Tesla Coils Resurrected

(continued)

Another demonstration that gave the audience many thrills was that of the electric chair. This was an ordinary chair with metallic plates fastened on the arms. These plates were connected to the terminal of the conical Oudin coil. The chair was placed on the insulated base, and when operated eight- to ten-inch sparks leaped from the metal parts. After receiving no offers from members of the audience to sit in the chair, one of the assistants was used as the “victim.” The person sitting in the chair felt no discomfort as long as the hands grasped the metal arm plates. A 40-watt light held between the occupant of the chair and another person was lighted to full brilliancy. An oil torch could be lighted by bringing it near to a metal strip held in the assistant's mouth. The “electric kiss” was shown when a spark four or five inches in length jumped between a metal strip held in the mouth of the assistant in the chair, and a similar strip in the mouth of another.

An Oudin coil, 39 inches high was demonstrated in action, discharges nearly 4 feet in length being obtained. Another identical Oudin coil was placed some distance away, the primaries of the two resonators being connected in series. By proper tuning a discharge 6 1/2 feet in length could be obtained between the secondary terminals. The two secondaries were then placed end on end on one of the primary bases, thus making a 6 1/2 foot Oudin coil. When operating at full power the discharges from the terminal which was a large brass sphere were more than six feet in length, the voltage being over a million volts. The sparks quite often flashed over to the lighting fixtures near the ceiling. The noise was very great whenever this coil was in operation. The demonstrator again showed his ability to take high frequency discharges, even of this voltage, into his body. A brass rod with metallic handles was held in his hands to act as a terminal. A rather unpleasant sensation is experienced when receiving these powerful sparks since several amperes of current must be conducted over the surface and through the body, and there is a very noticeable tensing of the muscles of the arms, but no real pain is experienced. These sparks possess quite a dynamic force as may be shown when a small rotor formed of radial wires all bent at their outer ends circumferentially in the same sense or direction, is placed on the terminal and caused to rotate rapidly by the force of the discharges from the tips of the wires.

The “final act” and the one which gave the greatest thrills to the audience, was that in which the human body was used as the terminal of a four-foot Oudin resonator. This resonator had a secondary 6 1/2 inches in diameter, being designed to give a very high frequency for a coil of this size. The terminal of the coil was connected to an aluminum plate 9 by 12 inches on which the demonstrator stood with bare feet, in order to obtain good contact. With thimbles on his fingers, long discharges flashed from the fingertips of his upraised hands. Thimbles were used to prevent cuticle burns on the fingers. The demonstrator then removed the thimbles and held a copper rod in his hand from which numerous sparks flashed. Two Geissler tubes, one held in each hand, were next lighted. The demonstrator then allowed the discharges to leave from the top of his head, a copper crown serving as the metallic terminal from which scores of sparks leaped into the air. The demonstrator then placed a short metal strip in his mouth; leaned his head back, and allowed a long heavy discharge to pass from his mouth in this manner.

These spectacular demonstrations are produced by apparatus which is relatively simple to build. Any experimenter could duplicate part or all of the experiments described with only a small outlay of capital, some work, and quite a bit of patience. The results so far obtained have been particularly satisfying, since the power transformer is only of 5 kilowatts rating, and the apparatus was built by students.

Part two of this article will be featured in the April 1985 issue of TCBA NEWS and will provide the construction details of all the coils shown in the photos.