134 Double Refraction in Glass and Bisulphide of Carbon. 



In a further experiment the electrodes were brass balls of 

 8*5 millim. diameter. With the nicols in the first position 

 fig. 5g appeared ; in the second, fig. 5 h. Horizontal and ver- 

 tical pressure upon the glass plate had the same effect as in 

 the first experiment. I obtained completely accordant phe- 

 nomena also with spherical electrodes of larger dimensions. 

 If one electrode was a sphere of 14 millim. and the other a 

 sphere of 8'5 millim. diameter, this made just as little dif- 

 ference. 



At first I thought that a movement of the electricity from 

 one of the electrodes to the other would have a great influence 

 upon the phenomenon. This induced me to make the follow- 

 ing experiments. 



Two cylindrical electrodes were placed coaxially. One of 

 their opposed surfaces was furnished with fine points. Fig. 5 d 

 shows the phenomenon which was observed with the nicols in 

 the first position. That which appeared with the second posi- 

 tion was very similar to fig. 5/. 



In the next experiment two thermometers whose spherical 

 bulbs had an external diameter of 13 millim. were employed 

 as electrodes, their mercury being conductively connected with 

 the Holtz machine : thereby neither a dark nor a spark-dis- 

 charge could take place through the liquid; so that the poten- 

 tial-difference could be raised very high. The striking-distance 

 of the machine was now as great as when the condensers were 

 not connected to the electrodes. The phenomena observed, 

 both with the first and with the second position of the nicols, 

 agreed with those obtained with spherical electrodes (figs, bg 

 and hit). Only with the first position of the nicols was the 

 field illuminated between the electrodes, while the black tails 

 at the sides of the electrodes were much less distinctly visible. 

 With the second position such a difference was not to be per- 

 ceived. On repeating this experiment with spherical copper 

 electrodes completely inclosed in glass tubes, I obtained the 

 same results. 



Further, it is noteworthy that the liquid, which in the expe- 

 riments with uncovered electrodes was constantly in motion, 

 now remained at rest. Only during a few seconds, as the 

 machine was beginning to work, were very delicate undula- 

 tions to be seen when the polarization-planes of the nicols 

 formed an angle of about 90° with one another, so that the 

 field of view was feebly illuminated previously. 



That with Kerr's and Rontgen's method of experiment a 

 dark discharge takes place through the liquid was ascertained 

 by both physicists ; and they deem this fact not unimportant 

 for the explanation of the phenomena. From the experiments 



