_4<> On the Electric Discharge in Rarefied Gases. 



mean time I have endeavoured to draw conclusions as to the 

 velocity of propagation of electricity in kathode-rays from 

 certain phenomena which I have observed, and have obtained, 

 as results, very great velocities. I venture here, shortly, to 

 indicate the method of precedure. If two kathodes, a and b, 

 are placed beside each other in a vacuum-tube, each of them 

 shuts off certain rays from the other from a particular portion 

 of the glass wall*. There result therefore, at suitable densities, 

 two phosphorescent surfaces which appear dark in comparison 

 with the surrounding parts of the glass wall, inasmuch as the 

 one receives no rays from a and the other no rays from 6, 

 whilst the surrounding portion of the glass receives rays from 

 both. If, now, the rays of the kathode a, for example, were 

 not permanently cut off, but alternately cut off and allowed to 

 pass during equal small intervals, this would be easy to 

 observe. 



It would only be necessary to emboss the kathode a and 

 to leave b smooth ; then in the dark surfaces to which the 

 rays from a have only alternately access, the pattern of the 

 electrode a w T ould be observed f . Its brightness would, of 

 course, only be the half of that which would be observed if a 

 could always send its rays without hindrance to the surface in 

 question; but the half of this illumination is, as experiments 

 by way of control show, amply sufficient. Experiments with 

 relief-kathodes show permanent exclusion of the rays from a, 

 even when the two kathodes are at a distance of 20 centims. 

 from each other. Hence it follows that when the discharge from 

 a reaches b each time, the discharge from b has not yet lasted 

 half its time, or the velocity of propagation of the discharge 

 in the kathode-rays is great enough to pass over the interval 

 between the two electrodes within half of the duration of a dis- 

 charge. But now the duration of the partial discharges which 

 constitute a (break) discharge is, according to experiments of 

 mine with a revolving mirror, less than -^ Q( * Q0Q second; so 

 that the velocity of the discharge is at least 2 x 2,000,000 x 

 20 centims. or 800,000 metres. It cannot be objected to this 

 conclusion that, as the discharges are separated from each 

 other by numerous very small intervals of time, a discharge 

 issuing from a in the electric ray might perhaps not reach b 

 until, with the arrangement described, the discharge simul- 

 taneously commenced at b had long ceased and another pro- 

 ducing a similar effect had begun. If this were the case, then 

 when the distance between the kathodes was varied, a point 

 would be reached at which the discharges which a sends out 



* Monatsber. d. Akad. 1876, p. 285. f Ibid. p. 286. 



