Tesla-Thomson Debate: Phenomena Of Alternating Currents Of Very High Frequency

Wednesday, April 11, 2891
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THE ELECTRICAL VVORLD. Mason 21. 1891. 2 2 3 Phenomena of Alternating Currents of Very High Frequency. BY NIKULA TESLA. In the issue of THE ELECTRICAL Wonnn of March 14 I find a note of Prof. Elihu Thomson relating to some of my experiments with alternating currents of very high fre- quency which have been described in Tim ELECTRICAL Wonm of Feb. 21, 1891. Prof. Thomson calls attention to the interesting fact that he has performed some experiments in the same line. I was not quite unprepared to hear this, as aletter from him appeared in The Electrician (London) a few months ago in which he mentioned a small alternate current ma- chine which was capable of giving, I believe, 5,000 alter- nations per second, from which lett/er it likewise appears that his investigations on that subject are of a more recent date. Prof. Thomson describes an experiment with a bulb in- closing a carbon Hlament which was brought to incandes- cence by the bombardment of the molecules of the residual gas when the bulb was immersed in water rendered slight- ly conducting by salt dissolved therein (Y) and a. potential of 1,000 volts, alternating 5.000 times il second, applied to the carbon strip. Similar experiments have, of course, been performed by many experimenters, the only distinctive feature in Prof. Thomson’s experiment being the compara- tively high rate of alternation. These experiments can alto

224 THE ELECTRICAL VVORLD. V°L~ XVII- NO- 12 be performed with s. steady difference of potential between the water and the carbon strip, in which case, of course, conduction through the gluss takes place, Uie di1Ter- ence of potential rrquirud heing in proportion lo the thick- ness ofthe glass. With 5,000 alteinalions per second con- duction still takes place, but the condenser effect is pre- ponderating. It goes, of course, without saying that the heating of the glass in such ri case is principally due to the bombardment of the molecules, partly also to leakage or conduction, but it is an undeniable fact that the glass may also be heated merely by the molecular displacement. The interesting feature in my experiment was that a lump would light up when brought near to an induction coil, and that it could he held in the hand and the filament brought to incanzlescence. Experiments of the kind described I have followed up for a. long time with some practical objects in view. In connection with the experiment descrihed hy Prof. Thom- son, it may be of interest to mention a very pretty phenomenon which may beohserved with an incandescent lamp. Ifalnmp be immersed in water ns fnr as practi- cable. and the filament and the vessel connected to the terminals of an induction coil operaterl from a machine such as I have used in my experiments, one may see the dull red filament surrounded by a very luminous globe, around which there is a less luminous space. The eiiect is probably due to rchectiun, as ihe globe is sharply de- fined, but mny also hc duo to xi “ dark spnce;” :it nny rate it is so pretty that it must be seen to be apprecintv