142 Prof. W. C. Rontgen on the Change in the Dovhle 



placed in the flask full of benzol, and the electro-optical 

 experiments repeated. The optical action of the electricity 

 was also compared with the action of a glass plate compressed 

 in a horizontal or in a vertical direction. In what follows such 

 a note as 



u Below + , above — ; upper end of band left ; horizontal 

 compression " 



is to be understood thus: — When the lower electrode was 

 positive and the upper one negative, the upper end of the 

 band lying on the left of the centre inclined towards the side 

 towards which the whole band was displaced by a compres- 

 sion of the glass plate in a horizontal direction. 



Experiment I. The rays of light traversed the plate parallel 

 to a and c; a on the left, c on the right. 



Below + , above — ; upper end of band left; vertical compres- 

 sion. 

 „—,„+; „ „ „ horizontal „ 



„+,„—; „ „ right; horizontal „ 



„ , „ + ; „ „ „ vertical ,, 



Experiment II. Rays of light parallel to a and c; a right, 



c left. 



Below -f, above— ; upper end of band left; horizontal com- 

 pression. 

 n ~ i n + 5 n n n vertical „ 



„ +, „ -; „ „ right; vertical „ 



„-,„+; „ „ „ horizontal „ 



Experiment III. Rays of light parallel to b and d ; b right, 

 dleft. 



Below + , above— ; upper end of band left; vertical compres- 

 sion, 

 horizontal 



ii i 

 v + , 



71 1 



n 



11 

 17 



j 



+ ; 



n 



n 



11 

 11 



g 11 

 right; 



n 



; horizontal 

 vertical 



ii 



ii 

 ii 



Experiment 

 d right. 



IV. Rays of light 



parallel to b and d; 



b left, 



Below +, 



above — ; 



upper 



end of band left; 



horizontal 



com- 



» + , 



n ? 



n 

 n 



+ ; 

 + ; 



n 



n 

 n 



11 



11 

 11 



m 11 

 right: 



ii 



[pr 

 vertical 

 ; vertical 

 horizontal 



ession. 



ii 

 ii 

 ii 



It is easy to convince one's self that these data are in all 



