On Experiments with Tesla Currents

BY F. HIMSTEDT IN "WIEDEMANN'S ANNALEN."

The author has succeeded in reproducing most of Tesla's experiments with very simple apparatus. He utilized at first the Lecher method of producing electrical oscillation, but later on used the still more common Leyden jar. The pole of a powerful Rubenkorff coil, 50 centimeters long and 20 centimeters in diameter, and used with five or six accumulator cells, was connected to the inner coatings of two medium-sized Leyden jars insulated from one another by standing on paraffine blocks, and also to a spark micrometer. The outer coatings of the jars were connected together by a copper wire four millimeters thick and 120 centimeters long, bent into U shape. A 16-volt glow lamp put in parallel with this wire was soon brought to incandescence when the spark micrometer was suitably adjusted. When jars 16 centimeters in diameter and 4: centimeters high were used, as many as three lamps could be made to glow — a 65-volt lamp below, a 16-volt lamp in the middle and a 2-volt lamp at the top. If the nipple of such a lamp be filed off it ceases almost entirely to glow. Tesla ascribes this fact to the alteration in the molecular bombardment in the lamp; but the author considers that it is due to the connection of heat by the air admitted.

If the incandescent body be a platinum of 0.05 to 0.1 millimeter diameter, it oscillates violently while glowing, not in one plane like a string under tension, but in every possible plane, becoming a model of a beam of natural light. It is essential to the success of this experiment to use a proper interruptor and a suitable spark micrometer. As interruptor the author used the Foucault form, with tough zinc amalgam in the place of mercury, and covered with machine oil. The balls of the micrometer are best made of zinc.

The Tesla transformer was made as follows: A glass tube of four centimeters diameter was taken, and on were wound 10 turns, one centimeter apart, of a wire four millimeters thick. Over this was pushed an ebonite tube, six millimeters thick, on which were 200 turns of wire one millimeter thick and spaced with one millimeter between each. The whole transformer was placed in an earthenware container filled with machine oil, the secondary terminals being two metal balls on ebonite pillars. The primary was put in the place of the U-shaped wire, between the outsides of the Leyden jars. When the interruptor begins working, brush discharges start from these balls, and sparks spring to a conductor put near. Two parallel wires starting from the balls have between them a broad band of light three to four meters long. If one pole be put to earth, and to the other be connected a wire 15 to 20 centimeters long, hanging freely downwards, it begins to move when the interruptor is started and describes the surface of a cone, which is easily seen in a dark room by the brush discharge, which renders it luminous.

If anyone takes hold of the pole of such a transformer with the hand. rays of light start from any part of his body when a conductor is held i near. If he stands on a metal plate he feels a pricking sensation in his feet, and in the dark the rays coming out of the soles of his shoes may easily be seen. If several persons form a chain, and the first touches one pole of the transformer, while the last holds in his hand a vacuum tube with or without electrodes, the tube glows brilliantly. None of the persons feel any symptom of the electrical phenomena.

If one pole of the transformer be earthed and the other connected to a metal sphere 60 centimeters in diameter, vacuum tubes glow brightly up to 15 feet away. A glow lamp connected to the unearthed pole glows faintly in a phosphorescent manner; but if a large metal reflector be placed over the lamp it glows brilliantly, while the filament oscillates so violently that it soon breaks. If a conductor be held near the point of the lamp, the glass is immediately punctured by the current, a continuous and brilliant stream of sparks passes through the opening, and the filament glows until it burns away.

In the second portion of the article the author remarks that a Tesla transformer differs in important particulars from an ordinary Ruhmkorff coil. A vacuum tube connected in any manner to the transformer shows kathode light at both electrodes, and evenly distributed anode light in the. center. An alteration of direction of the primary current, or alteration of pole, has no effect in altering this phenomenon. An electroscope is always charged positively if held to It either pole, and both poles give positive Lichtenberg figures only. was found that this effect depended on the nature of the surrounding medium. Air and oxygen produce positive discharge; hydrogen, illuminating gas, nitrogen, carbon dioxide and ammonia give negative discharges. If a pole have two points immersed in air and hydrogen, respectively, positive and negative discharges take place simultaneously, according to the medium. If a pole be in oxygen, and nitrogen be gradually added; an electroscope shows first a positive charge, first increasing, reaching a maximum at the mixture corresponding to air, and then diminishing, and ultimately becoming negative. With a Ruhmkorff coil the charge in the electroscope changes sign if the primary current be reversed.