REESE LIBRARY OF THE UNIVERSITY OF CALIFORNIA. Class The D. Van Nostrand Company intend this booK to be sold to the Public at the advertised price, and supply it to the Trade on terms which will not allow of discount. WIRELESS TELEGRAPHY; ITS ORIGINS, DEVELOPMENT, INVENTIONS, AND APPARATUS BY CHARLES HENRY SEWALL / AUTHOR OF " PATENTED TELEPHONY," " THE FUTURE OF LONG-DISTANCB COMMUNICATION " WITH 85 DIAGRAMS AND ILLUSTRATIONS SECOND EDITION CORRECTED. NEW YORK D. VAN NOSTRAND COMPANY 23 MURRAY AND 27 WARREN STS. 1904 WIRELESS TELEGRAPHY; ITS ORIGINS, DEVELOPMENT, INVENTIONS, AND APPARATUS BY CHARLES HENRY SEWALL 7 AUTHOR OF " PATENTED TELEPHONY," " THE FUTURE OF LONG-DISTANCE COMMUNICATION " WITH 85 DIAGRAMS AND ILLUSTRATIONS SECOND EDITION CORRECTED. NEW YORK D. VAN NOSTRAND COMPANY 23 MURRAY AND 27 WARREN STS. 1904 COPYRIGHT, 1903, BY D. VAN NOSTRAND COMPANY PREFACE THE aim of this book is to present a comprehensive view of wireless telegraphy, its history, principles, systems, and possibilities in theory and practice. In considering inventions controversy has been avoided, although the claims of individual inventors have been carefully defined. Because of the complexity of the subject a certain amount of allusion in one part, to matters dealt with in another, has been inevitable ; but it is hoped that such repetition may prove helpful to the reader. The book itself- is de- signed to be of use both to the general public and to the technical student. The author begs to acknowledge to the publishers his obligation for kind co-operation ; to the Century Magazine for extracts from the article by Mr. McGrath of St. Johns ; and to the Scientific American for extracts and diagrams from an article by Mr. A. F. Collins. CHARLES H. SEW ALL. NEW YORK, September, 1903. 196526 TABLE OF CONTENTS. PART I. PAGE PROPHECY i DISCOVERY 4 ACHIEVEMENT . u EXPLANATORY 24 DESCRIPTIVE 38 PART II. INVENTORS AND INVENTIONS 91 PART III. THE COMPARATIVE MERITS OF WIRELESS TELEGRAPHY AND OF TELEGRAPHY BY WIRES AND CABLES, AND THE COMMER- CIAL OUTLOOK FOR EACH 125 APPARATUS. PART IV ' NOMENCLATURE 143 TRANSMITTERS 145 WAVE-RESPONSIVE-DEVICES 152 WAVE-GATES 168 SHIELDS 179 CONDENSERS, INDUCTANCE COILS AND KEYS 182 APPENDIX . . . . . . . ... .-,. 190 INDEX . 226 UNIVERSITY ilL/FORjji WIRELESS TELEGRAPHY. PART I. PROPHECY. " Canst them send lightnings, that they may go, and say unto thee, * Here we are ? ' " JOB, 38th chapter, 35th verse. IN 1632 Galileo wrote a dialogue of which a Latin trans- lation appeared at Ley den in 1700. Mr. Robert Sabine, in his work on the Electric Telegraph?- rendered into English a paragraph from the Latin version, wherein Sagredus, one of the colloquists, is made to say : " You remind me of one who offered to sell me a secret art, by which through the attraction of a certain magnet needle it would be possible to converse across a space of two or three thousand miles. And I said to him that I would willingly become the purchaser provided only that I might first make a trial of the art, and that it would be sufficient for the purpose if I were to place myself in one corner of the sofa and he in the other. He replied that in so short a distance the action would be scarcely discernible : so I dismissed the fellow, and said that it was not convenient for me just then to travel into Egypt or Muscovy for the purpose of trying the experi- ment, but that if he chose to go there himself I would remain in Venice and attend to the rest." In the sixties of the nineteenth century Mr. Sabine supposed this expression to be a prescient description of telegraphy with wires. In 1877 it could be better associ- 1 D. Van Nostrand, New York, 1869. I 2 WIRELESS TELEGRAPHY. ated with telephone transmission over a conductor. To- day, however, we can readily see that Galileo wrote of "Wireless Telephony," an art not quite arrived. It will be observed that as translated the words are " to converse," not "to signal" ; and the correctness in translation is cor- roborated by the fact of the action at short distance being undiscernible. Readers of this generation will understand that between two persons sitting upon the same sofa, tele- phonic action is not palpable ; whereas nearness of sender and receiver is no bar to the observation of signals. It may be that Galileo had read the " Prolusiones Academicae" of Strada, published in 1617, and which de- scribed communication at a distance by means of two needles that had been touched with lodestone. These needles were mounted upon pivots. If either of them were moved it caused its mate to turn and to point in the same direction as itself. Possibly Galileo had an independent vision of wireless communication, seeing farther than Strada, and dared make of it but guarded mention. It is only necessary to read Galileo's biography to realize how disastrous in 1632 might have been the consequences of an announcement in scientific discovery. A work entitled "Voyage du Jeune Anacharsis " by the Abbe Barthelemy, published in 1788, mentions alphabetic dials, having hands or pointers which were electrically magnetized ; these hands on the clock faces being analo- gous to Strada's description one hundred and seventy years before. James Bowman Lindsay in 1854 made calculations to demonstrate that stations in England and Scotland could, without wires, signal across the Atlantic to stations in America. PROPHECY. 3 Sir William Crookes, 1892, reading a paper entitled "Some Possibilities of Electricity," said : "Rays of light will not pierce a wall, nor, as we know only too well, a London fog ; but electrical vibrations of a yard or more in wave-length will easily pierce such media, which, to them, will be transparent. Here is revealed the bewildering possibility of telegraphy without wires, posts, cables, or any of our present costly appliances." Again he said that Hertzian rays could be received "on a properly constituted instrument, and by concerted signals messages in the Morse code can thus pass from one operator to another." Tesla (1893) much in the manner outlined by his patents, 1 predicted the transmission through space and with- out conductors of electrical oscillations. Professor Lodge testifies that during the year 1894 Dr. Alexander Muirhead clearly foresaw the telegraphic im- portance of the transmission of Hertzian waves. Professor Ayrton, an English scientist, predicted, in 1897, that the time would come when the man with the electromagnetic voice in one part of the world would call to and be heard by the man with the electromagnetic ear at any other part of the world ; and just as housemates call to one another in the same dwelling would be the long-distance conversation ; excepting that in the latter communication only the selected ear might catch the sound. 1 See page 38. WIRELESS TELEGRAPHY. DISCOVERY. CONNECTED with electrical science are four great philos- ophers, Davy, Faraday, Helmholtz, and Hertz, whose discoveries all but span the nineteenth century ; and in- terwoven with the work of those four discoverers are the important achievements of Joseph Henry, Lord Kelvin, Feddersen, Maxwell, Lodge, Edison and Tesla. Sir Humphry Davy was born in 1778, and consequently commenced his scientific career with the century. Perhaps his greatest gift to electrical progress was his pupil Michael Faraday. The latter, in 1812, happening to be admitted to one of Davy's lectures, became at first his pupil, then his amanuensis and assistant, and finally in 1827 succeeded Sir Humphry as Professor of Chemistry at the Royal Institution of London. This happy combination in Eng- land whereby a great teacher was enabled to bequeath to a disciple equally talented the results of his researches was subsequently duplicated in Germany when Heinrich Hertz became assistant to Helmholtz. It was fortunate also that the early labors of Helmholtz were so timed that he could avail himself of the work already done by Davy and Faraday. The death of Helmholtz at an advanced age in 1894, and of Hertz in the same year as his gifted master, terminated the work of that remarkable quartet of scientists. Chronologically the thread of discovery begins with Huyghens, a Dutch philosopher (born 1629, died 1693), DISCOVERY. 5 who was apparently the originator of the undulatory theory which assumes that light is propagated by the vibrations of an imponderable medium called ether ; and although for many years after Huyghens the favored idea remained that enunciated by Sir Isaac Newton that light consists of material particles projected from luminous bodies New- ton's hypothesis has since been rejected, 1 and that of wave-motion is universally recognized. In 1807, when Sir Humphry Davy decomposed potash by electric-battery power there was inaugurated that won- derfully rapid development in electrical matters which characterized the nineteenth century. To this develop- ment Davy gave the initial impulse His was a genius so versatile that Coleridge said, "If Sir Humphry had not been the first chemist of his age, he probably would have been its first poet." At the age of twenty-three Sir Hum- phry's scientific knowledge and his eloquence were at- tracting in London brilliant audiences. He delivered a series of lectures on "Agricultural Chemistry," which made an epoch in that science ; he discovered the exhila- rating effect produced by the breathing of nitrous oxide gas ; his lecture on " Some Chemical Agencies of Elec- tricity " obtained for him the prize of the French In- stitute ; and the invention of the miner's safety lamp brought a baronetcy and world-wide fame. Six years sub- sequent to his electrical decomposition of potash, Davy used the galvanic battery of the Royal Institution, consist- ing of two thousand pairs of zinc and copper plates, and produced between two carbon electrodes a sparking dis- 1 The Newton hypothesis, sometimes called the " corpuscular theory of light," was suc- cessfully controverted by Dr. Thomas Young in 1773, who re-established " the undulatory theory." 6 WIRELESS TELEGRAPHY. charge four inches long in the air, and seven inches long in a vacuum. This constituted the first voltaic arc. Faraday in 1831 discovered the existence of a current in a hollow coil of wire whenever a permanent magnet or an electromagnet was introduced into, or withdrawn from, its interior. He discovered also the principles of inductive influences between electric currents, and found that dif- ferent insulating media had varying capacities to produce inductive effects. Maxwell quotes Faraday as saying, " It was allowable to admit that the propagation of electricity might be effected by means of the ether, because it was probable that if this ether existed it could fill another office besides serving as a medium for the transmission of light." In 1 842 Professor Joseph Henry of Princeton, United States, drew attention to the fact that the phenomena accompanying the discharge of a Leyden jar was oscillatory in character, and Helmholtz in 1847 confirmed this. Lord Kelvin in 1853 demonstrated mathematically the oscilla- tory effect, and Feddersen in 1859 proved it by experiment. Hermann Helmholtz was born at Potsdam, Prussia, in 1821, and was consequently beginning his life-work when Faraday had reached middle age. Like Davy, Helmholtz was a genius of great versatility. He was first a surgeon in the army, and during his medical practice invented the ophthalmascope, still an indispensable piece of apparatus for the oculist. He was metaphysician, mathematician, physi- ologist, and physicist. The most famous writing of Helm- holtz was his essay on "Conservation of Energy," which firmly established that law ; for by reason of diversified knowledge he was able to bring to its demonstration facts from all departments of science. In the same paper DISCOVERY. 7 Helmholtz proclaimed the oscillatory nature of a discharge from the Leyden jar; and explained that the oscillations would grow weaker and weaker until their entire energy was damped out by opposing resistances. By analyzing complex tones Helmholtz made science explain music, and his investigations in the laws of sound did much toward the establishment of modern wave theories. His paper on the vortex motion in fluids was probably the basis for Lord Kelvin's hypothesis that all matter is made up of small vortices of fluid, each rotating about a hollow space. It also helped to formulate Maxwell's proposition. During the period from 1863 to 1 873 there was developed the philosophical demonstration by James Clerk Maxwell, that the propagating medium of electromagnetic waves was identical with that of light ; and although he was not able to prove it by experiment, Maxwell was the first who fully understood what is now admitted to be the true nature of electrical phenomena. Thus by 1873 it had been established that light with a velocity of 1 86,000 miles per second consisted of a wave motion produced in a medium called " ether," which Maxwell defined as "a material sub- stance of a more subtle kind than visible bodies, and supposed to exist in those parts of space which are apparently empty." Recapitulating, Huyghens in the seventeenth century had proclaimed the existence of ether and the undulatory mo- tion of light, and this was confirmed by Dr. Thomas Young in the eighteenth. In the nineteenth century, Henry, Helmholtz, Kelvin, and Feddersen demonstrated that the discharge of a Leyden jar was oscillatory. Maxwell con- tended that if the velocity of propagation of electromag- netic disturbance was the same as that of light, which had, 8 WIRELESS TELEGRAPHY. he thought, been proved, then the media through which either light or electricity was transmitted occupied the same space and must be identical ; and the difference be- tween their resultant manifestations depended only upon the lengths of their respective waves. Thus the matter stood at the death of Maxwell in 1879. As has been said, Heinrich Hertz was a pupil of Helm- holtz. From 1883 to 1885 Hertz occupied at Kiel, Ger- many, the chair of theoretical physics, and in the latter year was appointed Professor of Physics in the Technical High School at Carlsruhe. During the delivery of a lecture at this institution, and while experimenting with a Leyden jar and two flat coils of wire, Hertz observed that the discharge of the jar through one of the coils would induce appreciable current in the other coil ( although the jar was a very small one ), provided that there was a spark gap in the inducing coil. This accidental discovery came to a man who has since proved to be perhaps the most brilliant experiment- alist and the ablest physicist the world has seen. Hertz demonstrated that the reasoning of Maxwell was correct ; the experiments proving conclusively that the medium which is vibrated by light and the medium which is vibrated by electromagnetism is one and the same ; that each travels with the same velocity ; that waves of electromagnetic disturbance ( now called " Hertzian " waves ) are reflected from conducting surfaces and refracted by dielectric sub- stances ; and are plainly analogous to the reflection of light from polished surfaces and its refraction through glass prisms. "This great discovery of Hertz," says Professor Lodge, " was by no means his only one. In addition to his well- known essays on electric waves, which marked an epoch in DISCOVERY. 9 experimental physics, no less than eighteen papers, all original, and all important, were, by him, contributed to German periodicals." After the experiments at Carlsruhe, Hertz in 1889 was called to the chair of physics in the University at Bonn. His health failed, however, and he died at Bonn in 1 894. He was the first understandingly to transmit electric waves through ether; and is the most important figure in the history of Wireless Telegraphy. From his discovery in 1886, that etheric vibrations would result from the passing of sparks across an air-gap, began the development of electric transmission without conductors. 10 WIRELESS TELEGRAPHY. ACHIEVEMENT. II ACHIEVEMENT. THE record of operative electric telegraphs begins in 1774 with that of Lesarge at Geneva, Switzerland, and prior to 1837 twelve had been constructed. In July, 1837, Steinheil operated in England a telegraph line twelve miles long, which, besides its two terminal points, was provided with three intermediate, or way, sta- tions. He used but one wire, employing the earth as a return circuit. There were alarm-bells for "calling," and the signals could be read either by sound, or by ink-marks recorded upon paper. In 1838 Professor Joseph Henry, of Princeton, making with an electrical machine and Ley den jar a one-inch spark in the top room of his residence, set up induced cur- rents in the cellar of the same building. During that year Steinheil endeavored, although without success, to utilize the two rails of a steam tramway as a telegraph circuit, but suggested the possibility of doing away altogether with conducting wires. Professor Morse, who had conceived his idea of the tele- graph in 1832, did not succeed in operating it until 1838. His plan was the most practical of any brought forward, and proved the most successful ; but he was by no means, as is popularly supposed, the originator of the electric tel- egraph with wires. There seems, however, to be no doubt but that he was the very first to signal without wires ; for on December i6th, 1842, he sent a wireless telegram 12 WIRELESS TELEGRAPHY. across a canal eighty feet wide ; and in November, 1 844, Mr. L. D. Gale, acting under instructions from Professor Morse, made wireless signals across the Susquehanna River at Havre de Grace, a distance of nearly one mile. In the latter experiment Mr. Gale used, as a source of energy, six pairs of plates in the form of a galvanic battery. He found that the best results were obtained when on each side of the river two plates were immersed near its bank, and were connected by an insulated wire stretched along each shore for a distance three times as great as that which measured either path of the crossing signals. The few chroniclers of wireless telegraphy have all spoken with respect and affection of Mr. James Bowman Lindsay. Several years after Mr. Gale's experiments on the Susquehanna River, Lindsay, having no knowledge of what Morse had done in America, reached the same results in Scotland. It is said that by gradually increasing his distances, Lindsay succeeded at last in signaling across the Tay where the river is two miles wide. In 1854 Lindsay took out an English patent, of which the follow- ing brief is from the Abridgements by the British Com- missioners of Patents : " This invention consists of a method of completing the circuit of elec- tric telegraphs through water without submarine cables or submerged wires extending across such water, water being the connecting and con- ducting medium for the electric fluid. "The two wires respectively connected with the battery and signal instrument on one side of the water are attached to metal balls, tubes, or plates placed in the water or in moist ground adjacent to the water. The same arrangement is placed on the other side of the water ; and the for- ward as well as the return current passes between the respective plates. " It is preferred to place the plates on one side of the water at a greater ACHIEVEMENT. 13 distance apart than the distance across the water ; but in case this is not practicable, the battery power must be augmented, and the size of the immersed plates increased. It is also necessary to place the plates for the forward current opposite to each other and the plates for the return cur- rent opposite to each other." Though a man of learning, Lindsay had little worldly wisdom. He was one of the best linguists, and for many years employed himself upon a dictionary of fifty lan- guages in one book. He foresaw and accurately predicted the universal employment of electric light and electric power. He thought that by his own plan of wireless telegraphy it would be possible to span the Atlantic Ocean. Lindsay was born in 1799, and died in 1862, re- siding chiefly at Dundee, Scotland. He was a bachelor, and his life was one of consistent and continuous self-sac- rifice to science. It is said that during the year 1835 he lived in one room, which was illumined, however, by an electric lamp whose installation was the work of his own hands. In 1859 ne rea d a paper before the British Asso- ciation on the subject 'of "Telegraphing without Wires," and among his hearers were Faraday and Sir William Thompson, now Lord Kelvin. While Lindsay was not an original discoverer in wireless telegraphy, he was a notable pioneer ; and his unselfish devotion to learning has won for him deserved distinction. The invention of the telephone in 1876 and 1877 fur- nished a detector of great delicacy, and immediately after its discovery novel electrical phenomena were noted. The author in 1877 was an observer of those remarkable induc- tive effects upon neighboring circuits during the progress of experiments made with Edison's " Singing Telephone " over a wire extending from New York to Saratoga Springs. 14 WIRELESS TELEGRAPHY. During that trial I had a Bell telephone receiver in cir- cuit upon a telegraph wire in my residence on the east side of the Hudson River at Albany. The wire to which the Bell telephone was connected ran parallel in Albany with the transmitting line for possibly three hundred feet ; but at no point were the respective circuits less than thirty feet apart. That particular Edison apparatus transmitted simply tones, no words. The receiving record of the Sing- ing Telephone was a series of peculiarly harsh and scrap- ing sounds, so that from the notes of a good soprano singer at the transmitter there were audible at the singing re- ceiver nothing but the different pitches of those tones, all the refinements of sound being lost. Upon the unattached circuits and with a Bell telephone receiver, however, the harsh features were eliminated ; and while no articulate word could be distinguished, the musical flow was accurate, smooth, and pleasing. Inductive effects from the same Singing Telephone were also manifest at Providence, R.I., probably by reason of the proximity in New York City of the wires leading to Providence, and those connected with Saratoga. In 1882 Mr. William H. Preece, Engineer-in-Chief of Government Telegraphs in England, succeeded in signaling across the Solent from England to the Isle of Wight. At two different points plates immersed in the sea near one shore were put in line with similar plates near the opposite shore ; and upon each side two of the plates were electri- cally connected by an over-land conductor. The arrange- ments of the circuits was the same as that used by Morse in 1842, and by Lindsay in 1854; but for apparatus Mr. Preece had an advantage over his predecessors in that he could use a receiving telephone to detect signals ; and he ACHIEVEMENT. 15 also improved upon former practice by employing as a transmitter, and in place of a contact key, a rapidly vibrat- ing reed called a "buzzer," signals appearing at the receiv- ing end as long and short buzzing sounds. At other times and localities in England Mr. Preece made transmissions in a similar way. The year 1882 was also that during which Professor Dolbear in America filed his application for United States Letters Patent l to protect devices for wireless signaling. His patent is further discussed under " Inventors and In- ventions." The distances over which he succeeded in sending impulses are variously reported to have been from half a mile to thirteen miles. Mr. Edison (1885), using just such inductive effects as were observed in 1877, when his Singing Telephone was tried, signaled through space to a moving train from a wire beside the railway. The crowning achievement was that of Hertz in 1886. Across the little gap in a ring of wire suspended in a room (there being no electrical contact with the charging appara- tus) Hertz made tiny sparks appear, as the result of the passage across another and longer spark gap of the oscilla- tory discharge from a Leyden jar. Calzecchi Onesti about 1886 observed the coherency among metal filings produced by the impulsive discharge of a previously electrified wire or coil. Second in importance only to Hertz is the connection with Wireless Telegraphy of Dr. Oliver Joseph Lodge. This eminent scientist, born in England in 1851, became Professor of Physics at the new University of Liverpool in 1880, and during 1887 was elected a Fellow of the Royal 1 Printed in full in the Appendix. See also Edison Patent of 1885, p. 96. 16 WIRELESS TELEGRAPHY. Society. At the date of Hertz's first etheric transmis- sion, his English contemporary was conducting experiments along the same lines, and Hertz said that in time Lodge would undoubtedly have reached the same results as him- self. Between the fil- ings tube of Onesti, 1886, and that of Bran- ly, 1891, there inter- venes an experiment of Dr. Lodge in 1889, described by him to the Institution of Electri- cal Engineers of Lon- don in 1890. He had observed "that two knobs sufficiently close together, far too close to stand any voltage such as an electroscope can show, would, when a spark passes between them, actually cohere, conducting, if a single voltaic cell was in circuit, an ordinary bell-ringing cur- rent." With permission there is here presented from Dr. Lodge's " Signalling through Space without Wires," the diagram shown as Fig. 3, and the following descrip- tion : Fig. 3. " The experiment of the syntonic Leyden jars can be conveniently shown with the double knob or 1889 coherer. The pair of knobs are arranged to connect the coatings of the receiving jar (a T .arge condenser being interposed to prevent their completing a purely metallic circuit), ACHIEVEMENT. 17 and in circuit with them is a battery and bell. Every time the receiving jar responds syntonically to the electric vibration of the other jar, the knobs cohere (if properly adjusted) and the bell rings. If the bell is free in air it continues ringing until the knobs are gently tapped asunder ; but if the bell stands on the same table as the knobs, especially if it rests one foot on the actual stand, then its first stroke taps them back instantly and automatically, and so every discharge of the sending jar is signaled by a single stroke of the bell. Here we have in essence a system of very distinctly syntonic telegraphy, for the jars and their circuits must be accurately tuned together if there is to be any response. A very little error in tuning, easily made by altering the position of the slider ( see s, Fig. 3), will make them quite unresponsive unless the distance between them is reduced." Much of the history of wireless telegraphy after 1889 is set forth in detail in succeeding divisions of this work. Briefly, Branly (1890-1891) made the filings coherer that is sensitive to Hertzian waves. Dr. Lodge in 1893, having learned of Branly's results, commenced a series of experiments, one of which led to inclosing the filings in a vacuum, and another to the making of a more positive de- coherer than was obtained by merely mounting the electric bell upon the- base of the filings tube. In 1894 Lodge delivered his famous lecture reviewing the work already done with Hertz's oscillators, with Branly's coherer, and by himself. In 1895 was accomplished the undertaking of Count Popoff of Russia, described under " Inventors and Inventions." In the same year Captain Jackson, by direc- tion of the British Board of Admiralty, passed electrical sig- nals between ships. In 1896 Marconi came to England, and signaled across a space of one hundred yards at the British Post Office in London. Soon afterwards he made a successful trial of two miles overland on Salisbury Plain. In May, 1897, a distance of nine miles over water was attained by Marconi, and from that time his signaling dis- 18 WIRELESS TELEGRAPHY. tances were gradually increased until he spanned the ocean. 1 Guglielmo Marconi was born at Bologna, Italy, on April 25th, 1874. His father is an Italian nobleman, and his mother of Irish nationality. He studied at Leghorn under Professor Rosa, and afterward under Righi at the Univer- sity of Bologna, of which institution he is a graduate, and has been interested in wireless telegraphy since his six- teenth year. He is of middle height, slim in figure, with blue eyes and brown hair, and his bearing indicates rather a nervous temperament. Upon November 25th, 1901, Mr. Marconi sailed from England, his destination being an ex- perimental station which had been established at Cape Race, some eighty miles from St. Johns, Newfoundland. When interviewed as to this journey by reporters, he said to them that there was a possibility of signaling over three hundred miles of sea, and felt quite sure that two hundred miles would be reached. During that same November, however, the author was privately assured by an official of the Marconi Company in New York City, that within thirty days there would be a record of transatlantic sig- naling. This prediction was confirmed by the event. There had been constructed at Poldhu, England, and at Cape Cod, Massachusetts, stations with powerful machinery 1 " Its progress has not been slow. Five years ago my system worked satisfactorily over a distance of about two miles. Since then its range has been rapidly increased, until, a few months ago, by means of improved and attuned apparatus, a distance of over two hundred miles was successfully bridged, and wireless communication at this distance is now an everyday occurence. A certain commercial application of my system has already been achieved. In all, seventy ships carry permanent installations, and there are over twenty land stations in Great Britain and on the continent of Europe, besides several in this coun- try. To what further extent the system may be commercially applied is not easy to foretell. My recent successful experiments between Poldhu and St. Johns, however, give great hopes of a regular transatlantic wireless telegraph service in the not too distant future." From Mar corn's prefatory note in Century of March, 1902. ACHIEVEMENT. 19 for generating electricity ; and especial attention had been paid to the vertical conductors or wave-gates by which the ether waves were emitted and received. These struc- tures consisted at either station of twenty poles, each two hundred and ten feet high, by which a large number of wires were supported. The poles and wires, both in Amer- ica and England, had been damaged by storm, in the latter country the structure at Poldhu being practically destroyed. Neither had been fully replaced. The aerial distance between Poldhu and Cape Cod was some six hundred miles farther than that between Poldhu and Cape Race. Before leaving England, Marconi had arranged with his Engineer at Poldhu to send signals in a certain manner after a date which would be fixed by cablegram, and upon December Qth Poldhu station was instructed (by cable) to begin sending signals every day at three o'clock in the afternoon, and to continue until six o'clock evening, these hours by Newfoundland time being respectively 11.30 A.M. and 2.30 P.M. The signals agreed upon were rep- etitions of the letter S (by telegraphic code three short marks ), to be repeated a certain number of times and then discontinued, for intervals of three minutes' duration^ On Thursday, December i2th, 1901, at 12.30 P.M. Marconi and an assistant, Mr. Kemp, received the first transatlantic signals. During the appointed hours these signals were detected a number of times, and upon the following day, Friday, were again noticed. The public announcement of this event caused great excitement. Marconi was the recipient of congratulatory messages from all over the world, and during the next few weeks he was met everywhere with a series of ovations, the most nota- ble, perhaps, being the dinner held in his honor at the 20 WIRELESS TELEGRAPHY. Waldorf-Astoria Hotel in New York City by the American Institute of Electrical Engineers. On the first day of March, 1902, Marconi arrived in New York City from England ; and declared that he had received on a moving vessel at a position fifteen hundred and fifty-one miles from the sending point 1 an actual mes- sage in words ; also that he had witnesses to prove beyond peradventure that he had done this through space without wires or cables. Further, that at a distance two thousand and ninety-nine miles l from the sending point he had received signals more or less distinct but unmistakable. The vessel conveying Marconi and his telegraphic devices was the steamship Philadelphia. Upon the following day, March 2d, arrived at New York the Umbria of the Cunard line ; and although the latter ship all the way across the Atlantic had been in the same receiving zone as the Philadelphia, and was actually nearer the Cornish coast during the time the latter was receiving messages from England, not a word or signal of those messages was impressed upon the apparatus of the Cunard steamer ; although with the Campania and Etruria, whose instruments were attuned with those upon the Umbria, perfect com- munication was had. The inventor contended that two sets of instruments of different electrical tone might work, without interference, within five inches of each other ; that he had two hundred and fifty tunes which would prevent " tapping the circuit"; that the secrecy of the message was complete. 2 1 See frontispiece. 2 " It seems to be a matter of popular belief that any receiver within effective range of the transmitter is capable of picking up the messages sent, or, in other words, that there can be no secrecy of communication by my system. Were this so, a very important limitation would be imposed upon the practical usefulness of the system ; but by the introduction of important and radical modifications in the original system, and by a systematic application ACHIEVEMENT. 21 In the communication between Cornwall and the steam- ship all the messages were one way, all from the station to the vessel. Mr. Marconi explained that while the PJiila- dclphia's equipment admitted the reception of signals, it had not a sufficiently powerful transmitting apparatus to reach to England ; but that the Cornwall station could put forth enough energy to overcome that distance. So far as is generally known, there was from the time of the messages to 5. 5. Philadelphia in March, 1902, no further signaling across the Atlantic until October 3ist of the same year, when transoceanic messages were received upon the Italian warship Carlo Alberto while that vessel lay at anchor in the harbor of Sydney, Nova Scotia. The wire- less telegrams were transmitted from Poldhu. The distance covered is estimated at twenty-three hundred miles. The Carlo Alberto had been placed by the King of Italy at Mar- coni's disposal as an assistance to wireless experiments. It was on Sunday, December 2ist, 1902, one year and nine days after the letter S from Poldhu was heard at Cape Race, that Marconi announced the transmission of three entire messages from Table Head station at Glace Bay, Cape Breton, to Poldhu station in Cornwall, England, viz. : one from the Governor General of Canada to King Edward of England ; another from the Commander of the Carlo Alberto to the King of Italy ; a third to the Times, in London, from its special correspondent. The latter was in the nature of formal evidence, and read as follows : " Being present at its transmission in Signer Marconi's Canadian station, I have the honor to send the Times the inventor's first wireless transatlantic message of greeting to England and Italy." of the principles of electrical resonance, this objection has, in very great measure, been overcome." From Marconi 's prefatory note in Century of March, iCj02- 22 WIRELESS TELEGRAPHY. Upon January iQth, 1903, the Marconi Station at Wellfleet, Cape Cod, Massachusetts, transmitted the follow- ing : His MAJESTY, EDWARD VII., LONDON, ENGLAND. In taking advantage of the wonderful triumph of scientific research and ingenuity which has been achieved in perfecting a system of wireless tele- graphy, I extend on behalf of the American people most cordial greetings and good wishes to you and to all the people of the British. Empire. THEODORE ROOSEVELT. WELLFLEET, MASS., JAN. 19, 1903. The reply which follows was returned by cable : SANDRINGHAM, JAN. 19, 1903. THE PRESIDENT, WHITE HOUSE, WASHINGTON, AMERICA. I thank you most sincerely for the kind message which I have just re- ceived from you, through Marconi's transatlantic wireless telegraphy. I sincerely reciprocate in the name of the people of the British Empire the cordial greetings and friendly sentiment expressed by you on behalf of the American Nation, and I heartily wish you and your country every possible prosperity. EDWARD R. AND I. Mr. Marconi explained that his apparatus not being quite ready for long-distance operation, the message from President Roosevelt was directed to be relayed by Table Head, Nova Scotia, station. It was found, however, that the Poldhu station in England had been able to copy the telegram while it was being sent to Table Head. Upon January 2ist, 1903, the Italian Government asked for an appropriation of $150,000 to erect, under the direc- tion of Marconi, wireless telegraph stations with a capacity of six thousand miles, for service between Italy and South America. ACHIEVEMENT. Fig. 4 . Outside the Cabot Tower on Signal Hill, St. Johns, Newfoundland. i. Mr. Kemp. 2. Mr. Marconi. 3- Mr. Paget. 4. The keeper of the station. From a photograph. Copyright by James Vey. By Courtesy of the Century Company. 24 WIRELESS TELEGRAPHY. EXPLANATORY. WHAT were the devices and methods employed to ac- complish the transmissions ? How were they used ? Why did they produce the results desired ? Coherer. The prime factor is the coherer, which in Fig. 5 to show clearly the position of the grains g, that constitute the kernel of the whole matter, is drawn some- what out of proportion. Those metallic grains are inclosed in a glass tube, G G G G, between two silver plugs, P and P' ; to which plugs are connected platinum wires, W and W. When proper action is taken at a transmitting station Fig. 5- the grains g at a receiving point cohere. If, after cohesion is established, the glass tube be gently tapped, the grains will separate, i.e., will decohere. When these minute par- ticles are together they close an electric circuit, producing an effect which, on account of the delicacy of the instru- ment, is rather weak, but which may be made through a relay to close another electric circuit sufficiently powerful to produce either an audible signal, as when a telephone or sounder is used, or to exhibit a visual one, as when ink EXPLANATORY. 25 marks are made upon paper tape. It is also possible, by means of this second and stronger electric circuit, auto- matically to set in motion, immediately after the mark has been made, a vibrating hammer such as is used in electric door-bells, and which the English call a "trembler." By directing the vibrating hammer against the coherer, or against anything to which the coherer is secured, the grains g may be separated, and the electric devices will then be in position to make another mark. 1 Signals. In telegraphy marks, or " signals," are made of two decidedly differing lengths, designated "the long and the short." Combinations of long and short marks are used for letters. Upon the paper ribbon of the wireless telegraph recorder the name of the genius who signaled from Poldhu to Cape Race would appear thus : ~M~ ~~A~ ~~R~ ~C~~ ~~0~ ~N~ T Circuits. Fig. 6 is a diagram devoid of many details which will be supplied hereafter in other drawings. Upon the receiving side letters H, B', and R represent respect- ively a coherer and the battery and relay of the weak electric circuit before noted. On the transmitting side B is a battery, and K a key for closing the primary circuit of a sparking appliance of which P is the primary winding and L the secondary part of a " step-up " induction coil. S G stands for the spark-gap. Upon each closure of the key K, there is produced sufficient strain to cause sparks to fly between terminating electrodes T T of the secondary coil 1 See Fig. 3, Part I., p. 16, and Fig. 31, Part II., p. 98, and accompanying descriptions. UNIVERSITY 26 WIRELESS TELEGRAPHY. L. A A' are vertical wires which in the first transatlantic transmission were respectively maintained in position by masts at Cornwall and by a kite in Newfoundland. They are sometimes called "antennae." It will be seen that at "Transmitter" one of the electrodes T is in connection with the high wire A, while the other is put to earth at E. When key K is brought onto the anvil V, an electric cir- cuit is made, and the current in it by inductive influence is Transmitter [B Receiver Fig. 6. communicated to the secondary coil and raised in pressure. The sparking across S G becomes the center of a disturb- ance from which waves spread in all directions. These are picked up by any vertical wire as A' and pass through P' to earth at E'. In the receiving apparatus, the sparking ( exceedingly weak by reason of dissipation of the energy on the long journey), being " stepped up" from P' to L' is now through the filings at H, causing them to cohere, the relay R is energized through coherer, and by a local circuit (not shown in Fig. 6) a mark is made. EXPLANATORY. 27 In a general way the action just described is what took place at Newfoundland when the Poldhu station sent the letter s, three short marks. It was also the method employed to send from Poldhu to the 5. 5. Philadelphia at sea. In the trial to Newfoundland the receiving station used an ordinary hand ( listening ) telephone in place of the relay R shown in Fig. 6, a telephone receiver being much more sensitive than a relay. Upon the Philadelphia, how- ever, ink-marks were recorded upon paper tape. TUNING. It will be remembered that immediately after the Corn- wall-Newfoundland demonstration, Marconi, upon being asked if it were not probable that he received the sig- nal s from some ship or station other than the Cornwall plant, replied, " It is impossible ; I was tuned only for Poldhu." Theory of Electrical Resonance. To understand the devices used for electrical tuning it will be necessary to consider first the theory by which " electrical resonance" is explained, and then the analogies that are used to demon- strate that theory. It is supposed that all matter, solid, liquid, or gaseous, is made up of molecules ; and that these molecules are combinations of atoms of different chemical elements, atoms being quantitatively the smallest divisions of matter, and an element an individual substance, as distinguished from those substances which are a combination of two or more elementary kinds of matter. The density, and to an extent the weight, of any substance depends upon the nearness of the molecules to one another. In air, or other gases, they 28 WIRELESS TELEGRAPHY. are widely separated. In metals they are very close to one another. In either substance there is between them space, and that space is said to be permeated by "ether." Scien- tists have not yet added a fourth dimension to length, breadth, and thickness ; but the three divisions of matter are now supplemented by a fourth, and they speak of the solid, the liquid, the gas, and the ether. Analogy of Jelly. An analogy to ether and matter is furnished by the contents of a vessel containing a mixture of lead bullets and jelly. Imagine the jelly to be so tremu- lous as to be capable of vibrating from a disturbance by which the bullets, being much more inert, move so little as to be practically still. Further imagine that the jelly be made to oscillate, being first pushed forward and then pulled backward, very rapidly. It will readily be under- stood that before the forward motion of the jelly has over- come the inertia of the bullets, the backward one will have reversed and neutralized that motion. Analogy of a Pool of Water. If a person standing upon one side of a pool of water strikes into the water with a paddle each time in the same direction and at regular intervals, so that he maintains a rhythmical beat, it will be found that after each stroke and up to a certain maximum the waves caused by the paddle will augment in size ; but that if strokes be afterward made at irregular intervals the waves will decrease in volume. Discord will tend to undo the work that has been done by rhythm. Analogy of Spring and Timber. Suppose, as in Fig. 7, a stick of timber L is suspended from a rigid support E by EXPLANATORY. 29 a spiral steel spring C, and that the timber be given a push upward, or a push downward, then it will vibrate a certain number of times per minute. If it be pushed gently it will move slowly through a small space, if pushed forcibly it will move more quickly through a greater space ; but the oscillations in a unit of time will always be the same. This rate of vibration is governed by the resiliency of the spring C and the weight of the load L. If the resiliency of the spring be increased, or the weight of the timber be decreased, the rate of vibration will be quickened. If C be made less springy, or L be made heavier, the rate will be slower. To change the rate by altering either or both of the conditions has been called by clockmakers " regu- lating" ; Scientists of to-day call it "tuning." Advantages of Harmonious Action. The pushing if continued should, in order to get the best results, be in accord with the rate of the apparatus ; that is to say, the strokes must be exactly as many per minute, or exactly one-half as many, or twice as many, or some even division or multiple of the rate. Irregular strokes will tend to stop the motion just as in the case of the paddle and waves. Now set the timber L upon the surface of the water on one side of a pool of considerable width, and so that the crest of a small wave will just uplift it. By moving the timber and timing its oscillations the rate may be ascer- Fig. 7. 30 WIRELESS TELEGRAPHY. tained. If the water upon the far side of the pool be struck with the paddle time after time at the timber's rate, waves will spread from the paddle ; and although only a few faint ripples may reach the timber-and-spring-device they will be attuned to it, and, if the strokes be regularly continued, each wave will tend to increase the length of the oscillation of the spring. At Poldhu a powerful source of vibration was sending waves into the ether, and the little ripples were caught at Newfoundland by a delicate receiving apparatus which had been adjusted to vibrate at the same rate as the Cornwall transmitter. Fig. 8 represents a guitar, which instrument may be used to demonstrate the fact that air waves when set in Fig. 8. motion by one string of a certain note will cause to vibrate another string tuned to the same note. In trying this experiment, to avoid troublesome stretching of strings, it will be advisable to keep about a half-tone below "concert pitch." When the A string is brought to such tension as to be in its proper relative tune with the E string, it will sound in unison with the latter, whenever the E is stopped by the finger pressing the E firmly against fret 5. EXPLANATORY. 31 Mechanical Tuning. To ascertain if the two notes are in unison, cut a piece of medium writing-paper to a size about five-eighths of an inch square, fold it one way in the middle and set it astride of the open A string. When the two strings are properly tuned, and the E string is struck below the stopped point at fret 5, the paper on A will vi- brate so strongly as to be perceptible both to the eye and also by a buzzing noise to the ear. If now the E string be stopped either on the 4th or the 6th fret, or if the tension on the A string be increased or decreased in the slightest degree, the paper will remain motionless, no matter how violently the E string may be set in motion. Such an operation is sometimes called " mechanical tuning," and more accurate results may be obtained than by the usual method of listening. Referring back to the spring and timber demonstration in a pool of water ( Fig. 7 ), the weight of the A string is analogous to that of the timber, the tension upon it to the elasticity of the spring. The stopped E sets up waves of exactly the same rate as those to which A is attuned. In the pool the waves are of water moving a few feet per second. In the guitar demonstration the waves are of air moving at the rate of 1400 or 1500 feet per second. In the transatlantic transmission of Marconi the waves were of ether, traveling 186,000 miles per second. Electrical Resonance in Practice. It is hoped that the foregoing illustrations will make clear the principles of electrical resonance. The practice is illustrated in Fig. 9. Transmitting Side. B is a battery or other source of energy. P is the primary winding of an induction coil, 32 WIRELESS TELEGRAPHY, and K the key of transmission. L is a secondary wind- ing complementary to the primary P. T T are electrodes of S G the spark-gap. C is a condenser. P2 and L2 are respectively the primary and secondary of another induc- tion coil in the transmitting apparatus which may, by way of distinction, be called a transformer, its function being to convert the waves that oscillate in the spark-gap to a still higher intensity. D is a variable inductive resistance Transmitter placed in the circuit between the vertical wire or wave-gate A and the earth at E. At the transmitter the condenser C is analogous to the resiliency of the stopped E string of Fig. 8, and L 2 and D represent the inertia of the spring, or the load. By moving the pointer d the load may be changed, and by giving the condenser more or less surface the force of oscillation may be intensified or diminished. EXPLANATORY. 33 Receiving Side. Looking now at the receiver in Fig. 9 A' is the vertical wire. The changeable inductive resis- tance D' and primary coil P 3 of a transformer is placed in that part of the wave circuit which reaches from A' to the earth at E'. D' with ?3 constitute the load, being analogous to the timber in Fig. 7. Inductive transference of the waves from ?3, to L3 and L4, increase the intensity of the faint ripples which come through space from the vertical wire A of transmitter. C' is a condenser placed in a bight of the long wire which forms the secondary winding of L3, L4. This condenser ( C' ) represents the steel spring C of Fig. 7. In tuning the receiver, either the load D' ?3, or the spring C' may be changed to in- crease or decrease the rate of the receiver. Infinitesimal waves passing through the gaps in metallic powder of H will cause those grains to cohere, and so close the electric circuit H B' R. Relay R translates the signal into a more powerful local circuit, which actuates an ink-marking regis- ter, and, at the same time, causes a " tapper " l ( not shown in Fig. 9) to strike the glass tube H and " decohere " the powder. The apparatus is then ready for another signal. LOCALIZATION. The following extract of a letter from Dr. A. Fleming, which was published in the London Times, October 4, 1900, will serve to define and illustrate the term used as a heading for this division : Two operators at St. Catherine's, Isle of Wight, were instructed to send simultaneously two different wireless messages to Poole, Dorset, and with- out delay or mistake the tw T o w r ere correctly recorded and printed down at 1 Similar to the device shown in Fig. 31, Part II. 34 WIRELESS TELEGRAPHY. the same time in Morse signals on the tapes of the two corresponding receivers at Poole. In this first demonstration each receiver was connected to its own independent aerial wire, hung from the same mast. But greater wonders followed. Mr. Marconi placed the receivers at Poole one on the top of the other, and connected them both to one and the same wire, about forty feet in length, attached to the mast. I then asked to have two messages sent at the same moment by the operator at St. Catherine's, one in English and the other in French. Without failure, each receiver at Poole rolled out its paper tape, the message in English perfect on one, and that in French on the other. When it is realized that these visible dots and dashes are the result of trains of intermingled electric waves rushing with the speed of light across the intervening thirty miles, caught on one and the same short aerial wire and disentangled and sorted out automatically by the two ma- chines into intelligible messages in different languages, the wonder of it all cannot but strike the mind. Your space is too valuable to be encroached upon by further details, or else I might mention some marvelous results exhibited by Mr. Marconi during the same demonstrations, of messages received from a transmitter thirty miles away, and recorded by an instrument in a closed room merely by the aid of a zinc cylinder, four feet high, placed on a chair. 1 More surprising is it to learn that, while these experiments have been proceeding between Poole and St. Catherine's, others have been taking place for the admiralty between Portsmouth and Portland, these lines of communication intersecting each other; yet so perfect is the independence that nothing done on one circuit now affects the other, unless desired. Mr. Marconi has insisted that his transmitted signals are perfectly localized. He has even challenged Professor Lodge and Mr. Preece either to interrupt or to intercept them, offering the use of his company's stations should those eminent scientists desire to experiment. If, however, they try, and fail to catch the signals, it does not follow that human ingenuity will never succeed in doing so. Un- less, indeed, Marconi has means other than those generally known to the electrical profession, it is believed that "syn- tony," as it is called, is a combination not difficult to unlock. 1 See Fig. 37, Part II. EXPLANATORY. 35 The company's experts claim first, that their spark-gap will not be known to unauthorized persons ; again, that their coherer may be made so insensitive that it will an- swer only to a considerable force at the sending station, and that all energies less than theirs will not affect it ; again, that in addition to a knowledge of the force required it will be necessary for the intercepter to know the self-induction ( the load ) and the condenser effect (the resiliency). It would seem, however, that it is not necessary to ascertain each of these facts, but merely to find the rate of beat to which the coherer will respond, and that may be any combination of load and spring which will produce the right wave-motion. If, then, a would-be tapper-in exposes a number of coherers differ- ently sensitized, and with each coherer connected with a maximum or a minimum condenser effect, he will need only to vary the load upon each coherer, which may be very rapidly done. Having found the "rate," he may "interrupt " as well as " intercept." QUANTITATIVE DATA. Power. In quantitative terms authorized statements in the March Century, 1902, give the energy used in the Cornwall-Newfoundland transmission as being supplied by a 40 h. p. alternating current dynamo, having an initial pressure of two thousand volts which was "stepped up" to fifty thousand volts. There were at Poldhu twenty 1 masts, each two hundred and ten feet high, the conductors upon each mast being in electrical connection with all the others. The metal spheres forming high-tension terminals 1 See Fig. 66, Part IV. 36 WIRELESS TELEGRAPHY. of the transformers were separated by a distance which varied from about ^ inch to about -f^ inch. At the Newfoundland station the aerial wire was elevated by a kite to an altitude of about four hundred feet ; its swaying varied the altitude, which variation was a serious obstacle to the uniform reception of signals. The coherer used was a small glass tube one and one-half inches long and one-tenth inch internal diameter. Within the tube were tightly fitted two silver plugs separated ^ inch. This lit- tle space was partly filled with a mixture of nickel and sil- ver filings to which a trace of mercury had been added. 1 Comparative Speed of Signal Propagation by Wireless Telegraph and by Cables. Marconi has said to his Eng- lish stockholders that whereas the speed of the submarine cable- is directly affected by length of transmission, the wireless system is not in the least affected by distance. That "it is just as easy to work at high speed across the Atlantic or Pacific as to work across the English Channel." He is confident of establishing direct communication be- tween England and New Zealand. 2 He says that the curv- ature of the earth does not affect the signals, and that ultimately he will be able to send them all around the world. Marconi's Conclusions. From that excellent article in the Century Magazine of March, 1902, already mentioned, there is a summing up of Marconi's conclusions at that date. Wireless telegraphy is most effective over marine areas. Over low lying country two-thirds of marine distance may *- See description of " silver coherer " in Part IV. 2 See chart, Fig. 39. EXPLANATORY. 37 be reached, but over ordinary diversified country the po- tency of vibrations is reduced to one-half what it is at sea. High hills do not constitute an obstacle, but the ground itself retards the signals. The vibrations seem to reach slightly farther in fog than in fine weather. Atmospheric conditions do not seriously affect the signals. Electrical disturbances are their only foe. Indications are that a pole two hundred feet high gives the best results. With a a balloon or kite elevated to four hundred feet, the wire must necessarily be very slight, and the ceaseless swaying of the upholder also interferes. A horizontal wire (as an antenna) gives no energy. No advantage in marine signal- ing is gained by setting a pole on a high hill. Proximity to the sea is desirable and a low-lying spit of land the best. Some geological formations are perverse, others are respon- sive. 38 WIRELESS TELEGRAPHY. DESCRIPTIVE. TESLA 1 IN WIRELESS TRANSMISSION. Tesla's Proposed Plan of 1893. Nikola Tesla devoted himself early to the problem of transmitting electrical energy without wires, not only for telegraphic, but also for industrial purposes. In February and March, 1893, he delivered lectures before the Franklin Institute in Phila- delphia and the National Electric Light Association in St. Louis, in which he advanced a plan of wireless transmis- sion, and expressed his conviction that " it certainly is possible to produce some electrical disturbance sufficiently powerful to be perceptible by suitable instruments at any point of the earth's surface." In describing his plan in detail he says : " Assume that a source of alternating currents, j, be connected, as in Fig. 10, with one of its terminals to earth (convenient to the water mains), and Fig. 10. with the other to a body of large surface, P. When the electric oscillation is set up, there will be a movement of electricity in and out of P, and 1 TESLA, NIKOLA, born at Smiljan, Lika, Austria-Hungary, in 1857. A noted physicist and electrician. He came to the United States in 1884 with a view of developing motors based on his discovery of the rotating magnetic field ; this he completed in 1888. He has in- vented a number of methods and appliances in the line of electrical vibrations aiming at the production of efficient light with lamps without filaments, and the production and transmis- sion of power and intelligence without wires. On his discovery of the action of air or gase- ous matter when subjected to rapidly alternating electrostatic stresses is based the modern art of insulating currents of very high tension. He has also constructed steam-engines and electrical generators (oscillators) with which otherwise unattainable results are obtained. Century Dictionary and Cyclopedia, 1895. WIRELESS TELEGRAPHY. 39 alternating currents will pass through the earth, converging to or diverging from the point C, where the ground connection is made. In this manner neighboring points on the earth's surface within a certain radius will be disturbed. But the disturbance will diminish with the distance, and the distance at which the effect will still be perceptible will depend on the quantity of electricity set in motion. Since the body P is insulated, in order to displace a considerable quantity the potential of the source must be excessive, since there would be limitations as to the surface of P. The conditions might be adjusted so that the generator, or source, s, will set up the same electrical movement as though its circuit were closed. Thus it is certainly practicable by means of proper machinery to impress an electric vibration, at least of a certain low period, upon the earth. Theo- retically it should not require a great amount of energy to produce a dis- turbance perceptible at great distance, or even all over the surface of the globe. Now, it is quite certain that at any point within a certain radius of the source, s, a properly adjusted self-induction and capacity device can be set in action by resonance. Not only can this be done, but another source, s, 1 Fig. 10, similar to s or any number of such sources may be set to work in synchronism with the latter, and the vibration thus intensified and spread over a large area ; or a flow of electricity produced to or from the source s, 1 if the same be of opposite phase to the source, s. Proper apparatus must first be produced, by means of which the problem can be attacked, and I have devoted much thought to this subject." In the same lectures he showed a number of novel ex- periments, among which was the operation of a variety of devices by using one wire, instead of two as is usual in elec- trical connections. He continued investigations along these lines, and in 1898 had already developed apparatus of great power, giving a pressure of four million volts and dis- charges extending through sixteen feet, which at that time were considered remarkable. 1 Tesla's First Two Patents on Methods and Apparatus for the Wireless Transmission of Energy. The patents are numbered 645,576 and 649,621, and were issued 1 See Electrical Review, New York, October 26, 1898. 40 DESCRIPTIVE. Fig. xi. Diagram of wireless transmission accompanying Tesla's U. S. patents No. 645,576 and No. 649,621. The transmitter comprises a generator of electric oscillations G, a primary conductor C, and a secondary coil A B, which is connected to ground and to an elevated terminal D, and tuned to the oscillations of the generator. The receiving apparatus has a similarly arranged coil A' D' tuned to the transmitted oscillations, and associated with a secondary circuit containing the receiving devices. The terminals D and D' are maintained above the surrounding objects, the height being determined by the amount and quality of the work to be performed. The length of the grounded conductors A D and A' D' is preferably made equal to one quarter of the wave length of the oscillations. The trans- mitter and receiver may be thousands of miles apart. DESCRIPTIVE. 41 respectively March 2Oth, and May I5th, 1900. The origi- nal application covering both inventions was filed September 2nd, 1 897. The system, as described by the inventor in these patents, is radically different from the Hertzian, both in the methods and apparatus employed. In the Hertzian system, the energy is transmitted to the receiver by elec- tro-magnetic waves which pass out laterally from the transmitting wire into space. In Tesla's system the energy radiated is not used, but a current is led to earth and to an elevated terminal, and the energy is transmitted by a process of conduction. Quoting from one of his patents : " It is to be noted that the phenomenon here involved in the trans- mission of electrical energy is one of true conduction, and is not to be confounded with the phenomena of electrical radiation which have here- tofore been observed, and which, from the very nature and mode of propa- gation, would render practically impossible the transmission of any appreci- able amount of energy to such distances as are of practical importance." The arrangement of his transmitting and receiving circuits is illustrated in Fig. n, and will be understood with reference to the explanatory note. As characteristic of these inventions the following two claims may be quoted : " The method hereinbefore described of transmitting electrical energy through the natural media, which consists in producing at a generating station a very high electrical pressure, causing thereby a propagation or flow of electrical energy, by conduction, through the earth and the air strata, and collecting or receiving at a distant point the electrical energy so propagated or caused to flow. The combination with a transmitting coil or conductor connected to ground and to an elevated terminal respectively, and means tor producing electrical currents or oscillations in the same, of a receiving coil or conduc- tor similarly connected to ground and to an elevated terminal, the said coil or coils having a length equal to one quarter of the wave length of the disturbance propagated, as set forth." 42 WIRELESS TELEGRAPHY. Description of Transmitter Giving Four Million Volts. - In describing a special apparatus Tesla says : " The transmitting apparatus was in this case one of my electrical oscillators, which are transformers of a special type, now well known and characterized by the passage of oscillatory discharges of a condenser through the primary. The source G, forming one of the elements of the transmitter, was a condenser of a capacity of about four one-hundr.edths of a microfarad, and was charged from a generator of alternating currents of fifty thousand volts pressure, and discharged by means of a mechanically operated break five thousand times per second through the primary C. The latter consisted of a single turn of stout, stranded cable of inappreciable resistance and of an inductance of about eight thousand centimeters, the diameter of the loop being very nearly two hundred and forty-four centime- ters. The total inductance of the primary circuit was approximately ten thousand centimeters, so that the primary circuit vibrated generally accord- ing to adjustment, from two hundred and thirty thousand to two hundred and fifty thousand times per second. The high-tension coil A in the form of a flat spiral was composed of fifty turns of heavily insulated cable No. 8 wound in one single layer, the turns beginning close to the primary loop and ending near its center. The outer end of the secondary or high-tension coil A was connected to the ground. The primary and secondary circuits in the transmitting apparatus being carefully synchronized, an electromotive force from two to four million volts and more was obtainable at the terminals of the secondary coil A." Curious Phenomena Produced. Tesla's apparatus seems to be capable of peculiar actions. He says : " For example, a conductor or terminal, to which impulses such as those here considered are supplied, but which is otherwise insulated in space and is remote from any conducting-bodies, is surrounded by a luminous flame-like brush or discharge often covering many hundreds or even as much as several thousands of square feet of surface, this striking phenomenon clearly attesting the high degree of conductivity which the atmosphere attains under the influence of the immense electrical stresses to which it is subjected. This influence is, however, not confined to that portion of the atmosphere which is discernible by the eye as luminous, and which, as has been the case in some instances actually observed, may fill the space within a spherical or cylindrical envelope of a diameter of sixty feet or more, but reaches out to far remote regions, the insulating qualities of the air being, NIKOLA TESLA. DESCRIPTIVE. 43 as I have ascertained, still sensibly impaired at a distance many hundred times that through which the luminous discharge projects from the terminal and in all probability much farther." The conductivity imparted to the air by these currents Tesla proposes to utilize in the wireless transmission of power on an industrial scale. Transmission of Enormous Energy Over Vast Dis- tances. " From my experiments and observations I con- clude tJiat with electromotive impulses not greatly exceeding fifteen or tiventy million volts the energy of many thousands of Jiorse-poiver may be transmitted over vast distances, measured by many hundreds and even thousands of miles, vvitJi terminals not more than thirty to thirty-five tJiousand feet above the level of the sea ; and even this comparatively small elevation will be required chiefly for reasons of econ- omy, and if desired it may be considerably reduced, since, by such means as have been described, practically any potential that is desired may be obtained and the currents through the air strata may be rendered very small, whereby the loss in the transmission may be reduced. It will be understood that the transmitting as well as the receiving coils, transformers, or other apparatus may be in some cases movable as, for example, when they are carried by vessels floating in the air, or by ships at sea." To express this idea in other language, if one captive balloon were put at seven miles' elevation over Niagara Falls, and another balloon at the same height in France, energy from a dynamo at the former station might without undue loss in transmission be made to set in motion upon French territory electric motors, or to supply the power to illumine electric lamps. 44 WIRELESS TELEGRAPHY. Tesla's "Telautomata." On July i, 1898, Mr. Tesla filed an application for another American Patent, No. 613,809. Its first claim is an excellent brief. It reads : " The improvement in the art of controlling the movements and opera- tion of a vessel or vehicle herein described, which consists in producing waves or disturbances which are conveyed to the vessel by the natural media, actuating thereby suitable apparatus on the vessel and effecting the control of the propelling engine, the steering and other mechanism by the operation of the said mechanism as set forth." Methods Described. The inventor describes a number of methods for producing waves. The preferred one seems to be the " passing through the conducting path currents of a specially designed high frequency alternator, or, better still, those of a strongly charged condenser," and then "adjusting the circuit on the moving body so as to be in exact electromagnetic synchronism with the primary dis- turbances ; " and he says that in such a way " this in- fluence may be utilized at great distances." Application to Warfare. In summing up the many use- ful purposes to which this invention may be applied, the pantentee thinks its " greatest value will result from its effect upon warfare and armaments, for by reason of its certain and unlimited destructiveness it will tend to bring about and maintain perfect peace among nations." It may be inferred that this refers more especially to the moving and direction of torpedoes. In the Tesla system methods of electrical conversion by means of condenser discharges and the so-called "Tesla coil " play an important part. The earliest records of these inventions in the U. S. Patent Office date from 1891. DESCRIPTIVE. . 45 v, Method of Electrical Conversion by Condenser Dis- charges. This method is described in Patent Number 462,418 of November 3, 1891 (application filed February 4, 1891). Quoting in the language of the inventor : " I employ a generator, preferably of very high tension, and capable of yielding either direct or alternating currents. This generator I connect up with a condenser or conductor of some capacity, and discharge the accumu- lated electrical energy disruptively through an air-space or otherwise into a working circuit containing translating devices and, when required, conden- sers. These discharges may be of the same direction or alternating and intermittent, succeeding each other more or less rapidly or oscillating to and fro with extreme rapidity. In the working circuit, by reason of the condenser action, the current impulses or discharges of high tension and small volume are converted into currents of lower tension and greater vol- ume. The production and application of a current of such rapid oscillations or alternations (the number may be many millions per second) secures, ( T i B c ) ( ^ Qc fj T Fig. 12. among others, the following exceptional advantages: First, the capacity of the condensers for a given output is much diminished ; second, the efficiency of the condensers is increased and the tendency to become heated reduced ; and, third, the range of conversion is enlarged. I have thus suc- ceeded in producing a system or method of conversion radically different from what has been done heretofore first, with respect to the number of impulses, alternations, or oscillations of current per unit of time, and, second, with respect to the manner in which the impulses are obtained. To express this result, I define the working current as one of an excessively small period or of an excessively large number of impulses or alternations or oscil- lations per unit of time, by which I mean not a thousand or even twenty or thirty thousand per second, but many times that number, and one which is made intermittent, alternating, or oscillating of itself without the employ- ment of mechanical devices." 46 WIRELESS TELEGRAPHY. Referring to the diagram in Fig. 1 2 : " A represents a generator of high tension ; B B, the conductors which lead out from the same. To these conductors are connected the conduc- tors C of a working circuit containing translating devices, such as incandes- cent lamps or motors G. In one or both conductors B is a break D, the two ends being separated by an air-space or a film of insulation, through which a disruptive discharge takes place. F is a condenser, the plates of which are connected to the generating-circuit. The discharges will follow each other the more rapidly the more nearly the rate of supply from the generator equals the rate at which the circuit including the generator is capable of taking up and getting rid of the energy. Since the resistance and self-induction of the working circuit C and the rapidity of the successive discharges may be varied at will, the cur- rent strengths in the working and in the generating circuit may bear to one another any desired relation. Tesla Coil. This invention is first described in Patent No. 454,622 of June 23, 1891 (application filed April 5th, 1891). In the description the inventor says : " To produce a current of very high frequency and very high potential, certain well-know r n devices may be employed. For instance, as the primary source of current or electrical energy, a continuous-current generator may be used, the circuit of which may be interrupted with extreme rapidity by mechanical devices, or a magneto-electric machine specially constructed to yield alternating currents of very small period may be used, and in either case, should the potential be too low, an induction-coil may be employed to raise it ; or, finally, in order to overcome the mechanical difficulties, which in such cases become practically insuperable before the best results are reached, the principle of the disruptive discharge may be utilized. By means of this latter plan I produce a much greater rate of change in the current than by the other means suggested, and in illustration of my invention I shall confine the description of the means or apparatus for pro- ducing the current to this plan, although I would not be understood as limiting myself to its use. The current of high frequency, therefore, that is necessary to the successful working of my invention, I produce by the dis- ruptive discharge of the accumulated energy of a condenser maintained by charging said condenser from a suitable source and discharging it into or through a circuit under proper relations of self-induction, capacity, resist- DESCRIPTIVE. 47 ance, and period, in well -understood ways. Such a discharge is known to be, under proper conditions, intermittent or oscillating in character, and in this way a current varying in strength at an enormously rapid rate may be pro- duced. Having produced in the above manner a current of excessive fre- quency, I obtain from it by means of an induction-coil enormously high potentials that is to say, in the circuit through which or into which the disruptive discharge of the condenser takes place I include the primary of a suitable induction-coil, and by a secondary coil of much longer and finer wire I convert to currents of extremely high 'potential." With reference to the diagram Fig. 13. " G is the primary source of current or electrical energy. I have explained above how various forms of generator might be used for this purpose ; but in the present illustration I assume that G is an alternating-current generator of comparatively low electromotive force. Under such circumstances I raise the potential of the current by means of an induction-coil hav- ing a primary P and a secondary S. Then by the current developed in this secondary I charge a condenser C, and this condenser I discharge through or into a circuit A, having an air-gap a, or, in general, means for maintaining a disruptive dis- charge. By the means above de- scribed a current of enormous fre- quency is produced. My object is next to convert this into a working- circuit of very high potential, for which purpose I connect up in the circuit A the primary P'of an induction coil having a long fine wire secondary S'. The current in the primary I" develops in the secondary S' a current or electrical effect of corresponding frequency, but of enormous difference of potential." Tesla has invented and patented numerous modifications of apparatus embodying these principles. One of the fea- tures in his later patents, for which great advantages are claimed, is a series of tuned circuits of high frequency exciting one another. Fig. 13. 48 WIRELESS TELEGRAPHY. System of Concatenated Tuned Circuits In his patent No. 568,178 of September 22, 1896 (application filed June 20, 1896), the inventor says in setting forth the invention: " It is well known that every electric circuit, provided its ohmic resistance does not exceed certain definite limits, has a period of vibration of its own analogous to the period of vibration of a weighted spring. In order to alternately charge a given circuit of this character by periodic impulses impressed upon it, and to discharge it most effectively, the frequency of the impressed impulses should bear a definite relation to the frequency of vibra- tion possessed by the circuit itself. Moreover, for like reasons, the period or vibration of the discharge-circuit should bear a similar relation to the impressed impulses or the period of the charging-circuit. When the con- ditions are such that the general law of harmonic vibrations is followed, the circuits are said to be in resonance or in electromagnetic synchronism, and this condition I have found in my system to be highly advantageous. Hence, in practice, I adjust the electrical constants of the circuits so that in normal operation, this condition of resonance is approximately attained. Any departure from this condition will result in a decreased output, and this fact I take advantage of in regulating such output by varying the fre- quencies of the impulses or vibrations in the several circuits. Inasmuch as the period of any given circuit depends upon the relations of its resistance, self induction, and capacity, a variation of any one or more of these may result in a variation in its period. There are, therefore, vari- ous ways in which the frequences of vibration of the several circuits in the system referred to may be varied, but the most practicable and efficient ways of accomplishing the desired result, are the following : (a) varying the rate of the impressed impulses of current, or those which are directed from the source of supply into the charging-circuit, as by varying the speed of the commutator or other circuit-controller; (b) varying the self-induction of the charging-circuit ; (c) varying the self-induction or capacity of the dis- charge circuit. Intensifying Electric Oscillations by Means of Refriger- ant. Another suggestion from Mr. Tesla is to employ as a means of increasing the intensity of electric oscillations a refrigerant. He says that " when a circuit adapted to vibrate freely is maintained at a low temperature, the THE TESLA WIRELESS PLANT ON LONG ISLAND. DESCRIPTIVE. 49 oscillations excited in the same are to an extraordinary degree magnified and prolonged, and that he is thus enabled to produce many valuable results which have heretofore been wholly impracticable " The cooling agent may be any freezing mixture. Liquid air is instanced. In the transmission of etheric waves, he would apply this refriger- ant to coils both at the transmitting and at the receiving ends. He says that the circuits at either end of the trans- mission should have the greatest possible self-induction and the smallest possible resistance. The invention is fully described in Patent No. 685,012 of October 22, 1901. (Application filed March 21, 1900.) Methods of Storing the Energy Transmitted, and Strength- ening Feeble Impulses. In another series of patents, bear- ing the numbers 685,953, 685,954, 686,955, and 685,956, all granted in 1901, Tesla advances other improvements in the transmission and utilization of electrical energy. The fundamental idea underlying these inventions is to store the energy transmitted in a condenser during any desired time interval, and to utilize the stored energy, either directly to operate a receiving device, or to control anothef circuit including the same. In a modification of the apparatus the latter circuit charges a condenser, and the impulses transmitted are used to control the charge of the con- denser. In order to effect a charging by the impulses conveyed from distance, they are commutated either by a mechanical device or by means of an electric valve with stationary electrodes. In a special arrangement shown, the energy accumulated in the condenser is discharged through the primary of an induction coil, the secondary of which is used for the purpose of controlling the operation of a 50 WIRELESS TELEGRAPHY. delicate receiver. In this way almost any degree of sensi- tiveness which may be desired can be attained. On this point the inventor says : " It will be seen that by the use of my invention results hitherto unattainable in utilizing disturbances or effects transmitted through natural media may be readily attained, since, however great the distance of such transmission, and however feeble or attenuated the impulses received, enough energy may be accumulated from them by storing up the energy of succeeding impulses for a sufficient interval of time to render the sudden liberation of it highly effective in operating a receiver." Improved Mercury Interrupters. In order to avoid waste of energy and deterioration of the electrodes, Tesla has designed a great variety of mercury interrupters, on which he has obtained a number of patents dated 1897 and 1898. In these devices the circuit is made and broken in an hermetically inclosed space and the wear of the elec- trodes entirely prevented, the contact surfaces being con- stituted of mercury. In some forms an inert gas under great pressure is employed to improve the action, the inventor claiming that he has discovered that "a gas under great compression nearly fulfills the ideal requirements." New Methods of Individualization. Instead of relying on simple tuning, Tesla has developed a new principle, which is set forth in his last two patents bearing the numbers 723,- 188 and 725,605 (original application filed July 16, 1900). In this invention the transmitter is made to give two, or a greater number, of different vibrations, simultaneously or in a certain order of succession. The receiver again has a number of tuned circuits, each of which responds to one of the vibrations of the transmitter, and the arrange- ment is such that only when all the receiving circuits are DESCRIPTIVE. 51 affected the indicating instrument is made to operate. By the use of this principle " a degree of safety against mutual and extraneous interference is attained, such as is comparable to that of a combination lock." On the other hand, any desired number of instruments can be simultane- ously operated through the earth or other conducting channel. The improvement is not limited to wireless telegraphy. " It will be seen," says the inventor, "from a consideration of the nature of the method, that the inven- tion is applicable not only in the special manner described, in which the transmission of the impulses is effected through the natural media, but for the transmission of energy for any purpose and whatever the medium through which the impulses are conveyed." Marvelous Effects Produced by Oscillators of Great Power. Early in 1889 Tesla went to Colorado to develop his methods and apparatus for the transmission of wireless energy, and to ascertain the laws of propagation of electri- cal waves through the earth. Upon his return he published an article which appeared in the " Century " of June, 1900, in which photographic views of some experiments with one of his oscillators were shown. It appears that with these machines there is no limit to the intensity of the effects and magnitude of the forces produced. According to Tesla even interplanetary space may be bridged by the terrific commotions of such an oscillator. He says : " However extraordinary the results shown may appear, they are but trifling compared with those which are attainable by apparatus designed on these same principles. I have produced electrical discharges, the actual path of which, from end to end, was probably more than one hundred feet long; but it would not be difficult to reach lengths one hundred times as 52 WIRELESS TELEGRAPHY. great. I have produced electrical movements occurring at the rate of ap- proximately one hundred thousand horse-power, but rates of one, five, or ten million horse-power are easily practicable. In these experiments effects were developed incomparably greater than any ever produced by human agencies, and yet these results are but an embryo of what is to be. That communication without wires to any point of the globe is practi- cable with such apparatus would need no demonstration, but through a dis- covery which I made I obtained absolute certitude. Popularly explained, it is exactly this : When we raise the voice and hear an echo in reply, we know that the sound of the voice must have reached a distant wall or boundary, and must have been reflected from the same. Exactly as the sound, so an electrical wave is reflected ; and the same evidence which is afforded by an echo is offered by an electrical phenomenon known as a " stationary " wave that is, a wave with fixed nodal and ventral regions. Instead of sending sound-vibrations toward a distant wall, I have sent elec- trical vibrations toward the remote boundaries of the earth, and instead of the wall the earth has replied. In place of an echo I have obtained a sta- tionary electrical wave, a wave reflected from afar. Stationary waves in the earth mean something more than mere tele- graphy without wires to any distance. They will enable us to attain many important specific results impossible otherwise. For instance, by their use we may produce at will, from a sending-station, an electrical effect in any particular region of the globe; we may determine the relative position or course of a moving object, such as a vessel at sea, the distance traversed by the same, or its speed ; or we may send over the earth a wave of elec- tricity traveling at any rate we desire, from the pace of a turtle up to lightning speed." One of the experiments produced with a comparatively small machine of this kind is illustrated in Fig. 14. As no person could be anywhere in the vicinity when the dis- play is going on, the picture was obtained by two succes- sive processes, the image of Mr. Tesla's assistant being taken at one exposure and the electrical discharges photo- graphed at another. Combined upon one plate they show relative sizes of the streams of light as compared with a human being. An idea of the force and volume of the sparks may be gained when it is stated that the thick- . X sS 5 2 11 S S W III' ^ rt ^ p^ S > ^ Q P DESCRIPTIVE. 53 est of them are about 23 feet long, and that a current of approximately 800 amperes is passing through the air. The roar of such a discharge can be heard several miles. Since his return from Colorado in 1901 Tesla has begun the erection of commercial plants ; but since two years nothing has been published about his work. It is under- stood that his wireless plant on Long Island is nearing completion. A photographic view of the same is shown in the illustration opposite page 49. The structure presents a curious appearance. As to the purpose for which the plant is designed, nothing has, as yet, been announced by Tesla. Recently, however, the " New York Sun " in an editorial authorized by him, stated that "the Tesla oscillator will deliver to the earth the shock that will be felt and recorded on its uttermost confines." Tesla's Sun-Motors. Fig. 15 and 16 illustrate other devices by the same inventor. These are called " appara- tus for the utilization of radiant energy." In Fig. 15, P is a plate exposed to rays, and P' a plate buried in the ground. C is a condenser, the plates of which should present as large a surface as possible, the inventor having ascertained the amount of energy con- veyed to it per unit of time to be, under otherwise identi- cal conditions, proportioned to the area exposed or nearly so. T and T' are terminals of condenser C. Ma relay magnet or any other device capable of being actuated by an electric current. , a local battery ; c, a condenser ; e, a connection to earth or other suitable capacity INVENTORS AND INVENTIONS. 107 /, a sensitive tube or imperfect contact ; k are choking-coils, and r a relay working a signaling or other instrument. The diagrams of the coils are greatly enlarged half-longitudinal sections, but are not strictly to scale. In place also of showing the section of each coil or layer of wire as a longi- tudinal row of dots or small circles, as it would actually appear, it is for simplicity shown as a single continuous longitudinal straight line. A is the end of the primary, w r hich is connected to the aerial conductor #, and E is the end connected to earth or a capacity. J is the end of the secondary, which is directly connected to the sensitive tube or imperfect contact/, and C is the end which is connected to it through the condenser. G is a glass tube on which the coils are wound. The wires are preferably insulated by a single covering of silk." Claims I, 2, and 16 fairly illustrate the inventive scope of the first one of this group, No. 647,007, and are as follows : CLAIM i. In a receiver for electrical oscillations, the combination of an imperfect electrical contact, a local circuit through it, an induction-coil, the secondary of which consists of several layers, the number of turns in the outer layers being less than in those next the primary, a capacity connected to one end of the primary, a conductor connected to the other end, and connections between the ends of the imperfect contact and the ends of the secondary. CLAIM 2. In a receiver for electrical oscillations, the combination of an imperfect electrical contact, a local circuit through it, an induction-coil, the secondary of which consists of several layers, the number of turns in the outer layers being less than in those next the primary, a capacity connected to one end of the primary, a conductor connected to the other end, con- nections between the ends of the imperfect contact and the ends of the secondary, and a condenser in one of the latter connections, CLAIM 16. In a receiver for electrical oscillations, the combination of an imperfect electrical contact, a local circuit through it, an induction-coil, the primary of which consists of two wires connected in parallel, wound in four layers, the first and second layers being formed of one wire and the third and fourth of the other, the secondary of which consists of several layers, the number of turns in the outer layers being less than in those next the primary, and wound unsymmetrically with a lump at one end, a capacity connected to one end of the primary, a conductor connected to the other I0 8 WIRELESS TELEGRAPHY. end, connections between the ends of the imperfect contact and the ends of the secondary, and a condenser in one of the latter connections. Claims /, 2, and 4 of the second of tJie group are inserted to show the distinctive features of that patent. Words are Italicized by the author to mark a phrase which does not occur in the first patent, but is found in all three of the following claims : CLAIM i. In a receiver for electrical oscillations, the combination of an imperfect electrical contact, a local circuit through it, an induction-coil, the secondary of which consists of several layers, the number of turns in the outer layers being less than in those next the primary, a capacity connected to one end of the primary, a conductor connected to the other end, connec- tions between the ends of the imperfect contact and the ends of the sec- ondary, and a condenser in the connection to the inner end of the secondary, CLAIM 2. In a receiver for electrical oscillations, the combination of an imperfect electrical contact, a local circuit through it, an induction-coil, the secondary of which consists of several layers, the number of turns in the outer layers being less than in those next the primary, and wound unsym- metrically with a lump at one end, a capacity connected to one end of the primary, a conductor connected to the other end, connections between the ends of the imperfect contact and the ends of the secondary, and a con- denser in the connection to the inner end of the secondary. CLAIM 4. In a receiver for electrical oscillations, the combination of an imperfect electrical contact, a local circuit through it, an induction-coil, the primary of which consists of two wires connected in parallel, wound in two layers, the secondary of which consists of several layers, the number of turns in the outer layers being less than in those next the primary, and wound unsymmetrically with a lump at one end, a capacity connected to one end of the primary, a conductor connected to the other end, connec- tions between the ends of the imperfect contact and the ends of the sec- ondary, and a condenser in the connection to the inner end of the secondary. Of the last of the series but one claim, the sixteenth, is shown where the Italicized word " two " is its only distinc- tion from claim 16 of the first of the series, in which the word " four " is also found in Italics. INVENTORS AND INVENTIONS. IOQ CLAIM 16. In a receiver for electrical oscillations, the combination of an imperfect electrical contact, a local circuit through it, an induction-coil, the primary of which consists of two wires connected in parallel, wound in two layers, the secondary of which consists of several layers, the number of turns in the outer layers being less than in those next the primary, and wound unsymmetrically with a lump at one end, a capacity connected to one end of the primary, a conductor connected to the other end, connec- tions between the ends of the imperfect contact and the ends of the sec- ondary, and a condenser in one of the latter connections. INVENTION OF IMPROVED TRANSMITTING KEYS, SEVENTH AND EIGHTH AMERICAN PATENTS OF MARCONI. Patent No. 650,110, filed December 28, 1899, * s a modi- fication of No. 650,109, filed on October 12 of the same year. The diagram which illustrates the former is shown as Fig. 77 in connection with " Keys," Part IV. The difference between the two patents is that in the first a connection is made from that electrode of the spark-gap which connects with the high wire to an insulated back terminal on the sending-key of the transmitting operator ; while in the second patent the high wire connecting directly with the insulated back terminal of the transmit- ting key does not make actual contact with the electrode of the spark-gap, but, instead, is brought very near to it. The first claim of 650,109 is as follows : CLAIM i. The combination of the primary and secondary of a sparking appliance, a battery and key in circuit w r ith the primary, an aerial conductor connected to one terminal of the secondary, a receiver, means for connect- ing the said terminal to the receiver, and a capacity connected to the other terminal. In the second claim there are substituted for the last eight words of Claim i the words " and an earth connec- tion connected to the other terminal." The first claim of No. 650,110 is as follows: I IO WIRELESS TELEGRAPHY. CLAIM i. The combination of the primary and secondary of a spark- ing appliance, a battery and key in circuit with the primary, an aerial con- ductor led in close proximity to one terminal of the secondary, means for connecting the said aerial conductor to the receiving instrument, and a capacity connected to the other terminal. The change of phrase noted in the companion patent, whereby " capacity " is substituted for "earth connection,'' occurs here also. NINTH AMERICAN PATENT OF MARCONI. In Fig. 34 there is shown a new set of connections in which the secondary winding of a step-down induction coil is divided into two parts, a condenser is placed between the two parts, and the relay circuit is connected to them on each side of that condenser. This diagram is the principal drawing of U. S. Patent No. 668,315, issued on February 19, 1901, the application for which, however, was filed July 17, 1900. While it is not the broadest claim, No. 4 offers the best brief to illustrate the invention. It is given here with interpolated explanatory references as follows : CLAIM 4. In a receiver for electrical oscillations, the combination of an induction coil, the secondary of which is wound in two parts (see /2, Fig. 34), an aerial conductor connected to one end of the primary (A), a capacity connected to the other end of the primary (E), a detector or coherer connected to the outer ends of the secondary (T), a condenser across the inner ends of the secondary (73), a local circuit connected to the condenser (BR), choking coils between the local circuit and condenser (ClC2). INVENTORS AND INVENTIONS. I II No. i, the broadest claim, has but five elements, and reads as follows : CLAIM i. In a receiver for electrical oscillations, the combination of an induction-coil, the secondary of which is wound in two parts, an aerial con- ductor connected to one end of the primary, a capacity connected to the other end of the primary, a detector connected to the outer ends of the secondary, and a local circuit connected to the inner ends of the secondary. The wording of one part of the specification leads to the belief that at the date of its filing, July 17, 1900, the in- ventor was beginning to question the efficacy of the Fig. 35- Fig. 36. tmsymmetrical winding advocated in former patents, al- though he still gives to it, as Fig. 35, precedence in order of description. The arrangement shown in Fig. 36, how- ever, is spoken of as one from which " very good results have been obtained." In it each half of the secondary consists of one hundred and sixty turns in a single layer. The specification states that in using coils in which the second- ary winding consists of one layer, the inventor had noticed that the best results were had when the length of the secondary winding was approximately equal to the length of the aerial conductor employed at the transmitting station, an observation somewhat in line with Professor Slaby's assertion that there is a law of transmission which governs the length both of the emitter and the antenna. 1 1 See in connection with Slaby, p. 58. 112 WIRELESS TELEGRAPHY. DOUBLE WAVE-GATES. TENTH AMERICAN PATENT OF MARCONI. At this writing the final Marconi patent, so far as known, is No. 676,332. The application was filed Febru- ary 23, 1901, and it was issued on June 11 of the same year. It relates to the employment of double emitters . -~<5flffl^|-0 ^-1 t e \ L vWW\AV- J Fig. 37- and antennae. These double conductors are shown either as concentric cylinders separated by an appreciable air- space, or as two distinct vertical wires, or as an aerial terminal consisting of two conductors arranged concentri- cally, the inner one being a solid wire covered with an insulating substance, and the outer being a tube fitting closely around the insulation of that which forms the core. INVENTORS AND INVENTIONS. 113 The typical diagram is Fig. 37, in which it may be noted that the inner conductor has one branch to earth and one through an inductance and the spark-gap to the outer one. In other drawings the patentee shows at the transmitting station the wire connecting secondary coil c with induct- ance i to the left as having a pointed top, and resting against one of the coils of z, thus indicating that the inductance may be varied. The scope of this final Mar- coni patent may be shown by an analysis of its five claims as follows : CLAIM i. Element one, Two aerial oscillation-producing conductors insulated from each other. Element two, An inductance connected in series with such conductors. Element three, A producer of electric oscillations (a Ruhmkorff coil, for instance). Element four, A signaling instrument controlling the spark-producer (as a key in the primary circuit). 1 CLAIM 2. There is added to the combination in claim i a fifth element, a connection from one of the emitters to the earth. CLAIM 3. Element one of first claim is modified by the statement that the two aerial oscillation-producing conductors are insulated from each other. CLAIM 4. Pertains to a receiving station and has four elements: One. Two antennae insulated from each other. Two. An inductance con- nected in series with the two antennae. Three. An imperfect electrical contact. CLAIM 5. Adds to the combination in claim 4 a connection from one of the antennae to the earth. There occurs in the specification of the patent now under consideration the remark that while " Lodge shows two large oscillation-producing conductors and an induct- ance device connected between them," yet he does not "use a plurality of aerial oscillation-producing conduc- tors." 2 1 Parenthetical phrases supplied by author. 2 See claims 6 and 8, Lodge's patent, No. 609,154, p. 101, Part II. 114 WIRELESS TELEGRAPHY. THE WIRELESS TRANSMISSION PATENTS OF TESLA. A number of inventions by Mr. Nikola Tesla have been described at length in Part I. Their relation to the general patent situation is, however, so complex, and may prove so far reaching that anything like an exhaustive discussion of such of his numerous patents as bear upon the art, would occupy many times the space which can be allotted in this work. Anything less than an exhaustive discussion would not do the subject justice. It has, therefore, been thought best to reproduce in the appendix, without any comment whatever, the numbers, titles, dates of filing and represen- tative claims, of such patents as may seem to give to the inventor a monopoly of any of the methods and devices necessary to the proper working of a wireless telegraph system. UNITED STATES PATENTS OF PROFESSOR REGINALD A. FESSENDEN. On August 12, 1902, there were issued to Professor Fessenden thirteen United States patents, which are here considered in the order of their filing as applications. Fessenden' s Initial United States Patents. The first two, filed December 15, 1899, and numbered 706,735 and 706,736, are companion patents, one concerning the meth- ods and the other the devices of the same improvements. The first claim of the method patent reads : CLAIM I. "As an improvement in the art of transmitting signals elec- trically by electromagnetic waves, the method herein described, which con- INVENTORS AND INVENTIONS. 115 sists in the generation of electromagnetic waves at one station and trans- forming the energy of the currents generated by such waves at the receiv- ing-station into the energy of motion, that is without the necessary interpo- sition of a secondary or auxiliary generator for the production of such motion." The auxiliary generator referred to as omitted is pre- sumably the battery which in coherer organizations actu- ates the relay. It will be observed that, as represented in Fig. 55, Part IV., there is no source of energy whatever at the receiving station. To a feature of this invention attention is called by another claim, as follows : CLAIM 6. " As an improvement in the art of transmitting electrical en- ergy by electromagnetic waves, the method herein described, which consists in prolonging the oscillations of an energy-radiating conductor by energy from a source external to the radiating-conductor and tuned to the period of the radiating-conductor." The external source here is condenser 18 in a shunt cir- cuit around the spark-gap as shown in Fig. 44, Part IV. Another novel feature is set forth in the ninth claim, and explained by Fig. 53, Part IV., and the accompanying description. CLAIM 9. "As an improvement in the art of transmitting electrical energy, the method herein described, which consists in varying the con- ductivity of a secondary circuit at the receiving-station by motion produced by currents generated by electromagnetic waves." The Device Patent The device patent 707,636 has the same drawings as 706,735. Its claims cover in gen- eral the means and combination of means which are used in the methods specified and claimed in its mate. n6 WIRELESS TELEGRAPHY. Fessenden's Patent for Electro-Magnetic Sending Con- ductor. No. 706,737 was filed May 29, 1901. Here No. 17 is a characteristic claim for a sending conductor. CLAIM 17. "A sending-conductor for electromagnetic waves having low resistance, small self-induction and great capacity." An illustration of the above is found in reference num- ber i of Fig. 38. Another feature is the receiver of claim 12, which is shown in Fig. 55, Part IV. The claim entire reads, Fig. CLAIM 12. "A system for signaling by electromagnetic waves, having in combination a conductor' adapted to ladiate waves of low frequency, and a receiver dependent for its action upon a constant or independently-vary- ing magnetic field and adapted to respond to currents produced by said waves." Fig. 38, as a whole, illustrates a system covered fairly well by claim 21, which reads : CLAIM 21. "A system for transmission of energy by electromagnetic waves, including in combination a radiating-conductor and a source of alter. nating electrical energy or potential, said radiating-conductor and source being co-ordinated and relatively adjusted to radiate a substantially con- tinuous stream of electromagnetic waves of substantially uniform strength." INVENTORS AND INVENTIONS. 117 Fessenden's U. S. Patent for Localizing by the Use of a Plurality of Tuned Circuits The features of No. 706,- 738, filed May 29, 1901, are well indicated by its claims I and 5 here quoted, and as an illustrating diagram refer- ence is had to Fig. 26, Part I. CLAIM i. "In a system of signaling by electromagnetic waves, a receiv- ing-conductor having a transforming device in series in the circuit, in com- bination with a circuit including a translating device, and having a local source of voltage and controlled by the transforming device and a source of voltage so arranged that its voltage will oppose the voltage from the local source operating the translating device. CLAIM 5. In a system of signaling by electromagnetic waves, a send- ing-conductor adapted to maintain and to radiate persistent oscillations, in combination with a receiving-conductor and one or more secondary circuits controlled by the receiving-conductor, the ratio of inductance to capacity being larger in a secondary circuit than in the sending-conductor, a wave- responsive device included in a secondary circuit of a series, the several cir- cuits being each tuned to correspond to the period of the sending-conductor." Fessenden's United States Patent for Increasing the Capacity of the Wave-Gate. The Fessenden patent 706,739 covers a device for surrounding the wave-gate with a medium of specific inductive capacity higher than air. Figs. 62 and 63 in Part IV. are respectively a plan and an elevation, and are there fully described. The first of the twenty claims may be quoted as follows : CLAIM i, "A conductor for radiating electromagnetic waves, in combi- nation with a medium having an electrical constant on which the wave length depends of a value greater than that of air arranged in suitable relation to the conductor." Fessenden's United States Patent for Localization by Generating and Receiving Two Sets of Waves of Different Periodicities No. 706,740, filed September 28, 1901, is an ingenious device for the localization of signals. It is Il8 WIRELESS TELEGRAPHY. described at length in connection with Fig. 28, Part I. Of the nine claims two are sufficient for illustration. 1 CLAIM i. "In a system of signaling by electromagnetic waves, the combination of a source of waves of different periodicities and two or more receivers responsive respectively to the differing waves or impulses and a wave-responsive device operative when the waves or impulses attain a certain predetermined phase relation. CLAIM 6. In a system of signaling by electromagnetic waves, the com- bination of means at the sending-station for generating two or more sets of waves of different periodicities, and a wave-responsive device at the receiving-station operative by the conjoint action of such set of waves." Fessenden's Wireless Telephony. The interesting claim of Patent No. 706,747, filed September 27, 1901, is the fourteenth referring to Wireless Telephony as follows : CLAIM 14. " In a system for transmission of speech by electromagnetic waves, the combination at the sending-station of means for the practically continuous generation of electromagnetic waves, a telephone-transmitter for modifying the character of the waves or impulses, and a telephone- receiver at the receiving-station responsive to currents generated by the electromagnetic waves." An illustration of the above is Fig. 27 in Part I., and there described. Fessenden's High Pressure Spark-Gap. Professor Fes- senden's Patent 706,741, filed November 5, 1901, is for a device to maintain a certain definite relation between the resistance and the self-inductance and capacity of the send- ing mechanism, regardless of the potential employed. It is described at length in connection with Figs. 46 and 47, Part IV. To indicate its patentable scope, two of its claims are subjoined. CLAIM 5. "An apparatus for the generation of radiation, having in combination a conductor for radiating electromagnetic waves, and sparking 1 See in Part I. description of Tesla Patents, Nos. 723,188 and 725,605, and in Appendix their dates and claims. INVENTORS AND INVENTIONS. 119 * ' - terminals, all gaps between sparking terminals being occupied by insulating material under pressure greater than atmospheric pressure, substantially as set forth. CLAIM n. An apparatus for the generation of radiation having in combination a conductor for radiating electromagnetic waves and spark- ing terminals, all gaps between sparking terminals being occupied by insulating material under pressure above a certain critical high pressure." Fessenden's Patent for a Selective System. In con- nection with "Keys" in Part IV., will be found as Figs. 74, 75, and 76, a reproduction of the third sheet of draw- ings of the Fessenden Patent No. 706,742, filed June 6, 1902. This document is long, containing five sheets of draw- ings, six printed pages of specifications, and twenty-nine claims. To show its features, five of the claims follow : CLAIM 5. " In a system for signaling, &c., by electromagnetic waves, the combination of a conductor adapted to radiate electromagnetic waves, means for causing the radiation of electromagnetic waves from said con- ductor, and means for modifying one or more of the characteristics of said waves. CLAIM 9. In a system of signaling by electromagnetic waves, the com- bination of a conductor and a spark-gap with means for changing the function of the conductor, i.e., from sending to receiving without bridging or disconnecting the spark-gap. CLAIM 16. In a system of signaling by electromagnetic waves, the combination of a receiving-circuit, a series of receivers, and means shifting any desired one of said receivers into and out of operative relation to the receiving-conductor. CLAIM 21. A system of signaling by electromagnetic waves, having in combination a sending-conductor and a key provided with fingers adapted to be brought into contact in succession with the sending-conductor at different points. CLAIM 26. A system of signaling by electromagnetic waves, having in 120 WIRELESS TELEGRAPHY. combination therewith means for indicating to a third station during send- ing or receiving that such sending or receiving station is busy." Fessenden's Patent for Recording on Photographic Paper. Patent No. 706,743, filed June 26, 1902, is for a method of catching the signals on photographic paper, and at the same time and in the same procedure applying chemicals to fix and develop them. There are but three claims, which are herewith reprinted. CLAIM i. "As an improvement in the art of signaling by electro- magnetic waves, the method herein described, which consists in producing interpretable characters or symbols on a strip or film by chemical action produced by currents generated by electromagnetic waves. CLAIM 2. As an improvement in the art of signaling by electro- magnetic waves, the method herein described, which consists in affecting a sensitive strip or film by currents generated by electromagnetic waves. CLAIM 3. As an improvement in the art of signaling by electromag- netic waves, the method herein described, which consists in producing interpretable characters or symbols on a strip or film by chemical action induced by electric currents generated by electromagnetic waves." Fessenden's Electromagnetic-Receiving-Device. No. 706,744, filed July i, 1902, is for an electromagnetic receiving-device. It is described at length in connection with Fig. 59, Part IV. The first three claims are suffi- ciently characteristic to show its patentable scope. CLAIM i. " A receiver for currents produced by electromagnetic waves consisting of a conductor having small heat capacity. CLAIM 2. A receiver for currents produced by electromagnetic waves consisting of a conductor having small radiating-surface. CLAIM 3. A receiver for currents produced by electromagnetic waves consisting of a conductor having low resistance and small heat capacity substantially as set forth." Fessenden's Patent for System. There will be found in connection with Fig. 29, Part I., a long description of INVENTORS AND INVENTIONS. 121 the invention embodied in No. 706,745, filed July I, 1902. The patent is for a system, and presumably presents the culmination of Mr. Fessenden's labors. Of its thirty claims the twenty-ninth may be quoted. CLAIM 29. "A system ot signaling by electromagnetic waves, having at the receiving-station a closed tuned secondary circuit and a constantly-re- ceptive, current-operated, wave-responsive device, in combination with a source of persistent radiation at the sending-station." Fessenden's Wave-Chute Patent Professor Fessenden's patent, No. 706,746, filed July i, 1902, is for a wave-chute. It is fully described in connection with wave-gates, and illustrated by Figs. 64 and 65, Part IV. One claim is as follows. CLAIM 5. " In a system for the transmission of energy by electromag- netic waves, a sending-conductor for radiating such waves, and an artificial ground connected to the lower end of the sending-conductor and connected at its outer end to ground." NOTICEABLE GROUP OF INVENTORS. It is impossible within the limits of this volume to men- tion, even briefly, all the inventions in this young art, for they are already numbered by hundreds. There is a notice- able group of inventors who assign, either directly or indirectly, to the American Wireless Telegraph Company. Among them Mr. A. F. Collins and Mr. Harry Shoe- maker are prominent, the latter being especially prolific. Unfortunately there is no public record of quantitative results by which the merits of their inventions may be measured. 122 WIRELESS TELEGRAPHY. EHRET S COMBINATION OF COHERER AND ANTI-COHERER. The patent of Mr. Cornelius D. Ehret, already noticed at some length as of promise, 1 is deserving of consideration from an inventive standpoint. It is numbered 699,158. The application was filed December 3, 1901, and the issue is dated May 6, 1902. It contains twelve claims, all of value. Three of them are herewith reprinted. CLAIM i. "In a signaling system the combination of dissimilar wave- responsive devices conjointly controlling a translating device. CLAIM 7. In a receiver the combination of a coherer and an anti- coherer conjointly controlling a translating device. CLAIM 12. In a receiver the combination of a coherer and an anti- coherer, a local circuit controlled by each, a coil of a relay included in each circuit, said coils operating differentially on the magnetic circuit of each relay, substantially as described." PUPIN PATENTS. Dr. M. I. Pupin, of Columbia University, has taken out two United States patents for multiple telegraphy with conductors. His claims, however, may have so broad a scope as to cover the principle of selective signalling by means of electrical resonance ; and for this reason it is reported that his rights have been purchased by the Mar- coni interests. The numbers are respectively 707,007, and 707,008, and both were i'ssued on August I2th, 1902. Application for the first was filed February 23rd, 1894. As an illustration of their bearing upon wireless telegraphy, claim number one of the earlier patent (707,007) is here- with quoted : 1 See p. 84 and Fig. 30 in Part I. INVENTORS AND INVENTIONS. 123 "CLAIM i. The method of distributing electrical energy which consists in throwing upon a common conductor a number of alternate currents of different frequencies and distributing the several energies of these currents each selectively to a separate electrical device substantially as described." SUMMARY. There is in Part I an account of the transmission of electric signals by Morse in 1 842 across a body of water ; and a similar achievement by Lindsay some ten years later. In the next decade James Clark Maxwell published his interpretation of electrical phenomena as a propagation of ether waves, differing from light only in the lesser number of vibrations within a given unit of time. In 1882 Dol- bear applied for a United States Patent for a method of telephonic transmission across space without wires ; and in 1885 Edison applied for one to cover methods and devices similar to Dolbear's. It seems, however, that the true period of invention in the field of ethereal transmission extends from the discovery of the minute sparks in the bent wire at Carlsruhe in 1886, to the reception of the Poldhu signals at Cape Race in 1901 ; that the first trans- mission was due to Hertz, and the discovery of the .prop- erties of the filings to Calzecchi-Onesti ; that the researches of Branly gave to the world the laws which govern the action of the coherer ; that Lodge sealed the filings in a vacuum, applied to the coherer thus improved the prin- ciples of electrical resonance, and in a laboratory combined the various elements which make a wireless telegraph ; that Tesla discovered many of the laws governing high fre- quencies and great pressures and devised means for the production and effective insulation of high potentials; and finally Marconi combined the results of these various dis- coverers in a system by which signals were observed at the distance of two thousand miles. 124 WIRELESS TELEGRAPHY. THE COMPARATIVE MERITS. 125 PART THE COMPARATIVE MERITS OF WIRELESS TELEGRAPHY AND OF TELEGRAPHY BY WIRES AND CABLES AND THE COM- MERCIAL OUTLOOK FOR EACH. THE history of the useful arts is evidence of the fact that each new development adapts itself to an especial field ; that old methods and devices, which seemed certain to be supplanted by new, often continue to be employed and even to multiply. The innumerable freight trains that now rumble between Buffalo and Albany have not dis- placed the mule and barge of Erie Canal ; and notwith- standing the existence of unnumbered freight-carrying iron steamers, wooden vessels with sail power are still being built on the Kennebec. Millions of electric lamps illumine the streets, theatres, hotels, and residences of New York City, yet "dollar gas" was very recently an issue in its politics. The pedestrians of our larger cities are compelled at each street crossing to calculate the relative speed of machine-moved vehicles ; yet the last United States Census records twenty-two millions of horses and mules ; and all the harness factories in the country at this writing are behind their orders. Telephone instruments are installed in every nook and corner of the City of New York, their 126 WIRELESS TELEGRAPHY. daily connections counting into thousands ; yet the mes- senger business of the American District Telegraph has not decreased during the last seventeen years, and that company is still paying dividends. It is the purpose of this section to speculate as to the influence that will be exerted by Wireless Telegraphy upcn its predecessors and competitors in the field of distant communication. The new art has, of course, an exclusive and profitable employment in signaling from ship to ship on the ocean, and from ship to shore. The English Marconi Company already derives a revenue from tolls for communications between passengers on incoming steam- ships and the near shores, receiving about two hundred and fifty dollars a voyage from messages sent within a short distance of either side of the Atlantic. The Lloyds have adopted the system, and are requiring steamships that get the best insurance rates to be equipped with it. It is easy to prophesy that in the immediate future the telegraphic news of the world will be scattered like seed from the sower over the whole Atlantic and may be picked up by any vessel equipped with properly attuned apparatus ; but that it will render the present system of ocean cables obsolete is alto- gether improbable. Ocean Cables as a Means of Communication. The cables are an excellent medium for the transmission of signals ; they are in position ; and the money that has been expended to make and to place them cannot now be recovered. Neither bonded indebtedness, nor other form of financial obligation, will have any physical effect upon the efficiency of the cables as a means of communi- cation. THE COMPARATIVE MERITS. 127 Expression of the Cable Company's Official. In this connection may be quoted an article from the New York Sun of March 4th, 1902, entitled "The Cable Company Cheerful " : An expression of confidence in the ability of submarine cables to main- tain their commercial supremacy in competition with wireless telegraphy was made yesterday by George G. Ward, Vice- President and General Man- ager of the Commercial Cable Company, in addressing as chairman the annual meeting of that company's shareholders in this city. Mr. Ward spoke as the representative of the officers of the company, who, he said, while they " did not intend to belittle the credit due to Mr. Marconi," for the advancement he has made in the field of wireless telegraphy, believed that submarine cables would hold their supremacy, even should wireless telegraphy " ever extend beyond its present experimental stage as regards trans-Atlantic or other long-distance transmissions." Mr. Ward added: " Our shareholders must not overlook the fact that it has taken the Commercial Cable Company and its land line system some seventeen or eighteen years to perfect their organization for the distribution and col- lection of telegrams throughout the United States and the rest of the world. Assuming that the Marconi system should become perfected so that it could really compete in a commercial sense, and commercial requirements are very exacting, it is fair to say that it would take as many years to put the Marconi system in a position that would enable it to serve the public. Messages are now transmitted across the Atlantic and answers received in two and three minutes. A message experiencing a delay of ten or fifteen minutes means the defeat of the object of the sender. A most important point is the fact that 95 per cent of the Atlantic messages are expressed in code or cipher language, the words or ciphers having no connected mean- ing. The words or cipher groups frequently only differ from each other in single letters, yet they have widely different meanings, and an error in the transmission of one of their letters might have disastrous consequences. These are some of the commercial exactions or demands made upon the telegraphs. No one as yet even has pretended that the speed with which messages may be transmitted by wireless apparatus even approaches the speed of the aerial or submarine wire. The company's net earnings for the year ended December 31, 1901, amounted to $2,2 59,897, a decrease of $19,770 compared with 1900. After payment of interest and dividends there was a balance of $409,538, against $493,003 in 1900." 128 WIRELESS TELEGRAPHY. Marconi's Belief. Herewith is reprinted by permission from the Century Magazine, Marconi's own contention. This item was published about the same time as that of Vice-President Ward of the Cable Company : " Mr. Marconi believes that his system may become a formidable com* petitor against the ocean cables. To compete on land is not so easy, as the lines there cost only one hundred dollars a mile, whereas the cables cost one thousand dollars a mile, and require expensive steamers to repair and maintain them. A transatlantic cable represents an initial outlay of at least three million dollars, besides the cost of its maintenance. A Marconi station can be built for sixty thousand dollars. Three of these, bringing the two worlds into contact, will cost only one hundred and eighty thousand dollars, while their maintenance should be insignificant. What his success will mean can be best grasped by considering the extent of the property which would be displaced thereby, although it is only since August 5th, 1858, that the first Atlantic cable was laid. There are now fourteen laid along the Atlantic bed, and in the whole world seventeen hundred and sixty- nine telegraph cables of various sizes, with a total length of almost one hundred and eighty-nine thousand nautical miles, enough to girdle the earth seven times. These require a great number of ocean-going cable steamers for their laying anal repairs, and while the total value of the cables cannot be easily computed, it is known to be a fact that British capitalists have one hundred million dollars invested in cable stocks." Marconi has said to his English stockholders that whereas the speed of the submarine cable is directly affected by length of transmission, the wireless system is not in the least affected by distance. That " it is just as easy to work at high speed across the Atlantic or Pacific as to work across the English Channel." He is confident of establishing direct communication between England and New Zealand. 1 He says that the curvature of the earth does not affect the signals, and that ultimately he will be able to send them all around the world. Speed of Transmission over Ocean Cables. Over the German Cable from New York to the Azores, two sets of 1 See chart, Fig. 39, p. 124. THE COMPARATIVE MERITS. 129 signals in opposite directions are simultaneously sent at a rate of about seventy words per minute for each circuit of a duplex transmission, making a total of one hundred and forty words. This, it is said, is the best that is done over any long submarine conductor. The principal limiting factor in this signaling is a delaying influence due to electrostatic capacity. Professor Pupin of Columbia Uni- versity, who has exhaustively investigated this subject, has pointed out that electrostatic capacity, being a storage of power, is an advantage rather than a detriment if properly controlled ; and in pursuance of his plans for such control, it is reported that the Bell Telephone Company has equipped three circuits from New York to Chicago with " Pupin Coils," and that the results are an increase in the efficiency of speech- communication equivalent to one hundred per cent. Professor Pupin is sanguine that equally good results will follow a similar treatment of ocean cables, but there is no way of demonstrating this fact in actual practice except by the construction of a new cable in conformity with his design. He has been quoted in newspaper paragraphs as saying that the ultimate possibility in submarine telegraphy is a rate of one thousand words per minute ; and while it may be feasible to attain this speed it seems that condi- tions other than those connected with induction will require for such rapid work both a larger conductor and an increased mass of insulating material, thus entailing an expense in construction which may prove prohibitive ; and that a safer estimate of probable future speed is five hun- dred words per minute. Progressive Invention in Cable Apparatus. It may be said also that there is progressive invention in cable appa- 130 WIRELESS TELEGRAPHY. ratus. Foresio Guarini, an Italian scientist of repute in the field of wireless telegraphy, has suggested the coherer as a device to be used in multiplexing ocean cables by means of electrical resonance. Chemical telegraphy, here- inafter explained, may also be mentioned in this connection. The foregoing suggestions will serve to point the fact that although etheric transmission has undoubtedly come to stay, the possibilities of wave propagation through copper still offer alluring fields of research. WIRELESS TELEGRAPHY OVERLAND. Hertzian-wave signaling overland, though still in em- bryo, will undoubtedly become an important factor. Marconi believes a thousand miles in one span to be a possible transmission. Guarini has been somewhat suc- cessful in devising automatic repeaters which may double or treble such a span. Fessenden predicts that a circuit will eventually be worked from New York to Chicago. A difficulty in making the comparison between wave and wire signaling overland arises from the fact that the land telegraph systems with wires seem to be far behind their possibilities ; which is to say that the telegraph com- panies do not begin to do what they might ; and in order to present an intelligent view it is thought best to explain at some length the present situation of commercial tele- graphy on land. Controversy in the Electrical World. There has re- cently occurred in the correspondence department of the Electrical Worlds controversy concerning the attitude of THE COMPARATIVE MERITS. 131 the Western Union Telegraph Company. This happening is fortunate in that the participants are representative men and have definitely announced their opinions. Professor Pupin had published a letter which virtually stated that the officials of the Western Union Telegraph Company were impervious to suggestions from inventors or scientists. The Electrical World editorially commenting upon this letter took the ground that the telegraph authorities, as compared with those in other electrical professions, had been noticeably backward in developing their art. The engineer of the Western Union Company replied that Pro- fessor Pupin 's lack of practical experience in telegraphy probably accounted for his misapprehension. The Morse System He also said that nothing had ever been found to equal what telegraphers call " Morse," a term used to define the method of reading signals by sound which renders it possible to write down a message as it is received, the telegram at the receiving end being ready for delivery as soon as the sending operator has fin- ished his work. It was further said that in times of emer- gency and for some purposes the Wheatstone system had value. Speed of Quadruplex The engineer of the Postal Tel- egraph Company gave some interesting data as to trans- mission by Quadruplex (a species of "Morse") between New York and Boston, by which it appears that the average number of words sent over one wire by four operators is four thousand nine hundred and fifty per hour, or a little less than twenty-one words per minute per sender, or eighty-four words per minute per wire. It may be 132 WIRELESS TELEGRAPHY. \ explained that in doing this work eight men are employed, four in sending and four in receiving. A circuit between Boston and New York, however, does not furnish the most essential data, for it is but two hun- dred and fifty miles in length. The great telegraphic highways are the wires between New York and Chicago, which are a thousand miles long. Upon these circuits the quadruplex rate is likely to be nearer to sixty words per wire per minute ; but for the purposes of comparison we may use the data given at eighty words, as it is certain that this rate may not be exceeded. The "Postal" engineer also stated that the public is not finding fault with the present telegraphic service, to which statement the reply may be made that the public is not fully enlightened. He further stated that the night or half-rate traffic " is naturally limited by reason of the splen- did mail facilities between our principal cities." Mail Service Following are actual facts in regard to mail service : To transport a letter from a street box at I25th St. and 8th Avenue, New York City, to 39th Street and Cottage Grove Avenue in Chicago, requires forty-five hours ; con- sequently the securing of an answer to an inquiry by such means requires more than four futl days. A person in the business district of St. Louis desiring to send a letter to New York at two in the afternoon may just as well mail the letter at midnight. A letter regis- tered on Thursday afternoon in St. Louis, with full postage, was not delivered in the business district of New York City until Monday morning. First class mail matter deposited in the Post Office in THE COMPARATIVE MERITS. 133 Detroit, Michigan, at six in the afternoon of Thursday, will not be delivered down town in New York until Satur- day morning. Between the service just described for two cents and the day rate of forty cents, and night rate of thirty cents for ten word telegrams, the telegraph companies have never been able to see an opportunity for employing at night their idle wires. DIFFERENT TYPES OF TELEGRAPH APPARATUS. Besides the "Morse," there is telegraphic apparatus known as the " Wheatstone," in which a paper ribbon is first perforated and then sent through a machine, recording at the distant end with ink marks upon paper tape ; the total speed of two sides of a "duplexed Wheatstone" is about two hundred words per wire per minute. There is also the Buckingham page-printer, which first perforates a tape by means of a device like a typewriting machine, feeds the messages through a transmitting ma- chine, and produces at the distant end typewritten copies at one hundred words per wire per minute. Another device is the Murray page-printer, which practi- cally accomplishes the same results as the Buckingham and attains about the same speed. Another and recent device is the Rowland octoplex, by which eight circuits are worked over one wire, each circuit transmitting thirty words per minute, a total of two hun- dred and forty words per wire per minute. The sending is done by manipulating typewriters, typewritten copies being automatically produced at the receiving station. It is said that the Wheatstone and Buckingham appa- 134 WIRELESS TELEGRAPHY. ratuses are both regularly employed by the Western Union Telegraph Company, but the latter system was not men- tioned by the company's engineer in the Electrical World controversy. If the Murray is in business use that fact is not known to the writer. The Rowland octoplex is said to be employed in Germany. All of these machines are complex in detail and costly to construct. If there be considered, however, the total investment of money in a copper wire one thousand miles long and weighing perhaps four hundred pounds per mile, together with the cost of planting poles, of attachments to those poles, and the expense of patrol and maintenance, the claims of inventors of telegraphic machines that their apparatuses will pay for themselves in a short time seems well founded. Either the Buckingham or Murray page- printers, or the Rowland octoplex, are rated at a speed much greater than that of quadruplexed Morse. All of them save nearly fifty per cent in operating labor. The officials, however, are obdurate, and while the equip- ment of perhaps one wire with a new device is occasionally allowed, the experiment seldom extends any further. The result of such policy in the past has produced a great array of abandoned machinery. After each trial, officials, engi- neers, and operating force are further strengthened in their admiration for the true and the tried ; and the disappointed inventors claim that to all arguments there is the same response, and to all appeals the same denial, " There is nothing like Morse." Morse Best Adapted to Certain Classes of Traffic. No one denies that for the class of service that transmits orders from the New York Produce Exchange to the Chicago THE COMPARATIVE MERITS. 135 Board of Trade it seems impossible to find a substitute for Morse. It is said that to the telegraphers in the Chicago Trade Room even a typewriting machine is less facile than the pen. They write upon a blank, using copying ink ; when the message has been written, a moist piece of paper is laid over the blank, the two are then fed between the rubber rollers of a wringer, and there is quickly in hand the original message, which may be handed the consignee, and an impression copy for the company's files. There are classes of business which require the same rapidity of delivery as do those of the grain and stock brokers, and for which Morse seems best adapted. There is, however, a traffic that comes from the general public which is poorly handled. It is not so much the way this class of business is being transmitted with present facilities as a matter of what might be done with other and better devices and with the lower tariffs those devices would warrant. The charges for sending miscellaneous telegrams are the same as for those of the preferred class. Under favorable conditions the telegraph companies may transmit an unpre- f erred message fairly well ; but if there be rain or wind or excitement in Wall Street, or an election, or a political con- vention, the wires are crowded ; and having thus to contend against frequent delays and high tariffs it is no wonder that the number of these unfavored communications is comparatively small. As Mr. Delany, in one of the letters of the recent discussion, has pointed out, there is no elas- ticity, no reserve power in the present telegraph service. For the class of business just described, low rates and the adoption of some of the new possibilities in multiplex or in chemical telegraphy would undoubtedly increase the re- 136 WIRELESS TELEGRAPHY. ceipts of the telegraph companies and prove as well a boon to the public. Chemical Telegraphy. Almost coeval with Professor Morse's inventions are those of Alexander Bain, who de- clared as long ago as 1845 that by the chemical method he could transmit two thousand words per minute. A system based on this principle was tried by the Atlantic and Pacific Telegraph Company in 1875. Its officials made two mistakes, first ordering that it be used for all kinds of traffic, and then that its use be entirely discontin- ued. In the eighties the American Rapid Company tried the system again, but that company was unsuccessfully financed and soon collapsed. The essential principle of chemical telegraphy is the fact that an impression is made whenever a current of elec- tricity passes from a metallic point resting upon chemically treated moist paper to a conductor which connects with a part of the same circuit from another point on the paper. The action is electrolytic. A copper point leaves a red mark, an iron one a deep blue. The number of signals is governed by the volume of current, by the time of exposure, and to some extent by the electrostatic capacity of the conductor connecting the sending and receiving stations. It may be expressed by the equation FT N - "RK where N is the number of signals per unit of time, E the electromotive force, T time, R resistance, and K capacity. While the author is not exactly informed as to quantita- tive results, it is safe to say that one five-thousandth of an ampere flowing from an iron point and impressed upon the THE COMPARATIVE MERITS. 137 sensitized paper for one second of time will leave a distinct mark ; and, conversely, that one-twentieth ampere unim- peded by capacity is sufficient current to produce two thousand words per minute, each word requiring from ten to twenty marks. Description of Chemical Telegraph Apparatus. Fig. 40 is a diagrammatic view of a chemical telegraph circuit, P being a source of current supply with one polarity, and N a second source, having a polarity the reverse of the first. B and B' are brushes terminating respectively conductors Fig. 40. from P and N. B" and B" ' are brushes on the surface of the sending tape ST which are brought into contact with B and B' by reason of the holes in the paper being moved past them whenever the paper is pulled along by friction rollers FF. The yoke y is of conducting material, and consequently B" and B" ' are electrically one piece which is connected to the line. At the far station RT is the chemically treated receiving tape, and resting upon it is an iron pen C which is joined by insulating material x to the platinum faced strip C' called the spacing pen. WIRELESS TELEGRAPHY. Operation of Chemical Telegraph. Whenever a contact is made oetween brush B and the line by reason of the passing of one of the lower holes in tape ST, current flows across RT from C to C' and colors the paper. After brush B has passed a hole, the charge of electricity which has become stored in the line flows to earth, and this secondary flow of current tends to prolong the mark. Thus the horizontal distance between a lower and an upper perfora- tion impresses upon the sensitized paper either a long or a short mark according as the distance between any lower opening and its relative upper opening is long or short ; for whenever brush B' is presented to line, it neutralizes the current flowing from C to C', and the pen C ceases to color the paper. Neutralizing Electrostatic Effects. The system of positive and negative presentations is an improvement upon the earlier methods, which used current of one polarity only. Under the plan just illustrated, inductive influence is partly neutralized ; and by another and very simple contrivance in connection with the apparatus, the details of which the author is not at liberty to make public, electrostatic capacity seems to be under absolute control. Speed. The speed of the chemical telegraph is marvel- ous. Mr. Delany, the chief exponent of that kind of transmission, has succeeded in recording in a laboratory, and over an artificial line the equivalent of an ordinary telegraphic circuit one hundred and twenty-five miles in length, eight thousand words per minute. The author has seen an initial force of one hundred and ten volts transmit one thousand words per minute over an artificial line hav- THE COMPARATIVE MERITS. 139 ing the resistance and electrostatic capacity of a circuit between New York and Chicago. There is no reason why machines should not be devised by which two thousand words per minute may be sent with one hundred volts ; nor is there any insuperable obstacle to the use of five hundred volts. Indeed the sending ten thousand words per minute over a copper wire a thousand miles long weighing four hundred pounds per mile is a possibility of the present development. Chemical transmission is now used by the Pennsylvania Railroad Company between Philadelphia and Altoona, and over the circuit employed, Mr. Delany has made a record of thirteen hundred words per minute. The line measures in resistance about fourteen hundred ohms, and is partly of iron wire. There has been a plan for perforating paper tape by the manipulation of a Morse Key ; and, as the action of a telegraph key is simply a down-and-up motion of a pivoted lever, this action may be reproduced at a considerable distance from the location of the sending operator. At the distant point the tape may be fed into a transmitter, and it may be reproduced by chemical signals over a second circuit. To illustrate the plan of operation, a telegram from New- ark, New Jersey, for delivery at Milwaukee, Wisconsin, under present conditions would be sent by Morse from Newark to the main office in New York City, thence by quadruplex to Chicago, thence by Morse to Milwaukee. By the perforator and chemical telegraph the Newark operator could make in the main office at New York a tape which would be used to transmit the message from New York to Chicago, where it would appear in the form of Morse signals on a moist paper ribbon, and this might UNIVERSITY 140 WIRELESS TELEGRAPHY. be handed to an operator in Chicago to be sent to Mil- waukee by Morse. In the first method the number of sets of human heads and hands occupied with the message is six ; in the latter three, and consequently this latter presents just one-half the chance for errors. Moreover, in the actual time of passage the gain is considerable. The saving in plant, al- lowing to the second method five thousand words per minute, is as sixty to one over quadruplexed Morse ; and would be as forty to one over any of the type-printers. So much space has been given to the chemical system because of its development. It is wonderful that an organ- ization so complete could have been perfected without the experience that comes from daily use ; and more wonder- ful still, that having been thus perfected, it should be entirely neglected by the telegraph companies. Other Means of Rapid Signaling. There are undevel- oped means of signaling, however, which to experts in wireless telegraphy seem certain of future attainment. Both Marconi and Fessenden are looking forward to ma- chine transmission at a speed of five hundred words per minute, and they are also hopeful of multiplexing wireless circuits. Many of the obstacles, however, which loom up in the future of wireless telegraphy do not present them- selves in transmission by wire, and there is every reason to suppose that a wire may not only be multiplexed many times, but that each of the phantom circuits, as they are called, may be made by machinery to convey some hundreds of words per minute ; always with more certainty and speed than without the wires. It is the apparent neglect of such great forces for which THE COMPARATIVE MERITS. 141 the telegraph officials are held accountable by those ac- quainted with the facts. Complication may not be urged, because the chemical system, for example, is far simpler, both in construction and operation, than is either the duplex or the quadruplex or the typewriter devices. The passage over a single wire of thousands of words per min- ute is as well assured as is wireless telegraphy ; and if brought into regular commercial use it may prove a greater public benefit. At present there is no outlook that etheric signaling overland will ever attain to the tremen- dous possibilities of telegraphy with wires. 142 WIRELESS TELEGRAPHY. S NOMENCLATURE. PART IV. APPARATUS. NOMENCLATURE. THE art which forms the subject-matter of this work is young and its nomenclature limited. " Wireless Tele- graphy" itself but a negative term is temporarily supplying the need of a positive designation. Neither " radio-tele- graphy" nor "wave-telegraphy" nor "etheric-transmission" satisfies. " Hertzian-wave telegraphy " is of unwieldy length and lacks euphony, No single word suitably denotes every kind of instru- mentality- affected by Hertzian or magnetic waves. " Detector " has been used in another sense. Mr. Tesla speaks of " sensitive-devices " ; Mr. Fessenden and others of a "wave-responsive-device." " Responder " is too closely identified with the DeForest system to be ac- ceptable to competitors. " Resonator," to denote a receiv- ing device, is objectionable on account of its alliterative and structural similarity with " radiator," a transmitter. Antenna is an excellent name for the conducting termi- nal that ends in air whenever the allusion is to a receiver of waves ; but it is not sufficiently aggressive to express the opposite meaning. Emitter seems a good term for designating anything that serves to send impulses outward. The terminating conductor, however, being employed both 144 WIRELESS TELEGRAPHY. as antenna and emitter, the necessity appears for that which denotes both uses. Mr. Fessenden speaks of an aggregation of five wires as a " harp." When the condi- tions are applicable, "high wire" is a good term, but not when cylinders or cones are used. The writer suggests as a comprehensive title, one used in this work, "wave-gate." For the instrument that acts bv diverse resistances of J a sensitive device and thus translates the signals to a local Fig. 42. Elevating the kite-supporting wave-gate at Signal Hill, St. Johns, Newfoundland, December 12, 1901. X Marconi. and more powerful circuit, no better name than "relay" can be found : but to speak in that connection, of a " rev ceiver," is to confuse it with the sensitive device itself. The circuit which contains a radio-receiver battery and relay has occasionally been designated "local," not in- trinsically a good term, and the less acceptable because to telegraphers it implies a second organization in contra- distinction to the connections of the main line. NOMENCLATURE. 145 As suggested by Mr. Tesla's " sensitive-device," the train of apparatus having the radio-receiver for one ele- ment might properly be denoted the " sensitive circuit," and the battery which actuates the relay in that circuit the " closing battery." For the wires and apparatus in series with the relay points, " recording-circuit," and for the energizing element of that group, " recording battery," are designations that should be clearly understood. The terms "spark-producer," "oscillator," and "oscil- lation-producer " are synonymously applied to all apparatus that sends electric charges across the spark-gap. " Induction-coil," the " primary " and " secondary " which compose it, and the "key " used to bring into operation the sparker, are terms well fixed in the public mind. The contact which rapidly opens and closes in the primary circuit is happily described in Marconi's patents as the " trembler-break." As both Professor Lodge and Signor Marconi, partly for the purpose of broadening their patent claims, have in- sisted that both the earth and the wave-gate are " capa- cities," that term may not now be understood as confined in meaning to a condenser or to a Leyden jar. TRANSMITTERS. Ruhmkorff Coil. Before the advent of wireless telegraphy the Ruhmhorff Coil was the standard spark- producer. Referring to Fig. 43 as an illustration of that coil, it may be described as follows : In a position of rest the contact of spring T is in touch with that of upright K. By the closure of the break at switch S, battery B energizes circuit B-S-T-K, causing 146 WIRELESS TELEGRAPHY. the iron coil I to become magnetic. The iron face of spring T is attracted towards coil I, but as the movement forward immediately breaks contact at a, I is demagne- tized, and the spring T resuming its first position in con- tact with K, coil I again becomes magnetized. On account of the quickly changing conditions in coil I, there occur continuous and rapid vibrations at point a. Fig. 43- When, however, the current, after being made, is inter- rupted at point a, there takes place an electric discharge which is, in effect, a flow of current in an opposite direc- tion to the charge which has just been made. This reverse current, though of high pressure, is attenuated, and has much less magnetic effect on the coil than the initial one. It tends, however, slightly to magnetize coil I at a time when that coil should be non-attractive : and it TRANSMITTERS. 147 is also true that the high pressure generated is apt to burn the contacts at a. The function of condenser C is to give back its charge with the same energy as that which emanates from the pri- mary coil, thus neutralizing the bad effect of the primary coil's discharge. It is seldom, however, that the adjust- ments of the two forces are quite in balance, and conse- quently there is generally more or less imperfect action at a. Marconi's Spark-Producer. In Marconi's patent 1 1,913 is described a device which partially obviates the difficulty of corrosive points, in that, by means of a small electric motor, it causes one of the points of the vibrating break continuously to revolve. The spark in this patent is shown with an interposition of two balls in the center in an ebonite casing. The distance between the center balls is one twenty-fifth inch, and the inside distance between each of the terminating electrodes and the center balls one and one-half inches. The space between the two middle spheres is filled with vaseline oil. It is said that Mr. f 8 Marconi afterward dis- carded the center globes and used a clear space between elec- trodes. A Fessenden Trans- mi tter. Fig. 44 showsatrans- m i 1 1 e r de- signed by Mr. Fig 44 I4 8 WIRELESS TELEGRAPHY. Fessenden, the patent for which was filed December 1 5, 1899. A distinctive feature is the condenser 18 bridging the spark gap between electrodes 4-4. This arrange- ment, the inventor says, is " for the purpose of maintain- ing sustained radiation," for "this shunt circuit by reason of its capacity stores up an additional amount of energy, and when a spark passes across the gap, since the sending conductor can radiate energy at a given rate, it must continue to radiate for a long time in order to dissipate this additional stored up energy." a A similar organization is shown in the Marconi patent 676,332, of later date than the Fessenden. 1 Alternating Current Dynamo Instead of Interrupter. - The interrupter in the primary coil of a direct current sparking appliance being difficult of control with currents of high potential, it is the practice in large installations to employ steam power connected with an alternating current dynamo, the voltage of which may be "stepped up" by transformers ; and where steam power is not available, but energy is had from storage batteries, as in field operations, direct current from the batteries may be made to turn an electric motor by which an alternating current dynamo may bejkept in motion to furnish the primary coil with energy to supply the spark gap. Fessenden Dynamo as Direct Emitter. The use of a dynamo for a direct emitter without the spark gap is shown in Fessenden's patent 706,737. He claims that he is able at once to produce a continuous train of radiant waves jof substantially uniform strength, as distinguished from 1 See Fig. 37 in Part II. TRANSMITTERS. 149 the well-known systems wherein the spark-discharge starts a train of waves of rapidly diminishing power, followed by relatively long intervals of no radia- tion. Fig. 45 is a diagram from the Fessenden patent where i is a short emitting wave-gate with large radia- ting surface, 2 a tuning inductance, 3 an alternating current dynamo with an earth connection. Fig. 45- DeForest Transmitter. The tran- smitter of the DeForest system uses an alternating cur- rent dynamo, a step-up transformer to increase the vol- tage ; and discharges across a gap in which is interposed a detached conductor. The discharging electrodes and the interposed member are of the same shape and size, being disks of metal about one-quarter inch thick, and upon the sides or faces about one and one-quarter inches in diameter. The spark gaps upon each side of the middle disk measure about one sixty-fourth inch. The DeForest experts claim that with electrodes of a surface relatively large as to the gap they get a " fat " spark, and that such a spark produces better results at the distant or responding end than would one of greater inten- sity but less volume. A Fessenden Transmitter. Figs. 46 and 47 are repro- ductions from drawings in one of Mr. Fessenden's patents, No. 706,641, filed November 5, 1901. The diagram of curves, Fig. 46, is a graphic representation of comparative efficiencies. The dots on horizontal line c indicate spark potential in inches, the vertical line d radiation or effective ISO WIRELESS TELEGRAPHY. Fig. 4 6. result, b is an efficiency curve which shows results obtain- ed under usual conditions, viz.: that within a certain length of spark, about one inch, the resultant radia- tion of electromagnetic waves is approximately proportional to the length of spark ; but that to increase the length of spark beyond one inch will result in no practical increase in radiation. The line a is another efficiency curve which is employed to demonstrate that with Mr. Fessenden's device, the wave force d is ex- actly proportional to spark gap c at whatever length the latter may be prolonged. Referring to Fig. 47, 10 is a rod pointed at its lower end, surrounded by an insulating sleeve n, and so introduced into the chamber 7 to form one electrode of the spark gap. The Fig * 47 ' TRANSMITTERS. 151 other electrode is the bottom plate of chamber 7, and thus one of the discharging terminals is a point 4, and the other a disk, 5. By means of pump 8, the air in chamber 7 is increased in pressure. It is found that when a certain critical pressure is reached, which, for instance, may be eighty pounds per square inch, the radiation for any length of spark becomes strictly proportional to the applied force. The term " radiation " in the foregoing explanation, and as shown by the height of vertical line d of the curve dia- gram, is an expression of an applied energy, that, if doubled or trebled, doubles or trebles the distance from such energy for which a wave-responsive device may be made to indi- cate signals. 152 WIRELESS TELEGRAPHY. WAVE-RESPONSIVE-DEVICES. Considering as a generic term either " sensitive-device," or "wave-responsive-device," or "radio-receiver," or "de- tector," there may be made as classifications of it "coher- ers," "anti-coherers," "micro-radiophones," and "mag- netic-radio-receivers." Coherers. If used without a qualifying word or prefix the word coherer is now understood to indicate that form of radio-receiver, which, being normally a high resistance, is, under the influence of Hertzian-waves, changed to a low resistance, becoming relatively a conductor, and remaining electrically conductive after the subsidence of the wave effect unless restored to its original state of resistivity by some sort of mechanical impact. Filings Tube of Calzecchi-Onesti. Decoherence by Re- volving So long ago as 1886, Professor Calzecchi- Onesti placed copper filings between two brass plates and changed the electrical property of the filings from a state of high resistance to one of low resistance by passing through them the secondary impulse that occurs when an electric circuit is broken. Afterward to facilitate decoher- ence he inclosed the filings in a revoluble glass tube. Branly's Filings. Tube Decoherence by Tapping. Branly, 1891, discovered that the filings could be rendered conductive by the passage of electric sparks across an air- gap in their vicinity, and that they could be decohered by a slight jar. WAVE-RESPONSIVE-DEVICES. 153 Lodge and Fitzgerald Needle and Tin-Foil. Dr. Lodge, in conjunction with Mr. Fitzgerald, made a coherer by causing the point of a sewing-needle to rest upon a strip of tin-foil. Later, this device was elaborated by contacting the needle point with a flat spring which was fixed within a clamp, the degree of pressure between point and spring being regulated by adjusting screws. Branly's Tripod of 1902. Professor Branly in 1902 placed a tripod having sharp steel points slightly oxidized upon a polished plane steel plate. A current of electricity passing from tripod to plate is, under normal conditions, subjected to a high resistance. This resistance is greatly diminished by Hertzian- wave effect, and may be re-estab- lished by so arranging a recording instrument, that imme- diately after the wave effect is discontinued, it will jar the plate. Tesla's Filings Tube. Decoherence by Inversion. In his patent No. 613,819, Mr. Tesla describes quite minutely a form of filings coherer which is decohered by being turned end for end, its position of rest being vertical. He makes the particles as nearly as possible alike in size, weight, and shape, having special tools to fashion them ; and then oxidizes them uniformly by placing the grains for a given time in an acid solution of predetermined strength. He prefers not to rarefy the atmosphere within the tube, since by rarefaction it is rendered less constant in dielec- tric property. He recommends an air-tight inclosure and a rigorous absence of moisture. In another patent he specifies decoherence by continuous revolution, instead of by inversion, of the glass tube. 154 WIRELESS TELEGRAPHY. The " Silver " Coherer So far as is known by records of practical tests the most sensitive type of the class under consideration is the "silver" coherer. It is carefully described in the American reissue patent No. 11,913 of Marconi. Briefly the tube is one and one-half inches in length, and one-twelfth inch internal diameter. Within it are tightly plugged two pieces of silver wire, each one- fifth inch long. The space between these plugs at center is one-thirtieth inch. This minute space contains a pow- der composed of ninety per cent of nickel filings, and ten per cent of silver filings. The grains are as large as may be produced with a coarse file, and are coated with an almost imperceptible globule of mercury. The tube must be sealed. A perfect vacuum is not essential, but is de- sirable, and one of one-thousandth atmosphere has been used. Sensitiveness to waves may be increased by using a greater percentage of silver grains in the powder, or by decreasing the distance between the silver stops. ANTI-COHERERS. Hertz Detector. The first radio-receiver in which cause and effect were observed and recognized was devised by Hertz in 1886. It con- sisted of a piece of wire, Fig. 48, bent into circular form, a small disconnecting gap being left in its circumference. If this de- vice were suspended at some distance from Fig. 48. a sparking Ruhmkorff Coil, there being no tangible connection between the coil and the circlet of wire, minute sparks could be seen to fly across the air-gap in the wire. WAVE-RESPONSIVE-DEVICES. 155 Righi Detector. Professor Righi obtained similar action by holding at a few feet from a spark-producer a sheet of glass covered with tin-foil, the metal being separated by a fine diamond point into several longitudinal bands. Action at the electrodes of the induction coil resulted in sparking from band to band over the gaps in the tin-foil. In 1899 a German scientist discovered that by placing a drop of water upon the slit formed by the tin-foil edges of the Righi bands, a very sensitive wave-detector was pro- duced. It is said the organizations just described differ from a coherer, in that the action of waves causes their electrical resistance to increase, an effect exactly opposite to that set up in the coherer proper. They are, therefore, named " anti-coherers," and differing in principle, are declared not to be subordinate to any patent claims which may cover a coherer method. There is a report, however, that the Marconi Company, presumably on the ground that the alleged anti-coherer is an "imperfect contact," is preparing to bring action for infringement against a competitor using an anti-coherer. DeForest Responder The DeForest "responder" is the most prominent type of anti-coherer. Fig. 49 illus- trates the receiving apparatus in which A and A' are two small brass rods, or wires, connected respectively to the wave-gate and to the earth. D and D are hard rubber tubes, into which is fitted the glass tube C. F and F' in- dicate the position of adjusting screws which serve to make greater or less the width of the gap which occurs at G between electrodes A and A'. B is a battery, gen- erally of two or three dry cells, and T is a telephone. The 156 WIRELESS TELEGRAPHY. ends of the wires A and A' are smeared at the gap G with a minute quantity of a paste which the inventor has named "goo." By means of the adjusting screws F F' the ends of A A' are first brought together within the tube, and Fig. 49. then slowly separated, until by repeated trials the amount of space which is best for clear signals has been attained. It will be understood that the " goo " thus bridges the gap between the electrodes. Through a microscope the paste is seen to lie in tiny globules which just touch one WAVE-RESPONSIVE-DEVICES. 157 another, but under the action of impinging waves these globules decompose and decohere, the effect being to increase the electrical resistance of the closed circuit, which, as in Fig. 49, contains a battery, a paste-filled gap G, and a telephone receiver. Now a telephone receiver gives forth audible sounds in response to the slightest change in resistance, whether diminished or augmented ; and thus, whenever a long- wave effect or a short-wave effect is produced at the sending end, it is indicated at the receiving end by long or short buzzing sounds in a telephone held or attached to the ear of an operator. Ehret System Reference to the text and diagrams which describe the system of Mr. Ehret l will serve to ex- plain one use of an anti-coherer in connection with a relay. MICRO-RADIOPHONES. Carbon Powder Wave-Detector of 1897 There is rec- ord of the employment, about 1897, of a carbon powder coherer by which Professor Jervis Smith of Oxford Uni- versity, England, maintained communication over more than a mile of space. So far as I can discover, this is the earliest specimen of a type that is now known as the micro-radiophone or micro-radio-receiver. Popoff's Micro-Radiophone of 1900 In May, 1900, Professor Popoff of Russia, as the result of experimenta- tion, concluded that it was possible to eliminate the 1 See Fig. 30, Part I., and accompanying description. WIRELESS TELEGRAPHY. coherer and relay by substituting for both either a micro- phonic arrangement of steel needles, having their extremi- ties resting upon plates of carbon, or by mixing steel filings and carbon powder. Shoemaker's Steel and Carbon Wave-Detector The steel and carbon powder type of Professor Popoff has been the subject of many patented inventions, one of which, by Mr. Shoemaker of Philadelphia, consists of a number of steel balls in a horizontal line, the space between the balls being filled with carbon powder. Shoemaker and Pickard Needle and Carbon Wave- Detector Another invention was patented in the United States, in August, 1902, by Messrs. Shoemaker and Pickard. As expressed in the patent, " It comprises a wave-responsive-device whose essential elements are of carbon and steel, respectively. A wave-responsive-device composed of these materials has the property of great delicacy and sensi- tiveness in respond- ing to electrical ra- diations, and has also the desirable property of regaining its normal condition after the cessation of influence of electrical waves. " More specifically, our invention comprises carbon terminal blocks, in contact with which are steel or iron needles, which serve to close the circuit from one carbon block to the other. As an alternative, however, it is to be understood that the terminal blocks may be of steel, and that car- bon filaments or rods may contact with them to close the circuit. ' The wave-responsive-device herein described is connected with any of the wireless signaling systems in the same relation as the numerous types of wave-responsive-devices heretofore used." In Fig. 50, 1 6 is a glass tube or any suitable envelope, on the right-hand WAVE-RESPONSIVE-DEVICES. 1 59 end of which is a metallic cap 17, through which is tapped the screw 18, which at its left-hand end screws into the central insulating portion 19, thereby clamping between said portion 19 and a brass nut 20 the carbon disk 21. 22 is a metallic cap upon the left-hand end of the tube 16, and from which extends into the tube rod 23, secured in said cap 22, and also into insulating block 19, thereby clamping between said block 19 and a nut 24 the carbon disk 25. 26 and 27 are disks of insulating material, which serve to center and steady the device in tube 16. It is to be noticed that the disks of carbon 21 and 25 are slightly smaller in diameter than the tube 16 for the purpose of preventing their contact with said tube during assemblage, inasmuch as such contact might serve to destroy the disks, due to the fact that they are thin and fragile. On to the left end of the cap 22 screws a cylin- drical piece 28, forming between 28 and 22 a cavity 29, designed to receive calcium chlorid or other desiccating material for keep- ing the air or other gas within the tube 16 perfectly dry. Communication between 29 and the interior of tube 16 is obtained by numerous holes, as 30. On the piece 28 is the binding-post 31, serving 25- fy_l_ " 21 as one terminal of the device, while cap 17 or screw 1 8 serves as the other terminal. Fig. 51 represents a plan view of one of the car- 34 bon disks as, for example, 25 which shows sym- Fig. 52. metrically-arranged small holes 32, while the inner large hole 33 permits the passage of the rods i8or 23. In Fig. 52 are shown the two carbon disks 21 and 25, supporting between them the needles 34. This Shoemaker and Pickard organization is an elabora- tion of the Popoff microphonic receiver of 1900, and is typical of its class. Fessenden. Silver Ring and Knife-edge Contact. Fig. 5 3 illustrates a radio-receiver designed by the United States Government expert, Mr. Fessenden. 7 repre- sents a coil of wire which is a magnetic field for an arma- ture 8, the latter being made preferably in the form of a i6o WIRELESS TELEGRAPHY. silver ring. Ring 8 is balanced upon two knife edges 13 and 13', one of which, as 13, is formed of a good electrical conductor, for example, silver ; and the other, 1 3', is out of circuit. A carbon block 14 is so arranged that the por- tion between it and knife edge 1 3 of the ring 8 forms part of an electrical circuit. Waves passing from the gate 6 to the earth and energizing field coil 7 will cause the ring 8 to press upon the carbon block 14, thereby increasing the conductivity of the contact between 8 and 14. " When using a telephone-receiver as a recording instru- ment, the generator 1 5 is preferably of a character capable of producing an alternating cur- rent, as such cur- rent causes a constant vibra- tion of the dia- phragm, the vibrations in- creasing in in- tensity with an increased flow of current in the circuit. This increase in intensity of action with in- creased flow of current is characteristic of this form of receiver. In this it is sharply differentiated from such devices as the coherer, which either give a strong indica- tion or do not give any. This characteristic is advanta- geous in that if the signal sent say a dot be too weak to give an action of the full intensity, it may still in most cases be read and not missed entirely, which is of value in sending code-messages." 15 Fig. 53- WAVE-RESPONSIVE-DEVICES. 161 The Code-Message Trouble. The above allusion to "code-messages" was probably first suggested by a declaration of the ocean cable companies that the Marconi Company could not transmit code-messages, an idea now prevalent among inventors competing with the Marconi Company. Why the transmission of dots should not be necessary in ordinary messages has not been made clear ; nor why there should be obstacles to the passage of code- messages which are sent by telegraphic signals exactly like other messages. Mr. Fessenden's description of Fig. 53 includes the alternate use of a telegraphic sounder as a recording in- strument in place of the telephone (i 6) shown; but it is hardly possible that a sounder in such position can have been successfully employed in practice. Marconi's Opinion of Non-Tapping Coherers. In a paper read before the Royal Institution of London in L/ CONNECTING V MERCURY V Fig. 54. June, 1902, Signer Marconi says of non-tapping coherers, that they are not sufficiently reliable for commercial work ; that under the influence of strong waves or of atmospheric discharges they cohere permanently ; and that there is an unpleasant tendency to suspend action in the middle of a telegram ; moreover, that as their resistance is continually varying, it is difficult to syntonize the circuits of which they form a part. 162 WIRELESS TELEGRAPHY. Italian Navy Radio-Receiver. The radio-receiver adopted by the Italian navy, a result of the combined efforts of its experts, is a composite of the coherer and the microphone receiver. It is used in connection with a circuit syntonized in the usual way by capa- city and self-induction. The marked illustration, Fig. 54, seems sufficiently to describe it. MAGNETIC-RADIO- RECEIVERS. In the class of magnetic- radio-receivers Mr. Fes- sen den has evolved three distinct types and Mr. Marconi one. A Fessenden Magneto- Receiver Fig. 55 is an illustration of one of Mr. Fessenden's magneto-re- ceivers, in which 7 and 7 represent field coils con- nected respectively to wave-gate 6 and to earth. 8 is an armature so sus- pended that the reaction of the current induced in 8 when- ever the coils 7 are energized will cause 8 to move. Such movement may be made observable by reflection of a WAVE-RESPONSIVE-DEVICES. I6 3 12 beam of light from the mirror 9 upon a scale. The slight move- ment of the mirror is seen in the larger movement of the spot. Another of Mr. Fessenden's devices is shown in Fig. 56, in which 10 is the wave-gate of a re- ceiving station ; 1 2 is a fine steel wire held under tension between the poles of magnet 13; 14 is a contact normally disconnected from wire 12 by the inter- action of currents. Fig. 56. -10 A Second Magneto-Receiver by Fessenden. Fig. 57 is a diagrammatic representation from Mr. Fes- senden's patent, No. 706,747, in which 10 is the antenna, 1 1 a coil having one terminal con- nected to the antenna 10, and the other ter- minal grounded. A telephone diaphragm 12, adapted to vibrate in unison with changes of current produced by waves radiated from the 12 sending station, is suitably supported in oper- ative relation to the coil 1 1 ; and the apparatus at the receiving station is tuned in harmony with the emitter of the sending station. Marconi's Hysteresis Detector. At this writing a description of the new Marconi re- ceiver has been published, but no authorized illustration of it has been printed. In Fig. Fig. 57. 58 an attempt is made to follow in diagram the 164 WIRELESS TELEGRAPHY. Marconi text. The discovery upon which this new appa- ratus is based is the fact that hysteresis is decreased by the action of Hertzian waves. Hysteresis Defined. Whenever iron is subjected to changes in magnetic strength or magnetic polarity it gen- erates and radiates heat. This phenomenon is called " hysteresis," and the amount of heat dissipated as loss by reason of such changes is known as " hysteresis loss." Changes of Polarity in Iron. How Produced. Differ- ences in polarity may occur from movements of the iron itself, as when the armature of a dynamo revolves ; or from the movements of a magnet, as when a dynamo field is caused to move about a stationary armature ; or from changes in the exciting cause, as when an alternating cur- rent is made to pulsate through a transformer. Quantitative Effects. Quantitatively, hysteresis effect depends upon the amount of iron under influence ; upon the quality of the metal, wrought-iron or steel being more affected than soft iron ; upon the density of magnetism in the iron ; and upon the rapidity of the movements which cause the changes in magnetic direction or magnetic power. Theory. Theoretically, it has been explained that heat is generated by friction as the molecules of iron in mag- netic action turn over and thus rub against one another. Description of Marconi Magnetic Detector. Referring to Fig. 58, upon a core C, which consists of fine iron wires, WAVE-RESPONSIVE-DEVICES. I6 5 are wound one or two layers B of thin insulated copper wires. Over this winding B, is an insulating coating G ; around the insu- lating envelope a bobbin F F ; and upon the bobbin a wind- ing of small in- sulated wires, D. The ends of C the winding B are connected respectively to the antenna A and the earth at E ; and the ends of the winding Fig - s8 - D to the telephone T. One face of the core C is pre- sented to, and magnetized by, the magnet M. Upon being revolved by clock work, W, the movements of M cause constant reversals in the polarity of core C, and conse- quently a certain hysteresis effect is produced. Whenever this effect is modified by the influence of Hertzian waves, an audible record of such waves is made on the tele- phone receiver. Practical Results From Marconi Magnetic Detector. For some time the form of detector just described has been in successful operation over a distance of one hun- dred and nine miles of sea surface, and forty-three miles of high land, a total of one hundred and fifty-two miles. Marconi seems to think it is more sensitive and more re- 1 66 WIRELESS TELEGRAPHY. liable than a filings coherer. Less electromotive force than with a coherer is required at the sending station ; its resistance is uniform ; and many of the precautions and delicate adjustments necessary where a coherer is used may be neglected with the hysteresis detector. ^f" : ~~ ~~-"~~ Coherer Organization Needed to Call. So far, however, in order to "call," it has been necessary to use with the new receiver, a coherer, relay, and bell. The only suc- cessful indicator of signals in connection with it is a tele- phone receiver. If, as the tests seem to indicate, a visual record can be made and retained, Mr. Marconi thinks it will be possible to transmit several hundred words per minute. A Wave-Responsive-Device by Fessenden. It may be assumed that the result of Mr. Fessenden' s labors for the United States Government, so far as wave-responsive- devices are concerned, is the subject of his patent No. 706,744, for which application was made on June 6, 1902, from the laboratory at Manteo, North Carolina. In patent No, 706,745, the inventor claims that with the device so fully described in 706,744 " messages at the rate of thirty words per minute were sent and received over a distance of fifty miles, from Cape Hatteras to Roanoke Island, using at the sending end a spark only one thirty-second of an inch long." This form of radio-receiver from the Fessenden patents cannot be included in any of the four classifications just discussed. The patentee himself describes it as "a current-actuated wave-responsive-device consisting of a con- ductor having a small heat capacity and arranged in a WAVE-RESPONSIVE-DEVICES. I6 7 Description of Fessenden's Heat-Receiver. Fig. 59 is a diagrammatic illustration- reproduced from Mr. Fes- senden's patent 706,744, in which 17 is a glass bulb. Into it are sealed two lead- ing-in conductors of plati- num wire, 1 6 16. 18 is a silver shell having at its top a glass brace 19, hold- ing the wires 16 16. The platinum wires, except at the tip 14, are coated with silver. The tip 14 which is left uncoated is a minute part, being but a few hun- dred thousandths of an inch in length. Having small volume and capacity, the loop 14 is capable of being quickly raised in tempera- ture an appreciable amount, and it is equally capable of quick cooling, thus pro- ducing rapid changes in electrical resistance. Fig. 59. 168 WIRELESS TELEGRAPHY. WAVE-GATES. Marconi's Early Experiments in England In England, about August, 1896, Mr. Marconi transmitted signals over- land a distance of two miles. No ground connection either at the sending or receiving stations was used. Adoption of High Wire and Earth Terminal The next steps in the Marconi system were the adoption of an ele- vated terminal and an earth terminal. On May n, 1897, Marconi, who was conducting experiments at Lavernock Point, England, failed of results. His receiving apparatus was set upon a cliff sixty feet above the level of the sea. Here was erected a pole ninety feet in height capped with a cylinder of zinc six feet long and three feet in diam- eter. An insulated copper wire was fastened to the cap, led down the pole, and from it made connection to one end of the coherer. The other end of the coherer was con- nected to a wire which was dropped down the cliff and dipped in the sea. Communication Established by Better Earth and Longer Wave-Gate. Both on that day and on the following, at- tempts at transmission were unsuccessful; but on May 13, the coherer and other receiving instruments having been carried to the bottom of the cliff, communication was at once established. The antenna by the change to the bottom of the cliff had been lengthened to one hundred and fifty feet. The earth connection had been strength- ened by the elimination of such resistance as was furnished by sixty feet of wire. WAVE-GATES. 169 Lodge's Early " Collecting Wire." In Dr. Lodge's first patent, filed December 20, 1897, his wave-gate served for the reception of impulses, and was called by the inventor a " collecting wire." Presumably it was but a few feet in length. Quoting from that patent : " In some cases I find that any bare wire, or a connection to earth direct or through the system of gas or water pipes, will serve suffi- ciently well as a collector or as an assistance to the insu- lated collector." Lodge Emitter. Lodge devised a form of emitter l in which electricity was "supplied to a single conductor a suddenly or disruptively by a couple of positive and nega- tive sparks from knobs b and c. A partial metallic inclos- ure d could be used to diminish waves in an undesired direction. There seems to have been no extension into space from the sphere a ; nor any switching communication between the sending and receiving sides of his apparatus. A Supposed Law. When virtue was found to exist in an elevated wire, Mr. Marconi made a number of experi- ments from which he deduced the law that the distance over which signals could be transmitted varied as the square of the height of the vertical conductors. Lodge's Cones. It was soon found, however, that no such law existed, and the attention of experts in wireless telegraphy was next given to devising wave-gates lower in height but greater in surface area. Dr. Lodge, in his United States patent filed February i, 1898, says: "I prefer for the purpose of combining low resistance with 1 Lodge patent, Appendix II. 1 70 WIRELESS TELEGRAPHY. great electrostatic capacity, cones, or triangles, or other such diverging surfaces, with the vertices adjoining and their larger areas spreading out into space." Manifestly such a construction as is shown in Fig. 25, Part I., would be especially weak to resist wind pressure, and so the inventor recommended a modification in the form of a roof, as illustrated in Fig. 21, Part I. Marconi's Thick Copper Cable. In a patent filed Janu- ary 5, 1899, Marconi describes two wave-gates. The first was an insulated cable consisting of seven strands, each strand made of seven copper wires, each one millimeter in diameter, thus making the total diameter of the cable, the number of wires being forty-nine, nine millimeters, or thirty-six hundredths of an inch. This copper cable was suspended vertically from a height of one hundred and thirty feet. Marconi's Iron Netting. The second was a galvanized wire netting two feet broad and one hundred and thirty feet long, the top of the netting being about one hundred and ten feet from the ground. Marconi's Observations on Wave-Gates in May, 1901. In a paper before the Royal Society of Arts of London, May 15, 1901, Signor Marconi said : " The original elevated straight wire which was used as a transmitter was a very good radiator of electric waves ; but its electric oscillations died away with great rapidity, though very powerful while they lasted. If a radiator be used giving off much less energy at each vibration, but emitting a series of waves WAVE-GATES. 171 over an extended period, then it will only affect a resonator tuned to that particular frequency. It will take some time, measured in thousandths of a second, for the radi- ator to set up a swinging electric force in the receiver sufficient to break down the insulation of the coherer." He further observed, in the same paper, that " early in 1900 the vertical wire was replaced by the zinc cylinder oscillators." The zinc cylinders are illustrated in Part II. as Fig. 37, and in the text accompanying that figure are described at length. Fessenden's Wave-Gates of Low Resistance and Large Capacity In May, 1901, Mr. Fessenden : who had evidently been working along the same lines as Marconi, filed two patent appli- cations whose subject matter chiefly concerned radiating conductors of low resistance and large capacity. Two of these are shown in Figs. 60 and 61. The inventor describes them as " sending conductors for electromag- netic waves," and says that they have a large capacity distributed with substantial uniform- ity over the radiating portion, and that this capacity is so adjusted that the waves radiated from the conductors have a low frequency. These conductors, it will be observed, differ from the Lodge cones in that, except for the enlargement in Fig. 61, they are uniform in figure. Mr. Fessenden says it has been held that the capacity of the upper portion of a conductor of uniform cross sec- tion is much lower than that of the middle or lower por- Fig. 60. 172 WIRELESS TELEGRAPHY. tion ; but that by actual measurements he has found this not to be the case, the upper portions having practically the same capacity as the lower. Further, he says, that when far from the ground the capa- city of a conductor with respect to that ground is dependent not upon its distance from the earth, but upon its size and shape. Of the en- largement (17) in the middle of the sending conductor shown in Fig. 61, the inventor says : " The effect of locally increasing the superficial area of the sending-conductor, or of locally increasing the capacity Fig. 61. ky any other suitable means, is to produce two or more sets of waves of different periodicities, the periodicity of the first being dependent upon the electrical constants of the sending-conductor as whole, and the periodicity of the other depending upon the position and amount of localized increase of capacity, in the same w y ay as by attaching a weight or spring to a piano wire between its extremities additional vibrations in the wire are created." Fessenden's Wave-Gates of High Specific Inductive Capa- city. Figs. 62 and 63 are from the Fessenden patent 706,739. The first is a sectional elevation, and the second Fig. 62. Fig. 63. a plan of a sending conductor similar in configuration to that shown in Fig. 61, but now surrounded by a coil of WAVE-GATES. 173 wire, between the turns of which is supplied an insulating medium of high specific inductive capacity. " By this means," the patent declares, "it is possible to increase the capacity of the conductor without altering its height, and yet without altering the relation between the wave length and the medium and the length of the conductor. In other words, to obtain the same effect as is produced in air by increasing the height of the conductor " ; or, again, "that all the functions or desirable results incident to the employ- ment of a long high conductor can be attained by a rela- tively short low conductor." In Figs. 62 and 63 reference number I indicates the radiating portion proper ; 2 may consist of a coil of insu- lated iron wires of No. 40 Brown & Sharpe gauge. The wires in the coil are maintained under tension, the turns being spaced a distance apart approximately one-fourth the diameter of the wire. The spaces between the wires 2 may be filled with an insulating material of high specific inductive capacity, 1 such as rubber, indicated by a black mass in the figure ; 3 is a reflecting plate formed of metal and arranged on the side of the conductor opposite that facing the direction in which the waves are to travel ; 4 4 are spark knobs ; 7 is an enlargement for a purpose similar to reference number 17 of Fig. 61. Of 7 the inventor says, it may be a band of conducting material, and that such a construction affords means for adjust- ing the capacity by adding or removing bands, or by changing their position along the conductor. The main advantage, and a matter of especial necessity to the Fes- senden system, is that this device enables the operator to obtain long waves from a short conductor, thereby avoid- ing the expense involved in the erection of high masts. 1 See p. 183. 174 WIRELESS TELEGRAPHY. Fessenden's Wave-Chute Another Fessenden inven- tion is for a "wave-chute," called also an "artificial ground." Of this device Fig. 64 is an elevation and Fig. 65 a plan. In those illustrations reference numbers 2 13 Fig. 64. are longitudinal wires in the wave-chute ; and 3, trans- verse wires connecting together wires 2 ; 1 1 is a metallic guy rope or chain for supporting the mast. In one of his descriptions of the wave-chute the inventor says : INVENTOR'S DESCRIPTION OF WAVE-CHUTE. "I have found that it is essential for the proper sending and receipt of these waves that the sur- face over which they are to travel should be highly conducting, more espe- Fig. 65. daily in the neighborhood of the point where the waves are generated. I have found that this highly-conducting portion of the surface should pref- erably extend to at least a distance from the origin equal to a quarter wave length of the wave in air, and in the direction toward the station or sta- tions to which it is desired to send the waves. Where the sending-station is in a city or similar place where the waves may be cut off by high build- ings or high trees, this highly-conducting path should be extended still */ WAVE-GATES, 1/5 farther, until it passes beyond the limits of the obstacle, and there the highly-conducting portion, which may be in the form of a strip of metal or other conductor, or of a number of wires, is connected to ground." and, further, that " on rocky shores," as an instance, " salt spray sometimes dashes, rendering the ground surface near the station a conducting one which was previously an insu- lating one ; and in such case an artificial ground makes the conditions constant in all weathers." Preventing Absorption of Waves into Iron or Steel Guys. " That it is preferable in such places to employ iron chains or iron wire ropes, and that such iron or steel guys would in general absorb waves rapidly," therefore he coats them and the mast with a non-magnetic film, such as zinc or lead, thus rendering their resistance to the currents pro- duced by electromagnetic waves of the frequency used so low that there is little absorption. It is desirable that the guys be insulated from the ground, and " in order to ren- der it certain that the natural period of the mast and guys is different from that of the electromagnetic waves, said mast and guys may be wrapped or encircled with one or more coils or turns (13) of iron strips, or wire, preferably insulated, thus increasing the inductance and natural period of the mast and guys, and permitting the employ- ment of conducting material e.g., iron or steel in the mast and guys. As shown in Fig. 64, the coils or turns may be either formed locally, i.e., extending a short dis- tance along the mast or guys, or such coils or turns may extend continuously along such parts. " While the coating of the mast and guys with non-mag- netic material need not necessarily be used with the coils or turns, it is preferred in most cases to both coat the mast and guys with non-magnetic material and also to WIRELESS TELEGRAPHY. employ the coils or turns of magnetic wire or strips, which may be formed of nickel or other magnetic material. No. 40 Brown & Sharpe gauge of wire is a size suitable for the purpose." Probable Law or Wave-Propagation Through Space. - It seems natural and probable that the dissipation of energy in wave-propagation through space follows laws analogous to those that govern the conduction of electrical currents along wires, that the amount of loss is inversely proportional to the cross-sectional area of the conducting medium and to the square of the applied pressure. If etheric waves are radiated in straight lines, then the cross-sectional area of a wireless conductor is the product of the height and the mean horizontal peri- phery of the wave-gate. It is also true that the amount of energy which may be transferred from the surface of the send- ing conductor to the other is modified by the resistance to vibrations of the carrier which conveys those vibrations from the initial source of wave generation to the emitting surfaces. The Marconi Wave-Gates at Poldhu and Glac< Bay. - Figs. 66, 67, and 68 are, respectively, illustrations of the Fig. 66. WAVE-GATES. 177 Marconi Company's wave-gates at Poldhu, England, and at Glace Bay, Cape Breton. Fig. 68 carries out the idea of Fig. 67. Professor Lodge, referred to at some length in Part II., and also mentioned in the present part in connection with Lodge's wave-gate. Fig. 68. Cape Breton is an island and politically a part of the prov- ince of Nova Scotia. It is twelve miles from Sydney, and 178 WIRELESS TELEGRAPHY. separated from the main land by the Strait of Canso. Each of the four towers, shown in the Glace Bay picture, are two hundred and fifteen feet high. They form a square, each side of which is two hundred feet in length. Between the eastern towers and the sea the ground is absolutely bare of soil. The structures are composed of strong steel timbers bolted together and firmly anchored in foundations of cement concrete. At different heights depend from the towers hundreds of steel guys (not shown in the picture) are secured to the rocky surface of the ledge from a few feet to fifty yards from their respective bases. SHIELDS. 179 SHIELDS. A device peculiar to Wireless Telegraphy is the metal shield used to protect the coherer from the strong waves of a transmitter in close proximity at the same station. Fig. 69 shows one of Dr. Lodge's devices, which he thus describes : COHERER SENSITIVE TO LOCAL AS WELL AS DISTANT OSCILLATIONS. " A coherer is sensitive not only to the desired impulse arriving from a h CIF Fig. 69. distance and conveyed to it by the collectors, but it is also liable to respond to any local sparks or electric surgings in its neighborhood, especially to oscillations in an adjacent emitter. It may be protected from all these by complete inclosure in a flawless metallic box." PROTECTION BY METALLIC COVERING. " For the purpose of protect- ing the coherer from undesired disturbance, therefore, I inclose it (some- times with all coils, wires, batteries, and the like connected to it) in a metallic covering or case, as shown in Fig. 69, leaving only one or 180 WIRELESS TELEGRAPHY. more round holes or short tubes w for the collector terminal or terminals to enter by, and for vision or other needful purpose requiring an aperture, for through round holes of moderate size large electric waves do not readily pass, whereas through chinks or long slits, no matter how infinitely narrow,' they can pass with ease. They likewise pass in by means of any insulated wire which enters the box ; but through any wire w r hich is thor- oughly joined to the metal wall of the box where it enters the waves cannot pass." DESCRIPTION OF FIG. 69. "In the particular arrangement shown in Fig. 69 a single terminal h is employed which is insulated from the cas- ing by tube w, and is connected to one terminal only of the coherer. This construction is effective and desirable in certain cases, and it is found that the Hertzian waves pass in readily through the single wire. Hence it is not absolutely necessary to remove the terminal h from its aperture when it is not being used for the purpose of establishing communication and enabling waves from the collector to enter the box and reach the coherer. " The only part of the coherer or detector portion outside the box is the index or needle mirror z of the telegraphic receiving instrument em- ployed, which is acted upon and deflected by its coil g inside acting magnetically through the metal wall. " When the plan of withdrawing the terminals of the box is adopted, it is sufficient to put the coherer above mentioned alone in the box." Marconi's Shield. Marconi's organization for shielding his coherer is illustrated in Fig. 70. His own description is as follows : " When both instruments are employed at the same station, it is found that the sensitive tube or sensitive imperfect contact is liable to injury by its close proximity to the sparking appliance. In order to obviate this objection, I inclose the receiver containing the sensitive tube or sensitive imperfect contact in a box of metal having only a small opening into it, and I employ the same conductor and earth-plate for both instruments. The earth-plate is permanently connected to one terminal of the sparking appliance and to the outside of the box. The insulated conductor can be connected by a plug either to the other terminal of the sparking appliance or to the other end of the imperfect contact. "According to my present invention I inclose the receiver in a metallic box A. One-twentieth of an inch is a suitable thickness for the metal. SHIELDS. 181 The inside of the box is connected by a wire A' to the relay-circuit, and its outside by wires A 2 A 3 to one terminal of the telegraphic instrument h and earth E, respectively. The other branch of the relay- circuit is connected by a wire A 4 , insulated from the box, to the other terminal of the instrument h. " B is a coil on the wire A 4 and outside the box. It is protected from mechani- cal injury by a wooden case C ; but this may be omitted. The coil B may contain about twenty yards of wire one seventy-fifth of an inch in diameter and have one hundred and twenty turns. "The wire is insulated with gutta-percha D, which is covered with tin-foil F, Fig ' 7 - as shown in Fig. 71. The tin-foil is in electric connection with the box. The coil B prevents oscillations of the transmitter Fig. 71. from reaching the coherer at the same station through the wire A 4 . The aerial conductor u can be connected by a flex- ible conductor, plug G', and spring-contacts H and H' either to one of the balls e for transmitting or to one end of the tube j for receiving. The other end of the tube/ is connected by a wire J to the inside of the box." 1 82 WIRELESS TELEGRAPHY. CONDENSERS, INDUCTANCE-COILS AND KEYS. To round out this division of the work and to furnish means of ready reference, there is presented here a brief account of important principles and devices connected with Wireless Telegraphy, which, however, are neither novel, nor peculiar to it. Condensers. When a source of electrical current is connected to a conductor, a long wire for instance, and that conductor is insulated both along its course and from a return wire or from the earth, it will become charged. Suppose instead of a long wire the conductor be a small sheet of tin-foil positively charged, and suppose another sheet of tin-foil negatively charged be placed near the first one, say, by gluing the two sheets upon opposite sides of a glass plate, then the amount of charge which may be spread upon the tin-foil sheets will be greatly in- creased. The total quan- Fig> 72> tity of electricity which may thus be stored depends upon the area of the surfaces in the metal, upon the nearness to each other of the two oppositely charged sheets, which is to say the thinness of insulation between them, and also upon the composition of the insulating medium or "dielectric." Suppose two tin- foil sheets are joined together at their edges and interlaced with and insulated from two other sheets connected at the edges, then a diagrammatic expression would be as in Fig. 72, that diagram being the accepted symbol for a condenser. Multiplication of sheets increases, in direct proportion, CONDENSERS, INDUCTANCE-COILS AND KEYS. 183 the capacity of the condenser for the storage of electricity. The amount stored is also more or less according to the " specific inductive capacity " of the insulating medium the " dielectric." If the effect of dry air be taken as I, that of rubber is equivalent to 3, of sulphur to 4, of mica to 7, and of glass to 9. For convenience and economy condensers are usually made of tin-foil plates separated by sheets of paraffined paper and sealed in a wood box. Marconi's Condenser. Marconi describes as follows the condenser used in connection with his earlier forms of apparatus for " tuning " the circuit. " It was composed of six tin-foil (or copper) plates connected to each terminal, each plate being 1.97 inches by 1.18 inches, the plates being insulated by paraffined paper, .067 inch thick. Its capacity measurement was one-fourth of one microfarad." Tesla Condenser. As has been shown already, the con- denser plays a very important part in Tesla's wireless transmissions. In his sun motor patent shown in Fig. 15, Part I., he uses mica as a dielectric, and treats the condens- ers by a process of his own invention, consisting in inclos- ing the device in an air-tight receptacle, exhausting the air from the receptacle, introducing into a vessel containing the device an insulating material rendered fluid by heat, and when this material has permeated the interstices of the condenser subjecting the whole to pressure which is maintained until the material has cooled and solidified. Improvements Other inventors have improved this process by so contriving the method of filling that the molten insulating material solidifies first in the interior 1 84 WIRELESS TELEGRAPHY. parts of the condenser and then on its edges. Paraffin wax is the principal ingredient of the insulating material in these later inventions. INDUCTANCE COILS. Illustration of Lines of Magnetic Force. Suppose a piece of cardboard be held horizontally so that iron filings will rest upon its surface, and that it be pierced through its center by a vertical copper wire. If the free ends of N Fig. 73- that wire above and below the card be connected to the poles of a battery, the filings will arrange themselves in radiating lines as in Fig. 73. The influences which ema- nate from the wire are named magnetic lines of force, and the area over which such influences are exerted is a mag- netic field. CONDENSERS, INDUCTANCE-COILS AND KEYS. 185 Induction Between Two , Circuits If st second wire with its ends joined together, to make an endless loop, be brought into a magnetic field, there will be developed in this loop an electric current. If, while the two wires are in proximity, either the loop or the battery circuit be moved or the pressure in the battery circuit be varied, or the lines of force are passed across the loop, or the loop cuts them, or any electrical change is made, an electric circuit is set up in the loop. Induction and Counter-Force in a Coil. If a portion of a wire in a charged circuit be wound in a coil, the lines of force which may emanate from any one turn are cut by the wires of the other turns, and so a varying current may produce an inductive effect in that coil. The counter pressure thus created tends to stop the development of the flowing current, because the induced force is opposite in direction to the initial one ; but if the flowing current be broken or weakened or strengthened, or in any way changed in direction or in force, then the secondary stream takes the same direction as the primary one, and, as both work together, there is a surge or impulse due to the sudden release of energy that has previously been bound. One Coil is Placed Within Another. It is the usual practice to place in the interior of a coil of one circuit turns of wire which are part of another. This arrange- ment secures the best results that may be had with coils alone, but a still greater effect is had by placing an iron core within the inner coil. 1 1 The analogy of inductive effect to the load upon a vibrating spring has been illus- trated by Fig. 7, p. 29, Part I. 186 WIRELESS TELEGRAPHY. One of Marconi's Inductance Coils. Mr. Marconi, de- scribing an inductance, says : Primary. " The primary is wound upon a glass tube .635 cm. (about i inch) in diameter. This primary wind- ing consists of two parallel windings of two hundred turns each of copper wire .012 cm. in diameter (about .005 inch, or No. 36, B. & S. Gauge), the wire being insulated by a single covering of silk. The resistance of these two wind- ings in parallel is about 3. 1 ohms." Secondary. The secondary winding consists of 800 turns of a wire .005 cm. (.002 inch) in diameter, having a resistance of about 140 ohms, and wound either over or under the primary winding. Another Marconi Winding. Another Marconi induc- tance coil has the secondary wound directly upon a glass tube .3 inch diameter, the copper wire being .002 inch diameter with a single silk covering, and making three hundred and seventy-five turns about the tube with a resistance of seventy-nine ohms. Over this secondary is wound the primary of copper wire .005 inch in diameter with a single silk wrapping. Resistance seven and one- tenth ohms. Each of the four windings described consists of a single layer. TRANSMITTING KEYS KEYS IN SECONDARY CIRCUIT AND CONTACTS IN OIL, In the initial American patent of Marconi, filed Decem- ber, 1896, it is said that when working with large amounts CONDENSERS, INDUCTANCE-COILS AND KEYS. l8/ of energy it is better to keep the primary circuit in con- stant operation and to interrupt the discharge of the secondary ; moreover, that in such cases the contacts of Fig. 74. the key should be immersed in oil, lest, owing to the length of the spark, the current continue to pass after the contacts have been separated. In the DeForest system the key contacts are also made in oil. Pig. 75- Fessenden Key-Contacts. One of Mr. Fessenden's inventions in keys is illustrated by a plan view, Fig. 74, and sectional views, Fig. 75 and Fig. 76. In this transmission it is intended to keep the generator in continuous operation, the manipulation of the key throwing the sending conductor out of tune with the 1 88 WIRELESS TELEGRAPHY. receiving circuit of the distant station by short-circuiting more or less of the tuning device. Referring to the figures, switch 3 is employed to render the generator inoperative while the apparatus is being used as a receiver ; 5 indicates one or more connected pairs of parallel wires to form a, tuning grid ; 6 indicates movable contacts adapted, to.- connect electrically the wires or con- ductors of each pair ; 7 is a box containing sufficient oil to 7- ,o Fig. 76- cover the wires to a depth of about one inch ; 8 are spring arms ; 9 are adjusting blocks mounted in arms in the cover of the box ; and 10, loa, lob, ice, icd are fingers arranged to be brought into successive contact with one or more of the wires of the grid, thus to shunt more or less of the capacity and self-inductance of the sending circuit. MARCONI'S TRANSMITTING KEY AND LIGHTNING-GUARD. In Fig. 77 is shown a key arrangement devised by Mar- coni for two objects, first, because the wave-gate is often charged with atmospheric electricity which, when it is shifted from the transmitting to the receiving circuit, is liable to impart to the operator and to the coherer an injurious shock ; and, second, to prevent the accidental CONDENSERS, INDUCTANCE-COILS AND KEYS. 189 operation of the transmitter when the aerial conductor is connected to receiver. The arm of the key is prolonged beyond its pivot, and carries an insulated contact which is permanently connected to the aerial conductor. Below this contact on the base of the instrument is the terminal of the receiver. The arm is so arranged that immediately Fig. 77- after its release by the operator, subsequent to the send- ing of a message, it turns about upon its pivot, bringing the above-mentioned contact and terminal together, so connecting the receiver with the aerial conductor. In the drawing b' and 4 indicate the contacts of an ordinary Morse key and a high insulating handle. The extension arm b has an insulated contact b2. When the key is released by the operator its longer arm falls by its own weight, the contact b2 descending upon the con- tact . 190 APPENDIX I. CQ a f Plate Ic Reproduction of drawing accompanying United States Patent of Amos E. Dolbear, No. 350,299, dated October 5, 1886. [See p. 96.] APPENDIX I. UNITED STATES PATENT OFFICE. AMOS EMERSON DOLBEAR, OF SOMERVILLE, MASSACHUSETTS, ASSIGNOR, BY MESNE ASSIGNMENTS, TO THE DOLBEAR ELECTRIC TELEPHONE COMPANY, OF NEW JERSEY. MODE OF ELECTRIC COMMUNICATION. Specification forming part of Letters Patent No. 350,299, dated October 5, 1886. Application filed March 24, 1882. Serial No. 56,264. (No model.) To all whom it may concern : Be it known that I, AMOS EMERSON DOLBEAR, of Somerville, in the county of Middlesex and State of Massachusetts, have invented a new Mode of Electric Communication, of which the following is a full, clear, concise, and exact description, reference being had to the accompanying diagram, forming a part hereof. My invention relates to establishing electric communication be- tween two or more places without the use of a wire or other like conductor ; and it consists in connecting the transmitting-instrument with a ground the potential of which is considerably above the normal, and the receiving-instrument with a ground the potential of which is considerably below the normal, the result being that an impulse from the transmitter sufficient to cause the receiver to give intelligible signals is transmitted through the earth without the need of any circuit, such as has heretofore been deemed essential In the diagram, A represents one place (say Tufts College), and B a distant place (say my residence). C is a wire leading into the ground at A, and D a wire leading into the ground at B. G is a secondary coil, one convolution of which is cut, the ends thus formed being connected with the poles of the battery/', which 191 I9 2 APPENDIX I. has a number of cells sufficient to establish in the wire C, which is connected with one terminal of the secondary coil G, an electro- motive force of, say, one hundred volts. G in this instance also rep- resents an induction-coil, T being a microphone-transmitter, f its primary circuit, and f its battery that is, the battery /' not only furnishes the current for the primary circuit, but also charges or elec- trifies the secondary coil G and its terminals C and H'. Now, if words be spoken in proximity to transmitter T, the vibra- tion of its diaphragm will disturb the electric condition of the coil G, and thereby vary the potential of the ground at A, and the variations of the potential at A will cause corresponding variations of the potential of the ground at B, and the receiver R at B will reproduce the words spoken in proximity to transmitter T, as if the wires C D were in contact or connected by a third wire. Electric communica- tion may be thus established between points certainly more than half a mile apart ; but how much farther I cannot now say. There are various well-known ways of electrifying the wire C to a positive potential far in excess of a hundred volts, and the wire D to a negative potential far in excess of a hundred volts. In the diagram, H H' H 2 represent condensers, the condenser H' being properly charged to give the desired effect. The condensers H and H 2 are not essential, but are of some benefit ; nor is the con- denser H' essential when the secondary G is otherwise charged. I prefer to charge all these condensers, as it is of prime importance to keep the grounds of wires C and D oppositely electrified, and while, as is obvious, this may be done by either the batteries or the condensers, I prefer to use both. The main difficulty in utilizing my invention on a large scale is that when there are many spots corresponding to A and B signals transmitted from any A will go to the nearest B, or to several B's, depending upon proximity and other causes. One method of obviat- ing this difficulty is to use a given A only during a certain assigned time for communicating with a certain B, the particular B being arranged to receive communications only during the assigned time. Thus, if there were ten B's within a given area, then the first B might be used for the first hour, the second B for the next hour, and so on, and the first A for the first five minutes of the first hour, the second A for the next five minutes, and so on, so that either one of the A's might have free communication with the first B, each for its assigned time during the first hour, and either A with the second B, each for its assigned five minutes of the second hour, and so on. APPENDIX I. 193 In practice there will be of course both a receiver and transmitter at A and B, proper switches being used to bring either into use, as will be well understood without description. I have spoken only of telephone-instruments, as these give the best results ; but any electric instruments may be used capable of utilizing the currents passing through the earth from C to D, and the strength of such currents can be largely increased by increasing the positive potential of C and the negative potential of D. It will also be obvious that if the end of coil G (shown in the diagram as con- nected with one armature of condenser H') be grounded, and the end shown grounded be connected with the condenser, then C will be minus, and D must therefore be made plus. What I claim is The art above described of communicating by electricity, consist- ing in first establishing a positive potential at one ground and a nega- tive at another ; secondly, varying the potential of one ground by means of transmitting apparatus, whereby the potential of the other ground is varied ; and, lastly, operating receiving apparatus by the potential so varied, all substantially as described. AMOS EMERSON DOLBEAR. Witnesses: G. B. MAYNADIER, JOHN R. SNOW. APPENDIX II. UNITED STATES PATENT OFFICE. OLIVER JOSEPH LODGE, OF LIVERPOOL, ENGLAND. ELECTRIC TELEGRAPHY. Specification forming part of Letters Patent No. 674,846, dated May 21, 1901. Application filed December 20, 1897. Serial No. 662,688. (No model.) To all whom it may concern : Be it known that I, OLIVER JOSEPH LODGE, a subject of the Queen of Great Britain, residing at Liverpool, in the county of Lan- caster, England, have invented certain new and useful Improvements in Electric Telegraphy, of which the following is a specification. My invention relates to electric telegraphy ; and it consists mainly in utilizing certain processes and combinations of apparatus whereby I am enabled to demonstrate the presence of, and to indicate in a receiving-circuit the reception of, what are known as "Hertzian waves " emitted from any suitable apparatus at a distance from the receiving-circuit and propagated through space. Thus after a suc- cession of electrical surgings of predetermined duration have been caused to emanate from the emitter in accordance with the Morse or other code of telegraphic signaling the same are taken up in the receiver-circuit and so rendered intelligible, and a telegraphic system is thus obtained. My invention relates, further, to certain improvements in connec- tion with the emitting apparatus, and comprises the other improve- ments hereinafter more particularly described and claimed. The annexed drawings, which are diagrammatic representations, illustrate my invention. 194 APPENDIX II. 195 Fig. 1 Plate II. Reproduction of drawing accompanying United States Patent of Oliver Joseph Lodge, No. 674,846, dated May 21, 1901. 196 APPENDIX II. Figure i shows the essential parts of one form of emitting appara tus. Fig. 2 illustrates one form, and Fig. 3 an alternative arrange- ment, of the apparatus and assembly of parts which constitute my receiving-circuit. Fig. 4 shows a form of "coherer," and likewise serves to illustrate a means for the automatic breaking down of the cohesion resulting from the reception of waves by the coherer, as hereinafter fully described. Fig. 5 illustrates an alternative form of coherer, and Fig. 6 a still further modified form thereof and an alter- native means of breaking down cohesion. Fig. 7 shows the coherer and other parts incased within a metallic covering, as hereinafter described. As emitter of the Hertzian waves for the purpose of this invention I may employ any known or suitable device in which a condenser or Leyden jar or other electric capacity consisting either of a pair of insulated plates or of a single plate and the earth is charged by an electrical machine (such as Wimshurst's), or a Ruhmkorff induction- coil, or a battery, or any other well-known means, to a high potential and then discharged suddenly with a spark between suitably arranged and prepared surfaces in air or in any medium, such as oil. In Fig. i I have shown a form of emitter in which electricity is supplied to a single conductor a (shown as a sphere, but which may be of dumb-bell or any other shape) suddenly or disruptively by a couple of positive and negative sparks from knobs b and c and there left to oscillate and emit waves. A partial metallic inclosure ^/may be used to diminish waves in undesired directions. Both of these arrangements are my invention. 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