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NIKOLA TESLA

by A. P. M. Fleming

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Journal of Institution of Electrical Engineers, London, Vol. 91, February 1944,
Reprinted in Tribute to Nikola Tesla, Nikola Tesla Museum, Beograd, 1961

On the occasion of his visit in 1892 to Belgrade, Tesla, in reply to a speech of welcome by the mayor of that city, spoke after this fashion: "There is something in me which is only perhaps illusory, like that which often comes to young, enthusiastic persons, but if I were to be sufficiently fortunate to bring about at least some of my ideas it would be for the benefit of all humanity.  If these hopes become one day a reality, my greatest joy would spring from the fact that this work would be the work of a Serb".

These sentiments reveal the human side of this great Serbian engineer and the abiding affection he always cherished for the land of his birth, notwithstanding that the greater part of his life was spent in a foreign country.

Nikola Tesla was born on the 9th July, 1856 in Smiljan in Yugoslavia within the borders of the old Austro-Hungarian Empire.

The village of Smiljan is situated at the northern extremity of the coast of Dalmatia.  Tesla's father, a Serb, was a priest of the Greek Church and was the son of an officer who served with the Grand Army of Napoleon.  His mother was of a distinguished Serbian family and came from a long line of inventors.  She also was very inventive and is credited with making improvements in agricultural implements, looms, and other rural apparatus.

Tesla received his early education at Smiljan and at the local town of Gospitch and later spent three years up to the age of 16 at the Higher Real School at Carlovatz.  At this time he was studying mathematics and physics with a view to teaching these subjects.  Later he changed his plans, took up engineering and studied at the Graz Polytechnic in Austria.  Later he completed his education at Prague University and graduated at the age of about 23.  In addition to his technical studies, he had by this time become a very accomplished linguist.

As a boy Tesla was frail and of by no means robust constitution.  On two occasions he nearly died before manhood; once from a severe attack of cholera and later from a very serious nervous breakdown, as a result . . .


[miscellaneous remarks]


. . . and, as already noted, Tesla had conceived the idea of the rotating field many years before 1888 -- the actual date of his patents.  As Dr. Eccles points out, however, this invention is of minor importance in comparison with the much more comprehensive one of the polyphase system.  About this time Shallenberger devised an induction meter employing the, same fundamental principles, but without knowledge then of Tesla's work.

There was at this time great rivalry between the alternating and direct current systems of electrical power generation and distribution, and Tesla experienced some difficulty in getting finance for his alternating current developments.  It is said of him that on one occasion, when trying to interest financiers in the possibilities of the rotating magnetic field motor, he made a sporting offer to outdo Columbus, who in somewhat similar circumstances had undertaken to make an egg stand on end.  Tesla promised to make the egg stand up by itself.  There may be some truth in this story because a picture of his New York Laboratory shows the paraphernalia used for the demonstration (Plate 4).



Plate 3  THE SQUIRREL CAGE ROTOR UNDER THE ACTION OF THE ROTATING FIELD.

The wound stator ring described above can serve to demonstrate Tesla's Egg Experiment.  A sheet of non-metallic material is placed over the windings on the stator ring; a metallic egg is placed on this sheet immediately revolves around its minor axis as soon as the windings are energised from a three-phase supply.  As the speed of the egg increases the egg rises on one end and continues to spin about its major axis, thus maintaining a vertical position without additional support.



Plate 4  THE SPINNING EGG EXPERIMENT.

The next few years were of great significance in Tesla's career and in the development of the electrical industry.  In 1888 George Westinghouse realised the importance of Tesla's patents covering the polyphase system of generation and transmission, and the application of the rotating magnetic field to the design of alternating current motors (Plate 8).  The Westinghouse Company secured these patents and at the same time engaged Tesla's services in order to develop the alternating current motor.  These developments led to the discovery that the 133-cycle A. C. systems then in vogue were not well suited for motor operation, and before long a frequency of 60 cycles per second became general practice.  Electrical events were now stirring in different parts of the world.  In 1889 Ferranti installed a single-phase plant at Deptford, transmitting power to four substations in London six or seven miles away at the then unprecedented voltage of 11,000.  In 1891, on the occasion of the Exhibition in Frankfort, power was transmitted to Frankfort from the waterfall at Lauffen, a distance of upwards of 100 miles.  The three-phase system on the Tesla principle was employed, and power was delivered to a 100 h. p. three-phase motor designed by Dobrowolski.

In 1893 came the Chicago Fair, where the Westinghouse Company exhibited the Tesla polyphase system of transmission.  In one exhibit power was supplied by a 500 h. p. induction motor driving a two-phase generator which provided power for motors and lamps, and by means of rotary converters and motor generators, for all kinds of direct current apparatus.

About this time the engineering world was stirred by the proposal to harness the power of the Niagara Falls, and in 1886 a charter had been obtained for this purpose. According to descriptions by Professor C. F. Scott, an early plan was to have a number of canals running at right angles to the upper river to supply separate wheel pits each with a 500 h. p. turbine discharging its water into an outflow-tunnel terminating at the foot of the falls. This idea reflects the state of the art at the time when a 500 h. p. water turbine and generator seemed to be the maximum size of unit that was practicable. Such a scheme was uneconomical, and there were no commercial enterprises within the locality that could absorb the energy developed. The nearest city likely to be able to do so was Buffalo, some 22 miles distant. This distance was too far for economic transmission by direct current, and although single-phase alternating current might have been employed, this was not -- as already indicated -- very favourable for motive-power purposes. A world-wide search for a suitable plan for the Niagara project was conducted by the International Niagara Commission, consisting of experts drawn from several countries, headed by Lord Kelvin. From six different countries seventeen projects were submitted, many of them being based on a hydraulic system of transmission. Four more employed compressed air, and there were six electrical schemes, of which four suggested the use of direct current. Typical of the latter was the proposal to connect ten generators each of 1,000 volts in series for a 10,000 volts transmission system to supply a similar arrangement of motors at Buffalo, for driving generators for local distribution. Among the remaining plans, Professor Forbes asserted a polyphase system, and he asserted that the only non-synchronising motor that had been developed in practical form was that devised by Tesla. Forbes proposed generators of 500 h. p. in a station having a total capacity of 50,000 h. p. with transformers of 100 h. p. each. 

The Commission found no proposal acceptable and no prize was awarded for a system of distribution. It is interesting that Lord Kelvin persisted in his opposition to alternating current until he was proved wrong by its successful operation.

Subsequently, the Niagara engineers invited proposals from the two great American companies -- the Westinghouse and General Electric, and in 1893 the Westinghouse Company was awarded a contract for three 5,000 h. p. Tesla generators, and later seven more, units completed the 50,000 h. p. equipment of the first station. A second power station was later equipped by the General Electric Company. 

The development of the Scott two-phase three-phase transformer enabled interchange to be made between the two-phase and three-phase system. Power was transmitted to Buffalo by a three-phase 11,000 volts line.

It will thus be seen. that this word-famous electric project, which was a pioneer development in hydro-electric power generation and transmission, became possible by virtue of the Tesla polyphase system of generation and transmission, and the invention ,of the induction motor following his discovery of the rotating magnetic field which facilitated the application of electrical power for motor drive. This project gave an enormous impetus to the prestige and development of these two great inventions.

After working with the Westinghouse Company mainly on the development of the induction motor, in 1889 Tesla returned to his own laboratory in New York, where he carried on work on the development of alternating current motors and generators.

He then commenced those investigations and study of high frequency phenomena which were to occupy much of his attention for the rest of his active career. By 1890 he had commenced construction of high frequency alternators generating currents at 81 frequency of 20 kilocycles, using them as a power source for radio transmitters, believing that undamped excitation was very important. It is interesting to note that round about 1910 the need for undamped excitation in radio became acute, and that from then on rotating alternators. were developed systematically and finally were used successfully in some high power transatlantic stations. The need for such alternators passed away with the development of the high power triode valve about 1922. Thus the form of generator which Tesla started off with did not come prominently into use until a quarter of a century later, and then only shortly before it was inevitably superseded by the valve.

In 1887 Hertz had demonstrated the existence of electro-magnetic waves predicted many years previously by Clerk Maxwell, and thereby brought the electro-magnetic theory into prominence and made it a popular subject for experimental work. Naturally Tesla brought his imaginative and inventive mind to bear on these problems and his experiment have had a marked influence on the development of radio. Tesla seems to have felt that some new mechanism of transmission would result if only the input power were large enough, and set himself to produce high frequency power on a vast scale, presumably' hoping to reach the order of magnitude of cosmic disturbances. Other experimenters of the time were content to use a few watts of power and did hot expect to do more than produce a very feeble signal at a distance.

Tesla required immensely high voltages to give him a chance to succeed in what he was trying to do and this led to producing very high voltages and much higher frequencies than possible with the rotating alternator, by means of sparks, electrical oscillations in a circuit containing a low frequency A. C. source, an induction coil, a condenser, and spark gap. It is now well known that it a simple electrical circuit, consisting of a condenser and a coil, is subjected to {in electrical shock, it will be found. that electrical oscillations are produced having a frequency of precise relationship to the size of condenser and coil used. This frequency is known as the natural or resonant frequency of the circuit.

By varying the size of the condenser or of the coil alone, the resonant frequency of the circuit can be altered, but if the condenser size is increased 8:nd the coil size decreased in the correct proportion, then the resonant frequency will remain unchanged. Conversely, the condenser size can be decreased and the coil size increased in the right proportion, f without altering the resonant frequency of the circuit.

'When either the condenser size or the coil size can be varied, it is possible to arrange that the resonant frequency of a circuit is either equal to or widely different from the frequency of an alternating current source; In the former case the circuit is said to be tuned to the source frequency, or to be in resonance with it, and the current flowing through the circuit will be a maximum for a given voltage applied.

In a similar way, two circuits can be tuned to the same resonant frequency, so that when connected together directly or placed in close proximity, the transfer of energy from one to the other is effected with the maximum efficiency. Two circuits arranged in this manner are said to be coupled one with the other.

So far we have considered only loss-free circuits. In all electrical circuits, however, there is a certain loss of energy incurred in overcoming the electrical resistance of the circuit. If this were not so, then in the simple condenser-coil circuit first mentioned the oscillations set up by an electrical shock would persist indefinitely with undiminished amplitude. Owing to the losses inevitable in such a circuit, the energy associated with the initial shock is eventually absorbed and the oscillations die away and are said to be attenuated or damped.

Tesla utilised the principle of tuned circuits in designing a high frequency transformer. The so-called Tesla coil consists in essentials of the following (Plate 5) : -- primary coil L1 with the primary condenser C1 which is charged by means of the low-frequency transformer T 1 T 2' The secondary circuit consists of the secondary coil L2 and the secondary condenser C2 .The primary and secondary circuits both have the same resonant frequency, i. e., they are in tune and they are coupled by reason of the fact that the two coils are concentric, one with the other.

In operation the behaviour of the Tesla transformer is as follows: -- The primary condenser C1 is charged to a voltage V1 by means of the transformer Tl T2. The source of supply has a frequency which is widely different from that of the resonant frequency of LJ and C1. The voltage V1 which can be developed across the condenser is limited by the flashover value of the air-gap G which, in breaking down, completes the oscillatory circuit L1 C1. Oscillations at the natural frequency of the circuit are thus generated in the primary circuit and the energy associated with these oscillations is gradually transferred to the secondary circuit by L2 C2. Hence the whole of the energy (apart from that absorbed in losses) originally supplied to the primary condenser C1 is eventually stored in the condenser C1. At this stage the process is reversed and the energy is gradually transferred back to the primary circuit and so on. At each stage of transference there is a certain amount of energy absorbed in losses so that eventually the oscillations die away, the spark across G is interrupted, and the process of charging the condenser C1 from the transformer T1 T2 recommences.



Plate 5  CIRCUIT DIAGRAM OF TESLA TRANSFORMER.

The primary condenser C1 is large and the primary coil L1 is small, whereas the opposite conditions obtain in the secondary circuit. By this means a large current at a comparatively low voltage V is transformed into a smaller current at a much higher voltage V I. (Apparatus used by Dr. Fleming to illustrate his Tesla Commemoration Lecture is shown in Plate 6).

The spectacular effects produced by the Tesla coil created much interest, and it is said that by 1895 almost every physics laboratory had built a Tesla coil, and interest in high frequency high voltage oscillations was greatly stimulated.

The Tesla coil represents the first application of what is now known as the "coupled oscillatory circuit". Thus in the development of his coil, as early as 1891, he invoked the principle of tuning as an essential factor in his radio system, and it has been an essential factor ever since. Moreover, his loosely coupled tuned transformer was soon employed in all spark transmitters. Thus in his initial approach to the radio problem he provided the art with the great principle of tuning.



Plate 6  TESLA TRANSFORMER AND OTHER H.V. APPARATUS USED IN DEMONSTRATIONS FOR THE NIKOLA TESLA COMMEMORATION LECTURE, NOV., 1943 (LONDON) AND APRIL, 1944 (MANCHESTER).

A convenient mechanical analogy to the Tesla transformer is provided by two pendulums hanging from a horizontal wire. These pendulums are of the same length and therefore have the same frequency of oscillation. They are coupled by being fixed to the same suspension wire. When the red pendulum (primary) is displaced from the horizontal and allowed to swing to and fro, it will be observed that the amplitude of the swings gradually becomes less. The yellow pendulum (secondary), which was stationary, now begins to oscillate, and as the amplitude of the swing on the red pendulum decreases, that on the yellow increases. Finally a stage Is reached when the red pendulum is stationary and the yellow pendulum is swinging at maximum amplitude. At this stage' the energy formerly supplied to the red pendulum has been transferred to the yellow and in the next stage it will be seen that the reverse process occurs.

If the red pendulum is held at a time when its oscillations have ceased, due to the energy of the system having been transferred to the yellow pendulum, then the yellow pendulum (secondary) continues to swing with a slightly damped oscillation until all the system energy is dispersed, i. e., there is no feed back of energy to the red pendulum (primary). This is analogous to the use in the Tesla transformer of an air blast across the primary spark gap. This air blast will interrupt the primary arc at a stage when the energy has first been fully transferred to the secondary winding so there is no feed back to the primary circuit as the oscillatory portion of the circuit is opened.

By sliding the suspension points of the two pendulums further apart on the horizontal wire, the coupling between the pendulums is decreased. The effect of this is to reduce the beat frequency of the system and so delay the transfer of energy from one pendulum to the other. The effect here is again in direct relation to the electrical case where the coupling is made looser.

When Tesla lectured before the Institution in 1892, he performed a number of experiments to show the light produced by high frequency discharges in free air, or in glass bulbs evacuated to a low gas pressure. Some of these experiments in a slightly modernised form are being performed this afternoon. The first three experiments show the glow discharge from a wire supported on a glass plate, the streamer discharge across the surface of a glass plate, and the development of glow discharge in a 12 ft. Geissler tube whilst being pumped from atmospheric pressure down to a pressure of less than one-hundredth of an atmosphere. To complete the latter experiment the air will be allowed to re-enter the tube until atmospheric pressure is again attained, thus showing the discharge sequence in reverse.

The idea of using streamer or glow discharge in air as a means of illumination has not proved to be practicable, but the use of the cold discharge in low gas pressure is a feature of the fluorescent lighting of to-day.

At this, point in his lecture Dr. Fleming demonstrated the following:

First the flashover of a porcelain insulator to illustrate one of the modern uses of the Tesla transformer, i.e., to detect surface cracks in porcelain by virtue of the sparks which tend to cling closely to the surface of the insulation (Plate 7); secondly the discharge in free air from a pointed terminal with occasional flashover to an earthed conductor. This illustrates on a small scale some or the magnificent effects Tesla later poduced in his laboratory at Long Island. The third experiment was to show that a long neon tube when brought in the electrical field surrounding the Tesla transformer can be made to glow even without any direct electrical connection.

Using a coreless coil submerged in oil so as to enable the primary and secondary windings to be brought close together, i. e., tightly coupled, Tesla was able to step up voltages to values of the order of millions of volts.

He devised a large mercury type interrupter capable of handling 50 h. p. at an interruption rate of 100,000 breaks per: second. He employed this device in his later researches in 1900, when he began his study of the wireless transmission of energy.

For some of his work he desired to make undamped high frequency currents audible in a telephone, and did so by inserting a vibrating contact, called a "ticker", in the circuit. The Tesla "ticker" was an indispensable adjunct in the early Paulsen Arc stations and was a standard piece of radio equipment until the introduction of the heterodyne beat note system now familiar to radio engineers. Thus again a piece of his incidental and minor apparatus was to hand and was used extensively years after he had invented it.

At a meeting in March 1893 before the Franklin Institute and the National Electric Light Association, Tesla demonstrated the physiological and luminous effects obtained by high frequency currents.  He announced the possibility of transmitting energy without transmission wires.  The diagram illustrating his proposals shows an elevated metal surface connected by a vertical wire to a large earthed metal plate excited from one of his high frequency transformers, with a similar arrangement at the receiving station.  He did not patent this aerial arrangement although it appears to be the first use of an antenna system.  An indication of Tesla's objective at this time was given in his own words in a lecture at the Franklin Institute, 1893, in which he said, "I do firmly believe that it is practicable by means of powerful machines to disturb the electrostatic condition of the earth and thus transmit intelligible signals and perhaps power".  He went on to suggest that the disturbance could be produced without a great deal of energy by using a suitably adjusted self-induction and capacity device set in action by resonance.

In 1895 his laboratory was destroyed by fire, but he continued his experiments in wireless transmission in 1896, and succeeded in transmitting signals without wires over a distance of 20 miles.  In 1898 he constructed a small ship, which he succeeded in directing from the shore by radio.

Following up his idea of making the whole terrestrial globe oscillate electrically, in 1899 in Colorado he erected a high aerial tower and connected a very high-voltage Tesla coil between it and the ground.  He hoped apparently that the large periodic electric charge which was thereby elevated high above the ground would excite an oscillation of the whole globe.  Immense power seemed essential to him, and he presumably hoped to achieve a resonance of the globe.  The mechanism of propagation he looked for was not the mechanism which Hertz and Maxwell thought of and which is used today, but the method he used in his attempt involved the employment of a high aerial and a ground connection, two of the most obvious features of present-day radio.  He transmitted enough power to light a lamp at a distance of 30 km. and to produce detectable signals at a distance of 1,000 km.



Plate 8  EARLY LABORATORY MODEL OF TESLA MOTOR WITH ROUND ROTOR AND SLIP RINGS.

Tesla showed that tuned coils placed a distance from the transformer could pick up energy from it, and that quite large voltages could be developed in such coils. Although we have not used a coil accurately tuned to the Tesla transformer in this demonstration, we have arranged a coil such that it is capable of demonstrating the principle involved. When the coil plane is vertical there is practically no pick-up of energy from the transformer. If the coil plane is horizontal there is appreciable pick-up, and sufficient voltage is developed across the coil to light a small neon lamp.

Some years after the experiments at Pike's Peak, Colorado, he built the famous tower on the beach at Long Island. It was some 200 feet high, surmounted by a metal sphere about 70 feet in diameter, designed to stand many millions of volts at high frequency. He called it a "Magnifying Transmitter" and spoke of broadcasting telegraphy, speech, vision and power. His concepts of its action are not clear. The tower was never finished, and it was dismantled about 1915.

Tesla's vision was focussed closely on an attempt to produce some large-scale effect at vast distances, and he did not succeed. In his strivings he produced almost incidentally a whole succession of apparatus which was employed successfully by other workers striving for less ambitious ends. Had his primary concentration allowed him to pay more attention to the tools which his inventive genius improvised freely, then the great influence he had on radio development would have been obvious to all. Reference to his writings and patents shows that many pieces of radio equipment had passed through his visualising mind, though many did not advance beyond the outline of the idea. Tesla was a most ingenious and prolific inventor, and all his inventions seem to have embodied some essentially novel principles.

Reviewing the outstanding features of Tesla's achievements, that of the most direct value to mankind was the development of the polyphase electric system of generation, which is the basis of all systems of electrical transmission allover the world, and the discovery of the rotating magnetic field and its application to the design of alternating current motors. These two inventions facilitated an enormous development of electrical power generation, distribution, and application. Additional achievements in connection with the power side of electrical engineering were his contributions to the developments of transformers, switch gear, meters, and arc lamps.

His contributions in regard to high frequency electrical phenomena, compared with his work in the field of power engineering, have been of importance in extending scientific knowledge, rather than taking the form of inventions of farreaching importance. He laid the foundtions of knowledge and developed apparatus which was brought to commercial success by others, and in this connection he reaped little in the way of material reward and inadequate recognition of his achievements.

He invoked the principle of tuning as an essential factor in his radio systems. He appears to have been the first to use a transmitting aerial and receiving antenna tuned to the same frequency. He very early conceived the idea that the upper conducting layers of the atmosphere might be helpful in the transmission of radio signals. He studied the physiological effects of high frequency phenomena and their application to bloodless surgery. He was successful in the production of ozone and other gases and constructed, among other devices, electrostatic condensers, frequency meters, etc.

It was characteristic of Tesla that he appeared indifferent to the commercial side of his work and left the working out of ideas and the commerciaJ development to other people.

Tesla died on January 7th 1943 in New York at the age of 86.

He is described as being very tall, very thin, plainly dressed and immaculately groomed and of delightful courtesy and charm. Dr. Eccles in his appreciation of Tesla says "his genius lay in conceiving broad schemes, in inventing means -- ingenious means -- of carrying them out, and in designing and building apparatus to prove them practicable".

An amazing feature of his work was its range which extended into almost every branch of electrical engineering of his day. We are proud that he was a member of this Institution, and we delight in recalling the achievements of one of the greatest electrical engineers of his generation. We pay grateful homage to his genius which has greatly enriched our knowledge of electrical science, and his inventions -- so lavishly produced -- which have added so greatly to the amenities and the material progress of mankind.

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