NIKOLA ~....., ÆTHERFORCE NIKOLA TESLA ON HIS WORK WITH ALTERNATING ÆTHERFORCE Second banquet meeting of the Institute of Radio Engineers (now part of the Institute of Electrical Engineers) at Luchow's in New York City, April 24, 1915. Photo by C.A. Schere Smithsonian Institution Standing at back from left, George W. Ferdinand John Stone Jonathan Lee de Nikola Fritz Alfred N. Ernst F.W. Pierce Braun Stone Zenneck Forest Tesla Lowenstein Goldsmith Alexanderson Tesla refers to these contemporaries in the interview at pages: not mentioned 103 16, 124 16, 133 100 178, 179 not mentioned 24, 171 ÆTHERFORCE Tesla Presents Series 1 NIKOLA TESLA ON HIS WORK WITH ALTERNATING CURRENTS AND THEIR APPLICATION TO WIRELESS TELEGRAPHY, AND TRANSMISSION OF POWER An Intervievv Leland 2002 Twenty First Century Books Breckenridge, Colorado ÆTHERFORCE Copyright © Twenty First Books All reserved. First Published 1992 Printed in the United States of America by Fidlar Doubleday, Inc. No part of this book may be reproduced in any form or by any means, electronic or mechanical, or by any information storage and retrieval system, without in from the publisher. Library of Long!:ess Cataloging-in-Publication Data Nikola, 1856-1943. Nikola Tesla on his work with currents and their to wireless telegraphy, telephony, and transmission of power: an extended interview / Leland U1(lerSOtl. editor. p. cm.-- Originally published: 1992. Includes index. ISBN 1-893817-01-6 2. Tesla, Nikola, 1856-1943--Interviews. 3. Electric States--Interviews. 4. systems--United States--Patents. 5. Electric currents, Alternating. 6. Telegraph, Wireless. 1. Anderson, Leland 1. II. Title. ill. Series. TK257 .T48 2002 621.382'092--dc21 2002072006 Originally & by Sun uu"uU'I"" Denver a subsidiary of Colorado ·~--··--Books Box 2001 .....,U.""""H.L~UJ<,", Colorado 80424 IV ÆTHERFORCE This work is dedicated to the late D. Jordan, Professor emeritus of American history, University of who pressed his to the review of legal records in historical research. few Istc::mans, librarians, and archivists L¥~'V~H"L.~the of materials. . .. Yet the law, in one way or is the basis of most institutions-political, social, cultural, economic.... It is unfortunately a truism that graduate students are seldom introduced to materials."* * "In Search of Legal n~~,,,,u,, American Archivist, Vol. No.4 (Oct. 1970). v ÆTHERFORCE ÆTHERFORCE Introduction CONTENTS I. High with Wireless and Mechanical rv. Apparatus Damped Waves Oscillators Condenser Discharges; for Transformation by Continuous Waves VI. Energy Transmission VIII. IX. Receiving of Remarks L .~"'~ ~t-""A of 1915 shipboard LLa,••,,,,.JLlL spiral antenna [Re£ from p. inventory Xl 1 9 36 48 76 125 148 1 169 181 1 1 237 ÆTHERFORCE FIGURES Figure Page 1 Diagrammatic illustration of first high frequency alternator with 384 poles. 4 2 Photographic view of alternator [shown in Fig. 1]. 6 3 Light and motive devices operated from this alternator in novel manner. 7 4 Vacuum tubes lighted in alternating electrostatic field. 8 5 Illustrating various ways of using a high frequency alternator. 10 6 Diagram of the second machine built with no wire on the rotating part. 13 7 Photograph of machine covered by US. Patent No. 447,921. 16 8 Diagrammatic drawing of the third and larger machine with 480 poles. 18 9 Photographic view of alternator covered by US. Patent No. 447,921. 19 10 Small alternator of very high frequency built for purposes of investigation (receivers). 20 11 Small high-frequency alternator of different construction, for the same purposes. 20 12 Diagrammatic illustration of machine with rotating magnetic field excitation. 22 13 Instrument to receive radio waves of 1896-1899 structure. 25 14 Electrical condenser described in US. Patent No. 464,667. 30 15 Electrical condenser described in US. Patent No. 567,818. 31 16 Improved form of electrolyte condenser as used in N.yC.laboratories. 33 17 Form of condenser with air under great pressure as dielectric. 33 18 Apparatus for manufacture of condensers and coils to exclude air. 34 19 Simple mechanical oscillator used in first experiments. 36 20 Mechanical oscillator with air spring combined with electric generator. 37 21 Another mechanical oscillator with controlling electromagnetic system. 38 22 Another type of small mechanical electromagnetically controlled oscillator. 39 23 Large electro-mechanical oscillator for generating isochronous oscillations. 40 24 Diagram of electro-mechanical oscillator for generating isochronous oscillations. 40 25 Double compound electro-mechanical isochronous oscillator. 41 26 Diagram of double compound electro-mechanical isochronous oscillator. 42 27 Large mechanical and electrical isochronous oscillator with four vibrating parts. 43 28 Diagram showing length of section of large mechanical and electrical oscillator. 44 29 Small high frequency mechanical and electrical oscillator used in many investigations. 45 30 Diagram of small high frequency electro-mechanical and electrical oscillator. 46 31 Method of transformation of electrical energy by oscillatory condenser discharges. 49 32 Series quenched spark gap. 50 33 Discharger working in hydrogen rich atmosphere, still further weakened by heat. 51 34 Oscillatory apparatus with interrupter in oil. 53 35 Apparatus with mechanical break as installed on a large scale in the N.yC.labs. 55 36 Isochronous mechanical break used in 35 So. Fifth Avenue laboratory. 57 37 Mechanical break with two oppositely rotating discs. 58 ÆTHERFORCE with break. ~""J'A""L."un HH."',llAUJ''-D.J. by condenser discharges (both ",,+"PIP"" transmitting -.u..........". illustrating transmission and transformation of through one vacuum tubes and lamps. U.a..l""LLLU"\..U through one wire. which a at the of a 88 56 which the coil is not directly \.Vl.lll,,\. 89 57 preceding were made. 91 with coils ,,,UU,,,,,'VH of energy with 93 60 Application of transmission messages. 93 61 .U.U""'"'''''''''U):; an eXJJer:tmc~nt alternator and 62 Striking expenrnen electrorrlag:net:1c waves. 95 An important experiment in the transmission of energy performed in 1899. 96 65 98 66 101 67 wave arr:~;errlefi1ts. 68 111 69 113 70 electricity set movement. 114 71 ",-'.H"''-H"0 were performed. 1 72 Diagram showing general arrarlj;;erneIlt of transmitting and receiving \...U.'.U"'-,,!. 1 Experimental at Colorado a later phase development. 117 74 at Colorado investigative structure. 118 75 of a "",-uao,.«'- transmitter a pressure of 12 volts. 121 Another discharge remarkable for symmetry at Colorado plant. IX ÆTHERFORCE 77 circuits. 123 78 the Houston 79 o f o f LL were, how he conceptualized he proceeded, perto>ttIled his historic when key results were how he L""''-'''"'-U himself, was results of his He asserts is experimentally Listen to electrical phenomena to his attorney: "magnificent," " "glorious," Edmund Spencer or a once said, me even in a legal briefing. He weaves imagination and us words! gossamer web of encnanrrrler.I(--~;n yet our nearly 80 years a stenographer recorded Who was Nikola Tesla? Philadelphia, Lord to his Society discovery. was one of the waves. * It may just be that magnifying is enough information reader will have to to solve the puzzle himself. ÆTHERFORCE It is commonly understood by power rotating field AC polyphase power distribution throughout However, most electrical engineers are unaware that, as late as 1943, he (not Marconit) was by the U.S. Court as having priority of" are aware that, when attempted to patent digital logic gates World War II, U.S. Parent Office Tesla's priority the electrical implementation of logic secure communications, control systems, As a a monopoly on digital logic in was unable to Tesia served the electrical engineering profession in its highest offices. In the early 1890s, was as \.,'\.,... L.... U of the Institute of now of Electrical and At Graham Bell was its president. Tesla two as and, a one his laboratory technicians at the Colorado Springs experiments served as first vice-president of the Institute of Radio when it was formed 1903. This was the now, famous consulting the grid biased amplifier (for 1918),4 the and two with comments on the propagation of £enn,~ck and sky waves by Austin, appeared in February and June issues of this It be that of the professional ..pr'p",,,.,; over 13 honorary from such as Columbia, £in;,p...,,,. H':>Wll .... '..lUl 1"""''''11,1''''' of Paris, Prague, and Sofia. Recently, fascinating fact about has come to all it is now known that was nominated for an undivided Nobel physics in 1937.5 Tesla's nominator, Ehernhaft, of Vienna, had Einstein for the Nobel * E. Scott, of has said, evolution power from the discovery of Faraday in 1831 to the initial great installation of the polyphase system in 1896 Niagara is undoubtedly the most tremendous all history." [Electrical 1943 (Vol. 62, 8), pp. t Although it took the courts decades to figure out, the facts were well understood by technical men of the day. Robert H, Marriott, once said that Marconi had, " ... played the of a sales engineer. A money getting company was formed, which in attempting to obtain a monopoly, set out to to everybody that Marconi was inventor and that they that patent on to a monopoly." [Radio oro'aat'aST. 1 (Vol. 8, No.2), XIV ÆTHERFORCE and """"""'u.. ,,"'.>.u;:;:. his admirers 1893, published a remarkable century now it will still along with electric waves, wrote, and fellows, and university prt:SlGlenrS scientific and engineering world. (1888-1889), edited and It is in print today, and a """'~H"HH" u,-""-aLYU... to progress of is descriptive Tesla Unlike most aforementioned no financial ;:'UIJIJ'.J.L to fall back on themselves in the felt no compulsion to these must dig (and to make it to one "skilled Dr~ so it is ",..,........",,..,..., a faculty position or res,eaJrCh ~H~""","'\"'. marketplace. It is not surprising, in the open literature day. For literature, only enough is U~c''-i'j''''U art." influence scientists simply did not 10 LV'-,J",.ull\." in The I t will Guly 20, 1931). XVll ÆTHERFORCE A Visit to a Law Office have been ushered into an oal:e-d.ec()rated law office New Tesla, now 60 years old, bushy black hair, slight U.L\.''''''','-' his piercing light blue-grey possesses a winning smile wears no jewelry or watch a somewhat voice, and '.II"",",,,"lY and convincingly. He is the cosmopolitan in his speech, manner, He numerous drawings, mUJcr:s. Across a wooden attorney. His demeanor is tJ.L\JU;;""'.LUU41 and serious, his are penetrating, manner is deliberate. He is aware professional reputation international regard esteemed gentleman that him, and he is understanding every that he can turn to his in the dramatic contests at law which will soon occur. present is a stenographer, providing the an accurate written tralrlS(:rll=lticln of every thought which soon unfold. The L>JL.LU''''.uLL....'' over, the counselor and References: (1) Martin, Inventions} Researches and Writings ofNikola Tesla, The Electrical J...jU~HJ."",",l. York, 1893; pp. 123 and 198-293, with Alternate Currents Potential and Frequency" by Tesla, book has been H ..'"' ... UU,Ul........ and is available several sources. (2) Nikolik, N" Yugoslavia, 1956; Frequency" (3) with Alternate Potential and High Frequenry, 1904, 162 pp. (4) Discussion Comments by 1254, 1256. of Some Foundations .L'.L'JU~•.LH Radio-Electronic Espenschied, Proceedings of July, 1959 (Vol. 47, No.7), (5) Crawford, J.L., and Ullrich, R., California, 1987. (6) Martin, 1919, The Story Electricity * t Battelle, Thornton, XVlll ÆTHERFORCE Counsel Please recount the history of your work with alternating currents and their application to wireless telegraphy, telephony, and wireless transmission of power. I. High Frequency Alternators Tesla Work on high frequency alternators was begun by me in 1888, in my laboratory at 89 Liberty Street. I had just completed my system of power transmission, which is now universally adopted, but several problems yet remained to be solved. One was to run my induction motors at very high speeds; another one was to adapt them to the then existing alternating circuits of supply of 133 cycles. These two problems, although they were diametrically opposite, both required the use of laminated structures with a great many poles or polar projections, and I constructed quite a number of these with the object of improving along the lines indicated. Among these was an alternator with 24 poles, which gave me 12 cycles per revolution. This I used originally in running some small induction motors at speeds up to 200 [revolutions] per second. Occasionally, however, I would use this alternator in other experiments, with transformers, etc., and condensers, and then by running it at high speed (10,000 RPM) developing something like 2,000 cycles [per second], which phenomena were entirely new. This, of course, interested me very much, but the work was interrupted in 1888 when I had to go to Pittsburgh to attend to the manufacture of the motors. On my return to New York the next year, that was early in 1889, I engaged a laboratory at 175 Grand Street, close to Center Street, and there is where I undertook to design and construct the first high frequency machines. I had at that time already perceived enough to get the idea that energy could be transmitted without wires. It was of no consequence to me at that time whether it was to be used for telegraphy, or telephony, or power transmission. I was on the problem of transmitting energy without wires; and as it is my custom always to analyze scientifically every problem that I undertake to solve, I devoted a great deal of thought to how to attack that problem, and the following crystallized out. ÆTHERFORCE 2 Work With Alternating Currents It was evident to me that wireless transmission of energy, if it could ever be accomplished, is not an invention; it is an art. Bell's telephone, Edison's phonograph, or my induction motor were inventions, but the wireless transmission of energy is an art that requires a great many inventions in combination. We are living on a planet that is rushing through space; this planet is partly conducting and partly insulating. If it were all conducting, or if it were all insulating, we could not transmit energy without wire. It is only because it is partly conducting and partly insulating that a glorious future for man is reserved through the application of this art. The steps to be taken which I recognized then as absolutely necessary were, first, that I had to produce electric oscillations of the required character. Now, granted that I had them, it still remained to be shown how these oscillations could be transformed into some sort of vibratory energy capable of penetrating into the distance. Therefore, the second step was the transformation of these oscillations into such form of energy as would go to a distance. To develop methods of and apparatus for reception, to collect the energy at any point, was the third step. The fourth step was to isolate the energy. If I simply transmitted energy in all directions without regard to its use, then that energy would be simply lost in space, and it would be no economical system. Consequently, I had to devise means to isolate that energy, and this problem again presented itself in two aspects, active and passive; that is, I had to make the transmitter noninterfering, and I had to make it noninterferable. Those are not two identical problems, but both had to be solved. Finally, as to the fifth step, I found that we could never transmit energy, or construct our machines and apply them with understanding, unless we discovered the laws according to which this energy flows through the planet, laws which would enable us to calculate accurately the energy we are to receive at any point, and to design our machines to suit the work. In reviewing these objectives, what I am going to show you, step by step, is how I proceeded until I finally realized my dream, and, in 1899, produced a transmitter of greater power than probably all the combined transmitters put up today, and, furthermore, perfected an apparatus by which unlimited energy can be transmitted very economically, thousands of horsepower if necessary, from one small, compact plant, much smaller than that at Sayville or Tuckerton. [*] * Editorial note: The large German-owned radio station at Sayville, Long Island, was constructed by Telefunken (Geselleschaft fur Drahtlose Telegraphie) a few years prior to WWI for communication with a station at Nauen, near Berlin. Suspected of rendering non-neutral service at the outbreak of hostilities, it was taken over by the U.S. Navy Department in July, 1915. The great Tuckerton, New Jersey, radio station was built by the Homag Company (Hochfrequenz-Maschinen ÆTHERFORCE Frequency Alternators - 3 The drawing [ . 1] shows the first s toward the evolution of a generator, or transmitter, which be used to flash energy to distances, under practical and economical con- ditions. This machine was described me in U.S. Patent 447, 0, of March 10, 89. It was the first alternator that was ex- h , and with ch tests were made c, although I alternators of frequency, as I said before, as far back as 1888. This was a machine from which I could from 10,000 to 20,000 cycles. We used to say, in old times, "alternations"; this term has been loose that my early machines were rather i but as a matter of fact, the des of machines was my specialty and, had spent e years in doing Therefore, the results I machine, and which I before the world in 1891, are results a machine that I could not, with all my present and experience, and all the devices of the art, improve one-half of one percent. And any other en- , no matter who he be, would have that same hard time as myself because in this I embodied every little device that was available. I utilized to the full and the maxi- mum out of the materials. I had the lowest armature resis which could be obta , I had the lowest self-induc- T I had the t periphery I had the greatest , far than any alternator that has ever been since that time. In fact, I united this machine fea- tures which no other that has been des since has ever Furthermore, the currents I deve were ly sinu 1. That have been known to other , that the currents should be sinusoidal, because that follows from certain theoretical researches; but remember that I had in- vented the "rotat ic field," the very product of that field was based on the use of ities which wax and wane alternately in accordance with the law of the sine as, I have out in a paper read before the American Institute of Electrical 1888, when I presented my motor before that Therefore, ng was done in this machine that could be done to secure by every possible device known to Aktiengesellschaft fur Drahtlose Telegraphie) for the Generale de Te sans Fil of France, but the German firm after the outbreak of hostilities. It, too, was Department, September, 1915. (See: Howeth, L.S., U.S. ing , ; pp. • consultant to the Tuckerton station and received monthl until it was taken over by the U.S. Navy ÆTHERFORCE 4 Work With Alternating Currents (No Model.) N. TESLA. METHOD OF OPERATING ARC LAMPS. No. 447.920. Patented Mar. 10.1891. -99'S .R Figure 1. Diagrammatic illustration of first high frequency alternator with 384 poles, patent application filed October 1, 1890, also in book ~Inventions, Researches and Writings of Nikola Tesla" by T.e. Martin, published by the Electrical Engineer, New York, 1893, Figs. 199-203, pp. 375-376. ÆTHERFORCE ernators ~ 5 Re to the . 1J, I employed a ring of the finest iron, and a steel disc with a r, of rotat at 1,400 feet per second, safely. No such veloci has ever been in any alternator. I had, furthermore, an armature resistance in this of only 0.5 ohm. If I would have had, say, 6 ohms, which is of such an alternator, the machine would have been burned out. Even at 0.5 ohm, I had a hard time to it when I really had the resonant rise. I used a trick [in this ] which enabled me to a f and you will see how I accomplished I con- structed my rotor with just one of thin wire, and by a special process I baked this wire so that it formed a sol mass with the rotor, and the force, no matter how h the , could not tear it off. Then I made my field very small. The result of this was that I had a tremendous ventilation which enabled me to put the field a cur- rent of 25 or 30 amperes per square millimeter, and out of the armature I could easily take 30 amperes per square millimeter. You know, in des, if you take out four to four-and- f amperes per square mill , that is a per- formance. I defy anyone to take out of the conductor [of these conventional machines] more than five or six amperes per square millimeter. But, I des this so that I could have 30 amperes per llimeter in the armature and 30 amperes per millimeter in the field on account of the So, therefore, when I show this , I have shown the most ne in wireless that has ever been up to this date. People, of to use a , but that is a If I had had a turbine to s done much better. Later on, however, I will show you a machine which I des fically for the turbine. I have recently heard that, as a result of [emphasis Tesla, [*] reported that to just the same machine which I exhibited in 1893, with which I showed s to Helmholtz, and which was a of s known all the world over from pictures; have been for years and years but exper this particular field. This machine 2] was exh ted before the American Institute of Electrical , where I showed my first ex- Sf and these experiments, as I shall state in a few * Editorial note: Reference is to John V.L. I at that time chief research engineer, National Electric was one of the driving forces in the of the Institute of I later its ident in 920. The refers to the General Electric Steinmetz, Berg and in collaboration with Fes of the National Elect Signaling to the production of successful alternators operating to ÆTHERFORCE 6 Work With Alternating Currents words, I obtained some striking results, which were the starting point of this whole development. Figure 2. Photographic view of alternator [shown in Fig. 1]. Illustration from Martin book, Fig. 97, p. 153. Fw. 97. Unfortunately, that [Fig. 2] is a reproduction from the only picture I have. This machine was destroyed in the fire that annihilated my laboratory in the Spring of 1895, and I had nothing left of it but a little piece. That photograph [was] taken from an old, very poor print; but it shows the general arrangement of the machine. This machine I operated at Columbia College with about 5,000 cycles; later on I attained 23,000 cycles running it at a higher speed, and it was in every way a most satisfactory piece of apparatus. It was used by me in experiments with wireless telephony, telegraphy, and all sorts of experiments until it was destroyed. When I published the results with this machine, I did not have the courage to run it as high as I wanted to so I operated only at about 3,000 or 3,600 revolutions and then I could get out of it approximately 4 kilowatts. But I could easily get out of it 12 or 13 kilowatts later on. This large output was only made possible through the tremendous ventilation. I remember that at Columbia College, Mr. [Gano] Dunn, who is now Vice-President of the White Company, I believe, and who was assisting me in the lecture, forgot to turn off the current in the field when the machine was stopped, and if I had not shut it off, the field would have burned out. This high output I could only get through this artifice. It was a fine machine, and I really do not see how anybody could produce a better device for the purposes of ÆTHERFORCE High Frequency Alternators ~ 7 radio telegraphy. There is no such thing. I have designed other machines which are, perhaps, better in some respects. This machine is extremely serviceable. There were two striking results which I showed in my lecture at Columbia College, and I will illustrate them because I wish to show these various ideas from their starting point. FIG. 114. FIG. 11.-.. Figure 3. Light and motive devices operated from this alternator in novel manner. Illustration from Martin book, Figs. 114 and 115, p. 177. The first result [Fig. 3] was one of the experiments which I at that time showed in a public lecture, motive devices operated by merely connecting them to one terminal of a source of oscillations -- a high frequency coil. I have often been told that my most important results in invention was the demonstration of the practicability of transmitting energy over one wire; because, once we can transmit energy over one wire we can use also the earth, for the earth is equivalent to a large conductor -- a better conductor than copper wire. This was one of the results I got, but the most striking one I will show you now. This second result [Fig. 4] shows how energy goes through space without any wire. That was a most striking experiment which was repeated all the world over and was published in thousands and thousands of papers. There is a field produced -- of high frequency -- and in this field I hold two tubes of glass in my hands. These glass tubes spring into powerful light. That was an experiment which carried the whole world by storm; but to me it was the first evidence that I was conveying energy to a distance, and it was a tremendous spur to my imagination and to my energy to develop what I had started. ÆTHERFORCE 8 Work With Alternating Currents Figure 4. Most striking results obtained -- vacuum tubes lighted in alternating electrostatic field. Illustrated in Martin book, Fig. 125, p. 188 . ÆTHERFORCE II. Experiments with Wireless and Telephony Tesla [Diag. 1 of have des but they were a different way. I used this machine which I wireless. These exon Grand Streett and carried on in Counsel What date was that? Tesla That was in 1891, to my to and to lecture before the s societies there, the Institution and the Institution of Electrical I had a wire run out through the t and on the roof all sorts of to const this capacity [shown in the diagrams as an elevated squareJ The first s was to connect this al- ternator [shown the agrams as a rcleJ with one terminal to the water p and the other end to the antenna. I had already my lecture at Columbia Col that I could transmit energy through one wire; therefore, I was pre- to find that a current of cons strength could be passed through this wire here the alternator to the elevated , was insulated. at that time was that I would disturb the in the ions of the earth, and the disturbed, this could then be ized to bring into in any way some instrument. That was what we now call, s y, ssing forced ions of very on an antenna. We have introduced the term "antenna" since that time. The second was as shown [in . 2 of Fig. 5J. You will notice that I have inserted a coil in the circu The for that arose from the fact that I could not to tune the prope to the alternator. I had in the a very large and you will note that in my exposi- tions of that f from 1891 to 1893, I insisted on the very largest capac that could be because, accord- to my which has since, of course, been con the amount of current that flows such a system is proportionate to that capacity. Therefore, as the effect in the distance is to that current, I had to use a b capacity; but not having a in the bui I introduced an coil to tune the s down to the of the that from the ground connection this circuit, , the coil, and ÆTHERFORCE 10 Work With Al ng Currents antenna, would have the natural of the zed the necess of introducing a means of and it is this [shown in Diag. 3 of . 5]. Next I usting, ways of ~~O~1~1m~~,tg a t the a high frequency a1ternator in street Laboratory: 1891-1893. NOw, I found that notwi I tuned this system successfully, I could not this antenna or these "cans," as we called them at that time, su high. But it occurred to me that if I transformed the current and raised the tension of the dynamo in could then the antenna to a splacement of electri like this [ . 4 of in I have dynamo supply a a second current of higher aI, and tune and ust the conditions so that this conductor [connecting the antenna to the transfor- mer], the secondary of the ,is aga tuned to the the was a fine ; it is s that is absolutely essential, because on in the fewest instances can the power of a or be taken up without transformation. ÆTHERFORCE E Wi Wire ss y Telephony - 11 Then, of course, I [an adjustable That was the fifth convenience the im- in . 5, Fig. 5]. r to increase the current in the primary, I ed an liary condenser ci t [shown in Diag. 6, . 5]. This auxiliary circuit I have, the way, already illustrated in a which was to me in 1891 [U.S. Pat. No. 454,622]. The condenser has the effect of magnifying very much the current, this magnification being proportionate to the ratio of the inductance to the resistance of the circuit, and that rat was very great so I a strong current which the current in the antenna . the next step 7, . 5], I have f s , but it was not drawn up . [*] I put a con- denser in se s with the That is exactly the way at Columbia Col At Columbia Col I had an ustable condenser, from W. Marshall, with very small , which I used in with an inductance coil, and the secondary I was then operating exhibited all the which have been described in the lecture. In [Diag. 8, Fig. 5] I show another modification which has certain virtues. I introduced ustable condensers here, with which I could, first, counteract the self-inductance of the dynamo in one circuit, then raise the tension in the reso nant circuit, and then tune the secondary of the sys tem to the same vibration. In [ . 9, Fig. 5], as you see, I came to this arrange ment where I have an ustable inductance and adjustable con- denser in the primary, and an ustable coil in the or antenna circuit. That is now a arrange- ment, and it is very and In the meantime, as I was deve all this, I had al- struck a new line of effort toward producing vibrations; namely, I had developed a system ing me to take or- current of any and transform it into any of vibrations I desired, either or undamped. I will dwe I on this [later], but I want to say now that I also as shown here [Diag. 10, Fig. 5]. I bri with an air gap. This I did in studying harmonics. I found that sometimes I could a very strong harmon , for instance, the third harmonic was often very this I work with the fundamental with a harmonic, and I made some interest which later on led me to very * Editorial note: Tesla refers adj table primary inductance rather than an adjustable secondary inductance as shown. ÆTHERFORCE 12 Work te Currents [Diag. 11, . 5 is a similar sposition in which I introduced ustable condenser, and had the same arrange- ment in And lly, [Diag. 12, 5] one of the most common ans which I have been us later in other laboratories - an ustable inductance in the antenna circuit, and an ad- justable condenser and ustable in the pr circuit. 1 Will you describe, Mr. Tesla, just how far these went into use, and how far they were shown and to others? Te la At the on] Grand Street, I had in following men: Mr. Sz , a electrician and wire man who had been a France and came over in 1884 or 1885, I do not recall now. Then there was Mr. F.W. Clark, a very skilled mechanic, formerly in the of Brown & Sharpe. Bes s these were Mr. Leonhardt, a young an Paul Noyes, a former employee of the Gordon Press where I him while I was my arc 1 was by the There was also a man by the name of David sell, a German-American s blower. At the time I made these experiments, there were very few of the el that since made a success with in , who would have known much They had seen me run the up had seen me operate continuous with those machines. I had shown them wonderful results, and had told them all the that I was going to energy without wire , te , run cars and 1 s at any distance that these were the toward s end. How much these men could tell, in the 1 of the present , that, of course, I am unable to say; but, cer- y, I had of witnesses to follow my and to know what I had been doing. This . 6] I was buil while I was carrying on the first As you will note, I had s the wire from the armature. I had taken the f st steel I could and constructed a machine with oppos poles, with what we call a" ff" field, and had done away all moving wire. I intended to connect a turbine and run s machine at a very , which I be up to 20,000 revolutions. The armature con- ductors were sposed in this f and the I that was ÆTHERFORCE Experiments With Wireless Telegraphy and Telephony - 13 (No Model.) N. TESLA. ~ Sbeets':""Sbeet 1. ALTERNATING ELECTRIC CURRENT GENERATOR. No. 447,921. Patented Mar. 1_0, 1891. -.!/ /IlIilne.r.se,s : ~=*~~ .ff~tS~. Figure 6. Diagrammatic illustration of the second machine built with no wire on the rotating part, designed for turbine drive, taken from U.S. Patent No. 447,921 of March 10, 1891. Application filed November 15, 1890. ÆTHERFORCE 14 Work th Alternating Currents the was the conductors, as this , I had two wires for the and two wires for the conductors. Usually, however, I had six binding posts because I had two ts splaced in the armature. I have and years in des and I have never It one machine but that the saw it complimented me on its ss and the s of my design. men were students; not know how to do it. made a machine which had an internal resistance of 6 ohms and to raise the tension one hundred fold. the resistance of my ne was 1/40 of an ohm on wanted to make a short conductor and made a conductor many feet The wire in my machine was but 4 feet So, you see, I had in this machine the t thoughts of design. It could not be any more because I had gone to the I ngi limit of tensile st , limit of air space, limit of copper, I of every other material. This ne I have used for many years with success, and I have discovered many, facts in con- nection wireless by its means, and some of these facts I will tell you. Counsel What has to that ? Tesla I used it for years and years; used it I That machine must still be in existence, but with fference that I have the number of s. It was to do away with the spark gap. That was an idea that I conceived 1892, but it dragged on I a later period. My idea was to construct a machine with a n small number of s, rotate it at an enormous , and thus ch would the same effect as the arc dis- my so-called "Tesla transformer." ly, s machine had 64 poles. Then [in 1901] I reduced them to 32, and to 16, and that form I have with it any osci lations, continuous trains or undamped oscillations of I desired. That is done a process not yet well only so far that electri ans have cs from low fundamentals; but in that have a very small energy. Now, I have me to take, for , s give me 3,000 or 4,000 oscillations, and from s 100,000 [oscillations], and there s train of waves. ÆTHERFORCE riments With reless Te Telephony ~ 15 Counsel During what years was this machine used? Tesla This certainly, was It in 189. I used it 1905 or 1906. When was it you reduced the number of poles? Tesla I reduced the number of es, I think, in 1901. But then I reduced it for the purpose of currents of f had a number of poles, could not realize my because these poles would come in succession and ce a rate of to the rate of change is obtainable denser owing to a sudden break of the electric. to say, a blow. It has to be a blow, see. I had to my y far f then run them at excessive and generate ly few impulses, but each of those impulses are of such tremendous intensity that the dynamo is ical short-ci ted. That gave me a blow which replaced the arc. And then, of course, there to be perfected a scheme enabl me to the energy of the alternator in the most economical manner, in harmonics. That is not known, at least I have not seen ing of that kind in literature, and I bel that if anybody would at- it without the devices which I have invented, he could not get much of the energy in harmonics. What was the of that in its form? Tesla The of the machine was about 8 kilowatts; but, ob- serve, I did not [then] have the turbine [patented in 1913] . If I had had the turbine, I could have run this mach [at] 20,000 revolutions, and then I would have had a [s ficantly h ] [The machine] had a s was of the finest steel, all taken from stat terminals. which, after al armature and no wire. It , and the current was [It] is the have come to. ÆTHERFORCE 16 Work With Alternating Currents Counsel How fast did you run that before you reduced the number of poles? Tesla Up to 12,000 [revolutions]. I used this machine in transmission of signals, particularly with the telephone, in a great many investigations, and I discovered a way, for instance, of measuring accurately capacities employing this machine. You know that, normally, the capacity of an antenna cannot be measured very closely. The ablest men [in the art] -- Prof. Zenneck and Prof. Stone -- know how it is. But, with the scheme I have developed, I could measure any capacity. With an antenna of 1,000 centimeters, I can very easily read half a centimeter. [*] There is no method known which would Figure 7. Photograph of machine covered by U.S. Patent No. 447,921 of March 10, 1891. Application filed November 15, 1890. * Editorial note: Capacitance values expressed in centimeters are in electrostatic units; to convert from centimeters to picofarads, mUltiply by 10/9. Thus, in the situation described, with an antenna of 0.0011 microfarad, Tesla could read an increment of 0.55 picofarad. ÆTHERFORCE Wi Wire ss y Telephony ~ 17 enable an expert to read as closely as that. I used this machine in as these. It was a very fine of for all sorts of s demonstrations. In those years, of course, I was deve c s. I have shown that five had to be before wireless was an art, a real art that could be ifically . . 7] shows this machine as it actually was. You here a wire [point to the ] a solid, thick wire. In the form that you see the machine here, I used it for developing harmonics, and in this case I had a condenser soldered to the alternator so that I would a system of no resistance, y. The resistance in my alternator was 1/40 of an ohm. I made a -- that seen here -- the resistance of which was also I com- bined it the condenser and tuned it so that I a cur- rent of tremendous volume in that circuit, and then I operated it with the . 8 shows] another machine. This is the third machine which I built, a one. This machine is de- sc by me in the U.S. Patent No. 447,921 of March 10, 1891. It was constructed early in 1891. Then I made a On my from [in 1892], I took it in a little ion in next at 35 South Fifth Avenue. In this , I had the same kind of what we call a "stiff" field -- and in that I a sc to which was cut out in a proper way so as to give me a I wanted to have a very 1 rotor, and rotating, the in [aJ plane force, would be a very one to experiment with. The machine was of very much larger capa- ; it was built with 480 s, and I could get from it, at ively low 30,000 cycles per I could , in fact, more. This machine was also de Of these three machines which I have second one was saved from my 1 [*J * Editorial note: Another machine, whi Company, a 1938 taken after the laboratory fire. to Westinghouse Electric & laboratory fire. See Appendix I, ÆTHERFORCE 18 Work With Alternating Currents (No Model.) N. TESLA. ~ Shp,ets-Sheet 2. ALTERNATING ELECTRIC CURRENT GENERATOR. No. 447,921. Patented Mar. 10, 1891. Figure 8. Diagrammatic drawing of the third and larger machine with 480 poles, taken from U.S. Patent No. 447,921. ÆTHERFORCE Experiments With Wireless Telegraphy and Telephony ~ 19 Figure 9. Photographic view of alternator covered by U.S. Patent No. 447,921. Illustrated in Martin book, Fig. 98, p. 154. [Fig. 9J is a photographic representation of the machine, but it is not so apparent that it was a machine of much larger capacity. I could get out if it readily 25 kilowatts. Those are not the only machines I built. I constructed quite a number of other high frequency machines. Some of these were obviously small, and I built them chiefly for scientific investigations and for use in connection with receiving circuits. One of my ideas was to generate at the receiving station oscillations of a certain frequency, and then combine them with an incoming oscillation to obtain beats. And later on, in 1898, I worked this idea into an invention which has been called a ~telautomaton,H and which has begun to be appreciated because Congress voted a certain expenditure of money, $750,000, for that machine which I vainly attempted to persuade them to accept. [*J I perfected the machine in 1898, and tried everything in my power to have it adopted; but, everybody was ridiculing my efforts. Everybody said it is impracticable, and after my patent expired only a few months ago, Congress appropriated this sum and I have now the pleasure of simply looking on when others are using my inventions, which I could not persuade people to adopt. This is usually so. [Fig. 10J shows a type of small alternator, one of two forms which I will show you, that from the constructive point of view, is rather poor. I will admit that. But, it was * Editorial note: For further remarks on attempts to persuade the U.S. Navy Department to fund the idea, see p. 158. ÆTHERFORCE 20 Work With Alternating Currents convenient for me to construct it that way. You see, the magnetic circuit is constituted by the laminated core here, [andJ there is an exciting coil. In this picture you will also note the field wires, and the rotor is indicated. With this machine I could get 200,000 cycles per second, [*J very readily, but the output was very small. It was used mostly for telephonic work and for scientific investigations. Figure 10. Small alternator of very high frequency built for purposes of investigation, chiefly in conjunction with receivers. Drawing. Measurement purposes. This [Fig. 11J, if you please, is another small machine which I built, and with it I also obtained a very high number of cycles. You see how that was made. Here [fieldJ I have 8 laminated magnets, and the circuit was formed through here, you see. On the rotating part I had 9 projections so that if, 0 '.· · 0 Figure 11. Another small high-frequency alternator of different construction intended for the same purposes. Drawing. Mercury interrupters, 1898. * Editorial note: This was accomplished by having the number of field magnets differing from the number of armature projections by one. For the general case, the number of field magnets and armature projections must have an even-odd relation. ÆTHERFORCE nts th Wireless Telegraphy and Telephony - 21 for tance, this armature was rotated, say, in the clockwise direction, then the ts will come successively into also in the lockwise direction. [*] But, as you will readily note, I had a very small electromotive force, for the reason that the inductance of seven coils while one was the electromotive force. However, [the] induc- tance I could overcome resonance, in properly ust so was no objection, and the machine was ex- serviceable. This machine s, by one 72 , there are 8 sand 9 ections. That means 8 x 9 = 72. And, of course, small, I , and balanced, I could rotate it a very and a very h Counsel In what was that shown? Tesla This was in my patents on mercury inter- s which were 1898. You will find the same my mercury I used 7 streams of mercury, ections. In fact, in one I have constructed, I used ect and 24 streams, and I could get a very which is unobta e with a very high frequency I have described so far were all of the ; that is, insofar as the mode of fie ex- citation was concerned . . 12] shows another type of machine which was me before I had conceived the princ of excit a , not rect current, but by current of fferent a whirl magnetic field, and then rotat in that field an armature and generating currents in the same. This has been taken up later by a very able German en- neer, Mr. Gol , and today it is known as the Gold- s machine. Of course, mentions me at all, and I suppose is in wireless as in love and war. But, I gave the of these machines, and I had several of them with which I continuously. There is s to be [about this type of ] . When you rotate the armature in the direction of the rotat s, but a velocity, then it is a which has the field excited by a simple current; * Editorial note: For the case where the number of field magnets is 8 and the number of armature projections is 7, resulting in 56 impulses revolution, and the armature is rotated in the clockwise direction, the magnets will come success into play in the counter-clockwise direction. ÆTHERFORCE 22 Work With Alternating Currents (No Model.) No. 390,721. N. TESLA. DYNAMO ELEOTRIC MACHINE. Patented Oct. 9, 1888. I I I I ! I I I I 1 -, I (~,,.-- ---} ,iI" ,iI Q~~ , I I I i ' , : I I I I,~--"~-I','1 , .1Jii~1 - I'1' . I , I I WITNESSES: ~.~,-- RoM.¥: ~a.;~ 1NVENTOO ~,~. BY r-""'-T-'" -OUc.c Ca c ~. ~z:" A % ATTORNEY~. Figure 12. Diagrammatic illustration of another type of machine with rotating magnetic field excitation, as described in U.S. Patent No. 390,721 of October 9, 1888. Application filed April 28, 1888. ÆTHERFORCE riments Wi re ss Te Telephony - 23 when you rotate it in the other di field really comes in, and you you rotate the field just as fast one rotated the other way, you have then, on, then the rotat frequency. If as the armature s example, the The objection to s machine I found to lie in the fact that the current is not strictly s You see, when flux in the f varies harmon there are two inductions; one is the induction due to the motion of the wire across the field and the other is the induction to that taking place a static transformer. This latter is ional to the sine, the other is onal to the square of the s ,and the result is that we get a little storted curve. Nevertheless, the is applicable, and [it] has been ied Golds commercial machine. Now I am to a very wonderful discovery which made in connection with high frequency alternators, and I do not believe that there is a man in the cal profession who dreams about it; not one. This scovery to me that, without further provision, was impossible to frequency alternator in wireless work that requi kind of fineness; and I made this scovery in the fol way. I was with three alternators in my at 35 South Fifth Avenue. I would run [any] one o the machines, tune a circuit, then go around the ci and the hum of the alternator in my tuned circuit, and this note the intens of sound I could j the of the devices that I was using. That was a very convenient way; I did it cont I most between the 1 on South the Hotel Gerlach on 27th Street, near Sixth Avenue, where I was s p While I was ca on this work I was perfect ods and for attunement, and I noticed that lly could not get as results as before. I could not understand this. But after a few of invest ,one happened that I was a note on the of the Gerlach could not get hum of the alternator. I was giving it up, when all of a sudden out it rang very and clear, and was off , as though a wire had been broken. I s to myself, a has been broken some- where in the ci t and went down to the laboratory where I examined all care lly. But eve was in order. Then the idea flashed upon me that my circuit was y and the alternator was not one but many ies; the alternator was all changing , like every alternator does. It does not one , it s many ies. ÆTHERFORCE 24 Work With Alternating Currents Now, I solved that problem in 1898, and I will tell you how I solved it. I said to myself, here is a generator that gives a dozen different frequencies, but very closely related. They follow one another in succession. How am I going to get selectivity, and at the same time have a perfect response? I solved this through what I term the principle of individualization. An ordinary circuit has one characteristic; it responds to a certain note. An individual has more than one characteristic; [he] comprises many in combination. Similarly, I combine several circuits and depend on the cooperation of these circuits to operate my device. My first step was to tune several circuits very closely together, so closely that they would pick up [any] of the frequencies within the range of the change of the alternator [speed], and I operated with all these circuits on my receiver. The moment I used that kind of a circuit, I found that I got very clearly the note of the alternator because my receiver was responding to any of the frequencies which were produced. On the other hand, when foreign frequencies would come in to disturb, I would only get a partial effect, as my normal effect was due to all the frequencies combined, whereas the outside effect was due to just the one frequency. I presented the same principle in a lecture before the New York Academy of Sciences on April 6, 1897, but which was not published. There were certain steps to be accomplished, [however,] before the wireless could be on a really practical and scientific basis. The next step to accomplish, after all had been done, was to design an apparatus which will exactly suit the earth; that is, which will give the proper wavelengths suitable for it, and will also be in all other respects adapted to the physical conditions of the globe on which we live, and to the place on which the plant is erected. The earth is not a sphere; it is an oblate spheroid, owing to the effect of centrifugal force. Now, it makes all the difference whether a scientifically correct apparatus is placed in a northern region, near the pole, or near the equator, because the length of the conductor is not the same. In the account of the experiments and machines which I [have earlier shown], I hope I have proved that those machines represented the farthest advancement in the art, not only of that time but of the present day. Not that I would say I was a better designer -- nothing would be further from my mind. I simply mean that my followers did not require the limitations of frequency, and I have stuck to those designs which were most efficient. Alexanderson said, "We are compelled to go to the very frequencies that you [i.e., Tesla] used in your earlier demonstrations." There were reasons why I made machines of low frequency ÆTHERFORCE Experiments With Wireless Telegraphy and Telephony ~ 25 in my experimental work, why I stuck to these frequencies which I have used in my early lectures and public demonstrations. Firstly, because such a machine can be efficiently built for high output, which a machine for 200,000 cannot. Secondly, the waves which are generated were less absorbed because they are of lower frequency. They went to greater distance; the effects were greater. But there was still a third reason: Whenever I received the effects of a transmitter, one of the most convenient and simplest ways [to detect them] was to apply a magnetic field to currents generated in a conductor, and when I did so, the low frequency gave audible notes. Figure 13. Instrument to receive radio waves of 1896-1899 structure. One of the simplest devices I used in my experiments between my laboratory on South Fifth Avenue and [at] the Gerlach Hotel, and other places in and outside the city, was an instrument constructed in 1896 with a magnet which sometimes was so designed as to give me a very intense magnetic field up to 20,000 lines per square centimeter. In this [field] I placed a conductor, a wire or a coil, and then I would get a note which I amplified and intensified in many ways. From the characteristics of the audible note, I would immediately judge the quality of my apparatus. When I speak of an audible note, I mean a note audible in a telephone as produced by the diaphragm of a telephone, or by a vibrating wire within the range of audibility. [Fig. 13] shows the general arrangement of [the receiving] apparatus. [*] Two condensers are the boxes at each end, * Editorial note: Also see discussion in association with Fig. 94, p. 162. ÆTHERFORCE 26 Work With Alternating Currents and in the center a coil, or two coils, according to necessity, with which I produced a strong magnetic field and [placed] in it a wire. These condensers and the wire form a circuit which I tune. The condensers are of comparatively large capacity because my conductor is so short. I usually would transform the current in the receiving circuit and make as close a connection as possible and then tune the circuit to the vibrations. I would also mechanically tune the wire, according to the frequency, to the same note or to a fundamental. This machine was suitable for transportation. I could put it under my arm with a couple of batteries. I had relays, which were very big, in which I produced (for stationary work) a very intense magnetic field so as to affect the conductor by the feeblest current. Furthermore, I used these relays particularly in connection with beats. When the frequencies were very high, I combined two frequencies very nearly alike. That gave me a low beat. One of the frequencies I sometimes produced at the receiving station, and at other times at both the receiving and transmitti n g stations. This always gave me the means of producing an audible note. I used machines of this character from 1892, but this specific instrument in my laboratory on Houston Street. This instrument comprising a magnet and chord or coil in the magnetic field -- I mean a wire or coil in the magnetic field -- is an old academic device, used in all sorts of demonstrations at the schools and the university where I was studying. My professor of physics has had similar instruments with an adjustable spring and magnet, and I have employed them in assisting him. There is nothing novel in the idea. The only novelty was that I kept my alternation low and I made this arrangement with conductors to tune. It was very convenient for producing audible effects because, if I used other forms of a receiver, I had a reading which was not at once translatable. If I listened to a note, I could immediately tell the quality of the transmission. For instance, I would tune a circuit in my laboratory, take it out to another building, and I would receive the signals; and from the quality of the signals I would see how I was progressing. Counsel In the experiments that you have spoken of with the instrument of which the picture is shown [as Fig. 13], what were the distances between the transmitting and receiving stations? Tesla The distance at that time, and I think the greatest distance at which I ever received signals from the Houston Street ÆTHERFORCE With re 55 Telegraphy Te 27 , was from Houston I think, a stance of about 1897 when Lord Kelvin came to my made certain demon before the the Patent Office, Mr. See and it was lity of to me. At that experiment were you at the Houston Street end or at the West Point end? Tesla In that I continuous of oscil- lations and went with the instrument to West Point. I did s two or three s. There were no s s actually en. I s the note, that was for me just the same. Counsel That is to say, you not make and break the circuit? Tesla No, and I did not receive the audible notes in but I did receive Counsel At West Point? Tesla Yes, in or about the year 1897. Counsel And did the cont from Houston Street? s tran ssion thus start Tesla Yes. Counsel Was one of your emp there? Tesla Yes, the employees knew that I was the ÆTHERFORCE 28 Alternating s On occas s, I would a to make and break the found it was much s er to just let the ap- run and the notes. Counsel What was the distance between ssion and reception? Tesla That was the distance from my Street to the Gerlach Hotel. on Houston Counsel Is this [Fig. 13] is colI ly known as a string type which Tes No, it is not. Such a sc the schools, for instance, in c strument is used in of demonst Counsel In 13], is that [wire) shown on the apparatus in series in the f and is it in of the ? Tesla Yes. I had a it made no f the f Id that , or a s wire, in the field -- It was the react of the currents on the note. Counsel What is the furthest distance from your source of transmission that you u the apparatus of this character? I think I used this once at the Western Union Build- ing -- on the roof -- in company with Mr. Alfred K. Brown. That would be a stance of 2 miles. Counsel What was character of the re on? Tesla Just the alternator was run and you could hear the note of the same when rcuit and st was tuned to ÆTHERFORCE s Wi re ss Te 29 the same Counsel Did you hear it? Tesla You could hear it allover the Coun 1 You mean you did not have to have your ear in the te to hear it? Te la No, not at all; I could hear it from a distance. The vibrations were very Counsel About when was that? Tesla That must have been late 1896 or in 1897. Counsel What was the us ? of alternation that you were Tesla The might have been say - in the neighborhood of 5,000. like I should Was there hidden about these uses, or were open so that anyone could use them? Tesla There were thousands of e, shed men of all kinds, from and artists and scientists in the down to some old of mine mechanics, to whom my laboratory was always open. I showed it to ; I talked about it. ÆTHERFORCE 30 Work With Alternating Currents ~li a Model.) No. 464,667. N. TESLA. ELECTRICAL CONDENSER. Patented Deo. 8, 1891. Jt)'!J. 1 -!f!I. 2 bwt'niol' 1U1~Y~ e&!a:u.v v-P~ .;yj!lorll~~ Figure 14. Construction described in U.S. Patent No. 464,667 of December 8, 1891. Application filed August 1, 1891. ÆTHERFORCE Experiments With Wireless Telegraphy and Telephony ~ 31 . (If 0 Model. ) No. 567,818 . N. TESLA. ELECTRICAL CONDENSER. Patented Sept. 15. 1896 . WITNESSES Figure 15. Forms described in U.S. Patent No. 567,818 of September 15, 1896. Application filed June 17, 1896. ÆTHERFORCE 32 Work With Alternating Currents Counsel When you said, "5,000," did you mean cycles or alternations? Tesla I mean cycles. On another occasion I have also operated going a little further into showing the reactions of high frequency currents upon magnetic fields -- I have operated motors, and at that time I have stated what frequencies had to be used in order to produce these rotations, which are, of course, due to reactions of the currents on the field. I have pointed out, in the Martin book, that they should be from 5,000 to 10,000. I would like to proceed, without going into details making this too hard to follow. I would like to have this simply a clean story with only the salient facts pointed out, and not a maze of little details which would complicate it and spoil the harmony. Proceeding, then, [Fig. 14] shows a form of condenser in which I have boiled out all the air bubbles, and the next drawing [Fig. 15] shows another form. I have made a notable advance in this condenser, with which I have operated in my laboratory on Houston Street and in experiments at my wireless station in Colorado. This is the most efficient form of condenser known, showing practically no loss whatever. And it is only with this condenser that really very fine results are obtainable because, even if we employ mica condensers immersed in oil, or glass of the best kind coated with tinfoil, we do not get the results which we get with this condenser, and they are obtained by substituting electrolyte for the metallic coatings as before. I used electrolytes which were especially adapted for that, and cheap -- for instance, like a solution of ordinary salt. It is cheap and readily obtainable. [Fig. 16] shows a type of this kind of condenser in finished form as I used them in my laboratories. There were many of these adapted to be secured on the bottom. They were readily transportable. Occasionally, I took some of these condensers with me when I experimented. [Fig. 17] shows another improved form of condenser. I do not have a photograph of a finished apparatus and this is a sketch that was made in 1896 shortly before a condenser of this kind was constructed. That was a condenser intended for high electric pressure and the insulation was obtained through the air. It was built for 500 atmospheres air pressure safely. There is a reference in my writings where I point out ÆTHERFORCE Experiments With Wireless Telegraphy and Telephony - 33 the use of compressed air, and therefore there was no creative effort involved in any patent in that direction by Fessenden and others. Figure 16. Improved form of electrolyte condenser as used in laboratories on 35 s. Fifth Avenue and 46 E. Houston Street. Figure 17. Form of condenser with air under great pressure as dielectric used at the same period, subsequently patented by others. The apparatus shown by the drawing [Fig. 18] which I designed and installed was for years employed to practice this process of manufacture. This process is [now] universally adopted; everybody uses it. There are millions and millions involved in it. If I could only get one cent for every apparatus that is manufactured in accordance with my invention, I could erect a building like the Woolworth and not feel the expense. [*] Everybody uses it, but nobody says thanks. That was arranged for what was called a vacuum pressure process. * Editorial note: At the time of this interview, Tesla had shortly before removed his offices from the Woolworth Building where they had been established for one year. ÆTHERFORCE 34 Work With Alternating Currents (No ModeL) N. TESLA. MANUFAOTURE OF ELEOTRIOAL CONDENSERS, COILS, &0. No. 677,671. Patented Feb. 23, 1897. /~.~~ i TTORIiEfa. Figure 18. Apparatus for manufacture of condensers and coils to exclude air as described in U.S. Patent No. 577,671 of February 23, 1897. Application filed November 5, 1896. The whole manufacture is now dependent on this or similar processes, and many patents have been secured by others. ÆTHERFORCE riments Wireless Tel and Te 35 Steinmetz says, "No, I have found a better way. I just " the thing in It is thin and s a s in the and, of course, he I am [next] coming to a in my life which was very fruitful. I was absorbed in the development of a new type of generator. The solution, which enables me to use the high alternator ical, was not yet found at that time. I saw that the high was not usable for any finer work. We were toward perfection and that if we attained it, the alternator would be s y thrown away as an absolute useless rument. That was my convic- tion, and I to results I subse- ly reached with the alternator in another way. To this end I built a many machines of a novel , which I called oscillators -- mechani electri oscillators it is with these that my best results in the investiga- tions of these le to wireless in many of ÆTHERFORCE III. Mechanical and Electrical Oscillators Tesla The photograph [Fig. 19J shows my earliest experimental oscillator which I used to generate electrical vibrations. Figure 19. Simple mechanical oscillator used in first experiments. My first efforts were to produce this vibratory mechanical motion, then attach to this system an electrical generator; that is, I would attach a conductor to it and vibrate it in a magnetic field. That was the first step in the evolution of the idea. The machine is shown here without any attachment. The drawing [Fig. 20J illustrates the next advance in the evolution of the idea. I have produced isochronous oscillation, and now I am applying considerable power to the piston to develop energy in this electric system. It is the energy of the mechanical system which produces the electrical energy in the circuit, but the vibration is controlled by the tremendous force of the air spring against which the small impressed force is nothing. In this manner, then, I first obtained isochronous electrical oscillations, which no transmitter made today furnishes except my own. The drawing [Fig. 21J illustrates the next improvement. I conceived the idea, instead of using a mechanical air spring ÆTHERFORCE Mechanical and Electrical Oscillators ~ 37 (lfo ModeL) No. 611,916. N. TESLA. ELECTRIC GENERATOR. 2 Sheets-Sheet 1. Patented Jan. 2, 1894. Figure 20 . Mechanical oscillator with air spring combined with electric generator as shown in U.S. Patent No. 511,916 of January 2, 1894. Application filed August 19, 1893. ÆTHERFORCE 38 Work With Alternating Currents (No ModeL) No. 611,916. N. TESLA . ELECTRIO GENERATOR. 2 Sheeta-Sheet 2. Patented Jan. 2, 1894. Figure 21. Another mechanical oscillator with controlling electromagnetic system described in U.S. Patent No. 511,916 of January 2, 1894. Application filed August 19, 1893. ÆTHERFORCE Mechanical and Electrical Oscillators - 39 for exercising the controlling force, to obtain it electrically. Boiling water was employed to keep the temperature of the air spring perfectly constant and the oscillations isochronous. I constructed an electromagnetic field so that it could be used for isochronous control. This invention I also exhibited at the Chicago World's Fair where scientific men, Helmholtz and others, saw it. The magnetic field [of the] core generates currents in the coils. Two coils are used for excitation and two for induction. I connect a condenser to the latter and adjust the period of the electromagnetic system, comprising the condenser and the self-inductance, so that it is just suitable for the conditions under which I wish to operate. Then the magnetic system, having a constant period of vibration, controls the admission of the fluid to the piston, and when I use the currents I find them perfectly isochronous. I can run a clock with them and it will show correct time. The vibrations obtained in this way would not vary onemillionth of a second in a thousand years. The photograph [Fig. 22] shows another form which I also exhibited at the Chicago World's Fair. There is a round coil, you see, in the field; on the other side is another such coil. I performed very curious experiments with this machine. For instance, among other things, I produced direct currents without commutation. Figure 22. Another type of small mechanical electromagnetically controlled mechanical oscillator. ÆTHERFORCE 40 Work With Alternating Currents Figure 23. Large electromagnetically controlled mechanical oscillator for generating isochronous oscillations, used in demonstration before the Electrical Congress at the Chicago World's Fair, August 25, 1893. Illustrated in Martin book, Fig. 312, p. 490. o M o o M o FIG. 31S. Figure 24. Diagrammatic representation of electro-magnetically controlled mechanical oscillator for generating isochronous oscillations. Shown in Martin book, Fig. 313, p. 491. ÆTHERFORCE Mechanical and Electrical Oscillators - 41 Here [Fig. 23] is, I might say, the first commercial oscillator which I designed and constructed and which was exhibited at the Chicago World's Fair. With this, I also performed many experiments. As you will observe, I have a powerful magnet in two parts for producing a strong field on both sides, and in it are conductors which are vibrated by an engine in the center. That [Fig. 24], as you see, diagramatically represents the arrangement. Here [at the center] is my little engine, and here [at Hand M] are the conductors and the magnets producing a very strong field. I observed very curious phenomena with this machine, which I subsequently turned to great advantage. We are now coming to a form of machine which was on an industrial scale. Figure 25. Double compound mechanical and electrical oscillator for generating current of perfect, constant, dynamo frequency of 10 horsepower. (Article by Martin ["Tesla's Oscillator and Other Inventions"], Century Magazine, April 1895, Fig. 2, p. 921.) (Built in 1893 . ) ÆTHERFORCE 42 Work With Alternating Currents With this one [shown in Fig. 25], I operated normally in my laboratory at 35 South Fifth Avenue. It was primarily installed there. The Babcock and Wilcox people had the kindness of specially constructing a boiler for me which could stand a pressure of 1,000 pounds. This machine was capable of developing up to 10 horsepower. It was, as you see, composed of two magnets or magnetic fields and a compound engine for imparting vibration to the conductors in the fields. It was controlled by an isochronous oscillator and, in addition, I tuned the electromagnetic system when I operated. Counsel What frequencies were developed? Tesla Those were low frequencies, but I will tell you how I solved the problem of high frequencies. Figure 26. Diagrammatic representation of double compound mechanical and electrical oscillator for generating currents of perfectly constant dynamo frequency. Shows mechanical and electrical parts. ÆTHERFORCE Mechanical and Electrical Oscillators ~ 43 Counsel When was that machine developed, Mr. Tesla? Tesla This machine was built in 1893 and was operated until May 1895, when a fire destroyed my laboratory. You will appreciate better this photograph [Fig. 25] if I show this drawing [Fig. 26] that was made for the patent specification at that period. I come now to a large machine which was built in my laboratory on Houston Street. Immediately after the destruction of my laboratory by fire, the first thing I did was to design this oscillator [shown in Fig. 27]. I was still recognizing Figure 27. Large mechanical and electrical oscillator with four vibrating parts installed in the laboratory at 46 E. Houston Street, for furnishing isochronous currents of desired wave frequencies, phases, and beats. ÆTHERFORCE 44 Work With Alternating Currents the absolute necessity of producing isochronous oscillations, and I could not get it with the alternator, so I constructed this machine. That was all a very expensive piece of work. It comprised four engines. Those four engines were put in pairs and there was an isochronous controller in the center, and furthermore, that controller was so arranged that I could set two pairs of engines to any phase or produce any beat I desired. Usually I operated quarter phase; that is, I generated currents of 90° displacement. By the way, now, for the first time you see my apparatus on Houston Street, which I used for obtaining oscillations, damped and undamped as well. But, it is necessary to state that while others, who had been using my apparatus, but without my experience, have produced with it damped oscillations, my oscillations were almost invariably continuous, or undamped, because my circuits were so designed that they had a very small damping factor. Even if I operated with very low frequencies, I always obtained continuous, or undamped, waves for the reason that I designed my circuits as nonradiative circuits. I will explain that later. Figure 28. Diagram showing length of section of large mechanical and electrical oscillator. ÆTHERFORCE Mechanical and Electrical Oscillators ~ 45 In this diagram [Fig. 28] I show the general arrangement of these engines installed in the laboratory at 46 East Houston Street. There were four, with four vibrating parts installed for furnishing isochronous currents of desired wave frequencies, phases, and beats. Figure 29. Small high frequency mechanical and electrical oscillator used in many investigations. That oscillator [Fig. 29] was one of high frequency for isochronous work, and I used it in many ways. The machine, you see, comprised a magnetic frame. The energizing coil, which is removed, produced a strong magnetic field in this region. I calculated the dimensions of the field to make it as intense as possible. There was a powerful tongue of steel which carried a conductor at the extreme end. When it was vibrated, it generated oscillations in the wire. The tongue was so rigid that a special arrangement was provided for giving it a blow; then it would start, and the air pressure would keep it going. The vibrating mechanical system would fall into synchronism with the electrical, and I would get isochronous currents from it. That was a machine of high frequency that emitted a note about like a mosquito. It was something like 4,000 or 5,000. It gave a pitch nearly that of my alternator of the [first] type which I have described. Of course this device was not intended for a big output, but simply to give me, when operating in connection with receiving circuits, isochronous currents. The excursions of the tongue were so small that one could not see it oscillate, but when the finger was pressed against it the vibration was felt. ÆTHERFORCE 46 Work With Alternating Currents This drawing [Fig. 30] shows the construction in detail. Here is the field coil, here are the conductors in the intense field, the valves for air supply, and the stops for limiting vibration. The stronger the field was excited, the [stronger] the vibrations became, but just the same, while the amplitude changed, the isochronism was not disturbed. Figure 30. Diagrammatic representation of small high frequency mechanical and electrical oscillator used in many investigations. I want to say now why these machines were the means of obtaining the best results in my wireless work. The machine at the Houston Street laboratory with which I could obtain any difference of phase, as well as that machine at 35 South Fifth Avenue, were the means of running a motor in perfect isochronism. That is, if I connected a synchronous motor to these machines and drove it with currents of different phase, I obtained an absolutely uniform rotation -- constant in time -and when I coupled this motor directly to an alternator, I obtained from the latter currents of absolutely constant frequency, all the more readily as I tuned the circuit of the alternator to the same frequency. These machines I have described in a general way only. The work has covered years, and it would take a long time to explain all about them. They enabled me to operate in whatever I did with currents of constant frequency, and the small ÆTHERFORCE cal Oscillators - 47 alternators in my were dr While work was go on, I was perfect other ways of e llations of absolutely constant fre- quency which were then not in the art. ÆTHERFORCE IV. Apparatus for Transformation by Condenser Discharges; Damped Waves This work [ . 31] was begun already in 1889. This of is identified with my name as certain as the law of gravitation is with that of Newton. I know that some have that Professor [Elihu] Thomson also invented the so- called Tesla coil, but those feeble chirps ne'er went beyond t. Professor Thomson is an odd sort of man; very , but he never was a wireless ; he never could be. Moreover, to realize that this le is The ence have told me that this was my best and, in connection with this [ to schematics of . 31], I may say that a lot of liberties have been taken. For instance, a man fills this space [break D] with hydrogen; he all my instrumentalities, that is neces- sary, but calls it a new wireless the Poulsen arc. I cannot Another man in here [ to space between self-inductive lines L L] a kind of gap -- he a Nobel My name is not Still another man s here [conductor B] a mercury[-arc] rectifier. That is my friend [Peter} Hewitt. But, as a matter of fact, those devices have nothing to do with the If these men knew what I do, would not touch my ; would leave my as it is. in here [break D] two wheels. one wheel; he shows two. And he says, "See what s when the wheels are a wonderful s!" What is the wonder- ful Why, when the teeth of the wheels pass one an- other, the currents are broken and That is the ful thing that ? The f could not make anything else happen unless he broke his own laws. So, in this way, invention debased, prosti- tuted, more in connection with my s than in else. Not a ves of invention as a creative effort is in the thousands of s that you see under the name of other a ves of invent It is exactly like in car which 6,000 have been taken out; but all are constructed and ex- actly the same way. The inventive effort involved is about the same as that of which a 30 mule is This is a fact. is one of most beautiful ever in the I take a of any kind. With the a condenser. Then I di the conden- ser under conditions which result in the of vibra- tions. it was known since Lord Kelvin that the condenser ÆTHERFORCE r Discharges: Waves - 49 Ufo Model.) N. TESLA. METHOD OF AND APPARATUS FOR ELECTRICAL CONVERSION AND DISTRIBUTION. No. 462,41 Patented Nov. 31 1891. 31. Method of transformation of electrical oscillatory condenser descr~ed in U.S. Patent No. of November 3, 1891. Application filed February 4, 1891. Announcement of this invention was made in Tes1a's lecture before the American Institute of Electrical Engineers at Columbia College, 20, 1891, where it was that this afforded vast and would an important in the future. Illustrated and descr~ed in Martin book, Figs. and 121, pp. 191-194. ÆTHERFORCE 50 Work With Alternating Currents discharge would give this vibration, but I perfected my apparatus to such a degree that it became an instrument utilizable in the arts, in a much broader way than Lord Kelvin had contemplated as possible. In fact, years afterwards when Lord Kelvin honored me by presenting to the British Association one of my oscillators of a perfected form, he said that it was "a wonderful development and destined to be of great importance." [Returning to a discussion of Fig. 31], [E] is supposed to be a condenser. That [A] is the generator. Now then, supposing that this is a generator of steady pressure. I can obtain oscillations of any frequency I desire. I can make them damped or undamped. I can make them of one direction or alternating in direction as I choose. At G are devices which operate -- lamps, or anything else. Some experimenters who have gone after me have found a difficulty. They said, "No, we cannot produce a constant train of oscillations." c --.. ..--4...---- .... -.:::....---__ R ~I t '::::~ , . . . . . .~'::a.-_ - : ! : ".' -- - - - - - ~"'... -_ :...... _ . " _.:::::':._--..g- - - . -.. .. - I I I I e e e Figure 32. Quenched spark gap. (Tesla at that t~e pointed out the future of quenching and showed that oscillations can be maintained without a spark being visible to the naked eye between the knobs.) Illustrated in Martin book, Figs. 135 and 136, p. 211. ÆTHERFORCE Condenser Discharges; Damped Waves - 51 Well, it is not my fault. I never have had the slightest difficulty. I produced constant oscillations and I have described how I produced them. Anyone who has no more than my own skill can do it. This [Fig. 32J is another improvement in that particular device, which was the weakness of the invention and which I tried to eliminate. This device incorporated many spark gaps in series. It had a peculiar feature; namely, through the great number of gaps, I was able, as I have pointed out in my writings, to produce oscillations without even a spark being visible between the knobs. This device is now known in the art as the "quenched spark gap." Professor Wein has formulated a beautiful theory about it, which I understand has netted him the Nobel prize. Wein's theories are admirable. The only trouble is that he has overlooked one very important fact. It is this: If the apparatus is properly designed and operated, there is no use for the quenched gap, for the oscillations are continuous anyway. The radio men who came after me had the problem before them of making a bell sound, and they immersed it in mercury. Now, you know mercury is heavy. When they struck their bell, the mercury did not permit it to vibrate long because it took away all the energy. I put my bell in a vacuum and make it vibrate for hours. I have designed circuits in connection with an enterprise in 1898 for transmission of energy which, once started, would vibrate three years, and even after that the oscillations could still be detected. Professor Wein's theory is very beautiful, but it really has no practical meaning. It will become useless as soon as the inefficient apparatus of the day, with antennae that radiate energy rapidly, [areJ replaced by a scientifically designed oscillator which does not give out energy except when it gets up to a tremendous electromagnetic momentum. c Figure 33. The discharger working in an atmosphere, chiefly consisting of hydrogen, still further weakened by heat. The use of hydrogen in this connection has been claimed as a discovery and patented. Presented in Tesla's lectures before the Franklin Institute and the National Electric Light Association. Martin book, Fig. 167, pp. 307-308. FlO . 107. ÆTHERFORCE 52 Work th ternat Currents In this form of break [ the atmo in which the arc was ing. was mostly hydrogen, and with this device I experiments before the Franklin Institute and the National As ion in St. Louis. has been used by Poulsen and is now called "Poulsen arc" and "Poulsen " But, of course, there is no ion in I am on record with prior publ , and besides, the does not have any other effect that it lowers the ten- sion under which the device can operate. It has the disadvan- of rical or dis waves, and the im- s not best suited for ng. s [ 34 is the position of 1893, at which to Professor Helmholtz my for I had shown Professor Helmholtz certain , he asked me, the cago Ex- the first time energy. After ific men there "Now, what is all this for?" I told him I was energy without purposes. When I idea, I said, to develop an for transmit- for telephony, and other ained to Professor Itz the whole "Excel do you think that my plan is realizable?" He ied, "Why, s." Y it is, but first you must the ap- I started then and there to the s . Was that conver at the Chicago ion? la Yes. a ion which was built espe- cially for my inventions and discoveries. I be- l Professor Wedding was there and some other s ists whom I cannot remember now. I showed Professor Helmholtz my vacuum tubes and performed many other Will you describe this apparatus in a Ie more detail? ÆTHERFORCE r s s; Damped Waves ~ 53 rN() ModeL) N. TESLA. MEANS FOR GENERATING ELECTRIO OORRENTS. No. 614,168. Patented Feb. 6, 1894. apparatus with interrupter in oil. Exhibited in the Exposition of 1893 before Helmholtz. Described in U.S. Patent ,168 of February 6, 1894. Application filed August 2, 1893. ÆTHERFORCE 54 Work With Alternating Currents Tesla The apparatus [Fig. 34], as you see, comprised primary and secondary coils immersed in a large tank of oil. The break was automatically effected by means of a turbine. The oil was circulated by a pump, and the current [i.e., stream flow] of oil drove the turbine which effected the make and break. Owing to the fact that the oil used was a very good insulator, rapidly flowing and of great dielectric strength, these make-and-break points were very close together, and the arcs extremely short. The effects were accordingly more intense. Here [T in Diag. 1 of Fig. 34J is a cooler through which the oil was circulated. The oil was forced through the gaps at great speed, and as it flowed out it was supplied again to the tank and the current driving the turbine. Counsel That device [Diag. 2 of Fig. 34] you call a turbine? Tesla Yes. It had vanes like those of a propeller and constituted a rotary break in the circuit. Counsel What was your prime source [of powerJ? Tesla The primary source was an alternator with a frequency of 133 cycles and, if I recollect rightly, the pressure [at the secondaryJ was about 20,000 volts. I may have had 10,000 volts. I am not sure what it was, but it must have been certainly from 10,000 to 20,000 volts -- within that range. Counsel I notice you have two sets of transformers in there marked Sand S', have you not? Tesla This [S'J is my oscillatory circuit. That [SJ is the transformer from which the condenser was charged. Here [at S] we had 20,000 volts, or whatever it was, from the commercial transformer and here [at S'] is my secondary which generated the high frequency currents. The rotary gap is shown in detail [Diag. 2 of Fig. 34J. I had a special reason for showing this. To meet that great man Helmholtz and other scientific men, and to bring ÆTHERFORCE Condenser Discharges; Damped Waves - 55 before them for the first time the results of years of previous labor, was an important moment in my life -- particularly because Professor Helmholtz gave me the assurance himself that what I explained to him was realizable, provided that I could produce the apparatus. I was very much encouraged. -- - ...... [ Figure 35. Apparatus with mechanical break as installed on a large scale in the laboratory at 35 So. Fifth Avenue and subsequently at 46 E. Houston Street. Described in U.S. Patent No. 645,576 of March 20, 1900. Application filed September 2, 1897. I h . - , .) ) .J > This [Fig. 35J is the apparatus I had at 35 South Fifth Avenue and also Houston Street. It shows the whole arrangement as I had it for the demonstration of effects which I investigated. [*J This cable you see [square loop in top half of Fig. 35J is stretched around the hall. These are my condensers. There is the mechanically operated break, and that is a transformer charged from the generator. That is the way I had it for the production of current effects which were rather of damped character because, at that period, I used circuits of great activity which radiated rapidly. In the Houston Street laboratory, I could take in my hands a coil * Editorial note: This diagram is not provided in the referenced patent. ÆTHERFORCE 56 Work rnating Currents tuned to my body and collect 3/4 re in the room without connection, and I have often disillu- sioned my vis to such effects. Some- times, I would flames shooting out from my head and run a motor in my hands, or light six or e could not understand festations of energy and that it was a transmiss of power. I told them that these were wonderful, but that a system of transmission, based on the same principle, was absolutely worthless. It was a transmission by e ic waves. The solution in a different direction. I am showing you s [diagram] s y as a typical form of of that pe and if you go over the 1 of the present you will find that the newest arrangements have nothing better to show. Counsel What was the rna and break that apparatus? you got from Tes It was 5,000, 6,000 -- sometimes r still. I had two oppositely rotating discs which I will show and with I could have y, 15,000 or 18,000. Counsel What wave s did you ? Tesla I could from a few thousand up to a million per second, if I wanted. Counsel What did you actually use? Tesla In these demonstrat , which I these effects, these most powerful e fects that were s of New York at that time, I with ies from 30,000 to 80,000. At that ck up a re, 1 it up, and tell what the vibrat would be, without any test, because I was experimenting and This [Fig. 36] is a form of break which I in working with alternators. I recognized that it was of tremen- dous advantage to break at the peak of the wave. If I used just an ordinary , it would make and bre the current at ÆTHERFORCE Condenser Discharges; Damped Waves ~ 57 (No Model.) N. TESLA. :.! Sheets-Sheet 2. APPARATUS rOR PRODUCING ELECTRICAL CURRENTS or HIGH FREQUENCY. No: 668,180. Patented Sept. 22, 1896. INVENTOR 8' AT TORNE'3 Figure 36. Isochronous mechanical break used in the laboratory at 35 South Fifth Avenue. Described in U.S. Patent Nos. 568,179 and 568,180 of September 22, 1896. Applications filed July 6 and 9, 1896. (Diagram taken from Patent No. 568,180.) ÆTHERFORCE 58 Work With Alternating Currents low as well as high points of the wave. Of this apparatus I had two forms; one in which I drove the break right from the shaft of the dynamo and the other in which I drove it with an isochronous motor. Then, by a movement of these knobs (K K), I would make the adjustments so that the makes would occur exactly at the top of the wave. That is a form of break which is embodied in hundreds of patents and used now extensively. < I ,t .::--.9 '~"",..-_ _ 1 . I i}· , " --.-~,I " . : -.."..-=__.~J ~. ; '- - Figure 37. Mechanical break with two oppositely rotating discs used for the purpose of increasing the number of breaks and alternating the oscillations practically undamped. (Subsequently patented by others.) Here [Fig. 37] I show an apparatus that was installed in the Houston Street laboratory prior to the other break because I wanted to get as high a number of impulses as possible. The drawing dates from the spring of 1896. It is a break with which I could reach from 15,000 to 18,000 interruptions per second. I used it very much until later I found it was not necessary. That is the innocent device which Marconi thought a great invention. Counsel This is also a rotary gap? ÆTHERFORCE r Dis Waves - 59 Tesla Yes, and it consists of two scs of a with teeth of side. were rotated by two motors in opposite y rotated they alternately closed and t. In some tances I used an uneven number of teeth on one and even number on the other so that I as many breaks as I desired. I will show you later an more perfect than s one, and of a different kind, in which I have 24 contacts, and 25 rotat elements that established the contact and broke one I 24 25, or 600 [per revolution]. el Whenever you say "the break", you mean "a gap"? la Yes: prefe I use the term "circuit controller," This [Fig. 38] illustrates another deve in a dif- ferent direct In order to increase number of breaks, currents of different I had in my labora- , ly, a and could between; that is, from apart, I could four s, 45 Here is an shown as I had it, with three [60 I and could obtain six , 30 ], and later on I had one with four s [45 apart, and could obtain e phases 22 1/2 You see, as I mult ied the number of the Sf I the number of the fundamental scharges. What is the date of this ? Tesla I in the 35 South Fifth Avenue labo remember that several sc ific soc s and it was know on one occasion there was the Society 0 another, the Electrotherapeutic Soc and then I tingu men like Mark Twain and Joseph Jefferson I gave them a demonstration which was published in Martin's article in the of il 1895, I know on Later on I made it four therefore, to the destruction of my laboratory ÆTHERFORCE 60 Work With Alternating Currents ) - ~" , Figure 38. Use of multi-phase generator with mechanical break. Experiments in the laboratory at 35 So. Fifth Avenue and subsequently. Counsel Do you recall any publication in which this diagram was illustrated? Tesla I made no publication, and I vividly remember that when I installed my apparatus on Long Island I had an arrangement with four transformers and four phases 45 apart. After I had been using this apparatus there, several years afterwards, I ran across a patent, I believe held by the General Electric Company, describing precisely the same arrangement. [*] It was a similar experience as with that patent of Fessenden on the compressed air condenser. Any time I want to use these improvements all I need to do is to produce my records and that will settle the patents. Counsel When was that drawing [Fig. 38]? * Editorial note: Tesla refers to U.S. Patent No. 996,580 dated June 27, 1911, of Charles Green with assignment to G.E.; application filed September 30, 1907. ÆTHERFORCE ser Dis Si Waves ~ 61 la This is from an old Netter. Counsel But that not go to which was made by Mr. ? No. I have hundreds of inventions that were to be but The expense was too and I could not do it. This form of with two and phases was used prior to the destruction of my labo in 1895, and it was instal on a scale with four in my plant on Island with which I was to tel around the world, but that is a long story. I In that use you made of it at your , was that connected up as shown there [ . 38], to an antenna? la I used the s, yes, in with the antenna too, but this is from a drawing in ch an antenna is shown; I mean, I used in every connection. [Fig. 38] il- lustrates an antenna with my tran circuit, but the ap- was used in all my work, in all my invest And when this was connected and used in an antenna, did you use it as in other instances -- go off and listen to the notes which you rece Tesla Oh, certai But I remember that, bes fferent nds Then I had a sensibly wave because at I still was laboring under the same ff It s as some do this day -- I had not learned how to a circuit which would give me, with very few cont s wave. That carne with the ces. When I carne to my in Colorado, I could take my like that and get a con- tinuous undamped wave, almost without except I between s s. ÆTHERFORCE 62 Work With Alternating Currents Counsel Speaking of your not having perfectly undamped waves at that time, you were referring to that character of circuit? Tesla Yes, but with another kind of circuit I could, of course. The advantage of this apparatus was the delivering of energy at short intervals whereby one could increase activity, and with this scheme I was able to perform all of those wonderful experiments which have been reprinted from time to time in the technical papers. I would take energy out of a circuit at rates of hundreds or thousands of horsepower. In Colorado, I reached 18 million horsepower activities, but that was always by this device: Energy stored in the condenser and discharged in an inconceivably small interval of time. You could not produce that activity with an undamped wave. The damped wave is of advantage because it gives you, with a generator of 1 kilowatt, an activity of 2,000, 3,000, 4,000, or 5,000 kilowatts; whereas, if you have a continuous or undamped wave, 1 kilowatt gives you only wave energy at the rate of 1 kilowatt and nothing more. That is the reason why the system with a quenched gap has become popular. I have refined this so that I have been able to take energy out of engines by drawing on their momentum. For instance, if the engine is of 200 horsepower, I take the energy out for a minute interval of time, at a rate of 5,000 or 6,000 horsepower, then I store [it] in a condenser and discharge the same at the rate of several millions of horsepower. That is how these wonderful effects are produced. The condenser is the most wonderful instrument, as I have stated in my writings, because it enables us to attain greater activities than are practical with explosives. There is no limit to the energy which you can develop with a condenser. There is a limit to the energy which you can develop with an explosive. A common experiment, for instance, in my laboratory on Houston Street, was to pass through a coil energy at a rate of several thousand horsepower, put a piece of thick tinfoil on a stick, and approach it to that coil. The tinfoil would melt, and would not only melt, but while it was still in that form, it would be evaporated and the whole process took place in so small an interval of time that it was like a cannon shot. Instantly I put it there, there was an explosion. That was a striking experiment. It simply showed the power of the condenser, and at that time I was so reckless that in order to demonstrate to my visitors that my theories were correct, I would stick my head into that coil and I was not hurt; but, I would not do it now. ÆTHERFORCE Condenser Discharges; Damped Waves ~ 63 [Fig. 39) shows a four-phase machine which was furnished me by the Westinghouse Electric Company at the close of 1895. My laboratory burned out in May, and I urged my friend, Mr. Albert Schmidt, who was the Superintendent, to give me this alternator as soon as possible. He worked day and night until he got it out, and he certainly did notable work because while the machine was rated at 30 horsepower, I have run it at 150 horsepower. Figure 39. Apparatus furnishing direct currents of high tension, producing undamped electrical oscillations of high frequency. (This is also shown in [Fig. 27]). Apparatus built in 1895. By the way, and this is a painful reflection, it was Schmidt and I who developed this type of frame and this general arrangement which is universally adopted now -- a base, with the magnets cast below, split at the center line, and a corresponding upper part. That is now used everywhere. I remember years ago, some of my friends, Messrs. Crocker and Wheeler, started with those long magnets and I told them, "The sooner you throw these away and adopt this construction, the better it will be for you." They have got it now; it is all right. Counsel How is this machine [Fig. 39) shown in connection with that? ÆTHERFORCE 64 Work With Alternating Currents Tesla This dynamo [Fig. 39], you see, is a two-phase machine; that is, I develop from it currents of two-phase. Now, there are four transformers, you see them down here [lower left of Fig. 39], that furnish the primary energy. From these two phases I develop four phases. [However,] this involves something else which I have referred to before; namely, an arrangement which enables me to produce from these alternating currents direct currents and undamped -- absolutely undamped isochronous oscillations of any period I like. This is accomplished in the following manner: The secondaries of the four transformers could each develop 44,000 volts. They were specially built for me by the Westinghouse Company. They could, however, be connected in such a way that each would give 11,000 volts, and then I would take these 11,000 volts and these four phases and commutate them by a commutator consisting of aluminum plates, or aluminum segments, which were rotated in synchronism with the alternator. Then I obtained a continuous pressure; that is, direct current of a tension of 44,000 volts, and with these 44,000 volts I charged my condensers. Then by discharging the condensers, either through a stationary gap or through a gap with a mechanical interrupter, I obtained any frequency I desired, and perfectly undamped waves. This arrangement was installed in 1901 in my wireless plant at Long Island, with which I was to telephone around the world. Counsel Who built that machine? Tesla The Westinghouse Company, [under direction of] Mr. Albert Schmidt, Superintendent. It was especially built for me and furnished to my laboratory on Houston Street. While I was with the Westinghouse Company, I did two things in addition to bringing my motors to them. I had discovered that Bessemer steel was a much better material for transformers and motors than the soft iron which was previously used. When I came to Pittsburgh, my motors gave results which their motors could not at first produce, and I told them that I had used Bessemer steel. I discovered, in following up the analysis of the steels which were used, that the Bessemer was not steel but really soft iron. The Westinghouse people then adopted my suggestion. At first, Mr. Shallenberger and other electricians there objected very much, but I persuaded them and when the transformers were built we found that we could get 2 1/2 times the output we got before. ÆTHERFORCE ser s Si Damped Waves ~ 65 The Westinghouse people kept a secret for a time and no one understood how they could make trans for- but all was to use the Bessemer steel, on my on, instead of the soft iron the General Electric and people used. Mr. Westinghouse e ally requested me efforts with Mr. Schmidt and the des of his and we did so. We evolved this design, introduced the which are pressed on the armature, and of s out with Mr. , and it. I nk like that, for my You have of the use of that Street. In what way was it used? ne at Houston Tesla I used s machine, as I said, either to alter- nat currents and then interrupt them with a cal break at high peaks of the wave; or, I used alternat currents and interrupted them with an i ng break ng a number of teeth. Or, I generated con- tinuous currents commutating the tension ternating currents of transformer. At that time I had two trans- formers from which I obtained a constant sure, the condenser, and produced undamped waves of any wanted. As to the machine here [ . 39J, that is the way it It was for the generat of cont elec force and production of waves from 1895 and on. purpose s was it connected up to for the Tesla I was same as shown here [ . 38]. It was con- nected to the condensers, and these condensers were discharged a primary which excited the ; the antenna was i in the secondary. At other s we scha the condensers rectly so that I could use antenna without the Counsel In the same way did you note the waves? ion of these ÆTHERFORCE 66 Work With Alternating Currents Tesla We did, of course, only in most cases the instrument of was different. When I with these con- or undamped, waves, in this way, I usually went frequencies. I [at] a very few thou but that gave me a smaller Such a machine you have to operate at high f power. Counsel What do you mean s? Te I mean frequencies of 30,000, 40,000, 50,000, or someth 1 that. 189S? by means of that , you undamped waves of about 50,000 into that antenna at Houston Street in not in 1895. Late in 1895 the machine was furnished to operate in early 1896. That when I to Then you did this, that I of, 1896? Tesla Yes, from 1896 to 1899, Counsel When you used s like that in your antenna, was your antenna tuned or untuned? Te 1 I could not use it untuned. That would be absurd. 1 What form of device did you use, and where did you use it, for the of these oscillations or waves in the antenna? ÆTHERFORCE Condenser Discharges; Damped Waves - 67 Tesla I suppose I had hundreds of devices, but the first device that I used, and it was very successful, was an improvement on the bolometer. I met Professor Langley in 1892 at the Royal Institution. He said to me, after I had delivered a lecture, that they were all proud of me. I spoke to him of the bolometer, and remarked that it was a beautiful instrument. I then said, "Professor Langley, I have a suggestion for making an improvement in the bolometer, if you will embody it in the principle." I explained to him how the bolometer could be improved. Professor Langley was very much interested and wrote in his notebook what I suggested. I used what I have termed a small-mass resistance, but of much smaller mass than in the bolometer of Langley, and of much smaller mass than that of any of the devices which have been recorded in patents issued since. Those are clumsy things. I used masses that were not a millionth of the smallest mass described in any of the patents, or in the publications. With such an instrument, I operated, for instance, in West Point -- I received signals from my laboratory on Houston Street in West Point. Counsel This was then the machine that you used when working with West Point? Tesla I operated once or twice with it at that distance, but usually as I was investigating in the city. My work at that time was to prepare for the development of a commercial plant, and with me the question was not to transmit signals, but to see what intensity I could get to put me in position to calculate out my apparatus, the dimensions and the forms, before I began the undertaking. It was nothing but preparatory work for the construction of a commercial plant, and I demonstrated its practicability through my experiments, a plant which was to accomplish much more than all others. Counsel What was the horsepower activity in the oscillating circuits when you used this machine? Tesla Usually something like 50 horsepower, and I would get, I should say, approximately 30 horsepower in the antenna; that ÆTHERFORCE 68 Work With Alternat Currents is, I would get 30 in the oscil rcui t. 1 I understood a little while ago when you made the state- ment of using several thousand horsepower put a conden- ser, you could take out of the condenser a mill horsepower. I if you the same condition with s machine. Yes; I charged with 40,000 When it full, I suddenly, a short which gave me a very rate of oscillation. Let us suppose that I had in the condenser 10 watts. Then, for such a wave there is a flux of energy of (4 x 04)2, and s is multiplied by the of 100,000. You see, it may go into thousands s of horsepower. What I wanted to suddenness of the dis was, did that upon the Yes. It is merely the electrical Ie or a hammer. You accumulate energy a long dis- tance and then you del th a tremendous suddenness. The distance ch the mass moves is small -- the pressure immense. Counsel Did you find that that was the best condition for transtt energy without the use of wire? Tesla No, I did not use that method when I was energy. I used on in the production of those freaks for I have been called a magician. If I had used merely un- would have been an ordinary e ian like Counsel You have Did you static? some delicate struments. those burning out on account of ÆTHERFORCE Condenser Discharges; Damped Waves ~ 69 Tesla My dear sir, I burned out so many instruments before I discovered what was the matter with them! They burned out instantly until I learned how to make them so that they could not burn out. Yes, that was a great trouble in the beginning. Counsel Did you succeed in getting them so they would not burn out? Tesla Yes. If lightning struck close by, it would not burn out my instrument that has a millionth of the smallest mass used in the instruments of others. .D .1\J.iV FIG. 165. rOOOOOOO) 'Sf Figure 40. Apparatus and method of conversion by condenser discharges applicable to both alternating and direct currents. Described in lectures before the Franklin Institute and the National Electric Light Association early in 1893. Illustrated in Martin book, Fig. 165, pp. 302-317. This [Fig. 40] is a systematic representation of the various ways which I gave in my lecture before the Franklin ÆTHERFORCE 70 Work With Alternating Currents Institute and the National Electric Light Association, embodying the general arrangements for the obtainment of continuous waves, undamped or damped waves, from direct and alternating current supply. On the one side [right] you have direct, on the other side alternating current supply. Some electricians have had difficulties in operating some of this apparatus. I had none. I can take an ordinary circuit of 50 volts and produce from it absolutely undamped oscillations and never have the slightest difficulty about it. Figure 41. Illustrating one of the early experiments with a tuned transformer in the laboratory at 35 So. Fifth Avenue. Figure 42. Another experiment illustrating one of the early experiments with a tuned transformer in the laboratory at 35 So. Fifth Avenue. (Article by Martin ["Tesla's Oscillator and Other Inventions"'], Century Magazine, April 1895, Fig. 9, p. 926.) ÆTHERFORCE er s s; Damped Waves ~ 71 Now I come to a few pieces of apparatus which I used the Houston Street and the South Fifth Avenue labo- I have here 41J what you might call a I emp usually another secondary and had my con- densers on the table. You see one of the coils in action. This is a tuned which responds to e c waves which are the room. Counsel This is be used as a receiver of waves? Te Yes. Th s t shown in Fig. 42] was used in the labo- on Fifth Avenue. Here [large rcular sc pos on coil] is the tuning table with the condensers, a thick , and another secondary wire. Somet s I operate with two and I would tune the first ci to one and the to the other. Here [re to nets in back of room] you see some of my historical Professor Fairf Id Osborn[*] came once to my said to me, "Why on earth do you keep in s I had all of this apparatus, 400 pieces, absolutely and offered to take it over to the Museum. But I heed s advice, and it is gone. * Editorial note: Fairfield Osborn, Dean, of Pure Science, Columbia College in Seth Low of New York. Osborn wrote in part, ar have lege President upon my mind two matters which to very rst is connected with Mr. Hill with Mr. New York. have is considered the mathematician in this country, and seems to be little doubt that Mr. is elec- trician. They both are in a measure connected with Columbia through lectures here, and the fact that Mr. Tesla at Professor fessor Crocker's invitat his first electrical lecture in that we have already establ a sympathetic relation with these men. r an afternoon recently with Tesla, and regard him as one of most dis men I have ever met. r happened to meet Professor Crocker shortly afterwards, and learned from him that he had spoken to you in regard giving Tesla an Honorary I would like to support this in the most earnest manner. Poulton [ . of at Oxford] tells me that Tesla was covered with honors while in England France. We certainly must not allow other University to anticipate us in honoring a man who lives under our In response to this, President Low recommended, in a letter dated 5, 1894, to the Trustees, that the honorary degree of LL.D. should be conferred on Tesla. The degree was awarded in June, 1894. Source: Columbia Archives ÆTHERFORCE 72 Work With Alternating Currents Counsel Where were the waves sent from? Tesla The whole room was energized by electromagnetic waves and the receiver responded at any place in the hall. The hall was bigger than this room [shown in Fig. 42], twice as long, and anywhere the intensity of action was the same. These discs [vertical, on top of tuning table] were, I think, about 14 or 15 inches in diameter, and you could see the streamers [shown as white between the discs] anywhere in the room. In a hall twice as long as this, wherever I placed the instrument, it would respond to the electromagnetic waves. Counsel In this particular instance you are speaking of, the waves were generated right there at 35 South Fifth Avenue? Tesla Yes. Counsel Was that the apparatus in which you had the primaries running entirely around the room? Tesla Yes. This was shown to many people and societies. This [Fig. 43] shows the first single step I made toward the evolution of an apparatus which, given primary oscillations, will transform them into oscillations capable of penetrating the medium. That experiment, which was marvelous at the time it was performed, was shown for the first time in 1894. I remember the incident perfectly. I called Mr. Edward Adams, the banker, to come and see it, and he was the first man to observe it and to hear my explanation of what it meant. This coil, which I have subsequently shown in my patents Nos. 645,576 and 649,621, in the form of a spiral, was, as you see, [earlier] in the form of a cone. The idea was to put the coil, with reference to the primary, in an inductive connection which was not close -- we call it now a loose coupling -but free to permit a great resonant rise. That was the first single step, as I say, toward the evolution of an invention which I have called my "magnifying transmitter." That means, a circuit connected to ground and to the antenna, of a tremendous electromagnetic momentum and small damping factor, with ÆTHERFORCE Condenser Discharges; Damped Waves - 73 all the conditions so determined that an immense accumulation of electrical energy can take place. Figure 43. Apparatus in action illustrating the first step in the evolution of the magnifying transmitter in the laboratory at 35 So. Fifth Avenue. (Article by Martin ["Tesla's Oscillator and Other Inventions"], Century Magazine, April 1895, Fig. 15, p. 932.) It was along this line that I finally arrived at the results described in my article in the Century Magazine of June 1900. [Fig. 43] shows an alternator; not the alternator that was furnished for my laboratory on Houston Street -- that was another one, [but] at 35 South Fifth Avenue [and] operated on the same principle. Here [lower left] are the condensers, ÆTHERFORCE 74 Work With Alternating Currents primary, and all the rest. The discharge there was 5 or 6 feet, comparatively small to what I subsequently obtained. I have produced discharges of 100 feet, and could produce some of 1,000 feet if necessary, with the greatest facility. Counsel Mr. Tesla, at that point, what did you mean by electromagnetic momentum? Tesla I mean that you have to have in the circuit, inertia. You have to have a large self-inductance in order that you may accomplish two things: First, a comparatively low frequency, which will reduce the radiation of the electromagnetic waves to a comparatively small value, and second, a great resonant effect. That is not possible in an antenna, for instance, of large capacity and small self-inductance. A large capacity and small self-inductance is the poorest kind of circuit which can be constructed; it gives a very small resonant effect. That was the reason why in my experiments in Colorado the energies were 1,000 times greater than in the present antennae. Counsel You say the energy was 1,000 times greater. Do you mean that the voltage was increased, or the current, or both? Tesla Yes [both]. To be more explicit, I take a very large self-inductance and a comparatively small capacity, which I have constructed in a certain way so that the electricity cannot leak out. I thus obtain a low frequency; but, as you know, the electromagnetic radiation is proportionate to the square root of the capacity divided by the self-induction. I do not permit the energy to go out; I accumulate in that circuit a tremendous energy. When the high potential is attained, if I want to give off electromagnetic waves, I do so, but I prefer to reduce those waves in quantity and pass a current into the earth, because electromagnetic wave energy is not recoverable while that [earth] current is entirely recoverable, being the energy stored in an elastic system. Counsel What elastic system do you refer to? Tesla I mean this: If you pass a current into a circuit with ÆTHERFORCE Condenser Discharges; Damped Waves - 75 large self-induction, and no radiation takes place, and you have a low resistance, there is no possibility of this energy getting out into space; therefore, the impressed impulses accumulate. Counsel Let's see if I understand this correctly. If you have radiation or electromagnetic waves going from your system, the energy is wasted? Tesla Absolutely wasted. From my circuit you can get either electromagnetic waves, 90 percent of electromagnetic waves if you like, and 10 percent in the current energy that passes through the earth. Or, you can reverse the process and get 10 percent of the energy in electromagnetic waves and 90 percent in energy of the current that passes through the earth. It is just like this: I have invented a knife. The knife can cut with the sharp edge. I tell the man who applies my invention, you must cut with the sharp edge. I know perfectly well you can cut butter with the blunt edge, but my knife is not intended for this. You must not make the antenna give off 90 percent in electromagnetic and 10 percent in current waves, because the electromagnetic waves are lost by the time you are a few arcs around the planet, while the current travels to the uttermost distance of the globe and can be recovered. This view, by the way, is now confirmed. Note, for instance, the mathematical treatise of Sommerfeld, [*] who shows that my theory is correct, that I was right in my explanations of the phenomena, and that the profession was completely misled. This is the reason why these followers of mine in high frequency currents have made a mistake. They wanted to make high frequency alternators of 200,000 cycles with the idea that they would produce electromagnetic waves, 90 percent in electromagnetic waves and the rest in current energy. I only used low alternations, and I produced 90 percent in current energy and only 10 percent in electromagnetic waves, which are wasted, and that is why I got my results. * Editorial note: Sommerfeld, Arnold N., ·Uber die Ausbreitung der Wellen in der drahtlosen Telegraphie," Annalen der Physik, March 16, 1909 (Vol. 28, No.4), pp. 665-736. ÆTHERFORCE v. Apparatus for Transformation by Condenser Discharges; Continuous Waves Figure 44. One of the many forms of mercury circuit controllers described in various U.S. Patents. Figure 45. Hermetically enclosed mercury circuit controller with compact oscillatory transformer. Described in U.S. Patent No. 609,245 of August 16, 1898. ÆTHERFORCE Discha Si Continuous Waves ~ 77 44 (verso). One of the many forms of mercury circuit controllers. Described in u.s. Patent Nos.: 609,245 of August 609,246 609,247 609,248 609,249 " 609,251 16, 1898, application filed December 2, 1897 " , 28, 1898 " , " March 12, " , " " ", " " " , June 3, 1897 611,719 " October 4, December 10, 1897 613,735 " November 8, " 19, 1898. Tesla This [Fig. 44] shows a further in the direc- tion of perfect a way of making and bre the current, and illustrates one the simplest forms of my apparatus, which was special built with a mercury interrupter i of cons That was from an circuit y and could stand a current of 20 or 25 amperes. It was a very compact instrument. I had dozens these instruments, obtained ei on the same; were all is in 1898. The next hermetically [ a motor, e I was to enclose the mercury break 45] • You see, here [ 46, overleaf] is de this ley. In this [referring to the cross is a jet of mercury, and there are around which make and break the current. The whole is encased hermetically. Here I have a German-silver cup that is ckel on the ins , and there is a d magnet outs which holds the mercury jet stat while the pulley tates. I could this instrument about 2,000 very nicely, and was a machine that would an of about 1 ki It was a fairly effi instrument, per- 80 percent of the energy of the was obtained in the secondary_ 47] come to another That was another of the of currents of very An rnator was difficult to construct; if one went into too h I became inefficient and worthless. But, in this way, I was able to any up to 200,000 per second, or more, in a perfectly reliable manner, and I could a couple of kilowatts output very easily. [*] That was especially built for telegraphy, te , and similar experiments. * Editorial note: In the article, "Dr. Nikola Tesla and His Achievements" Samuel Cohen, the Electrical magazine, February 19 (pp. 712, 713, ), 4 shows an having a similar external appearance and it is described as handling (37 kilowatts). ÆTHERFORCE 78 Work With Alternating Currents No. 609,245. (110 Model.) A It .TESLA. Patented Aug. 16, 1898. ELECTRICAL~IRC.lUT CONTROLLER. » - (.&ppli