648 PROCEEDINGS OF THE AMERICAN ACADEMY. 



strain on the propagation of light. 1 The first successful experiment was 

 the discovery of the effect hy Kerr in 1875, and in an admirable series 

 of papers extending over nearly twenty years, he continued to contri- 

 bute to the advance in this new field. 2 Other investigators, following 

 Kerr, are: Gordon, 3 Mackenzie, 4 Roentgen, 5 Grunmach, 6 Blondlot, 7 

 Brongersma, 8 Kundt, 9 Quincke, 10 Lemoine, 11 Abraham, 12 Schmidt, 13 

 and Elnien. 14 



Even after Kerr's discovery, Mackenzie, Grunmach, and Gordon in 

 his first attempt, failed to observe electric double refraction. Gordon 

 in his second attempt, and Brongersma confirmed Kerr's discovery. 

 Roentgen added new liquids to Kerr's list, and studied the electric 

 double refraction of quartz. Kundt observed quartz only. 



The first quantitative observations were made by Kerr, who showed 

 (with white light, but with great care) that the double refraction of 

 carbon bisulphide varies as the square of the strength of electric field. 

 In 1883 Quincke undertook to determine the coefficient of proportion- 

 ality between double refraction and field-strength. He worked partly 

 with white light and partly with light from a red color screen, but 

 did not mention dispersion, and his results do not show it. Lemoine 

 in 1896 redetermined this coefficient, which Quincke called " B, " for 

 carbon bisulphide, with a red color screen, but gave no data and few 

 details to show the accuracy of his result. Elmen, working with Brace, 

 in 1904, observed " B " in very weak electric fields. None of them 

 noted dispersion. 



It was left for Kerr in 1892 to show the existence of dispersion in 

 the phenomenon he had discovered and studied so successfully. He 

 did not multiply observations on his latest discovery, however, but in- 

 ferred from what seem scanty data, that in carbon bisulphide the double 



1 Experimental Researches in Electricity, Series VIII, §§ 951-955 (April, 1834). 



2 Phil. Mag., (4) 50, 337, 446 (1875) ; (5) 8, 85, 229 (1879) ; 9, 157 (1880) ; 13, 

 153, 248 (1882) ; 20, 363 (1885); 37, 380 (1894) ; 38, 144 (1894) ; Rep. Brit. Ass'n, 

 Edinb., 157 (1892). 



3 Phil. Mag., (5) 2, 203 (1876) ; Treat, on Elec. & Mag., 11, 247 (1880). 



4 Wied. Ann., 2, 356 (1877). 



* Wied. Ann., 10, 77 (1880) ; 18, 213 (1882) ; 19, 319 (1882). 

 6 Wied. Ann., 14, 110 (1881). 



» Jour, de Phys., (2) 1, 364 (1882) ; Compt. rend., 106, 349 (1888). 

 8 Wied. Ann., 16, 222 (1882); Ann. d. Phys., 7, 708 (1883). 



• Wied. Ann., 18, 228 (1882). " Jour, de Phys., (3) 9, 265 (1900). 

 io Wied. Ann., 19, 729 (1883). " Ann. d. Phys., (4) 7, 142 (1901). 

 11 Compt. Rend., 122, 835 (1896). " Phys. Rev., 20, 54 (1905). 



