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INVENTIONS OF NIKOLA TESLA.

could only explain on two suppositions, viz.: that under the conditions then ex-isting the specific inductive capacity of the gas was very great, or that a dis-charge could pass without being luminous. 4 he author had also observedthat the conductivity of a vacuum tube without electrodes increased as the pres-sure diminished, until a certain point was reached, and afterwards diminishedagain, thus showing that the high resistance of a nearly perfect vacuum is inno way due to the presence of the electrodes. One peculiarity of the dischargeswas their local nature, the rings of light being much more sharply defined thanwas to be expected. They were also found to be most easily produced whenthe chain of molecules in the discharge were all of the same kind. For ex-ample, a discharge could be easily sent through a tube many feet long, but theintroduction of a small pellet of mercury in the tube stopped the discharge,although the conductivity of the mercury was much greater than that of thevacuum. In some cases he had noticed that a very fine wire placed within atube, on the side remote from the primary circuit, would prevent a luminousdischarge in that tube.

Fig. 219 shows an exhausted secondary coil of one loop containing bulbs ;the discharge passed along the inner side of the bulbs, the primary coils beingplaced within the secondary.

1 In The Electrical Engineer of August 12, I find some re-marks of Prof. J. J. Thomson, which appeared originally in theLondon Electrician and which have a bearing upon some experi-ments described by me in your issue of July 1.

I did not, as Prof. J. J. Thomson seems to believe, misunder-stand his position in regard to the cause of the phenomenaconsidered, but I thought that in his experiments, as well as inmy own, electrostatic effects were of great importance. It didnot appear, from the meagre description of his experiments, thatall possible precautions had been taken to exclude these effects.I did not doubt that luminosity could be excited in a closed tubewhen electrostatic action is completely excluded. In fact, at theoutset, I myself looked for a purely electrodynamic effect andbelieved that I had obtained it. But many experiments per-formed at that time proved to ine that the electrostatic effectswere generally of far greater importance, and admitted of a moresatisfactory explanation of most of the phenomena observed.

In using the term electrostatic I had reference rather to thenature of the action than to a stationary condition, which is theusual acceptance of the term. To express myself more clearly,I will suppose that near a closed exhausted tube be placed a smallsphere charged to a very high potential. The sphere would actinductively upon the tube, and by distributing electricity over

1. Article by Mr. Tesla in The Electrical Engineer, N. Y., August 26, 1891.