THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



♦ 



[FOURTH SERIES.] 



NOVEMBER 1875. 



XL. A new Relation between Electricity and Light: Dielectrified 

 Media Birefringent. By John Kerr, LL.D., Mathematical 

 Lecturer of the Free- Church Training College, Glasgow*. 



THE thought which led me to the following inquiry was 

 briefly this : — that if a transparent and optically isotropic 

 insulator were subjected properly to intense electrostatic force, 

 it should act no longer as an isotropic body upon light sent 

 through it. Faraday was often occupied with expectations of 

 this kind ; and he has mentioned in his memoir on the Mag- 

 netization of Light, and elsewhere in his ' Researches/ how he ex- 

 perimented in this very direction, upon electrolytes as well as 

 dielectrics, at different times and in many ways, but always 

 without success f. As far as I remember, I have not read or 

 heard of an attempt in this field by any other naturalist. I pro- 

 ceed to offer a few notes of some recent experiments of my own. 

 The investigation is not so complete as I should wish it to be ; 

 but it has been carried forward as far as my limited time and 

 means would allow. At present I confine myself to solid dielec- 

 trics, reserving the case of liquids for a second paper. The 

 principal results given in this first paper are stated apart, in 

 articles 11, 17,23. 



1. Dielectric of Plate Glass. — A piece of good plate glass, f 

 inch thick, is formed roughly, before it leaves the shop, into a 

 rectangular block 6 inches long and 2 wide. In this and sub- 

 sequent operations, the original polish of the plate is carefully 



* Communicated by the Author. 



t Faraday's 'Experimental Researches,' 2216, p. 951, or Maxwell's 

 ' Treatise on Electricity,' vol. ii. p. 399. 



Phil. Mag. S. 4. Vol. 50. No. 332. Nov. 1875. Z 



