Tesla's Wonderful Electrical Experiments

Mr. Nicolas Tesla, of Now York, has lately repeated in London, at the Royal Institution, the remarkable electrical experiments first shown in this city. The lecturer was received with great enthusiasm in London. The proceedings are described by Engineering as follows: Wednesday, Feb. 3, saw another of those successful meetings for which the Royal Institution is famed. This time, however, the audience were not able to congratulate themselves that they were the first to view in public the striking experiments which were performed before them, as it is the custom of Royal Institution audiences to do, for on one occasion before, in America, Mr. Tesla, the lecturer of the evening, had been over the same ground. This was probably no disadvantage either to him or to the numerous members and associates of the Institution of Electrical Engineers who crowded to hear him, for the fame of his researches had had time to spread, and their significance to become more or less appreciated. Not that Mr. Tesla needed this to render him welcome in this country, for the man who shares with Professor Ferraris the honor of having invented the self-starting alternate current motor requires no introduction in England, nor, indeed, in any country where scientific ability is appreciated.

Our account of the previous lecture will have rendered our readers familiar with the line of Mr. Tesla’s researches. We may, however, briefly state that he has devoted himself for the last year or two to the investigation of the effects attending the use of alternate currents of very high frequency and of high potential. This matter of the frequency of alternation seems to have been neglected by former experimenters with vacuum tubes. They took great pains to got immense potentials, but paid little attention to the rate at which the current vibrated to and fro. It now appears, however, that the rate of alternation is as important as potential in evolving certain phenomena, and by increasing it to a very great extent perfectly new and unexpected results can be obtained. This can be done in various ways, of which Mr. Tesla employs two. He has an alternate current dynamo, the armature of which consists of a steel disk, having arrayed on its rim 380 poles. This runs within a ring of magnets of corresponding number, and with the machine rotating at 2,000 revolutions, gives 13,000 complete alternations per second. The current thus produced is sent through the primary wire of an induction coil, and its potential raised from 50,000 volts to more than a million, although, of course, the exact amount is a matter of conjecture. In another method of obtaining currents of high frequency there was employed an alternator lent by Messrs. Siemens Brothers. The current was sent through the primary of a large induction coil, in the circuit of which a special break was interposed. This consisted of two balls, between which the current sparked, and two powerful magnet poles, which blew out the spark as fast as it was formed, and thus greatly multiplied the effect. The current from the secondary coil was then sent through the primary coil of one of Mr. Tesla’s oil-insulated induction coils; in the circuit of the secondary coil there was interposed a battery of Leyden jars, which was constantly charged and discharged, the discharge being of an alternating character, with a frequency of immense rapidity.

Mr. Tesla’s coils are of peculiar form. The primary coil is on the outside, and is separated from the secondary by some little space. The whole is immersed in oil, and the inventor insists most strongly that a solid dielectric can never be used successfully in this position. If this be damaged, it is spoiled irretrievably, while the oil may be struck through time after time, and instantly repairs itself. Any bubbles of air that the oil may contain are soon warmed and rise, and thus the defects are rapidly expelled - an event which cannot occur in a solid substance, in which defects tend to aggravate and not to eliminate themselves.

Mr. Tesla began his lecture with a tribute to the work of Professor Crookes, which, he said, had fired his imagination when at college, and had given a bent to his studies. He then turned to his own researches, and in a second revealed to his audience the immense distance which separates himself from his predecessors, by taking in one hand an exhausted tube, 4 ft. long, while the other hand was connected to one terminal of a coil. Instantly the tube glowed with a brilliant lambent flame from end to end, and recalled to every one the idea of the magician’s enchanted wand. When the gas was turned out, the light was sufficient to reveal the lecturer and his assistants, and would have been enough to enable him to read newspaper print. It was a most striking experiment; the old ideas of electric circuits, metallic electrodes, and all the rest of time-honored notions, seemed to be flatly contradicted. From a single terminal of the coil the electro-magnetic radiations were conducted through the body of the lecturer to the tube, and entering through the glass, they put the few molecules of air that it contained info such active oscillation that they glowed in their mutual bombardment.

It was a breach of the dramatic canons to begin with an experiment of such brilliancy, and then to descend to others of less importance, but it was an indication of the power of the lecturer, and evoked rounds of applause. Indeed, the reception accorded to Mr. Tesla was one that must have raised feelings of pride in any breast. Both seats and standing room were filled, and on the front benches were to be seen most of our leading electricians and electrical engineers. All through the evening there was rapt attention, which never flagged, oven during the less striking experiments.

Putting down the tube, Mr. Tesla attached an exhausted bulb to one terminal of a coil, and showed that phosphorescence was immediately set up in it. When he placed his hand near to it this phosphorescence was immensely increased, and the lamp filled with a vivid glow. This was repeated in other ways with different, bulbs, and then two plates were attached to the terminals of a coil, with a sheet of vulcanite between them. The current then endeavored to spark across, and beat itself in purple rays on the sheet, branching out in streaming brushes to make its way round the edges of the plate. Turning to his audience, Mr. Tesla exclaimed: “Is there anything more fascinating than the study of alternating currents ?” It was evident to all in the room that use had not rendered the lecturer insusceptible to the beauties of the experiments that he showed, and that his mind was as completely filled with wonder and enthusiasm as that of the merest novice present, and probably far more so, as he saw further into the inner nature of the phenomena which he displayed, and grasped more of their significance.

The next experiment was the passage of sparks between two balls, to simulate the discharge from a Wimshurst machine. This was done most successfully, and it was difficult to believe that the well known disks were not being turned in the ante-room. At first a 2 inch spark was shown, and then one of 6 inches, the balls being changed, for the size of the balls appears to have a distinct effect on the appearance of the arc set up between them. Next came another of those brilliant sights which are always so effective with an audience, especially when it is in a cordial mood. Two wires were stretched across the wall of the theater, about a foot apart, and were connected to the poles of a coil. When the current was turned on they glowed for their entire length with a blue light, which streamed from one to the other, and was of sufficient intensity to reveal the faces of the audience. Here there was no case of exhausted globes; the light was given off in the open air, and if not, enough for the ordinary domestic purposes, was at any rate of very appreciable intensity. In this case the alternations were obtained by aid of the Leyden jars. The same idea was developed in another way in the next experiment. A wire ring, 3 feet in diameter, was connected to one terminal of a coil, and a second ring, 6 inches in diameter, was connected to the other, the two being concentric. The light streamed radially from one to the other, making a palpitating purple disk of great beauty.

Speaking on this subject of phosphorescence, Mr. Tesla stated his belief that it could be excited in all substances, if currents of sufficient frequency and potential were employed. He was also of opinion that exhaustion of the air was not necessary. Hitherto it has not been possible to drive the molecules on to the substance unless a fairly clear road were prepared for them, by removing all but an infinitesimal number. They could not get through the melee. But with sufficient initial velocity they will be able to proceed in straight lines, just as a cannon shot will pierce a crowd that would stop or deflect a cricket ball. All that is wanted is that the atoms shall fly fast enough and often enough to raise the surface, even of metal, to the phosphorescing or at least to the glowing stage. With extremely rapid alternation, also, the molecules never get far away from the substance they bombard, and so their heat is not diffused. Crookes’ phosphorescent tubes give a magnificent glow if only held in the hand, while the other hand is applied to a coil working with sufficient frequency and potential.

Visible light and heat are not necessary to prove the existence of the electric radiation, and Crookes’ radiometer placed near a ball connected to one pole of a coil rotates very briskly - curiously, however, in the opposite direction to that which it follows under the influence of light. This is explained as being due to the streams from the glass. In a second instance an unexhausted radiometer was made to rotate; the fans were covered on one side with mica, and the spindle was connected to the coil. The effect of the mica was to prevent the molecules heating one side of the vanes. As the current was increased, the speed diminished on account of the electrostatic action between the mica and the glass.

In a certain sense the most interesting part of the lecture was that dealing with lamps, because here we seem to get nearer to some practical result. Mr. Tesla’s lamps mostly consist of a bulb inclosing a button of carbon resting on the end of a wire or a filament. This wire is screened by being surrounded by a tube of aluminum, which forces the radiation to follow it to the button, and not stream off sideways. When the single conductor, which this lamp contains, is connected to one terminal of a coil, the carbon glows with a light the intensity of which varies with the character of the current. On Wednesday the light seemed to be about equal to 5 candle power. When a metal screen was put over the lamp, and the radiations that fell on it were deflected back on to the sphere, the light was doubled, and reached a perfectly useful limit. Wonderful as this was, a greater marvel appeared when two zinc plates, one at a height of 10 feet and one on the floor, were connected respectively to the poles of the coil. Then it only needed that a lamp of this construction should be brought into the intervening space to glow brilliantly without any electrical connection whatever. The radiation between plate and plate was so active that, in passing through the attenuated atmosphere in the globe, it evolved the molecular bombardment which made the carbon glow.

The practical man asked as the lecturer finished, “What is the use of it all?” Nearly fifty years ago he was present when Faraday explained the laws of electro-magnetic induction, and then he also asked the same question. It was not till the Paris Exhibition of 1878 that he got his answer, but we shall be much mistaken if he has to wait so long this time. Wait he must, and in the mean time he cannot do better than join in honoring such men as Mr. Tesla, who engage in researches which promise no immediate pecuniary benefit. He must, however, be dull if he cannot discern in the few experiments we have described, out of the many shown to the audience, a clew tending toward a great discovery that would entirely revolutionize our methods of artificial illumination. If a space measuring several feet in each direction can be brought into such a condition that an attenuated atmosphere introduced into it instantly becomes self-luminous, it does not call for any great stretch of imagination to see the whole of the atmosphere of our rooms in the same condition, and filled with the same clear light which bathes our planetary system. Just as the sun puts the ether into vibration of the kind revealed to our senses as light, so does electric energy also put it into vibration of the same kind, but of a different degree. Wednesday’s lecture marks one step in the progress toward luminous electric radiations; possibly some of us may live to see the remaining stages covered.