236 



Dr. J. Kerr's Electro-optic 



! - 



B. 



C. 



D. 



E. 



G. 



K 



i 







55, 59 



54 



60 



57 



231 



l 



2 



80,81 



79 



82 



801 





2 







GO 



68 



70 



69 



201 



2 



2 



79,81 



88 



91 



891 





3 







96, 98 



78 



82 



80 



17 



3 



2 



89,90 



951 



98£ 



97 





4 







108, 105 



871 



911 



891 



141 



4 



2 



95, 98 



1021 



1051 



104 





5 







112,116 



94 



99 



961 



171 



5 



2 



104, 107 



111 



118 



114 





6 







119,121 



103 



108 



1051 



HI 



6 



2 



113, 115 



118 



122 



120 





7 









112 



116 



114 



11 



7 



2 



122, 'i 23 



124 



126 



125 





8 







131, 132 



120 



124 



1221 



9 



8 



2 



125, 128 



130 



133 



1311 





9 







136, 137 



124 



129 



1261 



10 



9 



2 



130, 131 



135 



138 



1361 





10 







136, 139 



129 



132 



1301 



7 



10 



2 



132, 136 



135 



140 



1371 





11 







140, 143 



131 



137 



134 



71 



11 



2 





139 



144 



1411 





49. I proceed to draw several inferences, beginning with 

 an extension of the statement already made in 9. 



(1) Throughout the range of these observations, the optical 

 effects manifested are sensibly pure cases of double refrac- 

 tion ; the plate of carbon disulphide acts, under electric force, 

 as a positive uniaxal with axis .parallel to the lines of force. 

 This is evident from the nature of the arrangements, and from 

 the constantly observed fact that, as the potential rises through 

 a proper range of value, the light at the centre of the field 

 passes through sensibly pure extinction. 



(2) The total weight on the fixed compensator may be 

 adopted as a good approximate measure of the corresponding 

 birefringent action. The three following lines of numbers are 

 taken from the second Table. The first line gives the total 

 weights attached to the fixed compensator ; the second gives 

 the observed values of the neutralizing potential when the 

 whole weight is attached to the first plate ; the third gives 

 the observed values of the potential when the weight is dis- 

 tributed between the two plates, 2 pounds always on the second 

 plate. 



3 



4 



5 



6 



7 8 



80 



891 



961 



1051 



114 122 



80i 



89i 



97 



104 



114 120 



9 



10 11 

 30i 134 



125 131 



1361 



From these results, and others of the same kind, I infer that, 

 within the present range of measurement, the weight and the 



