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INVENTIONS OF NIKOLA TESLA.

Of all these phenomena observed with currents, or electricimpulses, of high frequency, the most fascinating for an aud-ience are certainly those which are noted in an electrostatic fieldacting through considerable distance; and the best an unskilledlecturer can do is to begin and finish with the exhibition of thesesingular effects. I take a tube in my hand and move it about,and it is lighted wherever I may hold it; throughout space theinvisible forces act. But I may take another tube and it mightnot light, the vacuum being very high. I excite it by means of adisruptive discharge coil, and now it will light in the electrostatic

Fig. 163. Fig. 164.

field. I may put it away for a few weeks or months, still it retainsthe faculty of being excited. What change have I produced in thetube in the act of exciting it? If a motion imparted to atoms, itis difficult to perceive how it can persist so long without beingarrested by frictional losses; and if a strain exerted in the dielec-tric, such as a simple electrification would produce, it is easy tosee how it may persist indefinitely, but very difficult to under-stand why such a condition should aid the excitation when wehave to deal with potentials which are rapidly alternating.