Nikola Tesla On His Work With Alternating Currents
and Their Application to Wireless Telegraphy,
Telephony, and Transmission of Power
IV. Apparatus for Transformation by Condenser Discharges; Damped Waves
This work [Fig. 31] was begun already in 1889. This type of
apparatus is identified with my name as certain as the law of
gravitation is with that of Newton. I know that some have claimed
that Professor Thomson also invented the so-called Tesla coil, but
those feeble chirps ne'er went beyond Swampscott. Professor
Thomson is an odd sort of man; very ingenious, but he never was a
wireless expert; he never could be. Moreover, it is important to
realize that this principle is universally employed everywhere.
The greatest men of science have told me that this was my best
achievement and, in connection with this apparatus [referring to
schematics of Fig. 31], I may say that a lot of liberties have been
taken. For instance, a man fills this space [break D] with
hydrogen; he employs all my instrumentalities, everything that is
necessary, but calls it a new wireless system -- the Poulsen arc.
I cannot stop it. Another man puts in here [referring to space
between self-inductive lines L L] a kind of gap -- he gets a Nobel
prize for doing it. My name is not mentioned. Still another man
inserts here [conductor B] a mercury[-arc] rectifier. That is my
friend Cooper Hewitt. But, as a matter of fact, those devices have
nothing to do with the performance.
Method of Transformation of electrical energy by oscillatory
condenser discharges described in U.S. Patent No. 462,418 of
November 3, 1891. Application filed February 4, 1891. Announcement of
this invention was made in Tesla's lecture before the American Institute of Electrical
Engineers at Columbia College, May 20, 1891, where it was predicted that this apparatus
afforded vast possibilities and would play an important part in the future.
Illustrated and described in T.C Martin book, Figs. 126 and 127, pp. 191-194.
If these men knew what I do, they would not touch my arrangements;
they would leave my apparatus as it is. Marconi puts in here
[break D] two wheels. I showed only one wheel; he shows two. And
he says, "See what happens when the wheels are rotated; a wonderful
thing happens!" What is the wonderful thing? Why, when the teeth
of the wheels pass one another, the currents are broken and
interrupted. That is the wonderful thing that happens? The Lord
himself could not make anything else happen unless he broke his own
laws. So, in this way, invention has been degraded, debased,
prostituted, more in connection with my apparatus than in anything
else. Not a vestige of invention as a creative effort is in the
thousands of arrangements that you see under the name of other
people -- not a vestige of invention. It is exactly like in car
couplings on which 6,000 patents have been taken out; but all the
couplings are constructed and operated exactly the same way. The
inventive effort involved is about the same as that of which a
30-year-old mule is capable. This is a fact.
This is one of most beautiful things ever produced in the way
of apparatus: I take a generator of any kind. With the generator
I charge a condenser. Then I discharge the condenser under
conditions which result in the production of vibrations. Now, it
was known since Lord Kelvin that the condenser 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
[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.
"No, we cannot produce a constant train of oscillations."
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
Quenched spark gap. (Tesla at that time 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 T.C. Martin book, Figs. 135 and
136, p. 211.
This [Fig. 32] 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, [are] replaced by a
scientifically designed oscillator which does not give out energy
except when it gets up to a tremendous electromagnetic momentum.
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 TesIa's
lectures before the Pranklin Institute and the National Electric Light Association. T.C. Martin book, Fig. 167. pp.
In this form of break [Fig. 33], I changed the atmosphere in
which the arc was operating. The atmosphere was mostly hydrogen,
and with this device I performed my experiments before the Franklin
Institute in Philadelphia and the National Electric Light
Association in St. Louis. This has been used by Poulsen and it is
now called the "Poulsen arc" and "Poulsen system." But, of course,
there is no invention in it. I am on record with prior
publications, and besides, the hydrogen does not have any other
effect except that it lowers the tension under which the device can
operate. It has the disadvantage of producing asymmetrical or
distorted waves, and the impulses obtained are not best suited for
Oscillatory apparatus with interrupter in oil. Exhibited in the Chicago Exposition of 1893 before Helmholtz.
Described in U.S. Patent No. 514,168 of February 6. 1894. Application filed August 2, 1893.
This [Fig. 34] is the apparatus used in the Chicago Exposition
of 1893, at which time I explained for the first time to Professor
Helmholtz my plan for transmitting energy. After I had shown
Professor Helmholtz and other scientific men there certain
phenomena, he asked me,
"Now, what is all this intended for?"
I told him I was trying to develop an apparatus for transmitting
energy without wire for telegraphy, telephony, and other purposes.
When I explained to Professor Helmholtz the whole idea, I said,
"Excellency, do you think that my plan is realizable?"
"Why, certainly it is, but first you must produce the
I started then and there to produce the apparatus.
Was that conversation at the the Chicago Exposition?
Yes. It took place in a pavilion which was built especially
for exhibiting my inventions and discoveries. I believe Professor
Wedding was there and some other scientists whom I cannot remember
now. I showed Professor Helmholtz my vacuum tubes and performed
many other experiments.
Will you describe this apparatus in a little more detail?
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. 34] 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.
That device [Diag. 2 of Fig. 34] you call a turbine?
Yes. It had vanes like those of a propeller and constituted
a rotary break in the circuit.
What was your prime source [of power]?
The primary source was an alternator with a frequency of 133
cycles and, if I recollect rightly, the pressure [at the secondary]
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.
I notice you have two sets of transformers in there
marked S and S', have you not?
This [S'] is my oscillatory circuit. That [S] 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. 34].
I had a special reason for showing this. To meet that great
man Helmholtz and other scientific men, and to bring 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.
Apparatus with mechanical break as installed on a large scale in
the laboratory at South Fifth Avenue and subsequently at 46 East
Houston Street. Described in U.S. Patent No. 645,576 of March 20,
1900. Application filed September 2, 1897.
This [Fig. 35] 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.[*] This
cable you see [square loop in top half of Fig. 35] 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 tuned to my body and collect 3/4 horsepower anywhere
in the room without tangible connection, and I have often
disillusioned my visitors in regard to such wonderful effects.
Sometimes, I would produce flames shooting out from my head and run
a motor in my hands, or light six or eight lamps. They could not
understand these manifestations of energy and thought that it was
a genuine transmission of power. I told them that these phenomena
were wonderful, but that a system of transmission, based on the
same principle, was absolutely worthless. It was a transmission by
electromagnetic waves. The solution lay in a different direction.
I am showing you this [diagram] simply as a typical form of
apparatus of that period, and if you go over the literature of the
present day you will find that the newest arrangements have nothing
better to show.
What was the make and break frequency that you got from that
It was 5,000, 6,000 -- sometimes higher still. I had two
oppositely rotating discs which I will show you and with which I
could have reached, probably, 15,000 or 18,000.
What wave frequencies did you develop?
I could operate from a few thousand up to a million per
second, if I wanted.
What did you actually use?
In these demonstrations, which I showed these effects, these
most powerful effects that were the sight of New York at that time,
I operated with frequencies from 30,000 to 80,000. At that time I
could pick up a wire, coil it up, and tell what the vibration would
be, without any test, because I was experimenting day and night.
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.)
This [Fig. 36] is a form of break which I developed in working
with alternators. I recognized that it was of tremendous advantage
to break at the peak of the wave. If I used just an ordinary
break, it would make and break the current at 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
Mechanical break with two oppositely rotating discs used for the
purpose of increasing the number of breaks and alternating
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.
This is also a rotary gap?
Yes, and it consists of two discs of aluminum, with teeth of
aluminum on the side. They were rotated by two motors in opposite
directions, and as they rotated they alternately closed and opened
the circuit. In some instances I used an uneven number of teeth on
one and and even number on the other so that I could produce as
many breaks as I desired. I will show you later an apparatus more
perfect than this one, and of a different kind, in which I have 24
stationary contacts, and 25 rotating elements that established the
contact and broke it, so that by one revolution I obtained 24 times
25, or 600 interruptions [per revolution].
Whenever you say "the break", you mean "a spark gap"?
Yes; otherwise I use the term "circuit controller," preferably.
Use of multi-phase generator with mechanical break.
Experiments in the laboratory at 35 South Fifth Avenue and subsiquently.
This [Fig. 38] illustrates another development in a different
direction. In order to increase the number of breaks, I employed
currents of different phase. I had in my laboratory, permanently,
a two-phase dynamo and could get phases between; that is, from two
phases, 90 apart, I could obtain four phases, 45 apart. Here is
an arrangement shown as I had it, working with three phases [60
apart, and could obtain six phases, 30 apart], and later on I had
one with four phases [45 apart, and could obtain eight phases 22
1/2 apart]. You see, as I multiplied the number of the phases, I
increased the number of the fundamental discharges.
What is the date of this apparatus?
This I employed already in the 35 South Fifth Avenue
laboratory, because I remember that I gave entertainments to
several scientific societies and it was then present there. I know
on one occasion there was the Society of Architects, and another,
the Electrotherapeutic Society, and then I had distinguished men
like Mark Twain and Joseph Jefferson -- I gave them a demonstration
which was published in Martin's article in the Century Magazine of
April 1895, and I know that on these occasions I used a two-phase
arrangement. Later on I made it four phase. That apparatus
existed, therefore, prior to the destruction of my laboratory in
Do you recall any publication in which this diagram was
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.
When was that drawing [Fig. 38]?
This is from an old patent drawing which was made by Mr.
But that did not go to patent?
No. I have hundreds of inventions that were to be patented
but side-stepped. The expense was too great and I could not do it.
This form of apparatus with two and four phases was used prior to
the destruction of my laboratory in 1895, and it was installed on
a large scale with four phases in my plant on Long Island with
which I was to telephone around the world, but that is a long
In that use you made of it at your laboratory, was that
connected up as shown there [Fig. 38], to an antenna?
I used the apparatus, yes, in connection with the antenna too,
but this is from a patent drawing in which an antenna is shown; I
mean, I used it in every connection. [Fig. 38] illustrates an
antenna with my transmitting circuit, but the apparatus was used in
all my work, in all my investigations.
And when this was connected in and used in an antenna, did you
use it as in other instances -- go off and listen to the notes
which you received?
Oh, certainly. But I remember that, besides this, I had
different kinds of apparatus. Then I had a sensibly damped wave
because at that time I still was laboring under the same
difficulties as some do this day -- I had not learned how to
produce a circuit which would give me, with very few fundamental
impulses, a perfectly continuous wave. That came with the
perfection of the devices. When I came to my experiments in
Colorado, I could take my apparatus like that and get a continuous
or undamped wave, almost without exception, between individual
Speaking of your not having perfectly undamped waves at that
time, you were referring to that character of circuit?
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.
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.
[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.
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.
How is this machine [Fig. 39] shown in connection with that?
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.
Who built that machine?
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.
The Westinghouse people kept it a secret for a long time and
no one understood how they could make such fine transformers, but
all they did was to use the Bessemer steel, on my suggestion,
instead of the soft iron the General Electric and other people
used. Mr. Westinghouse especially requested me to join efforts
with Mr. Schmidt and improve the design of his machines, and we did
so. We evolved this design, introduced the ready-made coils, which
are pressed on the armature, and other improvements. I took a
couple of patents out with Mr. Schmidt, and Mr. Westinghouse was
very nice about it. I think he compensated me with $10,000, or
something like that, for my suggestions.
You have spoken of the use of that machine at Houston Street.
In what way was it used?
I used this machine, as I said, either to produce alter-
nating currents and then interrupt them with a mechanical break at
the high peaks of the wave; or, I used alternating currents and
interrupted them with an independent rotating break having a great
number of teeth. Or, I generated continuous currents by
commutating the high tension alternating currents of the
transformer. At that time I had two transformers from which I
obtained a constant pressure, charged the condenser, and produced
undamped waves of any frequency I wanted. As to the machine here
[Fig. 39], that is the way it was arranged. It was for the
generation of continuous electromotive force and production of
undamped waves -- from 1895 and on.
What sort of apparatus was it connected up to for the purpose
of absorbing these waves?
It was the same as shown here [Fig. 38]. It was con- nected
to the condensers, and these condensers were discharged through a
primary which excited the secondary; the antenna was included in
the secondary. At other times we discharged the condensers
directly so that I could use the antenna without the secondary.
In the same way did you note the operation of these waves?
We did, of course, only in most cases the instrument of
reception was different. When I operated with these continuous, or
undamped, waves, generated in this way, I usually went to high
frequencies. I did operate [at] a very few thousand, but that gave
me a smaller output. Such a machine you have to operate at high
frequencies to get power.
What do you mean by high frequencies?
I mean frequencies of 30,000, 40,000, 50,000, or something
And by means of that machine, you put undamped waves of
frequency about 50,000 into that antenna at Houston Street in 1895?
No, not in 1895. Late in 1895 the machine was furnished and
I began to operate in early 1896. That is when I began to operate.
Then you did this, that I speak of, in 1896?
Yes, from 1896 to 1899, right along.
When you used frequencies like that in your antenna, was your
antenna tuned or untuned?
I could not use it untuned. That would be absurd.
What form of device did you use, and where did you use it, for
noting the generation of these oscillations or waves in the
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
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.
This was then the machine that you used when working with West
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
What was the horsepower activity in the oscillating circuits
when you used this machine?
Usually something like 50 horsepower, and I would get, I
should say, approximately 30 horsepower in the antenna; that is, I
would get 30 horsepower in the oscillating circuit.
I understood a little while ago when you made the statement of
using several thousand horsepower put into a condenser, you could
take out of the condenser a million horsepower. I wondered if you
got the same condition with this machine.
Yes; I charged the condenser with 40,000 volts. When it was
charged full, I discharged it suddenly, through a short circuit
which gave me a very rapid rate of oscillation. Let us suppose
that I had stored in the condenser 10 watts. Then, for such a wave
there is a flux of energy of (4 x 104)2, and this is multiplied by
the frequency of 100,000. You see, it may go into thousands or
millions of horsepower.
What I wanted to get at was, did that depend upon the
suddenness of the discharge?
Yes. It is merely the electrical analogue of a pile driver or
a hammer. You accumulate energy through a long distance and then
you deliver it with a tremendous suddenness. The distance through
which the mass moves is small -- the pressure immense.
Did you find that that was the best condition for transmitting
energy without the use of wire?
No, I did not use that method when I was transmitting energy.
I used it only in the production of those freaks for which I have
been called a magician. If I had used merely undamped waves, I
would have been an ordinary electrician like everybody else.
You have referred to some delicate receiving instruments. Did
you have any trouble with those burning out on account of static?
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.
Did you succeed in getting them so they would not burn out?
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.
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 T.C. 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 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
Illustrating one of the early experiments with a tuned transformer
in the laboratory at South Fifth Avenue.
Now I come to a few pieces of apparatus which I used in the
Houston Street laboratory and the South Fifth Avenue laboratory.
I have here [Fig. 41] what you might call a tuning coil. I
employed usually another secondary and had my condensers on the
table. You see one of the coils in action. This is a tuned
circuit which responds to electromagnetic waves which are sent
through the room.
This is being used as a receiver of waves?
Another illustration of one of the early experiments with a tuned
transformer in the laboratory at South Fifth Avenue. (Article by
T.C. Martin ["Tesla's Oscillator and Other Inventions"], Century
Magazine, April 1895, Fig. 9, p. 926.)
This [instrument shown in Fig. 42] was used in the laboratory
on South Fifth Avenue. Here [large circular disc lying on top of
coil] is the tuning table with the condensers, a thick primary, and
another secondary wire. Sometimes I would operate with two
vibrations and I would tune the first circuit to one and the second
to the other. Here [referring to cabinets in back of room] you see
some of my historical apparatus. Professor Fairfield Osborn[*]
came once to my laboratory and said to me, "Why on earth do you
keep it in this laboratory?" I had all of this apparatus, 400
pieces, absolutely priceless, and he offered to take it over to the
Museum. But I did not heed his advice, and it is gone.
Where were the waves sent from?
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
In this particular instance you are speaking of, the waves
were generated right there at 35 South Fifth Avenue?
Was that the apparatus in which you had the primaries running
entirely around the room?
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.
Apparatus in action illustrating the first step in the evolution of the
magnifying transmitter in the laboratory at 35 South Fifth Avenue. (Article by
T.C. Martin ["Tesla's Oscillator and Other Inventions"], Century
Magazine, April 1895, Fig. 15, p. 932.)
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 all the conditions so determined
that an immense accumulation of electrical energy can take place.
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, 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
Mr. Tesla, at that point, what did you mean by
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.
You say the energy was 1,000 times greater. Do you mean that
the voltage was increased, or the current, or both?
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
What elastic system do you refer to?
I mean this: If you pass a current into a circuit with 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.
Let's see if I understand this correctly. If you have
radiation or electromagnetic waves going from your system, the
energy is wasted?
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. . . .
You see, the apparatus which I have devised was an apparatus enabling one to produce
tremendous differences of potential and currents in an antenna circuit. These
requirements must be fulfilled, whether you transmit by currents of conduction, or whether
you transmit by electromagnetic waves. You want high potential currents, you want a
great amount of vibratory energy; but you can graduate this vibratory energy. By
proper design and choice of wave lengths, you can arrange it so that you get, for
instance, 5 percent in these electromagnetic waves and 95 percent in the current that goes
through the earth. That is what I am doing. Or you can get, as these radio
men, 95 percent in the energy of electromagnetic waves and only 5 percent in the energy of
the current. . . . The apparatus is suitable for one or the other method. I am not
producing radiation with my system; I am suppressing electromagnetic waves. . . .In my
system, you should free yourself of the idea that there is radiation, that the energy is
radiated. It is not radiated; it is conserved. . . .
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