An Evening in Tesla's Laboratory

While the American Electro-Therapeutic Association was accorded a great honor in being the first body to receive an invitation to visit the Tesla Laboratory, and showed its appreciation by a large muster, it must be said that to engineers present the demonstrations made were even more interesting than to the physicians. The feature of the reception on Thursday evening was the exhibition of a recent form of Mr. Tesla's new machine, the oscillator, which was running beautifully and with which the experiments were performed. Some of these experiments were certainly quite remarkable. The oscillator was run at 350 pounds steam pressure, and in the course of his conversational remarks Mr. Tesla said that he did not anticipate any difficulty in running at much higher pressure with such a machine. There were two pistons in the machine vibrating in opposite phase 80 times a second. The vibrations of these pistons, developed an electric current which was led to a bank of lamps, and some 50 incandescents were lit up by the current. Arc lights were also shown in operation, and Mr. Tesla pointed out the curious fact that when arcs were operated from this new type of machine, the oscillations of the pistons were but a fraction of the time of the oscillation of the carbon rod; and hence the lamps instead of pumping or jumping as they so often do when fed from the ordinary rotating machines, were as absolutely steady as though they were on a battery circuit. The ordinary rotating dynamo has inertia which requires time to respond, and hence considerable resistance, ohmic or inductive, must be provided in the ordinary arc armature; otherwise the amount of arc lights or variable load on the machine must be comparatively small in proportion to the steady load of incandescent lights.

Mr. Tesla repeated also what he said, as to another feature of advantage in the oscillator, at the time he first brought it to notice before the Chicago Electrical Congress, namely, the production of currents of constant period and the perfect maintenance of the regime once established. This enables him to perform experiments remarkable for the small amount of energy they take as compared with ordinary alternators. Mr. Tesla expressed the belief that by further perfecting such machines he will have at hand the means for transmitting intelligence to a distance without wires, as already pointed out in one of his recent lectures. He asserted that this problem depended solely on the perfection of this machine.

One of the very interesting and striking experiments shown was the following: Mr. Tesla had a circle or cylinder frame about 4 feet in diameter in a room about 40 feet by 80. This circle was composed of a number of turns of copper wire, and was entirely unconnected with anything and remote from anything, being in the centre of the open space. It was adjusted the vibration of a current which passed through a wire stretched around the room; and vacuum tubes and small incandescent lamps were lighted by proper adjustments of the capacity of the circuit. Another curious and suggestive experiment was the following. A small hoop or circle, about 3 feet in diameter was shown wound with fine wire. Mr. Tesla explained that he had adjusted the wire to the ordinary average capacity" of plain citizens, in such a way that the maximum current would flow through the wire. The ends of the wire were connected to two handles which could be grasped so as to allow the circle to be held out. The current induced in the wire sprang through the small air gap shunted by the handles, and powerful shocks were felt all around in the room, by means of this exploring instrument. When the area of the circle was compared with the area enclosed by the distant wire around the room, the effects were really remarkable.

Several motors were also on view, of the rotating field type, and single phase. There was one, of small dimensions, which served to count the oscillations, and which had been exhibited also at the World's Fair. Mr. Tesla touched incidentally on the advantages of the current curves employed in these machines, which are proportioned to the squares of the sines of the time. There are two such sine square curves superimposed in quadrature and Mr. Tesla commented on certain benefits obtained with such curves.

A great many other experiments were performed with static and electro dynamic induction, closing with the display of the vacuum tubes and phosphorescent bulbs lit up in the charged free spaces. Mr. Tesla frequently repeated the remark, which was obviously true to those who had seen his earlier experiments, that his oscillator is already proving of great value as a means of prosecuting further experiments and researches in the new field which he has opened up; while its promise of yielding great practical economy in the production of electricity is daily nearer realization. Among the advantages referred to were the ability of the machine to demonstrate the electro-magnetic theory of light, and its value as affording a crucial test of the Hertzian experiments and other investigations in that line. It may be added that besides the feature of running at almost any pressure, being, so to speak, frictionless, the most noteworthy fact to be appreciated by engineers is that when the piston vibrates at this great speed, and in spite of the high steam pressure, there is no packing on the piston whatever, and there is no leaking of the steam. As one watched the oscillator on Thursday evening, there was nothing to indicate that steam was present or was being used, except the steam gauge and its indication. The small boiler used by Mr. Tesla is one specially built for him by the Babcock & Wilcox Co., of their regular sectional type and tested up to 550 pounds. Mr. Tesla was really enthusiastic in praise of its working. The four arc lamps were of the Helios Company's make.