HIGH FREQUENCY AND HIGH POTENTIAL CURRENTS. 405

the same would undoubtedly produce luminosity (if the potentialbe sufficiently high), until a permanent condition would bereached. Assuming the tube to be perfectly well insulated,there would be only one instantaneous flash during the act ofdistribution. This would be due to the electrostatic actionsimply.

But now, suppose the charged sphere to be moved at short in-tervals with great speed along the exhausted tube. The tubewould now be permanently excited, as the moving sphere wouldcause a constant redistribution of electricity and collisions of themolecules of the rarefied gas. We would still have to deal withan electrostatic effect, and in addition an electrodynamic effectwould be observed. But if it were found that, for instance, theeffect produced depended more on the specific inductive capa-city than on the magnetic permeability of the medium—whichwould certainly be the case for speeds incomparably lower thanthat of light—then I believe I would be justified in saying thatthe effect produced was more of an electrostatic nature. I donot mean to say, however, that any similar condition prevails inthe case of the discharge of a Leyden jar through the primary,but I think that such an action would be desirable.

It is in the spirit of the above example that I used the terms“ more of an electrostatic nature,” and have investigated the in-fluence of bodies of high specific inductive capacity, and observed,for instance, the importance of the quality of glass of which thetube is made. I also endeavored to ascertain the influence of amedium of high permeability by using oxygen. It appearedfrom rough estimation that an oxygen tube when excited undersimilar conditions—that is, as far as could be determined—givesmore light; but this, of course, may be due to many causes.

Without doubting in the least that, with the care and precau-tions taken by Prof. J. J. Thomson, the luminosity excited wasdue solely to electrodynamic action, I would say that in manyexperiments I have observed curious instances of the ineffective-ness of the screening, and I have also found that the electrifica.tion through the air is often of very great importance, and may,in some cases, determine the excitation of the tube.

In his original communication to the Electrician , Prof. J. J.Thomson refers to the fact that the luminosity in a tube near awire through which a Leyden jar was discharged was noted by1 Iittorf. I think that the feeble luminous effect referred to has