372 Dr. E. Goldstein on the Electric 



the density of the gas is diminished ; the space in which the 

 discharge takes place conducts better the less gas it contains ; 

 and since this change is always in the same direction while 

 the density is continuously reduced, so far as the experiments 

 can be extended, we must conclude that the greatest conduc- 

 tivity would be obtained after complete removal of the gas. 

 But after complete removal of the gas the discharge-space 

 contains only free cether ; and I therefore regard this as the 

 true medium of the discharge. Any gas present seems to act 

 only as a hindrance to the aether. 



detailed speculations on the concrete form of the motion of 

 the free aether to which the discharge is due are, in my 

 opinion, premature. 



We are not justified in regarding the discharge as essen- 

 tially a progressive motion of the aether so long as, on the one 

 hand, we regard Doppler's principle as valid in optics, and, on 

 the other hand, refuse to attach any considerable value to the 

 progressive motion of gas-particles in the discharge. We 

 must' then ascribe to the motion of the aether amongst the 

 relatively stationary gas-molecules an optical effect precisely 

 similar to that produced by the motion of gas-molecules in 

 aether at rest. Experiments on the constancy of gaseous 

 spectra when observed in directions parallel and at right 

 angles to that of the electric rays, show at once the absence 

 of progressive motion of the aether (of velocity comparable 

 with the velocity of propagation of the ray-discharge), after 

 we have shown by other experiments* the relatively stationary 

 condition of the gas-molecules. 



It appears to me safest to characterize the motion of the 

 aether in discharge as radiant, in accordance with what has 

 been previously statedf. Every particle concerned in a pencil 

 of negative light assumes the same form of motion which is 

 excited at the point of origin of the pencil. 



The behaviour of the discharge towards magnetic forces has 

 frequently been brought forward in support of the view that 

 the gas-mass forms the medium of the discharge, since this 

 behaviour may obviously be explained by regarding the gas- 

 molecules as carriers of electricity. If the magnet acts upon 

 the positive light of an equatorially-placed cylindrical tube 

 with electrodes at the end, and finally compresses the light 

 which at first filled the width of the tube into a thin thread 

 lying in the equatorial plane against the wall of the tube, it is 

 generally assumed that the gas-molecules are compressed 

 together with the electricity; I have not found this confirmed. 



* Goldstein, 'A New Form of Electric Repulsion.' Chap. IV. 

 + Phil. Mag. i. p. 184. 



