462 Dr. E. Goldstein on the Influence of the 



longer to be obtained, and fig. 12 c is the last obtained at 

 extreme exhaustion. 



The results are qualitatively identical if we increase the 

 breadth of the arms in the same proportion*. 



7. The experiments mentioned in No. 5 show that the phase 

 alters when plane kathodes of similar shape are bent into 

 spherical surfaces of different curvature. Since the same 

 figure, formed to different spheres, will form a mirror of 

 greater aperture the smaller the radius of the sphere is, the 

 result described in No. 5 as to the influence of increased 

 curvature might possibly seem to be only another state- 

 ment of the influence mentioned in No. 6 of increased aper- 

 ture. In that case we should expect that kathodes of like form 

 and different curvature but like aperture, at distances forming 

 the same multiples of their radii of curvature, would give like 

 figures at like densities of gas. 



To test this I constructed a series of kathodes (e. g. three 

 four-armed crosses, I., II., III.), whose dimensions were as 

 follows : — 



Kadius of L h Breadth 



curvature (p). 8 of arms. 



millim. millim. millim. 



1 12i i2i 2 i 



II 20 20 4 



III 26f 26| 5j 



The kathodes thus all covered equal aliquot parts of the 

 spheres from which they were formed. They were placed at 

 a distance 2p from the spherical wall of the similar containing 

 vessels — that is, 25 millim., 40 millim., and 53^ millim. re- 

 spectively. 



Here also the result was obtained that there is no identity 

 of phase for equal density, but the figures given by kathodes 

 II. and III. corresponded to the figures which kathode I. 

 would have given if the distance of the wall had been increased. 

 This occurred indifferently, whether the two electrodes of each 

 of the three discharge-vessels were separately connected with 

 the poles of the induction-coil, or whether, in order to secure 

 equal intensity of discharge, the current was sent at the same 

 time through the three vessels, connected together in line. 



* The changes in curvature and aperture of kathode described in the 

 two preceding- paragraphs cannot, in one respect, be always compensated 

 by changes in density of gas or in distance of wall : the last term of the 

 series of figures (corresponding to fig. 15//) for a polygonal kathode shows 

 with kathodes of greater curvature or larger aperture richer differentia- 

 tion and finer detail. The rougher figure cannot be reproduced with these 

 kathodes. 



