Dissipation Of Energy
THE ELECTRICAL ENGINEER, JANUARY 6, 1893. 5 pended from the ceiling by insulating supports: (1) By attaching to the free pole an exhausted bulb furnished with one electrode and a straight carbon filament, the filament became luminous, though very feebly; (2) vacuum tubes, Crookes tubes, and phosphorescent-powder tubes became luminous when held in the hand below or near the plate- they seem to go out when passed from one hand to the other along all their length; (3) the tubes became luminous when laid on a block of paraffin below the suspended plate. (0) The two poles connected by a wire with an air space for the passage of the spark of the direct induced current: a vacuum tube lighted up when held near the coil. (ri) The same arrangement as for (c), but one of the poles is connected to the suspended plate: tubes lighted up near the coil, and under or near the plate. By using a Foucault contact-breaker, making only five oscilla- tions per second, the preceding experiments still succeed. With a much smaller coil the phenomena occur with prac- tically the same strength. One of the poles of the small coil can he touched with impunity by forming a chain of two persons holding a vacuum tube between them ; one person touching one of the poles and the other holding a second vacuum tube in the free hand, both tubes will light. Dissipation otllnergy.-Mr. Nikola Tesla contributes an article on the dissipation of electrical energy of the Hertz resonator to the American Electrical Engineer. The apparatus being immersed in air or other discontinuous medium, there occurs a dissipation of energy by " sound- waves of electrified air.” Owing to this dissipation the period of vibration of an air-condenser cannot be accurately determined. Mr. Tesla has already drawn attention tn this important point. These waves are propagated at right angles from charged surfaces, even if heavily insulated. Assuming that the charge imparted to a molecule or atom hy direct contact or inductively is proportionate to the electric density of the surface, the dissipation should be pro- portionate to the square of the density and to the number of waves per second. From a wire,'with high-frequency currents the dissipation is not far from proportionate to the frequency, and increases rapidly when the diameter is small. A wire made hot in the ordinary way behaves in some respects like one the charge of which is rapidly alternating, the dissipation depending on curvature of surface. In his experiments Mr. Tesla noticed that the mica vanes in Crookee’s instrument are repelled with greater force when the incandescent wire is exceedingly thin. This observa- tion led Mr. Tesla to produce the spin in alternating electrostatic fields. When he first undertook to produce incandescence of a wire in a bulb by connecting it to one only of the terminals of a high-tension transformer, he could not succeed for a long time. He reduced the length of wire without result. It then occurred to him to make the surface as large as possible, yet the hulk small-taking an exceedingly thin wire-and on turning on the current the wire instantly fused. Two very thin wires attached to the terminals of a high-frequency coil are capable of giving off an appreciable amount of energy. The waves are conspicuous at distances of 6ft., and differ from sound»waves only by being electrified, and cannot be entirely stopped by interposition of an insulated metal plate. The “ringing ” ofa condenser is due to the presence of air near the charged surfaces. Further, when a dis ruptive discharge coil is immersed in oil, the surface of the oil is agitated. This is not due to the oil: it is the air above the oil which is agitated. The action of the air is shown in a curious manner, for if a pointed metal bar is held \vith the point close over the coil, a hole 2in. deep is formed in the oil by the molecules of air violently projected from the point. It seems that the dissipation of energy is more rapid when the resonator is immersed in air than in oil; and the dissipation owing to the presence of air renders the difference between magnetic and non-magnetic metals more striking. A virtually as if its arrived at from his lead to the result fully as important, resonator of magnetic metal behaves circuit were longer. The conclusion own and Prof. Bjerknes’ experiments, that air must be considered as a factor if not more so, than the resistance of the metals.