_ to one side of the fixed condenser, the _positive_, or carbon, pole to one of the terminals of the head phones and the other terminal of this to the other post of the fixed condenser when your regenerative set is complete. an efficient regenerative receiving set. with three coil loose coupler.--to construct a really good regenerative set you must use a loose coupled tuner that has three coils, namely a _primary_, a _secondary_ and a _tickler coil_. a tuner of this kind is made like an ordinary loose coupled tuning coil but it has a _third_ coil as shown at a and b in fig. 49. the middle coil, which is the _secondary_, is fixed to the base, and the large outside coil, which is the _primary_, is movable, that is it slides to and fro over the middle coil, while the small inside coil, which is the _tickler_, is also movable and can slide in or out of the middle _coil_. none of these coils is variable; all are wound to receive waves up to 360 meters in length when used with a variable condenser of _.001 mfd_. capacitance. in other words you slide the coils in and out to get the right amount of coupling and you tune by adjusting the variable condenser to get the exact wave length you want. [illustration: (a) fig. 49.--diagram of a three coil coupler.] [illustration: (b) fig. 49.--three coil loose coupler tuner.] with compact coils.--compact coil tuners are formed of three fixed inductances wound in flat coils, and these are pivoted in a mounting so that the distance between them and, therefore, the coupling, can be varied, as shown at a in fig. 50. these coils are wound up by the makers for various wave lengths ranging from a small one that will receive waves of any length up to 360 meters to a large one that has a maximum of 24,000 meters. for an amateur set get three of the smallest coils when you can not only hear amateur stations that send on a 200 meter wave but broadcasting stations that send on a 360 meter wave. [illustration: fig. 50.--honeycomb inductance coil.] these three coils are mounted with panel plugs which latter fit into a stand, or mounting, so that the middle coil is fixed, that is, stationary, while the two outside coils can be swung to and fro like a door; this scheme permits small variations of coupling to be had between the coils and this can be done either by handles or by means of knobs on a panel board. while i have suggested the use of the smallest size coils, you can get and use those wound for any wave length you want to receive and when those are connected with variometers and variable condensers, and with a proper aerial, you will have a highly efficient receptor that will work over all ranges of wave lengths. the smallest size coils cost about $1.50 apiece and the mounting costs about $6 or $7 each. the a battery potentiometer.--this device is simply a resistance like the rheostat described in connection with the preceding vacuum tube receiving sets but it is wound to 200 or 300 ohms resistance as against 1-1/2 to 6 ohms of the rheostat. it is, however, used as well as the rheostat. with a vacuum tube detector, and especially with one having a gas-content, a potentiometer is very necessary as it is only by means of it that the potential of the plate of the detector can be accurately regulated. the result of proper regulation is that when the critical potential value is reached there is a marked increase in the loudness of the sounds that are emitted by the head phones. as you will see from a in fig. 51 it has three taps. the two taps which are connected with the ends of the resistance coil are shunted around the a battery and the third tap, which is attached to the movable contact arm, is connected with the b battery tap, see b, at which this battery gives 18 volts. since the a battery gives 6 volts you can vary the potential of the plate from 18 to 24 volts. the potentiometer must never be shunted around the b battery or the latter will soon run down. a potentiometer costs a couple of dollars. [illustration: (a) fig. 51.--the use of the potentiometer.] the parts and how to connect them up.--for this regenerative set you will need: (1) a _honeycomb_ or other compact _three-coil tuner_, (2) two _variable_ (_.001_ and _.0005 mfd_.) _condensers_; (3) a _.00025 mfd. fixed condenser_; (4) a _1/2 to 2 megohm grid leak_; (5) a _tube detector_; (6) a _6 volt a battery_; (7) _a rheostat_; (8) a _potentiometer_; (9) an _18_ or _20 volt b battery_; (10) a _fixed condenser_ of _.001 mfd. fixed condenser_; and (11) a _pair of 2000 ohm head phones_. to wire up the parts connect the leading-in wire of the aerial with the primary coil, which is the middle one of the tuner, and connect the other terminal with the ground. connect the ends of the secondary coil, which is the middle one, with the posts of the variable condenser and connect one of the posts of the latter with one post of the fixed .00025 mfd. condenser and the other post of this with the grid; then shunt the grid leak around it. next connect the other post of the variable condenser to the or _negative_ electrode of the _a battery_; the + or _positive_ electrode of this to one terminal of the detector filament and the other end of the latter to the electrode of the a battery. now connect one end of the tickler coil with the detector plate and the other post to the fixed .001 mfd. condenser, then the other end of this to the positive or carbon pole of the b battery. this done shunt the potentiometer around the a battery and run a wire from the movable contact of it (the potentiometer) over to the 18 volt tap, (see b, fig. 51), of the b battery. finally, shunt the head phones and the .001 mfd. fixed condenser and you are ready to try out conclusions. a regenerative audio frequency amplifier receiving set.--the use of amateur regenerative cascade audio frequency receiving sets is getting to be quite common. to get the greatest amplification possible with amplifying tubes you have to keep a negative potential on the grids. you can, however, get very good results without any special charging arrangement by simply connecting one post of the rheostat with the negative terminal of the filament and connecting the _low potential_ end of the secondary of the tuning coil with the or negative electrode of the a battery. this scheme will give the grids a negative bias of about 1 volt. you do not need to bother about these added factors that make for high efficiency until after you have got your receiving set in working order and understand all about it. the parts and how to connect them up.--exactly the same parts are needed for this set as the one described above, but in addition you will want: (1) two more _rheostats_; (2) _two_ more sets of b 22-1/2 _volt batteries_; (3) _two amplifier tubes_, and (4) _two audio frequency transformers_ as described in chapter ix and pictured at a in fig. 46. to wire up the parts begin by connecting the leading-in wire to one end of the primary of the tuning coil and then connect the other end of the coil with the ground. a variable condenser of .001 mfd. capacitance can be connected in the ground wire, as shown in fig. 52, to good advantage although it is not absolutely needed. now connect one end of the secondary coil to one post of a _.001 mfd._ variable condenser and the other end of the secondary to the other post of the condenser. [illustration: fig. 52.--regenerative audio frequency amplifier receiving set.] next bring a lead (wire) from the first post of the variable condenser over to the post of the first fixed condenser and connect the other post of the latter with the grid of the detector tube. shunt 1/2 to 2 megohm grid leak resistance around the fixed condenser and then connect the second post of the variable condenser to one terminal of the detector tube filament. run this wire on over and connect it with the first post of the second rheostat, the second post of which is connected with one terminal of the filament of the first amplifying tube; then connect the first post of the rheostat with one end of the secondary coil of the first audio frequency transformer, and the other end of this coil with the grid of the first amplifier tube. connect the lead that runs from the second post of variable condenser to the first post of the third rheostat, the second post of which is connected with one terminal of the second amplifying tube; then connect the first post of the rheostat with one end of the secondary coil of the second audio frequency transformer and the other end of this coil with the grid of the second amplifier tube. this done connect the or negative electrode of the a battery with the second post of the variable condenser and connect the + or positive electrode with the free post of the first rheostat, the other post of which connects with the free terminal of the filament of the detector. from this lead tap off a wire and connect it to the free terminal of the filament of the first amplifier tube, and finally connect the end of the lead with the free terminal of the filament of the second amplifier tube. next shunt a potentiometer around the a battery and connect the third post, which connects with the sliding contact, to the negative or zinc pole of a b battery, then connect the positive or carbon pole of it to the negative or zinc pole of a second b battery and the positive or carbon pole of the latter with one end of the primary coil of the second audio frequency transformer and the other end of it to the plate of the first amplifying tube. run the lead on over and connect it to one of the terminals of the second fixed condenser and the other terminal of this with the plate of the second amplifying tube. then shunt the headphones around the condenser. finally connect one end of the tickler coil of the tuner with the plate of the detector tube and connect the other end of the tickler to one end of the primary coil of the first audio frequency transformer and the other end of it to the wire that connects the two b batteries together. chapter xi short wave regenerative receiving sets a _short wave receiving set_ is one that will receive a range of wave lengths of from 150 to 600 meters while the distance over which the waves can be received as well as the intensity of the sounds reproduced by the headphones depends on: (1) whether it is a regenerative set and (2) whether it is provided with amplifying tubes. high-grade regenerative sets designed especially for receiving amateur sending stations that must use a short wave length are built on the regenerative principle just like those described in the last chapter and further amplification can be had by the use of amplifier tubes as explained in chapter ix, but the new feature of these sets is the use of the _variocoupler_ and one or more _variometers_. these tuning devices can be connected up in different ways and are very popular with amateurs at the present time. differing from the ordinary loose coupler the variometer has no movable contacts while the variometer is provided with taps so that you can connect it up for the wave length you want to receive. all you have to do is to tune the oscillation circuits to each other is to turn the _rotor_, which is the secondary coil, around in the _stator_, as the primary coil is called in order to get a very fine variation of the wave length. it is this construction that makes _sharp tuning_ with these sets possible, by which is meant that all wave lengths are tuned out except the one which the receiving set is tuned for. a short wave regenerative receiver--with one variometer and three variable condensers.--this set also includes a variocoupler and a _grid coil_. the way that the parts are connected together makes it a simple and at the same time a very efficient regenerative receiver for short waves. while this set can be used without shielding the parts from each other the best results are had when shields are used. the parts you need for this set include: (1) one _variocoupler_; (2) one _.001 microfarad variable condenser_; (3) one _.0005 microfarad variable condenser_; (4) one _.0007 microfarad variable condenser_; (5) _one 2 megohm grid leak_; (6) one _vacuum tube detector_; (7) one _6 volt a battery_; (8) one _6 ohm_, 1-1/2 _ampere rheostat_; (9) one _200 ohm potentiometer_; (10) one 22-1/2 _volt b battery_; (11) one _.001 microfarad fixed condenser_, (12) one pair of _2,000 ohm headphones_, and (13) a _variometer_. the variocoupler.--a variocoupler consists of a primary coil wound on the outside of a tube of insulating material and to certain turns of this taps are connected so that you can fix the wave length which your aerial system is to receive from the shortest wave; i.e., 150 meters on up by steps to the longest wave, i.e., 600 meters, which is the range of most amateur variocouplers that are sold in the open market. this is the part of the variocoupler that is called the _stator_. the secondary coil is wound on the section of a ball mounted on a shaft and this is swung in bearings on the stator so that it can turn in it. this part of the variocoupler is called the _rotor_ and is arranged so that it can be mounted on a panel and adjusted by means of a knob or a dial. a diagram of a variocoupler is shown at a in fig. 53, and the coupler itself at b. there are various makes and modifications of variocouplers on the market but all of them are about the same price which is $6.00 or $8.00. [illustration: fig. 53.--how the variocoupler is made and works.] the variometer.--this device is quite like the variocoupler, but with these differences: (1) the rotor turns in the stator, which is also the section of a ball, and (2) one end of the primary is connected with one end of the secondary coil. to be really efficient a variometer must have a small resistance and a large inductance as well as a small dielectric loss. to secure the first two of these factors the wire should be formed of a number of fine, pure copper wires each of which is insulated and the whole strand then covered with silk. this kind of wire is the best that has yet been devised for the purpose and is sold under the trade name of _litzendraht_. a new type of variometer has what is known as a _basket weave_, or _wavy wound_ stator and rotor. there is no wood, insulating compound or other dielectric materials in large enough quantities to absorb the weak currents that flow between them, hence weaker sounds can be heard when this kind of a variometer is used. with it you can tune sharply to waves under 200 meters in length and up to and including wave lengths of 360 meters. when amateur stations of small power are sending on these short waves this style of variometer keeps the electric oscillations at their greatest strength and, hence, the reproduced sounds will be of maximum intensity. a wiring diagram of a variometer is shown at a in fig. 54 and a _basketball_ variometer is shown complete at b. [illustration: fig. 54.--how the variometer is made and works.] connecting up the parts.--to hook-up the set connect the leading-in wire to one end of the primary coil, or stator, of the variocoupler and solder a wire to one of the taps that gives the longest wave length you want to receive. connect the other end of this wire with one post of a .001 microfarad variable condenser and connect the other post with the ground as shown in fig. 55. now connect one end of the secondary coil, or rotor, to one post of a .0007 mfd. variable condenser, the other post of this to one end of the grid coil and the other end of this with the remaining end of the rotor of the variocoupler. [illustration: fig. 55.--short wave regenerative receiving set (one variometer and three variable condensers.)] next connect one post of the .0007 mfd. condenser with one of the terminals of the detector filament; then connect the other post of this condenser with one post of the .0005 mfd. variable condenser and the other post of this with the grid of the detector, then shunt the megohm grid leak around the latter condenser. this done connect the other terminal of the filament to one post of the rheostat, the other post of this to the or negative electrode of the 6 volt a battery and the + or positive electrode of the latter to the other terminal of the filament. shunt the potentiometer around the a battery and connect the sliding contact with the or zinc pole of the b battery and the + or carbon pole with one terminal of the headphone; connect the other terminal to one of the posts of the variometer and the other post of the variometer to the plate of the detector. finally shunt a .001 mfd. fixed condenser around the headphones. if you want to amplify the current with a vacuum tube amplifier connect in the terminals of the amplifier circuit shown at a in figs. 44 or 45 at the point where they are connected with the secondary coil of the loose coupled tuning coil, in those diagrams with the binding posts of fig. 55 where the phones are usually connected in. short wave regenerative receiver. with two variometers and two variable condensers.--this type of regenerative receptor is very popular with amateurs who are using high-grade short-wave sets. when you connect up this receptor you must keep the various parts well separated. screw the variocoupler to the middle of the base board or panel, and secure the variometers on either side of it so that the distance between them will be 9 or 10 inches. by so placing them the coupling will be the same on both sides and besides you can shield them from each other easier. for the shield use a sheet of copper on the back of the panel and place a sheet of copper between the parts, or better, enclose the variometers and detector and amplifying tubes if you use the latter in sheet copper boxes. when you set up the variometers place them so that their stators are at right angles to each other for otherwise the magnetic lines of force set up by the coils of each one will be mutually inductive and this will make the headphones or loud speaker _howl_. whatever tendency the receptor has to howl with this arrangement can be overcome by putting in a grid leak of the right resistance and adjusting the condenser. the parts and how to connect them up.--for this set you require: (1) one _variocoupler_; (2) two _variometers_; (3) one _.001 microfarad variable condenser_; (4) one _.0005 microfarad variable condenser_; (5) one _2 megohm grid leak resistance_; (6) one _vacuum tube detector_; (7) one _6 volt a battery_; (8) one _200 ohm potentiometer_; (9) one _22-1/2 volt b battery_; (10) one _.001 microfarad fixed condenser_, and (11) one pair of _2,000 ohm headphones_. to wire up the set begin by connecting the leading-in wire to the fixed end of the primary coil, or _stator_, of the variocoupler, as shown in fig. 56, and connect one post of the .001 mfd. variable condenser to the stator by soldering a short length of wire to the tap of the latter that gives the longest wave you want to receive. now connect one end of the secondary coil, or _rotor_, of the variocoupler with one post of the .0005 mfd. variable condenser and the other part to the grid of the detector tube. connect the other end of the rotor of the variocoupler to one of the posts of the first variometer and the other post of this to one of the terminals of the detector filament. [illustration: fig. 56.--short wave regenerative receiving set (two variometers and two variable condensers.)] connect this filament terminal with the or negative electrode of the a battery and the + or positive electrode of this with one post of the rheostat and lead a wire from the other post to the free terminal of the filament. this done shunt the potential around the a battery and connect the sliding contact to the or zinc pole of the b battery and the + or carbon pole of this to one terminal of the headphones, while the other terminal of this leads to one of the posts of the second variometer, the other post of which is connected to the plate of the detector tube. if you want to add an amplifier tube then connect it to the posts instead of the headphones as described in the foregoing set. chapter xii intermediate and long wave regenerative receiving sets all receiving sets that receive over a range of wave lengths of from 150 meters to 3,000 meters are called _intermediate wave sets_ and all sets that receive wave lengths over a range of anything more than 3,000 meters are called _long wave sets_. the range of intermediate wave receptors is such that they will receive amateur, broadcasting, ship and shore navy, commercial, arlington's time and all other stations using _spark telegraph damped waves_ or _arc_ or _vacuum tube telephone continuous waves_ but not _continuous wave telegraph signals_, unless these have been broken up into groups at the transmitting station. to receive continuous wave telegraph signals requires receiving sets of special kind and these will be described in the next chapter. intermediate wave receiving sets.--there are two chief schemes employed to increase the range of wave lengths that a set can receive and these are by using: (1) _loading coils_ and _shunt condensers_, and (2) _bank-wound coils_ and _variable condensers_. if you have a short-wave set and plan to receive intermediate waves with it then loading coils and fixed condensers shunted around them affords you the way to do it, but if you prefer to buy a new receptor then the better way is to get one with bank-wound coils and variable condensers; this latter way preserves the electrical balance of the oscillation circuits better, the electrical losses are less and the tuning easier and sharper. intermediate wave set with loading coils.--for this intermediate wave set you can use either of the short-wave sets described in the foregoing chapter. for the loading coils use _honeycomb coils_, or other good compact inductance coils, as shown in chapter x and having a range of whatever wave length you wish to receive. the following table shows the range of wave length of the various sized coils when used with a variable condenser having a .001 microfarad _capacitance_, the approximate _inductance_ of each coil in _millihenries_ and prices at the present writing: table of characteristics of honeycomb coils approximate wave length in meters in millihenries inductance .001 mfd. variable mounted appx. air condenser. on plug .040 130- 375 $1.40 .075 180- 515 1.40 .15 240- 730 1.50 .3 330-1030 1.50 .6 450-1460 1.55 1.3 660-2200 1.60 2.3 930-2850 1.65 4.5 1300-4000 1.70 6.5 1550-4800 1.75 11. 2050-6300 1.80 20. 3000-8500 2.00 40. 4000--12000 2.15 65. 5000--15000 2.35 100. 6200--19000 2.60 125. 7000--21000 3.00 175. 8200--24000 3.50 these and other kinds of compact coils can be bought at electrical supply houses that sell wireless goods. if your aerial is not very high or long you can use loading coils, but to get anything like efficient results with them you must have an aerial of large capacitance and the only way to get this is to put up a high and long one with two or more parallel wires spaced a goodly distance apart. the parts and how to connect them up.--get (1) _two honeycomb or other coils_ of the greatest wave length you want to receive, for in order to properly balance the aerial, or primary oscillation circuit, and the closed, or secondary oscillation circuit, you have to tune them to the same wave length; (2) two _.001 mfd. variable condensers_, though fixed condensers will do, and (3) two small _single-throw double-pole knife switches_ mounted on porcelain bases. to use the loading coils all you have to do is to connect one of them in the aerial above the primary coil of the loose coupler, or variocoupler as shown in the wiring diagram in fig. 57, then shunt one of the condensers around it and connect one of the switches around this; this switch enables you to cut in or out the loading coil at will. likewise connect the other loading coil in one side of the closed, or secondary circuit between the variable .0007 mfd. condenser and the secondary coil of the loose coupler or variocoupler as shown in fig. 53. the other connections are exactly the same as shown in figs. 44 and 45. [illustration: fig. 57.--wiring diagram showing fixed loading coils for intermediate wave set.] an intermediate wave set with variocoupler inductance coils.--by using the coil wound on the rotor of the variocoupler as the tickler the coupling between the detector tube circuits and the aerial wire system increases as the set is tuned for greater wave lengths. this scheme makes the control of the regenerative circuit far more stable than it is where an ordinary loose coupled tuning coil is used. when the variocoupler is adjusted for receiving very long waves the rotor sets at right angles to the stator and, since when it is in this position there is no mutual induction between them, the tickler coil serves as a loading coil for the detector plate oscillation circuit. inductance coils for short wave lengths are usually wound in single layers but _bank-wound coils_, as they are called are necessary to get compactness where long wave lengths are to be received. by winding inductance coils with two or more layers the highest inductance values can be obtained with the least resistance. a wiring diagram of a multipoint inductance coil is shown in fig. 58. you can buy this intermediate wave set assembled and ready to use or get the parts and connect them up yourself. [illustration: fig. 58.--wiring diagram for intermediate wave receptor with one variocoupler and 12 section bank-wound inductance coil.] the parts and how to connect them up.--for this regenerative intermediate wave set get: (1) one _12 section triple bank-wound inductance coil_, (2) one _variometer_, and (3) all the other parts shown in the diagram fig. 58 except the variocoupler. first connect the free end of the condenser in the aerial to one of the terminals of the stator of the variocoupler; then connect the other terminal of the stator with one of the ends of the bank-wound inductance coil and connect the movable contact of this with the ground. next connect a wire to the aerial between the variable condenser and the stator and connect this to one post of a .0005 microfarad fixed condenser, then connect the other post of this with the grid of the detector and shunt a 2 megohm grid leak around it. connect a wire to the ground wire between the bank-wound inductance coil and the ground proper, i.e., the radiator or water pipe, connect the other end of this to the + electrode of the a battery and connect this end also to one of the terminals of the filament. this done connect the other terminal of the filament to one post of the rheostat and the other post of this to the or negative side of the a battery. to the + electrode of the a battery connect the or zinc pole of the b battery and connect the + or carbon pole of the latter with one post of the fixed .001 microfarad condenser. this done connect one terminal of the tickler coil which is on the rotor of the variometer to the plate of the detector and the other terminal of the tickler to the other post of the .001 condenser and around this shunt your headphones. or if you want to use one or more amplifying tubes connect the circuit of the first one, see fig. 45, to the posts on either side of the fixed condenser instead of the headphones. a long wave receiving set.--the vivid imagination of jules verne never conceived anything so fascinating as the reception of messages without wires sent out by stations half way round the world; and in these days of high power cableless stations on the five continents you can listen-in to the messages and hear what is being sent out by the lyons, paris and other french stations, by great britain, italy, germany and even far off russia and japan. a long wave set for receiving these stations must be able to tune to wave lengths up to 20,000 meters. differing from the way in which the regenerative action of the short wave sets described in the preceding chapter is secured and which depends on a tickler coil and the coupling action of the detector in this long wave set, [footnote: all of the short wave and intermediate wave receivers described, are connected up according to the wiring diagram used by the a. h. grebe company, richmond hill, long island, n. y.] this action is obtained by the use of a tickler coil in the plate circuit which is inductively coupled to the grid circuit and this feeds back the necessary amount of current. this is a very good way to connect up the circuits for the reason that: (1) the wiring is simplified, and (2) it gives a single variable adjustment for the entire range of wave lengths the receptor is intended to cover. the parts and how to connect them up.--the two chief features as far as the parts are concerned of this long wave length receiving set are (1) the _variable condensers_, and (2) the _tuning inductance coils_. the variable condenser used in series with the aerial wire system has 26 plates and is equal to a capacitance of _.0008 mfd._ which is the normal aerial capacitance. the condenser used in the secondary coil circuit has 14 plates and this is equal to a capacitance of _.0004 mfd_. there are a number of inductance coils and these are arranged so that they can be connected in or cut out and combinations are thus formed which give a high efficiency and yet allow them to be compactly mounted. the inductance coils of the aerial wire system and those of the secondary coil circuit are practically alike. for wave lengths up to 2,200 meters _bank litz-wound coils_ are used and these are wound up in 2, 4 and 6 banks in order to give the proper degree of coupling and inductance values. where wave lengths of more than 2,200 meters are to be received _coto-coils_ are used as these are the "last word" in inductance coil design, and are especially adapted for medium as well as long wave lengths. [footnote: can be had of the coto coil co., providence, r. i.] these various coils are cut in and out by means of two five-point switches which are provided with auxiliary levers and contactors for _dead-ending_ the right amount of the coils. in cutting in coils for increased wave lengths, that is from 10,000 to 20,000 meters, all of the coils of the aerial are connected in series as well as all of the coils of the secondary circuit. the connections for a long wave receptor are shown in the wiring diagram in fig. 59. [illustration: fig. 59.--wiring diagram showing long wave receptor with variocouplers and bank-wound inductance coils] chapter xiii heterodyne or beat long wave telegraph receiving set any of the receiving sets described in the foregoing chapters will respond to either: (1) a wireless telegraph transmitter that uses a spark gap and which sends out periodic electric waves, or to (2) a wireless telephone transmitter that uses an arc or a vacuum tube oscillator and which sends out continuous electric waves. to receive wireless _telegraph_ signals, however, from a transmitter that uses an arc or a vacuum tube oscillator and which sends out continuous waves, either the transmitter or the receptor must be so constructed that the continuous waves will be broken up into groups of audio frequency and this is done in several different ways. there are four different ways employed at the present time to break up the continuous waves of a wireless telegraph transmitter into groups and these are: (_a_) the _heterodyne_, or _beat_, method, in which waves of different lengths are impressed on the received waves and so produces beats; (_b_) the _tikker_, or _chopper_ method, in which the high frequency currents are rapidly broken up; (_c_) the variable condenser method, in which the movable plates are made to rapidly rotate; (_d_) the _tone wheel_, or _frequency transformer_, as it is often called, and which is really a modified form of and an improvement on the tikker. the heterodyne method will be described in this chapter. what the heterodyne or beat method is.--the word _heterodyne_ was coined from the greek words _heteros_ which means _other_, or _different_, and _dyne_ which means _power_; in other words it means when used in connection with a wireless receptor that another and different high frequency current is used besides the one that is received from the sending station. in music a _beat_ means a regularly recurrent swelling caused by the reinforcement of a sound and this is set up by the interference of sound waves which have slightly different periods of vibration as, for instance, when two tones take place that are not quite in tune with each other. this, then, is the principle of the heterodyne, or beat, receptor. in the heterodyne, or beat method, separate sustained oscillations, that are just about as strong as those of the incoming waves, are set up in the receiving circuits and their frequency is just a little higher or a little lower than those that are set up by the waves received from the distant transmitter. the result is that these oscillations of different frequencies interfere and reinforce each other when _beats_ are produced, the period of which is slow enough to be heard in the headphones, hence the incoming signals can be heard only when waves from the sending station are being received. a fuller explanation of how this is done will be found in chapter xv. the autodyne or self-heterodyne long-wave receiving set.--this is the simplest type of heterodyne receptor and it will receive periodic waves from spark telegraph transmitters or continuous waves from an arc or vacuum tube telegraph transmitter. in this type of receptor the detector tube itself is made to set up the _heterodyne oscillations_ which interfere with those that are produced by the incoming waves that are a little out of tune with it. with a long wave _autodyne_, or _self-heterodyne_ receptor, as this type is called, and a two-step audio-frequency amplifier you can clearly hear many of the cableless stations of europe and others that send out long waves. for receiving long wave stations, however, you must have a long aerial--a single wire 200 or more feet in length will do--and the higher it is the louder will be the signals. where it is not possible to put the aerial up a hundred feet or more above the ground, you can use a lower one and still get messages in _international morse_ fairly strong. the parts and connections of an autodyne, or self-heterodyne, receiving set.--for this long wave receiving set you will need: (1) one _variocoupler_ with the primary coil wound on the stator and the secondary coil and tickler coil wound on the rotor, or you can use three honeycomb or other good compact coils of the longest wave you want to receive, a table of which is given in chapter xii; (2) two _.001 mfd. variable condensers_; (3) one _.0005 mfd. variable condenser_; (4) one _.5 to 2 megohm grid leak resistance_; (5) one _vacuum tube detector_; (6) one _a battery_; (7) one _rheostat_; (8) one _b battery_; (9) one _potentiometer_; (10) one _.001 mfd. fixed condenser_ and (11) one pair of _headphones_. for the two-step amplifier you must, of course, have besides the above parts the amplifier tubes, variable condensers, batteries rheostats, potentiometers and fixed condensers as explained in chapter ix. the connections for the autodyne, or self-heterodyne, receiving set are shown in fig. 60. [illustration: fig. 60.--wiring diagram of long wave antodyne, or self-heterodyne receptor.] the separate heterodyne long wave receiving set.--this is a better long wave receptor than the self heterodyne set described above for receiving wireless telegraph signals sent out by a continuous long wave transmitter. the great advantage of using a separate vacuum tube to generate the heterodyne oscillations is that you can make the frequency of the oscillations just what you want it to be and hence you can make it a little higher or a little lower than the oscillations set up by the received waves. the parts and connections of a separate heterodyne long wave receiving set.--the parts required for this long wave receiving set are: (1) four honeycomb or other good _compact inductance_ coils of the longest wave length that you want to receive; (2) three _.001 mfd. variable condensers_; (3) one _.0005 mfd. variable condenser_; (4) one _1 megohm grid leak resistance_; (5) one _vacuum tube detector_; (6) one _a battery_; (7) two rheostats; (8) two _b batteries_, one of which is supplied with taps; (9) one _potentiometer_; (10) one _vacuum tube amplifier_, for setting up the heterodyne oscillations; (11) a pair of _headphones_ and (12) all of the parts for a _two-step amplifier_ as detailed in chapter ix, that is if you are going to use amplifiers. the connections are shown in fig. 61. [illustration: fig. 61.--wiring diagram of long wave separate heterodyne receiving set.] in using either of these heterodyne receivers be sure to carefully adjust the b battery by means of the potentiometer. [footnote: the amplifier tube in this case is used as a generator of oscillations.] chapter xiv headphones and loud speakers wireless headphones.--a telephone receiver for a wireless receiving set is made exactly on the same principle as an ordinary bell telephone receiver. the only difference between them is that the former is made flat and compact so that a pair of them can be fastened together with a band and worn on the head (when it is called a _headset_), while the latter is long and cylindrical so that it can be held to the ear. a further difference between them is that the wireless headphone is made as sensitive as possible so that it will respond to very feeble currents, while the ordinary telephone receiver is far from being sensitive and will respond only to comparatively large currents. how a bell telephone receiver is made.--an ordinary telephone receiver consists of three chief parts and these are: (1) a hard-rubber, or composition, shell and cap, (2) a permanent steel bar magnet on one end of which is wound a coil of fine insulated copper wire, and (3) a soft iron disk, or _diaphragm_, all of which are shown in the cross-section in fig. 62. the bar magnet is securely fixed inside of the handle so that the outside end comes to within about 1/32 of an inch of the diaphragm when this is laid on top of the shell and the cap is screwed on. [illustration: fig. 62.--cross-section of bell telephone receiver.] [illustration: original â© underwood and underwood. alexander graham bell, inventor of the telephone, now an ardent radio enthusiast.] the ends of the coil of wire are connected with two binding posts which are in the end of the shell, but are shown in the picture at the sides for the sake of clearness. this coil usually has a resistance of about 75 ohms and the meaning of the _ohmic resistance_ of a receiver and its bearing on the sensitiveness of it will be explained a little farther along. after the disk, or diaphragm, which is generally made of thin, soft sheet iron that has been tinned or japanned, [footnote: a disk of photographic tin-type plate is generally used.] is placed over the end of the magnet, the cap, which has a small opening in it, is screwed on and the receiver is ready to use. how a wireless headphone is made.--for wireless work a receiver of the watch-case type is used and nearly always two such receivers are connected with a headband. it consists of a permanent bar magnet bent so that it will fit into the shell of the receiver as shown at a in fig. 63. [illustration: fig. 63.--wireless headphone.] the ends of this magnet, which are called _poles_, are bent up, and hence this type is called a _bipolar_ receiver. the magnets are wound with fine insulated wire as before and the diaphragm is held securely in place over them by screwing on the cap. about resistance, turns of wire and sensitivity of headphones.--if you are a beginner in wireless you will hear those who are experienced speak of a telephone receiver as having a resistance of 75 ohms, 1,000 ohms, 2,000 or 3,000 ohms, as the case may be; from this you will gather that the higher the resistance of the wire on the magnets the more sensitive the receiver is. in a sense this is true, but it is not the resistance of the magnet coils that makes it sensitive, in fact, it cuts down the current, but it is the _number of turns_ of wire on them that determines its sensitiveness; it is easy to see that this is so, for the larger the number of turns the more often will the same current flow round the cores of the magnet and so magnetize them to a greater extent. but to wind a large number of turns of wire close enough to the cores to be effective the wire must be very small and so, of course, the higher the resistance will be. now the wire used for winding good receivers is usually no. 40, and this has a diameter of .0031 inch; consequently, when you know the ohmic resistance you get an idea of the number of turns of wire and from this you gather in a general way what the sensitivity of the receiver is. a receiver that is sensitive enough for wireless work should be wound to not less than 1,000 ohms (this means each ear phone), while those of a better grade are wound to as high as 3,000 ohms for each one. a high-grade headset is shown in fig. 64. each phone of a headset should be wound to the same resistance, and these are connected in series as shown. where two or more headsets are used with one wireless receiving set they must all be of the same resistance and connected in series, that is, the coils of one head set are connected with the coils of the next head set and so on to form a continuous circuit. [illustration: fig. 64.--wireless headphone.] the impedance of headphones.--when a current is flowing through a circuit the material of which the wire is made not only opposes its passage--this is called its _ohmic resistance_--but a _counter-electromotive force_ to the current is set up due to the inductive effects of the current on itself and this is called _impedance_. where a wire is wound in a coil the impedance of the circuit is increased and where an alternating current is used the impedance grows greater as the frequency gets higher. the impedance of the magnet coils of a receiver is so great for high frequency oscillations that the latter cannot pass through them; in other words, they are choked off. how the headphones work.--as you will see from the cross-sections in figs. 62 and 63 there is no connection, electrical or mechanical, between the diaphragm and the other parts of the receiver. now when either feeble oscillations, which have been rectified by a detector, or small currents from a b battery, flow through the magnet coils the permanent steel magnet is energized to a greater extent than when no current is flowing through it. this added magnetic energy makes the magnet attract the diaphragm more than it would do by its own force. if, on the other hand, the current is cut off the pull of the magnet is lessened and as its attraction for the diaphragm is decreased the latter springs back to its original position. when varying currents flow through the coils the diaphragm vibrates accordingly and sends out sound waves. about loud speakers.--the simplest acoustic instrument ever invented is the _megaphone_, which latter is a greek word meaning _great sound_. it is a very primitive device and our indians made it out of birch-bark before columbus discovered america. in its simplest form it consists of a cone-shaped horn and as the speaker talks into the small end the concentrated sound waves pass out of the large end in whatever direction it is held. now a loud speaker of whatever kind consists of two chief parts and these are: (1) a _telephone receiver_, and (2) a _megaphone_, or _horn_ as it is called. a loud speaker when connected with a wireless receiving set makes it possible for a room, or an auditorium, full of people, or an outdoor crowd, to hear what is being sent out by a distant station instead of being limited to a few persons listening-in with headphones. to use a loud speaker you should have a vacuum tube detector receiving set and this must be provided with a one-step amplifier at least. to get really good results you need a two-step amplifier and then energize the plate of the second vacuum tube amplifier with a 100 volt b battery; or if you have a three-step amplifier then use the high voltage on the plate of the third amplifier tube. amplifying tubes are made to stand a plate potential of 100 volts and this is the kind you must use. now it may seem curious, but when the current flows through the coils of the telephone receiver in one direction it gives better results than when it flows through in the other direction; to find out the way the current gives the best results try it out both ways and this you can do by simply reversing the connections. the simplest type of loud speaker.--this loud speaker, which is called, the arkay, [footnote: made by the riley-klotz mfg. co., newark, n. j.] will work on a oneor two-step amplifier. it consists of a brass horn with a curve in it and in the bottom there is an adapter, or frame, with a set screw in it so that you can fit in one of your headphones and this is all there is to it. the construction is rigid enough to prevent overtones, or distortion of speech or music. it is shown in fig. 65. [illustration: fig. 65.--arkay loud speaker.] another simple kind of loud speaker.--another loud speaker, see fig. 66, is known as the _amplitone_ [footnote: made by the american pattern, foundry and machine co., 82 church street, n. y. c.] and it likewise makes use of the headphones as the sound producer. this device has a cast metal horn which improves the quality of the sound, and all you have to do is to slip the headphones on the inlet tubes of the horn and it is ready for use. the two headphones not only give a longer volume of sound than where a single one is used but there is a certain blended quality which results from one phone smoothing out the imperfections of the other. [illustration: fig. 66.--amplitone loud speaker.] a third kind of simple loud speaker.--the operation of the _amplitron_, [footnote: made by the radio service co., 110 w. 40th street, n. y.] as this loud speaker is called, is slightly different from others used for the same purpose. the sounds set up by the headphone are conveyed to the apex of an inverted copper cone which is 7 inches long and 10 inches in diameter. here it is reflected by a parabolic mirror which greatly amplifies the sounds. the amplification takes place without distortion, the sounds remaining as clear and crisp as when projected by the transmitting station. by removing the cap from the receiver the shell is screwed into a receptacle on the end of the loud speaker and the instrument is ready for use. it is pictured in fig. 67. [illustration: fig. 67.--amplitron loud speaker.] a super loud speaker.--this loud speaker, which is known as the _magnavox telemegafone_, was the instrument used by lt. herbert e. metcalf, 3,000 feet in the air, and which startled the city of washington on april 2, 1919, by repeating president wilson's _victory loan message_ from an airplane in flight so that it was distinctly heard by 20,000 people below. this wonderful achievement was accomplished through the installation of the _magnavox_ and amplifiers in front of the treasury building. every word lt. metcalf spoke into his wireless telephone transmitter was caught and swelled in volume by the _telemegafones_ below and persons blocks away could hear the message plainly. two kinds of these loud speakers are made and these are: (1) a small loud speaker for the use of operators so that headphones need not be worn, and (2) a large loud speaker for auditorium and out-door audiences. [illustration: original â© underwood and underwood. world's largest loud speaker ever made. installed in lytle park, cincinnati, ohio, to permit president harding's address at point pleasant, ohio, during the grant centenary celebration to be heard within a radius of one square.] either kind may be used with a oneor two-step amplifier or with a cascade of half a dozen amplifiers, according to the degree of loudness desired. the _telemegafone_ itself is not an amplifier in the true sense inasmuch as it contains no elements which will locally increase the incoming current. it does, however, transform the variable electric currents of the wireless receiving set into sound vibrations in a most wonderful manner. a _telemegafone_ of either kind is formed of: (1) a telephone receiver of large proportions, (2) a step-down induction coil, and (3) a 6 volt storage battery that energizes a powerful electromagnet which works the diaphragm. an electromagnet is used instead of a permanent magnet and this is energized by a 6-volt storage battery as shown in the wiring diagram at a in fig. 68. one end of the core of this magnet is fixed to the iron case of the speaker and together these form the equivalent of a horseshoe magnet. a movable coil of wire is supported from the center of the diaphragm the edge of which is rigidly held between the case and the small end of the horn. this coil is placed over the upper end of the magnet and its terminals are connected to the secondary of the induction coil. now when the coil is energized by the current from the amplifiers it and the core act like a solenoid in that the coil tends to suck the core into it; but since the core is fixed and the coil is movable the core draws the coil down instead. the result is that with every variation of the current that flows through the coil it moves up and down and pulls and pushes the diaphragm down and up with it. the large amplitude of the vibrations of the latter set up powerful sound waves which can be heard several blocks away from the horn. in this way then are the faint incoming signals, speech and music which are received by the amplifying receiving set reproduced and magnified enormously. the _telemegafone_ is shown complete at b. [illustration: fig. 68.--magnavox loud speaker.] chapter xv operation of vacuum tube receptors from the foregoing chapters you have seen that the vacuum tube can be used either as a _detector_ or an _amplifier_ or as a _generator_ of electric oscillations, as in the case of the heterodyne receiving set. to understand how a vacuum tube acts as a detector and as an amplifier you must first know what _electrons_ are. the way in which the vacuum tube sets up sustained oscillations will be explained in chapter xviii in connection with the _operation of vacuum tube transmitters_. what electrons are.--science teaches us that masses of matter are made up of _molecules_, that each of these is made up of _atoms_, and each of these, in turn, is made up of a central core of positive particles of electricity surrounded by negative particles of electricity as shown in the schematic diagram, fig. 69. the little black circles inside the large circle represent _positive particles of electricity_ and the little white circles outside of the large circle represent _negative particles of electricity_, or _electrons_ as they are called. [illustration: fig. 69.--schematic diagram of an atom.] it is the number of positive particles of electricity an atom has that determines the kind of an element that is formed when enough atoms of the same kind are joined together to build it up. thus hydrogen, which is the lightest known element, has one positive particle for its nucleus, while uranium, the heaviest element now known, has 92 positive particles. now before leaving the atom please note that it is as much smaller than the diagram as the latter is smaller than our solar system. what is meant by ionization.--a hydrogen atom is not only lighter but it is smaller than the atom of any other element while an electron is more than a thousand times smaller than the atom of which it is a part. now as long as all of the electrons remain attached to the surface of an atom its positive and negative charges are equalized and it will, therefore, be neither positive nor negative, that is, it will be perfectly neutral. when, however, one or more of its electrons are separated from it, and there are several ways by which this can be done, the atom will show a positive charge and it is then called a _positive ion_. in other words a _positive ion_ is an atom that has lost some of its negative electrons while a _negative ion_ is one that has acquired some additional negative _electrons_. when a number of electrons are being constantly given by the atoms of an element, which let us suppose is a metal, and are being attracted to atoms of another element, which we will say is also a metal, a flow of electrons takes place between the two oppositely charged elements and form a current of negative electricity as represented by the arrows at a in fig. 70. [illustration: fig. 70.--action of two-electrode vacuum tube.] when a stream of electrons is flowing between two metal elements, as a filament and a plate in a vacuum tube detector, or an amplifier, they act as _carriers_ for more negative electrons and these are supplied by a battery as we shall presently explain. it has always been customary for us to think of a current of electricity as flowing from the positive pole of a battery to the negative pole of it and hence we have called this the _direction of the current_. since the electronic theory has been evolved it has been shown that the electrons, or negative charges of electricity, flow from the negative to the positive pole and that the ionized atoms, which are more positive than negative, flow in the opposite direction as shown at b. how electrons are separated from atoms.--the next question that arises is how to make a metal throw off some of the electrons of the atoms of which it is formed. there are several ways that this can be done but in any event each atom must be given a good, hard blow. a simple way to do this is to heat a metal to incandescence when the atoms will bombard each other with terrific force and many of the electrons will be knocked off and thrown out into the surrounding space. but all, or nearly all, of them will return to the atoms from whence they came unless a means of some kind is employed to attract them to the atoms of some other element. this can be done by giving the latter piece of metal a positive charge. if now these two pieces of metal are placed in a bulb from which the air has been exhausted and the first piece of metal is heated to brilliancy while the second piece of metal is kept positively electrified then a stream of electrons will flow between them. action of the two electrode vacuum tube.--now in a vacuum tube detector a wire filament, like that of an incandescent lamp, is connected with a battery and this forms the hot element from which the electrons are thrown off, and a metal plate with a terminal wire secured to it is connected to the positive or carbon tap of a dry battery; now connect the negative or zinc tap of this with one end of a telephone receiver and the other end of this with the terminals of the filament as shown at a in fig. 71. if now you heat the filament and hold the phone to your ear you can hear the current from the b battery flowing through the circuit. [illustration: (a) and (b) fig. 71.--how a two electrode tube acts as a relay or a detector.] [illustration: (c) fig. 71.--only the positive part of oscillations goes through the tube.] since the electrons are negative charges of electricity they are not only thrown off by the hot wire but they are attracted by the positive charged metal plate and when enough electrons pass, or flow, from the hot wire to the plate they form a conducting path and so complete the circuit which includes the filament, the plate and the b or plate battery, when the current can then flow through it. as the number of electrons that are thrown off by the filament is not great and the voltage of the plate is not high the current that flows between the filament and the plate is always quite small. how the two electrode tube acts as a detector.--as the action of a two electrode tube as a detector [footnote: the three electrode vacuum tube has entirely taken the place of the two electrode type.] is simpler than that of the three electrode vacuum tube we shall describe it first. the two electrode vacuum tube was first made by mr. edison when he was working on the incandescent lamp but that it would serve as a detector of electric waves was discovered by prof. fleming, of oxford university, london. as a matter of fact, it is not really a detector of electric waves, but it acts as: (1) a _rectifier_ of the oscillations that are set up in the receiving circuits, that is, it changes them into pulsating direct currents so that they will flow through and affect a telephone receiver, and (2) it acts as a _relay_ and the feeble received oscillating current controls the larger direct current from the b battery in very much the same way that a telegraph relay does. this latter relay action will be explained when we come to its operation as an amplifier. we have just learned that when the stream of electrons flow from the hot wire to the cold positive plate in the tube they form a conducting path through which the battery current can flow. now when the electric oscillations surge through the closed oscillation circuit, which includes the secondary of the tuning coil, the variable condenser, the filament and the plate as shown at b in fig. 71 the positive part of them passes through the tube easily while the negative part cannot get through, that is, the top, or positive, part of the wave-form remains intact while the lower, or negative, part is cut off as shown in the diagram at c. as the received oscillations are either broken up into wave trains of audio frequency by the telegraph transmitter or are modulated by a telephone transmitter they carry the larger impulses of the direct current from the b battery along with them and these flow through the headphones. this is the reason the vacuum tube amplifies as well as detects. how the three electrode tube acts as a detector.--the vacuum tube as a detector has been made very much more sensitive by the use of a third electrode shown in fig. 72. in this type of vacuum tube the third electrode, or _grid_, is placed between the filament and the plate and this controls the number of electrons flowing from the filament to the plate; in passing between these two electrodes they have to go through the holes formed by the grid wires. [illustration: (a) and (b) fig. 72.--how the positive and negative voltages of oscillations act on the electrons.] [illustration: (c) fig. 72.--how the three electrode tube acts as a detector and amplifier.] [illustration: (d) fig. 72.--how the oscillations control the flow of the battery current through the tube.] if now the grid is charged to a higher _negative_ voltage than the filament the electrons will be stopped by the latter, see a, though some of them will go through to the plate because they travel at a high rate of speed. the higher the negative charge on the grid the smaller will be the number of electrons that will reach the plate and, of course, the smaller will be the amount of current that will flow through the tube and the headphones from the b battery. on the other hand if the grid is charged _positively_, see b, then more electrons will strike the plate than when the grid is not used or when it is negatively charged. but when the three electrode tube is used as a detector the oscillations set up in the circuits change the grid alternately from negative to positive as shown at c and hence the voltage of the b battery current that is allowed to flow through the detector from the plate to the filament rises and falls in unison with the voltage of the oscillating currents. the way the positive and negative voltages of the oscillations which are set up by the incoming waves, energize the grid; how the oscillator tube clips off the negative parts of them, and, finally, how these carry the battery current through the tube are shown graphically by the curves at d. how the vacuum tube acts as an amplifier.--if you connect up the filament and the plate of a three electrode tube with the batteries and do not connect in the grid, you will find that the electrons which are thrown off by the filament will not get farther than the grid regardless of how high the voltage is that you apply to the plate. this is due to the fact that a large number of electrons which are thrown off by the filament strike the grid and give it a negative charge, and consequently, they cannot get any farther. since the electrons do not reach the plate the current from the b battery cannot flow between it and the filament. now with a properly designed amplifier tube a very small negative voltage on the grid will keep a very large positive voltage on the plate from sending a current through the tube, and oppositely, a very small positive voltage on the grid will let a very large plate current flow through the tube; this being true it follows that any small variation of the voltage from positive to negative on the grid and the other way about will vary a large current flowing from the plate to the filament. in the morse telegraph the relay permits the small current that is received from the distant sending station to energize a pair of magnets, and these draw an armature toward them and close a second circuit when a large current from a local battery is available for working the sounder. the amplifier tube is a variable relay in that the feeble currents set up by the incoming waves constantly and proportionately vary a large current that flows through the headphones. this then is the principle on which the amplifying tube works. the operation of a simple vacuum tube receiving set.--the way a simple vacuum tube detector receiving set works is like this: when the filament is heated to brilliancy it gives off electrons as previously described. now when the electric waves impinge on the aerial wire they set up oscillations in it and these surge through the primary coil of the loose coupled tuning coil, a diagram of which is shown at b in fig. 41. the energy of these oscillations sets up oscillations of the same frequency in the secondary coil and these high frequency currents whose voltage is first positive and then negative, surge in the closed circuit which includes the secondary coil and the variable condenser. at the same time the alternating positive and negative voltage of the oscillating currents is impressed on the grid; at each change from + to and back again it allows the electrons to strike the plate and then shuts them off; as the electrons form the conducting path between the filament and the plate the larger direct current from the b battery is permitted to flow through the detector tube and the headphones. operation of a regenerative vacuum tube receiving set.--by feeding back the pulsating direct current from the b battery through the tickler coil it sets up other and stronger oscillations in the secondary of the tuning coil when these act on the detector tube and increase its sensitiveness to a remarkable extent. the regenerative, or _feed back_, action of the receiving circuits used will be easily understood by referring back to b in fig. 47. when the waves set up oscillations in the primary of the tuning coil the energy of them produces like oscillations in the closed circuit which includes the secondary coil and the condenser; the alternating positive and negative voltages of these are impressed on the grid and these, as we have seen before, cause similar variations of the direct current from the b battery which acts on the plate and which flows between the latter and the filament. this varying direct current, however, is made to flow back through the third, or tickler coil of the tuning coil and sets up in the secondary coil and circuits other and larger oscillating currents and these augment the action of the oscillations produced by the incoming waves. these extra and larger currents which are the result of the feedback then act on the grid and cause still larger variations of the current in the plate voltage and hence of the current of the b battery that flows through the detector and the headphones. at the same time the tube keeps on responding to the feeble electric oscillations set up in the circuits by the incoming waves. this regenerative action of the battery current augments the original oscillations many times and hence produce sounds in the headphones that are many times greater than where the vacuum tube detector alone is used. operation of autodyne and heterodyne receiving sets.--on page 109 [chapter vii] we discussed and at a in fig. 36 is shown a picture of two tuning forks mounted on sounding boxes to illustrate the principle of electrical tuning. when a pair of these forks are made to vibrate exactly the same number of times per second there will be a condensation of the air between them and the sound waves that are sent out will be augmented. but if you adjust one of the forks so that it will vibrate 256 times a second and the other fork so that it will vibrate 260 times a second then there will be a phase difference between the two sets of waves and the latter will augment each other 4 times every second and you will hear these rising and falling sounds as _beats_. now electric oscillations set up in two circuits that are coupled together act in exactly the same way as sound waves produced by two tuning forks that are close to each other. since this is true if you tune one of the closed circuits so that the oscillations in it will have a frequency of a 1,000,000 and tune the other circuit so that the oscillations in it have a frequency of 1,001,000 a second then the oscillations will augment each other 1,000 times every second. as these rising and falling currents act on the pulsating currents from the b battery which flow through the detector tube and the headphones you will hear them as beats. a graphic representation of the oscillating currents set up by the incoming waves, those produced by the heterodyne oscillator and the beats they form is shown in fig. 73. to produce these beats a receptor can use: (1) a single vacuum tube for setting up oscillations of both frequencies when it is called an _autodyne_, or _self-heterodyne_ receptor, or (2) a separate vacuum tube for setting up the oscillations for the second circuit when it is called a _heterodyne_ receptor. [illustration: fig. 73.--how the heterodyne receptor works.] the autodyne, or self-heterodyne receiving set.--where only one vacuum tube is used for producing both frequencies you need only a regenerative, or feed-back receptor; then you can tune the aerial wire system to the incoming waves and tune the closed circuit of the secondary coil so that it will be out of step with the former by 1,000 oscillations per second, more or less, the exact number does not matter in the least. from this you will see that any regenerative set can be used for autodyne, or self-heterodyne, reception. the separate heterodyne receiving set.--the better way, however, is to use a separate vacuum tube for setting up the heterodyne oscillations. the latter then act on the oscillations that are produced by the incoming waves and which energize the grid of the detector tube. note that the vacuum tube used for producing the heterodyne oscillations is a _generator_ of electric oscillations; the latter are impressed on the detector circuits through the variable coupling, the secondary of which is in series with the aerial wire as shown in fig. 74. the way in which the tube acts as a generator of oscillations will be told in chapter xviii. [illustration: fig. 74.--separate heterodyne oscillator.] chapter xvi continuous wave telegraph transmitting sets with direct current in the first part of this book we learned about spark-gap telegraph sets and how the oscillations they set up are _damped_ and the waves they send out are _periodic_. in this and the next chapter we shall find out how vacuum tube telegraph transmitters are made and how they set up oscillations that are _sustained_ and radiate waves that are _continuous_. sending wireless telegraph messages by continuous waves has many features to recommend it as against sending them by periodic waves and among the most important of these are that the transmitter can be: (1) more sharply tuned, (2) it will send signals farther with the same amount of power, and (3) it is noiseless in operation. the disadvantageous features are that: (1) a battery current is not satisfactory, (2) its circuits are somewhat more complicated, and (3) the oscillator tubes burn out occasionally. there is, however, a growing tendency among amateurs to use continuous wave transmitters and they are certainly more up-to-date and interesting than spark gap sets. now there are two practical ways by which continuous waves can be set up for sending either telegraphic signals or telephonic speech and music and these are with: (a) an _oscillation arc lamp_, and (b) a _vacuum tube oscillator_. the oscillation arc was the earliest known way of setting up sustained oscillations, and it is now largely used for commercial high power, long distance work. but since the vacuum tube has been developed to a high degree of efficiency and is the scheme that is now in vogue for amateur stations we shall confine our efforts here to explaining the apparatus necessary and how to wire the various parts together to produce several sizes of vacuum tube telegraph transmitters. sources of current for telegraph transmitting sets.--differing from a spark-gap transmitter you cannot get any appreciable results with a low voltage battery current to start with. for a purely experimental vacuum tube telegraph transmitter you can use enough b batteries to operate it but the current strength of these drops so fact when they are in use, that they are not at all satisfactory for the work. you can, however, use 110 volt direct current from a lighting circuit as your initial source of power to energize the plate of the vacuum tube oscillator of your experimental transmitter. where you have a 110 volt _direct current_ lighting service in your home and you want a higher voltage for your plate, you will then have to use a motor-generator set and this costs money. if you have 110 volt _alternating current_ lighting service at hand your troubles are over so far as cost is concerned for you can step it up to any voltage you want with a power transformer. in this chapter will be shown how to use a direct current for your source of initial power and in the next chapter how to use an alternating current for the initial power. an experimental continuous wave telegraph transmitter.--you will remember that in chapter xv we learned how the heterodyne receiver works and that in the separate heterodyne receiving set the second vacuum tube is used solely to set up oscillations. now while this extra tube is used as a generator of oscillations these are, of course, very weak and hence a detector tube cannot be used to generate oscillations that are useful for other purposes than heterodyne receptors and measurements. there is a vacuum tube amplifier [footnote: this is the _radiation_ uv-201, made by the radio corporation of america, woolworth bldg., new york city.] made that will stand a plate potential of 100 volts, and this can be used as a generator of oscillations by energizing it with a 110 volt direct current from your lighting service. or in a pinch you can use five standard b batteries to develop the plate voltage, but these will soon run down. but whatever you do, never use a current from a lighting circuit on a tube of any kind that has a rated plate potential of less than 100 volts. the apparatus you need.--for this experimental continuous wave telegraph transmitter get the following pieces of apparatus: (1) one _single coil tuner with three clips_; (2) one _.002 mfd. fixed condenser_; (3) three _.001 mfd. condensers_; (4) one _adjustable grid leak_; (5) one _hot-wire ammeter_; (6) one _buzzer_; (7) one _dry cell_; (8) one _telegraph key_; (9) one _100 volt plate vacuum tube amplifier_; (10) one _6 volt storage battery_; (11) one _rheostat_; (12) one _oscillation choke coil_; (13) one _panel cut-out_ with a _single-throw, double-pole switch_, and a pair of _fuse sockets_ on it. the tuning coil.--you can either make this tuning coil or buy one. to make it get two disks of wood 3/4-inch thick and 5 inches in diameter and four strips of hard wood, or better, hard rubber or composition strips, such as _bakelite_, 1/2-inch thick, 1 inch wide and 5-3/4 inches long, and screw them to the disks as shown at a in fig. 75. now wrap on this form about 25 turns of no. 8 or 10, brown and sharpe gauge, bare copper wire with a space of 1/8-inch between each turn. get three of the smallest size terminal clips, see b, and clip them on to the different turns, when your tuning coil is ready for use. you can buy a coil of this kind for $4.00 or $5.00. the condensers.--for the aerial series condenser get one that has a capacitance of .002 mfd. and that will stand a potential of 3,000 volts. [footnote: the u c-1014 _faradon_ condenser made by the radio corporation of america will serve the purpose.] it is shown at c. the other three condensers, see d, are also of the fixed type and may have a capacitance of .001 mfd.; [footnote: list no. 266; fixed receiving condenser, sold by the manhattan electrical supply co.] the blocking condenser should preferably have a capacitance of 1/2 a mfd. in these condensers the leaves of the sheet metal are embedded in composition. the aerial condenser will cost you $2.00 and the others 75 cents each. [illustration: (a) fig. 75.--apparatus for experimental c. w. telegraph transmitter.] [illustration: fig. 75.--apparatus for experimental c. w. telegraph transmitter.] the aerial ammeter.--this instrument is also called a _hot-wire_ ammeter because the oscillating currents flowing through a piece of wire heat it according to their current strength and as the wire contracts and expands it moves a needle over a scale. the ammeter is connected in the aerial wire system, either in the aerial side or the ground side--the latter place is usually the most convenient. when you tune the transmitter so that the ammeter shows the largest amount of current surging in the aerial wire system you can consider that the oscillation circuits are in tune. a hot-wire ammeter reading to 2.5 amperes will serve your needs, it costs $6.00 and is shown at e in fig. 75. [illustration: united states naval high power station, arlington va. general view of power room. at the left can be seen the control switchboards, and overhead, the great 30 k.w. arc transmitter with accessories.] the buzzer and dry cell.--while a heterodyne, or beat, receptor can receive continuous wave telegraph signals an ordinary crystal or vacuum tube detector receiving set cannot receive them unless they are broken up into trains either at the sending station or at the receiving station, and it is considered the better practice to do this at the former rather than at the latter station. for this small transmitter you can use an ordinary buzzer as shown at f. a dry cell or two must be used to energize the buzzer. you can get one for about 75 cents. the telegraph key.--any kind of a telegraph key will serve to break up the trains of sustained oscillations into dots and dashes. the key shown at g is mounted on a composition base and is the cheapest key made, costing $1.50. the vacuum tube oscillator.--as explained before you can use any amplifying tube that is made for a plate potential of 100 volts. the current required for heating the filament is about 1 ampere at 6 volts. a porcelain socket should be used for this tube as it is the best insulating material for the purpose. an amplifier tube of this type is shown at h and costs $6.50. the storage battery.--a storage battery is used to heat the filament of the tube, just as it is with a detector tube, and it can be of any make or capacity as long as it will develop 6 volts. the cheapest 6 volt storage battery on the market has a 20 to 40 ampere-hour capacity and sells for $13.00. the battery rheostat.--as with the receptors a rheostat is needed to regulate the current that heats the filament. a rheostat of this kind is shown at i and is listed at $1.25. the oscillation choke coil.--this coil is connected in between the oscillation circuits and the source of current which feeds the oscillator tube to keep the oscillations set up by the latter from surging back into the service wires where they would break down the insulation. you can make an oscillation choke coil by winding say 100 turns of no. 28 brown and sharpe gauge double cotton covered magnet wire on a cardboard cylinder 2 inches in diameter and 2-1/2 inches long. transmitter connectors.--for connecting up the different pieces of apparatus of the transmitter it is a good scheme to use _copper braid_; this is made of braided copper wire in three sizes and sells for 7,15 and 20 cents a foot respectively. a piece of it is pictured at j. the panel cut-out.--this is used to connect the cord of the 110-volt lamp socket with the transmitter. it consists of a pair of _plug cutouts and a single-throw, double-pole_ switch mounted on a porcelain base as shown at k. in some localities it is necessary to place these in an iron box to conform to the requirements of the fire underwriters. connecting up the transmitting apparatus.--the way the various pieces of apparatus are connected together is shown in the wiring diagram. fig. 76. begin by connecting one post of the ammeter with the wire that leads to the aerial and the other post of it to one end of the tuning coil; connect clip _1_ to one terminal of the .002 mfd. 3,000 volt aerial condenser and the other post of this with the ground. [illustration: fig. 76--experimental c.w. telegraph transmitter] now connect the end of the tuning coil that leads to the ammeter with one end of the .001 mfd. grid condenser and the other end of this with the grid of the vacuum tube. connect the telegraph key, the buzzer and the dry cell in series and then shunt them around the grid condenser. next connect the plate of the tube with one end of the .001 mfd. blocking condenser and the other end of this with the clip _2_ on the tuning coil. connect one end of the filament with the + or positive electrode of the storage battery, the or negative electrode of this with one post of the rheostat and the other post of the latter with the other end of the filament; then connect clip _3_ with the + or positive side of the storage battery. this done connect one end of the choke coil to the conductor that leads to the plate and connect the other end of the choke coil to one of the taps of the switch on the panel cut-out. connect the + or positive electrode of the storage battery to the other switch tap and between the switch and the choke coil connect the protective condenser across the 110 volt feed wires. finally connect the lamp cord from the socket to the plug fuse taps when your experimental continuous wave telegraph transmitter is ready to use. a 100 mile c. w. telegraph transmitter.--here is a continuous wave telegraph transmitter that will cover distances up to 100 miles that you can rely on. it is built on exactly the same lines as the experimental transmitter just described, but instead of using a 100 volt plate amplifier as a makeshift generator of oscillations it employs a vacuum tube made especially for setting up oscillations and instead of having a low plate voltage it is energized with 350 volts. the apparatus you need.--for this transmitter you require: (1) one _oscillation transformer_; (2) one _hot-wire ammeter_; (3) one _aerial series condenser_; (4) one _grid leak resistance_; (5) one _chopper_; (6) one _key circuit choke coil_; (7) one _5 watt vacuum tube oscillator_; (8) one _6 volt storage battery_; (9) one _battery rheostat_; (10) one _battery voltmeter_; (11) one _blocking condenser_; (12) one _power circuit choke coil_, and (13) one _motor-generator_. the oscillation transformer.--the tuning coil, or _oscillation transformer_ as this one is called, is a conductively coupled tuner--that is, the primary and secondary coils form one continuous coil instead of two separate coils. this tuner is made up of 25 turns of thin copper strip, 3/8 inch wide and with its edges rounded, and this is secured to a wood base as shown at a in fig. 77. it is fitted with one fixed tap and three clips to each of which a length of copper braid is attached. it has a diameter of 6-1/4 inches, a height of 7-7/8 inches and a length of 9-3/8 inches, and it costs $11.00. [illustration: fig. 77.--apparatus of 100 mile c. w. telegraph transmitter.] the aerial condenser.--this condenser is made up of three fixed condensers of different capacitances, namely .0003, .0004 and .0005 mfd., and these are made to stand a potential of 7500 volts. the condenser is therefore adjustable and, as you will see from the picture b, it has one terminal wire at one end and three terminal wires at the other end so that one, two or three condensers can be used in series with the aerial. a condenser of this kind costs $5.40. the aerial ammeter.--this is the same kind of a hot-wire ammeter already described in connection with the experimental set, but it reads to 5 amperes. the grid and blocking condensers.--each of these is a fixed condenser of .002 mfd. capacitance and is rated to stand 3,000 volts. it is made like the aerial condenser but has only two terminals. it costs $2.00. the key circuit apparatus.--this consists of: (1) the _grid leak_; (2) the _chopper_; (3) the _choke coil_, and (4) the _key_. the grid leak is connected in the lead from the grid to the aerial to keep the voltage on the grid at the right potential. it has a resistance of 5000 ohms with a mid-tap at 2500 ohms as shown at c. it costs $2.00. the chopper is simply a rotary interrupter driven by a small motor. it comprises a wheel of insulating material in which 30 or more metal segments are set in an insulating disk as shown at d. a metal contact called a brush is fixed on either side of the wheel. it costs about $7.00 and the motor to drive it is extra. the choke coil is wound up of about 250 turns of no. 30 brown and sharpe gauge cotton covered magnet wire on a spool which has a diameter of 2 inches and a length of 3-1/4 inches. the 5 watt oscillator vacuum tube.--this tube is made like the amplifier tube described for use with the preceding experimental transmitter, but it is larger, has a more perfect vacuum, and will stand a plate potential of 350 volts while the plate current is .045 ampere. the filament takes a current of a little more than 2 amperes at 7.5 volts. a standard 4-tap base is used with it. the tube costs $8.00 and the porcelain base is $1.00 extra. it is shown at e. the storage battery and rheostat.--this must be a 5-cell battery so that it will develop 10 volts. a storage battery of any capacity can be used but the lowest priced one costs about $22.00. the rheostat for regulating the battery current is the same as that used in the preceding experimental transmitter. the filament voltmeter.--to get the best results it is necessary that the voltage of the current which heats the filament be kept at the same value all of the time. for this transmitter a direct current voltmeter reading from 0 to 15 volts is used. it is shown at f and costs $7.50. the oscillation choke coil.--this is made exactly like the one described in connection with the experimental transmitter. the motor-generator set.--where you have only a 110 or a 220 volt direct current available as a source of power you need a _motor-generator_ to change it to 350 volts, and this is an expensive piece of apparatus. it consists of a single armature core with a motor winding and a generator winding on it and each of these has its own commutator. where the low voltage current flows into one of the windings it drives its as a motor and this in turn generates the higher voltage current in the other winding. get a 100 watt 350 volt motor-generator; it is shown at f and costs about $75.00. the panel cut-out.--this switch and fuse block is the same as that used in the experimental set. the protective condenser.--this is a fixed condenser having a capacitance of 1 mfd. and will stand 750 volts. it costs $2.00. connecting up the transmitting apparatus.--from all that has gone before you have seen that each piece of apparatus is fitted with terminal, wires, taps or binding posts. to connect up the parts of this transmitter it is only necessary to make the connections as shown in the wiring diagram fig. 78. [illustration: fig. 78.--5 to 50 watt c. w. telegraph transmitter. (with single oscillation tube.)] a 200 mile c. w. telegraph transmitter.--to make a continuous wave telegraph transmitter that will cover distances up to 200 miles all you have to do is to use two 5 watt vacuum tubes in _parallel_, all of the rest of the apparatus being exactly the same. connecting the oscillator tubes up in parallel means that the two filaments are connected across the leads of the storage battery, the two grids on the same lead that goes to the aerial and the two plates on the same lead that goes to the positive pole of the generator. where two or more oscillator tubes are used only one storage battery is needed, but each filament must have its own rheostat. the wiring diagram fig. 79 shows how the two tubes are connected up in parallel. [illustration: fig. 79.--200 mile c.w. telegraph transmitter (with two tubes in parallel.)] a 500 mile c. w. telegraph transmitter.--for sending to distances of over 200 miles and up to 500 miles you can use either: (1) three or four 5 watt oscillator tubes in parallel as described above, or (2) one 50 watt oscillator tube. much of the apparatus for a 50 watt tube set is exactly the same as that used for the 5 watt sets. some of the parts, however, must be proportionately larger though the design all the way through remains the same. the apparatus and connections.--the aerial series condenser, the blocking condenser, the grid condenser, the telegraph key, the chopper, the choke coil in the key circuit, the filament voltmeter and the protective condenser in the power circuit are identical with those described for the 5 watt transmitting set. the 50 watt vacuum tube oscillator.--this is the size of tube generally used by amateurs for long distance continuous wave telegraphy. a single tube will develop 2 to 3 amperes in your aerial. the filament takes a 10 volt current and a plate potential of 1,000 volts is needed. one of these tubes is shown in fig. 80 and the cost is $30.00. a tube socket to fit it costs $2.50 extra. [illustration: fig. 80.--50 watt oscillator vacuum tube.] the aerial ammeter.--this should read to 5 amperes and the cost is $6.25. the grid leak resistance.--it has the same resistance, namely 5,000 ohms as the one used with the 5 watt tube transmitter, but it is a little larger. it is listed at $1.65. the oscillation choke coil.--the choke coil in the power circuit is made of about 260 turns of no. 30 b. & s. cotton covered magnet wire wound on a spool 2-1/4 inches in diameter and 3-1/4 inches long. the filament rheostat.--this is made to take care of a 10 volt current and it costs $10.00. the filament storage battery.--this must develop 12 volts and one having an output of 40 ampere-hours costs about $25.00. the protective condenser.--this condenser has a capacitance of 1 mfd. and costs $2.00. the motor-generator.--where you use one 50 watt oscillator tube you will need a motor-generator that develops a plate potential of 1000 volts and has an output of 200 watts. this machine will stand you about $100.00. the different pieces of apparatus for this set are connected up exactly the same as shown in the wiring diagram in fig. 78. a 1000 mile c. w. telegraph transmitter.--all of the parts of this transmitting set are the same as for the 500 mile transmitter just described except the motor generator and while this develops the same plate potential, i.e., 1,000 volts, it must have an output of 500 watts; it will cost you in the neighborhood of $175.00. for this long distance transmitter you use two 50 watt oscillator tubes in parallel and all of the parts are connected together exactly the same as for the 200 mile transmitter shown in the wiring diagram in fig. 79. chapter xvii continuous wave telegraph transmitting sets with alternating current within the last few years alternating current has largely taken the place of direct current for light, heat and power purposes in and around towns and cities and if you have alternating current service in your home you can install a long distance continuous wave telegraph transmitter with very little trouble and at a comparatively small expense. a 100 mile c. w. telegraph transmitting set.--the principal pieces of apparatus for this transmitter are the same as those used for the _100 mile continuous wave telegraph transmitting set_ described and pictured in the preceding chapter which used direct current, except that an _alternating current power transformer_ is employed instead of the more costly _motor-generator_. the apparatus required.--the various pieces of apparatus you will need for this transmitting set are: (1) one _hot-wire ammeter_ for the aerial as shown at e in fig. 75, but which reads to 5 amperes instead of to 2.5 amperes; (2) one _tuning coil_ as shown at a in fig. 77; (3) one aerial condenser as shown at b in fig. 77; (4) one _grid leak_ as shown at c in fig. 77; (5) one _telegraph key_ as shown at g in fig. 75; (6) one _grid condenser_, made like the aerial condenser but having only two terminals; (7) one _5 watt oscillator tube_ as shown at e in fig. 77; (8) one _.002 mfd. 3,000 volt by-pass condenser_, made like the aerial and grid condensers; (9) one pair of _choke coils_ for the high voltage secondary circuit; (10) one _milli-ammeter_; (11) one a. c. _power transformer_; (12) one _rheostat_ as shown at i in fig. 75, and (13) one _panel cut-out_ as shown at k in fig. 75. the choke coils.--each of these is made by winding about 100 turns of no. 28, brown and sharpe gauge, cotton covered magnet wire on a spool 2 inches in diameter and 2-1/2 inches long, when it will have an inductance of about 0.5 _millihenry_ [footnote: a millihenry is 1/1000th part of a henry.] at 1,000 cycles. the milli-ammeter.--this is an alternating current ammeter and reads from 0 to 250 _milliamperes_; [footnote: a _milliampere_ is the 1/1000th part of an ampere.] and is used for measuring the secondary current that energizes the plate of the oscillator tube. it looks like the aerial ammeter and costs about $7.50. the a. c. power transformer.--differing from the motor generator set the power transformer has no moving parts. for this transmitting set you need a transformer that has an input of 325 volts. it is made to work on a 50 to 60 cycle current at 102.5 to 115 volts, which is the range of voltage of the ordinary alternating lighting current. this adjustment for voltage is made by means of taps brought out from the primary coil to a rotary switch. the high voltage secondary coil which energizes the plate has an output of 175 watts and develops a potential of from 350 to 1,100 volts. the low voltage secondary coil which heats the filament has an output of 175 watts and develops 7.5 volts. this transformer, which is shown in fig. 81, is large enough to take care of from one to four 5 watt oscillator tubes. it weighs about 15 pounds and sells for $25.00. [illustration: fig. 81.--alternation current power transformer. (for c. w. telegraphy and wireless telephony.)] [illustration: the transformer and tuner of the world's largest radio station. owned by the radio corporation of america at rocky point near port jefferson l.i.] connecting up the apparatus.--the wiring diagram fig. 82 shows clearly how all of the connections are made. it will be observed that a storage battery is not needed as the secondary coil of the transformer supplies the current to heat the filament of the oscillator. the filament voltmeter is connected across the filament secondary coil terminals, while the plate milli-ammeter is connected to the mid-taps of the plate secondary coil and the filament secondary coil. [illustration: fig. 82. wiring diagram for 200 to 500 mile c.w. telegraph transmitting set. (with alternating current)] a 200 to 500 mile c. w. telegraph transmitting set.--distances of from 200 to 500 miles can be successfully covered with a telegraph transmitter using two, three or four 5 watt oscillator tubes in parallel. the apparatus needed is identical with that used for the 100 mile transmitter just described. the tubes are connected in parallel as shown in the wiring diagram in fig. 83. [illustration: fig. 83.--wiring diagram for 500 to 1000 mile c. w. telegraph transmitter.] a 500 to 1,000 mile c. w. telegraph transmitting set.--with the apparatus described for the above set and a single 50 watt oscillator tube a distance of upwards of 500 miles can be covered, while with two 50 watt oscillator tubes in parallel you can cover a distance of 1,000 miles without difficulty, and nearly 2,000 miles have been covered with this set. the apparatus required.--all of the apparatus for this c. w. telegraph transmitting set is the same as that described for the 100 and 200 mile sets but you will need: (1) one or two _50 watt oscillator tubes with sockets;_ (2) one _key condenser_ that has a capacitance of 1 mfd., and a rated potential of 1,750 volts; (3) one _0 to 500 milli-ammeter_; (4) one _aerial ammeter_ reading to 5 amperes, and (5) an _a. c. power transformer_ for one or two 50 watt tubes. [illustration: broadcasting government reports by wireless from washington. this shows mr. gale at work with his set in the post office department.] the alternating current power transformer.--this power transformer is made exactly like the one described in connection with the preceding 100 mile transmitter and pictured in fig. 81, but it is considerably larger. like the smaller one, however, it is made to work with a 50 to 60 cycle current at 102.5 to 115 volts and, hence, can be used with any a. c. lighting current. it has an input of 750 volts and the high voltage secondary coil which energizes the plate has an output of 450 watts and develops 1,500 to 3,000 volts. the low voltage secondary coil which heats the filament develops 10.5 volts. this transformer will supply current for one or two 50-watt oscillator tubes and it costs about $40.00. connecting up the apparatus.--where a single oscillator tube is used the parts are connected as shown in fig. 82, and where two tubes are connected in parallel the various pieces of apparatus are wired together as shown in fig. 83. the only difference between the 5 watt tube transmitter and the 50 watt tube transmitter is in the size of the apparatus with one exception; where one or two 50 watt tubes are used a second condenser of large capacitance (1 mfd.) is placed in the grid circuit and the telegraph key is shunted around it as shown in the diagram fig. 83. chapter xviii wireless telephone transmitting sets with direct and alternating currents in time past the most difficult of all electrical apparatus for the amateur to make, install and work was the wireless telephone. this was because it required a _direct current_ of not less than 500 volts to set up the sustained oscillations and all ordinary direct current for lighting purposes is usually generated at a potential of 110 volts. now as you know it is easy to _step-up_ a 110 volt alternating current to any voltage you wish with a power transformer but until within comparatively recent years an alternating current could not be used for the production of sustained oscillations for the very good reason that the state of the art had not advanced that far. in the new order of things these difficulties have all but vanished and while a wireless telephone transmitter still requires a high voltage direct current to operate it this is easily obtained from 110 volt source of alternating current by means of _vacuum tube rectifiers_. the pulsating direct currents are then passed through a filtering reactance coil, called a _reactor_, and one or more condensers, and these smooth them out until they approximate a continuous direct current. the latter is then made to flow through a vacuum tube oscillator when it is converted into high frequency oscillations and these are _varied_, or _modulated_, as it is called, by a _microphone transmitter_ such as is used for ordinary wire telephony. the energy of these sustained modulated oscillations is then radiated into space from the aerial in the form of electric waves. the distance that can be covered with a wireless telephone transmitter is about one-fourth as great as that of a wireless telegraph transmitter having the same input of initial current, but it is long enough to satisfy the most enthusiastic amateur. for instance with a wireless telephone transmitter where an amplifier tube is used to set up the oscillations and which is made for a plate potential of 100 volts, distances up to 10 or 15 miles can be covered. with a single 5 watt oscillator tube energized by a direct current of 350 volts from either a motor-generator or from a power transformer (after it has been rectified and smoothed out) speech and music can be transmitted to upwards of 25 miles. where two 5 watt tubes connected in parallel are used wireless telephone messages can be transmitted to distances of 40 or 50 miles. further, a single 50 watt oscillator tube will send to distances of 50 to 100 miles while two of these tubes in parallel will send from 100 to 200 miles. finally, where four or five oscillator tubes are connected in parallel proportionately greater distances can be covered. a short distance wireless telephone transmitting set-with 110 volt direct lighting current.--for this very simple, short distance wireless telephone transmitting set you need the same apparatus as that described and pictured in the beginning of chapter xvi for a _short distance c. w. telegraph transmitter_, except that you use a _microphone transmitter_ instead of a _telegraph key_. if you have a 110 volt direct lighting current in your home you can put up this short distance set for very little money and it will be well worth your while to do so. the apparatus you need.--for this set you require: (1) one _tuning coil_ as shown at a and b in fig. 75; (2) one _aerial ammeter_ as shown at c in fig. 75; (3) one _aerial condenser_ as shown at c in fig. 75; (4) one _grid, blocking and protective condenser_ as shown at d in fig. 75; (5) one _grid leak_ as shown at c in fig. 77; (6) one _vacuum tube amplifier_ which is used as an _oscillator_; (7) one _6 volt storage battery_; (8) one _rheostat_ as shown at i in fig. 75; (9) one _oscillation choke coil_; (10) one _panel cut-out_ as shown at k in fig. 75 and an ordinary _microphone transmitter_. the microphone transmitter.--the best kind of a microphone to use with this and other telephone transmitting sets is a _western electric no. 284-w_. [footnote: made by the western electric company, chicago, ill.] this is known as a solid back transmitter and is the standard commercial type used on all long distance bell telephone lines. it articulates sharply and distinctly and there are no current variations to distort the wave form of the voice and it will not buzz or sizzle. it is shown in fig. 84 and costs $2.00. any other good microphone transmitter can be used if desired. [illustration: fig. 84.--standard microphone transmitter.] connecting up the apparatus.--begin by connecting the leading-in wire with one of the terminals of the microphone transmitter, as shown in the wiring diagram fig. 85, and the other terminal of this to one end of the tuning coil. now connect _clip 1_ of the tuning coil to one of the posts of the hot-wire ammeter, the other post of this to one end of aerial condenser and, finally, the other end of the latter with the water pipe or other ground. the microphone can be connected in the ground wire and the ammeter in the aerial wire and the results will be practically the same. [illustration: fig. 85.--wiring diagram of short distance wireless telephone set. (microphone in aerial wire.)] next connect one end of the grid condenser to the post of the tuning coil that makes connection with the microphone and the other end to the grid of the tube, and then shunt the grid leak around the condenser. connect the + or _positive_ electrode of the storage battery with one terminal of the filament of the vacuum tube, the other terminal of the filament with one post of the rheostat and the other post of this with the or _negative_ electrode of the battery. this done, connect _clip 2_ of the tuning coil to the + or _positive_ electrode of the battery and bring a lead from it to one of the switch taps of the panel cut-out. now connect _clip 3_ of the tuning coil with one end of the blocking condenser, the other end of this with one terminal of the choke coil and the other terminal of the latter with the other switch tap of the cut-out. connect the protective condenser across the direct current feed wires between the panel cut-out and the choke coil. finally connect the ends of a lamp cord to the fuse socket taps of the cut-out, and connect the other ends to a lamp plug and screw it into the lamp socket of the feed wires. screw in a pair of 5 ampere _fuse plugs_, close the switch and you are ready to tune the transmitter and talk to your friends. a 25 to 50 mile wireless telephone transmitter--with direct current motor generator.--where you have to start with 110 or 220 volt direct current and you want to transmit to a distance of 25 miles or more you will have to install a _motor-generator_. to make this transmitter you will need exactly the same apparatus as that described and pictured for the _100 mile c. w. telegraph transmitting set_ in chapter xvi, except that you must substitute a _microphone transmitter_ and a _telephone induction coil_, or a _microphone transformer_, or still better, a _magnetic modulator_, for the telegraph key and chopper. the apparatus you need.--to reiterate; the pieces of apparatus you need are: (1) one _aerial ammeter_ as shown at e in fig. 75; (2) one _tuning coil_ as shown at a in fig. 77; (3) one _aerial condenser_ as shown at b in fig. 77; (4) one _grid leak_ as shown at c in fig. 77; (5) one _grid, blocking_ and _protective condenser_; (6) one _5 watt oscillator tube_ as shown at e in fig. 77; (7) one _rheostat_ as shown at i in fig. 75; (8) one _10 volt (5 cell) storage battery_; (9) one _choke coil_; (10) one _panel cut-out_ as shown at k in fig. 75, and (11) a _motor-generator_ having an input of 110 or 220 volts and an output of 350 volts. in addition to the above apparatus you will need: (12) a _microphone transmitter_ as shown in fig. 84; (13) a battery of four dry cells or a 6 volt storage battery, and either (14) a _telephone induction coil_ as shown in fig. 86; (15) a _microphone transformer_ as shown in fig. 87; or a _magnetic modulator_ as shown in fig. 88. all of these parts have been described, as said above, in chapter xvi, except the microphone modulators. [illustration: fig. 86.--telephone induction coil. (used with microphone transmitter.)] [illustration: fig. 87.--microphone transformer. (used with microphone transmitter.)] [illustration: fig. 88.--magnetic modulator. (used with microphone transmitter.)] the telephone induction coil.--this is a little induction coil that transforms the 6-volt battery current after it has flowed through and been modulated by the microphone transmitter into alternating currents that have a potential of 1,000 volts of more. it consists of a primary coil of _no. 20 b. and s._ gauge cotton covered magnet wire wound on a core of soft iron wires while around the primary coil is wound a secondary coil of _no. 30_ magnet wire. get a _standard telephone induction coil_ that has a resistance of 500 or 750 ohms and this will cost you a couple of dollars. the microphone transformer.--this device is built on exactly the same principle as the telephone induction coil just described but it is more effective because it is designed especially for modulating the oscillations set up by vacuum tube transmitters. as with the telephone induction coil, the microphone transmitter is connected in series with the primary coil and a 6 volt dry or storage battery. in the better makes of microphone transformer, there is a third winding, called a _side tone_ coil, to which a headphone can be connected so that the operator who is speaking into the microphone can listen-in and so learn if his transmitter is working up to standard. the magnetic modulator.--this is a small closed iron core transformer of peculiar design and having a primary and a secondary coil wound on it. this device is used to control the variations of the oscillating currents that are set up by the oscillator tube. it is made in three sizes and for the transmitter here described you want the smallest size, which has an output of 1/2 to 1-1/2 amperes. it costs about $10.00. how the apparatus is connected up.--the different pieces of apparatus are connected together in exactly the same way as the _100 mile c. w. telegraph set_ in chapter xvi except that the microphone transmitter and microphone modulator (whichever kind you use) is substituted for the telegraph key and chopper. now there are three different ways that the microphone and its modulator can be connected in circuit. two of the best ways are shown at a and b in fig. 89. in the first way the secondary terminals of the modulator are shunted around the grid leak in the grid circuit as at a, and in the second the secondary terminals are connected in the aerial as at b. where an induction coil or a microphone transformer is used they are shunted around a condenser, but this is not necessary with the magnetic modulator. where a second tube is used as in fig. 90 then the microphone and its modulator are connected with the grid circuit and _clip 3_ of the tuning coil. [illustration: fig. 89.--wiring diagram of 25 to 50 mile wireless telephone. (microphone modulator shunted around grid-leak condenser.)] [illustration: (b) fig. 89.--microphone modulator connected in aerial wire.] [illustration: fig. 90.--wiring diagram of 50 to 100 mile wireless telephone transmitting set.] a 50 to 100 mile wireless telephone transmitter--with direct current motor generator.--as the initial source of current available is taken to be a 110 or 220 volt direct current a motor-generator having an output of 350 volts must be used as before. the only difference between this transmitter and the preceding one is that: (1) two 5 watt tubes are used, the first serving as an _oscillator_ and the second as a _modulator_; (2) an _oscillation choke coil_ is used in the plate circuit; (3) a _reactance coil_ or _reactor_, is used in the plate circuit; and (4) a _reactor_ is used in the grid circuit. the oscillation choke coil.--you can make this choke coil by winding about 275 turns of _no. 28 b. and s. gauge_ cotton covered magnet wire on a spool 2 inches in diameter and 4 inches long. give it a good coat of shellac varnish and let it dry thoroughly. the plate and grid circuit reactance coils.--where a single tube is used as an oscillator and a second tube is employed as a modulator, a _reactor_, which is a coil of wire wound on an iron core, is used in the plate circuit to keep the high voltage direct current of the motor-generator the same at all times. likewise the grid circuit reactor is used to keep the voltage of the grid at a constant value. these reactors are made alike and a picture of one of them is shown in fig. 91 and each one will cost you $5.75. [illustration: fig. 91.--plate and grid circuit reactor.] connecting up the apparatus.--all of the different pieces of apparatus are connected up as shown in fig. 89. one of the ends of the secondary of the induction coil, or the microphone transformer, or the magnetic modulator is connected to the grid circuit and the other end to _clip 3_ of the tuning coil. a 100 to 200 mile wireless telephone transmitter--with direct current motor generator.--by using the same connections shown in the wiring diagrams in fig. 89 and a single 50 watt oscillator tube your transmitter will then have a range of 100 miles or so, while if you connect up the apparatus as shown in fig. 90 and use two 50 watt tubes you can work up to 200 miles. much of the apparatus for a 50 watt oscillator set where either one or two tubes are used is of the same size and design as that just described for the 5 watt oscillator sets, but, as in the c. w. telegraph sets, some of the parts must be proportionately larger. the required parts are (1) the _50 watt tube_; (2) the _grid leak resistance_; (3) the _filament rheostat_; (4) the _filament storage battery_; and (5) the _magnetic modulator_. all of these parts, except the latter, are described in detail under the heading of a _500 mile c. w. telegraph transmitting set_ in chapter xvi, and are also pictured in that chapter. it is not advisable to use an induction coil for the modulator for this set, but use, instead, either a telephone transformer, or better, a magnetic modulator of the second size which has an output of from 1-1/2 to 3-1/2 amperes. the magnetic modulator is described and pictured in this chapter. a 50 to 100 mile wireless telephone transmitting set--with 110 volt alternating current.--if you have a 110 volt [footnote: alternating current for lighting purposes ranges from 102.5 volts to 115 volts, so we take the median and call it 110 volts.] alternating current available you can use it for the initial source of energy for your wireless telephone transmitter. the chief difference between a wireless telephone transmitting set that uses an alternating current and one that uses a direct current is that: (1) a _power transformer_ is used for stepping up the voltage instead of a motor-generator, and (2) a _vacuum tube rectifier_ must be used to convert the alternating current into direct current. the apparatus you need.--for this telephone transmitting set you need: (1) one _aerial ammeter_; (2) one _tuning coil_; (3) one _telephone modulator_; (4) one _aerial series condenser_; (5) one _4 cell dry battery_ or a 6 volt storage battery; (6) one _microphone transmitter_; (7) one _battery switch_; (8) one _grid condenser_; (9) one _grid leak_; (10) two _5 watt oscillator tubes with sockets_; (11) one _blocking condenser_; (12) one _oscillation choke coil_; (13) two _filter condensers_; (14) one _filter reactance coil_; (15) an _alternating current power transformer_, and (16) two _20 watt rectifier vacuum tubes_. all of the above pieces of apparatus are the same as those described for the _100 mile c. w. telegraph transmitter_ in chapter xvii, except: (a) the _microphone modulator_; (b) the _microphone transmitter_ and (c) the _dry_ or _storage battery_, all of which are described in this chapter; and the new parts which are: (d) the _rectifier vacuum tubes_; (e) the _filter condensers_; and (f) the _filter reactance coil_; further and finally, the power transformer has a _third_ secondary coil on it and it is this that feeds the alternating current to the rectifier tubes, which in turn converts it into a pulsating direct current. the vacuum tube rectifier.--this rectifier has two electrodes, that is, it has a filament and a plate like the original vacuum tube detector, the smallest size rectifier tube requires a plate potential of 550 volts which is developed by one of the secondary coils of the power transformer. the filament terminal takes a current of 7.5 volts and this is supplied by another secondary coil of the transformer. this rectifier tube delivers a direct current of 20 watts at 350 volts. it looks exactly like the 5 watt oscillator tube which is pictured at e in fig. 77. the price is $7.50. the filter condensers.--these condensers are used in connection with the reactance coil to smooth out the pulsating direct current after it has passed through the rectifier tube. they have a capacitance of 1 mfd. and will stand 750 volts. these condensers cost about $2.00 each. the filter reactance coil.--this reactor which is shown in fig. 92, has about the same appearance as the power transformer but it is somewhat smaller. it consists of a coil of wire wound on a soft iron core and has a large inductance, hence the capacitance of the filter condensers are proportionately smaller than where a small inductance is used which has been the general practice. the size you require for this set has an output of 160 milliamperes and it will supply current for one to four 5 watt oscillator tubes. this size of reactor costs $11.50. [illustration: fig. 92.--filter reactor for smoothing out rectified currents.] connecting up the apparatus.--the wiring diagram in fig. 93 shows how the various pieces of apparatus for this telephone transmitter are connected up. you will observe: (1) that the terminals of the power transformer secondary coil which develops 10 volts are connected to the filaments of the oscillator tubes; (2) that the terminals of the other secondary coil which develops 10 volts are connected with the filaments of the rectifier tubes; (3) that the terminals of the third secondary coil which develops 550 volts are connected with the plates of the rectifier tubes; (4) that the pair of filter condensers are connected in parallel and these are connected to the mid-taps of the two filament secondary coils; (5) that the reactance coil and the third filter condenser are connected together in series and these are shunted across the filter condensers, which are in parallel; and, finally, (6) a lead connects the mid-tap of the 550-volt secondary coil of the power transformer with the connection between the reactor and the third filter condenser. [illustration: fig 93.--100 to 200 mile wireless telephone transmitter.] a 100 to 200 mile wireless telephone transmitting set--with 110 volt alternating current.--this telephone transmitter is built up of exactly the same pieces of apparatus and connected up in precisely the same way as the one just described and shown in fig. 93. apparatus required.--the only differences between this and the preceding transmitter are: (1) the _magnetic modulator_, if you use one, should have an output of 3-1/2 to 5 amperes; (2) you will need two _50 watt oscillator tubes with sockets_; (3) two _150 watt rectifier tubes with sockets_; (4) an _aerial ammeter_ that reads to _5 amperes_; (5) three _1 mfd. filter condensers_ in parallel; (6) _two filter condensers of 1 mfd. capacitance_ that will stand _1750 volts_; and (6) a _300 milliampere filter reactor_. the apparatus is wired up as shown in fig. 93. chapter xix the operation of vacuum tube transmitters the three foregoing chapters explained in detail the design and construction of (1) two kinds of c. w. telegraph transmitters, and (2) two kinds of wireless telephone transmitters, the difference between them being whether they used (a) a direct current, or (b) an alternating current as the initial source of energy. of course there are other differences between those of like types as, for instance, the apparatus and connections used (_a_) in the key circuits, and (_b_) in the microphone circuits. but in all of the transmitters described of whatever type or kind the same fundamental device is used for setting up sustained oscillations and this is the _vacuum tube_. the operation of the vacuum tube oscillator.--the operation of the vacuum tube in producing sustained oscillations depends on (1) the action of the tube as a valve in setting up the oscillations in the first place and (2) the action of the grid in amplifying the oscillations thus set up, both of which we explained in chapter xiv. in that chapter it was also pointed out that a very small change in the grid potential causes a corresponding and larger change in the amount of current flowing from the plate to the filament; and that if a vacuum tube is used for the production of oscillations the initial source of current must have a high voltage, in fact the higher the plate voltage the more powerful will be the oscillations. to understand how oscillations are set up by a vacuum tube when a direct current is applied to it, take a look at the simple circuits shown in fig. 94. now when you close the switch the voltage from the battery charges the condenser and keeps it charged until you open it again; the instant you do this the condenser discharges through the circuit which includes it and the inductance coil, and the discharge of a condenser is always oscillatory. [illustration: (a) and (b) fig. 94. operation of vacuum tube oscillators.] where an oscillator tube is included in the circuits as shown at a and b in fig. 94, the grid takes the place of the switch and any slight change in the voltage of either the grid or the plate is sufficient to start a train of oscillations going. as these oscillations surge through the tube the positive parts of them flow from the plate to the filament and these carry more of the direct current with them. to make a tube set up powerful oscillations then, it is only necessary that an oscillation circuit shall be provided which will feed part of the oscillations set up by the tube back to the grid circuit and when this is done the oscillations will keep on being amplified until the tube reaches the limit of its output. [illustration: (c) fig. 94.--how a direct current sets up oscillations.] the operation of c. w. telegraph transmitters with direct current--short distance c. w. transmitter.--in the transmitter shown in the wiring diagram in fig. 76 the positive part of the 110 volt direct current is carried down from the lamp socket through one side of the panel cut-out, thence through the choke coil and to the plate of the oscillator tube, when the latter is charged to the positive sign. the negative part of the 110 volt direct current then flows down the other wire to the filament so that there is a difference of potential between the plate and the filament of 110 volts. now when the 6-volt battery current is switched on the filament is heated to brilliancy, and the electrons thrown off by it form a conducting path between it and the plate; the 110 volt current then flows from the latter to the former. now follow the wiring from the plate over to the blocking condenser, thence to _clip 3_ of the tuning coil, through the turns of the latter to _clip 2_ and over to the filament and, when the latter is heated, you have a _closed oscillation circuit_. the oscillations surging in the latter set up other and like oscillations in the tuning coil between the end of which is connected with the grid, the aerial and the _clip 2_, and these surge through the circuit formed by this portion of the coil, the grid condenser and the filament; this is the amplifying circuit and it corresponds to the regenerative circuit of a receiving set. when oscillations are set up in it the grid is alternately charged to the positive and negative signs. these reversals of voltage set up stronger and ever stronger oscillations in the plate circuit as before explained. not only do the oscillations surge in the closed circuits but they run to and fro on the aerial wire when their energy is radiated in the form of electric waves. the oscillations are varied by means of the telegraph key which is placed in the grid circuit as shown in fig. 76. the operation of the key circuit.--the effect in a c. w. transmitter when a telegraph key is connected in series with a buzzer and a battery and these are shunted around the condenser in the grid circuit, is to rapidly change the wave form of the sustained oscillations, and hence, the length of the waves that are sent out. while no sound can be heard in the headphones at the receiving station so long as the points of the key are not in contact, when they are in contact the oscillations are modulated and sounds are heard in the headphones that correspond to the frequency of the buzzer in the key circuit. the operation of c. w. telegraph transmitters with direct current.--the chief differences between the long distance sets which use a direct current, i.e., those described in chapter xvi, and the short distance transmitting sets are that the former use: (1) a motor-generator set for changing the low voltage direct current into high voltage direct current, and (2) a chopper in the key circuit. the way the motor-generator changes the lowinto high-voltage current has been explained in chapter xvi. the chopper interrupts the oscillations surging through the grid circuit at a frequency that the ear can hear, that is to say, about 800 to 1,000 times per second. when the key is open, of course, the sustained oscillations set up in the circuits will send out continuous waves but when the key is closed these oscillations are broken up and then they send out discontinuous waves. if a heterodyne receiving set, see chapter xv, is being used at the other end you can dispense with the chopper and the key circuit needed is very much simplified. the operation of key circuits of the latter kind will be described presently. the operation of c. w. telegraph transmitters with alternating current--with a single oscillator tube.--where an oscillator tube telegraph transmitter is operated by a 110 volt alternating current as the initial source of energy, a buzzer, chopper or other interruptor is not needed in the key circuit. this is because oscillations are set up only when the plate is energized with the positive part of the alternating current and this produces an intermittent musical tone in the headphones. hence this kind of a sending set is called a _tone transmitter_. since oscillations are set up only by the positive part or voltage of an alternating current it is clear that, as a matter of fact, this kind of a transmitter does not send out continuous waves and therefore it is not a c. w. transmitter. this is graphically shown by the curve of the wave form of the alternating current and the oscillations that are set up by the positive part of it in fig. 95. whenever the positive half of the alternating current energizes the plate then oscillations are set up by the tube and, conversely, when the negative half of the current charges the plate no oscillations are produced. [illustration: fig. 95.--positive voltage only sets up oscillations.] you will also observe that the oscillations set up by the positive part of the current are not of constant amplitude but start at zero the instant the positive part begins to energize the plate and they keep on increasing in amplitude as the current rises in voltage until the latter reaches its maximum; then as it gradually drops again to zero the oscillations decrease proportionately in amplitude with it. heating the filament with alternating current.--where an alternating current power transformer is used to develop the necessary plate voltage a second secondary coil is generally provided for heating the filament of the oscillation tube. this is better than a direct current for it adds to the life of the filament. when you use an alternating current to heat the filament keep it at the same voltage rather than at the same amperage (current strength). to do this you need only to use a voltmeter across the filament terminals instead of an ammeter in series with it; then regulate the voltage of the filament with a rheostat. the operation of c. w. telegraph transmitters with alternating current--with two oscillator tubes.--by using two oscillator tubes and connecting them up with the power transformer and oscillating circuits as shown in the wiring diagram in fig. 83 the plates are positively energized alternately with every reversal of the current and, consequently, there is no time period between the ending of the oscillations set up by one tube and the beginning of the oscillations set up by the other tube. in other words these oscillations are sustained but as in the case of those of a single tube, their amplitude rises and falls. this kind of a set is called a _full wave rectification transmitter_. the waves radiated by this transmitter can be received by either a crystal detector or a plain vacuum-tube detector but the heterodyne receptor will give you better results than either of the foregoing types. the operation of wireless telephone transmitters with direct current--short distance transmitter.--the operation of this short distance wireless telephone transmitter, a wiring diagram of which is shown in fig. 85 is exactly the same as that of the _direct current short distance c. w. telegraph transmitter_ already explained in this chapter. the only difference in the operation of these sets is the substitution of the _microphone transmitter_ for the telegraph key. the microphone transmitter.--the microphone transmitter that is used to vary, or modulate, the sustained oscillations set up by the oscillator tube and circuits is shown in fig. 84. by referring to the diagram at a in this figure you will readily understand how it operates. when you speak into the mouthpiece the _sound waves_, which are waves in the air, impinge upon the diaphragm and these set it into vibration--that is, they make it move to and fro. when the diaphragm moves toward the back of the transmitter it forces the carbon granules that are in the cup closer together; this lowers their resistance and allows more current from the battery to flow through them; when the pressure of the air waves is removed from the diaphragm it springs back toward the mouth-piece and the carbon granules loosen up when the resistance offered by them is increased and less current can flow through them. where the oscillation current in the aerial wire is small the transmitter can be connected directly in series with the latter when the former will surge through it. as you speak into the microphone transmitter its resistance is varied and the current strength of the oscillations is varied accordingly. the operation of wireless telephone transmitters with direct current--long distance transmitters.--in the wireless telephone transmitters for long distance work which were shown and described in the preceding chapter a battery is used to energize the microphone transmitter, and these two elements are connected in series with a _microphone modulator_. this latter device may be either (1) a _telephone induction coil_, (2) a _microphone transformer_, or (3) a _magnetic modulator_; the first two of these devices step-up the voltage of the battery current and the amplified voltage thus developed is impressed on the oscillations that surge through the closed oscillation circuit or the aerial wire system according to the place where you connect it. the third device works on a different principle and this will be described a little farther along. the operation of microphone modulators--the induction coil.--this device is really a miniature transformer, see a in fig. 86, and its purpose is to change the 6 volt direct current that flows through the microphone into 100 volts alternating current; in turn, this is impressed on the oscillations that are surging in either (1) the grid circuit as shown at a in fig. 89, and in fig. 90, (2) the aerial wire system, as shown at b in fig. 89 and fig. 93. when the current from the battery flows through the primary coil it magnetizes the soft iron core and as the microphone varies the strength of the current the high voltage alternating currents set up in the secondary coil of the induction coil are likewise varied, when they are impressed upon and modulate the oscillating currents. the microphone transformer.--this is an induction coil that is designed especially for wireless telephone modulation. the iron core of this transformer is also of the open magnetic circuit type, see a in fig. 87, and the _ratio_ of the turns [footnote: see chapter vi] of the primary and the secondary coil is such that when the secondary current is impressed upon either the grid circuit or the aerial wire system it controls the oscillations flowing through it with the greatest efficiency. the magnetic modulator.--this piece of apparatus is also called a _magnetic amplifier_. the iron core is formed of very thin plates, or _laminations_ as they are called, and this permits high-frequency oscillations to surge in a coil wound on it. in this transformer, see a in fig. 88, the current flowing through the microphone varies the magnetic permeability of the soft iron core by the magnetic saturation of the latter. since the microphone current is absolutely distinct from the oscillating currents surging through the coil of the transformer a very small direct current flowing through a coil on the latter will vary or modulate very large oscillating currents surging through the former. it is shown connected in the aerial wire system at a in fig. 88, and in fig. 93. operation of the vacuum tube as a modulator.--where a microphone modulator of the induction coil or microphone transformer type is connected in the grid circuit or aerial wire system the modulation is not very effective, but by using a second tube as a _modulator_, as shown in fig. 90, an efficient degree of modulation can be had. now there are two methods by which a vacuum tube can be used as a modulator and these are: (1) by the _absorption_ of the energy of the current set up by the oscillator tube, and (2) by _varying_ the direct current that energizes the plate of the oscillator tube. the first of these two methods is not used because it absorbs the energy of the oscillating current produced by the tube and it is therefore wasteful. the second method is an efficient one, as the direct current is varied before it passes into the oscillator tube. this is sufficient reason for describing only the second method. the voltage of the grid of the modulator tube is varied by the secondary coil of the induction coil or microphone transformer, above described. in this way the modulator tube acts like a variable resistance but it amplifies the variations impressed on the oscillations set up by the oscillator tube. as the magnetic modulator does the same thing a vacuum tube used as a modulator is not needed where the former is employed. for this reason a magnetic modulator is the cheapest in the long run. the operation of wireless telephone transmitters with alternating current.--where an initial alternating current is used for wireless telephony, the current must be rectified first and then smoothed out before passing into the oscillator tube to be converted into oscillations. further so that the oscillations will be sustained, two oscillator tubes must be used, and, finally, in order that the oscillations may not vary in amplitude the alternating current must be first changed into direct current by a pair of rectifier vacuum tubes, as shown in fig. 93. when this is done the plates will be positively charged alternately with every reversal of the current in which case there will be no break in the continuity of the oscillations set up and therefore in the waves that are sent out. the operation of rectifier vacuum tubes.--the vacuum tube rectifier is simply a two electrode vacuum tube. the way in which it changes a commercial alternating current into pulsating direct current is the same as that in which a two electrode vacuum tube detector changes an oscillating current into pulsating direct currents and this has been explained in detail under the heading of _the operation of a two electrode vacuum tube detector_ in chapter xii. in the _c. w. telegraph transmitting sets_ described in chapter xvii, the oscillator tubes act as rectifiers as well as oscillators but for wireless telephony the alternating current must be rectified first so that a continuous direct current will result. the operation of reactors and condensers.--a reactor is a single coil of wire wound on an iron core, see fig. 90 and a in fig. 91, and it should preferably have a large inductance. the reactor for the plate and grid circuit of a wireless telephone transmitter where one or more tubes are used as modulators as shown in the wiring diagram in fig. 90, and the filter reactor shown in fig. 92, operate in the same way. when an alternating current flows through a coil of wire the reversals of the current set up a _counter electromotive force_ in it which opposes, that is _reacts_, on the current, and the _higher_ the frequency of the current the _greater_ will be the _reactance_. when the positive half of an alternating current is made to flow through a large resistance the current is smoothed out but at the same time a large amount of its energy is used up in producing heat. but when the positive half of an alternating current is made to flow through a large inductance it acts like a large resistance as before and likewise smooths out the current, but none of its energy is wasted in heat and so a coil having a large inductance, which is called an _inductive reactance_, or just _reactor_ for short, is used to smooth out, or filter, the alternating current after it has been changed into a pulsating direct current by the rectifier tubes. a condenser also has a reactance effect on an alternating current but different from an induction coil the _lower_ the frequency the _greater_ will be the reactance. for this reason both a filter reactor and _filter condensers_ are used to smooth out the pulsating direct currents. chapter xx how to make a receiving set for $5.00 or less in the chapters on _receptors_ you have been told how to build up high-grade sets. but there are thousands of boys, and, probably, not a few men, who cannot afford to invest $25.00, more or less, in a receiving set and would like to experiment in a small way. the following set is inexpensive, and with this cheap, little portable receptor you can get the morse code from stations a hundred miles distant and messages and music from broadcasting stations if you do not live too far away from them. all you need for this set are: (1) a _crystal detector_, (2) a _tuning coil_ and (3) an _earphone_. you can make a crystal detector out of a couple of binding posts, a bit of galena and a piece of brass wire, or, better, you can buy one all ready to use for 50 cents. [illustration: wireless receptor, the size of a safety match box. a youthful genius in the person of kenneth r. hinman, who is only twelve years old, has made a wireless receiving set that fits neatly into a safety match box. with this instrument and a pair of ordinary receivers, he is able to catch not only code messages but the regular broadcasting programs from stations twenty and thirty miles distant.] the crystal detector.--this is known as the _rasco baby_ detector and it is made and sold by the _radio specialty company_, 96 park place, new york city. it is shown in fig. 96. the base is made of black composition and on it is mounted a standard in which a rod slides and on one end of this there is fixed a hard rubber adjusting knob while the other end carries a thin piece of _phosphor-bronze wire_, called a _cat-whisker_. to secure the galena crystal in the cup you simply unscrew the knurled cap, place it in the cavity of the post and screw the cap back on again. the free end of the cat-whisker wire is then adjusted so that it will rest lightly on the exposed part of the galena. [illustration: fig. 96.--rasco baby crystal detector.] the tuning coil.--you will have to make this tuning coil, which you can do at a cost of less than $1.00, as the cheapest tuning coil you can buy costs at least $3.00, and we need the rest of our $5.00 to invest in the earphone. get a cardboard tube, such as is used for mailing purposes, 2 inches in diameter and 3 inches long, see a in fig. 97. now wind on 250 turns of _no. 40 brown and sharpe gauge plain enameled magnet wire_. you can use _no. 40 double cotton covered magnet wire_, in which case you will have to shellac the tube and the wire after you get it on. [illustration: fig. 97.--how the tuning coil is made.] as you wind on the wire take off a tap at every 15th turn, that is, scrape the wire and solder on a piece about 7 inches long, as shown in fig. 99; and do this until you have 6 taps taken off. instead of leaving the wires outside of the tube bring them to the inside of it and then out through one of the open ends. now buy a _round wood-base switch_ with 7 contact points on it as shown at b in fig. 97. this will cost you 25 or 50 cents. the headphone.--an ordinary bell telephone receiver is of small use for wireless work as it is wound to too low a resistance and the diaphragm is much too thick. if you happen to have a bell phone you can rewind it with _no. 40_ single covered silk magnet wire, or enameled wire of the same size, when its sensitivity will be very greatly improved. then you must get a thin diaphragm and this should _not_ be enameled, as this tends to dampen the vibrations of it. you can get a diaphragm of the right kind for 5 cents. the better way, though, is to buy an earphone made especially for wireless work. you can get one wound to 1000 ohms resistance for $1.75 and this price includes a cord. [footnote: this is mesco, no. 470 wireless phone. sold by the manhattan electrical supply co., park place, n.y.c.] for $1.00 extra you can get a head-band for it, and then your phone will look like the one pictured in fig. 98. [illustration: fig. 98.--mesco 1000 ohm head set.] how to mount the parts.--now mount the coil on a wood base, 1/2 or 1 inch thick, 3-1/2 inches wide and 5-1/2 inches long, and then connect one end of the coil to one of the end points on the switch, and connect each succeeding tap to one of the switch points, as shown schematically in fig. 99 and diagrammatically in fig. 100. this done, screw the switch down to the base. finally screw the detector to the base and screw two binding posts in front of the coil. these are for the earphone. [illustration: fig. 99.--schematic layout of $5.00 receiving set.] [illustration: fig. 100.--wiring diagram for $5.00 receiving set.] the condenser.--you do not have to connect a condenser across the earphone but if you do you will improve the receiving qualities of the receptor. how to connect up the receptor.--now connect up all the parts as shown in figs. 99 and 100, then connect the leading-in wire of the aerial with the lever of the switch; and connect the free end of the tuning coil with the _ground_. if you have no aerial wire try hooking it up to a rain pipe that is _not grounded_ or the steel frame of an umbrella. for a _ground_ you can use a water pipe, an iron pipe driven into the ground, or a hydrant. put on your headphone, adjust the detector and move the lever over the switch contacts until it is in adjustment and then, if all your connections are properly made, you should be able to pick up messages. [illustration: wireless set made into a ring, designed by alfred g. rinehart, of elizabeth, new jersey. this little receptor is a practical set; it will receive messages, concerts, etc., measures 1" by 5/8" by 7/8". an ordinary umbrella is used as an aerial.] appendix useful information abbreviations of units unit abbreviation ampere amp. ampere-hours amp.-hr. centimeter cm. centimeter-gram-second c.g.s. cubic centimeters cm.^3 cubic inches cu. in. cycles per second ~ degrees centigrade â°c. degrees fahrenheit â°f. feet ft. foot-pounds ft.-lb. grams g. henries h. inches in. kilograms kg. kilometers km. kilowatts kw. kilowatt-hours kw.-hr. kilovolt-amperes kv.-a. meters m. microfarads [greek: mu]f. micromicrofarads [greek: mu mu]f. millihenries mh. millimeters mm. pounds lb. seconds sec. square centimeters cm.^2 square inches sq. in. volts v. watts w. prefixes used with metric system units prefix abbreviation meaning micro [greek: mu]. 1 millionth milli m. 1 thousandth centi c. 1 hundredth deci d. 1 tenth deka dk. 10 hekto h. 1 hundred kilo k. 1 thousand mega m. 1 million symbols used for various quantities quantity symbol capacitance c conductance g coupling co-efficient k current, instantaneous i current, effective value i decrement [greek: delta] dielectric constant [greek: alpha] electric field intensity [greek: epsilon] electromotive force, instantaneous value e electromotive force, effective value f energy w force f frequency f frequency x 2[greek: pi] [greek: omega] impedance z inductance, self l inductance, mutual m magnetic field intensity a magnetic flux [greek: phi] magnetic induction b period of a complete oscillation t potential difference v quantity of electricity q ratio of the circumference of a circle to its diameter =3.1416 [greek: pi] reactance x resistance r time t velocity v velocity of light c wave length [greek: lambda] wave length in meters [greek: lambda]m work w permeability [greek: mu] square root [math: square root] table of enameled wire no. of turns turns ohms per wire, per per cubic inch b.& s. linear square of gauge inch inch winding 20 30 885 .748 22 37 1400 1.88 24 46 2160 4.61 26 58 3460 11.80 28 73 5400 29.20 30 91 8260 70.90 32 116 21,000 7547.00 34 145 13,430 2968.00 36 178 31,820 1098.00 38 232 54,080 456.00 40 294 86,500 183.00 table of frequency and wave lengths w. l.--wave lengths in meters. f.--number of oscillations per second. o. or square root l. c. is called oscillation constant. c.--capacity in microfarads. l.--inductance in centimeters. 1000 centimeters = 1 microhenry. w.l. f o l.c. 50 6,000,000 .839 .7039 100 3,000,000 1.68 2.82 150 2,000,000 2.52 6.35 200 1,500,000 3.36 11.29 250 1,200,000 4.19 17.55 300 1,000,000 5.05 25.30 350 857,100 5.87 34.46 400 750,000 6.71 45.03 450 666,700 7.55 57.00 500 600,000 8.39 70.39 550 545,400 9.23 85.19 600 500,000 10.07 101.41 700 428,600 11.74 137.83 800 375,000 13.42 180.10 900 333,300 15.10 228.01 1,000 300,000 16.78 281.57 1,100 272,730 18.45 340.40 1,200 250,000 20.13 405.20 1,300 230,760 21.81 475.70 1,400 214,380 23.49 551.80 1,500 200,000 25.17 633.50 1,600 187,500 26.84 720.40 1,700 176,460 28.52 813.40 1,800 166,670 30.20 912.00 1,900 157,800 31.88 1,016.40 2,000 150,000 33.55 1,125.60 2,100 142,850 35.23 1,241.20 2,200 136,360 36.91 1,362.40 2,300 130,430 38.59 1,489.30 2,400 125,000 40.27 1,621.80 2,500 120,000 41.95 1,759.70 2,600 115,380 43.62 1,902.60 2,700 111,110 45.30 2,052.00 2,800 107,140 46.89 2,207.00 2,900 103,450 48.66 2,366.30 3,000 100,000 50.33 2,533.20 4,000 75,000 67.11 4,504.00 5,000 60,000 83.89 7,038.00 6,000 50,000 100.7 10,130.00 7,000 41,800 117.3 13,630.00 8,000 37,500 134.1 18,000.00 9,000 33,300 151.0 22,820.00 10,000 30,000 167.9 28,150.00 11,000 27,300 184.8 34,150.00 12,000 25,000 201.5 40,600.00 13,000 23,100 218.3 47,600.00 14,000 21,400 235.0 55,200.00 15,000 20,000 252.0 63,500.00 16,000 18,750 269.0 72,300.00 pronunciation of greek letters many of the physical quantities use greek letters for symbols. the following is the greek alphabet with the way the letters are pronounced: a alpha b beta g gamma d delta e epsilon z zeta ae eta th theta i iota k kappa l lambda m mu n nu x xi(zi) o omicron p pi r rho s sigma t tau u upsilon ph phi ch chi ps psi o omega table of sparking distances in air for various voltages between needle points volts distance inches centimeter 5,000 .225 .57 10,000 .470 1.19 15,000 .725 1.84 20,000 1.000 2.54 25,000 1.300 3.30 30,000 1.625 4.10 35,000 2.000 5.10 40,000 2.450 6.20 45,000 2.95 7.50 50,000 3.55 9.90 60,000 4.65 11.8 70,000 5.85 14.9 80,000 7.10 18.0 90,000 8.35 21.2 100,000 9.60 24.4 110,000 10.75 27.3 120,000 11.85 30.1 130,000 12.95 32.9 140,000 13.95 35.4 150,000 15.00 38.1 feet per pound of insulated magnet wire no. of single double single double b.& s. cotton, cotton, silk, silk, enamel gauge 4-mils 8-mils 1-3/4-mils 4-mils 20 311 298 319 312 320 21 389 370 408 389 404 22 488 461 503 498 509 23 612 584 636 631 642 24 762 745 800 779 810 25 957 903 1,005 966 1,019 26 1,192 1,118 1,265 1,202 1,286 27 1,488 1,422 1,590 1,543 1,620 28 1,852 1,759 1,972 1,917 2,042 29 2,375 2,207 2,570 2,435 2,570 30 2,860 2,534 3,145 2,900 3,240 31 3,800 2,768 3,943 3,683 4,082 32 4,375 3,737 4,950 4,654 5,132 33 5,590 4,697 6,180 5,689 6,445 34 6,500 6,168 7,740 7,111 8,093 35 8,050 6,737 9,600 8,584 10,197 36 9,820 7,877 12,000 10,039 12,813 37 11,860 9,309 15,000 10,666 16,110 38 14,300 10,636 18,660 14,222 20,274 39 17,130 11,907 23,150 16,516 25,519 40 21,590 14,222 28,700 21,333 32,107 international morse code and conventional signals to be used for all general public service radio communication 1. a dash is equal to three dots. 2. the space between parts of the same letter is equal to one dot. 3. the space between two letters is equal to three dots. 4. the space between two words is equal to five dots. [note: period denotes morse dot, hyphen denotes morse dash] a .b -... c -.-. d -.. e . f ..-. g --. h .... i .. j .--k -.l .-.. m -n -. o --p .--. q --.r .-. s ... t u ..v ...w .-x -..y -.-z --.. ã� (german) .-.ã� or ã� (spanish-scandinavian) .--.ch (german-spanish) ---ã� (french) ..-.. ã� (spanish) --.-ã� (german) ---. ã� (german) ..-1 .---2 ..--3 ...-4 ....5 ..... 6 -.... 7 --... 8 ---.. 9 ----. 0 ----period .. .. .. semicolon -.-.-. comma -.-.-. colon ---... interrogation ..--.. exclamation point --..-apostrophe .----. hyphen -....bar indicating fraction -..-. parenthesis -.--.inverted commas .-..-. underline ..--.double dash -...distress call ...---... attention call to precede every transmission -.-.general inquiry call -.-. --.from (de) -.. . invitation to transmit (go ahead) -.warning--high power --..-question (please repeat after ...)--interrupting long messages ..--.. wait .-... break (bk.) (double dash) -...understand ...-. error ........ received (o.k.) .-. position report (to precede all position messages) .-. end of each message (cross) .-.-. transmission finished (end of work) (conclusion of correspondence) ...-.international radiotelegraphic convention list of abbreviations to be used in radio communication abbreviation question answer or reply prb do you wish to communicate i wish to communicate by means by means of the international of the international signal code. signal code? qra what ship or coast station is this is.... that? qrb what is your distance? my distance is.... qrc what is your true bearing? my true bearing is.... qrd where are you bound for? i am bound for.... qrf where are you bound from? i am bound from.... qrg what line do you belong to? i belong to the ... line. qrh what is your wave length in my wave length is ... meters. meters? qrj how many words have you to send? i have ... words to send. qrk how do you receive me? i am receiving well. qrl are you receiving badly? i am receiving badly. please shall i send 20? send 20. ...-. ...-. for adjustment? for adjustment. qrm are you being interfered with? i am being interfered with. qrn are the atmospherics strong? atmospherics are very strong. qro shall i increase power? increase power. qrp shall i decrease power? decrease power. qrq shall i send faster? send faster. qrs shall i send slower? send slower. qrt shall i stop sending? stop sending. qru have you anything for me? i have nothing for you. qrv are you ready? i am ready. all right now. qrw are you busy? i am busy (or: i am busy with...). please do not interfere. qrx shall i stand by? stand by. i will call you when required. qry when will be my turn? your turn will be no.... qrz are my signals weak? you signals are weak. qsa are my signals strong? you signals are strong. qsb is my tone bad? the tone is bad. is my spark bad? the spark is bad. qsc is my spacing bad? your spacing is bad. qsd what is your time? my time is.... qsf is transmission to be in transmission will be in alternate order or in series? alternate order. qsg transmission will be in a series of 5 messages. qsh transmission will be in a series of 10 messages. qsj what rate shall i collect for...? collect.... qsk is the last radiogram canceled? the last radiogram is canceled. qsl did you get my receipt? please acknowledge. qsm what is your true course? my true course is...degrees. qsn are you in communication with land? i am not in communication with land. qso are you in communication with i am in communication with... any ship or station (through...). (or: with...)? qsp shall i inform...that you are inform...that i am calling him. calling him? qsq is...calling me? you are being called by.... qsr will you forward the radiogram? i will forward the radiogram. qst have you received the general general call to all stations. call? qsu please call me when you have will call when i have finished. finished (or: at...o'clock)? qsv is public correspondence being public correspondence is being handled? handled. please do not interfere. [footnote: public correspondence is any radio work, official or private, handled on commercial wave lengths.] qsw shall i increase my spark increase your spark frequency. frequency? qsx shall i decrease my spark decrease your spark frequency. frequency? qsy shall i send on a wavelength let us change to the wave length of ... meters? of ... meters. qsz send each word twice. i have difficulty in receiving you. qta repeat the last radiogram. when an abbreviation is followed by a mark of interrogation, it refers to the question indicated for that abbreviation. useful information symbols used for apparatus alternator ammeter aerial arc battery buzzer condenser variable condenser connection of wires no connection coupled coils variable coupling detector gap, plain gap, quenched ground hot wire ammeter inductor variable inductor key resistor variable resistor switch s.p.s.t. " s.p.d.t. " d.p.s.t. " d.p.d.t. " reversing phone receiver " transmitter thermoelement transformer vacuum tube voltmeter choke coil definitions of electric and magnetic units the _ohm_ is the resistance of a thread of mercury at the temperature of melting ice, 14.4521 grams in mass, of uniform cross-section and a length of 106.300 centimeters. the _ampere_ is the current which when passed through a solution of nitrate of silver in water according to certain specifications, deposits silver at the rate of 0.00111800 of a gram per second. the _volt_ is the electromotive force which produces a current of 1 ampere when steadily applied to a conductor the resistance of which is 1 ohm. the _coulomb_ is the quantity of electricity transferred by a current of 1 ampere in 1 second. the _ampere-hour_ is the quantity of electricity transferred by a current of 1 ampere in 1 hour and is, therefore, equal to 3600 coulombs. the _farad_ is the capacitance of a condenser in which a potential difference of 1 volt causes it to have a charge of 1 coulomb of electricity. the _henry_ is the inductance in a circuit in which the electromotive force induced is 1 volt when the inducing current varies at the rate of 1 ampere per second. the _watt_ is the power spent by a current of 1 ampere in a resistance of 1 ohm. the _joule_ is the energy spent in i second by a flow of 1 ampere in 1 ohm. the _horse-power_ is used in rating steam machinery. it is equal to 746 watts. the _kilowatt_ is 1,000 watts. the units of capacitance actually used in wireless work are the _microfarad_, which is the millionth part of a farad, because the farad is too large a unit; and the _c. g. s. electrostatic unit of capacitance_, which is often called the _centimeter of capacitance_, which is about equal to 1.11 microfarads. the units of inductance commonly used in radio work are the _millihenry_, which is the thousandth part of a henry; and the _centimeter of inductance_, which is one one-thousandth part of a microhenry. note.--for further information about electric and magnetic units get the _bureau of standards circular no. 60_, called _electric units and standards_, the price of which is 15 cents; also get _scientific paper no. 292_, called _international system of electric and magnetic units_, price 10 cents. these and other informative papers can be had from the _superintendent of documents, government printing office_, washington, d. c. wireless books the admiralty manual of wireless telegraphy. 1920. published by his majesty's stationery office, london. ralph e. batcher.--prepared radio measurements. 1921. wireless press, inc., new york city. elmer e. bucher.--practical wireless telegraphy. 1918. wireless press, inc., new york city. elmer e. bucher.--vacuum tubes in wireless communication. 1919. wireless press, inc., new york city. elmer e. bucher.--the wireless experimenter's manual. 1920. wireless press, inc., new york city. a. frederick collins.--wireless telegraphy, its history, theory, and practice. 1905. mcgraw pub. co., new york city. j. h. dellinger.--principles underlying radio communication. 1921. signal corps, u. s. army, washington, d. c. h. m. dorsett.--wireless telegraphy and telephony. 1920. wireless press, ltd., london. j. a. fleming.--principles of electric wave telegraphy. 1919. longmans, green and co., london. charles b. hayward.--how to become a wireless operator. 1918. american technical society, chicago, ill. g. d. robinson.--manual of radio telegraphy and telephony. 1920. united states naval institute, annapolis, md. rupert stanley.--textbook of wireless telegraphy. 1919. longmans, green and co., london. e. w. stone.--elements of radio telegraphy. 1919. d, van nostrand co., new york city. l. b. turner.--wireless telegraphy and telephony. 1921. cambridge university press. cambridge, england. send to the _superintendent of documents, government printing office_, washington, d. c., for a copy of _price list no. 64_ which lists the government's books and pamphlets on wireless. it will be sent to you free of charge. the government publishes; (1) _a list of commercial government and special wireless stations_, every year, price 15 cents; (2) _a list of amateur wireless stations_, yearly, price 15 cents; (3) _a wireless service bulletin_ is published monthly, price 5 cents a copy, or 25 cents yearly; and (4) _wireless communication laws of the united states_, the _international wireless telegraphic convention and regulations governing wireless operators and the use of wireless on ships and land stations_, price 15 cents a copy. orders for the above publications should be addressed to the _superintendent of documents, government printing office, washington, d. c._ manufacturers and dealers in wireless apparatus and supplies: adams-morgan co., upper montclair, n. j. american hard rubber co., 11 mercer street, new york city. american radio and research corporation, medford hillside, mass. brach (l. s.) mfg. co., 127 sussex ave., newark, n. j. brandes (c.) inc., 237 lafayette st., new york city. bunnell (j. h.) company, park place, new york city. burgess battery company, harris trust co. bldg., chicago, ill. clapp-eastman co., 120 main st., cambridge, mass. connecticut telephone and telegraph co., meriden, conn. continental fiber co., newark, del. coto-coil co., providence, r. i. crosley mfg. co., cincinnati, ohio. doolittle (f. m.), 817 chapel st., new haven, conn. edelman (philip e.), 9 cortlandt st., new york city. edison storage battery co., orange, n. j. electric specialty co., stamford, conn. electrose mfg. co., 60 washington st., brooklyn, n. y. general electric co., schenectady, n. y. grebe (a. h.) and co., inc., richmond hill, n. y. c. international brass and electric co., 176 beekman st., new york city. international insulating co., 25 west 45th st., new york city. king amplitone co., 82 church st., new york city. kennedy (colin b.) co., rialto bldg., san francisco, cal. magnavox co., oakland, cal. manhattan electrical supply co., park place, n. y. marshall-gerken co., toledo, ohio. michigan paper tube and can co., 2536 grand river ave., detroit, mich. murdock (wm. j.) co., chelsea, mass. national carbon co., inc., long island city, n. y. pittsburgh radio and appliance co., 112 diamond st., pittsburgh, pa, radio corporation of america, 233 broadway, new york city. riley-klotz mfg. co., 17-19 mulberry st., newark, n. j. radio specialty co., 96 park place, new york city. roller-smith co., 15 barclay st., new york city. tuska (c. d.) co., hartford, conn. western electric co., chicago, ill. westinghouse electric co., pittsburgh, pa. weston electrical instrument co., 173 weston ave., newark, n. j. westfield machine co., westfield, mass. abbreviations of common terms a. ..............aerial a.c. ............alternating current a.f. ............audio frequency b. and s. .......brown & sharpe wire gauge c. ..............capacity or capacitance c.g.s. ..........centimeter-grain-second cond. ...........condenser coup. ...........coupler c.w. ............continuous waves d.c. ............direct current d.p.d.t. ........double point double throw d.p.s.t. ........double point single throw d.x. ............distance e. ..............short for electromotive force (volt) e.m.f. ..........electromotive force f. ..............filament or frequency g. ..............grid gnd. ............ground i. ..............current strength (ampere) i.c.w. ..........interrupted continuous waves kw. .............kilowatt l. ..............inductance l.c. ............loose coupler litz. ...........litzendraht mfd. ............microfarad neg. ............negative o.t. ............oscillation transformer p. ..............plate prim. ...........primary pos. ............positive r. ..............resistance r.f. ............radio frequency sec. ............secondary s.p.d.t. ........single point double throw s.p.s.t. ........single point single throw s.r. ............self rectifying t. ..............telephone or period (time) of complete oscillation tick. ...........tickler v. ..............potential difference var. ............variometer var. cond. ......variable condenser v.t. ............vacuum tube w.l. ............wave length x. ..............reactance glossary a battery.--see battery a. abbreviations, code.--abbreviations of questions and answers used in wireless communication. the abbreviation _of a question_ is usually in three letters of which the first is q. thus q r b is the code abbreviation of "_what is your distance?_" and the answer "_my distance is_..." see page 306 [appendix: list of abbreviations]. abbreviations, units.--abbreviations of various units used in wireless electricity. these abbreviations are usually lower case letters of the roman alphabet, but occasionally greek letters are used and other signs. thus _amperes_ is abbreviated _amp., micro_, which means _one millionth_, [greek: mu], etc. see page 301 [appendix: useful abbreviations]. abbreviations of words and terms.--letters used instead of words and terms for shortening them up where there is a constant repetition of them, as _a.c._ for _alternating current; c.w._ for _continuous waves; v.t._ for _vacuum tube_, etc. see page 312 [appendix: abbreviations of common terms]. aerial.--also called _antenna_. an aerial wire. one or more wires suspended in the air and insulated from its supports. it is the aerial that sends out the waves and receives them. aerial, amateur.--an aerial suitable for sending out 200 meter wave lengths. such an aerial wire system must not exceed 120 feet in length from the ground up to the aerial switch and from this through the leading-in wire to the end of the aerial. aerial ammeter.--see _ammeter, hot wire_. aerial, bed-springs.--where an outdoor aerial is not practicable _bed-springs_ are often made to serve the purpose. aerial capacity.--see _capacity, aerial._ aerial counterpoise.--where it is not possible to get a good ground an _aerial counterpoise_ or _earth capacity_ can be used to advantage. the counterpoise is made like the aerial and is supported directly under it close to the ground but insulated from it. aerial, directional.--a flat-top or other aerial that will transmit and receive over greater distances to and from one direction than to and from another. aerial, ground.--signals can be received on a single long wire when it is placed on or buried in the earth or immersed in water. it is also called a _ground antenna_ and an _underground aerial._ aerial, loop.--also called a _coil aerial, coil antenna, loop aerial, loop antenna_ and when used for the purpose a _direction finder_. a coil of wire wound on a vertical frame. aerial resistance.--see _resistance, aerial._ aerial switch.--see _switch aerial._ aerial wire.--(1) a wire or wires that form the aerial. (2) wire that is used for aerials; this is usually copper or copper alloy. aerial wire system.--an aerial and ground wire and that part of the inductance coil which connects them. the open oscillation circuit of a sending or a receiving station. air core transformer.--see _transformer, air core._ amateur aerial or antenna.--see _aerial, amateur._ alternator.--an electric machine that generates alternating current. alphabet, international code.--a modified morse alphabet of dots and dashes originally used in continental europe and, hence, called the _continental code_. it is now used for all general public service wireless communication all over the world and, hence, it is called the _international code_. see page 305 [appendix: international morse code]. alternating current (_a.c._)--see _current._ alternating current transformer.--see _transformer_. amateur ground.--see _ground, amateur_. ammeter.--an instrument used for measuring the current strength, in terms of amperes, that flows in a circuit. ammeters used for measuring direct and alternating currents make use of the _magnetic effects_ of the currents. high frequency currents make use of the _heating effects_ of the currents. ammeter, hot-wire.--high frequency currents are usually measured by means of an instrument which depends on heating a wire or metal strip by the oscillations. such an instrument is often called a _thermal ammeter_, _radio ammeter_ and _aerial ammeter_. ammeter, aerial.--see _ammeter, hot wire_. ammeter, radio.--see _ammeter, hot wire_. ampere.--the current which when passed through a solution of nitrate of silver in water according to certain specifications, deposits silver at the rate of 0.00111800 of a gram per second. ampere-hour.--the quantity of electricity transferred by a current of 1 ampere in 1 hour and is, therefore, equal to 3600 coulombs. ampere-turns.--when a coil is wound up with a number of turns of wire and a current is made to flow through it, it behaves like a magnet. b the strength of the magnetic field inside of the coil depends on (1) the strength of the current and (2) the number of turns of wire on the coil. thus a feeble current flowing through a large number of turns will produce as strong a magnetic field as a strong current flowing through a few turns of wire. this product of the current in amperes times the number of turns of wire on the coil is called the _ampere-turns_. amplification, audio frequency.--a current of audio frequency that is amplified by an amplifier tube or other means. amplification, cascade.--see _cascade amplification_. amplification, radio frequency.--a current of radio frequency that is amplified by an amplifier tube or other means before it reaches the detector. amplification, regenerative.--a scheme that uses a third circuit to feed back part of the oscillations through a vacuum tube and which increases its sensitiveness when used as a detector and multiplies its action as an amplifier and an oscillator. amplifier, audio frequency.--a vacuum tube or other device that amplifies the signals after passing through the detector. amplifier, magnetic.--a device used for controlling radio frequency currents either by means of a telegraph key or a microphone transmitter. the controlling current flows through a separate circuit from that of the radio current and a fraction of an ampere will control several amperes in the aerial wire. amplifiers, multi-stage.--a receiving set using two or more amplifiers. also called _cascade amplification_. amplifier, vacuum tube.--a vacuum tube that is used either to amplify the radio frequency currents or the audio frequency currents. amplitude of wave.--the greatest distance that a point moves from its position of rest. amplifying transformer, audio.--see _transformer, audio amplifying_. amplifying modulator vacuum tube.--see _vacuum tube, amplifying modulator_. amplifying transformer radio.--see _transformer, radio amplifying_. antenna, amateur.--see _aerial, amateur_. antenna switch.--see _switch, aerial_. apparatus symbols.--see _symbols, apparatus_. armstrong circuit.--see _circuit, armstrong_. atmospherics.--same as _static_, which see. attenuation.--in sending wireless telegraph and telephone messages the amplitude of the electric waves is damped out as the distance increases. this is called _attenuation_ and it increases as the frequency is increased. this is the reason why short wave lengths will not carry as far as long wave lengths. audio frequency amplifier.--see _amplifier, audio frequency_. audio frequency amplification.--see _amplification, audio frequency_. audibility meter.--see _meter, audibility_. audio frequency.--see _frequency, audio_. audio frequency current.--see _current, audio frequency_. audion.--an early trade name given to the vacuum tube detector. autodyne receptor.--see _receptor, autodyne_. auto transformer.--see _transformer, auto_. bakelite.--a manufactured insulating compound. b battery.--see _battery b_. band, wave length.--see _wave length band_. basket wound coils.--see _coils, inductance_. battery, a.--the 6-volt storage battery used to heat the filament of a vacuum tube, detector or amplifier. battery, b.--the 22-1/2-volt dry cell battery used to energize the plate of a vacuum tube detector or amplifier. battery, booster.--this is the battery that is connected in series with the crystal detector. battery, c.--a small dry cell battery sometimes used to give the grid of a vacuum tube detector a bias potential. battery, edison storage.--a storage battery in which the elements are made of nickel and iron and immersed in an alkaline _electrolyte_. battery, lead storage.--a storage battery in which the elements are made of lead and immersed in an acid electrolyte. battery poles.--see _poles, battery_. battery, primary.--a battery that generates current by chemical action. battery, storage.--a battery that develops a current after it has been charged. beat reception.--see _heterodyne reception_. bed springs aerial.--see _aerial, bed springs_. blub blub.--over modulation in wireless telephony. broad wave.--see _wave, broad_. brush discharge.--see _discharge_. buzzer modulation.--see _modulation, buzzer_. blue glow discharge.--see _discharge_. booster battery.--see _battery, booster_. broadcasting.--sending out intelligence and music from a central station for the benefit of all who live within range of it and who have receiving sets. capacitance.--also called by the older name of _capacity_. the capacity of a condenser, inductance coil or other device capable of retaining a charge of electricity. capacitance is measured in terms of the _microfarad_. capacitive coupling.--see _coupling, capacitive_. capacity.--any object that will retain a charge of electricity; hence an aerial wire, a condenser or a metal plate is sometimes called a _capacity_. capacity, aerial.--the amount to which an aerial wire system can be charged. the _capacitance_ of a small amateur aerial is from 0.0002 to 0.0005 microfarad. capacity, distributed.--a coil of wire not only has inductance, but also a certain small capacitance. coils wound with their turns parallel and having a number of layers have a _bunched capacitance_ which produces untoward effects in oscillation circuits. in honeycomb and other stagger wound coils the capacitance is more evenly distributed. capacity reactance.--see _reactance, capacity_. capacity unit.--see _farad_. carbon rheostats.--see _rheostat, carbon_. carborundum detector.--see _detector_. carrier current telephony.--see _wired-wireless_. carrier frequency.--see _frequency, carrier_. carrier frequency telephony.--see _wired-wireless_. cascade amplification.--two or more amplifying tubes hooked up in a receiving set. cat whisker contact.--a long, thin wire which makes contact with the crystal of a detector. centimeter of capacitance.--equal to 1.11 _microfarads_. centimeter of inductance.--equal to one one-thousandth part of a _microhenry_. cellular coils.--see _coils, inductance_. c.g.s. electrostatic unit of capacitance.--see _centimeter of capacitance_. characteristics.--the special behavior of a device, such as an aerial, a detector tube, etc. characteristics, grid.--see _grid characteristics_. choke coils.--coils that prevent the high voltage oscillations from surging back into the transformer and breaking down the insulation. chopper modulation.--see _modulation, chopper_. circuit.--any electrical conductor through which a current can flow. a low voltage current requires a loop of wire or other conductor both ends of which are connected to the source of current before it can flow. a high frequency current will surge in a wire which is open at both ends like the aerial. closed circuit.--a circuit that is continuous. open circuit.--a conductor that is not continuous. coupled circuits.--open and closed circuits connected together by inductance coils, condensers or resistances. see _coupling_. close coupled circuits.--open and closed circuits connected directly together with a single inductance coil. loose coupled circuits.--opened and closed currents connected together inductively by means of a transformer. stand-by circuits.--also called _pick-up_ circuits. when listening-in for possible calls from a number of stations, a receiver is used which will respond to a wide band of wave lengths. armstrong circuits.--the regenerative circuit invented by major e. h. armstrong. close coupled circuits.--see _currents, close coupled_. closed circuit.--see _circuit, closed_. closed core transformer.--see _transformer, closed core_. code.-continental.--same as _international_. international.--on the continent of europe land lines use the _continental morse_ alphabetic code. this code has come to be used throughout the world for wireless telegraphy and hence it is now called the _international code_. it is given on page 305. [appendix: international morse code]. morse.--the code devised by samuel f. b. morse and which is used on the land lines in the u. s. national electric.--a set of rules and requirements devised by the _national board of fire underwriters_ for the electrical installations in buildings on which insurance companies carry risks. this code also covers the requirements for wireless installations. a copy may be had from the _national board of fire underwriters_, new york city, or from your insurance agent. national electric safety.--the bureau of standards, washington, d. c., have investigated the precautions which should be taken for the safe operation of all electric equipment. a copy of the _bureau of standards handbook no. 3_ can be had for 40 cents from the _superintendent of documents_. coefficient of coupling.--see _coupling, coefficient of_. coil aerial.--see _aerial, loop_. coil antenna.--see _aerial, loop_. coil, induction.--an apparatus for changing low voltage direct currents into high voltage, low frequency alternating currents. when fitted with a spark gap the high voltage, low frequency currents are converted into high voltage, high frequency currents. it is then also called a _spark coil_ and a _ruhmkorff coil_. coil, loading.--a coil connected in the aerial or closed oscillation circuit so that longer wave lengths can be received. coil, repeating.--see _repeating coil_. coil, rotating.--one which rotates on a shaft instead of sliding as in a _loose coupler_. the rotor of a _variometer_ or _variocoupler_ is a _rotating coil_. coils, inductance.--these are the tuning coils used for sending and receiving sets. for sending sets they are formed of one and two coils, a single sending coil is generally called a _tuning inductance coil_, while a two-coil tuner is called an _oscillation transformer_. receiving tuning coils are made with a single layer, single coil, or a pair of coils, when it is called an oscillation _transformer_. some tuning inductance coils have more than one layer, they are then called _lattice wound_, _cellular_, _basket wound_, _honeycomb_, _duo-lateral_, _stagger wound_, _spider-web_ and _slab_ coils. commercial frequency.--see _frequency, commercial_. condenser, aerial series.--a condenser placed in the aerial wire system to cut down the wave length. condenser, vernier.--a small variable condenser used for receiving continuous waves where very sharp tuning is desired. condenser.--all conducting objects with their insulation form capacities, but a _condenser_ is understood to mean two sheets or plates of metal placed closely together but separated by some insulating material. adjustable condenser.--where two or more condensers can be coupled together by means of plugs, switches or other devices. aerial condenser.--a condenser connected in the aerial. air condenser.--where air only separates the sheets of metal. by-pass condenser.--a condenser connected in the transmitting currents so that the high frequency currents cannot flow back through the power circuit. filter condenser.--a condenser of large capacitance used in combination with a filter reactor for smoothing out the pulsating direct currents as they come from the rectifier. fixed condenser.--where the plates are fixed relatively to one another. grid condenser.--a condenser connected in series with the grid lead. leyden jar condenser.--where glass jars are used. mica condenser.--where mica is used. oil condenser.--where the plates are immersed in oil. paper condenser.--where paper is used as the insulating material. protective.--a condenser of large capacity connected across the low voltage supply circuit of a transmitter to form a by-path of kick-back oscillations. variable condenser.--where alternate plates can be moved and so made to interleave more or less with a set of fixed plates. vernier.--a small condenser with a vernier on it so that it can be very accurately varied. it is connected in parallel with the variable condenser used in the primary circuit and is used for the reception of continuous waves where sharp tuning is essential. condensite.--a manufactured insulating compound. conductivity.--the conductance of a given length of wire of uniform cross section. the reciprocal of _resistivity_. contact detectors.--see _detectors, contact_. continental code.--see _code, continental_. coulomb.--the quantity of electricity transferred by a current of 1 ampere in 1 second. convective discharge.--see _discharge_. conventional signals.--see _signals, conventional_. counter electromotive force.--see _electromotive force, counter_. counterpoise. a duplicate of the aerial wire that is raised a few feet above the earth and insulated from it. usually no connection is made with the earth itself. coupled circuits.--see _circuit, coupled_. coupling.--when two oscillation circuits are connected together either by the magnetic field of an inductance coil, or by the electrostatic field of a condenser. coupling, capacitive.--oscillation circuits when connected together by condensers instead of inductance coils. coupling, coefficient of.--the measure of the closeness of the coupling between two coils. coupling, inductive.--oscillation circuits when connected together by inductance coils. coupling, resistance.--oscillation circuits connected together by a resistance. crystal rectifier.--a crystal detector. current, alternating (a.c.).--a low frequency current that surges to and fro in a circuit. current, audio frequency.--a current whose frequency is low enough to be heard in a telephone receiver. such a current usually has a frequency of between 200 and 2,000 cycles per second. current, plate.--the current which flows between the filament and the plate of a vacuum tube. current, pulsating.--a direct current whose voltage varies from moment to moment. current, radio frequency.--a current whose frequency is so high it cannot be heard in a telephone receiver. such a current may have a frequency of from 20,000 to 10,000,000 per second. currents, high frequency.--(1) currents that oscillate from 10,000 to 300,000,000 times per second. (2) electric oscillations. currents, high potential.--(1) currents that have a potential of more than 10,000 volts. (2) high voltage currents. cycle.--(1) a series of changes which when completed are again at the starting point. (2) a period of time at the end of which an alternating or oscillating current repeats its original direction of flow. damping.--the degree to which the energy of an electric oscillation is reduced. in an open circuit the energy of an oscillation set up by a spark gap is damped out in a few swings, while in a closed circuit it is greatly prolonged, the current oscillating 20 times or more before the energy is dissipated by the sum of the resistances of the circuit. decrement.--the act or process of gradually becoming less. detector.--any device that will (1) change the oscillations set up by the incoming waves into direct current, that is which will rectify them, or (2) that will act as a relay. carborundum.--one that uses a _carborundum_ crystal for the sensitive element. carborundum is a crystalline silicon carbide formed in the electric furnace. cat whisker contact.--see _cat whisker contact_. chalcopyrite.--copper pyrites. a brass colored mineral used as a crystal for detectors. see _zincite_. contact.--a crystal detector. any kind of a detector in which two dissimilar but suitable solids make contact. ferron.--a detector in which iron pyrites are used as the sensitive element. galena.--a detector that uses a galena crystal for the rectifying element. iron pyrites.--a detector that uses a crystal of iron pyrites for its sensitive element. molybdenite.--a detector that uses a crystal of _sulphide of molybdenum_ for the sensitive element. perikon.--a detector in which a _bornite_ crystal makes contact with a _zincite_ crystal. silicon.--a detector that uses a crystal of silicon for its sensitive element. vacuum tube.--a vacuum tube (which see) used as a detector. zincite.--a detector in which a crystal of _zincite_ is used as the sensitive element. de tuning.--a method of signaling by sustained oscillations in which the key when pressed down cuts out either some of the inductance or some of the capacity and hence greatly changes the wave length. dielectric.--an insulating material between two electrically charged plates in which there is set up an _electric strain_, or displacement. dielectric strain.--the electric displacement in a dielectric. directional aerial.--see _aerial, directional_. direction finder.--see _aerial, loop_. discharge.--(1) a faintly luminous discharge that takes place from the positive pointed terminal of an induction coil, or other high potential apparatus; is termed a _brush discharge_. (2) a continuous discharge between the terminals of a high potential apparatus is termed a _convective discharge_. (3) the sudden breaking-down of the air between the balls forming the spark gap is termed a _disruptive discharge_; also called an _electric spark_, or just _spark_ for short. (4) when a tube has a poor vacuum, or too large a battery voltage, it glows with a blue light and this is called a _blue glow discharge_. disruptive discharge.--see _discharge_. distress call. [morse code:] ...---... (sos). distributed capacity.--see _capacity, distributed_. double hump resonance curve.--a resonance curve that has two peaks or humps which show that the oscillating currents which are set up when the primary and secondary of a tuning coil are closely coupled have two frequencies. duo-lateral coils.--see _coils, inductance_. duplex communication.--a wireless telephone system with which it is possible to talk between both stations in either direction without the use of switches. this is known as the _duplex system_. earth capacity.--an aerial counterpoise. earth connection.--metal plates or wires buried in the ground or immersed in water. any kind of means by which the sending and receiving apparatus can be connected with the earth. edison storage battery.--see _storage battery, edison_. electric energy.--the power of an electric current. electric oscillations.--see _oscillations, electric_. electric spark.--see _discharge, spark_. electricity, negative.--the opposite of _positive electricity_. negative electricity is formed of negative electrons which make up the outside particles of an atom. electricity, positive.--the opposite of _negative electricity_. positive electricity is formed of positive electrons which make up the inside particles of an atom. electrodes.--usually the parts of an apparatus which dip into a liquid and carry a current. the electrodes of a dry battery are the zinc and carbon elements. the electrodes of an edison storage battery are the iron and nickel elements, and the electrodes of a lead storage battery are the lead elements. electrolytes.--the acid or alkaline solutions used in batteries. electromagnetic waves.--see _waves, electric_. electromotive force.--abbreviated _emf_. the force that drives an electric current along a conductor. also loosely called _voltage_. electromotive force, counter.--the emf. that is set up in a direction opposite to that in which the current is flowing in a conductor. electron.--(1) a negative particle of electricity that is detached from an atom. (2) a negative particle of electricity thrown off from the incandescent filament of a vacuum tube. electron flow.--the passage of electrons between the incandescent filament and the cold positively charged plate of a vacuum tube. electron relay.--see _relay, electron_. electron tube.--a vacuum tube or a gas-content tube used for any purpose in wireless work. see _vacuum tube_. electrose insulators.--insulators made of a composition material the trade name of which is _electrose_. energy, electric.--see _electric energy_. energy unit.--the _joule_, which see, page 308 [appendix: definitions of electric and magnetic units]. fading.--the sudden variation in strength of signals received from a transmitting station when all the adjustments of both sending and receiving apparatus remain the same. also called _swinging_. farad.--the capacitance of a condenser in which a potential difference of 1 volt causes it to have a charge of 1 coulomb of electricity. feed-back action.--feeding back the oscillating currents in a vacuum tube to amplify its power. also called _regenerative action_. ferromagnetic control.--see _magnetic amplifier_. filament.--the wire in a vacuum tube that is heated to incandescence and which throws off electrons. filament rheostat.--see _rheostat, filament_. filter.--inductance coils or condensers or both which (1) prevent troublesome voltages from acting on the different circuits, and (2) smooth out alternating currents after they have been rectified. filter reactor.--see _reactor, filter_. fire underwriters.--see _code, national electric_. fixed gap.--see _gap_. fleming valve.--a two-electrode vacuum tube. forced oscillations.--see _oscillations, forced_. free oscillations.--see _oscillations, free_. frequency, audio.--(1) an alternating current whose frequency is low enough to operate a telephone receiver and, hence, which can be heard by the ear. (2) audio frequencies are usually around 500 or 1,000 cycles per second, but may be as low as 200 and as high as 10,000 cycles per second. carrier.--a radio frequency wave modulated by an audio frequency wave which results in setting of _three_ radio frequency waves. the principal radio frequency is called the carrier frequency, since it carries or transmits the audio frequency wave. commercial.--(1) alternating current that is used for commercial purposes, namely, light, heat and power. (2) commercial frequencies now in general use are from 25 to 50 cycles per second. natural.--the pendulum and vibrating spring have a _natural frequency_ which depends on the size, material of which it is made, and the friction which it has to overcome. likewise an oscillation circuit has a natural frequency which depends upon its _inductance_, _capacitance_ and _resistance_. radio.--(1) an oscillating current whose frequency is too high to affect a telephone receiver and, hence, cannot be heard by the ear. (2) radio frequencies are usually between 20,000 and 2,000,000 cycles per second but may be as low as 10,000 and as high as 300,000,000 cycles per second. spark.--the number of sparks per second produced by the discharge of a condenser. gap, fixed.--one with fixed electrodes. gap, non-synchronous.--a rotary spark gap run by a separate motor which may be widely different from that of the speed of the alternator. gap, quenched.--(1) a spark gap for the impulse production of oscillating currents. (2) this method can be likened to one where a spring is struck a single sharp blow and then continues to set up vibrations. gap, rotary.--one having fixed and rotating electrodes. gap, synchronous.--a rotary spark gap run at the same speed as the alternator which supplies the power transformer. such a gap usually has as many teeth as there are poles on the generator. hence one spark occurs per half cycle. gas-content tube.--see _vacuum tube._ generator tube.--a vacuum tube used to set up oscillations. as a matter of fact it does not _generate_ oscillations, but changes the initial low voltage current that flows through it into oscillations. also called an _oscillator tube_ and a _power tube._ grid battery.--see _battery c._ grid characteristics.--the various relations that could exist between the voltages and currents of the grid of a vacuum tube, and the values which do exist between them when the tube is in operation. these characteristics are generally shown by curves. grid condenser.--see _condenser, grid._ grid leak.--a high resistance unit connected in the grid lead of both sending and receiving sets. in a sending set it keeps the voltage of the grid at a constant value and so controls the output of the aerial. in a receiving set it controls the current flowing between the plate and filament. grid modulation.--see _modulation, grid._ grid potential.--the negative or positive voltage of the grid of a vacuum tube. grid voltage.--see _grid potential._ grinders.--the most common form of _static,_ which see. they make a grinding noise in the headphones. ground.--see _earth connection._ ground, amateur.--a water-pipe ground. ground, waterpipe.--a common method of grounding by amateurs is to use the waterpipe, gaspipe or radiator. guided wave telephony.--see _wired wireless._ hard tube.--a vacuum tube in which the vacuum is _high,_ that is, exhausted to a high degree. helix.--(1) any coil of wire. (2) specifically a transmitter tuning inductance coil. henry.--the inductance in a circuit in which the electromotive force induced is 1 volt when the inducing current varies at the rate of 1 ampere per second. heterodyne reception.--(1) receiving by the _beat_ method. (2) receiving by means of superposing oscillations generated at the receiving station on the oscillations set up in the aerial by the incoming waves. heterodyne receptor.--see _receptor, heterodyne._ high frequency currents.--see _currents, high frequency._ high frequency resistance.--see _resistance, high frequency._ high potential currents.--see _currents, high potential._ high voltage currents.--see _currents, high potential._ honeycomb coils.--see _coils, inductance._ horse-power.--used in rating steam machinery. it is equal to 746 watts. hot wire ammeter.--see _ammeter, hot wire._ howling.--where more than three stages of radio amplification, or more than two stages of audio amplification, are used howling noises are apt to occur in the telephone receivers. impedance.--an oscillation circuit has _reactance_ and also _resistance,_ and when these are combined the total opposition to the current is called _impedance._ inductance coils.--see _coils, inductance._ inductance coil, loading.--see _coil, loading inductance._ inductive coupling.--see _coupling, inductive._ inductive reactance.--see _reactance, inductive._ induction coil.--see _coil, induction._ induction, mutual.--induction produced between two circuits or coils close to each other by the mutual interaction of their magnetic fields. insulation.--materials used on and around wires and other conductors to keep the current from leaking away. inspector, radio.--a u. s. inspector whose business it is to issue both station and operators' licenses in the district of which he is in charge. interference.--the crossing or superposing of two sets of electric waves of the same or slightly different lengths which tend to oppose each other. it is the untoward interference between electric waves from different stations that makes selective signaling so difficult a problem. intermediate waves.--see _waves._ ionic tubes.--see _vacuum tubes._ international code.--see code, international. jamming.--waves that are of such length and strength that when they interfere with incoming waves they drown them out. joule.--the energy spent in 1 second by a flow of 1 ampere in 1 ohm. joule's law.--the relation between the heat produced in seconds to the resistance of the circuit, to the current flowing in it. kenotron.--the trade name of a vacuum tube rectifier made by the _radio corporation of america._ kick-back.--oscillating currents that rise in voltage and tend to flow back through the circuit that is supplying the transmitter with low voltage current. kick-back prevention.--see _prevention, kick-back._ kilowatt.--1,000 watts. lambda.--see pages 301, 302. [appendix: useful abbreviations]. lattice wound coils.--see _coils, inductance._ lightning switch.--see _switch, lightning._ line radio communication.--see _wired wireless._ line radio telephony.--see _telephony, line radio._ litzendraht.--a conductor formed of a number of fine copper wires either twisted or braided together. it is used to reduce the _skin effect._ see _resistance, high frequency._ load flicker.--the flickering of electric lights on lines that supply wireless transmitting sets due to variations of the voltage on opening and closing the key. loading coil.--see _coil, loading._ long waves.--see _waves._ loop aerial.--see _aerial, loop._ loose coupled circuits.--see _circuits, loose coupled._ loud speaker.--a telephone receiver connected to a horn, or a specially made one, that reproduces the incoming signals, words or music loud enough to be heard by a room or an auditorium full of people, or by large crowds out-doors. magnetic poles.--see _poles, magnetic._ megohm.--one million ohms. meter, audibility.--an instrument for measuring the loudness of a signal by comparison with another signal. it consists of a pair of headphones and a variable resistance which have been calibrated. mho.--the unit of conductance. as conductance is the reciprocal of resistance it is measured by the _reciprocal ohm_ or _mho._ mica.--a transparent mineral having a high insulating value and which can be split into very thin sheets. it is largely used in making condensers both for transmitting and receiving sets. microfarad.--the millionth part of a _farad._ microhenry.--the millionth part of a _farad._ micromicrofarad.--the millionth part of a _microfarad._ microhm.--the millionth part of an _ohm._ microphone transformer.--see _transformer, microphone._ microphone transmitter.--see _transmitter, microphone._ milli-ammeter.--an ammeter that measures a current by the one-thousandth of an ampere. modulation.--(1) inflection or varying the voice. (2) varying the amplitude of oscillations by means of the voice. modulation, buzzer.--the modulation of radio frequency oscillations by a buzzer which breaks up the sustained oscillations of a transmitter into audio frequency impulses. millihenry.--the thousandth part of a _henry._ modulation, chopper.--the modulation of radio frequency oscillations by a chopper which breaks up the sustained oscillations of a transmitter into audio frequency impulses. modulation, grid.--the scheme of modulating an oscillator tube by connecting the secondary of a transformer, the primary of which is connected with a battery and a microphone transmitter, in the grid lead. modulation, over.--see _blub blub._ modulation, plate.--modulating the oscillations set up by a vacuum tube by varying the current impressed on the plate. modulator tube.--a vacuum tube used as a modulator. motion, wave.--(1) the to and fro motion of water at sea. (2) waves transmitted by, in and through the air, or sound waves. (3) waves transmitted by, in and through the _ether,_ or _electromagnetic waves,_ or _electric waves_ for short. motor-generator.--a motor and a dynamo built to run at the same speed and mounted on a common base, the shafts being coupled together. in wireless it is used for changing commercial direct current into direct current of higher voltages for energizing the plate of a vacuum tube oscillator. multi-stage amplifiers.--see _amplifiers, multi-stage._ mutual induction.--see _induction, mutual._ mush.--irregular intermediate frequencies set up by arc transmitters which interfere with the fundamental wave lengths. mushy note.--a note that is not clear cut, and hence hard to read, which is received by the _heterodyne method_ when damped waves or modulated continuous waves are being received. national electric code.--see _code, national electric._ national electric safety code.--see _code, national electric safety._ negative electricity.--see _electricity, negative._ non-synchronous gap.--see _gap, non-synchronous._ ohm.--the resistance of a thread of mercury at the temperature of melting ice, 14.4521 grams in mass, of uniform cross-section and a length of 106.300 centimeters. ohm's law.--the important fixed relation between the electric current, its electromotive force and the resistance of the conductor in which it flows. open circuit.--see _circuit, open._ open core transformer.--see _transformer, open core._ oscillation transformer.--see _transformer, oscillation._ oscillations, electric.--a current of high frequency that surges through an open or a closed circuit. (1) electric oscillations may be set up by a spark gap, electric arc or a vacuum tube, when they have not only a high frequency but a high potential, or voltage. (2) when electric waves impinge on an aerial wire they are transformed into electric oscillations of a frequency equal to those which emitted the waves, but since a very small amount of energy is received their potential or voltage is likewise very small. sustained.--oscillations in which the damping factor is small. damped.--oscillations in which the damping factor is large. free.--when a condenser discharges through an oscillation circuit, where there is no outside electromotive force acting on it, the oscillations are said to be _free._ forced.--oscillations that are made to surge in a circuit whose natural period is different from that of the oscillations set up in it. oscillation transformer.--see _transformer._ oscillation valve.--see _vacuum tube._ oscillator tube.--a vacuum tube which is used to produce electric oscillations. over modulation.--see _blub blub._ pancake oscillation transformer.--disk-shaped coils that are used for receiving tuning inductances. permeability, magnetic.--the degree to which a substance can be magnetized. iron has a greater magnetic permeability than air. phase.--a characteristic aspect or appearance that takes place at the same point or part of a cycle. pick-up circuits.--see _circuits, stand-by._ plate circuit reactor.--see _reactor, plate circuit._ plate current.--see _current, plate._ plate modulation.--see _modulation, plate._ plate voltage.--see _foliage, plate._ poles, battery.--the positive and negative terminals of the elements of a battery. on a storage battery these poles are marked + and respectively. poles, magnetic.--the ends of a magnet. positive electricity.--see _electricity, positive._ potential difference.--the electric pressure between two charged conductors or surfaces. potentiometer.--a variable resistance used for subdividing the voltage of a current. a _voltage divider._ power transformer.--see _transformer, power._ power tube.--see _generator tube._ primary battery.--see _battery, primary._ prevention, kick-back.--a choke coil placed in the power circuit to prevent the high frequency currents from getting into the transformer and breaking down the insulation. q s t.--an abbreviation used in wireless communication for (1) the question "have you received the general call?" and (2) the notice, "general call to all stations." quenched gap.--see _gap, quenched._ radiation.--the emission, or throwing off, of electric waves by an aerial wire system. radio ammeter.--see _ammeter, hot wire._ radio frequency.--see _frequency, radio._ radio frequency amplification.--see _amplification, radio frequency._ radio frequency current.--see _current, radio frequency._ radio inspector.--see _inspector, radio_. radiotron.--the trade name of vacuum tube detectors, amplifiers, oscillators and modulators made by the _radio corporation of america_. radio waves.--see _waves, radio_. reactance.--when a circuit has inductance and the current changes in value, it is opposed by the voltage induced by the variation of the current. reactance, capacity.--the capacity reactance is the opposition offered to a current by a capacity. it is measured as a resistance, that is, in _ohms_. receiving tuning coils.--see _coils, inductance_. receiver, loud speaking.--see _loud speakers_. receiver, watch case.--a compact telephone receiver used for wireless reception. reactance, inductive.--the inductive reactance is the opposition offered to the current by an inductance coil. it is measured as a resistance, that is, in _ohms_. reactor, filter.--a reactance coil for smoothing out the pulsating direct currents as they come from the rectifier. reactor, plate circuit.--a reactance coil used in the plate circuit of a wireless telephone to keep the direct current supply at a constant voltage. receiver.--(1) a telephone receiver. (2) an apparatus for receiving signals, speech or music. (3) better called a _receptor_ to distinguish it from a telephone receiver. rectifier.--(1) an apparatus for changing alternating current into pulsating direct current. (2) specifically in wireless (_a_) a crystal or vacuum tube detector, and (_b_) a two-electrode vacuum tube used for changing commercial alternating current into direct current for wireless telephony. regenerative amplification.--see _amplification, regenerative_. receptor.--a receiving set. receptor, autodyne.--a receptor that has a regenerative circuit and the same tube is used as a detector and as a generator of local oscillations. receptor, beat.--a heterodyne receptor. receptor, heterodyne.--a receiving set that uses a separate vacuum tube to set up the second series of waves for beat reception. regenerative action.--see _feed-back action._ regenerative amplification.--see _amplification, regenerative._ relay, electron.--a vacuum tube when used as a detector or an amplifier. repeating coil.--a transformer used in connecting up a wireless receiver with a wire transmitter. resistance.--the opposition offered by a wire or other conductor to the passage of a current. resistance, aerial.--the resistance of the aerial wire to oscillating currents. this is greater than its ordinary ohmic resistance due to the skin effect. see _resistance, high frequency._ resistance box.--see _resistor._ resistance coupling.--see _coupling, resistance._ resistance, high frequency.--when a high frequency current oscillates on a wire two things take place that are different than when a direct or alternating current flows through it, and these are (1) the current inside of the wire lags behind that of the current on the surface, and (2) the amplitude of the current is largest on the surface and grows smaller as the center of the wire is reached. this uneven distribution of the current is known as the _skin effect_ and it amounts to the same thing as reducing the size of the wire, hence the resistance is increased. resistivity.--the resistance of a given length of wire of uniform cross section. the reciprocal of _conductivity._ resistor.--a fixed or variable resistance unit or a group of such units. variable resistors are also called _resistance boxes_ and more often _rheostats._ resonance.--(1) simple resonance of sound is its increase set up by one body by the sympathetic vibration of a second body. (2) by extension the increase in the amplitude of electric oscillations when the circuit in which they surge has a _natural_ period that is the same, or nearly the same, as the period of the first oscillation circuit. rheostat.--a variable resistance unit. see _resistor._ rheostat, carbon.--a carbon rod, or carbon plates or blocks, when used as variable resistances. rheostat, filament.--a variable resistance used for keeping the current of the storage battery which heats the filament of a vacuum tube at a constant voltage. rotating coil.--see _coil._ rotary gap.--see _gap._ rotor.--the rotating coil of a variometer or a variocoupler. ruhmkorff coil.--see _coil, induction._ saturation.--the maximum plate current that a vacuum tube will take. sensitive spots.--spots on detector crystals that are sensitive to the action of electric oscillations. short waves.--see _waves._ side waves.--see _wave length band._ signals, conventional.--(1) the international morse alphabet and numeral code, punctuation marks, and a few important abbreviations used in wireless telegraphy. (2) dot and dash signals for distress call, invitation to transmit, etc. now used for all general public service wireless communication. skin effect.--see _resistance, high frequency._ soft tube.--a vacuum tube in which the vacuum is low, that is, it is not highly exhausted. space charge effect.--the electric field intensity due to the pressure of the negative electrons in the space between the filament and plate which at last equals and neutralizes that due to the positive potential of the plate so that there is no force acting on the electrons near the filament. spark.--see _discharge._ spark coil.--see _coil, induction._ spark discharge.--see _spark, electric._ spark frequency.--see _frequency, spark._ spark gap.--(1) a _spark gap,_ without the hyphen, means the apparatus in which sparks take place; it is also called a _spark discharger._ (2) _spark-gap,_ with the hyphen, means the air-gap between the opposed faces of the electrodes in which sparks are produced. plain.--a spark gap with fixed electrodes. rotary.--a spark gap with a pair of fixed electrodes and a number of electrodes mounted on a rotating element. quenched.--a spark gap formed of a number of metal plates placed closely together and insulated from each other. spider web inductance coil.--see _coil, spider web inductance._ spreader.--a stick of wood, or spar, that holds the wires of the aerial apart. stagger wound coils.--see _coils, inductance._ stand-by circuits.--see _circuits, stand-by._ static.--also called _atmospherics, grinders, strays, x's,_ and, when bad enough, by other names. it is an electrical disturbance in the atmosphere which makes noises in the telephone receiver. stator.--the fixed or stationary coil of a variometer or a variocoupler. storage battery.--see _battery, storage._ stray elimination.--a method for increasing the strength of the signals as against the strength of the strays. see _static._ strays.--see _static_. stranded wire.--see _wire, stranded_. super-heterodyne receptor.--see _heterodyne, super_. swinging.--see _fading_. switch, aerial.--a switch used to change over from the sending to the receiving set, and the other way about, and connect them with the aerial. switch, lightning.--the switch that connects the aerial with the outside ground when the apparatus is not in use. symbols, apparatus.--also called _conventional symbols_. these are diagrammatic lines representing various parts of apparatus so that when a wiring diagram of a transmitter or a receptor is to be made it is only necessary to connect them together. they are easy to make and easy to read. see page 307 [appendix: symbols used for apparatus]. synchronous gap.--see _gap, synchronous_. telephony, line radio.--see _wired wireless_. thermal ammeter.--see _ammeter, hot wire_. three electrode vacuum tube.--_see vacuum tube, three electrode_. tikker.--a slipping contact device that breaks up the sustained oscillations at the receiving end into groups so that the signals can be heard in the head phones. the device usually consists of a fine steel or gold wire slipping in the smooth groove of a rotating brass wheel. transformer.--a primary and a secondary coil for stepping up or down a primary alternating or oscillating current. a. c.--see _power transformer_. air cooled.--a transformer in which the coils are exposed to the air. air core.--with high frequency currents it is the general practice not to use iron cores as these tend to choke off the oscillations. hence the core consists of the air inside of the coils. auto.--a single coil of wire in which one part forms the primary and the other part the secondary by bringing out an intermediate tap. audio amplifying.--this is a transformer with an iron core and is used for frequencies up to say 3,000. closed core.--a transformer in which the path of the magnetic flux is entirely through iron. power transformers have closed cores. microphone.--a small transformer for modulating the oscillations set up by an arc or a vacuum tube oscillator. oil cooled.--a transformer in which the coils are immersed in oil. open core.--a transformer in which the path of the magnetic flux is partly through iron and partly through air. induction coils have open cores. oscillation.--a coil or coils for transforming or stepping down or up oscillating currents. oscillation transformers usually have no iron cores when they are also called _air core transformers._ power.--a transformer for stepping down a commercial alternating current for lighting and heating the filament and for stepping up the commercial a.c., for charging the plate of a vacuum tube oscillator. radio amplifying.--this is a transformer with an air core. it does not in itself amplify but is so called because it is used in connection with an amplifying tube. transmitter, microphone.--a telephone transmitter of the kind that is used in the bell telephone system. transmitting tuning coils.--see _coils, inductance._ tuning.--when the open and closed oscillation circuits of a transmitter or a receptor are adjusted so that both of the former will permit electric oscillations to surge through them with the same frequency, they are said to be tuned. likewise, when the sending and receiving stations are adjusted to the same wave length they are said to be _tuned._ coarse tuning.--the first adjustment in the tuning oscillation circuits of a receptor is made with the inductance coil and this tunes them coarse, or roughly. fine tuning.--after the oscillation circuits have been roughly tuned with the inductance coil the exact adjustment is obtained with the variable condenser and this is _fine tuning._ sharp.--when a sending set will transmit or a receiving set will receive a wave of given length only it is said to be sharply tuned. the smaller the decrement the sharper the tuning. tuning coils.--see _coils, inductance._ two electrode vacuum tube.--see _vacuum tube, two electrode._ vacuum tube.--a tube with two or three electrodes from which the air has been exhausted, or which is filled with an inert gas, and used as a detector, an amplifier, an oscillator or a modulator in wireless telegraphy and telephony. amplifier.--see _amplifier, vacuum tube._ amplifying modulator.--a vacuum tube used for modulating and amplifying the oscillations set up by the sending set. gas content.--a tube made like a vacuum tube and used as a detector but which contains an inert gas instead of being exhausted. hard.--see _hard tube._ rectifier.--(1) a vacuum tube detector. (2) a two-electrode vacuum tube used for changing commercial alternating current into direct current for wireless telephony. soft.--see _soft tube._ three electrode.--a vacuum tube with three electrodes, namely a filament, a grid and a plate. two electrode.--a vacuum tube with two electrodes, namely the filament and the plate. valve.--see _vacuum tube._ valve, fleming.--see _fleming valve._ variable condenser.--see _condenser, variable._ variable inductance.--see _inductance, variable._ variable resistance.--see _resistance, variable._ variocoupler.--a tuning device for varying the inductance of the receiving oscillation circuits. it consists of a fixed and a rotatable coil whose windings are not connected with each other. variometer.--a tuning device for varying the inductance of the receiving oscillation currents. it consists of a fixed and a rotatable coil with the coils connected in series. vernier condenser.--see _condenser, vernier._ volt.--the electromotive force which produces a current of 1 ampere when steadily applied to a conductor the resistance of which is one ohm. voltage divider.--see _potentiometer._ voltage, plate.--the voltage of the current that is used to energize the plate of a vacuum tube. voltmeter.--an instrument for measuring the voltage of an electric current. watch case receiver.--see _receiver, watch case._ water-pipe ground.--see _ground, water-pipe._ watt.--the power spent by a current of 1 ampere in a resistance of 1 ohm. wave, broad.--a wave having a high decrement, when the strength of the signals is nearly the same over a wide range of wave lengths. wave length.--every wave of whatever kind has a length. the wave length is usually taken to mean the distance between the crests of two successive waves. wave length band.--in wireless reception when continuous waves are being sent out and these are modulated by a microphone transmitter the different audio frequencies set up corresponding radio frequencies and the energy of these are emitted by the aerial; this results in waves of different lengths, or a band of waves as it is called. wave meter.--an apparatus for measuring the lengths of electric waves set up in the oscillation circuits of sending and receiving sets. wave motion.--disturbances set up in the surrounding medium as water waves in and on the water, sound waves in the air and electric waves in the ether. waves.--see _wave motion_. waves, electric.--electromagnetic waves set up in and transmitted by and through the ether. continuous. abbreviated c.w.--waves that are emitted without a break from the aerial. also called _undamped waves_. discontinuous.--waves that are emitted periodically from the aerial. also called _damped waves_. damped.--see _discontinuous waves_. intermediate.--waves from 600 to 2,000 meters in length. long.--waves over 2,000 meters in length. radio.--electric waves used in wireless telegraphy and telephony. short.--waves up to 600 meters in length. wireless.--electric waves used in wireless telegraphy and telephony. undamped.--see _continuous waves_. wireless telegraph code.--see _code, international_. wire, enamelled.--wire that is given a thin coat of enamel which insulates it. wire, phosphor bronze.--a very strong wire made of an alloy of copper and containing a trace of phosphorus. wired wireless.--continuous waves of high frequency that are sent over telephone wires instead of through space. also called _line radio communication; carrier frequency telephony, carrier current telephony; guided wave telephony_ and _wired wireless._ x's.--see _static._ zincite.--see _detector._ wireless don'ts aerial wire don'ts _don't_ use iron wire for your aerial. _don't_ fail to insulate it well at both ends. _don't_ have it longer than 75 feet for sending out a 200-meter wave. _don't_ fail to use a lightning arrester, or better, a lightning switch, for your receiving set. _don't_ fail to use a lightning switch with your transmitting set. _don't_ forget you must have an outside ground. _don't_ fail to have the resistance of your aerial as small as possible. use stranded wire. _don't_ fail to solder the leading-in wire to the aerial. _don't_ fail to properly insulate the leading-in wire where it goes through the window or wall. _don't_ let your aerial or leading-in wire touch trees or other objects. _don't_ let your aerial come too close to overhead wires of any kind. _don't_ run your aerial directly under, or over, or parallel with electric light or other wires. _don't_ fail to make a good ground connection with the water pipe inside. transmitting don'ts _don't_ attempt to send until you get your license. _don't_ fail to live up to every rule and regulation. _don't_ use an input of more than 1/2 a kilowatt if you live within 5 nautical miles of a naval station. _don't_ send on more than a 200-meter wave if you have a restricted or general amateur license. _don't_ use spark gap electrodes that are too small or they will get hot. _don't_ use too long or too short a spark gap. the right length can be found by trying it out. _don't_ fail to use a safety spark gap between the grid and the filament terminals where the plate potential is above 2,000 volts. _don't_ buy a motor-generator set if you have commercial alternating current in your home. _don't_ overload an oscillation vacuum tube as it will greatly shorten its life. use two in parallel. _don't_ operate a transmitting set without a hot-wire ammeter in the aerial. _don't_ use solid wire for connecting up the parts of transmitters. use stranded or braided wire. _don't_ fail to solder each connection. _don't_ use soldering fluid, use rosin. _don't_ think that all of the energy of an oscillation tube cannot be used for wave lengths of 200 meters and under. it can be if the transmitting set and aerial are properly designed. _don't_ run the wires of oscillation circuits too close together. _don't_ cross the wires of oscillation circuits except at right angles. _don't_ set the transformer of a transmitting set nearer than 3 feet to the condenser and tuning coil. _don't_ use a rotary gap in which the wheel runs out of true. receiving don'ts _don't_ expect to get as good results with a crystal detector as with a vacuum tube detector. _don't_ be discouraged if you fail to hit the sensitive spot of a crystal detector the first time--or several times thereafter. _don't_ use a wire larger than _no. 80_ for the wire electrode of a crystal detector. _don't_ try to use a loud speaker with a crystal detector receiving set. _don't_ expect a loop aerial to give worthwhile results with a crystal detector. _don't_ handle crystals with your fingers as this destroys their sensitivity. use tweezers or a cloth. _don't_ imbed the crystal in solder as the heat destroys its sensitivity. use _wood's metal,_ or some other alloy which melts at or near the temperature of boiling water. _don't_ forget that strong static and strong signals sometimes destroy the sensitivity of crystals. _don't_ heat the filament of a vacuum tube to greater brilliancy than is necessary to secure the sensitiveness required. _don't_ use a plate voltage that is less or more than it is rated for. _don't_ connect the filament to a lighting circuit. _don't_ use dry cells for heating the filament except in a pinch. _don't_ use a constant current to heat the filament, use a constant voltage. _don't_ use a vacuum tube in a horizontal position unless it is made to be so used. _don't_ fail to properly insulate the grid and plate leads. _don't_ use more than 1/3 of the rated voltage on the filament and on the plate when trying it out for the first time. _don't_ fail to use alternating current for heating the filament where this is possible. _don't_ fail to use a voltmeter to find the proper temperature of the filament. _don't_ expect to get results with a loud speaker when using a single vacuum tube. _don't_ fail to protect your vacuum tubes from mechanical shocks and vibration. _don't_ fail to cut off the a battery entirely from the filament when you are through receiving. _don't_ switch on the a battery current all at once through the filament when you start to receive. _don't_ expect to get the best results with a gas-content detector tube without using a potentiometer. _don't_ connect a potentiometer across the b battery or it will speedily run down. _don't_ expect to get as good results with a single coil tuner as you would with a loose coupler. _don't_ expect to get as good results with a two-coil tuner as with one having a third, or _tickler_, coil. _don't_ think you have to use a regenerative circuit, that is, one with a tickler coil, to receive with a vacuum tube detector. _don't_ think you are the only amateur who is troubled with static. _don't_ expect to eliminate interference if the amateurs around you are sending with spark sets. _don't_ lay out or assemble your set on a panel first. connect it up on a board and find out if everything is right. _don't_ try to connect up your set without a wiring diagram in front of you. _don't_ fail to shield radio frequency amplifiers. _don't_ set the axes of the cores of radio frequency transformers in a line. set them at right angles to each other. _don't_ use wire smaller than _no. 14_ for connecting up the various parts. _don't_ fail to adjust the b battery after putting in a fresh vacuum tube, as its sensitivity depends largely on the voltage. _don't_ fail to properly space the parts where you use variometers. _don't_ fail to put a copper shield between the variometer and the variocoupler. _don't_ fail to keep the leads to the vacuum tube as short as possible. _don't_ throw your receiving set out of the window if it _howls_. try placing the audio-frequency transformers farther apart and the cores of them at right angles to each other. _don't_ use condensers with paper dielectrics for an amplifier receiving set or it will be noisy. _don't_ expect as good results with a loop aerial, or when using the bed springs, as an out-door aerial will give you. _don't_ use an amplifier having a plate potential of less than 100 volts for the last step where a loud speaker is to be used. _don't_ try to assemble a set if you don't know the difference between a binding post and a blue print. buy a set ready to use. _don't_ expect to get arlington time signals and the big cableless stations if your receiver is made for short wave lengths. _don't_ take your headphones apart. you are just as apt to spoil them as you would a watch. _don't_ expect to get results with a bell telephone receiver. _don't_ forget that there are other operators using the ether besides yourself. _don't_ let your b battery get damp and don't let it freeze. _don't_ try to recharge your b battery unless it is constructed for the purpose. storage battery don'ts _don't_ connect a source of alternating current direct to your storage battery. you have to use a rectifier. _don't_ connect the positive lead of the charging circuit with the negative terminal of your storage battery. _don't_ let the electrolyte get lower than the tops of the plates of your storage battery. _don't_ fail to look after the condition of your storage battery once in a while. _don't_ buy a storage battery that gives less than 6 volts for heating the filament. _don't_ fail to keep the specific gravity of the electrolyte of your storage battery between 1.225 and 1.300 baume. this you can do with a hydrometer. _don't_ fail to recharge your storage battery when the hydrometer shows that the specific gravity of the electrolyte is close to 1.225. _don't_ keep charging the battery after the hydrometer shows that the specific gravity is 1.285. _don't_ let the storage battery freeze. _don't_ let it stand for longer than a month without using unless you charge it. _don't_ monkey with the storage battery except to add a little sulphuric acid to the electrolyte from time to time. if anything goes wrong with it better take it to a service station and let the expert do it. extra don'ts _don't_ think you have an up-to-date transmitting station unless you are using c.w. _don't_ use a wire from your lightning switch down to the outside ground that is smaller than no. _4_. _don't_ try to operate your spark coil with 110-volt direct lighting current without connecting in a rheostat. _don't_ try to operate your spark coil with 110-volt alternating lighting current without connecting in an electrolytic interrupter. _don't_ try to operate an alternating current power transformer with 110-volt direct current without connecting in an electrolytic interruptor. _don't_--no never--connect one side of the spark gap to the aerial wire and the other side of the spark gap to the ground. the government won't have it--that's all. _don't_ try to tune your transmitter to send out waves of given length by guesswork. use a wavemeter. _don't_ use _hard fiber_ for panels. it is a very poor insulator where high frequency currents are used. _don't_ think you are the only one who doesn't know all about wireless. wireless is a very complex art and there are many things that those experienced have still to learn. the end. [transcriber's note: the illustrations have been included with the ebook version of this work. the image files have been named in a straightforward manner that corresponds to the numbering in the text; thus, illustration 7 is included as file "fig007.png", while illustration (a) 22 is included as file "fig022a.png".] the radio amateur's hand book [illustration: a. frederick collins, inventor of the wireless telephone, 1899. awarded gold medal for same, alaska yukon pacific exposition, 1909.] the radio amateur's hand book a complete, authentic and informative work on wireless telegraphy and telephony by a. frederick collins inventor of the wireless telephone 1899; historian of wireless 1901-1910; author of "wireless telegraphy" 1905 1922 to william marconi inventor of the wireless telegraph introduction before delving into the mysteries of receiving and sending messages without wires, a word as to the history of the art and its present day applications may be of service. while popular interest in the subject has gone forward by leaps and bounds within the last two or three years, it has been a matter of scientific experiment for more than a quarter of a century. the wireless telegraph was invented by william marconi, at bologna, italy, in 1896, and in his first experiments he sent dot and dash signals to a distance of 200 or 300 feet. the wireless telephone was invented by the author of this book at narberth, penn., in 1899, and in his first experiments the human voice was transmitted to a distance of three blocks. the first vital experiments that led up to the invention of the wireless telegraph were made by heinrich hertz, of germany, in 1888 when he showed that the spark of an induction coil set up electric oscillations in an open circuit, and that the energy of these waves was, in turn, sent out in the form of electric waves. he also showed how they could be received at a distance by means of a ring detector, which he called a _resonator_ in 1890, edward branly, of france, showed that metal filings in a tube cohered when electric waves acted on them, and this device he termed a _radio conductor_; this was improved upon by sir oliver lodge, who called it a coherer. in 1895, alexander popoff, of russia, constructed a receiving set for the study of atmospheric electricity, and this arrangement was the earliest on record of the use of a detector connected with an aerial and the earth. marconi was the first to connect an aerial to one side of a spark gap and a ground to the other side of it. he used an induction coil to energize the spark gap, and a telegraph key in the primary circuit to break up the current into signals. adding a morse register, which printed the dot and dash messages on a tape, to the popoff receptor he produced the first system for sending and receiving wireless telegraph messages. [illustration: collins' wireless telephone exhibited at the madison square garden, october 1908.] after marconi had shown the world how to telegraph without connecting wires it would seem, on first thought, to be an easy matter to telephone without wires, but not so, for the electric spark sets up damped and periodic oscillations and these cannot be used for transmitting speech. instead, the oscillations must be of constant amplitude and continuous. that a direct current arc light transforms a part of its energy into electric oscillations was shown by firth and rogers, of england, in 1893. the author was the first to connect an arc lamp with an aerial and a ground, and to use a microphone transmitter to modulate the sustained oscillations so set up. the receiving apparatus consisted of a variable contact, known as a _pill-box_ detector, which sir oliver lodge had devised, and to this was connected an ericsson telephone receiver, then the most sensitive made. a later improvement for setting up sustained oscillations was the author's _rotating oscillation arc_. since those memorable days of more than two decades ago, wonderful advances have been made in both of these methods of transmitting intelligence, and the end is as yet nowhere in sight. twelve or fifteen years ago the boys began to get fun out of listening-in to what the ship and shore stations were sending and, further, they began to do a little sending on their own account. these youngsters, who caused the professional operators many a pang, were the first wireless amateurs, and among them experts were developed who are foremost in the practice of the art today. away back there, the spark coil and the arc lamp were the only known means for setting up oscillations at the sending end, while the electrolytic and crystal detectors were the only available means for the amateur to receive them. as it was next to impossible for a boy to get a current having a high enough voltage for operating an oscillation arc lamp, wireless telephony was out of the question for him, so he had to stick to the spark coil transmitter which needed only a battery current to energize it, and this, of course, limited him to sending morse signals. as the electrolytic detector was cumbersome and required a liquid, the crystal detector which came into being shortly after was just as sensitive and soon displaced the former, even as this had displaced the coherer. a few years ahead of these amateurs, that is to say in 1905, j. a. fleming, of england, invented the vacuum tube detector, but ten more years elapsed before it was perfected to a point where it could compete with the crystal detector. then its use became general and workers everywhere sought to, and did improve it. further, they found that the vacuum tube would not only act as a detector, but that if energized by a direct current of high voltage it would set up sustained oscillations like the arc lamp, and the value of sustained oscillations for wireless telegraphy as well as wireless telephony had already been discovered. the fact that the vacuum tube oscillator requires no adjustment of its elements, that its initial cost is much less than the oscillation arc, besides other considerations, is the reason that it popularized wireless telephony; and because continuous waves have many advantages over periodic oscillations is the reason the vacuum tube oscillator is replacing the spark coil as a wireless telegraph transmitter. moreover, by using a number of large tubes in parallel, powerful oscillations can be set up and, hence, the waves sent out are radiated to enormous distances. while oscillator tubes were being experimented with in the research laboratories of the general electric, the westinghouse, the radio corporation of america, and other big companies, all the youthful amateurs in the country had learned that by using a vacuum tube as a detector they could easily get messages 500 miles away. the use of these tubes as amplifiers also made it possible to employ a loud speaker, so that a room, a hall, or an out-of-door audience could hear clearly and distinctly everything that was being sent out. the boy amateur had only to let father or mother listen-in, and they were duly impressed when he told them they were getting it from kdka (the pittsburgh station of the westinghouse co.), for was not pittsburgh 500 miles away! and so they, too, became enthusiastic wireless amateurs. this new interest of the grown-ups was at once met not only by the manufacturers of apparatus with complete receiving and sending sets, but also by the big companies which began broadcasting regular programs consisting of music and talks on all sorts of interesting subjects. this is the wireless, or radio, as the average amateur knows it today. but it is by no means the limit of its possibilities. on the contrary, we are just beginning to realize what it may mean to the human race. the government is now utilizing it to send out weather, crop and market reports. foreign trade conditions are being reported. the naval observatory at arlington is wirelessing time signals. department stores are beginning to issue programs and advertise by radio! cities are also taking up such programs, and they will doubtless be included soon among the regular privileges of the tax-payers. politicians address their constituents. preachers reach the stay-at-homes. great singers thrill thousands instead of hundreds. soon it will be possible to hear the finest musical programs, entertainers, and orators, without budging from one's easy chair. in the world war wireless proved of inestimable value. airplanes, instead of flying aimlessly, kept in constant touch with headquarters. bodies of troops moved alertly and intelligently. ships at sea talked freely, over hundreds of miles. scouts reported. everywhere its invisible aid was invoked. in time of peace, however, it has proved and will prove the greatest servant of mankind. wireless messages now go daily from continent to continent, and soon will go around the world with the same facility. ships in distress at sea can summon aid. vessels everywhere get the day's news, even to baseball scores. daily new tasks are being assigned this tireless, wireless messenger. messages have been sent and received by moving trains, the lackawanna and the rock island railroads being pioneers in this field. messages have also been received by automobiles, and one inventor has successfully demonstrated a motor car controlled entirely by wireless. this method of communication is being employed more and more by newspapers. it is also of great service in reporting forest fires. colleges are beginning to take up the subject, some of the first being tufts college, hunter college, princeton, yale, harvard, and columbia, which have regularly organized departments for students in wireless. instead of the unwieldy and formidable looking apparatus of a short time ago, experimenters are now vying with each other in making small or novel equipment. portable sets of all sorts are being fashioned, from one which will go into an ordinary suitcase, to one so small it will easily slip into a brownie camera. one receiver depicted in a newspaper was one inch square! another was a ring for the finger, with a setting one inch by five-eighths of an inch, and an umbrella as a "ground." walking sets with receivers fastened to one's belt are also common. daily new novelties and marvels are announced. meanwhile, the radio amateur to whom this book is addressed may have his share in the joys of wireless. to get all of these good things out of the ether one does not need a rod or a gun--only a copper wire made fast at either end and a receiving set of some kind. if you are a sheer beginner, then you must be very careful in buying your apparatus, for since the great wave of popularity has washed wireless into the hearts of the people, numerous companies have sprung up and some of these are selling the veriest kinds of junk. and how, you may ask, are you going to be able to know the good from the indifferent and bad sets? by buying a make of a firm with an established reputation. i have given a few offhand at the end of this book. obviously there are many others of merit--so many, indeed, that it would be quite impossible to get them all in such a list, but these will serve as a guide until you can choose intelligently for yourself. a. f. c. contents chapter i. how to begin wireless kinds of wireless systems--parts of a wireless system--the easiest way to start--about aerial wire systems--about the receiving apparatus--about transmitting stations--kinds of transmitters--the spark gap wireless telegraph transmitter--the vacuum table telegraph transmitter--the wireless telephone transmitter. ii. putting up your aerial kinds of aerial wire systems--how to put up a cheap receiving aerial--a two-wire aerial--connecting in the ground--how to put up a good aerial--an inexpensive good aerial--the best aerial that can be made--assembling the aerial--making a good ground. iii. simple telegraph and telephone receiving sets assembled wireless receiving sets--assembling your own receiving set--the crystal detector--the tuning coil--the loose coupled tuning coil--fixed and variable condensers--about telephone receivers-connecting up the parts--receiving set no. 2--adjusting the no. 1 set--the tuning coil--adjusting the no. 2 set. iv. simple telegraph sending sets a cheap transmitting set (no. 1)--the spark coil--the battery--the telegraph key--the spark gap--the tuning coil--the high-tension condenser--a better transmitting set (no. 2)--the alternating current transformer--the wireless key--the spark gap--the high-tension condenser--the oscillation transformer--connecting up the apparatus--for direct current--how to adjust your transmitter. turning with a hot wire ammeter--to send out a 200-meter wave length--the use of the aerial switch--aerial switch for a complete sending and receiving set--connecting in the lightning switch. v. electricity simply explained electricity at rest and in motion--the electric current and its circuit--current and the ampere--resistance and the ohm--what ohm's law is--what the watt and kilowatt are--electromagnetic induction--mutual induction--high-frequency currents--constants of an oscillation circuit--what capacitance is--what inductance is--what resistance is--the effect of capacitance. vi. how the transmitting and receiving sets work how transmitting set no. 1 works--the battery and spark coil circuit--changing the primary spark coil current into secondary currents--what ratio of transformation means--the secondary spark coil circuit--the closed oscillation circuit--how transmitting set no. 2 works-with alternating current--with direct current--the rotary spark gap--the quenched spark gap--the oscillation transformer--how receiving set no. 1 works--how receiving set no. 2 works. vii. mechanical and electrical tuning damped and sustained mechanical vibrations--damped and sustained oscillations--about mechanical tuning--about electric tuning. viii. a simple vacuum tube detector receiving set assembled vacuum tube receiving set--a simple vacuum tube receiving set--the vacuum tube detector--three electrode vacuum tube detector--the dry cell and storage batteries--the filament rheostat--assembling the parts--connecting up the parts--adjusting the vacuum tube detector receiving set. ix. vacuum tube amplifier receiving sets a grid leak amplifier receiving set. with crystal detector--the fixed resistance unit, or grid leak--assembling the parts for a crystal detector set--connecting up the parts for a crystal detector--a grid leak amplifying receiving set with vacuum tube detector--a radio frequency transformer amplifying receiving set--an audio frequency transformer amplifying receiving set--a six step amplifier receiving set with a loop aerial--how to prevent howling. x. regenerative amplification receiving sets the simplest type of regenerative receiving set--with loose coupled tuning coil--connecting up the parts--an efficient regenerative receiving set. with three coil loose coupler--the a battery potentiometer--the parts and how to connect them up--a regenerative audio frequency amplifier--the parts and how to connect them up. xi. short wave regenerative receiving sets a short wave regenerative receiver, with one variometer and three variable condensers--the variocoupler--the variometer--connecting up the parts--short wave regenerative receiver with two variometers and two variable condensers--the parts and how to connect them up. xii. intermediate and long wave regenerative receiving sets intermediate wave receiving sets--intermediate wave set with loading coils--the parts and how to connect them up--an intermediate wave set with variocoupler inductance coils--the parts and how to connect them up--a long wave receiving set--the parts and how to connect them up. xiii. heterodyne or beat long wave telegraph receiving set what the heterodyne or beat method is--the autodyne or self-heterodyne long wave receiving set--the parts and connections of an autodyne or self-heterodyne, receiving set--the separate heterodyne long wave receiving set--the parts and connections of a separate heterodyne long wave receiving set. xiv. headphones and loud speakers wireless headphones--how a bell telephone receiver is made--how a wireless headphone is made--about resistance, turns of wire and sensitivity of headphones--the impedance of headphones--how the headphones work--about loud speakers--the simplest type of loud speaker--another simple kind of loud speaker--a third kind of simple loud speaker--a super loud speaker. xv. operation of vacuum tube receptors what is meant by ionization--how electrons are separated from atoms--action of the two electrode vacuum tube--how the two electrode tube acts as a detector--how the three electrode tube acts as a detector--how the vacuum tube acts as an amplifier--the operation of a simple vacuum tube receiving set--operation of a regenerative vacuum tube receiving set--operation of autodyne and heterodyne receiving sets--the autodyne, or self-heterodyne receiving set--the separate heterodyne receiving set. xvi. continuous wave telegraph transmitting sets with direct current sources of current for telegraph transmitting sets--an experimental continuous wave telegraph transmitter--the apparatus you need--the tuning coil--the condensers--the aerial ammeter--the buzzer and dry cell--the telegraph key--the vacuum tube oscillator--the storage battery--the battery rheostat--the oscillation choke coil--transmitter connectors--the panel cutout--connecting up the transmitting apparatus--a 100-mile c. w. telegraph transmitter--the apparatus you need--the tuning coil--the aerial condenser--the aerial ammeter--the grid and blocking condensers--the key circuit apparatus--the 5 watt oscillator vacuum tube--the storage battery and rheostat--the filament voltmeter--the oscillation choke coil--the motor-generator set--the panel cut-out--the protective condenser--connecting up the transmitting apparatus--a 200-mile c. w. telegraph transmitter--a 500-mile c. w. telegraph transmitter--the apparatus and connections-the 50-watt vacuum tube oscillator--the aerial ammeter--the grid leak resistance--the oscillation choke coil--the filament rheostat--the filament storage battery--the protective condenser--the motor-generator--a 1000-mile c. w. telegraph transmitter. xvii. continuous wave telegraph transmitting sets with alternating current a 100-mile c. w. telegraph transmitting set--the apparatus required--the choke coils--the milli-ammeter--the a. c. power transformer--connecting up the apparatus--a 200to 500-mile c. w. telegraph transmitting set-a 500to 1000-mile c. w. telegraph transmitting set--the apparatus required--the alternating current power transformer-connecting up the apparatus. xviii. wireless telephone transmitting sets with direct and alternating currents a short distance wireless telephone transmitting set--with 110-volt direct lighting current--the apparatus you need--the microphone transmitter--connecting up the apparatus--a 25to 50-mile wireless telephone transmitter--with direct current motor generator--the apparatus you need--the telephone induction coil--the microphone transformer--the magnetic modulator--how the apparatus is connected up--a 50to 100-mile wireless telephone transmitter--with direct current motor generator--the oscillation choke coil--the plate and grid circuit reactance coils--connecting up the apparatus--a 100to 200-mile wireless telephone transmitter--with direct current motor generator--a 50to 100-mile wireless telephone transmitting set--with 100-volt alternating current--the apparatus you need--the vacuum tube rectifier--the filter condensers--the filter reactance coil-connecting up the apparatus--a 100to 200-mile wireless telephone transmitting set--with 110-volt alternating current--apparatus required. xix. the operation of vacuum tube transmitters the operation of the vacuum tube oscillator--the operation of c. w. telegraph transmitters with direct current--short distance c. w. transmitter--the operation of the key circuit--the operation of c. w. telegraph transmitting with direct current--the operation of c. w. telegraph transmitters with alternating current--with a single oscillator tube--heating the filament with alternating current--the operation of c. w. telegraph transmitters with alternating current-with two oscillator tubes--the operation of wireless telephone transmitters with direct current--short distance transmitter--the microphone transmitter--the operation of wireless telephone transmitters with direct current--long distance transmitters--the operation of microphone modulators--the induction coil--the microphone transformer--the magnetic modulator--operation of the vacuum tube as a modulator--the operation of wireless telephone transmitters with alternating current--the operation of rectifier vacuum tubes--the operation of reactors and condensers. xx. how to make a receiving set for $5.00 or less. the crystal detector--the tuning coil--the headphone--how to mount the parts--the condenser--how to connect up the receptor. appendix useful information--glossary--wireless don'ts. list of figures fig. 1.--simple receiving set fig. 2.--simple transmitting set (a) fig. 3.--flat top, or horizontal aerial (b) fig. 3.--inclined aerial (a) fig. 4.--inverted l aerial (b) fig. 4--t aerial fig. 5.--material for a simple aerial wire system (a) fig. 6.--single wire aerial for receiving (b) fig. 6.--receiving aerial with spark gap lightning arrester (c) fig. 6.--aerial with lightning switch fig. 7.--two-wire aerial (a) fig. 8.--part of a good aerial (b) fig. 8.--the spreaders (a) fig. 9.--the middle spreader (b) fig. 9.--one end of aerial complete (c) fig. 9.--the leading in spreader (a) fig. 10.--cross section of crystal detector (b) fig. 10.--the crystal detector complete (a) fig. 11.--schematic diagram of a double slide tuning coil (b) fig. 11.--double slide tuning coil complete (a) fig. 12.--schematic diagram of a loose coupler (b) fig. 12.--loose coupler complete (a) fig. 13.--how a fixed receiving condenser is built up (b) fig. 13.--the fixed condenser complete (c) and (d) fig. 13.--variable rotary condenser fig. 14.--pair of wireless headphones (a) fig. 15.--top view of apparatus layout for receiving set no. 1 (b) fig. 15.--wiring diagram for receiving set no. 1 (a) fig. 16.--top view of apparatus layout for receiving set no. 2 (b) fig. 16.--wiring diagram for receiving set no. 2 fig. 17.--adjusting the receiving set (a) and (b) fig. 18.--types of spark coils for set no. 1 (c) fig. 18.--wiring diagram of spark coil fig. 19.--other parts for transmitting set no. 1 (a) fig. 20.--top view of apparatus layout for sending set no. 1 (b) fig. 20.--wiring of diagram for sending set no. 1 fig. 21.--parts for transmitting set no. 2 (a) fig. 22.--top view of apparatus layout for sending set no. 2 (b) fig. 22.--wiring diagram for sending set no. 2 fig. 23.--using a 110-volt direct current with an alternating current transformer fig. 24.--principle of the hot wire ammeter fig. 25.--kinds of aerial switches fig. 26.--wiring diagram for a complete sending and receiving set no. 1 fig. 27.--wiring diagram for complete sending and receiving set no. 2 fig. 28.--water analogue for electric pressure fig. 29.--water analogues for direct and alternating currents fig. 30.--how the ammeter and voltmeter are used fig. 31.--water valve analogue of electric resistance (a) and (b) fig. 32.--how an electric current is changed into magnetic lines of force and these into an electric current (c) and (d) fig. 32.--how an electric current sets up a magnetic field fig. 33.--the effect of resistance on the discharge of an electric current fig. 34.--damped and sustained mechanical vibrations fig. 35.--damped and sustained electric oscillations fig. 36.--sound wave and electric wave tuned senders and receptors fig. 37.--two electrode vacuum tube detectors fig. 38.--three electrode vacuum tube detector and battery connections fig. 39.--a and b batteries for vacuum tube detectors fig. 40.--rheostat for the a or storage-battery current (a) fig. 41.--top view of apparatus layout for vacuum tube detector receiving set (b) fig. 41.--wiring diagram of a simple vacuum tube receiving set fig. 42.--grid leaks and how to connect them up fig. 43.--crystal detector receiving set with vacuum tube amplifier (resistance coupled) (a) fig. 44.--vacuum tube detector receiving set with one step amplifier (resistance coupled) (b) fig. 44.--wiring diagram for using one a or storage battery with an amplifier and a detector tube (a) fig. 45.--wiring diagram for radio frequency transformer amplifying receiving set (b) fig. 45.--radio frequency transformer (a) fig. 46.--audio frequency transformer (b) fig. 46.--wiring diagram for audio frequency transformer amplifying receiving set. (with vacuum tube detector and two step amplifier tubes) (a) fig. 47.--six step amplifier with loop aerial (b) fig. 47.--efficient regenerative receiving set (with three coil loose coupler tuner) fig. 48.--simple regenerative receiving set (with loose coupler tuner) (a) fig. 49.--diagram of three coil loose coupler (b) fig. 49.--three coil loose coupler tuner fig. 50.--honeycomb inductance coil fig. 51.--the use of the potentiometer fig. 52.--regenerative audio frequency amplifier receiving set fig. 53.--how the vario coupler is made and works fig. 54.--how the variometer is made and works fig. 55.--short wave regenerative receiving set (one variometer and three variable condensers) fig. 56.--short wave regenerative receiving set (two variometer and two variable condensers) fig. 57.--wiring diagram showing fixed loading coils for intermediate wave set fig. 58.--wiring digram of intermediate wave receptor with one vario coupler and 12 section bank-wound inductance coil fig. 59.--wiring diagram showing long wave receptor with vario couplers and 8 bank-wound inductance coils fig. 60.--wiring diagram of long wave autodyne, or self-heterodyne receptor (compare with fig. 77) fig. 61.--wiring diagram of long wave separate heterodyne receiving set fig. 62.--cross section of bell telephone receiver fig. 63.--cross section of wireless headphone fig. 64.--the wireless headphone fig. 65.--arkay loud speaker fig. 66.--amplitone loud speaker fig. 67.--amplitron loud speaker fig. 68.--magnavox loud speaker fig. 69.--schematic diagram of an atom fig. 70.--action of two-electrode vacuum tube (a) and (b) fig. 71.--how a two-electrode tube acts as relay or a detector (c) fig. 71--only the positive part of oscillations goes through the tube (a) and (b) fig. 72.--how the positive and negative voltages of the oscillations act on the electrons (c) fig. 72.--how the three-electrode tube acts as detector and amplifier (d) fig. 72.--how the oscillations control the flow of the battery current through the tube fig. 73.--how the heterodyne receptor works fig. 74.--separate heterodyne oscillator (a) fig. 75.--apparatus for experimental c. w. telegraph transmitter. (b) fig. 75.--apparatus for experimental c. w. telegraph transmitter. fig. 76.--experimental c. w. telegraph transmitter fig. 77--apparatus of 100-mile c. w. telegraph transmitter fig. 78.--5to 50-watt c. w. telegraph transmitter (with a single oscillation tube) fig. 79.--200-mile c. w. telegraph transmitter (with two tubes in parallel) fig. 80.--50-watt oscillator vacuum tube fig. 81.--alternating current power transformer (for c. w. telegraphy and wireless telephony) fig. 82.--wiring diagram for 200to 500-mile c. w. telegraph transmitting set. (with alternating current.) fig. 83--wiring diagram for 500to 1000-mile c. w. telegraph transmitter fig. 84.--standard microphone transmitter fig. 85.--wiring diagram of short distance wireless telephone set. (microphone in aerial wire.) fig. 86.--telephone induction coil (used with microphone transmitter). fig. 87.--microphone transformer used with microphone transmitter fig. 88.--magnetic modulator used with microphone transmitter (a) fig. 89.--wiring diagram of 25--to 50-mile wireless telephone. (microphone modulator shunted around grid-leak condenser) (b) fig. 89.--microphone modulator connected in aerial wire fig. 90.--wiring diagram of 50to 100-mile wireless telephone transmitting set fig. 91.--plate and grid circuit reactor fig. 92.--filter reactor for smoothing out rectified currents fig. 93.--100to 200-mile wireless telephone transmitter (a) and (b) fig. 94.--operation of vacuum tube oscillators (c) fig. 94.--how a direct current sets up oscillations fig. 95.--positive voltage only sets up oscillations fig. 96.--rasco baby crystal detector fig. 97.--how the tuning coil is made fig. 98.--mesco loop-ohm head set fig. 99.--schematic layout of the $5.00 receiving set fig. 100.--wiring diagram for the $5.00 receiving set list of illustrations a. frederick collins, inventor of the wireless telephone, 1899. awarded gold medal for same, alaska yukon pacific exposition, 1909 collins' wireless telephone exhibited at the madison square garden, october, 1908 general pershing "listening-in" the world's largest radio receiving station. owned by the radio corporation of america at rocky point near port jefferson, l. i. first wireless college in the world, at tufts college, mass alexander graham bell, inventor of the telephone, now an ardent radio enthusiast world's largest loud speaker ever made. installed in lytle park, cincinnati, ohio, to permit president harding's address at point pleasant, ohio, during the grant centenary celebration to be heard within a radius of one square united states naval high power station, arlington, va. general view of power room. at the left can be seen the control switchboards, and overhead, the great 30 k.w. arc transmitter with accessories the transformer and tuner of the world's largest radio station. owned by the radio corporation of america at rocky point near port jefferson, l. i. broadcasting government reports by wireless from washington. this shows mr. gale at work with his set in the post office department wireless receptor, the size of a safety match box. a youthful genius in the person of kenneth r. hinman, who is only twelve years old, has made a wireless receiving set that fits neatly into a safety match box. with this instrument and a pair of ordinary receivers, he is able to catch not only code messages but the regular broadcasting programs from stations twenty and thirty miles distant wireless set made into a ring, designed by alfred g. rinehart, of elizabeth, new jersey. this little receptor is a practical set; it will receive messages, concerts, etc., measures 1" by 5/8" by 7/8". an ordinary umbrella is used as an aerial chapter i how to begin wireless in writing this book it is taken for granted that you are: _first_, one of the several hundred thousand persons in the united states who are interested in wireless telegraphy and telephony; _second_, that you would like to install an apparatus in your home, and _third_, that it is all new to you. now if you live in a city or town large enough to support an electrical supply store, there you will find the necessary apparatus on sale, and someone who can tell you what you want to know about it and how it works. if you live away from the marts and hives of industry you can send to various makers of wireless apparatus [footnote: a list of makers of wireless apparatus will be found in the _appendix_.] for their catalogues and price-lists and these will give you much useful information. but in either case it is the better plan for you to know before you start in to buy an outfit exactly what apparatus you need to produce the result you have in mind, and this you can gain in easy steps by reading this book. kinds of wireless systems.--there are two distinct kinds of wireless systems and these are: the _wireless telegraph_ system, and the _wireless telephone_ system. the difference between the wireless telegraph and the wireless telephone is that the former transmits messages by means of a _telegraph key_, and the latter transmits conversation and music by means of a _microphone transmitter_. in other words, the same difference exists between them in this respect as between the morse telegraph and the bell telephone. parts of a wireless system.--every complete wireless station, whether telegraph or telephone, consists of three chief separate and distinct parts and these are: (a) the _aerial wire system_, or _antenna_ as it is often called, (b) the _transmitter_, or _sender_, and (c) the _receiver_, or, more properly, the _receptor_. the aerial wire is precisely the same for either wireless telegraphy or wireless telephony. the transmitter of a wireless telegraph set generally uses a _spark gap_ for setting up the electric oscillations, while usually for wireless telephony a _vacuum tube_ is employed for this purpose. the receptor for wireless telegraphy and telephony is the same and may include either a _crystal detector_ or a _vacuum tube detector_, as will be explained presently. the easiest way to start.--first of all you must obtain a government license to operate a sending set, but you do not need a license to put up and use a receiving set, though you are required by law to keep secret any messages which you may overhear. since no license is needed for a receiving set the easiest way to break into the wireless game is to put up an aerial and hook up a receiving set to it; you can then listen-in and hear what is going on in the all-pervading ether around you, and you will soon find enough to make things highly entertaining. nearly all the big wireless companies have great stations fitted with powerful telephone transmitters and at given hours of the day and night they send out songs by popular singers, dance music by jazz orchestras, fashion talks by and for the ladies, agricultural reports, government weather forecasts and other interesting features. then by simply shifting the slide on your tuning coil you can often tune-in someone who is sending _morse_, that is, messages in the dot and dash code, or, perhaps a friend who has a wireless telephone transmitter and is talking. of course, if you want to _talk back_ you must have a wireless transmitter, either telegraphic or telephonic, and this is a much more expensive part of the apparatus than the receptor, both in its initial cost and in its operation. a wireless telegraph transmitter is less costly than a wireless telephone transmitter and it is a very good scheme for you to learn to send and receive telegraphic messages. at the present time, however, there are fifteen amateur receiving stations in the united states to every sending station, so you can see that the majority of wireless folks care more for listening in to the broadcasting of news and music than to sending out messages on their own account. the easiest way to begin wireless, then, is to put up an aerial and hook up a receiving set to it. about aerial wire systems.--to the beginner who wants to install a wireless station the aerial wire system usually looms up as the biggest obstacle of all, and especially is this true if his house is without a flag pole, or other elevation from which the aerial wire can be conveniently suspended. if you live in the congested part of a big city where there are no yards and, particularly, if you live in a flat building or an apartment house, you will have to string your aerial wire on the roof, and to do this you should get the owner's, or agent's, permission. this is usually an easy thing to do where you only intend to receive messages, for one or two thin wires supported at either end of the building are all that are needed. if for any reason you cannot put your aerial on the roof then run a wire along the building outside of your apartment, and, finally, if this is not feasible, connect your receiver to a wire strung up in your room, or even to an iron or a brass bed, and you can still get the near-by stations. an important part of the aerial wire system is the _ground_, that is, your receiving set must not only be connected with the aerial wire, but with a wire that leads to and makes good contact with the moist earth of the ground. where a house or a building is piped for gas, water or steam, it is easy to make a ground connection, for all you have to do is to fasten the wire to one of the pipes with a clamp. [footnote: pipes are often insulated from the ground, which makes them useless for this purpose.] where the house is isolated then a lot of wires or a sheet of copper or of zinc must be buried in the ground at a sufficient depth to insure their being kept moist. about the receiving apparatus.--you can either buy the parts of the receiving apparatus separate and hook them up yourself, or you can buy the apparatus already assembled in a set which is, in the beginning, perhaps, the better way. the simplest receiving set consists of (1) a _detector_, (2) a _tuning coil_, and (3) a _telephone receiver_ and these three pieces of apparatus are, of course, connected together and are also connected to the aerial and ground as the diagram in fig. 1 clearly shows. there are two chief kinds of detectors used at the present time and these are: (a) the _crystal detector_, and (b) the _vacuum tube detector_. the crystal detector is the cheapest and simplest, but it is not as sensitive as the vacuum tube detector and it requires frequent adjustment. a crystal detector can be used with or without a battery while the vacuum tube detector requires two small batteries. [illustration: fig. 1.--simple receiving set.] a tuning coil of the simplest kind consists of a single layer of copper wire wound on a cylinder with an adjustable, or sliding, contact, but for sharp tuning you need a _loose coupled tuning coil_. where a single coil tuner is used a _fixed_ condenser should be connected around the telephone receivers. where a loose coupled tuner is employed you should have a variable condenser connected across the _closed oscillation circuit_ and a _fixed condenser_ across the telephone receivers. when listening-in to distant stations the energy of the received wireless waves is often so very feeble that in order to hear distinctly an _amplifier_ must be used. to amplify the incoming sounds a vacuum tube made like a detector is used and sometimes as many as half-a-dozen of these tubes are connected in the receiving circuit, or in _cascade_, as it is called, when the sounds are _amplified_, that is magnified, many hundreds of times. the telephone receiver of a receiving set is equally as important as the detector. a single receiver can be used but a pair of receivers connected with a head-band gives far better results. then again the higher the resistance of the receivers the more sensitive they often are and those wound to as high a resistance as 3,200 ohms are made for use with the best sets. to make the incoming signals, conversation or music, audible to a room full of people instead of to just yourself you must use what is called a _loud speaker_. in its simplest form this consists of a metal cone like a megaphone to which is fitted a telephone receiver. about transmitting stations--getting your license.--if you are going to install a wireless sending apparatus, either telegraphic or telephonic, you will have to secure a government license for which no fee or charge of any kind is made. there are three classes of licenses issued to amateurs who want to operate transmitting stations and these are: (1) the _restricted amateur license_, (2) the _general amateur license_, and (3) the _special amateur license_. if you are going to set up a transmitter within five nautical miles of any naval wireless station then you will have to get a _restricted amateur license_ which limits the current you use to half a _kilowatt_ [footnote: a _kilowatt_ is 1,000 _watts_. there are 746 watts in a horsepower.] and the wave length you send out to 200 _meters_. should you live outside of the five-mile range of a navy station then you can get a general amateur license and this permits you to use a current of 1 kilowatt, but you are likewise limited to a wave length of 200 meters. but if you can show that you are doing some special kind of wireless work and not using your sending station for the mere pleasure you are getting out of it you may be able to get a _special amateur license_ which gives you the right to send out wave lengths up to 375 meters. when you are ready to apply for your license write to the _radio inspector_ of whichever one of the following districts you live in: first district..............boston, mass. second " ..............new york city third " ..............baltimore, md. fourth " ..............norfolk, va. fifth " ..............new orleans, la. sixth " ............. san francisco, cal. seventh " ............. seattle, wash. eighth " ............. detroit, mich. ninth " ..............chicago, ill. kinds of transmitters.--there are two general types of transmitters used for sending out wireless messages and these are: (1) _wireless telegraph_ transmitters, and (2) _wireless telephone_ transmitters. telegraph transmitters may use either: (a) a _jump-spark_, (b) an _electric arc_, or (c) a _vacuum tube_ apparatus for sending out dot and dash messages, while telephone transmitters may use either, (a) an _electric arc_, or (b) a _vacuum tube_ for sending out vocal and musical sounds. amateurs generally use a _jump-spark_ for sending wireless telegraph messages and the _vacuum tube_ for sending wireless telephone messages. the spark gap wireless telegraph transmitter.--the simplest kind of a wireless telegraph transmitter consists of: (1) a _source of direct or alternating current_, (2) a _telegraph key_, (3) a _spark-coil_ or a _transformer_, (4) a _spark gap_, (5) an _adjustable condenser_ and (6) an _oscillation transformer_. where _dry cells_ or a _storage battery_ must be used to supply the current for energizing the transmitter a spark-coil can be employed and these may be had in various sizes from a little fellow which gives 1/4-inch spark up to a larger one which gives a 6-inch spark. where more energy is needed it is better practice to use a transformer and this can be worked on an alternating current of 110 volts, or if only a 110 volt direct current is available then an _electrolytic interrupter_ must be used to make and break the current. a simple transmitting set with an induction coil is shown in fig. 2. [illustration: fig 2.--simple transmitting set.] a wireless key is made like an ordinary telegraph key except that where large currents are to be used it is somewhat heavier and is provided with large silver contact points. spark gaps for amateur work are usually of: (1) the _plain_ or _stationary type_, (2) the _rotating type_, and (3) the _quenched gap_ type. the plain spark-gap is more suitable for small spark-coil sets, and it is not so apt to break down the transformer and condenser of the larger sets as the rotary gap. the rotary gap on the other hand tends to prevent _arcing_ and so the break is quicker and there is less dragging of the spark. the quenched gap is more efficient than either the plain or rotary gap and moreover it is noiseless. condensers for spark telegraph transmitters can be ordinary leyden jars or glass plates coated with tin or copper foil and set into a frame, or they can be built up of mica and sheet metal embedded in an insulating composition. the glass plate condensers are the cheapest and will serve your purpose well, especially if they are immersed in oil. tuning coils, sometimes called _transmitting inductances_ and _oscillation transformers_, are of various types. the simplest kind is a transmitting inductance which consists of 25 or 30 turns of copper wire wound on an insulating tube or frame. an oscillation transformer is a loose coupled tuning coil and it consists of a primary coil formed of a number of turns of copper wire wound on a fixed insulating support, and a secondary coil of about twice the number of turns of copper wire which is likewise fixed in an insulating support, but the coils are relatively movable. an _oscillation transformer_ (instead of a _tuning coil_), is required by government regulations unless _inductively coupled_. the vacuum tube telegraph transmitter.--this consists of: (1) a _source of direct or alternating current_, (2) a _telegraph key_, (3) a _vacuum tube oscillator_, (4) a _tuning coil_, and (5) a _condenser_. this kind of a transmitter sets up _sustained_ oscillations instead of _periodic_ oscillations which are produced by a spark gap set. the advantages of this kind of a system will be found explained in chapter xvi. the wireless telephone transmitter.--because a jump-spark sets up _periodic oscillations_, that is, the oscillations are discontinuous, it cannot be used for wireless telephony. an electric arc or a vacuum tube sets up _sustained_ oscillations, that is, oscillations which are continuous. as it is far easier to keep the oscillations going with a vacuum tube than it is with an arc the former means has all but supplanted the latter for wireless telephone transmitters. the apparatus required and the connections used for wireless telephone sets will be described in later chapters. useful information.--it would be wise for the reader to turn to the appendix, beginning with page 301 of this book, and familiarize himself with the information there set down in tabular and graphic form. for example, the first table gives abbreviations of electrical terms which are in general use in all works dealing with the subject. you will also find there brief definitions of electric and magnetic units, which it would be well to commit to memory; or, at least, to make so thoroughly your own that when any of these terms is mentioned, you will know instantly what is being talked about. chapter ii putting up your aerial as inferred in the first chapter, an aerial for receiving does not have to be nearly as well made or put up as one for sending. but this does not mean that you can slipshod the construction and installation of it, for however simple it is, the job must be done right and in this case it is as easy to do it right as wrong. to send wireless telegraph and telephone messages to the greatest distances and to receive them as distinctly as possible from the greatest distances you must use for your aerial (1) copper or aluminum wire, (2) two or more wires, (3) have them the proper length, (4) have them as high in the air as you can, (5) have them well apart from each other, and (6) have them well insulated from their supports. if you live in a flat building or an apartment house you can string your aerial wires from one edge of the roof to the other and support them by wooden stays as high above it as may be convenient. should you live in a detached house in the city you can usually get your next-door neighbor to let you fasten one end of the aerial to his house and this will give you a good stretch and a fairly high aerial. in the country you can stretch your wires between the house and barn or the windmill. from this you will see that no matter where you live you can nearly always find ways and means of putting up an aerial that will serve your needs without going to the expense of erecting a mast. kinds of aerial wire systems.--an amateur wireless aerial can be anywhere from 25 feet to 100 feet long and if you can get a stretch of the latter length and a height of from 30 to 75 feet you will have one with which you can receive a thousand miles or more and send out as much energy as the government will allow you to send. the kind of an aerial that gives the best results is one whose wire, or wires, are _horizontal_, that is, parallel with the earth under it as shown at a in fig. 3. if only one end can be fixed to some elevated support then you can secure the other end to a post in the ground, but the slope of the aerial should not be more than 30 or 35 degrees from the horizontal at most as shown at b. [illustration: (a) fig. 3.--flat top, or horizontal aerial.] [illustration: (b) fig. 3.--inclined aerial.] the _leading-in wire_, that is, the wire that leads from and joins the aerial wire with your sending and receiving set, can be connected to the aerial anywhere it is most convenient to do so, but the best results are had when it is connected to one end as shown at a in fig. 4, in which case it is called an _inverted l aerial_, or when it is connected to it at the middle as shown at b, when it is called a _t aerial_. the leading-in wire must be carefully insulated from the outside of the building and also where it passes through it to the inside. this is done by means of an insulating tube known as a _leading-in insulator_, or _bulkhead insulator_ as it is sometimes called. [illustration: (a) fig. 4.--inverted l aerial.] [illustration: (b) fig. 4.--t aerial.] as a protection against lightning burning out your instruments you can use either: (1) an _air-gap lightning arrester,_ (2) a _vacuum tube protector_, or (3) a _lightning switch_, which is better. whichever of these devices is used it is connected in between the aerial and an outside ground wire so that a direct circuit to the earth will be provided at all times except when you are sending or receiving. so your aerial instead of being a menace really acts during an electrical storm like a lightning rod and it is therefore a real protection. the air-gap and vacuum tube lightning arresters are little devices that can be used only where you are going to receive, while the lightning switch must be used where you are going to send; indeed, in some localities the _fire underwriters_ require a large lightning switch to be used for receiving sets as well as sending sets. how to put up a cheap receiving aerial.--the kind of an aerial wire system you put up will depend, chiefly, on two things, and these are: (1) your pocketbook, and (2) the place where you live. a single wire aerial.--this is the simplest and cheapest kind of a receiving aerial that can be put up. the first thing to do is to find out the length of wire you need by measuring the span between the two points of support; then add a sufficient length for the leading-in wire and enough more to connect your receiving set with the radiator or water pipe. you can use any size of copper or aluminum wire that is not smaller than _no. 16 brown and sharpe gauge._ when you buy the wire get also the following material: (1) two _porcelain insulators_ as shown at a in fig. 5; (2) three or four _porcelain knob insulators_, see b; (3) either (a) an _air gap lightning arrester,_ see c, or (b) a _lightning switch_ see d; (4) a _leading-in porcelain tube insulator,_ see e, and (5) a _ground clamp_, see f. [illustration: fig. 5.--material for a simple aerial wire system.] to make the aerial slip each end of the wire through a hole in each insulator and twist it fast; next cut off and slip two more pieces of wire through the other holes in the insulators and twist them fast and then secure these to the supports at the ends of the building. take the piece you are going to use for the leading-in wire, twist it around the aerial wire and solder it there when it will look like a in fig. 6. now if you intend to use the _air gap lightning arrester_ fasten it to the wall of the building outside of your window, and bring the leading-in wire from the aerial to the top binding post of your arrester and keep it clear of everything as shown at b. if your aerial is on the roof and you have to bring the leading-in wire over the cornice or around a corner fix a porcelain knob insulator to the one or the other and fasten the wire to it. [illustration: (a) fig. 6.--single wire aerial for receiving.] [illustration: (b) fig. 6.--receiving aerial with air gap lightning arrester.] [illustration: (c) fig. 6.--aerial with lightning switch.] next bore a hole through the frame of the window at a point nearest your receiving set and push a porcelain tube 5/8 inch in diameter and 5 or 6 inches long, through it. connect a length of wire to the top post of the arrester or just above it to the wire, run this through the leading-in insulator and connect it to the slider of your tuning coil. screw the end of a piece of heavy copper wire to the lower post of the arrester and run it to the ground, on porcelain knobs if necessary, and solder it to an iron rod or pipe which you have driven into the earth. finally connect the fixed terminal of your tuning coil with the water pipe or radiator inside of the house by means of the ground clamp as shown in the diagrammatic sketch at b in fig. 6 and you are ready to tune in. if you want to use a lightning switch instead of the air-gap arrester then fasten it to the outside wall instead of the latter and screw the free end of the leading-in wire from the aerial to the middle post of it as shown at c in fig. 6. run a wire from the top post through the leading-in insulator and connect it with the slider of your tuning coil. next screw one end of a length of heavy copper wire to the lower post of the aerial switch and run it to an iron pipe in the ground as described above in connection with the spark-gap lightning arrester; then connect the fixed terminal of your tuning coil with the radiator or water pipe and your aerial wire system will be complete as shown at c in fig. 6. a two-wire aerial.--an aerial with two wires will give better results than a single wire and three wires are better than two, but you must keep them well apart. to put up a two-wire aerial get (1) enough _no. 16_, or preferably _no. 14_, solid or stranded copper or aluminum wire, (2) four porcelain insulators, see b in fig. 5, and (3) two sticks about 1 inch thick, 3 inches wide and 3 or 4 feet long, for the _spreaders_, and bore 1/8-inch hole through each end of each one. now twist the ends of the wires to the insulators and then cut off four pieces of wire about 6 feet long and run them through the holes in the wood spreaders. finally twist the ends of each pair of short wires to the free ends of the insulators and then twist the free ends of the wires together. for the leading-in wire that goes to the lightning switch take two lengths of wire and twist one end of each one around the aerial wires and solder them there. twist the short wire around the long wire and solder this joint also when the aerial will look like fig. 7. bring the free end of the leading-in wire down to the middle post of the lightning switch and fasten it there and connect up the receiver to it and the ground as described under the caption of _a single wire aerial_. [illustration: fig. 7.--two wire aerial.] connecting in the ground.--if there is a gas or water system or a steam-heating plant in your house you can make your ground connection by clamping a ground clamp to the nearest pipe as has been previously described. connect a length of bare or insulated copper wire with it and bring this up to the table on which you have your receiving set. if there are no grounded pipes available then you will have to make a good ground which we shall describe presently and lead the ground wire from your receiving set out of the window and down to it. how to put up a good aerial.--while you can use the cheap aerial already described for a small spark-coil sending set you should have a better insulated one for a 1/2 or a 1 kilowatt transformer set. the cost for the materials for a good aerial is small and when properly made and well insulated it will give results that are all out of proportion to the cost of it. an inexpensive good aerial.--a far better aerial, because it is more highly insulated, can be made by using _midget insulators_ instead of the porcelain insulators described under the caption of _a single wire aerial_ and using a small _electrose leading-in insulator_ instead of the porcelain bushing. this makes a good sending aerial for small sets as well as a good receiving aerial. the best aerial that can be made.--to make this aerial get the following material together: (1) enough _stranded or braided wire_ for three or four lengths of parallel wires, according to the number you want to use (2) six or eight _electrose ball insulators_, see b, fig. 8; (3) two 5-inch or 10-inch _electrose strain insulators_, see c; (4) six or eight _s-hooks_, see d; one large _withe_ with one eye for middle of end spreader, see e; (6) two smaller _withes_ with one eye each for end spreader, see e; (7) two still smaller _withes_, with two eyes each for the ends of the end spreaders, see e (8) two _thimbles_, see f, for 1/4-inch wire cable; (9) six or eight _hard rubber tubes_ or _bushings_ as shown at g; and (10) two _end spreaders_, see h; one _middle spreader_, see i; and one _leading-in spreader_, see j. [illustration: (a) fig. 8--part of a good aerial.] [illustration: (b) fig. 8.--the spreaders.] for this aerial any one of a number of kinds of wire can be used and among these are (a) _stranded copper wire;_ (b) _braided copper wire;_ (c) _stranded silicon bronze wire,_ and (d) _stranded phosphor bronze wire_. stranded and braided copper wire is very flexible as it is formed of seven strands of fine wire twisted or braided together and it is very good for short and light aerials. silicon bronze wire is stronger than copper wire and should be used where aerials are more than 100 feet long, while phosphor bronze wire is the strongest aerial wire made and is used for high grade aerials by the commercial companies and the government for their high-power stations. the spreaders should be made of spruce, and should be 4 feet 10 inches long for a three-wire aerial and 7 feet 1 inch long for a four-wire aerial as the distance between the wires should be about 27 inches. the end spreaders can be turned cylindrically but it makes a better looking job if they taper from the middle to the ends. they should be 2-1/4 inches in diameter at the middle and 1-3/4 inches at the ends. the middle spreader can be cylindrical and 2 inches in diameter. it must have holes bored through it at equidistant points for the hard rubber tubes; each of these should be 5/8 inch in diameter and have a hole 5/32 inch in diameter through it for the aerial wire. the leading-in spreader is also made of spruce and is 1-1/2 inches square and 26 inches long. bore three or four 5/8-inch holes at equidistant points through this spreader and insert hard rubber tubes in them as with the middle spreader. assembling the aerial.--begin by measuring off the length of each wire to be used and see to it that all of them are of exactly the same length. now push the hard rubber insulators through the holes in the middle spreader and thread the wires through the holes in the insulators as shown at a in fig 9. next twist the ends of each wire to the rings of the ball insulators and then put the large withes on the middle of each of the end spreaders; fix the other withes on the spreaders so that they will be 27 inches apart and fasten the ball insulators to the eyes in the withes with the s-hooks. now slip a thimble through the eye of one of the long strain insulators, thread a length of stranded steel wire 1/4 inch in diameter through it and fasten the ends of it to the eyes in the withes on the ends of the spreaders. [illustration: (a) fig. 9.--middle spreader.] [illustration: (b) fig. 9.--one end of aerial complete.] [illustration: (c) fig. 9.--leading in spreader.] finally fasten a 40-inch length of steel stranded wire to each of the eyes of the withes on the middle of each of the spreaders, loop the other end over the thimble and then wrap the end around the wires that are fixed to the ends of the spreaders. one end of the aerial is shown complete at b in fig. 9, and from this you can see exactly how it is assembled. now cut off three or four pieces of wire 15 or 20 feet long and twist and solder each one to one of the aerial wires; then slip them through the hard rubber tubes in the leading-in spreader, bring their free ends together as at c and twist and solder them to a length of wire long enough to reach to your lightning switch or instruments. making a good ground.--where you have to make a _ground_ you can do so either by (1) burying sheets of zinc or copper in the moist earth; (2) burying a number of wires in the moist earth, or (3) using a _counterpoise_. to make a ground of the first kind take half a dozen large sheets of copper or zinc, cut them into strips a foot wide, solder them all together with other strips and bury them deeply in the ground. it is easier to make a wire ground, say of as many or more wires as you have in your aerial and connect them together with cross wires. to put such a ground in the earth you will have to use a plow to make the furrows deep enough to insure them always being moist. in the counterpoise ground you make up a system of wires exactly like your aerial, that is, you insulate them just as carefully; then you support them so that they will be as close to the ground as possible and yet not touch it or anything else. this and the other two grounds just described should be placed directly under the aerial wire if the best results are to be had. in using a counterpoise you must bring the wire from it up to and through another leading-in insulator to your instruments. chapter iii simple telegraph and telephone receiving sets with a crystal detector receiving set you can receive either telegraphic dots and dashes or telephonic speech and music. you can buy a receiving set already assembled or you can buy the different parts and assemble them yourself. an assembled set is less bother in the beginning but if you like to experiment you can _hook up_, that is, connect the separate parts together yourself and it is perhaps a little cheaper to do it this way. then again, by so doing you get a lot of valuable experience in wireless work and an understanding of the workings of wireless that you cannot get in any other way. assembled wireless receiving sets.--the cheapest assembled receiving set [footnote: the marvel, made by the radio mfg. co., new york city.] advertised is one in which the detector and tuning coil is mounted in a box. it costs $15.00, and can be bought of dealers in electric supplies generally. this price also includes a crystal detector, an adjustable tuning coil, a single telephone receiver with head-band and the wire, porcelain insulators, lightning switch and ground clamp for the aerial wire system. it will receive wireless telegraph and telephone messages over a range of from 10 to 25 miles. another cheap unit receptor, that is, a complete wireless receiving set already mounted which can be used with a single aerial is sold for $25.00. [footnote: the aeriola jr., made by the westinghouse company, pittsburgh, pa.] this set includes a crystal detector, a variable tuning coil, a fixed condenser and a pair of head telephone receivers. it can also be used to receive either telegraph or telephone messages from distances up to 25 miles. the aerial equipment is not included in this price, but it can be bought for about $2.50 extra. assembling your own receiving set.--in this chapter we shall go only into the apparatus used for two simple receiving sets, both of which have a _crystal detector_. the first set includes a _double-slide tuning coil_ and the second set employs a _loose-coupled tuning coil_, or _loose coupler_, as it is called for short. for either set you can use a pair of 2,000or 3,000-ohm head phones. [illustration: original â© underwood and underwood. general pershing listening in.] the crystal detector.--a crystal detector consists of: (1) _the frame_, (2) _the crystal_, and (3) _the wire point_. there are any number of different designs for frames, the idea being to provide a device that will (a) hold the sensitive crystal firmly in place, and yet permit of its removal, (b) to permit the _wire point_, or _electrode_, to be moved in any direction so that the free point of it can make contact with the most sensitive spot on the crystal and (c) to vary the pressure of the wire on the crystal. a simple detector frame is shown in the cross-section at a in fig. 10; the crystal, which may be _galena_, _silicon_ or _iron pyrites_, is held securely in a holder while the _phosphor-bronze wire point_ which makes contact with it, is fixed to one end of a threaded rod on the other end of which is a knob. this rod screws into and through a sleeve fixed to a ball that sets between two brass standards and this permits an up and down or a side to side adjustment of the metal point while the pressure of it on the crystal is regulated by the screw. [illustration: (a) fig. 10.--cross section of crystal detector.] [illustration: (b) fig. 10.--the crystal detector complete.] a crystal of this kind is often enclosed in a glass cylinder and this makes it retain its sensitiveness for a much longer time than if it were exposed to dust and moisture. an upright type of this detector can be bought for $2.25, while a horizontal type, as shown at b, can be bought for $2.75. galena is the crystal that is generally used, for, while it is not quite as sensitive as silicon and iron pyrites, it is easier to obtain a sensitive piece. the tuning coil.--it is with the tuning coil that you _tune in_ and _tune out_ different stations and this you do by sliding the contacts to and fro over the turns of wire; in this way you vary the _inductance_ and _capacitance_, that is, the _constants_ of the receiving circuits and so make them receive _electric waves_, that is, wireless waves, of different lengths. the double slide tuning coil.--with this tuning coil you can receive waves from any station up to 1,000 meters in length. one of the ends of the coil of wire connects with the binding post marked _a_ in fig. 11, and the other end connects with the other binding post marked _b_, while one of the sliding contacts is connected to the binding post _c_, and the _other sliding contact_ is connected with the binding post _d_. [illustration: (a) fig. 11.--schematic diagram of double slide tuning coil.] [illustration: (b) fig. 11.--double slide tuning coil complete.] when connecting in the tuning coil, only the post _a_ or the post _b_ is used as may be most convenient, but the other end of the wire which is connected to a post is left free; just bear this point in mind when you come to connect the tuning coil up with the other parts of your receiving set. the tuning coil is shown complete at b and it costs $3.00 or $4.00. a _triple slide_ tuning coil constructed like the double slide tuner just described, only with more turns of wire on it, makes it possible to receive wave lengths up to 1,500 meters. it costs about $6.00. the loose coupled tuning coil.--with a _loose coupler_, as this kind of a tuning coil is called for short, very _selective tuning_ is possible, which means that you can tune in a station very sharply, and it will receive any wave lengths according to size of coils. the primary coil is wound on a fixed cylinder and its inductance is varied by means of a sliding contact like the double slide tuning coil described above. the secondary coil is wound on a cylinder that slides in and out of the primary coil. the inductance of this coil is varied by means of a switch that makes contact with the fixed points, each of which is connected with every twentieth turn of wire as shown in the diagram a in fig. 12. the loose coupler, which is shown complete at b, costs in the neighborhood of $8.00 or $10.00. [illustration: (a) fig. 12.--schematic diagram of loose coupler.] [illustration: (b) fig. 12.--loose coupler complete.] fixed and variable condensers.--you do not require a condenser for a simple receiving set, but if you will connect a _fixed condenser_ across your headphones you will get better results, while a _variable condenser_ connected in the _closed circuit of a direct coupled receiving set_, that is, one where a double slide tuning coil is used, makes it easy to tune very much more sharply; a variable condenser is absolutely necessary where the circuits are _inductively coupled_, that is, where a loose coupled tuner is used. a fixed condenser consists of a number of sheets of paper with leaves of tin-foil in between them and so built up that one end of every other leaf of tin-foil projects from the opposite end of the paper as shown at a in fig. 13. the paper and tin-foil are then pressed together and impregnated with an insulating compound. a fixed condenser of the exact capacitance required for connecting across the head phones is mounted in a base fitted with binding posts, as shown at b, and costs 75 cents. (paper ones 25 cents.) [illustration: (a) fig. 13.--how a fixed receiving condenser is built up.] [illustration: (b) fig. 13.--the fixed condenser complete.] [illustration: (c) and (d) fig. 13.--the variable rotary condenser.] a variable condenser, see c, of the rotating type is formed of a set of fixed semi-circular metal plates which are slightly separated from each other and between these a similar set of movable semi-circular metal plates is made to interleave; the latter are secured to a shaft on the top end of which is a knob and by turning it the capacitance of the condenser, and, hence, of the circuit in which it is connected, is varied. this condenser, which is shown at d, is made in two sizes, the smaller one being large enough for all ordinary wave lengths while the larger one is for proportionately longer wave lengths. these condensers cost $4.00 and $5.00 respectively. about telephone receivers.--there are a number of makes of head telephone receivers on the market that are designed especially for wireless work. these phones are wound to _resistances_ of from 75 _ohms_ to 8,000 _ohms_, and cost from $1.25 for a receiver without a cord or headband to $15.00 for a pair of phones with a cord and head band. you can get a receiver wound to any resistance in between the above values but for either of the simple receiving sets such as described in this chapter you ought to have a pair wound to at least 2,000 ohms and these will cost you about $5.00. a pair of head phones of this type is shown in fig. 14. [illustration: fig. 14.--pair of wireless head phones.] connecting up the parts--receiving set no. 1.--for this set get (1) a _crystal detector_, (2) a _two-slide tuning coil_, (3) a _fixed condenser_, and (4) a pair of 2,000 ohm head phones. mount the detector on the right-hand side of a board and the tuning coil on the left-hand side. screw in two binding posts for the cord ends of the telephone receivers at _a_ and _b_ as shown at a in fig. 15. this done connect one of the end binding posts of the tuning coil with the ground wire and a post of one of the contact slides with the lightning arrester or switch which leads to the aerial wire. [illustration: fig. 15.--top view of apparatus layout for receiving set no. 1.] [illustration: (b) fig. 15.--wiring diagram for receiving set no. 1.] now connect the post of the other contact slide to one of the posts of the detector and the other post of the latter with the binding post _a_, then connect the binding post _b_ to the ground wire and solder the joint. next connect the ends of the telephone receiver cord to the posts _a_ and _b_ and connect a fixed condenser also with these posts, all of which are shown in the wiring diagram at b, and you are ready to adjust the set for receiving. receiving set no. 2.--use the same kind of a detector and pair of head phones as for _set no. 1_, but get (1) a _loose coupled tuning coil_, and (2) a _variable condenser_. mount the loose coupler at the back of a board on the left-hand side and the variable condenser on the right-hand side. then mount the detector in front of the variable condenser and screw two binding posts, _a_ and _b_, in front of the tuning coil as shown at a in fig. 16. [illustration: fig. 16.--top view of apparatus layout for receiving set no. 2.] [illustration: (b) fig. 16.--wiring diagram for receiving set no. 2.] now connect the post of the sliding contact of the loose coupler with the wire that runs to the lightning switch and thence to the aerial; connect the post of the primary coil, which is the outside coil, with the ground wire; then connect the binding post leading to the switch of the secondary coil, which is the inside coil, with one of the posts of the variable condenser, and finally, connect the post that is joined to one end of the secondary coil with the other post of the variable condenser. this done, connect one of the posts of the condenser with one of the posts of the detector, the other post of the detector with the binding post _a_, and the post _b_ to the other post of the variable condenser. next connect a fixed condenser to the binding posts _a_ and _b_ and then connect the telephone receivers to these same posts, all of which is shown in the wiring diagram at b. you are now ready to adjust the instruments. in making the connections use no. 16 or 18 insulated copper wire and scrape the ends clean where they go into the binding posts. see, also, that all of the connections are tight and where you have to cross the wires keep them apart by an inch or so and always cross them at right angles. adjusting the no. 1 set--the detector.--the first thing to do is to test the detector in order to find out if the point of the contact wire is on a sensitive spot of the crystal. to do this you need a _buzzer_, a _switch_ and a _dry cell_. an electric bell from which the gong has been removed will do for the buzzer, but you can get one that is made specially for the purpose, for 75 cents, which gives out a clear, high-pitched note that sounds like a high-power station. connect one of the binding posts of the buzzer with one post of the switch, the other post of the latter with the zinc post of the dry cell and the carbon post of this to the other post of the buzzer. then connect the post of the buzzer that is joined to the vibrator, to the ground wire as shown in the wiring diagram, fig. 17. now close the switch of the buzzer circuit, put on your head phones, and move the wire point of the detector to various spots on the crystal until you hear the sparks made by the buzzer in your phones. [illustration: fig. 17.--adjusting the receiving set.] then vary the pressure of the point on the crystal until you hear the sparks as loud as possible. after you have made the adjustment open the switch and disconnect the buzzer wire from the ground wire of your set. this done, be very careful not to jar the detector or you will throw it out of adjustment and then you will have to do it all over again. you are now ready to tune the set with the tuning coil and listen in. the tuning coil.--to tune this set move the slide a of the double-slide tuner, see b in fig. 15, over to the end of the coil that is connected with the ground wire and the slide b near the opposite end of the coil, that is, the one that has the free end. now move the slide a toward the b slide and when you hear the dots and dashes, or speech or music, that is coming in as loud as you can move the b slide toward the a slide until you hear still more loudly. a very few trials on your part and you will be able to tune in or tune out any station you can hear, if not too close or powerful. [illustration: original â© underwood and underwood. the world's largest radio receiving station. owned by the radio corporation of america at rocky point near point jefferson, l.i.] adjusting the no. 2 set.--first adjust the crystal detector with the buzzer set as described above with _set no. 1,_ then turn the knob of your variable condenser so that the movable plates are just half-way in, pull the secondary coil of your loose-coupled tuner half way out; turn the switch lever on it until it makes a contact with the middle contact point and set the slider of the primary coil half way between the ends. now listen in for telegraphic signals or telephonic speech or music; when you hear one or the other slide the secondary coil in and out of the primary coil until the sounds are loudest; now move the contact switch over the points forth and back until the sounds are still louder, then move the slider to and fro until the sounds are yet louder and, finally, turn the knob of the condenser until the sounds are clear and crisp. when you have done all of these things you have, in the parlance of the wireless operator, _tuned in_ and you are ready to receive whatever is being sent. chapter iv simple telegraph sending sets a wireless telegraph transmitting set can be installed for a very small amount of money provided you are content with one that has a limited range. larger and better instruments can, of course, be had for more money, but however much you are willing to spend still you are limited in your sending radius by the government's rules and regulations. the best way, and the cheapest in the end, to install a telegraph set is to buy the separate parts and hook them up yourself. the usual type of wireless telegraph transmitter employs a _disruptive discharge,_ or _spark,_ as it is called, for setting up the oscillating currents in the aerial wire system and this is the type of apparatus described in this chapter. there are two ways to set up the sparks and these are: (1) with an _induction coil,_ or _spark-coil,_ as it is commonly called, and (2) with an _alternating current transformer_, or _power transformer_, as it is sometimes called. where you have to generate the current with a battery you must use a spark coil, but if you have a 110-volt direct or alternating lighting current in your home you can use a transformer which will give you more power. a cheap transmitting set (no. 1).--for this set you will need: (1) a _spark-coil_, (2) a _battery_ of dry cells, (3) a _telegraph key_, (4) a _spark gap_, (5) a _high-tension condenser_, and (6) an _oscillation transformer_. there are many different makes and styles of these parts but in the last analysis all of them are built on the same underlying bases and work on the same fundamental principles. the spark-coil.--spark coils for wireless work are made to give sparks from 1/4 inch in length up to 6 inches in length, but as a spark coil that gives less than a 1-inch spark has a very limited output it is best to get a coil that gives at least a 1-inch spark, as this only costs about $8.00, and if you can get a 2or a 4-inch spark coil so much the better. there are two general styles of spark coils used for wireless and these are shown at a and b in fig. 18. [illustration: (a) and (b) fig. 18.--types of spark coils for set. no. 1.] [illustration: (c) fig. 18.--wiring diagram of spark coil] a spark coil of either style consists of (_a_) a soft _iron core_ on which is wound (_b_) a couple of layers of heavy insulated wire and this is called the _primary coil_, (_c_) while over this, but insulated from it, is wound a large number of turns of very fine insulated copper wire called the _secondary coil_; (d) an _interrupter_, or _vibrator_, as it is commonly called, and, finally, (e) a _condenser_. the core, primary and secondary coils form a unit and these are set in a box or mounted on top of a hollow wooden base. the condenser is placed in the bottom of the box, or on the base, while the vibrator is mounted on one end of the box or on top of the base, and it is the only part of the coil that needs adjusting. the vibrator consists of a stiff, flat spring fixed at one end to the box or base while it carries a piece of soft iron called an _armature_ on its free end and this sets close to one end of the soft iron core. insulated from this spring is a standard that carries an adjusting screw on the small end of which is a platinum point and this makes contact with a small platinum disk fixed to the spring. the condenser is formed of alternate sheets of paper and tinfoil built up in the same fashion as the receiving condenser described under the caption of _fixed and variable condensers_, in chapter iii. the wiring diagram c shows how the spark coil is wired up. one of the battery binding posts is connected with one end of the primary coil while the other end of the latter which is wound on the soft iron core connects with the spring of the vibrator. the other battery binding post connects with the standard that supports the adjusting screw. the condenser is shunted across the vibrator, that is, one end of the condenser is connected with the spring and the other end of the condenser is connected with the adjusting screw standard. the ends of the secondary coil lead to two binding posts, which are usually placed on top of the spark coil and it is to these that the spark gap is connected. the battery.--this can be formed of dry cells or you can use a storage battery to energize your coil. for all coils that give less than a 1-inch spark you should use 5 dry cells; for 1-and 2-inch spark coils use 6 or 8 dry cells, and for 3 to 4-inch spark coils use 8 to 10 dry cells. the way the dry cells are connected together to form a battery will be shown presently. a dry cell is shown at a in fig, 19. [illustration: fig. 19.--other parts for transmitting set no. 1] the telegraph key.--you can use an ordinary morse telegraph key for the sending set and you can get one with a japanned iron base for $1.50 (or better, one made of brass and which has 1/8-inch silver contact points for $3.00. a key of the latter kind is shown at b). the spark gap.--it is in the _spark gap_ that the high tension spark takes place. the apparatus in which the spark takes place is also called the _spark gap_. it consists of a pair of zinc plugs, called _electrodes_, fixed to the ends of a pair of threaded rods, with knobs on the other ends, and these screw into and through a pair of standards as shown at _c_. this is called a _fixed_, or _stationary spark gap_ and costs about $1.00. the tuning coil.--the _transmitting inductance_, or _sending tuning coil_, consists of 20 to 30 turns of _no. 8 or 9_ hard drawn copper wire wound on a slotted insulated form and mounted on a wooden base. it is provided with _clips_ so that you can cut in and cut out as many turns of wire as you wish and so tune the sending circuits to send out whatever wave length you desire. it is shown at _d_, and costs about $5.00. see also _oscillation transformer_, page 63 [chapter iv]. the high tension condenser.--high tension condensers, that is, condensers which will stand up under _high potentials_, or electric pressures, can be bought in units or sections. these condensers are made up of thin brass plates insulated with a special compound and pressed into a compact form. the _capacitance_ [footnote: this is the capacity of the condenser.] of one section is enough for a transmitting set using a spark coil that gives a 2 inch spark or less and two sections connected together should be used for coils giving from 2 to 4 inch sparks. it is shown at _e_. connecting up the apparatus.--your sending set should be mounted on a table, or a bench, where it need not be moved. place the key in about the middle of the table and down in front, and the spark coil to the left and well to the back but so that the vibrator end will be to the right, as this will enable you to adjust it easily. place the battery back of the spark coil and the tuning coil (oscillation transformer) to the right of the spark coil and back of the key, all of which is shown in the layout at a in fig. 20. [illustration: (a) fig. 20.--top view of apparatus layout for sending set no. 1.] [illustration: (b) fig. 20.--wiring of diagram for sending set no. 1.] for the _low voltage circuit_, that is the battery circuit, use _no. 12_ or _14_ insulated copper wire. connect all of the dry cells together in _series_, that is, connect the zinc of one cell with the carbon of the next and so on until all of them are connected up. then connect the carbon of the end cell with one of the posts of the key, the zinc of the other end cell with one of the primary posts of the spark coil and the other primary post of the spark coil with the other post of the key, when the primary circuit will be complete. for the _high tension circuits_, that is, the _oscillation circuits_, you may use either bare or insulated copper wire but you must be careful that they do not touch the table, each other, or any part of the apparatus, except, of course, the posts they are connected with. connect one of the posts of the secondary coil of the spark coil with one of the posts of the spark gap, and the other post with one of the posts of the condenser; then connect the other post of the condenser with the lower spring clip of the tuning coil and also connect this clip with the ground. this done, connect the middle spring clip with one of the posts of the spark gap, and, finally, connect the top clip with the aerial wire and your transmitting set is ready to be tuned. a wiring diagram of the connections is shown at b. as this set is tuned in the same way as _set no. 2_ which follows, you are referred to the end of this chapter. a better transmitting set (no. 2).--the apparatus for this set includes: (1) an _alternating current transformer_, (2) a _wireless telegraph key_, (3) a _fixed_, a _rotary_, or a _quenched spark gap_, (4) a _condenser_, and (5) an _oscillation transformer_. if you have a 110 volt direct lighting current in your home instead of 110 volt alternating current, then you will also need (6) an _electrolytic interrupter_, for in this case the primary circuit of the transformer must be made and broken rapidly in order to set up alternating currents in the secondary coil. the alternating current transformer.--an alternating current, or power, transformer is made on the same principle as a spark coil, that is, it has a soft iron core, a primary coil formed of a couple of layers of heavy wire, and a secondary coil wound up of a large number of turns of very fine wire. unlike the spark coil, however, which has an _open magnetic core_ and whose secondary coil is wound on the primary coil, the transformer has a _closed magnetic core_, with the primary coil wound on one of the legs of the core and the secondary wound on the other leg. it has neither a vibrator nor a condenser. a plain transformer is shown at a in fig. 21. [illustration: fig. 21.--parts for transmitting set no. 2.] a transformer of this kind can be bought either (a) _unmounted_, that is, just the bare transformer, or (b) _fully mounted_, that is, fitted with an iron stand, mounted on an insulating base on which are a pair of primary binding posts, while the secondary is provided with a _safety spark gap_. there are three sizes of transformers of this kind made and they are rated at 1/4, 1/2 and 1 kilowatt, respectively, they deliver a secondary current of 9,000, 11,000 and 25,000 volts, according to size, and cost $16.00, $22.00 and $33.00 when fully mounted; a reduction of $3.00, $4.00 and $5.00 is made when they are unmounted. all of these transformers operate on 110 volt, 60 cycle current and can be connected directly to the source of alternating current. the wireless key.--for this transmitting set a standard wireless key should be used as shown at b. it is made about the same as a regular telegraph key but it is much heavier, the contact points are larger and instead of the current being led through the bearings as in an ordinary key, it is carried by heavy conductors directly to the contact points. this key is made in three sizes and the first will carry a current of 5 _amperes_[footnote: see _appendix_ for definition.] and costs $4.00, the second will carry a current of 10 amperes and costs $6.50, while the third will carry a current of 20 amperes and costs $7.50. the spark gap.--either a fixed, a rotary, or a quenched spark gap can be used with this set, but the former is seldom used except with spark-coil sets, as it is very hard to keep the sparks from arcing when large currents are used. a rotary spark gap comprises a wheel, driven by a small electric motor, with projecting plugs, or electrodes, on it and a pair of stationary plugs on each side of the wheel as shown at c. the number of sparks per second can be varied by changing the speed of the wheel and when it is rotated rapidly it sends out signals of a high pitch which are easy to read at the receiving end. a rotary gap with a 110-volt motor costs about $25.00. a quenched spark gap not only eliminates the noise of the ordinary gap but, when properly designed, it increases the range of an induction coil set some 200 per cent. a 1/4 kilowatt quenched gap costs $10.00. [footnote: see appendix for definition.] the high tension condenser.--since, if you are an amateur, you can only send out waves that are 200 meters in length, you can only use a condenser that has a capacitance of .007 _microfarad_. [footnote: see appendix for definition.] a sectional high tension condenser like the one described in connection with _set no. 1_ can be used with this set but it must have a capacitance of not more than .007 microfarad. a condenser of this value for a 1/4-kilowatt transformer costs $7.00; for a 1/2-kilowatt transformer $14.00, and for a 1-kilowatt transformer $21.00. see e, fig. 19. the oscillation transformer.--with an oscillation transformer you can tune much more sharply than with a single inductance coil tuner. the primary coil is formed of 6 turns of copper strip, or no. 9 copper wire, and the secondary is formed of 9 turns of strip, or wire. the primary coil, which is the outside coil, is hinged to the base and can be raised or lowered like the lid of a box. when it is lowered the primary and secondary coils are in the same plane and when it is raised the coils set at an angle to each other. it is shown at d and costs $5.00. connecting up the apparatus. for alternating current.--screw the key to the table about the middle of it and near the front edge; place the high tension condenser back of it and the oscillation transformer back of the latter; set the alternating current transformer to the left of the oscillation transformer and place the rotary or quenched spark gap in front of it. now bring a pair of _no. 12_ or _14_ insulated wires from the 110 volt lighting leads and connect them with a single-throw, double-pole switch; connect one pole of the switch with one of the posts of the primary coil of the alternating power transformer and connect the other post of the latter with one of the posts of your key, and the other post of this with the other pole of the switch. now connect the motor of the rotary spark gap to the power circuit and put a single-pole, single-throw switch in the motor circuit, all of which is shown at a in fig. 22. [illustration: (a) fig. 22.--top view of apparatus layout for sending set no. 2.] [illustration: (b) fig. 22.--wiring diagram for sending set no. 2.] next connect the posts of the secondary coil to the posts of the rotary or quenched spark gap and connect one post of the latter to one post of the condenser, the other post of this to the post of the primary coil of the oscillation transformer, which is the inside coil, and the clip of the primary coil to the other spark gap post. this completes the closed oscillation circuit. finally connect the post of the secondary coil of the oscillation transformer to the ground and the clip of it to the wire leading to the aerial when you are ready to tune the set. a wiring diagram of the connections is shown at b. for direct current.--where you have 110 volt direct current you must connect in an electrolytic interrupter. this interrupter, which is shown at a and b in fig. 23, consists of (1) a jar filled with a solution of 1 part of sulphuric acid and 9 parts of water, (2) a lead electrode having a large surface fastened to the cover of surface that sets in a porcelain sleeve and whose end rests on the bottom of the jar. [illustration: fig. 23.--using 110 volt direct current with an alternating current transformer.] when these electrodes are connected in series with the primary of a large spark coil or an alternating current transformer, see c, and a direct current of from 40 to 110 volts is made to pass through it, the current is made and broken from 1,000 to 10,000 times a minute. by raising or lowering the sleeve, thus exposing more or less of the platinum, or alloy point, the number of interruptions per minute can be varied at will. as the electrolytic interrupter will only operate in one direction, you must connect it with its platinum, or alloy anode, to the + or _positive_ power lead and the lead cathode to the or _negative_ power lead. you can find out which is which by connecting in the interrupter and trying it, or you can use a polarity indicator. an electrolytic interrupter can be bought for as little as $3.00. how to adjust your transmitter. tuning with a hot wire ammeter.--a transmitter can be tuned in two different ways and these are: (1) by adjusting the length of the spark gap and the tuning coil so that the greatest amount of energy is set up in the oscillating circuits, and (2) by adjusting the apparatus so that it will send out waves of a given length. to adjust the transmitter so that the circuits will be in tune you should have a _hot wire ammeter_, or radiation ammeter, as it is called, which is shown in fig. 24. it consists of a thin platinum wire through which the high-frequency currents surge and these heat it; the expansion and contraction of the wire moves a needle over a scale marked off into fractions of an ampere. when the spark gap and tuning coil of your set are properly adjusted, the needle will swing farthest to the right over the scale and you will then know that the aerial wire system, or open oscillation circuit, and the closed oscillation circuit are in tune and radiating the greatest amount of energy. [illustration: fig. 24.--principle of the hot wire ammeter.] to send out a 200 meter wave length.--if you are using a condenser having a capacitance of .007 microfarad, which is the largest capacity value that the government will allow an amateur to use, then if you have a hot wire ammeter in your aerial and tune the inductance coil or coils until the ammeter shows the largest amount of energy flowing through it you will know that your transmitter is tuned and that the aerial is sending out waves whose length is 200 meters. to tune to different wave lengths you must have a _wave-meter_. the use of the aerial switch.--where you intend to install both a transmitter and a receptor you will need a throwover switch, or _aerial switch_, as it is called. an ordinary double-pole, double-throw switch, as shown at a in fig. 25, can be used, or a switch made especially for the purpose as at b is handier because the arc of the throw is much less. [illustration: fig. 25.--kinds of aerial switches.] aerial switch for a complete sending and receiving set.--you can buy a double-pole, double-throw switch mounted on a porcelain base for about 75 cents and this will serve for _set no. 1_. screw this switch on your table between the sending and receiving sets and then connect one of the middle posts of it with the ground wire and the other middle post with the lightning switch which connects with the aerial. connect the post of the tuning coil with one of the end posts of the switch and the clip of the tuning coil with the other and complementary post of the switch. this done, connect one of the opposite end posts of the switch to the post of the receiving tuning coil and connect the sliding contact of the latter with the other and complementary post of the switch as shown in fig. 26. [illustration: fig. 26.--wiring diagram for complete sending and receiving set no. 1.] connecting in the lightning switch.--the aerial wire connects with the middle post of the lightning switch, while one of the end posts lead to one of the middle posts of the aerial switch. the other end post of the lightning switch leads to a separate ground outside the building, as the wiring diagrams figs. 26 and 27 show. [illustration: fig. 27.--wiring diagram for complete sending and receiving set no. 2.] chapter v electricity simply explained it is easy to understand how electricity behaves and what it does if you get the right idea of it at the start. in the first place, if you will think of electricity as being a fluid like water its fundamental actions will be greatly simplified. both water and electricity may be at rest or in motion. when at rest, under certain conditions, either one will develop pressure, and this pressure when released will cause them to flow through their respective conductors and thus produce a current. electricity at rest and in motion.--any wire or a conductor of any kind can be charged with electricity, but a leyden jar, or other condenser, is generally used to hold an electric charge because it has a much larger _capacitance_, as its capacity is called, than a wire. as a simple analogue of a condenser, suppose you have a tank of water raised above a second tank and that these are connected together by means of a pipe with a valve in it, as shown at a in fig. 28. [illustration: fig. 28.--water analogue for electric pressure.] [illustration: original â© underwood and underwood. first wireless college in the world, at tufts college, mass.] now if you fill the upper tank with water and the valve is turned off, no water can flow into the lower tank but there is a difference of pressure between them, and the moment you turn the valve on a current of water will flow through the pipe. in very much the same way when you have a condenser charged with electricity the latter will be under _pressure,_ that is, a _difference of potential_ will be set up, for one of the sheets of metal will be charged positively and the other one, which is insulated from it, will be charged negatively, as shown at b. on closing the switch the opposite charges rush together and form a current which flows to and fro between the metal plates. [footnote: strictly speaking it is the difference of potential that sets up the electromotive force.] the electric current and its circuit.--just as water flowing through a pipe has _quantity_ and _pressure_ back of it and the pipe offers friction to it which tends to hold back the water, so, likewise, does electricity flowing in a circuit have: (1) _quantity_, or _current strength_, or just _current_, as it is called for short, or _amperage_, and (2) _pressure_, or _potential difference_, or _electromotive force_, or _voltage_, as it is variously called, and the wire, or circuit, in which the current is flowing has (3) _resistance_ which tends to hold back the current. a definite relation exists between the current and its electromotive force and also between the current, electromotive force and the resistance of the circuit; and if you will get this relationship clearly in your mind you will have a very good insight into how direct and alternating currents act. to keep a quantity of water flowing in a loop of pipe, which we will call the circuit, pressure must be applied to it and this may be done by a rotary pump as shown at a in fig. 29; in the same way, to keep a quantity of electricity flowing in a loop of wire, or circuit, a battery, or other means for generating electric pressure must be used, as shown at b. [illustration: fig. 29.--water analogues for direct and alternating currents.] if you have a closed pipe connected with a piston pump, as at c, as the piston moves to and fro the water in the pipe will move first one way and then the other. so also when an alternating current generator is connected to a wire circuit, as at d, the current will flow first in one direction and then in the other, and this is what is called an _alternating current_. current and the ampere.--the amount of water flowing in a closed pipe is the same at all parts of it and this is also true of an electric current, in that there is exactly the same quantity of electricity at one point of the circuit as there is at any other. the amount of electricity, or current, flowing in a circuit in a second is measured by a unit called the _ampere_, [footnote: for definition of _ampere_ see _appendix._] and it is expressed by the symbol i. [footnote: this is because the letter c is used for the symbol of _capacitance_] just to give you an idea of the quantity of current an _ampere_ is we will say that a dry cell when fresh gives a current of about 20 amperes. to measure the current in amperes an instrument called an _ammeter_ is used, as shown at a in fig. 30, and this is always connected in _series_ with the line, as shown at b. [illustration: fig. 30.--how the ammeter and voltmeter are used.] electromotive force and the volt.--when you have a pipe filled with water or a circuit charged with electricity and you want to make them flow you must use a pump in the first case and a battery or a dynamo in the second case. it is the battery or dynamo that sets up the electric pressure as the circuit itself is always charged with electricity. the more cells you connect together in _series_ the greater will be the electric pressure developed and the more current it will move along just as the amount of water flowing in a pipe can be increased by increasing the pressure of the pump. the unit of electromotive force is the _volt_, and this is the electric pressure which will force a current of _1 ampere_ through a resistance of _1 ohm_; it is expressed by the symbol _e_. a fresh dry cell will deliver a current of about 1.5 volts. to measure the pressure of a current in volts an instrument called a _voltmeter_ is used, as shown at c in fig. 30, and this is always connected across the circuit, as shown at d. resistance and the ohm.--just as a water pipe offers a certain amount of resistance to the flow of water through it, so a circuit opposes the flow of electricity in it and this is called _resistance_. further, in the same way that a small pipe will not allow a large amount of water to flow through it, so, too, a thin wire limits the flow of the current in it. if you connect a _resistance coil_ in a circuit it acts in the same way as partly closing the valve in a pipe, as shown at a and b in fig. 31. the resistance of a circuit is measured by a unit called the _ohm_, and it is expressed by the symbol _r_. a no. 10, brown and sharpe gauge soft copper wire, 1,000 feet long, has a resistance of about 1 ohm. to measure the resistance of a circuit an apparatus called a _resistance bridge is used_. the resistance of a circuit can, however, be easily calculated, as the following shows. [illustration: fig. 31.--water valve analogue of electric resistance. aa valve limits the flow of water. ba resistance limits the flow of current.] what ohm's law is.--if, now, (1) you know what the current flowing in a circuit is in _amperes_, and the electromotive force, or pressure, is in _volts_, you can then easily find what the resistance is in _ohms_ of the circuit in which the current is flowing by this formula: volts e --------= ohms, or --= r amperes i that is, if you divide the current in amperes by the electromotive force in volts the quotient will give you the resistance in ohms. or (2) if you know what the electromotive force of the current is in _volts_ and the resistance of the circuit is in _ohms_ then you can find what the current flowing in the circuit is in _amperes_, thus: volts e ----= amperes, or --= i ohms r that is, by dividing the resistance of the circuit in ohms, by the electromotive force of the current you will get the amperes flowing in the circuit. finally (3) if you know what the resistance of the circuit is in _ohms_ and the current is in _amperes_ then you can find what the electromotive force is in _volts_ since: ohms x amperes = volts, or r x i = e that is, if you multiply the resistance of the circuit in ohms by the current in amperes the result will give you the electromotive force in volts. from this you will see that if you know the value of any two of the constants you can find the value of the unknown constant by a simple arithmetical process. this relation between these three constants is known as _ohm's law_ and as they are very important you should memorize them. what the watt and kilowatt are.--just as _horsepower_ or _h.p._, is the unit of work that steam has done or can do, so the _watt_ is the unit of work that an electric current has done or can do. to find the _watts_ a current develops you need only to multiply the _amperes_ by the _volts_. there are _746 watts_ to _1 horsepower, and 1,000 watts are equal to 1 kilowatt_. electromagnetic induction.--to show that a current of electricity sets up a magnetic field around it you have only to hold a compass over a wire whose ends are connected with a battery when the needle will swing at right angles to the length of the wire. by winding an insulated wire into a coil and connecting the ends of the latter with a battery you will find, if you test it with a compass, that the coil is magnetic. this is due to the fact that the energy of an electric current flowing in the wire is partly changed into magnetic lines of force which rotate at right angles about it as shown at a in fig. 32. the magnetic field produced by the current flowing in the coil is precisely the same as that set up by a permanent steel magnet. conversely, when a magnetic line of force is set up a part of its energy goes to make up electric currents which whirl about in a like manner, as shown at b. [illustration: (a) and (b) fig. 32.--how an electric current is changed into magnetic lines of force and these into an electric current.] [illustration: (c) and (d) fig. 32.--how an electric current sets up a magnetic field.] self-induction or inductance.--when a current is made to flow in a coil of wire the magnetic lines of force produced are concentrated, as at c, just as a lens concentrates rays of light, and this forms an intense _magnetic field_, as it is called. now if a bar of soft iron is brought close to one end of the coil of wire, or, better still, if it is pushed into the coil, it will be magnetized by _electromagnetic induction,_ see d, and it will remain a magnet until the current is cut off. mutual induction.--when two loops of wire, or better, two coils of wire, are placed close together the electromagnetic induction between them is reactive, that is, when a current is made to flow through one of the coils closed magnetic lines of force are set up and when these cut the other loop or turns of wire of the other coil, they in turn produce electric currents in it. it is the mutual induction that takes place between two coils of wire which makes it possible to transform _low voltage currents_ from a battery or a 110 volt source of current into high pressure currents, or _high potential currents_, as they are called, by means of a spark coil or a transformer, as well as to _step up_ and _step down_ the potential of the high frequency currents that are set up in sending and receiving oscillation transformers. soft iron cores are not used in oscillation inductance coils and oscillation transformers for the reason that the frequency of the current is so high the iron would not have time to magnetize and demagnetize and so would not help along the mutual induction to any appreciable extent. high-frequency currents.--high frequency currents, or electric oscillations as they are called, are currents of electricity that surge to and fro in a circuit a million times, more or less, per second. currents of such high frequencies will _oscillate_, that is, surge to and fro, in an _open circuit_, such as an aerial wire system, as well as in a _closed circuit_. now there is only one method by which currents of high frequency, or _radio-frequency_, as they are termed, can be set up by spark transmitters, and this is by discharging a charged condenser through a circuit having a small resistance. to charge a condenser a spark coil or a transformer is used and the ends of the secondary coil, which delivers the high potential alternating current, are connected with the condenser. to discharge the condenser automatically a _spark,_ or an _arc,_ or the _flow of electrons_ in a vacuum tube, is employed. constants of an oscillation circuit.--an oscillation circuit, as pointed out before, is one in which high frequency currents surge or oscillate. now the number of times a high frequency current will surge forth and back in a circuit depends upon three factors of the latter and these are called the constants of the circuit, namely: (1) its _capacitance,_ (2) its _inductance_ and (3) its _resistance._ what capacitance is.--the word _capacitance_ means the _electrostatic capacity_ of a condenser or a circuit. the capacitance of a condenser or a circuit is the quantity of electricity which will raise its pressure, or potential, to a given amount. the capacitance of a condenser or a circuit depends on its size and form and the voltage of the current that is charging it. the capacitance of a condenser or a circuit is directly proportional to the quantity of electricity that will keep the charge at a given potential. the _farad,_ whose symbol is _m,_ is the unit of capacitance and a condenser or a circuit to have a capacitance of one farad must be of such size that one _coulomb,_ which is the unit of electrical quantity, will raise its charge to a potential of one volt. since the farad is far too large for practical purposes a millionth of a farad, or _microfarad_, whose symbol is _mfd._, is used. what inductance is.--under the sub-caption of _self-induction_ and _inductance_ in the beginning of this chapter it was shown that it was the inductance of a coil that makes a current flowing through it produce a strong magnetic field, and here, as one of the constants of an oscillation circuit, it makes a high-frequency current act as though it possessed _inertia_. inertia is that property of a material body that requires time and energy to set in motion, or stop. inductance is that property of an oscillation circuit that makes an electric current take time to start and time to stop. because of the inductance, when a current flows through a circuit it causes the electric energy to be absorbed and changes a large part of it into magnetic lines of force. where high frequency currents surge in a circuit the inductance of it becomes a powerful factor. the practical unit of inductance is the _henry_ and it is represented by the symbol _l_. what resistance is.--the resistance of a circuit to high-frequency currents is different from that for low voltage direct or alternating currents, as the former do not sink into the conductor to nearly so great an extent; in fact, they stick practically to the surface of it, and hence their flow is opposed to a very much greater extent. the resistance of a circuit to high frequency currents is generally found in the spark gap, arc gap, or the space between the electrodes of a vacuum tube. the unit of resistance is, as stated, the _ohm_, and its symbol is _r_. the effect of capacitance, inductance and resistance on electric oscillations.--if an oscillation circuit in which high frequency currents surge has a large resistance, it will so oppose the flow of the currents that they will be damped out and reach zero gradually, as shown at a in fig. 33. but if the resistance of the circuit is small, and in wireless circuits it is usually so small as to be negligible, the currents will oscillate, until their energy is damped out by radiation and other losses, as shown at b. [illustration: fig. 33.--the effect of resistance on the discharge of an electric current.] as the capacitance and the inductance of the circuit, which may be made of any value, that is amount, you wish, determines the _time period_, that is, the length of time for a current to make one complete oscillation, it must be clear that by varying the values of the condenser and the inductance coil you can make the high frequency current oscillate as fast or as slow as you wish within certain limits. where the electric oscillations that are set up are very fast, the waves sent out by the aerial will be short, and, conversely, where the oscillations are slow the waves emitted will be long. chapter vi how the transmitting and receiving sets work the easiest way to get a clear conception of how a wireless transmitter sends out electric waves and how a wireless receptor receives them is to take each one separately and follow: (1) in the case of the transmitter, the transformation of the low voltage direct, or alternating current into high potential alternating currents; then find out how these charge the condenser, how this is discharged by the spark gap and sets up high-frequency currents in the oscillation circuits; then (2) in the case of the receptor, to follow the high frequency currents that are set up in the aerial wire and learn how they are transformed into oscillations of lower potential when they have a larger current strength, how these are converted into intermittent direct currents by the detector and which then flow into and operate the telephone receiver. how transmitting set no. 1 works. the battery and spark coil circuit.--when you press down on the knob of the key the silver points of it make contact and this closes the circuit; the low voltage direct current from the battery now flows through the primary coil of the spark coil and this magnetizes the soft iron core. the instant it becomes magnetic it pulls the spring of the vibrator over to it and this breaks the circuit; when this takes place the current stops flowing through the primary coil; this causes the core to lose its magnetism when the vibrator spring flies back and again makes contact with the adjusting screw; then the cycle of operations is repeated. a condenser is connected across the contact points of the vibrator since this gives a much higher voltage at the ends of the secondary coil than where the coil is used without it; this is because: (1) the self-induction of the primary coil makes the pressure of the current rise and when the contact points close the circuit again it discharges through the primary coil, and (2) when the break takes place the current flows into the condenser instead of arcing across the contact points. changing the primary spark coil current into secondary currents.--now every time the vibrator contact points close the primary circuit the electric current in the primary coil is changed into closed magnetic lines of force and as these cut through the secondary coil they set up in it a _momentary current_ in one direction. then the instant the vibrator points break apart the primary circuit is opened and the closed magnetic lines of force contract and as they do so they cut the turns of wire in the secondary coil in the opposite direction and this sets up another momentary current in the secondary coil in the other direction. the result is that the low voltage direct current of the battery is changed into alternating currents whose frequency is precisely that of the spring vibrator, but while the frequency of the currents is low their potential, or voltage, is enormously increased. what ratio of transformation means.--to make a spark coil step up the low voltage direct current into high potential alternating current the primary coil is wound with a couple of layers of thick insulated copper wire and the secondary is wound with a thousand, more or less, number of turns with very fine insulated copper wire. if the primary and secondary coils were wound with the same number of turns of wire then the pressure, or voltage, of the secondary coil at its terminals would be the same as that of the current which flowed through the primary coil. under these conditions the _ratio of transformation_, as it is called, would be unity. the ratio of transformation is directly proportional to the number of turns of wire on the primary and secondary coils and, since this is the case, if you wind 10 turns of wire on the primary coil and 1,000 turns of wire on the secondary coil then you will get 100 times as high a pressure, or voltage, at the terminals of the secondary as that which you caused to flow through the primary coil, but, naturally, the current strength, or amperage, will be proportionately decreased. the secondary spark coil circuit.--this includes the secondary coil and the spark gap which are connected together. when the alternating, but high potential, currents which are developed by the secondary coil, reach the balls, or _electrodes_, of the spark gap the latter are alternately charged positively and negatively. now take a given instant when one electrode is charged positively and the other one is charged negatively, then when they are charged to a high enough potential the electric strain breaks down the air gap between them and the two charges rush together as described in the chapter before this one in connection with the discharge of a condenser. when the charges rush together they form a current which burns out the air in the gap and this gives rise to the spark, and as the heated gap between the two electrodes is a very good conductor the electric current surges forth and back with high frequency, perhaps a dozen times, before the air replaces that which has burned out. it is the inrushing air to fill the vacuum of the gap that makes the crackling noise which accompanies the discharge of the electric spark. in this way then electric oscillations of the order of a million, more or less, are produced and if an aerial and a ground wire are connected to the spark balls, or electrodes, the oscillations will surge up and down it and the energy of these in turn, are changed into electric waves which travel out into space. an open circuit transmitter of this kind will send out waves that are four times as long as the aerial itself, but as the waves it sends out are strongly damped the government will not permit it to be used. the closed oscillation circuit.--by using a closed oscillation circuit the transmitter can be tuned to send out waves of a given length and while the waves are not so strongly damped more current can be sent into the aerial wire system. the closed oscillation circuit consists of: (1) a _spark gap_, (2) a _condenser_ and (3) an _oscillation transformer_. the high potential alternating current delivered by the secondary coil not only charges the spark gap electrodes which necessarily have a very small capacitance, but it charges the condenser which has a large capacitance and the value of which can be changed at will. now when the condenser is fully charged it discharges through the spark gap and then the electric oscillations set up surge to and fro through the closed circuit. as a closed circuit is a very poor radiator of energy, that is, the electric oscillations are not freely converted into electric waves by it, they surge up to, and through the aerial wire; now as the aerial wire is a good radiator nearly all of the energy of the electric oscillations which surge through it are converted into electric waves. how transmitting set no. 2 works. with alternating current. the operation of a transmitting set that uses an alternating current transformer, or _power transformer,_ as it is sometimes called, is even more simple than one using a spark coil. the transformer needs no vibrator when used with alternating current. the current from a generator flows through the primary coil of the transformer and the alternations of the usual lighting current is 60 cycles per second. this current sets up an alternating magnetic field in the core of the transformer and as these magnetic lines of force expand and contract they set up alternating currents of the same frequency but of much higher voltage at the terminals of the secondary coil according to the ratio of the primary and secondary turns of wire as explained under the sub-caption of _ratio of transformation_. with direct current.--when a 110 volt direct current is used to energize the power transformer an _electrolytic_ interruptor is needed to make and break the primary circuit, just as a vibrator is needed for the same purpose with a spark coil. when the electrodes are connected in series with the primary coil of a transformer and a source of direct current having a potential of 40 to 110 volts, bubbles of gas are formed on the end of the platinum, or alloy anode, which prevent the current from flowing until the bubbles break and then the current flows again, in this way the current is rapidly made and broken and the break is very sharp. where this type of interrupter is employed the condenser that is usually shunted around the break is not necessary as the interrupter itself has a certain inherent capacitance, due to electrolytic action, and which is called its _electrolytic capacitance_, and this is large enough to balance the self-induction of the circuit since the greater the number of breaks per minute the smaller the capacitance required. the rotary spark gap.--in this type of spark gap the two fixed electrodes are connected with the terminals of the secondary coil of the power transformer and also with the condenser and primary of the oscillation transformer. now whenever any pair of electrodes on the rotating disk are in a line with the pair of fixed electrodes a spark will take place, hence the pitch of the note depends on the speed of the motor driving the disk. this kind of a rotary spark-gap is called _non-synchronous_ and it is generally used where a 60 cycle alternating current is available but it will work with other higher frequencies. the quenched spark gap.--if you strike a piano string a single quick blow it will continue to vibrate according to its natural period. this is very much the way in which a quenched spark gap sets up oscillations in a coupled closed and open circuit. the oscillations set up in the primary circuit by a quenched spark make only three or four sharp swings and in so doing transfer all of their energy over to the secondary circuit, where it will oscillate some fifty times or more before it is damped out, because the high frequency currents are not forced, but simply oscillate to the natural frequency of the circuit. for this reason the radiated waves approach somewhat the condition of continuous waves, and so sharper tuning is possible. the oscillation transformer.--in this set the condenser in the closed circuit is charged and discharged and sets up oscillations that surge through the closed circuit as in _set no. 1_. in this set, however, an oscillation transformer is used and as the primary coil of it is included in the closed circuit the oscillations set up in it produce strong oscillating magnetic lines of force. the magnetic field thus produced sets up in turn electric oscillations in the secondary coil of the oscillation transformer and these surge through the aerial wire system where their energy is radiated in the form of electric waves. the great advantage of using an oscillation transformer instead of a simple inductance coil is that the capacitance of the closed circuit can be very much larger than that of the aerial wire system. this permits more energy to be stored up by the condenser and this is impressed on the aerial when it is radiated as electric waves. how receiving set no. i works.--when the electric waves from a distant sending station impinge on the wire of a receiving aerial their energy is changed into electric oscillations that are of exactly the same frequency (assuming the receptor is tuned to the transmitter) but whose current strength (amperage) and potential (voltage) are very small. these electric waves surge through the closed circuit but when they reach the crystal detector the contact of the metal point on the crystal permits more current to flow through it in one direction than it will allow to pass in the other direction. for this reason a crystal detector is sometimes called a _rectifier_, which it really is. thus the high frequency currents which the steel magnet cores of the telephone receiver would choke off are changed by the detector into intermittent direct currents which can flow through the magnet coils of the telephone receiver. since the telephone receiver chokes off the oscillations, a small condenser can be shunted around it so that a complete closed oscillation circuit is formed and this gives better results. when the intermittent rectified current flows through the coils of the telephone receiver it energizes the magnet as long as it lasts, when it is de-energized; this causes the soft iron disk, or _diaphragm_ as it is called, which sets close to the ends of the poles of the magnet, to vibrate; and this in turn gives forth sounds such as dots and dashes, speech or music, according to the nature of the electric waves that sent them out at the distant station. how receiving set no. 2 works.--when the electric oscillations that are set up by the incoming electric waves on the aerial wire surge through the primary coil of the oscillation transformer they produce a magnetic field and as the lines of force of the latter cut the secondary coil, oscillations of the same frequency are set up in it. the potential (voltage) of these oscillations are, however, _stepped down_ in the secondary coil and, hence, their current strength (amperes) is increased. the oscillations then flow through the closed circuit where they are rectified by the crystal detector and transformed into sound waves by the telephone receiver as described in connection with _set no. 1_. the variable condenser shunted across the closed circuit permits finer secondary tuning to be done than is possible without it. where you are receiving continuous waves from a wireless telephone transmitter (speech or music) you have to tune sharper than is possible with the tuning coil alone and to do this a variable condenser connected in parallel with the secondary coil is necessary. chapter vii mechanical and electrical tuning there is a strikingly close resemblance between _sound waves_ and the way they are set up in _the air_ by a mechanically vibrating body, such as a steel spring or a tuning fork, and _electric waves_ and the way they are set up in _the ether_ by a current oscillating in a circuit. as it is easy to grasp the way that sound waves are produced and behave something will be told about them in this chapter and also an explanation of how electric waves are produced and behave and thus you will be able to get a clear understanding of them and of tuning in general. damped and sustained mechanical vibrations.--if you will place one end of a flat steel spring in a vice and screw it up tight as shown at a in fig. 34, and then pull the free end over and let it go it will vibrate to and fro with decreasing amplitude until it comes to rest as shown at b. when you pull the spring over you store up energy in it and when you let it go the stored up energy is changed into energy of motion and the spring moves forth and back, or _vibrates_ as we call it, until all of its stored up energy is spent. [illustration: fig. 34.--damped and sustained mechanical vibrations.] if it were not for the air surrounding it and other frictional losses, the spring would vibrate for a very long time as the stored up energy and the energy of motion would practically offset each other and so the energy would not be used up. but as the spring beats the air the latter is sent out in impulses and the conversion of the vibrations of the spring into waves in the air soon uses up the energy you have imparted to it and it comes to rest. in order to send out _continuous waves_ in the air instead of _damped waves_ as with a flat steel spring you can use an _electric driven tuning fork_, see c, in which an electromagnet is fixed on the inside of the prongs and when this is energized by a battery current the vibrations of the prongs of the fork are kept going, or are _sustained_, as shown in the diagram at d. damped and sustained electric oscillations.--the vibrating steel spring described above is a very good analogue of the way that damped electric oscillations which surge in a circuit set up and send out periodic electric waves in the ether while the electric driven tuning fork just described is likewise a good analogue of how sustained oscillations surge in a circuit and set up and send out continuous electric waves in the ether as the following shows. now the inductance and resistance of a circuit such as is shown at a in fig. 35, slows down, and finally damps out entirely, the electric oscillations of the high frequency currents, see b, where these are set up by the periodic discharge of a condenser, precisely as the vibrations of the spring are damped out by the friction of the air and other resistances that act upon it. as the electric oscillations surge to and fro in the circuit it is opposed by the action of the ether which surrounds it and electric waves are set up in and sent out through it and this transformation soon uses up the energy of the current that flows in the circuit. [illustration: fig. 35.--damped and sustained electric oscillations.] to send out _continuous waves_ in the ether such as are needed for wireless telephony instead of _damped waves_ which are, at the present writing, generally used for wireless telegraphy, an _electric oscillation arc_ or a _vacuum tube oscillator_ must be used, see c, instead of a spark gap. where a spark gap is used the condenser in the circuit is charged periodically and with considerable lapses of time between each of the charging processes, when, of course, the condenser discharges periodically and with the same time element between them. where an oscillation arc or a vacuum tube is used the condenser is charged as rapidly as it is discharged and the result is the oscillations are sustained as shown at d. about mechanical tuning.--a tuning fork is better than a spring or a straight steel bar for setting up mechanical vibrations. as a matter of fact a tuning fork is simply a steel bar bent in the middle so that the two ends are parallel. a handle is attached to middle point of the fork so that it can be held easily and which also allows it to vibrate freely, when the ends of the prongs alternately approach and recede from one another. when the prongs vibrate the handle vibrates up and down in unison with it, and imparts its motion to the _sounding box_, or _resonance case_ as it is sometimes called, where one is used. if, now, you will mount the fork on a sounding box which is tuned so that it will be in resonance with the vibrations of the fork there will be a direct reinforcement of the vibrations when the note emitted by it will be augmented in strength and quality. this is called _simple resonance_. further, if you mount a pair of forks, each on a separate sounding box, and have the forks of the same size, tone and pitch, and the boxes synchronized, that is, tuned to the same frequency of vibration, then set the two boxes a foot or so apart, as shown at a in fig. 36, when you strike one of the forks with a rubber hammer it will vibrate with a definite frequency and, hence, send out sound waves of a given length. when the latter strike the second fork the impact of the molecules of air of which the sound waves are formed will set its prongs to vibrating and it will, in turn, emit sound waves of the same length and this is called _sympathetic resonance_, or as we would say in wireless the forks are _in tune_. [illustration: fig. 36.--sound wave and electric wave tuned senders and receptors. a variable tuning forks for showing sound wave tuning. b variable oscillation circuits for showing electric wave tuning.] tuning forks are made with adjustable weights on their prongs and by fixing these to different parts of them the frequency with which the forks vibrate can be changed since the frequency varies inversely with the square of the length and directly with the thickness [footnote: this law is for forks having a rectangular cross-section. those having a round cross-section vary as the radius.] of the prongs. now by adjusting one of the forks so that it vibrates at a frequency of, say, 16 per second and adjusting the other fork so that it vibrates at a frequency of, say, 18 or 20 per second, then the forks will not be in tune with each other and, hence, if you strike one of them the other will not respond. but if you make the forks vibrate at the same frequency, say 16, 20 or 24 per second, when you strike one of them the other will vibrate in unison with it. about electric tuning.--electric resonance and electric tuning are very like those of acoustic resonance and acoustic tuning which i have just described. just as acoustic resonance may be simple or sympathetic so electric resonance may be simple or sympathetic. simple acoustic resonance is the direct reinforcement of a simple vibration and this condition is had when a tuning fork is mounted on a sounding box. in simple electric resonance an oscillating current of a given frequency flowing in a circuit having the proper inductance and capacitance may increase the voltage until it is several times greater than its normal value. tuning the receptor circuits to the transmitter circuits are examples of sympathetic electric resonance. as a demonstration if you have two leyden jars (capacitance) connected in circuit with two loops of wire (inductance) whose inductance can be varied as shown at b in fig. 36, when you make a spark pass between the knobs of one of them by means of a spark coil then a spark will pass in the gap of the other one provided the inductance of the two loops of wire is the same. but if you vary the inductance of the one loop so that it is larger or smaller than that of the other loop no spark will take place in the second circuit. when a tuning fork is made to vibrate it sends out waves in the air, or sound waves, in all directions and just so when high frequency currents surge in an oscillation circuit they send out waves in the ether, or electric waves, that travel in all directions. for this reason electric waves from a transmitting station cannot be sent to one particular station, though they do go further in one direction than in another, according to the way your aerial wire points. since the electric waves travel out in all directions any receiving set properly tuned to the wave length of the sending station will receive the waves and the only limit on your ability to receive from high-power stations throughout the world depends entirely on the wave length and sensitivity of your receiving set. as for tuning, just as changing the length and the thickness of the prongs of a tuning fork varies the frequency with which it vibrates and, hence, the length of the waves it sends out, so, too, by varying the capacitance of the condenser and the inductance of the tuning coil of the transmitter the frequency of the electric oscillations set up in the circuit may be changed and, consequently, the length of the electric waves they send out. likewise, by varying the capacitance and the inductance of the receptor the circuits can be tuned to receive incoming electric waves of whatever length within the limitation of the apparatus. chapter viii a simple vacuum tube detector receiving set while you can receive dots and dashes from spark wireless telegraph stations and hear spoken words and music from wireless telephone stations with a crystal detector receiving set such as described in chapter iii, you can get stations that are much farther away and hear them better with a _vacuum tube detector_ receiving set. though the vacuum tube detector requires two batteries to operate it and the receiving circuits are somewhat more complicated than where a crystal detector is used still the former does not have to be constantly adjusted as does the latter and this is another very great advantage. taken all in all the vacuum tube detector is the most sensitive and the most satisfactory of the detectors that are in use at the present time. not only is the vacuum tube a detector of electric wave signals and speech and music but it can also be used to _amplify_ them, that is, to make them stronger and, hence, louder in the telephone receiver and further its powers of amplification are so great that it will reproduce them by means of a _loud speaker_, just as a horn amplifies the sounds of a phonograph reproducer, until they can be heard by a room or an auditorium full of people. there are two general types of loud speakers, though both use the principle of the telephone receiver. the construction of these loud speakers will be fully described in a later chapter. assembled vacuum tube receiving sets.--you can buy a receiving set with a vacuum tube detector from the very simplest type, which is described in this chapter, to those that are provided with _regenerative circuits_ and _amplifying_ tubes or both, which we shall describe in later chapters, from dealers in electrical apparatus generally. while one of these sets costs more than you can assemble a set for yourself, still, especially in the beginning, it is a good plan to buy an assembled one for it is fitted with a _panel_ on which the adjusting knobs of the rheostat, tuning coil and condenser are mounted and this makes it possible to operate it as soon as you get it home and without the slightest trouble on your part. you can, however, buy all the various parts separately and mount them yourself. if you want the receptor simply for receiving then it is a good scheme to have all of the parts mounted in a box or enclosed case, but if you want it for experimental purposes then the parts should be mounted on a base or a panel so that all of the connections are in sight and accessible. a simple vacuum tube receiving set.--for this set you should use: (1) a _loose coupled tuning coil,_ (2) a _variable condenser,_ (3) a _vacuum tube detector,_ (4) an a or _storage battery_ giving 6 volts, (5) a b or _dry cell battery_ giving 22-1/2 volts, (6) a _rheostat_ for varying the storage battery current, and (7) a pair of 2,000-ohm _head telephone receivers_. the loose coupled tuning coil, the variable condenser and the telephone receivers are the same as those described in chapter iii. the vacuum tube detector. with two electrodes.--a vacuum tube in its simplest form consists of a glass bulb like an incandescent lamp in which a _wire filament_ and a _metal plate_ are sealed as shown in fig. 37, the air is then pumped out of the tube and a vacuum left or after it is exhausted it is filled with nitrogen, which cannot burn. [illustration: fig. 37.--two electrode vacuum tube detectors.] when the vacuum tube is used as a detector, the wire filament is heated red-hot and the metal plate is charged with positive electricity though it remains cold. the wire filament is formed into a loop like that of an incandescent lamp and its outside ends are connected with a 6-volt storage battery, which is called the a battery; then the + or _positive_ terminal of a 22-1/2 volt dry cell battery, called the b battery, is connected to the metal plate while the or _negative_ terminal of the battery is connected to one of the terminals of the wire filament. the diagram, fig. 37, simply shows how the two electrode vacuum tube, the a or dry battery, and the b or storage battery are connected up. three electrode vacuum tube detector.--the three electrode vacuum tube detector shown at a in fig. 38, is much more sensitive than the two electrode tube and has, in consequence, all but supplanted it. in this more recent type of vacuum tube the third electrode, or _grid_, as it is called, is placed between the wire filament and the metal plate and this allows the current to be increased or decreased at will to a very considerable extent. [illustration: fig. 38.--three electrode vacuum tube detector and battery connections.] the way the three electrode vacuum tube detector is connected with the batteries is shown at b. the plate, the a or dry cell battery and one terminal of the filament are connected in _series_--that is, one after the other, and the ends of the filament are connected to the b or storage battery. in assembling a receiving set you must, of course, have a socket for the vacuum tube. a vacuum tube detector costs from $5.00 to $6.00. the dry cell and storage batteries.--the reason that a storage battery is used for heating the filament of the vacuum tube detector is because the current delivered is constant, whereas when a dry cell battery is used the current soon falls off and, hence, the heat of the filament gradually grows less. the smallest a or 6 volt storage battery on the market has a capacity of 20 to 40 ampere hours, weighs 13 pounds and costs about $10.00. it is shown at a in fig. 39. the b or dry cell battery for the vacuum tube plate circuit that gives 22-1/2 volts can be bought already assembled in sealed boxes. the small size is fitted with a pair of terminals while the larger size is provided with _taps_ so that the voltage required by the plate can be adjusted as the proper operation of the tube requires careful regulation of the plate voltage. a dry cell battery for a plate circuit is shown at b. [illustration: fig. 39.--a and b batteries for vacuum tube detectors.] the filament rheostat.--an adjustable resistance, called a _rheostat_, must be used in the filament and storage battery circuit so that the current flowing through the filament can be controlled to a nicety. the rheostat consists of an insulating and a heat resisting form on which is wound a number of turns of resistance wire. a movable contact arm that slides over and presses on the turns of wire is fixed to the knob on top of the rheostat. a rheostat that has a resistance of 6 ohms and a current carrying capacity of 1.5 amperes which can be mounted on a panel board is the right kind to use. it is shown at a and b in fig. 40 and costs $1.25. [illustration: fig. 40.--rheostat for the a or storage battery current.] assembling the parts.--begin by placing all of the separate parts of the receiving set on a board or a base of other material and set the tuning coil on the left hand side with the adjustable switch end toward the right hand side so that you can reach it easily. then set the variable condenser in front of it, set the vacuum tube detector at the right hand end of the tuning coil and the rheostat in front of the detector. place the two sets of batteries back of the instruments and screw a couple of binding posts _a_ and _b_ to the right hand lower edge of the base for connecting in the head phones all of which is shown at a in fig. 41. [illustration: (a) fig. 41.--top view of apparatus layout for a vacuum tube detector receiving set.] [illustration: (b) fig. 41.--wiring diagram of a simple vacuum tube receiving set.] connecting up the parts.--to wire up the different parts begin by connecting the sliding contact of the primary coil of the loose coupled tuning coil (this you will remember is the outside one that is wound with fine wire) to the upper post of the lightning switch and connect one terminal of this coil with the water pipe. now connect the free end of the secondary coil of the tuning coil (this is the inside coil that is wound with heavy wire) to one of the binding posts of the variable condenser and connect the movable contact arm of the adjustable switch of the primary of the tuning coil with the other post of the variable condenser. next connect the grid of the vacuum tube to one of the posts of the condenser and then connect the plate of the tube to the _carbon terminal_ of the b or dry cell battery which is the + or _positive pole_ and connect the _zinc terminal_ of the or _negative_ pole to the binding post _a_, connect the post _b_ to the other side of the variable condenser and then connect the terminals of the head phones to the binding posts _a_ and _b_. whatever you do be careful not to get the plate connections of the battery reversed. now connect one of the posts of the rheostat to one terminal of the filament and the other terminal of the filament to the or _negative_ terminal of the a or storage battery and the + or _positive_ terminal of the a or storage battery to the other post of the rheostat. finally connect the + or positive terminal of the a or storage battery with the wire that runs from the head phones to the variable condenser, all of which is shown in the wiring diagram at b in fig. 41. adjusting the vacuum tube detector receiving set.--a vacuum tube detector is tuned exactly in the same way as the _crystal detector set no. 2_ described in chapter iii, in-so-far as the tuning coil and variable condenser are concerned. the sensitivity of the vacuum tube detector receiving set and, hence, the distance over which signals and other sounds can be heard depends very largely on the sensitivity of the vacuum tube itself and this in turn depends on: (1) the right amount of heat developed by the filament, or _filament brilliancy_ as it is called, (2) the right amount of voltage applied to the plate, and (3) the extent to which the tube is exhausted where this kind of a tube is used. to vary the current flowing from the a or storage battery through the filament so that it will be heated to the right degree you adjust the rheostat while you are listening in to the signals or other sounds. by carefully adjusting the rheostat you can easily find the point at which it makes the tube the most sensitive. a rheostat is also useful in that it keeps the filament from burning out when the current from the battery first flows through it. you can very often increase the sensitiveness of a vacuum tube after you have used it for a while by recharging the a or storage battery. the degree to which a vacuum tube has been exhausted has a very pronounced effect on its sensitivity. the longer the tube is used the lower its vacuum gets and generally the less sensitive it becomes. when this takes place (and you can only guess at it) you can very often make it more sensitive by warming it over the flame of a candle. vacuum tubes having a gas content (in which case they are, of course, no longer vacuum tubes in the strict sense) make better detectors than tubes from which the air has been exhausted and which are sealed off in this evacuated condition because their sensitiveness is not dependent on the degree of vacuum as in the latter tubes. moreover, a tube that is completely exhausted costs more than one that is filled with gas. chapter ix vacuum tube amplifier receiving sets the reason a vacuum tube detector is more sensitive than a crystal detector is because while the latter merely _rectifies_ the oscillating current that surges in the receiving circuits, the former acts as an _amplifier_ at the same time. the vacuum tube can be used as a separate amplifier in connection with either: (1) a _crystal detector_ or (2) a _vacuum tube detector_, and (_a_) it will amplify either the _radio frequency currents_, that is the high frequency oscillating currents which are set up in the oscillation circuits or (_b_) it will amplify the _audio frequency currents_, that is, the _low frequency alternating_ currents that flow through the head phone circuit. to use the amplified radio frequency oscillating currents or amplified audio frequency alternating currents that are set up by an amplifier tube either a high resistance, called a _grid leak_, or an _amplifying transformer_, with or without an iron core, must be connected with the plate circuit of the first amplifier tube and the grid circuit of the next amplifier tube or detector tube, or with the wire point of a crystal detector. where two or more amplifier tubes are coupled together in this way the scheme is known as _cascade amplification._ where either a _radio frequency transformer_, that is one without the iron core, or an _audio frequency transformer_, that is one with the iron core, is used to couple the amplifier tube circuits together better results are obtained than where a high resistance grid leak is used, but the amplifying tubes have to be more carefully shielded from each other or they will react and set up a _howling_ noise in the head phones. on the other hand grid leaks cost less but they are more troublesome to use as you have to find out for yourself the exact resistance value they must have and this you can do only by testing them out. a grid leak amplifier receiving set. with crystal detector.--the apparatus you need for this set includes: (1) a _loose coupled tuning coil_, (2) a _variable condenser_, (3) _two fixed condensers_, (4) a _crystal detector_, or better a _vacuum tube detector_, (5) an a or _6 volt storage battery_, (6) a _rheostat_, (7) a b or 22-1/2 _volt dry cell battery_, (8) a fixed resistance unit, or _leak grid_ as it is called, and (9) a pair of _head-phones_. the tuning coil, variable condenser, fixed condensers, crystal detectors and head-phones are exactly the same as those described in _set no. 2_ in chapter iii. the a and b batteries are exactly the same as those described in chapter viii. the _vacuum tube amplifier_ and the _grid leak_ are the only new pieces of apparatus you need and not described before. the vacuum tube amplifier.--this consists of a three electrode vacuum tube exactly like the vacuum tube detector described in chapter viii and pictured in fig. 38, except that instead of being filled with a non-combustible gas it is evacuated, that is, the air has been completely pumped out of it. the gas filled tube, however, can be used as an amplifier and either kind of tube can be used for either radio frequency or audio frequency amplification, though with the exhausted tube it is easier to obtain the right plate and filament voltages for good working. the fixed resistance unit, or grid leak.--grid leaks are made in different ways but all of them have an enormously high resistance. one way of making them consists of depositing a thin film of gold on a sheet of mica and placing another sheet of mica on top to protect it the whole being enclosed in a glass tube as shown at a in fig. 42. these grid leaks are made in units of from 50,000 ohms (.05 megohm) to 5,000,000 ohms (5 megohms) and cost from $1 to $2. [illustration: fig. 42.--grid leaks and how to connect them up.] as the _value_ of the grid leak you will need depends very largely upon the construction of the different parts of your receiving set and on the kind of aerial wire system you use with it you will have to try out various resistances until you hit the right one. the resistance that will give the best results, however, lies somewhere between 500,000 ohms (1/2 a megohm) and 3,000,000 ohms (3 megohms) and the only way for you to find this out is to buy 1/2, 1 and 2 megohm grid leak resistances and connect them up in different ways, as shown at b, until you find the right value. assembling the parts for a crystal detector set.--begin by laying the various parts out on a base or a panel with the loose coupled tuning coil on the left hand side, but with the adjustable switch of the secondary coil on the right hand end or in front according to the way it is made. then place the variable condenser, the rheostat, the crystal detector and the binding posts for the head phones in front of and in a line with each other. set the vacuum tube amplifier back of the rheostat and the a and b batteries back of the parts or in any other place that may be convenient. the fixed condensers and the grid leak can be placed anywhere so that it will be easy to connect them in and you are ready to wire up the set. connecting up the parts for a crystal detector.--first connect the sliding contact of the primary of the tuning coil to the leading-in wire and one of the end wires of the primary to the water pipe, as shown in fig. 43. now connect the adjustable arm that makes contact with one end of the secondary of the tuning coil to one of the posts of the variable condenser; then connect the other post of the latter with a post of the fixed condenser and the other post of this with the grid of the amplifying tube. [illustration: fig. 43.--crystal detector receiving set with vacuum tube amplifier (resistance coupled).] connect the first post of the variable condenser to the + or _positive electrode_ of the a battery and its or _negative electrode_ with the rotating contact arm of the rheostat. next connect one end of the resistance coil of the rheostat to one of the posts of the amplifier tube that leads to the filament and the other filament post to the + or _positive electrode_ of the a battery. this done connect the _negative_, that is, the _zinc pole_ of the b battery to the positive electrode of the a battery and connect the _positive_, or _carbon pole_ of the former with one end of the grid leak and connect the other end of this to the plate of the amplifier tube. to the end of the grid leak connected with the plate of the amplifier tube connect the metal point of your crystal detector, the crystal of the latter with one post of the head phones and the other post of them with the other end of the grid leak and, finally, connect a fixed condenser in _parallel_ with--that is across the ends of the grid leak, all of which is shown in the wiring diagram in fig. 43. a grid leak amplifying receiving set with vacuum tube detector.--a better amplifying receiving set can be made than the one just described by using a vacuum tube detector instead of the crystal detector. this set is built up exactly like the crystal detector described above and shown in fig. 43 up to and including the grid leak resistance, but shunted across the latter is a vacuum tube detector, which is made and wired up precisely like the one shown at a in fig. 41 in the chapter ahead of this one. the way a grid leak and vacuum tube detector with a one-step amplifier are connected up is shown at a in fig. 44. where you have a vacuum tube detector and one or more amplifying tubes connected up, or in _cascade_ as it is called, you can use an a, or storage battery of 6 volts for all of them as shown at b in fig. 44, but for every vacuum tube you use you must have a b or 22-1/2 volt dry battery to charge the plate with. [illustration: (a) fig. 44--vacuum tube detector set with one step amplifier (resistance coupled).] [illustration: (b) fig. 44.--wiring diagram for using one a or storage battery with an amplifier and a detector tube.] a radio frequency transformer amplifying receiving set.--instead of using a grid leak resistance to couple up the amplifier and detector tube circuits you can use a _radio frequency transformer_, that is, a transformer made like a loose coupled tuning coil, and without an iron core, as shown in the wiring diagram at a in fig. 45. in this set, which gives better results than where a grid leak is used, the amplifier tube is placed in the first oscillation circuit and the detector tube in the second circuit. [illustration: (a) fig. 45.--wiring diagram for a radio frequency transformer amplifying receiving set.] [illustration: (b) fig. 45.--radio frequency transformer.] since the radio frequency transformer has no iron core the high frequency, or _radio frequency_ oscillating currents, as they are called, surge through it and are not changed into low frequency, or _audio frequency_ pulsating currents, until they flow through the detector. since the diagram shows only one amplifier and one radio frequency transformer, it is consequently a _one step amplifier_; however, two, three or more, amplifying tubes can be connected up by means of an equal number of radio frequency transformers when you will get wonderful results. where a six step amplifier, that is, where six amplifying tubes are connected together, or in _cascade_, the first three are usually coupled up with radio frequency transformers and the last three with audio frequency transformers. a radio frequency transformer is shown at b and costs $6 to $7. an audio frequency transformer amplifying receiving set.--where audio frequency transformers are used for stepping up the voltage of the current of the detector and amplifier tubes, the radio frequency current does not get into the plate circuit of the detector at all for the reason that the iron core of the transformer chokes them off, hence, the succeeding amplifiers operate at audio frequencies. an audio frequency transformer is shown at a in fig. 46 and a wiring diagram showing how the tubes are connected in _cascade_ with the transformers is shown at b; it is therefore a two-step audio frequency receiving set. [illustration: (a) fig. 46.--audio frequency transformer.] [illustration: (b) fig. 46--wiring diagram for an audio frequency transformer amplifying receiving set. (with vacuum tube detector and two step amplifier tubes.)] a six step amplifier receiving set with a loop aerial.--by using a receiving set having a three step radio frequency and a three step audio frequency, that is, a set in which there are coupled three amplifying tubes with radio frequency transformers and three amplifying tubes with audio frequency transformers as described under the caption _a radio frequency transformer receiving set_, you can use a _loop aerial_ in your room thus getting around the difficulties--if such there be--in erecting an out-door aerial. you can easily make a loop aerial by winding 10 turns of _no. 14_ or _16_ copper wire about 1/16 inch apart on a wooden frame two feet on the side as shown in fig. 47. with this six step amplifier set and loop aerial you can receive wave lengths of 150 to 600 meters from various high power stations which are at considerable distances away. [illustration: (a) fig. 47.--six step amplifier with loop aerial.] [illustration: (b) fig. 47.--efficient regenerative receiving set. (with three coil loose coupler tuner.)] how to prevent howling.--where radio frequency or audio frequency amplifiers are used to couple your amplifier tubes in cascade you must take particular pains to shield them from one another in order to prevent the _feed back_ of the currents through them, which makes the head phones or loud speaker _howl_. to shield them from each other the tubes should be enclosed in metal boxes and placed at least 6 inches apart while the transformers should be set so that their cores are at right angles to each other and these also should be not less than six inches apart. chapter x regenerative amplification receiving sets while a vacuum tube detector has an amplifying action of its own, and this accounts for its great sensitiveness, its amplifying action can be further increased to an enormous extent by making the radio frequency currents that are set up in the oscillation circuits react on the detector. such currents are called _feed-back_ or _regenerative_ currents and when circuits are so arranged as to cause the currents to flow back through the detector tube the amplification keeps on increasing until the capacity of the tube itself is reached. it is like using steam over and over again in a steam turbine until there is no more energy left in it. a system of circuits which will cause this regenerative action to take place is known as the _armstrong circuits_ and is so called after the young man who discovered it. since the regenerative action of the radio frequency currents is produced by the detector tube itself and which sets up an amplifying effect without the addition of an amplifying tube, this type of receiving set has found great favor with amateurs, while in combination with amplifying tubes it multiplies their power proportionately and it is in consequence used in one form or another in all the better sets. there are many different kinds of circuits which can be used to produce the regenerative amplification effect while the various kinds of tuning coils will serve for coupling them; for instance a two or three slide single tuning coil will answer the purpose but as it does not give good results it is not advisable to spend either time or money on it. a better scheme is to use a loose coupler formed of two or three honeycomb or other compact coils, while a _variocoupler_ or a _variometer_ or two will produce the maximum regenerative action. the simplest type of regenerative receiving set. with loose coupled tuning coil.--while this regenerative set is the simplest that will give anything like fair results it is here described not on account of its desirability, but because it will serve to give you the fundamental idea of how the _feed-back_ circuit is formed. for this set you need: (1) a _loose-coupled tuning coil_ such as described in chapter iii, (2) a _variable condenser_ of _.001 mfd._ (microfarad) capacitance; (3) one _fixed condenser_ of _.001 mfd._; (4) one _fixed condenser_ for the grid leak circuit of _.00025 mfd._; (5) a _grid leak_ of 1/2 to 2 megohms resistance; (6) a _vacuum tube detector_; (7) an _a 6 volt battery_; (8) a _rheostat_; (9) a _b 22 1/2 volt battery_; and (10) a pair of _2000 ohm head phones_. connecting up the parts.--begin by connecting the leading-in wire of the aerial with the binding post end of the primary coil of the loose coupler as shown in the wiring diagram fig. 48 and then connect the sliding contact with the water pipe or other ground. connect the binding post end of the primary coil with one post of the variable condenser, connect the other post of this with one of the posts of the _.00025 mfd._ condenser and the other end of this with the grid of the detector tube; then around this condenser shunt the grid leak resistance. [illustration: fig. 48.--simple regenerative receiving set. (with loose coupler tuner.)] next connect the sliding contact of the primary coil with the other post of the variable condenser and from this lead a wire on over to one of the terminals of the filament of the vacuum tube; to the other terminal of the filament connect one of the posts of the rheostat and connect the other post to the or negative electrode of the a battery and then connect the + or positive electrode of it to the other terminal of the filament. connect the + or positive electrode of the a battery with one post of the .001 mfd. fixed condenser and connect the other post of this to one of the ends of the secondary coil of the tuning coil and which is now known as the _tickler coil_; then connect the other end of the secondary, or tickler coil to the plate of the vacuum tube. in the wiring diagram the secondary, or tickler coil is shown above and in a line with the primary coil but this is only for the sake of making the connections clear; in reality the secondary, or tickler coil slides to and fro in the primary coil as shown and described in chapter iii. finally connect the _negative_, or zinc pole of the _b battery_ to one side of the fixed condenser, the _positive_, or carbon, pole to one of the terminals of the head phones and the other terminal of this to the other post of the fixed condenser when your regenerative set is complete. an efficient regenerative receiving set. with three coil loose coupler.--to construct a really good regenerative set you must use a loose coupled tuner that has three coils, namely a _primary_, a _secondary_ and a _tickler coil_. a tuner of this kind is made like an ordinary loose coupled tuning coil but it has a _third_ coil as shown at a and b in fig. 49. the middle coil, which is the _secondary_, is fixed to the base, and the large outside coil, which is the _primary_, is movable, that is it slides to and fro over the middle coil, while the small inside coil, which is the _tickler_, is also movable and can slide in or out of the middle _coil_. none of these coils is variable; all are wound to receive waves up to 360 meters in length when used with a variable condenser of _.001 mfd_. capacitance. in other words you slide the coils in and out to get the right amount of coupling and you tune by adjusting the variable condenser to get the exact wave length you want. [illustration: (a) fig. 49.--diagram of a three coil coupler.] [illustration: (b) fig. 49.--three coil loose coupler tuner.] with compact coils.--compact coil tuners are formed of three fixed inductances wound in flat coils, and these are pivoted in a mounting so that the distance between them and, therefore, the coupling, can be varied, as shown at a in fig. 50. these coils are wound up by the makers for various wave lengths ranging from a small one that will receive waves of any length up to 360 meters to a large one that has a maximum of 24,000 meters. for an amateur set get three of the smallest coils when you can not only hear amateur stations that send on a 200 meter wave but broadcasting stations that send on a 360 meter wave. [illustration: fig. 50.--honeycomb inductance coil.] these three coils are mounted with panel plugs which latter fit into a stand, or mounting, so that the middle coil is fixed, that is, stationary, while the two outside coils can be swung to and fro like a door; this scheme permits small variations of coupling to be had between the coils and this can be done either by handles or by means of knobs on a panel board. while i have suggested the use of the smallest size coils, you can get and use those wound for any wave length you want to receive and when those are connected with variometers and variable condensers, and with a proper aerial, you will have a highly efficient receptor that will work over all ranges of wave lengths. the smallest size coils cost about $1.50 apiece and the mounting costs about $6 or $7 each. the a battery potentiometer.--this device is simply a resistance like the rheostat described in connection with the preceding vacuum tube receiving sets but it is wound to 200 or 300 ohms resistance as against 1-1/2 to 6 ohms of the rheostat. it is, however, used as well as the rheostat. with a vacuum tube detector, and especially with one having a gas-content, a potentiometer is very necessary as it is only by means of it that the potential of the plate of the detector can be accurately regulated. the result of proper regulation is that when the critical potential value is reached there is a marked increase in the loudness of the sounds that are emitted by the head phones. as you will see from a in fig. 51 it has three taps. the two taps which are connected with the ends of the resistance coil are shunted around the a battery and the third tap, which is attached to the movable contact arm, is connected with the b battery tap, see b, at which this battery gives 18 volts. since the a battery gives 6 volts you can vary the potential of the plate from 18 to 24 volts. the potentiometer must never be shunted around the b battery or the latter will soon run down. a potentiometer costs a couple of dollars. [illustration: (a) fig. 51.--the use of the potentiometer.] the parts and how to connect them up.--for this regenerative set you will need: (1) a _honeycomb_ or other compact _three-coil tuner_, (2) two _variable_ (_.001_ and _.0005 mfd_.) _condensers_; (3) a _.00025 mfd. fixed condenser_; (4) a _1/2 to 2 megohm grid leak_; (5) a _tube detector_; (6) a _6 volt a battery_; (7) _a rheostat_; (8) a _potentiometer_; (9) an _18_ or _20 volt b battery_; (10) a _fixed condenser_ of _.001 mfd. fixed condenser_; and (11) a _pair of 2000 ohm head phones_. to wire up the parts connect the leading-in wire of the aerial with the primary coil, which is the middle one of the tuner, and connect the other terminal with the ground. connect the ends of the secondary coil, which is the middle one, with the posts of the variable condenser and connect one of the posts of the latter with one post of the fixed .00025 mfd. condenser and the other post of this with the grid; then shunt the grid leak around it. next connect the other post of the variable condenser to the or _negative_ electrode of the _a battery_; the + or _positive_ electrode of this to one terminal of the detector filament and the other end of the latter to the electrode of the a battery. now connect one end of the tickler coil with the detector plate and the other post to the fixed .001 mfd. condenser, then the other end of this to the positive or carbon pole of the b battery. this done shunt the potentiometer around the a battery and run a wire from the movable contact of it (the potentiometer) over to the 18 volt tap, (see b, fig. 51), of the b battery. finally, shunt the head phones and the .001 mfd. fixed condenser and you are ready to try out conclusions. a regenerative audio frequency amplifier receiving set.--the use of amateur regenerative cascade audio frequency receiving sets is getting to be quite common. to get the greatest amplification possible with amplifying tubes you have to keep a negative potential on the grids. you can, however, get very good results without any special charging arrangement by simply connecting one post of the rheostat with the negative terminal of the filament and connecting the _low potential_ end of the secondary of the tuning coil with the or negative electrode of the a battery. this scheme will give the grids a negative bias of about 1 volt. you do not need to bother about these added factors that make for high efficiency until after you have got your receiving set in working order and understand all about it. the parts and how to connect them up.--exactly the same parts are needed for this set as the one described above, but in addition you will want: (1) two more _rheostats_; (2) _two_ more sets of b 22-1/2 _volt batteries_; (3) _two amplifier tubes_, and (4) _two audio frequency transformers_ as described in chapter ix and pictured at a in fig. 46. to wire up the parts begin by connecting the leading-in wire to one end of the primary of the tuning coil and then connect the other end of the coil with the ground. a variable condenser of .001 mfd. capacitance can be connected in the ground wire, as shown in fig. 52, to good advantage although it is not absolutely needed. now connect one end of the secondary coil to one post of a _.001 mfd._ variable condenser and the other end of the secondary to the other post of the condenser. [illustration: fig. 52.--regenerative audio frequency amplifier receiving set.] next bring a lead (wire) from the first post of the variable condenser over to the post of the first fixed condenser and connect the other post of the latter with the grid of the detector tube. shunt 1/2 to 2 megohm grid leak resistance around the fixed condenser and then connect the second post of the variable condenser to one terminal of the detector tube filament. run this wire on over and connect it with the first post of the second rheostat, the second post of which is connected with one terminal of the filament of the first amplifying tube; then connect the first post of the rheostat with one end of the secondary coil of the first audio frequency transformer, and the other end of this coil with the grid of the first amplifier tube. connect the lead that runs from the second post of variable condenser to the first post of the third rheostat, the second post of which is connected with one terminal of the second amplifying tube; then connect the first post of the rheostat with one end of the secondary coil of the second audio frequency transformer and the other end of this coil with the grid of the second amplifier tube. this done connect the or negative electrode of the a battery with the second post of the variable condenser and connect the + or positive electrode with the free post of the first rheostat, the other post of which connects with the free terminal of the filament of the detector. from this lead tap off a wire and connect it to the free terminal of the filament of the first amplifier tube, and finally connect the end of the lead with the free terminal of the filament of the second amplifier tube. next shunt a potentiometer around the a battery and connect the third post, which connects with the sliding contact, to the negative or zinc pole of a b battery, then connect the positive or carbon pole of it to the negative or zinc pole of a second b battery and the positive or carbon pole of the latter with one end of the primary coil of the second audio frequency transformer and the other end of it to the plate of the first amplifying tube. run the lead on over and connect it to one of the terminals of the second fixed condenser and the other terminal of this with the plate of the second amplifying tube. then shunt the headphones around the condenser. finally connect one end of the tickler coil of the tuner with the plate of the detector tube and connect the other end of the tickler to one end of the primary coil of the first audio frequency transformer and the other end of it to the wire that connects the two b batteries together. chapter xi short wave regenerative receiving sets a _short wave receiving set_ is one that will receive a range of wave lengths of from 150 to 600 meters while the distance over which the waves can be received as well as the intensity of the sounds reproduced by the headphones depends on: (1) whether it is a regenerative set and (2) whether it is provided with amplifying tubes. high-grade regenerative sets designed especially for receiving amateur sending stations that must use a short wave length are built on the regenerative principle just like those described in the last chapter and further amplification can be had by the use of amplifier tubes as explained in chapter ix, but the new feature of these sets is the use of the _variocoupler_ and one or more _variometers_. these tuning devices can be connected up in different ways and are very popular with amateurs at the present time. differing from the ordinary loose coupler the variometer has no movable contacts while the variometer is provided with taps so that you can connect it up for the wave length you want to receive. all you have to do is to tune the oscillation circuits to each other is to turn the _rotor_, which is the secondary coil, around in the _stator_, as the primary coil is called in order to get a very fine variation of the wave length. it is this construction that makes _sharp tuning_ with these sets possible, by which is meant that all wave lengths are tuned out except the one which the receiving set is tuned for. a short wave regenerative receiver--with one variometer and three variable condensers.--this set also includes a variocoupler and a _grid coil_. the way that the parts are connected together makes it a simple and at the same time a very efficient regenerative receiver for short waves. while this set can be used without shielding the parts from each other the best results are had when shields are used. the parts you need for this set include: (1) one _variocoupler_; (2) one _.001 microfarad variable condenser_; (3) one _.0005 microfarad variable condenser_; (4) one _.0007 microfarad variable condenser_; (5) _one 2 megohm grid leak_; (6) one _vacuum tube detector_; (7) one _6 volt a battery_; (8) one _6 ohm_, 1-1/2 _ampere rheostat_; (9) one _200 ohm potentiometer_; (10) one 22-1/2 _volt b battery_; (11) one _.001 microfarad fixed condenser_, (12) one pair of _2,000 ohm headphones_, and (13) a _variometer_. the variocoupler.--a variocoupler consists of a primary coil wound on the outside of a tube of insulating material and to certain turns of this taps are connected so that you can fix the wave length which your aerial system is to receive from the shortest wave; i.e., 150 meters on up by steps to the longest wave, i.e., 600 meters, which is the range of most amateur variocouplers that are sold in the open market. this is the part of the variocoupler that is called the _stator_. the secondary coil is wound on the section of a ball mounted on a shaft and this is swung in bearings on the stator so that it can turn in it. this part of the variocoupler is called the _rotor_ and is arranged so that it can be mounted on a panel and adjusted by means of a knob or a dial. a diagram of a variocoupler is shown at a in fig. 53, and the coupler itself at b. there are various makes and modifications of variocouplers on the market but all of them are about the same price which is $6.00 or $8.00. [illustration: fig. 53.--how the variocoupler is made and works.] the variometer.--this device is quite like the variocoupler, but with these differences: (1) the rotor turns in the stator, which is also the section of a ball, and (2) one end of the primary is connected with one end of the secondary coil. to be really efficient a variometer must have a small resistance and a large inductance as well as a small dielectric loss. to secure the first two of these factors the wire should be formed of a number of fine, pure copper wires each of which is insulated and the whole strand then covered with silk. this kind of wire is the best that has yet been devised for the purpose and is sold under the trade name of _litzendraht_. a new type of variometer has what is known as a _basket weave_, or _wavy wound_ stator and rotor. there is no wood, insulating compound or other dielectric materials in large enough quantities to absorb the weak currents that flow between them, hence weaker sounds can be heard when this kind of a variometer is used. with it you can tune sharply to waves under 200 meters in length and up to and including wave lengths of 360 meters. when amateur stations of small power are sending on these short waves this style of variometer keeps the electric oscillations at their greatest strength and, hence, the reproduced sounds will be of maximum intensity. a wiring diagram of a variometer is shown at a in fig. 54 and a _basketball_ variometer is shown complete at b. [illustration: fig. 54.--how the variometer is made and works.] connecting up the parts.--to hook-up the set connect the leading-in wire to one end of the primary coil, or stator, of the variocoupler and solder a wire to one of the taps that gives the longest wave length you want to receive. connect the other end of this wire with one post of a .001 microfarad variable condenser and connect the other post with the ground as shown in fig. 55. now connect one end of the secondary coil, or rotor, to one post of a .0007 mfd. variable condenser, the other post of this to one end of the grid coil and the other end of this with the remaining end of the rotor of the variocoupler. [illustration: fig. 55.--short wave regenerative receiving set (one variometer and three variable condensers.)] next connect one post of the .0007 mfd. condenser with one of the terminals of the detector filament; then connect the other post of this condenser with one post of the .0005 mfd. variable condenser and the other post of this with the grid of the detector, then shunt the megohm grid leak around the latter condenser. this done connect the other terminal of the filament to one post of the rheostat, the other post of this to the or negative electrode of the 6 volt a battery and the + or positive electrode of the latter to the other terminal of the filament. shunt the potentiometer around the a battery and connect the sliding contact with the or zinc pole of the b battery and the + or carbon pole with one terminal of the headphone; connect the other terminal to one of the posts of the variometer and the other post of the variometer to the plate of the detector. finally shunt a .001 mfd. fixed condenser around the headphones. if you want to amplify the current with a vacuum tube amplifier connect in the terminals of the amplifier circuit shown at a in figs. 44 or 45 at the point where they are connected with the secondary coil of the loose coupled tuning coil, in those diagrams with the binding posts of fig. 55 where the phones are usually connected in. short wave regenerative receiver. with two variometers and two variable condensers.--this type of regenerative receptor is very popular with amateurs who are using high-grade short-wave sets. when you connect up this receptor you must keep the various parts well separated. screw the variocoupler to the middle of the base board or panel, and secure the variometers on either side of it so that the distance between them will be 9 or 10 inches. by so placing them the coupling will be the same on both sides and besides you can shield them from each other easier. for the shield use a sheet of copper on the back of the panel and place a sheet of copper between the parts, or better, enclose the variometers and detector and amplifying tubes if you use the latter in sheet copper boxes. when you set up the variometers place them so that their stators are at right angles to each other for otherwise the magnetic lines of force set up by the coils of each one will be mutually inductive and this will make the headphones or loud speaker _howl_. whatever tendency the receptor has to howl with this arrangement can be overcome by putting in a grid leak of the right resistance and adjusting the condenser. the parts and how to connect them up.--for this set you require: (1) one _variocoupler_; (2) two _variometers_; (3) one _.001 microfarad variable condenser_; (4) one _.0005 microfarad variable condenser_; (5) one _2 megohm grid leak resistance_; (6) one _vacuum tube detector_; (7) one _6 volt a battery_; (8) one _200 ohm potentiometer_; (9) one _22-1/2 volt b battery_; (10) one _.001 microfarad fixed condenser_, and (11) one pair of _2,000 ohm headphones_. to wire up the set begin by connecting the leading-in wire to the fixed end of the primary coil, or _stator_, of the variocoupler, as shown in fig. 56, and connect one post of the .001 mfd. variable condenser to the stator by soldering a short length of wire to the tap of the latter that gives the longest wave you want to receive. now connect one end of the secondary coil, or _rotor_, of the variocoupler with one post of the .0005 mfd. variable condenser and the other part to the grid of the detector tube. connect the other end of the rotor of the variocoupler to one of the posts of the first variometer and the other post of this to one of the terminals of the detector filament. [illustration: fig. 56.--short wave regenerative receiving set (two variometers and two variable condensers.)] connect this filament terminal with the or negative electrode of the a battery and the + or positive electrode of this with one post of the rheostat and lead a wire from the other post to the free terminal of the filament. this done shunt the potential around the a battery and connect the sliding contact to the or zinc pole of the b battery and the + or carbon pole of this to one terminal of the headphones, while the other terminal of this leads to one of the posts of the second variometer, the other post of which is connected to the plate of the detector tube. if you want to add an amplifier tube then connect it to the posts instead of the headphones as described in the foregoing set. chapter xii intermediate and long wave regenerative receiving sets all receiving sets that receive over a range of wave lengths of from 150 meters to 3,000 meters are called _intermediate wave sets_ and all sets that receive wave lengths over a range of anything more than 3,000 meters are called _long wave sets_. the range of intermediate wave receptors is such that they will receive amateur, broadcasting, ship and shore navy, commercial, arlington's time and all other stations using _spark telegraph damped waves_ or _arc_ or _vacuum tube telephone continuous waves_ but not _continuous wave telegraph signals_, unless these have been broken up into groups at the transmitting station. to receive continuous wave telegraph signals requires receiving sets of special kind and these will be described in the next chapter. intermediate wave receiving sets.--there are two chief schemes employed to increase the range of wave lengths that a set can receive and these are by using: (1) _loading coils_ and _shunt condensers_, and (2) _bank-wound coils_ and _variable condensers_. if you have a short-wave set and plan to receive intermediate waves with it then loading coils and fixed condensers shunted around them affords you the way to do it, but if you prefer to buy a new receptor then the better way is to get one with bank-wound coils and variable condensers; this latter way preserves the electrical balance of the oscillation circuits better, the electrical losses are less and the tuning easier and sharper. intermediate wave set with loading coils.--for this intermediate wave set you can use either of the short-wave sets described in the foregoing chapter. for the loading coils use _honeycomb coils_, or other good compact inductance coils, as shown in chapter x and having a range of whatever wave length you wish to receive. the following table shows the range of wave length of the various sized coils when used with a variable condenser having a .001 microfarad _capacitance_, the approximate _inductance_ of each coil in _millihenries_ and prices at the present writing: table of characteristics of honeycomb coils approximate wave length in meters in millihenries inductance .001 mfd. variable mounted appx. air condenser. on plug .040 130- 375 $1.40 .075 180- 515 1.40 .15 240- 730 1.50 .3 330-1030 1.50 .6 450-1460 1.55 1.3 660-2200 1.60 2.3 930-2850 1.65 4.5 1300-4000 1.70 6.5 1550-4800 1.75 11. 2050-6300 1.80 20. 3000-8500 2.00 40. 4000--12000 2.15 65. 5000--15000 2.35 100. 6200--19000 2.60 125. 7000--21000 3.00 175. 8200--24000 3.50 these and other kinds of compact coils can be bought at electrical supply houses that sell wireless goods. if your aerial is not very high or long you can use loading coils, but to get anything like efficient results with them you must have an aerial of large capacitance and the only way to get this is to put up a high and long one with two or more parallel wires spaced a goodly distance apart. the parts and how to connect them up.--get (1) _two honeycomb or other coils_ of the greatest wave length you want to receive, for in order to properly balance the aerial, or primary oscillation circuit, and the closed, or secondary oscillation circuit, you have to tune them to the same wave length; (2) two _.001 mfd. variable condensers_, though fixed condensers will do, and (3) two small _single-throw double-pole knife switches_ mounted on porcelain bases. to use the loading coils all you have to do is to connect one of them in the aerial above the primary coil of the loose coupler, or variocoupler as shown in the wiring diagram in fig. 57, then shunt one of the condensers around it and connect one of the switches around this; this switch enables you to cut in or out the loading coil at will. likewise connect the other loading coil in one side of the closed, or secondary circuit between the variable .0007 mfd. condenser and the secondary coil of the loose coupler or variocoupler as shown in fig. 53. the other connections are exactly the same as shown in figs. 44 and 45. [illustration: fig. 57.--wiring diagram showing fixed loading coils for intermediate wave set.] an intermediate wave set with variocoupler inductance coils.--by using the coil wound on the rotor of the variocoupler as the tickler the coupling between the detector tube circuits and the aerial wire system increases as the set is tuned for greater wave lengths. this scheme makes the control of the regenerative circuit far more stable than it is where an ordinary loose coupled tuning coil is used. when the variocoupler is adjusted for receiving very long waves the rotor sets at right angles to the stator and, since when it is in this position there is no mutual induction between them, the tickler coil serves as a loading coil for the detector plate oscillation circuit. inductance coils for short wave lengths are usually wound in single layers but _bank-wound coils_, as they are called are necessary to get compactness where long wave lengths are to be received. by winding inductance coils with two or more layers the highest inductance values can be obtained with the least resistance. a wiring diagram of a multipoint inductance coil is shown in fig. 58. you can buy this intermediate wave set assembled and ready to use or get the parts and connect them up yourself. [illustration: fig. 58.--wiring diagram for intermediate wave receptor with one variocoupler and 12 section bank-wound inductance coil.] the parts and how to connect them up.--for this regenerative intermediate wave set get: (1) one _12 section triple bank-wound inductance coil_, (2) one _variometer_, and (3) all the other parts shown in the diagram fig. 58 except the variocoupler. first connect the free end of the condenser in the aerial to one of the terminals of the stator of the variocoupler; then connect the other terminal of the stator with one of the ends of the bank-wound inductance coil and connect the movable contact of this with the ground. next connect a wire to the aerial between the variable condenser and the stator and connect this to one post of a .0005 microfarad fixed condenser, then connect the other post of this with the grid of the detector and shunt a 2 megohm grid leak around it. connect a wire to the ground wire between the bank-wound inductance coil and the ground proper, i.e., the radiator or water pipe, connect the other end of this to the + electrode of the a battery and connect this end also to one of the terminals of the filament. this done connect the other terminal of the filament to one post of the rheostat and the other post of this to the or negative side of the a battery. to the + electrode of the a battery connect the or zinc pole of the b battery and connect the + or carbon pole of the latter with one post of the fixed .001 microfarad condenser. this done connect one terminal of the tickler coil which is on the rotor of the variometer to the plate of the detector and the other terminal of the tickler to the other post of the .001 condenser and around this shunt your headphones. or if you want to use one or more amplifying tubes connect the circuit of the first one, see fig. 45, to the posts on either side of the fixed condenser instead of the headphones. a long wave receiving set.--the vivid imagination of jules verne never conceived anything so fascinating as the reception of messages without wires sent out by stations half way round the world; and in these days of high power cableless stations on the five continents you can listen-in to the messages and hear what is being sent out by the lyons, paris and other french stations, by great britain, italy, germany and even far off russia and japan. a long wave set for receiving these stations must be able to tune to wave lengths up to 20,000 meters. differing from the way in which the regenerative action of the short wave sets described in the preceding chapter is secured and which depends on a tickler coil and the coupling action of the detector in this long wave set, [footnote: all of the short wave and intermediate wave receivers described, are connected up according to the wiring diagram used by the a. h. grebe company, richmond hill, long island, n. y.] this action is obtained by the use of a tickler coil in the plate circuit which is inductively coupled to the grid circuit and this feeds back the necessary amount of current. this is a very good way to connect up the circuits for the reason that: (1) the wiring is simplified, and (2) it gives a single variable adjustment for the entire range of wave lengths the receptor is intended to cover. the parts and how to connect them up.--the two chief features as far as the parts are concerned of this long wave length receiving set are (1) the _variable condensers_, and (2) the _tuning inductance coils_. the variable condenser used in series with the aerial wire system has 26 plates and is equal to a capacitance of _.0008 mfd._ which is the normal aerial capacitance. the condenser used in the secondary coil circuit has 14 plates and this is equal to a capacitance of _.0004 mfd_. there are a number of inductance coils and these are arranged so that they can be connected in or cut out and combinations are thus formed which give a high efficiency and yet allow them to be compactly mounted. the inductance coils of the aerial wire system and those of the secondary coil circuit are practically alike. for wave lengths up to 2,200 meters _bank litz-wound coils_ are used and these are wound up in 2, 4 and 6 banks in order to give the proper degree of coupling and inductance values. where wave lengths of more than 2,200 meters are to be received _coto-coils_ are used as these are the "last word" in inductance coil design, and are especially adapted for medium as well as long wave lengths. [footnote: can be had of the coto coil co., providence, r. i.] these various coils are cut in and out by means of two five-point switches which are provided with auxiliary levers and contactors for _dead-ending_ the right amount of the coils. in cutting in coils for increased wave lengths, that is from 10,000 to 20,000 meters, all of the coils of the aerial are connected in series as well as all of the coils of the secondary circuit. the connections for a long wave receptor are shown in the wiring diagram in fig. 59. [illustration: fig. 59.--wiring diagram showing long wave receptor with variocouplers and bank-wound inductance coils] chapter xiii heterodyne or beat long wave telegraph receiving set any of the receiving sets described in the foregoing chapters will respond to either: (1) a wireless telegraph transmitter that uses a spark gap and which sends out periodic electric waves, or to (2) a wireless telephone transmitter that uses an arc or a vacuum tube oscillator and which sends out continuous electric waves. to receive wireless _telegraph_ signals, however, from a transmitter that uses an arc or a vacuum tube oscillator and which sends out continuous waves, either the transmitter or the receptor must be so constructed that the continuous waves will be broken up into groups of audio frequency and this is done in several different ways. there are four different ways employed at the present time to break up the continuous waves of a wireless telegraph transmitter into groups and these are: (_a_) the _heterodyne_, or _beat_, method, in which waves of different lengths are impressed on the received waves and so produces beats; (_b_) the _tikker_, or _chopper_ method, in which the high frequency currents are rapidly broken up; (_c_) the variable condenser method, in which the movable plates are made to rapidly rotate; (_d_) the _tone wheel_, or _frequency transformer_, as it is often called, and which is really a modified form of and an improvement on the tikker. the heterodyne method will be described in this chapter. what the heterodyne or beat method is.--the word _heterodyne_ was coined from the greek words _heteros_ which means _other_, or _different_, and _dyne_ which means _power_; in other words it means when used in connection with a wireless receptor that another and different high frequency current is used besides the one that is received from the sending station. in music a _beat_ means a regularly recurrent swelling caused by the reinforcement of a sound and this is set up by the interference of sound waves which have slightly different periods of vibration as, for instance, when two tones take place that are not quite in tune with each other. this, then, is the principle of the heterodyne, or beat, receptor. in the heterodyne, or beat method, separate sustained oscillations, that are just about as strong as those of the incoming waves, are set up in the receiving circuits and their frequency is just a little higher or a little lower than those that are set up by the waves received from the distant transmitter. the result is that these oscillations of different frequencies interfere and reinforce each other when _beats_ are produced, the period of which is slow enough to be heard in the headphones, hence the incoming signals can be heard only when waves from the sending station are being received. a fuller explanation of how this is done will be found in chapter xv. the autodyne or self-heterodyne long-wave receiving set.--this is the simplest type of heterodyne receptor and it will receive periodic waves from spark telegraph transmitters or continuous waves from an arc or vacuum tube telegraph transmitter. in this type of receptor the detector tube itself is made to set up the _heterodyne oscillations_ which interfere with those that are produced by the incoming waves that are a little out of tune with it. with a long wave _autodyne_, or _self-heterodyne_ receptor, as this type is called, and a two-step audio-frequency amplifier you can clearly hear many of the cableless stations of europe and others that send out long waves. for receiving long wave stations, however, you must have a long aerial--a single wire 200 or more feet in length will do--and the higher it is the louder will be the signals. where it is not possible to put the aerial up a hundred feet or more above the ground, you can use a lower one and still get messages in _international morse_ fairly strong. the parts and connections of an autodyne, or self-heterodyne, receiving set.--for this long wave receiving set you will need: (1) one _variocoupler_ with the primary coil wound on the stator and the secondary coil and tickler coil wound on the rotor, or you can use three honeycomb or other good compact coils of the longest wave you want to receive, a table of which is given in chapter xii; (2) two _.001 mfd. variable condensers_; (3) one _.0005 mfd. variable condenser_; (4) one _.5 to 2 megohm grid leak resistance_; (5) one _vacuum tube detector_; (6) one _a battery_; (7) one _rheostat_; (8) one _b battery_; (9) one _potentiometer_; (10) one _.001 mfd. fixed condenser_ and (11) one pair of _headphones_. for the two-step amplifier you must, of course, have besides the above parts the amplifier tubes, variable condensers, batteries rheostats, potentiometers and fixed condensers as explained in chapter ix. the connections for the autodyne, or self-heterodyne, receiving set are shown in fig. 60. [illustration: fig. 60.--wiring diagram of long wave antodyne, or self-heterodyne receptor.] the separate heterodyne long wave receiving set.--this is a better long wave receptor than the self heterodyne set described above for receiving wireless telegraph signals sent out by a continuous long wave transmitter. the great advantage of using a separate vacuum tube to generate the heterodyne oscillations is that you can make the frequency of the oscillations just what you want it to be and hence you can make it a little higher or a little lower than the oscillations set up by the received waves. the parts and connections of a separate heterodyne long wave receiving set.--the parts required for this long wave receiving set are: (1) four honeycomb or other good _compact inductance_ coils of the longest wave length that you want to receive; (2) three _.001 mfd. variable condensers_; (3) one _.0005 mfd. variable condenser_; (4) one _1 megohm grid leak resistance_; (5) one _vacuum tube detector_; (6) one _a battery_; (7) two rheostats; (8) two _b batteries_, one of which is supplied with taps; (9) one _potentiometer_; (10) one _vacuum tube amplifier_, for setting up the heterodyne oscillations; (11) a pair of _headphones_ and (12) all of the parts for a _two-step amplifier_ as detailed in chapter ix, that is if you are going to use amplifiers. the connections are shown in fig. 61. [illustration: fig. 61.--wiring diagram of long wave separate heterodyne receiving set.] in using either of these heterodyne receivers be sure to carefully adjust the b battery by means of the potentiometer. [footnote: the amplifier tube in this case is used as a generator of oscillations.] chapter xiv headphones and loud speakers wireless headphones.--a telephone receiver for a wireless receiving set is made exactly on the same principle as an ordinary bell telephone receiver. the only difference between them is that the former is made flat and compact so that a pair of them can be fastened together with a band and worn on the head (when it is called a _headset_), while the latter is long and cylindrical so that it can be held to the ear. a further difference between them is that the wireless headphone is made as sensitive as possible so that it will respond to very feeble currents, while the ordinary telephone receiver is far from being sensitive and will respond only to comparatively large currents. how a bell telephone receiver is made.--an ordinary telephone receiver consists of three chief parts and these are: (1) a hard-rubber, or composition, shell and cap, (2) a permanent steel bar magnet on one end of which is wound a coil of fine insulated copper wire, and (3) a soft iron disk, or _diaphragm_, all of which are shown in the cross-section in fig. 62. the bar magnet is securely fixed inside of the handle so that the outside end comes to within about 1/32 of an inch of the diaphragm when this is laid on top of the shell and the cap is screwed on. [illustration: fig. 62.--cross-section of bell telephone receiver.] [illustration: original â© underwood and underwood. alexander graham bell, inventor of the telephone, now an ardent radio enthusiast.] the ends of the coil of wire are connected with two binding posts which are in the end of the shell, but are shown in the picture at the sides for the sake of clearness. this coil usually has a resistance of about 75 ohms and the meaning of the _ohmic resistance_ of a receiver and its bearing on the sensitiveness of it will be explained a little farther along. after the disk, or diaphragm, which is generally made of thin, soft sheet iron that has been tinned or japanned, [footnote: a disk of photographic tin-type plate is generally used.] is placed over the end of the magnet, the cap, which has a small opening in it, is screwed on and the receiver is ready to use. how a wireless headphone is made.--for wireless work a receiver of the watch-case type is used and nearly always two such receivers are connected with a headband. it consists of a permanent bar magnet bent so that it will fit into the shell of the receiver as shown at a in fig. 63. [illustration: fig. 63.--wireless headphone.] the ends of this magnet, which are called _poles_, are bent up, and hence this type is called a _bipolar_ receiver. the magnets are wound with fine insulated wire as before and the diaphragm is held securely in place over them by screwing on the cap. about resistance, turns of wire and sensitivity of headphones.--if you are a beginner in wireless you will hear those who are experienced speak of a telephone receiver as having a resistance of 75 ohms, 1,000 ohms, 2,000 or 3,000 ohms, as the case may be; from this you will gather that the higher the resistance of the wire on the magnets the more sensitive the receiver is. in a sense this is true, but it is not the resistance of the magnet coils that makes it sensitive, in fact, it cuts down the current, but it is the _number of turns_ of wire on them that determines its sensitiveness; it is easy to see that this is so, for the larger the number of turns the more often will the same current flow round the cores of the magnet and so magnetize them to a greater extent. but to wind a large number of turns of wire close enough to the cores to be effective the wire must be very small and so, of course, the higher the resistance will be. now the wire used for winding good receivers is usually no. 40, and this has a diameter of .0031 inch; consequently, when you know the ohmic resistance you get an idea of the number of turns of wire and from this you gather in a general way what the sensitivity of the receiver is. a receiver that is sensitive enough for wireless work should be wound to not less than 1,000 ohms (this means each ear phone), while those of a better grade are wound to as high as 3,000 ohms for each one. a high-grade headset is shown in fig. 64. each phone of a headset should be wound to the same resistance, and these are connected in series as shown. where two or more headsets are used with one wireless receiving set they must all be of the same resistance and connected in series, that is, the coils of one head set are connected with the coils of the next head set and so on to form a continuous circuit. [illustration: fig. 64.--wireless headphone.] the impedance of headphones.--when a current is flowing through a circuit the material of which the wire is made not only opposes its passage--this is called its _ohmic resistance_--but a _counter-electromotive force_ to the current is set up due to the inductive effects of the current on itself and this is called _impedance_. where a wire is wound in a coil the impedance of the circuit is increased and where an alternating current is used the impedance grows greater as the frequency gets higher. the impedance of the magnet coils of a receiver is so great for high frequency oscillations that the latter cannot pass through them; in other words, they are choked off. how the headphones work.--as you will see from the cross-sections in figs. 62 and 63 there is no connection, electrical or mechanical, between the diaphragm and the other parts of the receiver. now when either feeble oscillations, which have been rectified by a detector, or small currents from a b battery, flow through the magnet coils the permanent steel magnet is energized to a greater extent than when no current is flowing through it. this added magnetic energy makes the magnet attract the diaphragm more than it would do by its own force. if, on the other hand, the current is cut off the pull of the magnet is lessened and as its attraction for the diaphragm is decreased the latter springs back to its original position. when varying currents flow through the coils the diaphragm vibrates accordingly and sends out sound waves. about loud speakers.--the simplest acoustic instrument ever invented is the _megaphone_, which latter is a greek word meaning _great sound_. it is a very primitive device and our indians made it out of birch-bark before columbus discovered america. in its simplest form it consists of a cone-shaped horn and as the speaker talks into the small end the concentrated sound waves pass out of the large end in whatever direction it is held. now a loud speaker of whatever kind consists of two chief parts and these are: (1) a _telephone receiver_, and (2) a _megaphone_, or _horn_ as it is called. a loud speaker when connected with a wireless receiving set makes it possible for a room, or an auditorium, full of people, or an outdoor crowd, to hear what is being sent out by a distant station instead of being limited to a few persons listening-in with headphones. to use a loud speaker you should have a vacuum tube detector receiving set and this must be provided with a one-step amplifier at least. to get really good results you need a two-step amplifier and then energize the plate of the second vacuum tube amplifier with a 100 volt b battery; or if you have a three-step amplifier then use the high voltage on the plate of the third amplifier tube. amplifying tubes are made to stand a plate potential of 100 volts and this is the kind you must use. now it may seem curious, but when the current flows through the coils of the telephone receiver in one direction it gives better results than when it flows through in the other direction; to find out the way the current gives the best results try it out both ways and this you can do by simply reversing the connections. the simplest type of loud speaker.--this loud speaker, which is called, the arkay, [footnote: made by the riley-klotz mfg. co., newark, n. j.] will work on a oneor two-step amplifier. it consists of a brass horn with a curve in it and in the bottom there is an adapter, or frame, with a set screw in it so that you can fit in one of your headphones and this is all there is to it. the construction is rigid enough to prevent overtones, or distortion of speech or music. it is shown in fig. 65. [illustration: fig. 65.--arkay loud speaker.] another simple kind of loud speaker.--another loud speaker, see fig. 66, is known as the _amplitone_ [footnote: made by the american pattern, foundry and machine co., 82 church street, n. y. c.] and it likewise makes use of the headphones as the sound producer. this device has a cast metal horn which improves the quality of the sound, and all you have to do is to slip the headphones on the inlet tubes of the horn and it is ready for use. the two headphones not only give a longer volume of sound than where a single one is used but there is a certain blended quality which results from one phone smoothing out the imperfections of the other. [illustration: fig. 66.--amplitone loud speaker.] a third kind of simple loud speaker.--the operation of the _amplitron_, [footnote: made by the radio service co., 110 w. 40th street, n. y.] as this loud speaker is called, is slightly different from others used for the same purpose. the sounds set up by the headphone are conveyed to the apex of an inverted copper cone which is 7 inches long and 10 inches in diameter. here it is reflected by a parabolic mirror which greatly amplifies the sounds. the amplification takes place without distortion, the sounds remaining as clear and crisp as when projected by the transmitting station. by removing the cap from the receiver the shell is screwed into a receptacle on the end of the loud speaker and the instrument is ready for use. it is pictured in fig. 67. [illustration: fig. 67.--amplitron loud speaker.] a super loud speaker.--this loud speaker, which is known as the _magnavox telemegafone_, was the instrument used by lt. herbert e. metcalf, 3,000 feet in the air, and which startled the city of washington on april 2, 1919, by repeating president wilson's _victory loan message_ from an airplane in flight so that it was distinctly heard by 20,000 people below. this wonderful achievement was accomplished through the installation of the _magnavox_ and amplifiers in front of the treasury building. every word lt. metcalf spoke into his wireless telephone transmitter was caught and swelled in volume by the _telemegafones_ below and persons blocks away could hear the message plainly. two kinds of these loud speakers are made and these are: (1) a small loud speaker for the use of operators so that headphones need not be worn, and (2) a large loud speaker for auditorium and out-door audiences. [illustration: original â© underwood and underwood. world's largest loud speaker ever made. installed in lytle park, cincinnati, ohio, to permit president harding's address at point pleasant, ohio, during the grant centenary celebration to be heard within a radius of one square.] either kind may be used with a oneor two-step amplifier or with a cascade of half a dozen amplifiers, according to the degree of loudness desired. the _telemegafone_ itself is not an amplifier in the true sense inasmuch as it contains no elements which will locally increase the incoming current. it does, however, transform the variable electric currents of the wireless receiving set into sound vibrations in a most wonderful manner. a _telemegafone_ of either kind is formed of: (1) a telephone receiver of large proportions, (2) a step-down induction coil, and (3) a 6 volt storage battery that energizes a powerful electromagnet which works the diaphragm. an electromagnet is used instead of a permanent magnet and this is energized by a 6-volt storage battery as shown in the wiring diagram at a in fig. 68. one end of the core of this magnet is fixed to the iron case of the speaker and together these form the equivalent of a horseshoe magnet. a movable coil of wire is supported from the center of the diaphragm the edge of which is rigidly held between the case and the small end of the horn. this coil is placed over the upper end of the magnet and its terminals are connected to the secondary of the induction coil. now when the coil is energized by the current from the amplifiers it and the core act like a solenoid in that the coil tends to suck the core into it; but since the core is fixed and the coil is movable the core draws the coil down instead. the result is that with every variation of the current that flows through the coil it moves up and down and pulls and pushes the diaphragm down and up with it. the large amplitude of the vibrations of the latter set up powerful sound waves which can be heard several blocks away from the horn. in this way then are the faint incoming signals, speech and music which are received by the amplifying receiving set reproduced and magnified enormously. the _telemegafone_ is shown complete at b. [illustration: fig. 68.--magnavox loud speaker.] chapter xv operation of vacuum tube receptors from the foregoing chapters you have seen that the vacuum tube can be used either as a _detector_ or an _amplifier_ or as a _generator_ of electric oscillations, as in the case of the heterodyne receiving set. to understand how a vacuum tube acts as a detector and as an amplifier you must first know what _electrons_ are. the way in which the vacuum tube sets up sustained oscillations will be explained in chapter xviii in connection with the _operation of vacuum tube transmitters_. what electrons are.--science teaches us that masses of matter are made up of _molecules_, that each of these is made up of _atoms_, and each of these, in turn, is made up of a central core of positive particles of electricity surrounded by negative particles of electricity as shown in the schematic diagram, fig. 69. the little black circles inside the large circle represent _positive particles of electricity_ and the little white circles outside of the large circle represent _negative particles of electricity_, or _electrons_ as they are called. [illustration: fig. 69.--schematic diagram of an atom.] it is the number of positive particles of electricity an atom has that determines the kind of an element that is formed when enough atoms of the same kind are joined together to build it up. thus hydrogen, which is the lightest known element, has one positive particle for its nucleus, while uranium, the heaviest element now known, has 92 positive particles. now before leaving the atom please note that it is as much smaller than the diagram as the latter is smaller than our solar system. what is meant by ionization.--a hydrogen atom is not only lighter but it is smaller than the atom of any other element while an electron is more than a thousand times smaller than the atom of which it is a part. now as long as all of the electrons remain attached to the surface of an atom its positive and negative charges are equalized and it will, therefore, be neither positive nor negative, that is, it will be perfectly neutral. when, however, one or more of its electrons are separated from it, and there are several ways by which this can be done, the atom will show a positive charge and it is then called a _positive ion_. in other words a _positive ion_ is an atom that has lost some of its negative electrons while a _negative ion_ is one that has acquired some additional negative _electrons_. when a number of electrons are being constantly given by the atoms of an element, which let us suppose is a metal, and are being attracted to atoms of another element, which we will say is also a metal, a flow of electrons takes place between the two oppositely charged elements and form a current of negative electricity as represented by the arrows at a in fig. 70. [illustration: fig. 70.--action of two-electrode vacuum tube.] when a stream of electrons is flowing between two metal elements, as a filament and a plate in a vacuum tube detector, or an amplifier, they act as _carriers_ for more negative electrons and these are supplied by a battery as we shall presently explain. it has always been customary for us to think of a current of electricity as flowing from the positive pole of a battery to the negative pole of it and hence we have called this the _direction of the current_. since the electronic theory has been evolved it has been shown that the electrons, or negative charges of electricity, flow from the negative to the positive pole and that the ionized atoms, which are more positive than negative, flow in the opposite direction as shown at b. how electrons are separated from atoms.--the next question that arises is how to make a metal throw off some of the electrons of the atoms of which it is formed. there are several ways that this can be done but in any event each atom must be given a good, hard blow. a simple way to do this is to heat a metal to incandescence when the atoms will bombard each other with terrific force and many of the electrons will be knocked off and thrown out into the surrounding space. but all, or nearly all, of them will return to the atoms from whence they came unless a means of some kind is employed to attract them to the atoms of some other element. this can be done by giving the latter piece of metal a positive charge. if now these two pieces of metal are placed in a bulb from which the air has been exhausted and the first piece of metal is heated to brilliancy while the second piece of metal is kept positively electrified then a stream of electrons will flow between them. action of the two electrode vacuum tube.--now in a vacuum tube detector a wire filament, like that of an incandescent lamp, is connected with a battery and this forms the hot element from which the electrons are thrown off, and a metal plate with a terminal wire secured to it is connected to the positive or carbon tap of a dry battery; now connect the negative or zinc tap of this with one end of a telephone receiver and the other end of this with the terminals of the filament as shown at a in fig. 71. if now you heat the filament and hold the phone to your ear you can hear the current from the b battery flowing through the circuit. [illustration: (a) and (b) fig. 71.--how a two electrode tube acts as a relay or a detector.] [illustration: (c) fig. 71.--only the positive part of oscillations goes through the tube.] since the electrons are negative charges of electricity they are not only thrown off by the hot wire but they are attracted by the positive charged metal plate and when enough electrons pass, or flow, from the hot wire to the plate they form a conducting path and so complete the circuit which includes the filament, the plate and the b or plate battery, when the current can then flow through it. as the number of electrons that are thrown off by the filament is not great and the voltage of the plate is not high the current that flows between the filament and the plate is always quite small. how the two electrode tube acts as a detector.--as the action of a two electrode tube as a detector [footnote: the three electrode vacuum tube has entirely taken the place of the two electrode type.] is simpler than that of the three electrode vacuum tube we shall describe it first. the two electrode vacuum tube was first made by mr. edison when he was working on the incandescent lamp but that it would serve as a detector of electric waves was discovered by prof. fleming, of oxford university, london. as a matter of fact, it is not really a detector of electric waves, but it acts as: (1) a _rectifier_ of the oscillations that are set up in the receiving circuits, that is, it changes them into pulsating direct currents so that they will flow through and affect a telephone receiver, and (2) it acts as a _relay_ and the feeble received oscillating current controls the larger direct current from the b battery in very much the same way that a telegraph relay does. this latter relay action will be explained when we come to its operation as an amplifier. we have just learned that when the stream of electrons flow from the hot wire to the cold positive plate in the tube they form a conducting path through which the battery current can flow. now when the electric oscillations surge through the closed oscillation circuit, which includes the secondary of the tuning coil, the variable condenser, the filament and the plate as shown at b in fig. 71 the positive part of them passes through the tube easily while the negative part cannot get through, that is, the top, or positive, part of the wave-form remains intact while the lower, or negative, part is cut off as shown in the diagram at c. as the received oscillations are either broken up into wave trains of audio frequency by the telegraph transmitter or are modulated by a telephone transmitter they carry the larger impulses of the direct current from the b battery along with them and these flow through the headphones. this is the reason the vacuum tube amplifies as well as detects. how the three electrode tube acts as a detector.--the vacuum tube as a detector has been made very much more sensitive by the use of a third electrode shown in fig. 72. in this type of vacuum tube the third electrode, or _grid_, is placed between the filament and the plate and this controls the number of electrons flowing from the filament to the plate; in passing between these two electrodes they have to go through the holes formed by the grid wires. [illustration: (a) and (b) fig. 72.--how the positive and negative voltages of oscillations act on the electrons.] [illustration: (c) fig. 72.--how the three electrode tube acts as a detector and amplifier.] [illustration: (d) fig. 72.--how the oscillations control the flow of the battery current through the tube.] if now the grid is charged to a higher _negative_ voltage than the filament the electrons will be stopped by the latter, see a, though some of them will go through to the plate because they travel at a high rate of speed. the higher the negative charge on the grid the smaller will be the number of electrons that will reach the plate and, of course, the smaller will be the amount of current that will flow through the tube and the headphones from the b battery. on the other hand if the grid is charged _positively_, see b, then more electrons will strike the plate than when the grid is not used or when it is negatively charged. but when the three electrode tube is used as a detector the oscillations set up in the circuits change the grid alternately from negative to positive as shown at c and hence the voltage of the b battery current that is allowed to flow through the detector from the plate to the filament rises and falls in unison with the voltage of the oscillating currents. the way the positive and negative voltages of the oscillations which are set up by the incoming waves, energize the grid; how the oscillator tube clips off the negative parts of them, and, finally, how these carry the battery current through the tube are shown graphically by the curves at d. how the vacuum tube acts as an amplifier.--if you connect up the filament and the plate of a three electrode tube with the batteries and do not connect in the grid, you will find that the electrons which are thrown off by the filament will not get farther than the grid regardless of how high the voltage is that you apply to the plate. this is due to the fact that a large number of electrons which are thrown off by the filament strike the grid and give it a negative charge, and consequently, they cannot get any farther. since the electrons do not reach the plate the current from the b battery cannot flow between it and the filament. now with a properly designed amplifier tube a very small negative voltage on the grid will keep a very large positive voltage on the plate from sending a current through the tube, and oppositely, a very small positive voltage on the grid will let a very large plate current flow through the tube; this being true it follows that any small variation of the voltage from positive to negative on the grid and the other way about will vary a large current flowing from the plate to the filament. in the morse telegraph the relay permits the small current that is received from the distant sending station to energize a pair of magnets, and these draw an armature toward them and close a second circuit when a large current from a local battery is available for working the sounder. the amplifier tube is a variable relay in that the feeble currents set up by the incoming waves constantly and proportionately vary a large current that flows through the headphones. this then is the principle on which the amplifying tube works. the operation of a simple vacuum tube receiving set.--the way a simple vacuum tube detector receiving set works is like this: when the filament is heated to brilliancy it gives off electrons as previously described. now when the electric waves impinge on the aerial wire they set up oscillations in it and these surge through the primary coil of the loose coupled tuning coil, a diagram of which is shown at b in fig. 41. the energy of these oscillations sets up oscillations of the same frequency in the secondary coil and these high frequency currents whose voltage is first positive and then negative, surge in the closed circuit which includes the secondary coil and the variable condenser. at the same time the alternating positive and negative voltage of the oscillating currents is impressed on the grid; at each change from + to and back again it allows the electrons to strike the plate and then shuts them off; as the electrons form the conducting path between the filament and the plate the larger direct current from the b battery is permitted to flow through the detector tube and the headphones. operation of a regenerative vacuum tube receiving set.--by feeding back the pulsating direct current from the b battery through the tickler coil it sets up other and stronger oscillations in the secondary of the tuning coil when these act on the detector tube and increase its sensitiveness to a remarkable extent. the regenerative, or _feed back_, action of the receiving circuits used will be easily understood by referring back to b in fig. 47. when the waves set up oscillations in the primary of the tuning coil the energy of them produces like oscillations in the closed circuit which includes the secondary coil and the condenser; the alternating positive and negative voltages of these are impressed on the grid and these, as we have seen before, cause similar variations of the direct current from the b battery which acts on the plate and which flows between the latter and the filament. this varying direct current, however, is made to flow back through the third, or tickler coil of the tuning coil and sets up in the secondary coil and circuits other and larger oscillating currents and these augment the action of the oscillations produced by the incoming waves. these extra and larger currents which are the result of the feedback then act on the grid and cause still larger variations of the current in the plate voltage and hence of the current of the b battery that flows through the detector and the headphones. at the same time the tube keeps on responding to the feeble electric oscillations set up in the circuits by the incoming waves. this regenerative action of the battery current augments the original oscillations many times and hence produce sounds in the headphones that are many times greater than where the vacuum tube detector alone is used. operation of autodyne and heterodyne receiving sets.--on page 109 [chapter vii] we discussed and at a in fig. 36 is shown a picture of two tuning forks mounted on sounding boxes to illustrate the principle of electrical tuning. when a pair of these forks are made to vibrate exactly the same number of times per second there will be a condensation of the air between them and the sound waves that are sent out will be augmented. but if you adjust one of the forks so that it will vibrate 256 times a second and the other fork so that it will vibrate 260 times a second then there will be a phase difference between the two sets of waves and the latter will augment each other 4 times every second and you will hear these rising and falling sounds as _beats_. now electric oscillations set up in two circuits that are coupled together act in exactly the same way as sound waves produced by two tuning forks that are close to each other. since this is true if you tune one of the closed circuits so that the oscillations in it will have a frequency of a 1,000,000 and tune the other circuit so that the oscillations in it have a frequency of 1,001,000 a second then the oscillations will augment each other 1,000 times every second. as these rising and falling currents act on the pulsating currents from the b battery which flow through the detector tube and the headphones you will hear them as beats. a graphic representation of the oscillating currents set up by the incoming waves, those produced by the heterodyne oscillator and the beats they form is shown in fig. 73. to produce these beats a receptor can use: (1) a single vacuum tube for setting up oscillations of both frequencies when it is called an _autodyne_, or _self-heterodyne_ receptor, or (2) a separate vacuum tube for setting up the oscillations for the second circuit when it is called a _heterodyne_ receptor. [illustration: fig. 73.--how the heterodyne receptor works.] the autodyne, or self-heterodyne receiving set.--where only one vacuum tube is used for producing both frequencies you need only a regenerative, or feed-back receptor; then you can tune the aerial wire system to the incoming waves and tune the closed circuit of the secondary coil so that it will be out of step with the former by 1,000 oscillations per second, more or less, the exact number does not matter in the least. from this you will see that any regenerative set can be used for autodyne, or self-heterodyne, reception. the separate heterodyne receiving set.--the better way, however, is to use a separate vacuum tube for setting up the heterodyne oscillations. the latter then act on the oscillations that are produced by the incoming waves and which energize the grid of the detector tube. note that the vacuum tube used for producing the heterodyne oscillations is a _generator_ of electric oscillations; the latter are impressed on the detector circuits through the variable coupling, the secondary of which is in series with the aerial wire as shown in fig. 74. the way in which the tube acts as a generator of oscillations will be told in chapter xviii. [illustration: fig. 74.--separate heterodyne oscillator.] chapter xvi continuous wave telegraph transmitting sets with direct current in the first part of this book we learned about spark-gap telegraph sets and how the oscillations they set up are _damped_ and the waves they send out are _periodic_. in this and the next chapter we shall find out how vacuum tube telegraph transmitters are made and how they set up oscillations that are _sustained_ and radiate waves that are _continuous_. sending wireless telegraph messages by continuous waves has many features to recommend it as against sending them by periodic waves and among the most important of these are that the transmitter can be: (1) more sharply tuned, (2) it will send signals farther with the same amount of power, and (3) it is noiseless in operation. the disadvantageous features are that: (1) a battery current is not satisfactory, (2) its circuits are somewhat more complicated, and (3) the oscillator tubes burn out occasionally. there is, however, a growing tendency among amateurs to use continuous wave transmitters and they are certainly more up-to-date and interesting than spark gap sets. now there are two practical ways by which continuous waves can be set up for sending either telegraphic signals or telephonic speech and music and these are with: (a) an _oscillation arc lamp_, and (b) a _vacuum tube oscillator_. the oscillation arc was the earliest known way of setting up sustained oscillations, and it is now largely used for commercial high power, long distance work. but since the vacuum tube has been developed to a high degree of efficiency and is the scheme that is now in vogue for amateur stations we shall confine our efforts here to explaining the apparatus necessary and how to wire the various parts together to produce several sizes of vacuum tube telegraph transmitters. sources of current for telegraph transmitting sets.--differing from a spark-gap transmitter you cannot get any appreciable results with a low voltage battery current to start with. for a purely experimental vacuum tube telegraph transmitter you can use enough b batteries to operate it but the current strength of these drops so fact when they are in use, that they are not at all satisfactory for the work. you can, however, use 110 volt direct current from a lighting circuit as your initial source of power to energize the plate of the vacuum tube oscillator of your experimental transmitter. where you have a 110 volt _direct current_ lighting service in your home and you want a higher voltage for your plate, you will then have to use a motor-generator set and this costs money. if you have 110 volt _alternating current_ lighting service at hand your troubles are over so far as cost is concerned for you can step it up to any voltage you want with a power transformer. in this chapter will be shown how to use a direct current for your source of initial power and in the next chapter how to use an alternating current for the initial power. an experimental continuous wave telegraph transmitter.--you will remember that in chapter xv we learned how the heterodyne receiver works and that in the separate heterodyne receiving set the second vacuum tube is used solely to set up oscillations. now while this extra tube is used as a generator of oscillations these are, of course, very weak and hence a detector tube cannot be used to generate oscillations that are useful for other purposes than heterodyne receptors and measurements. there is a vacuum tube amplifier [footnote: this is the _radiation_ uv-201, made by the radio corporation of america, woolworth bldg., new york city.] made that will stand a plate potential of 100 volts, and this can be used as a generator of oscillations by energizing it with a 110 volt direct current from your lighting service. or in a pinch you can use five standard b batteries to develop the plate voltage, but these will soon run down. but whatever you do, never use a current from a lighting circuit on a tube of any kind that has a rated plate potential of less than 100 volts. the apparatus you need.--for this experimental continuous wave telegraph transmitter get the following pieces of apparatus: (1) one _single coil tuner with three clips_; (2) one _.002 mfd. fixed condenser_; (3) three _.001 mfd. condensers_; (4) one _adjustable grid leak_; (5) one _hot-wire ammeter_; (6) one _buzzer_; (7) one _dry cell_; (8) one _telegraph key_; (9) one _100 volt plate vacuum tube amplifier_; (10) one _6 volt storage battery_; (11) one _rheostat_; (12) one _oscillation choke coil_; (13) one _panel cut-out_ with a _single-throw, double-pole switch_, and a pair of _fuse sockets_ on it. the tuning coil.--you can either make this tuning coil or buy one. to make it get two disks of wood 3/4-inch thick and 5 inches in diameter and four strips of hard wood, or better, hard rubber or composition strips, such as _bakelite_, 1/2-inch thick, 1 inch wide and 5-3/4 inches long, and screw them to the disks as shown at a in fig. 75. now wrap on this form about 25 turns of no. 8 or 10, brown and sharpe gauge, bare copper wire with a space of 1/8-inch between each turn. get three of the smallest size terminal clips, see b, and clip them on to the different turns, when your tuning coil is ready for use. you can buy a coil of this kind for $4.00 or $5.00. the condensers.--for the aerial series condenser get one that has a capacitance of .002 mfd. and that will stand a potential of 3,000 volts. [footnote: the u c-1014 _faradon_ condenser made by the radio corporation of america will serve the purpose.] it is shown at c. the other three condensers, see d, are also of the fixed type and may have a capacitance of .001 mfd.; [footnote: list no. 266; fixed receiving condenser, sold by the manhattan electrical supply co.] the blocking condenser should preferably have a capacitance of 1/2 a mfd. in these condensers the leaves of the sheet metal are embedded in composition. the aerial condenser will cost you $2.00 and the others 75 cents each. [illustration: (a) fig. 75.--apparatus for experimental c. w. telegraph transmitter.] [illustration: fig. 75.--apparatus for experimental c. w. telegraph transmitter.] the aerial ammeter.--this instrument is also called a _hot-wire_ ammeter because the oscillating currents flowing through a piece of wire heat it according to their current strength and as the wire contracts and expands it moves a needle over a scale. the ammeter is connected in the aerial wire system, either in the aerial side or the ground side--the latter place is usually the most convenient. when you tune the transmitter so that the ammeter shows the largest amount of current surging in the aerial wire system you can consider that the oscillation circuits are in tune. a hot-wire ammeter reading to 2.5 amperes will serve your needs, it costs $6.00 and is shown at e in fig. 75. [illustration: united states naval high power station, arlington va. general view of power room. at the left can be seen the control switchboards, and overhead, the great 30 k.w. arc transmitter with accessories.] the buzzer and dry cell.--while a heterodyne, or beat, receptor can receive continuous wave telegraph signals an ordinary crystal or vacuum tube detector receiving set cannot receive them unless they are broken up into trains either at the sending station or at the receiving station, and it is considered the better practice to do this at the former rather than at the latter station. for this small transmitter you can use an ordinary buzzer as shown at f. a dry cell or two must be used to energize the buzzer. you can get one for about 75 cents. the telegraph key.--any kind of a telegraph key will serve to break up the trains of sustained oscillations into dots and dashes. the key shown at g is mounted on a composition base and is the cheapest key made, costing $1.50. the vacuum tube oscillator.--as explained before you can use any amplifying tube that is made for a plate potential of 100 volts. the current required for heating the filament is about 1 ampere at 6 volts. a porcelain socket should be used for this tube as it is the best insulating material for the purpose. an amplifier tube of this type is shown at h and costs $6.50. the storage battery.--a storage battery is used to heat the filament of the tube, just as it is with a detector tube, and it can be of any make or capacity as long as it will develop 6 volts. the cheapest 6 volt storage battery on the market has a 20 to 40 ampere-hour capacity and sells for $13.00. the battery rheostat.--as with the receptors a rheostat is needed to regulate the current that heats the filament. a rheostat of this kind is shown at i and is listed at $1.25. the oscillation choke coil.--this coil is connected in between the oscillation circuits and the source of current which feeds the oscillator tube to keep the oscillations set up by the latter from surging back into the service wires where they would break down the insulation. you can make an oscillation choke coil by winding say 100 turns of no. 28 brown and sharpe gauge double cotton covered magnet wire on a cardboard cylinder 2 inches in diameter and 2-1/2 inches long. transmitter connectors.--for connecting up the different pieces of apparatus of the transmitter it is a good scheme to use _copper braid_; this is made of braided copper wire in three sizes and sells for 7,15 and 20 cents a foot respectively. a piece of it is pictured at j. the panel cut-out.--this is used to connect the cord of the 110-volt lamp socket with the transmitter. it consists of a pair of _plug cutouts and a single-throw, double-pole_ switch mounted on a porcelain base as shown at k. in some localities it is necessary to place these in an iron box to conform to the requirements of the fire underwriters. connecting up the transmitting apparatus.--the way the various pieces of apparatus are connected together is shown in the wiring diagram. fig. 76. begin by connecting one post of the ammeter with the wire that leads to the aerial and the other post of it to one end of the tuning coil; connect clip _1_ to one terminal of the .002 mfd. 3,000 volt aerial condenser and the other post of this with the ground. [illustration: fig. 76--experimental c.w. telegraph transmitter] now connect the end of the tuning coil that leads to the ammeter with one end of the .001 mfd. grid condenser and the other end of this with the grid of the vacuum tube. connect the telegraph key, the buzzer and the dry cell in series and then shunt them around the grid condenser. next connect the plate of the tube with one end of the .001 mfd. blocking condenser and the other end of this with the clip _2_ on the tuning coil. connect one end of the filament with the + or positive electrode of the storage battery, the or negative electrode of this with one post of the rheostat and the other post of the latter with the other end of the filament; then connect clip _3_ with the + or positive side of the storage battery. this done connect one end of the choke coil to the conductor that leads to the plate and connect the other end of the choke coil to one of the taps of the switch on the panel cut-out. connect the + or positive electrode of the storage battery to the other switch tap and between the switch and the choke coil connect the protective condenser across the 110 volt feed wires. finally connect the lamp cord from the socket to the plug fuse taps when your experimental continuous wave telegraph transmitter is ready to use. a 100 mile c. w. telegraph transmitter.--here is a continuous wave telegraph transmitter that will cover distances up to 100 miles that you can rely on. it is built on exactly the same lines as the experimental transmitter just described, but instead of using a 100 volt plate amplifier as a makeshift generator of oscillations it employs a vacuum tube made especially for setting up oscillations and instead of having a low plate voltage it is energized with 350 volts. the apparatus you need.--for this transmitter you require: (1) one _oscillation transformer_; (2) one _hot-wire ammeter_; (3) one _aerial series condenser_; (4) one _grid leak resistance_; (5) one _chopper_; (6) one _key circuit choke coil_; (7) one _5 watt vacuum tube oscillator_; (8) one _6 volt storage battery_; (9) one _battery rheostat_; (10) one _battery voltmeter_; (11) one _blocking condenser_; (12) one _power circuit choke coil_, and (13) one _motor-generator_. the oscillation transformer.--the tuning coil, or _oscillation transformer_ as this one is called, is a conductively coupled tuner--that is, the primary and secondary coils form one continuous coil instead of two separate coils. this tuner is made up of 25 turns of thin copper strip, 3/8 inch wide and with its edges rounded, and this is secured to a wood base as shown at a in fig. 77. it is fitted with one fixed tap and three clips to each of which a length of copper braid is attached. it has a diameter of 6-1/4 inches, a height of 7-7/8 inches and a length of 9-3/8 inches, and it costs $11.00. [illustration: fig. 77.--apparatus of 100 mile c. w. telegraph transmitter.] the aerial condenser.--this condenser is made up of three fixed condensers of different capacitances, namely .0003, .0004 and .0005 mfd., and these are made to stand a potential of 7500 volts. the condenser is therefore adjustable and, as you will see from the picture b, it has one terminal wire at one end and three terminal wires at the other end so that one, two or three condensers can be used in series with the aerial. a condenser of this kind costs $5.40. the aerial ammeter.--this is the same kind of a hot-wire ammeter already described in connection with the experimental set, but it reads to 5 amperes. the grid and blocking condensers.--each of these is a fixed condenser of .002 mfd. capacitance and is rated to stand 3,000 volts. it is made like the aerial condenser but has only two terminals. it costs $2.00. the key circuit apparatus.--this consists of: (1) the _grid leak_; (2) the _chopper_; (3) the _choke coil_, and (4) the _key_. the grid leak is connected in the lead from the grid to the aerial to keep the voltage on the grid at the right potential. it has a resistance of 5000 ohms with a mid-tap at 2500 ohms as shown at c. it costs $2.00. the chopper is simply a rotary interrupter driven by a small motor. it comprises a wheel of insulating material in which 30 or more metal segments are set in an insulating disk as shown at d. a metal contact called a brush is fixed on either side of the wheel. it costs about $7.00 and the motor to drive it is extra. the choke coil is wound up of about 250 turns of no. 30 brown and sharpe gauge cotton covered magnet wire on a spool which has a diameter of 2 inches and a length of 3-1/4 inches. the 5 watt oscillator vacuum tube.--this tube is made like the amplifier tube described for use with the preceding experimental transmitter, but it is larger, has a more perfect vacuum, and will stand a plate potential of 350 volts while the plate current is .045 ampere. the filament takes a current of a little more than 2 amperes at 7.5 volts. a standard 4-tap base is used with it. the tube costs $8.00 and the porcelain base is $1.00 extra. it is shown at e. the storage battery and rheostat.--this must be a 5-cell battery so that it will develop 10 volts. a storage battery of any capacity can be used but the lowest priced one costs about $22.00. the rheostat for regulating the battery current is the same as that used in the preceding experimental transmitter. the filament voltmeter.--to get the best results it is necessary that the voltage of the current which heats the filament be kept at the same value all of the time. for this transmitter a direct current voltmeter reading from 0 to 15 volts is used. it is shown at f and costs $7.50. the oscillation choke coil.--this is made exactly like the one described in connection with the experimental transmitter. the motor-generator set.--where you have only a 110 or a 220 volt direct current available as a source of power you need a _motor-generator_ to change it to 350 volts, and this is an expensive piece of apparatus. it consists of a single armature core with a motor winding and a generator winding on it and each of these has its own commutator. where the low voltage current flows into one of the windings it drives its as a motor and this in turn generates the higher voltage current in the other winding. get a 100 watt 350 volt motor-generator; it is shown at f and costs about $75.00. the panel cut-out.--this switch and fuse block is the same as that used in the experimental set. the protective condenser.--this is a fixed condenser having a capacitance of 1 mfd. and will stand 750 volts. it costs $2.00. connecting up the transmitting apparatus.--from all that has gone before you have seen that each piece of apparatus is fitted with terminal, wires, taps or binding posts. to connect up the parts of this transmitter it is only necessary to make the connections as shown in the wiring diagram fig. 78. [illustration: fig. 78.--5 to 50 watt c. w. telegraph transmitter. (with single oscillation tube.)] a 200 mile c. w. telegraph transmitter.--to make a continuous wave telegraph transmitter that will cover distances up to 200 miles all you have to do is to use two 5 watt vacuum tubes in _parallel_, all of the rest of the apparatus being exactly the same. connecting the oscillator tubes up in parallel means that the two filaments are connected across the leads of the storage battery, the two grids on the same lead that goes to the aerial and the two plates on the same lead that goes to the positive pole of the generator. where two or more oscillator tubes are used only one storage battery is needed, but each filament must have its own rheostat. the wiring diagram fig. 79 shows how the two tubes are connected up in parallel. [illustration: fig. 79.--200 mile c.w. telegraph transmitter (with two tubes in parallel.)] a 500 mile c. w. telegraph transmitter.--for sending to distances of over 200 miles and up to 500 miles you can use either: (1) three or four 5 watt oscillator tubes in parallel as described above, or (2) one 50 watt oscillator tube. much of the apparatus for a 50 watt tube set is exactly the same as that used for the 5 watt sets. some of the parts, however, must be proportionately larger though the design all the way through remains the same. the apparatus and connections.--the aerial series condenser, the blocking condenser, the grid condenser, the telegraph key, the chopper, the choke coil in the key circuit, the filament voltmeter and the protective condenser in the power circuit are identical with those described for the 5 watt transmitting set. the 50 watt vacuum tube oscillator.--this is the size of tube generally used by amateurs for long distance continuous wave telegraphy. a single tube will develop 2 to 3 amperes in your aerial. the filament takes a 10 volt current and a plate potential of 1,000 volts is needed. one of these tubes is shown in fig. 80 and the cost is $30.00. a tube socket to fit it costs $2.50 extra. [illustration: fig. 80.--50 watt oscillator vacuum tube.] the aerial ammeter.--this should read to 5 amperes and the cost is $6.25. the grid leak resistance.--it has the same resistance, namely 5,000 ohms as the one used with the 5 watt tube transmitter, but it is a little larger. it is listed at $1.65. the oscillation choke coil.--the choke coil in the power circuit is made of about 260 turns of no. 30 b. & s. cotton covered magnet wire wound on a spool 2-1/4 inches in diameter and 3-1/4 inches long. the filament rheostat.--this is made to take care of a 10 volt current and it costs $10.00. the filament storage battery.--this must develop 12 volts and one having an output of 40 ampere-hours costs about $25.00. the protective condenser.--this condenser has a capacitance of 1 mfd. and costs $2.00. the motor-generator.--where you use one 50 watt oscillator tube you will need a motor-generator that develops a plate potential of 1000 volts and has an output of 200 watts. this machine will stand you about $100.00. the different pieces of apparatus for this set are connected up exactly the same as shown in the wiring diagram in fig. 78. a 1000 mile c. w. telegraph transmitter.--all of the parts of this transmitting set are the same as for the 500 mile transmitter just described except the motor generator and while this develops the same plate potential, i.e., 1,000 volts, it must have an output of 500 watts; it will cost you in the neighborhood of $175.00. for this long distance transmitter you use two 50 watt oscillator tubes in parallel and all of the parts are connected together exactly the same as for the 200 mile transmitter shown in the wiring diagram in fig. 79. chapter xvii continuous wave telegraph transmitting sets with alternating current within the last few years alternating current has largely taken the place of direct current for light, heat and power purposes in and around towns and cities and if you have alternating current service in your home you can install a long distance continuous wave telegraph transmitter with very little trouble and at a comparatively small expense. a 100 mile c. w. telegraph transmitting set.--the principal pieces of apparatus for this transmitter are the same as those used for the _100 mile continuous wave telegraph transmitting set_ described and pictured in the preceding chapter which used direct current, except that an _alternating current power transformer_ is employed instead of the more costly _motor-generator_. the apparatus required.--the various pieces of apparatus you will need for this transmitting set are: (1) one _hot-wire ammeter_ for the aerial as shown at e in fig. 75, but which reads to 5 amperes instead of to 2.5 amperes; (2) one _tuning coil_ as shown at a in fig. 77; (3) one aerial condenser as shown at b in fig. 77; (4) one _grid leak_ as shown at c in fig. 77; (5) one _telegraph key_ as shown at g in fig. 75; (6) one _grid condenser_, made like the aerial condenser but having only two terminals; (7) one _5 watt oscillator tube_ as shown at e in fig. 77; (8) one _.002 mfd. 3,000 volt by-pass condenser_, made like the aerial and grid condensers; (9) one pair of _choke coils_ for the high voltage secondary circuit; (10) one _milli-ammeter_; (11) one a. c. _power transformer_; (12) one _rheostat_ as shown at i in fig. 75, and (13) one _panel cut-out_ as shown at k in fig. 75. the choke coils.--each of these is made by winding about 100 turns of no. 28, brown and sharpe gauge, cotton covered magnet wire on a spool 2 inches in diameter and 2-1/2 inches long, when it will have an inductance of about 0.5 _millihenry_ [footnote: a millihenry is 1/1000th part of a henry.] at 1,000 cycles. the milli-ammeter.--this is an alternating current ammeter and reads from 0 to 250 _milliamperes_; [footnote: a _milliampere_ is the 1/1000th part of an ampere.] and is used for measuring the secondary current that energizes the plate of the oscillator tube. it looks like the aerial ammeter and costs about $7.50. the a. c. power transformer.--differing from the motor generator set the power transformer has no moving parts. for this transmitting set you need a transformer that has an input of 325 volts. it is made to work on a 50 to 60 cycle current at 102.5 to 115 volts, which is the range of voltage of the ordinary alternating lighting current. this adjustment for voltage is made by means of taps brought out from the primary coil to a rotary switch. the high voltage secondary coil which energizes the plate has an output of 175 watts and develops a potential of from 350 to 1,100 volts. the low voltage secondary coil which heats the filament has an output of 175 watts and develops 7.5 volts. this transformer, which is shown in fig. 81, is large enough to take care of from one to four 5 watt oscillator tubes. it weighs about 15 pounds and sells for $25.00. [illustration: fig. 81.--alternation current power transformer. (for c. w. telegraphy and wireless telephony.)] [illustration: the transformer and tuner of the world's largest radio station. owned by the radio corporation of america at rocky point near port jefferson l.i.] connecting up the apparatus.--the wiring diagram fig. 82 shows clearly how all of the connections are made. it will be observed that a storage battery is not needed as the secondary coil of the transformer supplies the current to heat the filament of the oscillator. the filament voltmeter is connected across the filament secondary coil terminals, while the plate milli-ammeter is connected to the mid-taps of the plate secondary coil and the filament secondary coil. [illustration: fig. 82. wiring diagram for 200 to 500 mile c.w. telegraph transmitting set. (with alternating current)] a 200 to 500 mile c. w. telegraph transmitting set.--distances of from 200 to 500 miles can be successfully covered with a telegraph transmitter using two, three or four 5 watt oscillator tubes in parallel. the apparatus needed is identical with that used for the 100 mile transmitter just described. the tubes are connected in parallel as shown in the wiring diagram in fig. 83. [illustration: fig. 83.--wiring diagram for 500 to 1000 mile c. w. telegraph transmitter.] a 500 to 1,000 mile c. w. telegraph transmitting set.--with the apparatus described for the above set and a single 50 watt oscillator tube a distance of upwards of 500 miles can be covered, while with two 50 watt oscillator tubes in parallel you can cover a distance of 1,000 miles without difficulty, and nearly 2,000 miles have been covered with this set. the apparatus required.--all of the apparatus for this c. w. telegraph transmitting set is the same as that described for the 100 and 200 mile sets but you will need: (1) one or two _50 watt oscillator tubes with sockets;_ (2) one _key condenser_ that has a capacitance of 1 mfd., and a rated potential of 1,750 volts; (3) one _0 to 500 milli-ammeter_; (4) one _aerial ammeter_ reading to 5 amperes, and (5) an _a. c. power transformer_ for one or two 50 watt tubes. [illustration: broadcasting government reports by wireless from washington. this shows mr. gale at work with his set in the post office department.] the alternating current power transformer.--this power transformer is made exactly like the one described in connection with the preceding 100 mile transmitter and pictured in fig. 81, but it is considerably larger. like the smaller one, however, it is made to work with a 50 to 60 cycle current at 102.5 to 115 volts and, hence, can be used with any a. c. lighting current. it has an input of 750 volts and the high voltage secondary coil which energizes the plate has an output of 450 watts and develops 1,500 to 3,000 volts. the low voltage secondary coil which heats the filament develops 10.5 volts. this transformer will supply current for one or two 50-watt oscillator tubes and it costs about $40.00. connecting up the apparatus.--where a single oscillator tube is used the parts are connected as shown in fig. 82, and where two tubes are connected in parallel the various pieces of apparatus are wired together as shown in fig. 83. the only difference between the 5 watt tube transmitter and the 50 watt tube transmitter is in the size of the apparatus with one exception; where one or two 50 watt tubes are used a second condenser of large capacitance (1 mfd.) is placed in the grid circuit and the telegraph key is shunted around it as shown in the diagram fig. 83. chapter xviii wireless telephone transmitting sets with direct and alternating currents in time past the most difficult of all electrical apparatus for the amateur to make, install and work was the wireless telephone. this was because it required a _direct current_ of not less than 500 volts to set up the sustained oscillations and all ordinary direct current for lighting purposes is usually generated at a potential of 110 volts. now as you know it is easy to _step-up_ a 110 volt alternating current to any voltage you wish with a power transformer but until within comparatively recent years an alternating current could not be used for the production of sustained oscillations for the very good reason that the state of the art had not advanced that far. in the new order of things these difficulties have all but vanished and while a wireless telephone transmitter still requires a high voltage direct current to operate it this is easily obtained from 110 volt source of alternating current by means of _vacuum tube rectifiers_. the pulsating direct currents are then passed through a filtering reactance coil, called a _reactor_, and one or more condensers, and these smooth them out until they approximate a continuous direct current. the latter is then made to flow through a vacuum tube oscillator when it is converted into high frequency oscillations and these are _varied_, or _modulated_, as it is called, by a _microphone transmitter_ such as is used for ordinary wire telephony. the energy of these sustained modulated oscillations is then radiated into space from the aerial in the form of electric waves. the distance that can be covered with a wireless telephone transmitter is about one-fourth as great as that of a wireless telegraph transmitter having the same input of initial current, but it is long enough to satisfy the most enthusiastic amateur. for instance with a wireless telephone transmitter where an amplifier tube is used to set up the oscillations and which is made for a plate potential of 100 volts, distances up to 10 or 15 miles can be covered. with a single 5 watt oscillator tube energized by a direct current of 350 volts from either a motor-generator or from a power transformer (after it has been rectified and smoothed out) speech and music can be transmitted to upwards of 25 miles. where two 5 watt tubes connected in parallel are used wireless telephone messages can be transmitted to distances of 40 or 50 miles. further, a single 50 watt oscillator tube will send to distances of 50 to 100 miles while two of these tubes in parallel will send from 100 to 200 miles. finally, where four or five oscillator tubes are connected in parallel proportionately greater distances can be covered. a short distance wireless telephone transmitting set-with 110 volt direct lighting current.--for this very simple, short distance wireless telephone transmitting set you need the same apparatus as that described and pictured in the beginning of chapter xvi for a _short distance c. w. telegraph transmitter_, except that you use a _microphone transmitter_ instead of a _telegraph key_. if you have a 110 volt direct lighting current in your home you can put up this short distance set for very little money and it will be well worth your while to do so. the apparatus you need.--for this set you require: (1) one _tuning coil_ as shown at a and b in fig. 75; (2) one _aerial ammeter_ as shown at c in fig. 75; (3) one _aerial condenser_ as shown at c in fig. 75; (4) one _grid, blocking and protective condenser_ as shown at d in fig. 75; (5) one _grid leak_ as shown at c in fig. 77; (6) one _vacuum tube amplifier_ which is used as an _oscillator_; (7) one _6 volt storage battery_; (8) one _rheostat_ as shown at i in fig. 75; (9) one _oscillation choke coil_; (10) one _panel cut-out_ as shown at k in fig. 75 and an ordinary _microphone transmitter_. the microphone transmitter.--the best kind of a microphone to use with this and other telephone transmitting sets is a _western electric no. 284-w_. [footnote: made by the western electric company, chicago, ill.] this is known as a solid back transmitter and is the standard commercial type used on all long distance bell telephone lines. it articulates sharply and distinctly and there are no current variations to distort the wave form of the voice and it will not buzz or sizzle. it is shown in fig. 84 and costs $2.00. any other good microphone transmitter can be used if desired. [illustration: fig. 84.--standard microphone transmitter.] connecting up the apparatus.--begin by connecting the leading-in wire with one of the terminals of the microphone transmitter, as shown in the wiring diagram fig. 85, and the other terminal of this to one end of the tuning coil. now connect _clip 1_ of the tuning coil to one of the posts of the hot-wire ammeter, the other post of this to one end of aerial condenser and, finally, the other end of the latter with the water pipe or other ground. the microphone can be connected in the ground wire and the ammeter in the aerial wire and the results will be practically the same. [illustration: fig. 85.--wiring diagram of short distance wireless telephone set. (microphone in aerial wire.)] next connect one end of the grid condenser to the post of the tuning coil that makes connection with the microphone and the other end to the grid of the tube, and then shunt the grid leak around the condenser. connect the + or _positive_ electrode of the storage battery with one terminal of the filament of the vacuum tube, the other terminal of the filament with one post of the rheostat and the other post of this with the or _negative_ electrode of the battery. this done, connect _clip 2_ of the tuning coil to the + or _positive_ electrode of the battery and bring a lead from it to one of the switch taps of the panel cut-out. now connect _clip 3_ of the tuning coil with one end of the blocking condenser, the other end of this with one terminal of the choke coil and the other terminal of the latter with the other switch tap of the cut-out. connect the protective condenser across the direct current feed wires between the panel cut-out and the choke coil. finally connect the ends of a lamp cord to the fuse socket taps of the cut-out, and connect the other ends to a lamp plug and screw it into the lamp socket of the feed wires. screw in a pair of 5 ampere _fuse plugs_, close the switch and you are ready to tune the transmitter and talk to your friends. a 25 to 50 mile wireless telephone transmitter--with direct current motor generator.--where you have to start with 110 or 220 volt direct current and you want to transmit to a distance of 25 miles or more you will have to install a _motor-generator_. to make this transmitter you will need exactly the same apparatus as that described and pictured for the _100 mile c. w. telegraph transmitting set_ in chapter xvi, except that you must substitute a _microphone transmitter_ and a _telephone induction coil_, or a _microphone transformer_, or still better, a _magnetic modulator_, for the telegraph key and chopper. the apparatus you need.--to reiterate; the pieces of apparatus you need are: (1) one _aerial ammeter_ as shown at e in fig. 75; (2) one _tuning coil_ as shown at a in fig. 77; (3) one _aerial condenser_ as shown at b in fig. 77; (4) one _grid leak_ as shown at c in fig. 77; (5) one _grid, blocking_ and _protective condenser_; (6) one _5 watt oscillator tube_ as shown at e in fig. 77; (7) one _rheostat_ as shown at i in fig. 75; (8) one _10 volt (5 cell) storage battery_; (9) one _choke coil_; (10) one _panel cut-out_ as shown at k in fig. 75, and (11) a _motor-generator_ having an input of 110 or 220 volts and an output of 350 volts. in addition to the above apparatus you will need: (12) a _microphone transmitter_ as shown in fig. 84; (13) a battery of four dry cells or a 6 volt storage battery, and either (14) a _telephone induction coil_ as shown in fig. 86; (15) a _microphone transformer_ as shown in fig. 87; or a _magnetic modulator_ as shown in fig. 88. all of these parts have been described, as said above, in chapter xvi, except the microphone modulators. [illustration: fig. 86.--telephone induction coil. (used with microphone transmitter.)] [illustration: fig. 87.--microphone transformer. (used with microphone transmitter.)] [illustration: fig. 88.--magnetic modulator. (used with microphone transmitter.)] the telephone induction coil.--this is a little induction coil that transforms the 6-volt battery current after it has flowed through and been modulated by the microphone transmitter into alternating currents that have a potential of 1,000 volts of more. it consists of a primary coil of _no. 20 b. and s._ gauge cotton covered magnet wire wound on a core of soft iron wires while around the primary coil is wound a secondary coil of _no. 30_ magnet wire. get a _standard telephone induction coil_ that has a resistance of 500 or 750 ohms and this will cost you a couple of dollars. the microphone transformer.--this device is built on exactly the same principle as the telephone induction coil just described but it is more effective because it is designed especially for modulating the oscillations set up by vacuum tube transmitters. as with the telephone induction coil, the microphone transmitter is connected in series with the primary coil and a 6 volt dry or storage battery. in the better makes of microphone transformer, there is a third winding, called a _side tone_ coil, to which a headphone can be connected so that the operator who is speaking into the microphone can listen-in and so learn if his transmitter is working up to standard. the magnetic modulator.--this is a small closed iron core transformer of peculiar design and having a primary and a secondary coil wound on it. this device is used to control the variations of the oscillating currents that are set up by the oscillator tube. it is made in three sizes and for the transmitter here described you want the smallest size, which has an output of 1/2 to 1-1/2 amperes. it costs about $10.00. how the apparatus is connected up.--the different pieces of apparatus are connected together in exactly the same way as the _100 mile c. w. telegraph set_ in chapter xvi except that the microphone transmitter and microphone modulator (whichever kind you use) is substituted for the telegraph key and chopper. now there are three different ways that the microphone and its modulator can be connected in circuit. two of the best ways are shown at a and b in fig. 89. in the first way the secondary terminals of the modulator are shunted around the grid leak in the grid circuit as at a, and in the second the secondary terminals are connected in the aerial as at b. where an induction coil or a microphone transformer is used they are shunted around a condenser, but this is not necessary with the magnetic modulator. where a second tube is used as in fig. 90 then the microphone and its modulator are connected with the grid circuit and _clip 3_ of the tuning coil. [illustration: fig. 89.--wiring diagram of 25 to 50 mile wireless telephone. (microphone modulator shunted around grid-leak condenser.)] [illustration: (b) fig. 89.--microphone modulator connected in aerial wire.] [illustration: fig. 90.--wiring diagram of 50 to 100 mile wireless telephone transmitting set.] a 50 to 100 mile wireless telephone transmitter--with direct current motor generator.--as the initial source of current available is taken to be a 110 or 220 volt direct current a motor-generator having an output of 350 volts must be used as before. the only difference between this transmitter and the preceding one is that: (1) two 5 watt tubes are used, the first serving as an _oscillator_ and the second as a _modulator_; (2) an _oscillation choke coil_ is used in the plate circuit; (3) a _reactance coil_ or _reactor_, is used in the plate circuit; and (4) a _reactor_ is used in the grid circuit. the oscillation choke coil.--you can make this choke coil by winding about 275 turns of _no. 28 b. and s. gauge_ cotton covered magnet wire on a spool 2 inches in diameter and 4 inches long. give it a good coat of shellac varnish and let it dry thoroughly. the plate and grid circuit reactance coils.--where a single tube is used as an oscillator and a second tube is employed as a modulator, a _reactor_, which is a coil of wire wound on an iron core, is used in the plate circuit to keep the high voltage direct current of the motor-generator the same at all times. likewise the grid circuit reactor is used to keep the voltage of the grid at a constant value. these reactors are made alike and a picture of one of them is shown in fig. 91 and each one will cost you $5.75. [illustration: fig. 91.--plate and grid circuit reactor.] connecting up the apparatus.--all of the different pieces of apparatus are connected up as shown in fig. 89. one of the ends of the secondary of the induction coil, or the microphone transformer, or the magnetic modulator is connected to the grid circuit and the other end to _clip 3_ of the tuning coil. a 100 to 200 mile wireless telephone transmitter--with direct current motor generator.--by using the same connections shown in the wiring diagrams in fig. 89 and a single 50 watt oscillator tube your transmitter will then have a range of 100 miles or so, while if you connect up the apparatus as shown in fig. 90 and use two 50 watt tubes you can work up to 200 miles. much of the apparatus for a 50 watt oscillator set where either one or two tubes are used is of the same size and design as that just described for the 5 watt oscillator sets, but, as in the c. w. telegraph sets, some of the parts must be proportionately larger. the required parts are (1) the _50 watt tube_; (2) the _grid leak resistance_; (3) the _filament rheostat_; (4) the _filament storage battery_; and (5) the _magnetic modulator_. all of these parts, except the latter, are described in detail under the heading of a _500 mile c. w. telegraph transmitting set_ in chapter xvi, and are also pictured in that chapter. it is not advisable to use an induction coil for the modulator for this set, but use, instead, either a telephone transformer, or better, a magnetic modulator of the second size which has an output of from 1-1/2 to 3-1/2 amperes. the magnetic modulator is described and pictured in this chapter. a 50 to 100 mile wireless telephone transmitting set--with 110 volt alternating current.--if you have a 110 volt [footnote: alternating current for lighting purposes ranges from 102.5 volts to 115 volts, so we take the median and call it 110 volts.] alternating current available you can use it for the initial source of energy for your wireless telephone transmitter. the chief difference between a wireless telephone transmitting set that uses an alternating current and one that uses a direct current is that: (1) a _power transformer_ is used for stepping up the voltage instead of a motor-generator, and (2) a _vacuum tube rectifier_ must be used to convert the alternating current into direct current. the apparatus you need.--for this telephone transmitting set you need: (1) one _aerial ammeter_; (2) one _tuning coil_; (3) one _telephone modulator_; (4) one _aerial series condenser_; (5) one _4 cell dry battery_ or a 6 volt storage battery; (6) one _microphone transmitter_; (7) one _battery switch_; (8) one _grid condenser_; (9) one _grid leak_; (10) two _5 watt oscillator tubes with sockets_; (11) one _blocking condenser_; (12) one _oscillation choke coil_; (13) two _filter condensers_; (14) one _filter reactance coil_; (15) an _alternating current power transformer_, and (16) two _20 watt rectifier vacuum tubes_. all of the above pieces of apparatus are the same as those described for the _100 mile c. w. telegraph transmitter_ in chapter xvii, except: (a) the _microphone modulator_; (b) the _microphone transmitter_ and (c) the _dry_ or _storage battery_, all of which are described in this chapter; and the new parts which are: (d) the _rectifier vacuum tubes_; (e) the _filter condensers_; and (f) the _filter reactance coil_; further and finally, the power transformer has a _third_ secondary coil on it and it is this that feeds the alternating current to the rectifier tubes, which in turn converts it into a pulsating direct current. the vacuum tube rectifier.--this rectifier has two electrodes, that is, it has a filament and a plate like the original vacuum tube detector, the smallest size rectifier tube requires a plate potential of 550 volts which is developed by one of the secondary coils of the power transformer. the filament terminal takes a current of 7.5 volts and this is supplied by another secondary coil of the transformer. this rectifier tube delivers a direct current of 20 watts at 350 volts. it looks exactly like the 5 watt oscillator tube which is pictured at e in fig. 77. the price is $7.50. the filter condensers.--these condensers are used in connection with the reactance coil to smooth out the pulsating direct current after it has passed through the rectifier tube. they have a capacitance of 1 mfd. and will stand 750 volts. these condensers cost about $2.00 each. the filter reactance coil.--this reactor which is shown in fig. 92, has about the same appearance as the power transformer but it is somewhat smaller. it consists of a coil of wire wound on a soft iron core and has a large inductance, hence the capacitance of the filter condensers are proportionately smaller than where a small inductance is used which has been the general practice. the size you require for this set has an output of 160 milliamperes and it will supply current for one to four 5 watt oscillator tubes. this size of reactor costs $11.50. [illustration: fig. 92.--filter reactor for smoothing out rectified currents.] connecting up the apparatus.--the wiring diagram in fig. 93 shows how the various pieces of apparatus for this telephone transmitter are connected up. you will observe: (1) that the terminals of the power transformer secondary coil which develops 10 volts are connected to the filaments of the oscillator tubes; (2) that the terminals of the other secondary coil which develops 10 volts are connected with the filaments of the rectifier tubes; (3) that the terminals of the third secondary coil which develops 550 volts are connected with the plates of the rectifier tubes; (4) that the pair of filter condensers are connected in parallel and these are connected to the mid-taps of the two filament secondary coils; (5) that the reactance coil and the third filter condenser are connected together in series and these are shunted across the filter condensers, which are in parallel; and, finally, (6) a lead connects the mid-tap of the 550-volt secondary coil of the power transformer with the connection between the reactor and the third filter condenser. [illustration: fig 93.--100 to 200 mile wireless telephone transmitter.] a 100 to 200 mile wireless telephone transmitting set--with 110 volt alternating current.--this telephone transmitter is built up of exactly the same pieces of apparatus and connected up in precisely the same way as the one just described and shown in fig. 93. apparatus required.--the only differences between this and the preceding transmitter are: (1) the _magnetic modulator_, if you use one, should have an output of 3-1/2 to 5 amperes; (2) you will need two _50 watt oscillator tubes with sockets_; (3) two _150 watt rectifier tubes with sockets_; (4) an _aerial ammeter_ that reads to _5 amperes_; (5) three _1 mfd. filter condensers_ in parallel; (6) _two filter condensers of 1 mfd. capacitance_ that will stand _1750 volts_; and (6) a _300 milliampere filter reactor_. the apparatus is wired up as shown in fig. 93. chapter xix the operation of vacuum tube transmitters the three foregoing chapters explained in detail the design and construction of (1) two kinds of c. w. telegraph transmitters, and (2) two kinds of wireless telephone transmitters, the difference between them being whether they used (a) a direct current, or (b) an alternating current as the initial source of energy. of course there are other differences between those of like types as, for instance, the apparatus and connections used (_a_) in the key circuits, and (_b_) in the microphone circuits. but in all of the transmitters described of whatever type or kind the same fundamental device is used for setting up sustained oscillations and this is the _vacuum tube_. the operation of the vacuum tube oscillator.--the operation of the vacuum tube in producing sustained oscillations depends on (1) the action of the tube as a valve in setting up the oscillations in the first place and (2) the action of the grid in amplifying the oscillations thus set up, both of which we explained in chapter xiv. in that chapter it was also pointed out that a very small change in the grid potential causes a corresponding and larger change in the amount of current flowing from the plate to the filament; and that if a vacuum tube is used for the production of oscillations the initial source of current must have a high voltage, in fact the higher the plate voltage the more powerful will be the oscillations. to understand how oscillations are set up by a vacuum tube when a direct current is applied to it, take a look at the simple circuits shown in fig. 94. now when you close the switch the voltage from the battery charges the condenser and keeps it charged until you open it again; the instant you do this the condenser discharges through the circuit which includes it and the inductance coil, and the discharge of a condenser is always oscillatory. [illustration: (a) and (b) fig. 94. operation of vacuum tube oscillators.] where an oscillator tube is included in the circuits as shown at a and b in fig. 94, the grid takes the place of the switch and any slight change in the voltage of either the grid or the plate is sufficient to start a train of oscillations going. as these oscillations surge through the tube the positive parts of them flow from the plate to the filament and these carry more of the direct current with them. to make a tube set up powerful oscillations then, it is only necessary that an oscillation circuit shall be provided which will feed part of the oscillations set up by the tube back to the grid circuit and when this is done the oscillations will keep on being amplified until the tube reaches the limit of its output. [illustration: (c) fig. 94.--how a direct current sets up oscillations.] the operation of c. w. telegraph transmitters with direct current--short distance c. w. transmitter.--in the transmitter shown in the wiring diagram in fig. 76 the positive part of the 110 volt direct current is carried down from the lamp socket through one side of the panel cut-out, thence through the choke coil and to the plate of the oscillator tube, when the latter is charged to the positive sign. the negative part of the 110 volt direct current then flows down the other wire to the filament so that there is a difference of potential between the plate and the filament of 110 volts. now when the 6-volt battery current is switched on the filament is heated to brilliancy, and the electrons thrown off by it form a conducting path between it and the plate; the 110 volt current then flows from the latter to the former. now follow the wiring from the plate over to the blocking condenser, thence to _clip 3_ of the tuning coil, through the turns of the latter to _clip 2_ and over to the filament and, when the latter is heated, you have a _closed oscillation circuit_. the oscillations surging in the latter set up other and like oscillations in the tuning coil between the end of which is connected with the grid, the aerial and the _clip 2_, and these surge through the circuit formed by this portion of the coil, the grid condenser and the filament; this is the amplifying circuit and it corresponds to the regenerative circuit of a receiving set. when oscillations are set up in it the grid is alternately charged to the positive and negative signs. these reversals of voltage set up stronger and ever stronger oscillations in the plate circuit as before explained. not only do the oscillations surge in the closed circuits but they run to and fro on the aerial wire when their energy is radiated in the form of electric waves. the oscillations are varied by means of the telegraph key which is placed in the grid circuit as shown in fig. 76. the operation of the key circuit.--the effect in a c. w. transmitter when a telegraph key is connected in series with a buzzer and a battery and these are shunted around the condenser in the grid circuit, is to rapidly change the wave form of the sustained oscillations, and hence, the length of the waves that are sent out. while no sound can be heard in the headphones at the receiving station so long as the points of the key are not in contact, when they are in contact the oscillations are modulated and sounds are heard in the headphones that correspond to the frequency of the buzzer in the key circuit. the operation of c. w. telegraph transmitters with direct current.--the chief differences between the long distance sets which use a direct current, i.e., those described in chapter xvi, and the short distance transmitting sets are that the former use: (1) a motor-generator set for changing the low voltage direct current into high voltage direct current, and (2) a chopper in the key circuit. the way the motor-generator changes the lowinto high-voltage current has been explained in chapter xvi. the chopper interrupts the oscillations surging through the grid circuit at a frequency that the ear can hear, that is to say, about 800 to 1,000 times per second. when the key is open, of course, the sustained oscillations set up in the circuits will send out continuous waves but when the key is closed these oscillations are broken up and then they send out discontinuous waves. if a heterodyne receiving set, see chapter xv, is being used at the other end you can dispense with the chopper and the key circuit needed is very much simplified. the operation of key circuits of the latter kind will be described presently. the operation of c. w. telegraph transmitters with alternating current--with a single oscillator tube.--where an oscillator tube telegraph transmitter is operated by a 110 volt alternating current as the initial source of energy, a buzzer, chopper or other interruptor is not needed in the key circuit. this is because oscillations are set up only when the plate is energized with the positive part of the alternating current and this produces an intermittent musical tone in the headphones. hence this kind of a sending set is called a _tone transmitter_. since oscillations are set up only by the positive part or voltage of an alternating current it is clear that, as a matter of fact, this kind of a transmitter does not send out continuous waves and therefore it is not a c. w. transmitter. this is graphically shown by the curve of the wave form of the alternating current and the oscillations that are set up by the positive part of it in fig. 95. whenever the positive half of the alternating current energizes the plate then oscillations are set up by the tube and, conversely, when the negative half of the current charges the plate no oscillations are produced. [illustration: fig. 95.--positive voltage only sets up oscillations.] you will also observe that the oscillations set up by the positive part of the current are not of constant amplitude but start at zero the instant the positive part begins to energize the plate and they keep on increasing in amplitude as the current rises in voltage until the latter reaches its maximum; then as it gradually drops again to zero the oscillations decrease proportionately in amplitude with it. heating the filament with alternating current.--where an alternating current power transformer is used to develop the necessary plate voltage a second secondary coil is generally provided for heating the filament of the oscillation tube. this is better than a direct current for it adds to the life of the filament. when you use an alternating current to heat the filament keep it at the same voltage rather than at the same amperage (current strength). to do this you need only to use a voltmeter across the filament terminals instead of an ammeter in series with it; then regulate the voltage of the filament with a rheostat. the operation of c. w. telegraph transmitters with alternating current--with two oscillator tubes.--by using two oscillator tubes and connecting them up with the power transformer and oscillating circuits as shown in the wiring diagram in fig. 83 the plates are positively energized alternately with every reversal of the current and, consequently, there is no time period between the ending of the oscillations set up by one tube and the beginning of the oscillations set up by the other tube. in other words these oscillations are sustained but as in the case of those of a single tube, their amplitude rises and falls. this kind of a set is called a _full wave rectification transmitter_. the waves radiated by this transmitter can be received by either a crystal detector or a plain vacuum-tube detector but the heterodyne receptor will give you better results than either of the foregoing types. the operation of wireless telephone transmitters with direct current--short distance transmitter.--the operation of this short distance wireless telephone transmitter, a wiring diagram of which is shown in fig. 85 is exactly the same as that of the _direct current short distance c. w. telegraph transmitter_ already explained in this chapter. the only difference in the operation of these sets is the substitution of the _microphone transmitter_ for the telegraph key. the microphone transmitter.--the microphone transmitter that is used to vary, or modulate, the sustained oscillations set up by the oscillator tube and circuits is shown in fig. 84. by referring to the diagram at a in this figure you will readily understand how it operates. when you speak into the mouthpiece the _sound waves_, which are waves in the air, impinge upon the diaphragm and these set it into vibration--that is, they make it move to and fro. when the diaphragm moves toward the back of the transmitter it forces the carbon granules that are in the cup closer together; this lowers their resistance and allows more current from the battery to flow through them; when the pressure of the air waves is removed from the diaphragm it springs back toward the mouth-piece and the carbon granules loosen up when the resistance offered by them is increased and less current can flow through them. where the oscillation current in the aerial wire is small the transmitter can be connected directly in series with the latter when the former will surge through it. as you speak into the microphone transmitter its resistance is varied and the current strength of the oscillations is varied accordingly. the operation of wireless telephone transmitters with direct current--long distance transmitters.--in the wireless telephone transmitters for long distance work which were shown and described in the preceding chapter a battery is used to energize the microphone transmitter, and these two elements are connected in series with a _microphone modulator_. this latter device may be either (1) a _telephone induction coil_, (2) a _microphone transformer_, or (3) a _magnetic modulator_; the first two of these devices step-up the voltage of the battery current and the amplified voltage thus developed is impressed on the oscillations that surge through the closed oscillation circuit or the aerial wire system according to the place where you connect it. the third device works on a different principle and this will be described a little farther along. the operation of microphone modulators--the induction coil.--this device is really a miniature transformer, see a in fig. 86, and its purpose is to change the 6 volt direct current that flows through the microphone into 100 volts alternating current; in turn, this is impressed on the oscillations that are surging in either (1) the grid circuit as shown at a in fig. 89, and in fig. 90, (2) the aerial wire system, as shown at b in fig. 89 and fig. 93. when the current from the battery flows through the primary coil it magnetizes the soft iron core and as the microphone varies the strength of the current the high voltage alternating currents set up in the secondary coil of the induction coil are likewise varied, when they are impressed upon and modulate the oscillating currents. the microphone transformer.--this is an induction coil that is designed especially for wireless telephone modulation. the iron core of this transformer is also of the open magnetic circuit type, see a in fig. 87, and the _ratio_ of the turns [footnote: see chapter vi] of the primary and the secondary coil is such that when the secondary current is impressed upon either the grid circuit or the aerial wire system it controls the oscillations flowing through it with the greatest efficiency. the magnetic modulator.--this piece of apparatus is also called a _magnetic amplifier_. the iron core is formed of very thin plates, or _laminations_ as they are called, and this permits high-frequency oscillations to surge in a coil wound on it. in this transformer, see a in fig. 88, the current flowing through the microphone varies the magnetic permeability of the soft iron core by the magnetic saturation of the latter. since the microphone current is absolutely distinct from the oscillating currents surging through the coil of the transformer a very small direct current flowing through a coil on the latter will vary or modulate very large oscillating currents surging through the former. it is shown connected in the aerial wire system at a in fig. 88, and in fig. 93. operation of the vacuum tube as a modulator.--where a microphone modulator of the induction coil or microphone transformer type is connected in the grid circuit or aerial wire system the modulation is not very effective, but by using a second tube as a _modulator_, as shown in fig. 90, an efficient degree of modulation can be had. now there are two methods by which a vacuum tube can be used as a modulator and these are: (1) by the _absorption_ of the energy of the current set up by the oscillator tube, and (2) by _varying_ the direct current that energizes the plate of the oscillator tube. the first of these two methods is not used because it absorbs the energy of the oscillating current produced by the tube and it is therefore wasteful. the second method is an efficient one, as the direct current is varied before it passes into the oscillator tube. this is sufficient reason for describing only the second method. the voltage of the grid of the modulator tube is varied by the secondary coil of the induction coil or microphone transformer, above described. in this way the modulator tube acts like a variable resistance but it amplifies the variations impressed on the oscillations set up by the oscillator tube. as the magnetic modulator does the same thing a vacuum tube used as a modulator is not needed where the former is employed. for this reason a magnetic modulator is the cheapest in the long run. the operation of wireless telephone transmitters with alternating current.--where an initial alternating current is used for wireless telephony, the current must be rectified first and then smoothed out before passing into the oscillator tube to be converted into oscillations. further so that the oscillations will be sustained, two oscillator tubes must be used, and, finally, in order that the oscillations may not vary in amplitude the alternating current must be first changed into direct current by a pair of rectifier vacuum tubes, as shown in fig. 93. when this is done the plates will be positively charged alternately with every reversal of the current in which case there will be no break in the continuity of the oscillations set up and therefore in the waves that are sent out. the operation of rectifier vacuum tubes.--the vacuum tube rectifier is simply a two electrode vacuum tube. the way in which it changes a commercial alternating current into pulsating direct current is the same as that in which a two electrode vacuum tube detector changes an oscillating current into pulsating direct currents and this has been explained in detail under the heading of _the operation of a two electrode vacuum tube detector_ in chapter xii. in the _c. w. telegraph transmitting sets_ described in chapter xvii, the oscillator tubes act as rectifiers as well as oscillators but for wireless telephony the alternating current must be rectified first so that a continuous direct current will result. the operation of reactors and condensers.--a reactor is a single coil of wire wound on an iron core, see fig. 90 and a in fig. 91, and it should preferably have a large inductance. the reactor for the plate and grid circuit of a wireless telephone transmitter where one or more tubes are used as modulators as shown in the wiring diagram in fig. 90, and the filter reactor shown in fig. 92, operate in the same way. when an alternating current flows through a coil of wire the reversals of the current set up a _counter electromotive force_ in it which opposes, that is _reacts_, on the current, and the _higher_ the frequency of the current the _greater_ will be the _reactance_. when the positive half of an alternating current is made to flow through a large resistance the current is smoothed out but at the same time a large amount of its energy is used up in producing heat. but when the positive half of an alternating current is made to flow through a large inductance it acts like a large resistance as before and likewise smooths out the current, but none of its energy is wasted in heat and so a coil having a large inductance, which is called an _inductive reactance_, or just _reactor_ for short, is used to smooth out, or filter, the alternating current after it has been changed into a pulsating direct current by the rectifier tubes. a condenser also has a reactance effect on an alternating current but different from an induction coil the _lower_ the frequency the _greater_ will be the reactance. for this reason both a filter reactor and _filter condensers_ are used to smooth out the pulsating direct currents. chapter xx how to make a receiving set for $5.00 or less in the chapters on _receptors_ you have been told how to build up high-grade sets. but there are thousands of boys, and, probably, not a few men, who cannot afford to invest $25.00, more or less, in a receiving set and would like to experiment in a small way. the following set is inexpensive, and with this cheap, little portable receptor you can get the morse code from stations a hundred miles distant and messages and music from broadcasting stations if you do not live too far away from them. all you need for this set are: (1) a _crystal detector_, (2) a _tuning coil_ and (3) an _earphone_. you can make a crystal detector out of a couple of binding posts, a bit of galena and a piece of brass wire, or, better, you can buy one all ready to use for 50 cents. [illustration: wireless receptor, the size of a safety match box. a youthful genius in the person of kenneth r. hinman, who is only twelve years old, has made a wireless receiving set that fits neatly into a safety match box. with this instrument and a pair of ordinary receivers, he is able to catch not only code messages but the regular broadcasting programs from stations twenty and thirty miles distant.] the crystal detector.--this is known as the _rasco baby_ detector and it is made and sold by the _radio specialty company_, 96 park place, new york city. it is shown in fig. 96. the base is made of black composition and on it is mounted a standard in which a rod slides and on one end of this there is fixed a hard rubber adjusting knob while the other end carries a thin piece of _phosphor-bronze wire_, called a _cat-whisker_. to secure the galena crystal in the cup you simply unscrew the knurled cap, place it in the cavity of the post and screw the cap back on again. the free end of the cat-whisker wire is then adjusted so that it will rest lightly on the exposed part of the galena. [illustration: fig. 96.--rasco baby crystal detector.] the tuning coil.--you will have to make this tuning coil, which you can do at a cost of less than $1.00, as the cheapest tuning coil you can buy costs at least $3.00, and we need the rest of our $5.00 to invest in the earphone. get a cardboard tube, such as is used for mailing purposes, 2 inches in diameter and 3 inches long, see a in fig. 97. now wind on 250 turns of _no. 40 brown and sharpe gauge plain enameled magnet wire_. you can use _no. 40 double cotton covered magnet wire_, in which case you will have to shellac the tube and the wire after you get it on. [illustration: fig. 97.--how the tuning coil is made.] as you wind on the wire take off a tap at every 15th turn, that is, scrape the wire and solder on a piece about 7 inches long, as shown in fig. 99; and do this until you have 6 taps taken off. instead of leaving the wires outside of the tube bring them to the inside of it and then out through one of the open ends. now buy a _round wood-base switch_ with 7 contact points on it as shown at b in fig. 97. this will cost you 25 or 50 cents. the headphone.--an ordinary bell telephone receiver is of small use for wireless work as it is wound to too low a resistance and the diaphragm is much too thick. if you happen to have a bell phone you can rewind it with _no. 40_ single covered silk magnet wire, or enameled wire of the same size, when its sensitivity will be very greatly improved. then you must get a thin diaphragm and this should _not_ be enameled, as this tends to dampen the vibrations of it. you can get a diaphragm of the right kind for 5 cents. the better way, though, is to buy an earphone made especially for wireless work. you can get one wound to 1000 ohms resistance for $1.75 and this price includes a cord. [footnote: this is mesco, no. 470 wireless phone. sold by the manhattan electrical supply co., park place, n.y.c.] for $1.00 extra you can get a head-band for it, and then your phone will look like the one pictured in fig. 98. [illustration: fig. 98.--mesco 1000 ohm head set.] how to mount the parts.--now mount the coil on a wood base, 1/2 or 1 inch thick, 3-1/2 inches wide and 5-1/2 inches long, and then connect one end of the coil to one of the end points on the switch, and connect each succeeding tap to one of the switch points, as shown schematically in fig. 99 and diagrammatically in fig. 100. this done, screw the switch down to the base. finally screw the detector to the base and screw two binding posts in front of the coil. these are for the earphone. [illustration: fig. 99.--schematic layout of $5.00 receiving set.] [illustration: fig. 100.--wiring diagram for $5.00 receiving set.] the condenser.--you do not have to connect a condenser across the earphone but if you do you will improve the receiving qualities of the receptor. how to connect up the receptor.--now connect up all the parts as shown in figs. 99 and 100, then connect the leading-in wire of the aerial with the lever of the switch; and connect the free end of the tuning coil with the _ground_. if you have no aerial wire try hooking it up to a rain pipe that is _not grounded_ or the steel frame of an umbrella. for a _ground_ you can use a water pipe, an iron pipe driven into the ground, or a hydrant. put on your headphone, adjust the detector and move the lever over the switch contacts until it is in adjustment and then, if all your connections are properly made, you should be able to pick up messages. [illustration: wireless set made into a ring, designed by alfred g. rinehart, of elizabeth, new jersey. this little receptor is a practical set; it will receive messages, concerts, etc., measures 1" by 5/8" by 7/8". an ordinary umbrella is used as an aerial.] appendix useful information abbreviations of units unit abbreviation ampere amp. ampere-hours amp.-hr. centimeter cm. centimeter-gram-second c.g.s. cubic centimeters cm.^3 cubic inches cu. in. cycles per second ~ degrees centigrade â°c. degrees fahrenheit â°f. feet ft. foot-pounds ft.-lb. grams g. henries h. inches in. kilograms kg. kilometers km. kilowatts kw. kilowatt-hours kw.-hr. kilovolt-amperes kv.-a. meters m. microfarads [greek: mu]f. micromicrofarads [greek: mu mu]f. millihenries mh. millimeters mm. pounds lb. seconds sec. square centimeters cm.^2 square inches sq. in. volts v. watts w. prefixes used with metric system units prefix abbreviation meaning micro [greek: mu]. 1 millionth milli m. 1 thousandth centi c. 1 hundredth deci d. 1 tenth deka dk. 10 hekto h. 1 hundred kilo k. 1 thousand mega m. 1 million symbols used for various quantities quantity symbol capacitance c conductance g coupling co-efficient k current, instantaneous i current, effective value i decrement [greek: delta] dielectric constant [greek: alpha] electric field intensity [greek: epsilon] electromotive force, instantaneous value e electromotive force, effective value f energy w force f frequency f frequency x 2[greek: pi] [greek: omega] impedance z inductance, self l inductance, mutual m magnetic field intensity a magnetic flux [greek: phi] magnetic induction b period of a complete oscillation t potential difference v quantity of electricity q ratio of the circumference of a circle to its diameter =3.1416 [greek: pi] reactance x resistance r time t velocity v velocity of light c wave length [greek: lambda] wave length in meters [greek: lambda]m work w permeability [greek: mu] square root [math: square root] table of enameled wire no. of turns turns ohms per wire, per per cubic inch b.& s. linear square of gauge inch inch winding 20 30 885 .748 22 37 1400 1.88 24 46 2160 4.61 26 58 3460 11.80 28 73 5400 29.20 30 91 8260 70.90 32 116 21,000 7547.00 34 145 13,430 2968.00 36 178 31,820 1098.00 38 232 54,080 456.00 40 294 86,500 183.00 table of frequency and wave lengths w. l.--wave lengths in meters. f.--number of oscillations per second. o. or square root l. c. is called oscillation constant. c.--capacity in microfarads. l.--inductance in centimeters. 1000 centimeters = 1 microhenry. w.l. f o l.c. 50 6,000,000 .839 .7039 100 3,000,000 1.68 2.82 150 2,000,000 2.52 6.35 200 1,500,000 3.36 11.29 250 1,200,000 4.19 17.55 300 1,000,000 5.05 25.30 350 857,100 5.87 34.46 400 750,000 6.71 45.03 450 666,700 7.55 57.00 500 600,000 8.39 70.39 550 545,400 9.23 85.19 600 500,000 10.07 101.41 700 428,600 11.74 137.83 800 375,000 13.42 180.10 900 333,300 15.10 228.01 1,000 300,000 16.78 281.57 1,100 272,730 18.45 340.40 1,200 250,000 20.13 405.20 1,300 230,760 21.81 475.70 1,400 214,380 23.49 551.80 1,500 200,000 25.17 633.50 1,600 187,500 26.84 720.40 1,700 176,460 28.52 813.40 1,800 166,670 30.20 912.00 1,900 157,800 31.88 1,016.40 2,000 150,000 33.55 1,125.60 2,100 142,850 35.23 1,241.20 2,200 136,360 36.91 1,362.40 2,300 130,430 38.59 1,489.30 2,400 125,000 40.27 1,621.80 2,500 120,000 41.95 1,759.70 2,600 115,380 43.62 1,902.60 2,700 111,110 45.30 2,052.00 2,800 107,140 46.89 2,207.00 2,900 103,450 48.66 2,366.30 3,000 100,000 50.33 2,533.20 4,000 75,000 67.11 4,504.00 5,000 60,000 83.89 7,038.00 6,000 50,000 100.7 10,130.00 7,000 41,800 117.3 13,630.00 8,000 37,500 134.1 18,000.00 9,000 33,300 151.0 22,820.00 10,000 30,000 167.9 28,150.00 11,000 27,300 184.8 34,150.00 12,000 25,000 201.5 40,600.00 13,000 23,100 218.3 47,600.00 14,000 21,400 235.0 55,200.00 15,000 20,000 252.0 63,500.00 16,000 18,750 269.0 72,300.00 pronunciation of greek letters many of the physical quantities use greek letters for symbols. the following is the greek alphabet with the way the letters are pronounced: a alpha b beta g gamma d delta e epsilon z zeta ae eta th theta i iota k kappa l lambda m mu n nu x xi(zi) o omicron p pi r rho s sigma t tau u upsilon ph phi ch chi ps psi o omega table of sparking distances in air for various voltages between needle points volts distance inches centimeter 5,000 .225 .57 10,000 .470 1.19 15,000 .725 1.84 20,000 1.000 2.54 25,000 1.300 3.30 30,000 1.625 4.10 35,000 2.000 5.10 40,000 2.450 6.20 45,000 2.95 7.50 50,000 3.55 9.90 60,000 4.65 11.8 70,000 5.85 14.9 80,000 7.10 18.0 90,000 8.35 21.2 100,000 9.60 24.4 110,000 10.75 27.3 120,000 11.85 30.1 130,000 12.95 32.9 140,000 13.95 35.4 150,000 15.00 38.1 feet per pound of insulated magnet wire no. of single double single double b.& s. cotton, cotton, silk, silk, enamel gauge 4-mils 8-mils 1-3/4-mils 4-mils 20 311 298 319 312 320 21 389 370 408 389 404 22 488 461 503 498 509 23 612 584 636 631 642 24 762 745 800 779 810 25 957 903 1,005 966 1,019 26 1,192 1,118 1,265 1,202 1,286 27 1,488 1,422 1,590 1,543 1,620 28 1,852 1,759 1,972 1,917 2,042 29 2,375 2,207 2,570 2,435 2,570 30 2,860 2,534 3,145 2,900 3,240 31 3,800 2,768 3,943 3,683 4,082 32 4,375 3,737 4,950 4,654 5,132 33 5,590 4,697 6,180 5,689 6,445 34 6,500 6,168 7,740 7,111 8,093 35 8,050 6,737 9,600 8,584 10,197 36 9,820 7,877 12,000 10,039 12,813 37 11,860 9,309 15,000 10,666 16,110 38 14,300 10,636 18,660 14,222 20,274 39 17,130 11,907 23,150 16,516 25,519 40 21,590 14,222 28,700 21,333 32,107 international morse code and conventional signals to be used for all general public service radio communication 1. a dash is equal to three dots. 2. the space between parts of the same letter is equal to one dot. 3. the space between two letters is equal to three dots. 4. the space between two words is equal to five dots. [note: period denotes morse dot, hyphen denotes morse dash] a .b -... c -.-. d -.. e . f ..-. g --. h .... i .. j .--k -.l .-.. m -n -. o --p .--. q --.r .-. s ... t u ..v ...w .-x -..y -.-z --.. ã� (german) .-.ã� or ã� (spanish-scandinavian) .--.ch (german-spanish) ---ã� (french) ..-.. ã� (spanish) --.-ã� (german) ---. ã� (german) ..-1 .---2 ..--3 ...-4 ....5 ..... 6 -.... 7 --... 8 ---.. 9 ----. 0 ----period .. .. .. semicolon -.-.-. comma -.-.-. colon ---... interrogation ..--.. exclamation point --..-apostrophe .----. hyphen -....bar indicating fraction -..-. parenthesis -.--.inverted commas .-..-. underline ..--.double dash -...distress call ...---... attention call to precede every transmission -.-.general inquiry call -.-. --.from (de) -.. . invitation to transmit (go ahead) -.warning--high power --..-question (please repeat after ...)--interrupting long messages ..--.. wait .-... break (bk.) (double dash) -...understand ...-. error ........ received (o.k.) .-. position report (to precede all position messages) .-. end of each message (cross) .-.-. transmission finished (end of work) (conclusion of correspondence) ...-.international radiotelegraphic convention list of abbreviations to be used in radio communication abbreviation question answer or reply prb do you wish to communicate i wish to communicate by means by means of the international of the international signal code. signal code? qra what ship or coast station is this is.... that? qrb what is your distance? my distance is.... qrc what is your true bearing? my true bearing is.... qrd where are you bound for? i am bound for.... qrf where are you bound from? i am bound from.... qrg what line do you belong to? i belong to the ... line. qrh what is your wave length in my wave length is ... meters. meters? qrj how many words have you to send? i have ... words to send. qrk how do you receive me? i am receiving well. qrl are you receiving badly? i am receiving badly. please shall i send 20? send 20. ...-. ...-. for adjustment? for adjustment. qrm are you being interfered with? i am being interfered with. qrn are the atmospherics strong? atmospherics are very strong. qro shall i increase power? increase power. qrp shall i decrease power? decrease power. qrq shall i send faster? send faster. qrs shall i send slower? send slower. qrt shall i stop sending? stop sending. qru have you anything for me? i have nothing for you. qrv are you ready? i am ready. all right now. qrw are you busy? i am busy (or: i am busy with...). please do not interfere. qrx shall i stand by? stand by. i will call you when required. qry when will be my turn? your turn will be no.... qrz are my signals weak? you signals are weak. qsa are my signals strong? you signals are strong. qsb is my tone bad? the tone is bad. is my spark bad? the spark is bad. qsc is my spacing bad? your spacing is bad. qsd what is your time? my time is.... qsf is transmission to be in transmission will be in alternate order or in series? alternate order. qsg transmission will be in a series of 5 messages. qsh transmission will be in a series of 10 messages. qsj what rate shall i collect for...? collect.... qsk is the last radiogram canceled? the last radiogram is canceled. qsl did you get my receipt? please acknowledge. qsm what is your true course? my true course is...degrees. qsn are you in communication with land? i am not in communication with land. qso are you in communication with i am in communication with... any ship or station (through...). (or: with...)? qsp shall i inform...that you are inform...that i am calling him. calling him? qsq is...calling me? you are being called by.... qsr will you forward the radiogram? i will forward the radiogram. qst have you received the general general call to all stations. call? qsu please call me when you have will call when i have finished. finished (or: at...o'clock)? qsv is public correspondence being public correspondence is being handled? handled. please do not interfere. [footnote: public correspondence is any radio work, official or private, handled on commercial wave lengths.] qsw shall i increase my spark increase your spark frequency. frequency? qsx shall i decrease my spark decrease your spark frequency. frequency? qsy shall i send on a wavelength let us change to the wave length of ... meters? of ... meters. qsz send each word twice. i have difficulty in receiving you. qta repeat the last radiogram. when an abbreviation is followed by a mark of interrogation, it refers to the question indicated for that abbreviation. useful information symbols used for apparatus alternator ammeter aerial arc battery buzzer condenser variable condenser connection of wires no connection coupled coils variable coupling detector gap, plain gap, quenched ground hot wire ammeter inductor variable inductor key resistor variable resistor switch s.p.s.t. " s.p.d.t. " d.p.s.t. " d.p.d.t. " reversing phone receiver " transmitter thermoelement transformer vacuum tube voltmeter choke coil definitions of electric and magnetic units the _ohm_ is the resistance of a thread of mercury at the temperature of melting ice, 14.4521 grams in mass, of uniform cross-section and a length of 106.300 centimeters. the _ampere_ is the current which when passed through a solution of nitrate of silver in water according to certain specifications, deposits silver at the rate of 0.00111800 of a gram per second. the _volt_ is the electromotive force which produces a current of 1 ampere when steadily applied to a conductor the resistance of which is 1 ohm. the _coulomb_ is the quantity of electricity transferred by a current of 1 ampere in 1 second. the _ampere-hour_ is the quantity of electricity transferred by a current of 1 ampere in 1 hour and is, therefore, equal to 3600 coulombs. the _farad_ is the capacitance of a condenser in which a potential difference of 1 volt causes it to have a charge of 1 coulomb of electricity. the _henry_ is the inductance in a circuit in which the electromotive force induced is 1 volt when the inducing current varies at the rate of 1 ampere per second. the _watt_ is the power spent by a current of 1 ampere in a resistance of 1 ohm. the _joule_ is the energy spent in i second by a flow of 1 ampere in 1 ohm. the _horse-power_ is used in rating steam machinery. it is equal to 746 watts. the _kilowatt_ is 1,000 watts. the units of capacitance actually used in wireless work are the _microfarad_, which is the millionth part of a farad, because the farad is too large a unit; and the _c. g. s. electrostatic unit of capacitance_, which is often called the _centimeter of capacitance_, which is about equal to 1.11 microfarads. the units of inductance commonly used in radio work are the _millihenry_, which is the thousandth part of a henry; and the _centimeter of inductance_, which is one one-thousandth part of a microhenry. note.--for further information about electric and magnetic units get the _bureau of standards circular no. 60_, called _electric units and standards_, the price of which is 15 cents; also get _scientific paper no. 292_, called _international system of electric and magnetic units_, price 10 cents. these and other informative papers can be had from the _superintendent of documents, government printing office_, washington, d. c. wireless books the admiralty manual of wireless telegraphy. 1920. published by his majesty's stationery office, london. ralph e. batcher.--prepared radio measurements. 1921. wireless press, inc., new york city. elmer e. bucher.--practical wireless telegraphy. 1918. wireless press, inc., new york city. elmer e. bucher.--vacuum tubes in wireless communication. 1919. wireless press, inc., new york city. elmer e. bucher.--the wireless experimenter's manual. 1920. wireless press, inc., new york city. a. frederick collins.--wireless telegraphy, its history, theory, and practice. 1905. mcgraw pub. co., new york city. j. h. dellinger.--principles underlying radio communication. 1921. signal corps, u. s. army, washington, d. c. h. m. dorsett.--wireless telegraphy and telephony. 1920. wireless press, ltd., london. j. a. fleming.--principles of electric wave telegraphy. 1919. longmans, green and co., london. charles b. hayward.--how to become a wireless operator. 1918. american technical society, chicago, ill. g. d. robinson.--manual of radio telegraphy and telephony. 1920. united states naval institute, annapolis, md. rupert stanley.--textbook of wireless telegraphy. 1919. longmans, green and co., london. e. w. stone.--elements of radio telegraphy. 1919. d, van nostrand co., new york city. l. b. turner.--wireless telegraphy and telephony. 1921. cambridge university press. cambridge, england. send to the _superintendent of documents, government printing office_, washington, d. c., for a copy of _price list no. 64_ which lists the government's books and pamphlets on wireless. it will be sent to you free of charge. the government publishes; (1) _a list of commercial government and special wireless stations_, every year, price 15 cents; (2) _a list of amateur wireless stations_, yearly, price 15 cents; (3) _a wireless service bulletin_ is published monthly, price 5 cents a copy, or 25 cents yearly; and (4) _wireless communication laws of the united states_, the _international wireless telegraphic convention and regulations governing wireless operators and the use of wireless on ships and land stations_, price 15 cents a copy. orders for the above publications should be addressed to the _superintendent of documents, government printing office, washington, d. c._ manufacturers and dealers in wireless apparatus and supplies: adams-morgan co., upper montclair, n. j. american hard rubber co., 11 mercer street, new york city. american radio and research corporation, medford hillside, mass. brach (l. s.) mfg. co., 127 sussex ave., newark, n. j. brandes (c.) inc., 237 lafayette st., new york city. bunnell (j. h.) company, park place, new york city. burgess battery company, harris trust co. bldg., chicago, ill. clapp-eastman co., 120 main st., cambridge, mass. connecticut telephone and telegraph co., meriden, conn. continental fiber co., newark, del. coto-coil co., providence, r. i. crosley mfg. co., cincinnati, ohio. doolittle (f. m.), 817 chapel st., new haven, conn. edelman (philip e.), 9 cortlandt st., new york city. edison storage battery co., orange, n. j. electric specialty co., stamford, conn. electrose mfg. co., 60 washington st., brooklyn, n. y. general electric co., schenectady, n. y. grebe (a. h.) and co., inc., richmond hill, n. y. c. international brass and electric co., 176 beekman st., new york city. international insulating co., 25 west 45th st., new york city. king amplitone co., 82 church st., new york city. kennedy (colin b.) co., rialto bldg., san francisco, cal. magnavox co., oakland, cal. manhattan electrical supply co., park place, n. y. marshall-gerken co., toledo, ohio. michigan paper tube and can co., 2536 grand river ave., detroit, mich. murdock (wm. j.) co., chelsea, mass. national carbon co., inc., long island city, n. y. pittsburgh radio and appliance co., 112 diamond st., pittsburgh, pa, radio corporation of america, 233 broadway, new york city. riley-klotz mfg. co., 17-19 mulberry st., newark, n. j. radio specialty co., 96 park place, new york city. roller-smith co., 15 barclay st., new york city. tuska (c. d.) co., hartford, conn. western electric co., chicago, ill. westinghouse electric co., pittsburgh, pa. weston electrical instrument co., 173 weston ave., newark, n. j. westfield machine co., westfield, mass. abbreviations of common terms a. ..............aerial a.c. ............alternating current a.f. ............audio frequency b. and s. .......brown & sharpe wire gauge c. ..............capacity or capacitance c.g.s. ..........centimeter-grain-second cond. ...........condenser coup. ...........coupler c.w. ............continuous waves d.c. ............direct current d.p.d.t. ........double point double throw d.p.s.t. ........double point single throw d.x. ............distance e. ..............short for electromotive force (volt) e.m.f. ..........electromotive force f. ..............filament or frequency g. ..............grid gnd. ............ground i. ..............current strength (ampere) i.c.w. ..........interrupted continuous waves kw. .............kilowatt l. ..............inductance l.c. ............loose coupler litz. ...........litzendraht mfd. ............microfarad neg. ............negative o.t. ............oscillation transformer p. ..............plate prim. ...........primary pos. ............positive r. ..............resistance r.f. ............radio frequency sec. ............secondary s.p.d.t. ........single point double throw s.p.s.t. ........single point single throw s.r. ............self rectifying t. ..............telephone or period (time) of complete oscillation tick. ...........tickler v. ..............potential difference var. ............variometer var. cond. ......variable condenser v.t. ............vacuum tube w.l. ............wave length x. ..............reactance glossary a battery.--see battery a. abbreviations, code.--abbreviations of questions and answers used in wireless communication. the abbreviation _of a question_ is usually in three letters of which the first is q. thus q r b is the code abbreviation of "_what is your distance?_" and the answer "_my distance is_..." see page 306 [appendix: list of abbreviations]. abbreviations, units.--abbreviations of various units used in wireless electricity. these abbreviations are usually lower case letters of the roman alphabet, but occasionally greek letters are used and other signs. thus _amperes_ is abbreviated _amp., micro_, which means _one millionth_, [greek: mu], etc. see page 301 [appendix: useful abbreviations]. abbreviations of words and terms.--letters used instead of words and terms for shortening them up where there is a constant repetition of them, as _a.c._ for _alternating current; c.w._ for _continuous waves; v.t._ for _vacuum tube_, etc. see page 312 [appendix: abbreviations of common terms]. aerial.--also called _antenna_. an aerial wire. one or more wires suspended in the air and insulated from its supports. it is the aerial that sends out the waves and receives them. aerial, amateur.--an aerial suitable for sending out 200 meter wave lengths. such an aerial wire system must not exceed 120 feet in length from the ground up to the aerial switch and from this through the leading-in wire to the end of the aerial. aerial ammeter.--see _ammeter, hot wire_. aerial, bed-springs.--where an outdoor aerial is not practicable _bed-springs_ are often made to serve the purpose. aerial capacity.--see _capacity, aerial._ aerial counterpoise.--where it is not possible to get a good ground an _aerial counterpoise_ or _earth capacity_ can be used to advantage. the counterpoise is made like the aerial and is supported directly under it close to the ground but insulated from it. aerial, directional.--a flat-top or other aerial that will transmit and receive over greater distances to and from one direction than to and from another. aerial, ground.--signals can be received on a single long wire when it is placed on or buried in the earth or immersed in water. it is also called a _ground antenna_ and an _underground aerial._ aerial, loop.--also called a _coil aerial, coil antenna, loop aerial, loop antenna_ and when used for the purpose a _direction finder_. a coil of wire wound on a vertical frame. aerial resistance.--see _resistance, aerial._ aerial switch.--see _switch aerial._ aerial wire.--(1) a wire or wires that form the aerial. (2) wire that is used for aerials; this is usually copper or copper alloy. aerial wire system.--an aerial and ground wire and that part of the inductance coil which connects them. the open oscillation circuit of a sending or a receiving station. air core transformer.--see _transformer, air core._ amateur aerial or antenna.--see _aerial, amateur._ alternator.--an electric machine that generates alternating current. alphabet, international code.--a modified morse alphabet of dots and dashes originally used in continental europe and, hence, called the _continental code_. it is now used for all general public service wireless communication all over the world and, hence, it is called the _international code_. see page 305 [appendix: international morse code]. alternating current (_a.c._)--see _current._ alternating current transformer.--see _transformer_. amateur ground.--see _ground, amateur_. ammeter.--an instrument used for measuring the current strength, in terms of amperes, that flows in a circuit. ammeters used for measuring direct and alternating currents make use of the _magnetic effects_ of the currents. high frequency currents make use of the _heating effects_ of the currents. ammeter, hot-wire.--high frequency currents are usually measured by means of an instrument which depends on heating a wire or metal strip by the oscillations. such an instrument is often called a _thermal ammeter_, _radio ammeter_ and _aerial ammeter_. ammeter, aerial.--see _ammeter, hot wire_. ammeter, radio.--see _ammeter, hot wire_. ampere.--the current which when passed through a solution of nitrate of silver in water according to certain specifications, deposits silver at the rate of 0.00111800 of a gram per second. ampere-hour.--the quantity of electricity transferred by a current of 1 ampere in 1 hour and is, therefore, equal to 3600 coulombs. ampere-turns.--when a coil is wound up with a number of turns of wire and a current is made to flow through it, it behaves like a magnet. b the strength of the magnetic field inside of the coil depends on (1) the strength of the current and (2) the number of turns of wire on the coil. thus a feeble current flowing through a large number of turns will produce as strong a magnetic field as a strong current flowing through a few turns of wire. this product of the current in amperes times the number of turns of wire on the coil is called the _ampere-turns_. amplification, audio frequency.--a current of audio frequency that is amplified by an amplifier tube or other means. amplification, cascade.--see _cascade amplification_. amplification, radio frequency.--a current of radio frequency that is amplified by an amplifier tube or other means before it reaches the detector. amplification, regenerative.--a scheme that uses a third circuit to feed back part of the oscillations through a vacuum tube and which increases its sensitiveness when used as a detector and multiplies its action as an amplifier and an oscillator. amplifier, audio frequency.--a vacuum tube or other device that amplifies the signals after passing through the detector. amplifier, magnetic.--a device used for controlling radio frequency currents either by means of a telegraph key or a microphone transmitter. the controlling current flows through a separate circuit from that of the radio current and a fraction of an ampere will control several amperes in the aerial wire. amplifiers, multi-stage.--a receiving set using two or more amplifiers. also called _cascade amplification_. amplifier, vacuum tube.--a vacuum tube that is used either to amplify the radio frequency currents or the audio frequency currents. amplitude of wave.--the greatest distance that a point moves from its position of rest. amplifying transformer, audio.--see _transformer, audio amplifying_. amplifying modulator vacuum tube.--see _vacuum tube, amplifying modulator_. amplifying transformer radio.--see _transformer, radio amplifying_. antenna, amateur.--see _aerial, amateur_. antenna switch.--see _switch, aerial_. apparatus symbols.--see _symbols, apparatus_. armstrong circuit.--see _circuit, armstrong_. atmospherics.--same as _static_, which see. attenuation.--in sending wireless telegraph and telephone messages the amplitude of the electric waves is damped out as the distance increases. this is called _attenuation_ and it increases as the frequency is increased. this is the reason why short wave lengths will not carry as far as long wave lengths. audio frequency amplifier.--see _amplifier, audio frequency_. audio frequency amplification.--see _amplification, audio frequency_. audibility meter.--see _meter, audibility_. audio frequency.--see _frequency, audio_. audio frequency current.--see _current, audio frequency_. audion.--an early trade name given to the vacuum tube detector. autodyne receptor.--see _receptor, autodyne_. auto transformer.--see _transformer, auto_. bakelite.--a manufactured insulating compound. b battery.--see _battery b_. band, wave length.--see _wave length band_. basket wound coils.--see _coils, inductance_. battery, a.--the 6-volt storage battery used to heat the filament of a vacuum tube, detector or amplifier. battery, b.--the 22-1/2-volt dry cell battery used to energize the plate of a vacuum tube detector or amplifier. battery, booster.--this is the battery that is connected in series with the crystal detector. battery, c.--a small dry cell battery sometimes used to give the grid of a vacuum tube detector a bias potential. battery, edison storage.--a storage battery in which the elements are made of nickel and iron and immersed in an alkaline _electrolyte_. battery, lead storage.--a storage battery in which the elements are made of lead and immersed in an acid electrolyte. battery poles.--see _poles, battery_. battery, primary.--a battery that generates current by chemical action. battery, storage.--a battery that develops a current after it has been charged. beat reception.--see _heterodyne reception_. bed springs aerial.--see _aerial, bed springs_. blub blub.--over modulation in wireless telephony. broad wave.--see _wave, broad_. brush discharge.--see _discharge_. buzzer modulation.--see _modulation, buzzer_. blue glow discharge.--see _discharge_. booster battery.--see _battery, booster_. broadcasting.--sending out intelligence and music from a central station for the benefit of all who live within range of it and who have receiving sets. capacitance.--also called by the older name of _capacity_. the capacity of a condenser, inductance coil or other device capable of retaining a charge of electricity. capacitance is measured in terms of the _microfarad_. capacitive coupling.--see _coupling, capacitive_. capacity.--any object that will retain a charge of electricity; hence an aerial wire, a condenser or a metal plate is sometimes called a _capacity_. capacity, aerial.--the amount to which an aerial wire system can be charged. the _capacitance_ of a small amateur aerial is from 0.0002 to 0.0005 microfarad. capacity, distributed.--a coil of wire not only has inductance, but also a certain small capacitance. coils wound with their turns parallel and having a number of layers have a _bunched capacitance_ which produces untoward effects in oscillation circuits. in honeycomb and other stagger wound coils the capacitance is more evenly distributed. capacity reactance.--see _reactance, capacity_. capacity unit.--see _farad_. carbon rheostats.--see _rheostat, carbon_. carborundum detector.--see _detector_. carrier current telephony.--see _wired-wireless_. carrier frequency.--see _frequency, carrier_. carrier frequency telephony.--see _wired-wireless_. cascade amplification.--two or more amplifying tubes hooked up in a receiving set. cat whisker contact.--a long, thin wire which makes contact with the crystal of a detector. centimeter of capacitance.--equal to 1.11 _microfarads_. centimeter of inductance.--equal to one one-thousandth part of a _microhenry_. cellular coils.--see _coils, inductance_. c.g.s. electrostatic unit of capacitance.--see _centimeter of capacitance_. characteristics.--the special behavior of a device, such as an aerial, a detector tube, etc. characteristics, grid.--see _grid characteristics_. choke coils.--coils that prevent the high voltage oscillations from surging back into the transformer and breaking down the insulation. chopper modulation.--see _modulation, chopper_. circuit.--any electrical conductor through which a current can flow. a low voltage current requires a loop of wire or other conductor both ends of which are connected to the source of current before it can flow. a high frequency current will surge in a wire which is open at both ends like the aerial. closed circuit.--a circuit that is continuous. open circuit.--a conductor that is not continuous. coupled circuits.--open and closed circuits connected together by inductance coils, condensers or resistances. see _coupling_. close coupled circuits.--open and closed circuits connected directly together with a single inductance coil. loose coupled circuits.--opened and closed currents connected together inductively by means of a transformer. stand-by circuits.--also called _pick-up_ circuits. when listening-in for possible calls from a number of stations, a receiver is used which will respond to a wide band of wave lengths. armstrong circuits.--the regenerative circuit invented by major e. h. armstrong. close coupled circuits.--see _currents, close coupled_. closed circuit.--see _circuit, closed_. closed core transformer.--see _transformer, closed core_. code.-continental.--same as _international_. international.--on the continent of europe land lines use the _continental morse_ alphabetic code. this code has come to be used throughout the world for wireless telegraphy and hence it is now called the _international code_. it is given on page 305. [appendix: international morse code]. morse.--the code devised by samuel f. b. morse and which is used on the land lines in the u. s. national electric.--a set of rules and requirements devised by the _national board of fire underwriters_ for the electrical installations in buildings on which insurance companies carry risks. this code also covers the requirements for wireless installations. a copy may be had from the _national board of fire underwriters_, new york city, or from your insurance agent. national electric safety.--the bureau of standards, washington, d. c., have investigated the precautions which should be taken for the safe operation of all electric equipment. a copy of the _bureau of standards handbook no. 3_ can be had for 40 cents from the _superintendent of documents_. coefficient of coupling.--see _coupling, coefficient of_. coil aerial.--see _aerial, loop_. coil antenna.--see _aerial, loop_. coil, induction.--an apparatus for changing low voltage direct currents into high voltage, low frequency alternating currents. when fitted with a spark gap the high voltage, low frequency currents are converted into high voltage, high frequency currents. it is then also called a _spark coil_ and a _ruhmkorff coil_. coil, loading.--a coil connected in the aerial or closed oscillation circuit so that longer wave lengths can be received. coil, repeating.--see _repeating coil_. coil, rotating.--one which rotates on a shaft instead of sliding as in a _loose coupler_. the rotor of a _variometer_ or _variocoupler_ is a _rotating coil_. coils, inductance.--these are the tuning coils used for sending and receiving sets. for sending sets they are formed of one and two coils, a single sending coil is generally called a _tuning inductance coil_, while a two-coil tuner is called an _oscillation transformer_. receiving tuning coils are made with a single layer, single coil, or a pair of coils, when it is called an oscillation _transformer_. some tuning inductance coils have more than one layer, they are then called _lattice wound_, _cellular_, _basket wound_, _honeycomb_, _duo-lateral_, _stagger wound_, _spider-web_ and _slab_ coils. commercial frequency.--see _frequency, commercial_. condenser, aerial series.--a condenser placed in the aerial wire system to cut down the wave length. condenser, vernier.--a small variable condenser used for receiving continuous waves where very sharp tuning is desired. condenser.--all conducting objects with their insulation form capacities, but a _condenser_ is understood to mean two sheets or plates of metal placed closely together but separated by some insulating material. adjustable condenser.--where two or more condensers can be coupled together by means of plugs, switches or other devices. aerial condenser.--a condenser connected in the aerial. air condenser.--where air only separates the sheets of metal. by-pass condenser.--a condenser connected in the transmitting currents so that the high frequency currents cannot flow back through the power circuit. filter condenser.--a condenser of large capacitance used in combination with a filter reactor for smoothing out the pulsating direct currents as they come from the rectifier. fixed condenser.--where the plates are fixed relatively to one another. grid condenser.--a condenser connected in series with the grid lead. leyden jar condenser.--where glass jars are used. mica condenser.--where mica is used. oil condenser.--where the plates are immersed in oil. paper condenser.--where paper is used as the insulating material. protective.--a condenser of large capacity connected across the low voltage supply circuit of a transmitter to form a by-path of kick-back oscillations. variable condenser.--where alternate plates can be moved and so made to interleave more or less with a set of fixed plates. vernier.--a small condenser with a vernier on it so that it can be very accurately varied. it is connected in parallel with the variable condenser used in the primary circuit and is used for the reception of continuous waves where sharp tuning is essential. condensite.--a manufactured insulating compound. conductivity.--the conductance of a given length of wire of uniform cross section. the reciprocal of _resistivity_. contact detectors.--see _detectors, contact_. continental code.--see _code, continental_. coulomb.--the quantity of electricity transferred by a current of 1 ampere in 1 second. convective discharge.--see _discharge_. conventional signals.--see _signals, conventional_. counter electromotive force.--see _electromotive force, counter_. counterpoise. a duplicate of the aerial wire that is raised a few feet above the earth and insulated from it. usually no connection is made with the earth itself. coupled circuits.--see _circuit, coupled_. coupling.--when two oscillation circuits are connected together either by the magnetic field of an inductance coil, or by the electrostatic field of a condenser. coupling, capacitive.--oscillation circuits when connected together by condensers instead of inductance coils. coupling, coefficient of.--the measure of the closeness of the coupling between two coils. coupling, inductive.--oscillation circuits when connected together by inductance coils. coupling, resistance.--oscillation circuits connected together by a resistance. crystal rectifier.--a crystal detector. current, alternating (a.c.).--a low frequency current that surges to and fro in a circuit. current, audio frequency.--a current whose frequency is low enough to be heard in a telephone receiver. such a current usually has a frequency of between 200 and 2,000 cycles per second. current, plate.--the current which flows between the filament and the plate of a vacuum tube. current, pulsating.--a direct current whose voltage varies from moment to moment. current, radio frequency.--a current whose frequency is so high it cannot be heard in a telephone receiver. such a current may have a frequency of from 20,000 to 10,000,000 per second. currents, high frequency.--(1) currents that oscillate from 10,000 to 300,000,000 times per second. (2) electric oscillations. currents, high potential.--(1) currents that have a potential of more than 10,000 volts. (2) high voltage currents. cycle.--(1) a series of changes which when completed are again at the starting point. (2) a period of time at the end of which an alternating or oscillating current repeats its original direction of flow. damping.--the degree to which the energy of an electric oscillation is reduced. in an open circuit the energy of an oscillation set up by a spark gap is damped out in a few swings, while in a closed circuit it is greatly prolonged, the current oscillating 20 times or more before the energy is dissipated by the sum of the resistances of the circuit. decrement.--the act or process of gradually becoming less. detector.--any device that will (1) change the oscillations set up by the incoming waves into direct current, that is which will rectify them, or (2) that will act as a relay. carborundum.--one that uses a _carborundum_ crystal for the sensitive element. carborundum is a crystalline silicon carbide formed in the electric furnace. cat whisker contact.--see _cat whisker contact_. chalcopyrite.--copper pyrites. a brass colored mineral used as a crystal for detectors. see _zincite_. contact.--a crystal detector. any kind of a detector in which two dissimilar but suitable solids make contact. ferron.--a detector in which iron pyrites are used as the sensitive element. galena.--a detector that uses a galena crystal for the rectifying element. iron pyrites.--a detector that uses a crystal of iron pyrites for its sensitive element. molybdenite.--a detector that uses a crystal of _sulphide of molybdenum_ for the sensitive element. perikon.--a detector in which a _bornite_ crystal makes contact with a _zincite_ crystal. silicon.--a detector that uses a crystal of silicon for its sensitive element. vacuum tube.--a vacuum tube (which see) used as a detector. zincite.--a detector in which a crystal of _zincite_ is used as the sensitive element. de tuning.--a method of signaling by sustained oscillations in which the key when pressed down cuts out either some of the inductance or some of the capacity and hence greatly changes the wave length. dielectric.--an insulating material between two electrically charged plates in which there is set up an _electric strain_, or displacement. dielectric strain.--the electric displacement in a dielectric. directional aerial.--see _aerial, directional_. direction finder.--see _aerial, loop_. discharge.--(1) a faintly luminous discharge that takes place from the positive pointed terminal of an induction coil, or other high potential apparatus; is termed a _brush discharge_. (2) a continuous discharge between the terminals of a high potential apparatus is termed a _convective discharge_. (3) the sudden breaking-down of the air between the balls forming the spark gap is termed a _disruptive discharge_; also called an _electric spark_, or just _spark_ for short. (4) when a tube has a poor vacuum, or too large a battery voltage, it glows with a blue light and this is called a _blue glow discharge_. disruptive discharge.--see _discharge_. distress call. [morse code:] ...---... (sos). distributed capacity.--see _capacity, distributed_. double hump resonance curve.--a resonance curve that has two peaks or humps which show that the oscillating currents which are set up when the primary and secondary of a tuning coil are closely coupled have two frequencies. duo-lateral coils.--see _coils, inductance_. duplex communication.--a wireless telephone system with which it is possible to talk between both stations in either direction without the use of switches. this is known as the _duplex system_. earth capacity.--an aerial counterpoise. earth connection.--metal plates or wires buried in the ground or immersed in water. any kind of means by which the sending and receiving apparatus can be connected with the earth. edison storage battery.--see _storage battery, edison_. electric energy.--the power of an electric current. electric oscillations.--see _oscillations, electric_. electric spark.--see _discharge, spark_. electricity, negative.--the opposite of _positive electricity_. negative electricity is formed of negative electrons which make up the outside particles of an atom. electricity, positive.--the opposite of _negative electricity_. positive electricity is formed of positive electrons which make up the inside particles of an atom. electrodes.--usually the parts of an apparatus which dip into a liquid and carry a current. the electrodes of a dry battery are the zinc and carbon elements. the electrodes of an edison storage battery are the iron and nickel elements, and the electrodes of a lead storage battery are the lead elements. electrolytes.--the acid or alkaline solutions used in batteries. electromagnetic waves.--see _waves, electric_. electromotive force.--abbreviated _emf_. the force that drives an electric current along a conductor. also loosely called _voltage_. electromotive force, counter.--the emf. that is set up in a direction opposite to that in which the current is flowing in a conductor. electron.--(1) a negative particle of electricity that is detached from an atom. (2) a negative particle of electricity thrown off from the incandescent filament of a vacuum tube. electron flow.--the passage of electrons between the incandescent filament and the cold positively charged plate of a vacuum tube. electron relay.--see _relay, electron_. electron tube.--a vacuum tube or a gas-content tube used for any purpose in wireless work. see _vacuum tube_. electrose insulators.--insulators made of a composition material the trade name of which is _electrose_. energy, electric.--see _electric energy_. energy unit.--the _joule_, which see, page 308 [appendix: definitions of electric and magnetic units]. fading.--the sudden variation in strength of signals received from a transmitting station when all the adjustments of both sending and receiving apparatus remain the same. also called _swinging_. farad.--the capacitance of a condenser in which a potential difference of 1 volt causes it to have a charge of 1 coulomb of electricity. feed-back action.--feeding back the oscillating currents in a vacuum tube to amplify its power. also called _regenerative action_. ferromagnetic control.--see _magnetic amplifier_. filament.--the wire in a vacuum tube that is heated to incandescence and which throws off electrons. filament rheostat.--see _rheostat, filament_. filter.--inductance coils or condensers or both which (1) prevent troublesome voltages from acting on the different circuits, and (2) smooth out alternating currents after they have been rectified. filter reactor.--see _reactor, filter_. fire underwriters.--see _code, national electric_. fixed gap.--see _gap_. fleming valve.--a two-electrode vacuum tube. forced oscillations.--see _oscillations, forced_. free oscillations.--see _oscillations, free_. frequency, audio.--(1) an alternating current whose frequency is low enough to operate a telephone receiver and, hence, which can be heard by the ear. (2) audio frequencies are usually around 500 or 1,000 cycles per second, but may be as low as 200 and as high as 10,000 cycles per second. carrier.--a radio frequency wave modulated by an audio frequency wave which results in setting of _three_ radio frequency waves. the principal radio frequency is called the carrier frequency, since it carries or transmits the audio frequency wave. commercial.--(1) alternating current that is used for commercial purposes, namely, light, heat and power. (2) commercial frequencies now in general use are from 25 to 50 cycles per second. natural.--the pendulum and vibrating spring have a _natural frequency_ which depends on the size, material of which it is made, and the friction which it has to overcome. likewise an oscillation circuit has a natural frequency which depends upon its _inductance_, _capacitance_ and _resistance_. radio.--(1) an oscillating current whose frequency is too high to affect a telephone receiver and, hence, cannot be heard by the ear. (2) radio frequencies are usually between 20,000 and 2,000,000 cycles per second but may be as low as 10,000 and as high as 300,000,000 cycles per second. spark.--the number of sparks per second produced by the discharge of a condenser. gap, fixed.--one with fixed electrodes. gap, non-synchronous.--a rotary spark gap run by a separate motor which may be widely different from that of the speed of the alternator. gap, quenched.--(1) a spark gap for the impulse production of oscillating currents. (2) this method can be likened to one where a spring is struck a single sharp blow and then continues to set up vibrations. gap, rotary.--one having fixed and rotating electrodes. gap, synchronous.--a rotary spark gap run at the same speed as the alternator which supplies the power transformer. such a gap usually has as many teeth as there are poles on the generator. hence one spark occurs per half cycle. gas-content tube.--see _vacuum tube._ generator tube.--a vacuum tube used to set up oscillations. as a matter of fact it does not _generate_ oscillations, but changes the initial low voltage current that flows through it into oscillations. also called an _oscillator tube_ and a _power tube._ grid battery.--see _battery c._ grid characteristics.--the various relations that could exist between the voltages and currents of the grid of a vacuum tube, and the values which do exist between them when the tube is in operation. these characteristics are generally shown by curves. grid condenser.--see _condenser, grid._ grid leak.--a high resistance unit connected in the grid lead of both sending and receiving sets. in a sending set it keeps the voltage of the grid at a constant value and so controls the output of the aerial. in a receiving set it controls the current flowing between the plate and filament. grid modulation.--see _modulation, grid._ grid potential.--the negative or positive voltage of the grid of a vacuum tube. grid voltage.--see _grid potential._ grinders.--the most common form of _static,_ which see. they make a grinding noise in the headphones. ground.--see _earth connection._ ground, amateur.--a water-pipe ground. ground, waterpipe.--a common method of grounding by amateurs is to use the waterpipe, gaspipe or radiator. guided wave telephony.--see _wired wireless._ hard tube.--a vacuum tube in which the vacuum is _high,_ that is, exhausted to a high degree. helix.--(1) any coil of wire. (2) specifically a transmitter tuning inductance coil. henry.--the inductance in a circuit in which the electromotive force induced is 1 volt when the inducing current varies at the rate of 1 ampere per second. heterodyne reception.--(1) receiving by the _beat_ method. (2) receiving by means of superposing oscillations generated at the receiving station on the oscillations set up in the aerial by the incoming waves. heterodyne receptor.--see _receptor, heterodyne._ high frequency currents.--see _currents, high frequency._ high frequency resistance.--see _resistance, high frequency._ high potential currents.--see _currents, high potential._ high voltage currents.--see _currents, high potential._ honeycomb coils.--see _coils, inductance._ horse-power.--used in rating steam machinery. it is equal to 746 watts. hot wire ammeter.--see _ammeter, hot wire._ howling.--where more than three stages of radio amplification, or more than two stages of audio amplification, are used howling noises are apt to occur in the telephone receivers. impedance.--an oscillation circuit has _reactance_ and also _resistance,_ and when these are combined the total opposition to the current is called _impedance._ inductance coils.--see _coils, inductance._ inductance coil, loading.--see _coil, loading inductance._ inductive coupling.--see _coupling, inductive._ inductive reactance.--see _reactance, inductive._ induction coil.--see _coil, induction._ induction, mutual.--induction produced between two circuits or coils close to each other by the mutual interaction of their magnetic fields. insulation.--materials used on and around wires and other conductors to keep the current from leaking away. inspector, radio.--a u. s. inspector whose business it is to issue both station and operators' licenses in the district of which he is in charge. interference.--the crossing or superposing of two sets of electric waves of the same or slightly different lengths which tend to oppose each other. it is the untoward interference between electric waves from different stations that makes selective signaling so difficult a problem. intermediate waves.--see _waves._ ionic tubes.--see _vacuum tubes._ international code.--see code, international. jamming.--waves that are of such length and strength that when they interfere with incoming waves they drown them out. joule.--the energy spent in 1 second by a flow of 1 ampere in 1 ohm. joule's law.--the relation between the heat produced in seconds to the resistance of the circuit, to the current flowing in it. kenotron.--the trade name of a vacuum tube rectifier made by the _radio corporation of america._ kick-back.--oscillating currents that rise in voltage and tend to flow back through the circuit that is supplying the transmitter with low voltage current. kick-back prevention.--see _prevention, kick-back._ kilowatt.--1,000 watts. lambda.--see pages 301, 302. [appendix: useful abbreviations]. lattice wound coils.--see _coils, inductance._ lightning switch.--see _switch, lightning._ line radio communication.--see _wired wireless._ line radio telephony.--see _telephony, line radio._ litzendraht.--a conductor formed of a number of fine copper wires either twisted or braided together. it is used to reduce the _skin effect._ see _resistance, high frequency._ load flicker.--the flickering of electric lights on lines that supply wireless transmitting sets due to variations of the voltage on opening and closing the key. loading coil.--see _coil, loading._ long waves.--see _waves._ loop aerial.--see _aerial, loop._ loose coupled circuits.--see _circuits, loose coupled._ loud speaker.--a telephone receiver connected to a horn, or a specially made one, that reproduces the incoming signals, words or music loud enough to be heard by a room or an auditorium full of people, or by large crowds out-doors. magnetic poles.--see _poles, magnetic._ megohm.--one million ohms. meter, audibility.--an instrument for measuring the loudness of a signal by comparison with another signal. it consists of a pair of headphones and a variable resistance which have been calibrated. mho.--the unit of conductance. as conductance is the reciprocal of resistance it is measured by the _reciprocal ohm_ or _mho._ mica.--a transparent mineral having a high insulating value and which can be split into very thin sheets. it is largely used in making condensers both for transmitting and receiving sets. microfarad.--the millionth part of a _farad._ microhenry.--the millionth part of a _farad._ micromicrofarad.--the millionth part of a _microfarad._ microhm.--the millionth part of an _ohm._ microphone transformer.--see _transformer, microphone._ microphone transmitter.--see _transmitter, microphone._ milli-ammeter.--an ammeter that measures a current by the one-thousandth of an ampere. modulation.--(1) inflection or varying the voice. (2) varying the amplitude of oscillations by means of the voice. modulation, buzzer.--the modulation of radio frequency oscillations by a buzzer which breaks up the sustained oscillations of a transmitter into audio frequency impulses. millihenry.--the thousandth part of a _henry._ modulation, chopper.--the modulation of radio frequency oscillations by a chopper which breaks up the sustained oscillations of a transmitter into audio frequency impulses. modulation, grid.--the scheme of modulating an oscillator tube by connecting the secondary of a transformer, the primary of which is connected with a battery and a microphone transmitter, in the grid lead. modulation, over.--see _blub blub._ modulation, plate.--modulating the oscillations set up by a vacuum tube by varying the current impressed on the plate. modulator tube.--a vacuum tube used as a modulator. motion, wave.--(1) the to and fro motion of water at sea. (2) waves transmitted by, in and through the air, or sound waves. (3) waves transmitted by, in and through the _ether,_ or _electromagnetic waves,_ or _electric waves_ for short. motor-generator.--a motor and a dynamo built to run at the same speed and mounted on a common base, the shafts being coupled together. in wireless it is used for changing commercial direct current into direct current of higher voltages for energizing the plate of a vacuum tube oscillator. multi-stage amplifiers.--see _amplifiers, multi-stage._ mutual induction.--see _induction, mutual._ mush.--irregular intermediate frequencies set up by arc transmitters which interfere with the fundamental wave lengths. mushy note.--a note that is not clear cut, and hence hard to read, which is received by the _heterodyne method_ when damped waves or modulated continuous waves are being received. national electric code.--see _code, national electric._ national electric safety code.--see _code, national electric safety._ negative electricity.--see _electricity, negative._ non-synchronous gap.--see _gap, non-synchronous._ ohm.--the resistance of a thread of mercury at the temperature of melting ice, 14.4521 grams in mass, of uniform cross-section and a length of 106.300 centimeters. ohm's law.--the important fixed relation between the electric current, its electromotive force and the resistance of the conductor in which it flows. open circuit.--see _circuit, open._ open core transformer.--see _transformer, open core._ oscillation transformer.--see _transformer, oscillation._ oscillations, electric.--a current of high frequency that surges through an open or a closed circuit. (1) electric oscillations may be set up by a spark gap, electric arc or a vacuum tube, when they have not only a high frequency but a high potential, or voltage. (2) when electric waves impinge on an aerial wire they are transformed into electric oscillations of a frequency equal to those which emitted the waves, but since a very small amount of energy is received their potential or voltage is likewise very small. sustained.--oscillations in which the damping factor is small. damped.--oscillations in which the damping factor is large. free.--when a condenser discharges through an oscillation circuit, where there is no outside electromotive force acting on it, the oscillations are said to be _free._ forced.--oscillations that are made to surge in a circuit whose natural period is different from that of the oscillations set up in it. oscillation transformer.--see _transformer._ oscillation valve.--see _vacuum tube._ oscillator tube.--a vacuum tube which is used to produce electric oscillations. over modulation.--see _blub blub._ pancake oscillation transformer.--disk-shaped coils that are used for receiving tuning inductances. permeability, magnetic.--the degree to which a substance can be magnetized. iron has a greater magnetic permeability than air. phase.--a characteristic aspect or appearance that takes place at the same point or part of a cycle. pick-up circuits.--see _circuits, stand-by._ plate circuit reactor.--see _reactor, plate circuit._ plate current.--see _current, plate._ plate modulation.--see _modulation, plate._ plate voltage.--see _foliage, plate._ poles, battery.--the positive and negative terminals of the elements of a battery. on a storage battery these poles are marked + and respectively. poles, magnetic.--the ends of a magnet. positive electricity.--see _electricity, positive._ potential difference.--the electric pressure between two charged conductors or surfaces. potentiometer.--a variable resistance used for subdividing the voltage of a current. a _voltage divider._ power transformer.--see _transformer, power._ power tube.--see _generator tube._ primary battery.--see _battery, primary._ prevention, kick-back.--a choke coil placed in the power circuit to prevent the high frequency currents from getting into the transformer and breaking down the insulation. q s t.--an abbreviation used in wireless communication for (1) the question "have you received the general call?" and (2) the notice, "general call to all stations." quenched gap.--see _gap, quenched._ radiation.--the emission, or throwing off, of electric waves by an aerial wire system. radio ammeter.--see _ammeter, hot wire._ radio frequency.--see _frequency, radio._ radio frequency amplification.--see _amplification, radio frequency._ radio frequency current.--see _current, radio frequency._ radio inspector.--see _inspector, radio_. radiotron.--the trade name of vacuum tube detectors, amplifiers, oscillators and modulators made by the _radio corporation of america_. radio waves.--see _waves, radio_. reactance.--when a circuit has inductance and the current changes in value, it is opposed by the voltage induced by the variation of the current. reactance, capacity.--the capacity reactance is the opposition offered to a current by a capacity. it is measured as a resistance, that is, in _ohms_. receiving tuning coils.--see _coils, inductance_. receiver, loud speaking.--see _loud speakers_. receiver, watch case.--a compact telephone receiver used for wireless reception. reactance, inductive.--the inductive reactance is the opposition offered to the current by an inductance coil. it is measured as a resistance, that is, in _ohms_. reactor, filter.--a reactance coil for smoothing out the pulsating direct currents as they come from the rectifier. reactor, plate circuit.--a reactance coil used in the plate circuit of a wireless telephone to keep the direct current supply at a constant voltage. receiver.--(1) a telephone receiver. (2) an apparatus for receiving signals, speech or music. (3) better called a _receptor_ to distinguish it from a telephone receiver. rectifier.--(1) an apparatus for changing alternating current into pulsating direct current. (2) specifically in wireless (_a_) a crystal or vacuum tube detector, and (_b_) a two-electrode vacuum tube used for changing commercial alternating current into direct current for wireless telephony. regenerative amplification.--see _amplification, regenerative_. receptor.--a receiving set. receptor, autodyne.--a receptor that has a regenerative circuit and the same tube is used as a detector and as a generator of local oscillations. receptor, beat.--a heterodyne receptor. receptor, heterodyne.--a receiving set that uses a separate vacuum tube to set up the second series of waves for beat reception. regenerative action.--see _feed-back action._ regenerative amplification.--see _amplification, regenerative._ relay, electron.--a vacuum tube when used as a detector or an amplifier. repeating coil.--a transformer used in connecting up a wireless receiver with a wire transmitter. resistance.--the opposition offered by a wire or other conductor to the passage of a current. resistance, aerial.--the resistance of the aerial wire to oscillating currents. this is greater than its ordinary ohmic resistance due to the skin effect. see _resistance, high frequency._ resistance box.--see _resistor._ resistance coupling.--see _coupling, resistance._ resistance, high frequency.--when a high frequency current oscillates on a wire two things take place that are different than when a direct or alternating current flows through it, and these are (1) the current inside of the wire lags behind that of the current on the surface, and (2) the amplitude of the current is largest on the surface and grows smaller as the center of the wire is reached. this uneven distribution of the current is known as the _skin effect_ and it amounts to the same thing as reducing the size of the wire, hence the resistance is increased. resistivity.--the resistance of a given length of wire of uniform cross section. the reciprocal of _conductivity._ resistor.--a fixed or variable resistance unit or a group of such units. variable resistors are also called _resistance boxes_ and more often _rheostats._ resonance.--(1) simple resonance of sound is its increase set up by one body by the sympathetic vibration of a second body. (2) by extension the increase in the amplitude of electric oscillations when the circuit in which they surge has a _natural_ period that is the same, or nearly the same, as the period of the first oscillation circuit. rheostat.--a variable resistance unit. see _resistor._ rheostat, carbon.--a carbon rod, or carbon plates or blocks, when used as variable resistances. rheostat, filament.--a variable resistance used for keeping the current of the storage battery which heats the filament of a vacuum tube at a constant voltage. rotating coil.--see _coil._ rotary gap.--see _gap._ rotor.--the rotating coil of a variometer or a variocoupler. ruhmkorff coil.--see _coil, induction._ saturation.--the maximum plate current that a vacuum tube will take. sensitive spots.--spots on detector crystals that are sensitive to the action of electric oscillations. short waves.--see _waves._ side waves.--see _wave length band._ signals, conventional.--(1) the international morse alphabet and numeral code, punctuation marks, and a few important abbreviations used in wireless telegraphy. (2) dot and dash signals for distress call, invitation to transmit, etc. now used for all general public service wireless communication. skin effect.--see _resistance, high frequency._ soft tube.--a vacuum tube in which the vacuum is low, that is, it is not highly exhausted. space charge effect.--the electric field intensity due to the pressure of the negative electrons in the space between the filament and plate which at last equals and neutralizes that due to the positive potential of the plate so that there is no force acting on the electrons near the filament. spark.--see _discharge._ spark coil.--see _coil, induction._ spark discharge.--see _spark, electric._ spark frequency.--see _frequency, spark._ spark gap.--(1) a _spark gap,_ without the hyphen, means the apparatus in which sparks take place; it is also called a _spark discharger._ (2) _spark-gap,_ with the hyphen, means the air-gap between the opposed faces of the electrodes in which sparks are produced. plain.--a spark gap with fixed electrodes. rotary.--a spark gap with a pair of fixed electrodes and a number of electrodes mounted on a rotating element. quenched.--a spark gap formed of a number of metal plates placed closely together and insulated from each other. spider web inductance coil.--see _coil, spider web inductance._ spreader.--a stick of wood, or spar, that holds the wires of the aerial apart. stagger wound coils.--see _coils, inductance._ stand-by circuits.--see _circuits, stand-by._ static.--also called _atmospherics, grinders, strays, x's,_ and, when bad enough, by other names. it is an electrical disturbance in the atmosphere which makes noises in the telephone receiver. stator.--the fixed or stationary coil of a variometer or a variocoupler. storage battery.--see _battery, storage._ stray elimination.--a method for increasing the strength of the signals as against the strength of the strays. see _static._ strays.--see _static_. stranded wire.--see _wire, stranded_. super-heterodyne receptor.--see _heterodyne, super_. swinging.--see _fading_. switch, aerial.--a switch used to change over from the sending to the receiving set, and the other way about, and connect them with the aerial. switch, lightning.--the switch that connects the aerial with the outside ground when the apparatus is not in use. symbols, apparatus.--also called _conventional symbols_. these are diagrammatic lines representing various parts of apparatus so that when a wiring diagram of a transmitter or a receptor is to be made it is only necessary to connect them together. they are easy to make and easy to read. see page 307 [appendix: symbols used for apparatus]. synchronous gap.--see _gap, synchronous_. telephony, line radio.--see _wired wireless_. thermal ammeter.--see _ammeter, hot wire_. three electrode vacuum tube.--_see vacuum tube, three electrode_. tikker.--a slipping contact device that breaks up the sustained oscillations at the receiving end into groups so that the signals can be heard in the head phones. the device usually consists of a fine steel or gold wire slipping in the smooth groove of a rotating brass wheel. transformer.--a primary and a secondary coil for stepping up or down a primary alternating or oscillating current. a. c.--see _power transformer_. air cooled.--a transformer in which the coils are exposed to the air. air core.--with high frequency currents it is the general practice not to use iron cores as these tend to choke off the oscillations. hence the core consists of the air inside of the coils. auto.--a single coil of wire in which one part forms the primary and the other part the secondary by bringing out an intermediate tap. audio amplifying.--this is a transformer with an iron core and is used for frequencies up to say 3,000. closed core.--a transformer in which the path of the magnetic flux is entirely through iron. power transformers have closed cores. microphone.--a small transformer for modulating the oscillations set up by an arc or a vacuum tube oscillator. oil cooled.--a transformer in which the coils are immersed in oil. open core.--a transformer in which the path of the magnetic flux is partly through iron and partly through air. induction coils have open cores. oscillation.--a coil or coils for transforming or stepping down or up oscillating currents. oscillation transformers usually have no iron cores when they are also called _air core transformers._ power.--a transformer for stepping down a commercial alternating current for lighting and heating the filament and for stepping up the commercial a.c., for charging the plate of a vacuum tube oscillator. radio amplifying.--this is a transformer with an air core. it does not in itself amplify but is so called because it is used in connection with an amplifying tube. transmitter, microphone.--a telephone transmitter of the kind that is used in the bell telephone system. transmitting tuning coils.--see _coils, inductance._ tuning.--when the open and closed oscillation circuits of a transmitter or a receptor are adjusted so that both of the former will permit electric oscillations to surge through them with the same frequency, they are said to be tuned. likewise, when the sending and receiving stations are adjusted to the same wave length they are said to be _tuned._ coarse tuning.--the first adjustment in the tuning oscillation circuits of a receptor is made with the inductance coil and this tunes them coarse, or roughly. fine tuning.--after the oscillation circuits have been roughly tuned with the inductance coil the exact adjustment is obtained with the variable condenser and this is _fine tuning._ sharp.--when a sending set will transmit or a receiving set will receive a wave of given length only it is said to be sharply tuned. the smaller the decrement the sharper the tuning. tuning coils.--see _coils, inductance._ two electrode vacuum tube.--see _vacuum tube, two electrode._ vacuum tube.--a tube with two or three electrodes from which the air has been exhausted, or which is filled with an inert gas, and used as a detector, an amplifier, an oscillator or a modulator in wireless telegraphy and telephony. amplifier.--see _amplifier, vacuum tube._ amplifying modulator.--a vacuum tube used for modulating and amplifying the oscillations set up by the sending set. gas content.--a tube made like a vacuum tube and used as a detector but which contains an inert gas instead of being exhausted. hard.--see _hard tube._ rectifier.--(1) a vacuum tube detector. (2) a two-electrode vacuum tube used for changing commercial alternating current into direct current for wireless telephony. soft.--see _soft tube._ three electrode.--a vacuum tube with three electrodes, namely a filament, a grid and a plate. two electrode.--a vacuum tube with two electrodes, namely the filament and the plate. valve.--see _vacuum tube._ valve, fleming.--see _fleming valve._ variable condenser.--see _condenser, variable._ variable inductance.--see _inductance, variable._ variable resistance.--see _resistance, variable._ variocoupler.--a tuning device for varying the inductance of the receiving oscillation circuits. it consists of a fixed and a rotatable coil whose windings are not connected with each other. variometer.--a tuning device for varying the inductance of the receiving oscillation currents. it consists of a fixed and a rotatable coil with the coils connected in series. vernier condenser.--see _condenser, vernier._ volt.--the electromotive force which produces a current of 1 ampere when steadily applied to a conductor the resistance of which is one ohm. voltage divider.--see _potentiometer._ voltage, plate.--the voltage of the current that is used to energize the plate of a vacuum tube. voltmeter.--an instrument for measuring the voltage of an electric current. watch case receiver.--see _receiver, watch case._ water-pipe ground.--see _ground, water-pipe._ watt.--the power spent by a current of 1 ampere in a resistance of 1 ohm. wave, broad.--a wave having a high decrement, when the strength of the signals is nearly the same over a wide range of wave lengths. wave length.--every wave of whatever kind has a length. the wave length is usually taken to mean the distance between the crests of two successive waves. wave length band.--in wireless reception when continuous waves are being sent out and these are modulated by a microphone transmitter the different audio frequencies set up corresponding radio frequencies and the energy of these are emitted by the aerial; this results in waves of different lengths, or a band of waves as it is called. wave meter.--an apparatus for measuring the lengths of electric waves set up in the oscillation circuits of sending and receiving sets. wave motion.--disturbances set up in the surrounding medium as water waves in and on the water, sound waves in the air and electric waves in the ether. waves.--see _wave motion_. waves, electric.--electromagnetic waves set up in and transmitted by and through the ether. continuous. abbreviated c.w.--waves that are emitted without a break from the aerial. also called _undamped waves_. discontinuous.--waves that are emitted periodically from the aerial. also called _damped waves_. damped.--see _discontinuous waves_. intermediate.--waves from 600 to 2,000 meters in length. long.--waves over 2,000 meters in length. radio.--electric waves used in wireless telegraphy and telephony. short.--waves up to 600 meters in length. wireless.--electric waves used in wireless telegraphy and telephony. undamped.--see _continuous waves_. wireless telegraph code.--see _code, international_. wire, enamelled.--wire that is given a thin coat of enamel which insulates it. wire, phosphor bronze.--a very strong wire made of an alloy of copper and containing a trace of phosphorus. wired wireless.--continuous waves of high frequency that are sent over telephone wires instead of through space. also called _line radio communication; carrier frequency telephony, carrier current telephony; guided wave telephony_ and _wired wireless._ x's.--see _static._ zincite.--see _detector._ wireless don'ts aerial wire don'ts _don't_ use iron wire for your aerial. _don't_ fail to insulate it well at both ends. _don't_ have it longer than 75 feet for sending out a 200-meter wave. _don't_ fail to use a lightning arrester, or better, a lightning switch, for your receiving set. _don't_ fail to use a lightning switch with your transmitting set. _don't_ forget you must have an outside ground. _don't_ fail to have the resistance of your aerial as small as possible. use stranded wire. _don't_ fail to solder the leading-in wire to the aerial. _don't_ fail to properly insulate the leading-in wire where it goes through the window or wall. _don't_ let your aerial or leading-in wire touch trees or other objects. _don't_ let your aerial come too close to overhead wires of any kind. _don't_ run your aerial directly under, or over, or parallel with electric light or other wires. _don't_ fail to make a good ground connection with the water pipe inside. transmitting don'ts _don't_ attempt to send until you get your license. _don't_ fail to live up to every rule and regulation. _don't_ use an input of more than 1/2 a kilowatt if you live within 5 nautical miles of a naval station. _don't_ send on more than a 200-meter wave if you have a restricted or general amateur license. _don't_ use spark gap electrodes that are too small or they will get hot. _don't_ use too long or too short a spark gap. the right length can be found by trying it out. _don't_ fail to use a safety spark gap between the grid and the filament terminals where the plate potential is above 2,000 volts. _don't_ buy a motor-generator set if you have commercial alternating current in your home. _don't_ overload an oscillation vacuum tube as it will greatly shorten its life. use two in parallel. _don't_ operate a transmitting set without a hot-wire ammeter in the aerial. _don't_ use solid wire for connecting up the parts of transmitters. use stranded or braided wire. _don't_ fail to solder each connection. _don't_ use soldering fluid, use rosin. _don't_ think that all of the energy of an oscillation tube cannot be used for wave lengths of 200 meters and under. it can be if the transmitting set and aerial are properly designed. _don't_ run the wires of oscillation circuits too close together. _don't_ cross the wires of oscillation circuits except at right angles. _don't_ set the transformer of a transmitting set nearer than 3 feet to the condenser and tuning coil. _don't_ use a rotary gap in which the wheel runs out of true. receiving don'ts _don't_ expect to get as good results with a crystal detector as with a vacuum tube detector. _don't_ be discouraged if you fail to hit the sensitive spot of a crystal detector the first time--or several times thereafter. _don't_ use a wire larger than _no. 80_ for the wire electrode of a crystal detector. _don't_ try to use a loud speaker with a crystal detector receiving set. _don't_ expect a loop aerial to give worthwhile results with a crystal detector. _don't_ handle crystals with your fingers as this destroys their sensitivity. use tweezers or a cloth. _don't_ imbed the crystal in solder as the heat destroys its sensitivity. use _wood's metal,_ or some other alloy which melts at or near the temperature of boiling water. _don't_ forget that strong static and strong signals sometimes destroy the sensitivity of crystals. _don't_ heat the filament of a vacuum tube to greater brilliancy than is necessary to secure the sensitiveness required. _don't_ use a plate voltage that is less or more than it is rated for. _don't_ connect the filament to a lighting circuit. _don't_ use dry cells for heating the filament except in a pinch. _don't_ use a constant current to heat the filament, use a constant voltage. _don't_ use a vacuum tube in a horizontal position unless it is made to be so used. _don't_ fail to properly insulate the grid and plate leads. _don't_ use more than 1/3 of the rated voltage on the filament and on the plate when trying it out for the first time. _don't_ fail to use alternating current for heating the filament where this is possible. _don't_ fail to use a voltmeter to find the proper temperature of the filament. _don't_ expect to get results with a loud speaker when using a single vacuum tube. _don't_ fail to protect your vacuum tubes from mechanical shocks and vibration. _don't_ fail to cut off the a battery entirely from the filament when you are through receiving. _don't_ switch on the a battery current all at once through the filament when you start to receive. _don't_ expect to get the best results with a gas-content detector tube without using a potentiometer. _don't_ connect a potentiometer across the b battery or it will speedily run down. _don't_ expect to get as good results with a single coil tuner as you would with a loose coupler. _don't_ expect to get as good results with a two-coil tuner as with one having a third, or _tickler_, coil. _don't_ think you have to use a regenerative circuit, that is, one with a tickler coil, to receive with a vacuum tube detector. _don't_ think you are the only amateur who is troubled with static. _don't_ expect to eliminate interference if the amateurs around you are sending with spark sets. _don't_ lay out or assemble your set on a panel first. connect it up on a board and find out if everything is right. _don't_ try to connect up your set without a wiring diagram in front of you. _don't_ fail to shield radio frequency amplifiers. _don't_ set the axes of the cores of radio frequency transformers in a line. set them at right angles to each other. _don't_ use wire smaller than _no. 14_ for connecting up the various parts. _don't_ fail to adjust the b battery after putting in a fresh vacuum tube, as its sensitivity depends largely on the voltage. _don't_ fail to properly space the parts where you use variometers. _don't_ fail to put a copper shield between the variometer and the variocoupler. _don't_ fail to keep the leads to the vacuum tube as short as possible. _don't_ throw your receiving set out of the window if it _howls_. try placing the audio-frequency transformers farther apart and the cores of them at right angles to each other. _don't_ use condensers with paper dielectrics for an amplifier receiving set or it will be noisy. _don't_ expect as good results with a loop aerial, or when using the bed springs, as an out-door aerial will give you. _don't_ use an amplifier having a plate potential of less than 100 volts for the last step where a loud speaker is to be used. _don't_ try to assemble a set if you don't know the difference between a binding post and a blue print. buy a set ready to use. _don't_ expect to get arlington time signals and the big cableless stations if your receiver is made for short wave lengths. _don't_ take your headphones apart. you are just as apt to spoil them as you would a watch. _don't_ expect to get results with a bell telephone receiver. _don't_ forget that there are other operators using the ether besides yourself. _don't_ let your b battery get damp and don't let it freeze. _don't_ try to recharge your b battery unless it is constructed for the purpose. storage battery don'ts _don't_ connect a source of alternating current direct to your storage battery. you have to use a rectifier. _don't_ connect the positive lead of the charging circuit with the negative terminal of your storage battery. _don't_ let the electrolyte get lower than the tops of the plates of your storage battery. _don't_ fail to look after the condition of your storage battery once in a while. _don't_ buy a storage battery that gives less than 6 volts for heating the filament. _don't_ fail to keep the specific gravity of the electrolyte of your storage battery between 1.225 and 1.300 baume. this you can do with a hydrometer. _don't_ fail to recharge your storage battery when the hydrometer shows that the specific gravity of the electrolyte is close to 1.225. _don't_ keep charging the battery after the hydrometer shows that the specific gravity is 1.285. _don't_ let the storage battery freeze. _don't_ let it stand for longer than a month without using unless you charge it. _don't_ monkey with the storage battery except to add a little sulphuric acid to the electrolyte from time to time. if anything goes wrong with it better take it to a service station and let the expert do it. extra don'ts _don't_ think you have an up-to-date transmitting station unless you are using c.w. _don't_ use a wire from your lightning switch down to the outside ground that is smaller than no. _4_. _don't_ try to operate your spark coil with 110-volt direct lighting current without connecting in a rheostat. _don't_ try to operate your spark coil with 110-volt alternating lighting current without connecting in an electrolytic interrupter. _don't_ try to operate an alternating current power transformer with 110-volt direct current without connecting in an electrolytic interruptor. _don't_--no never--connect one side of the spark gap to the aerial wire and the other side of the spark gap to the ground. the government won't have it--that's all. _don't_ try to tune your transmitter to send out waves of given length by guesswork. use a wavemeter. _don't_ use _hard fiber_ for panels. it is a very poor insulator where high frequency currents are used. _don't_ think you are the only one who doesn't know all about wireless. wireless is a very complex art and there are many things that those experienced have still to learn. the end. 