370 The Followers of Maxwell. 



metals, were extensively studied* in the years following the 

 publication of Kowland's memoir: but it was not until the 

 modern theory of electrons had been developed that a satisfactory 

 representation of the molecular processes involved in magneto- 

 optic phenomena was attained. 



The allied phenomenon of rotary polarization in naturally 

 active bodies was investigated in 1892 by Goldhammer.f It 



* The theory of Basset (Phil. Trans, clxxxii (1891), p. 371) was, like Rowland's, 

 based on the idea of extending Hall's phenomenon to dielectric media. An objec- 

 tion to this theory was that the tangential component of the electromotive force 

 was not continuous across the interface between a magnetized and an unmagnetized 

 medium ; but Basset subsequently overcame this difficulty (Nature, Hi (1 895), p. 618 ; 

 liii (1895), p. 130; Amer. Jour. Math, xix (1897), p. 60) the effect analogous to 

 Hall's being introduced into the equation connecting electric displacement with 

 electric force, so that the equation took the form 



E = (47rc 2 / ) D + ff [K . D]. 



Basset, in 1893 (Proc. Camb. Phil. Soc. viii, p. 68), derived analytical 

 expressions which represent Kerr's magneto-optic phenomenon by substituting u 

 complex quantity for the refractive index in the formulae applicable to transparent 

 magnetized substances. 



The magnetic rotation of light and Kerr's phenomenon have been investigated 

 also by R. T. Glazebrook, Phil. Mag. xi (1881), p. 397 ; by J. J. Thomson, 

 Recent Researches, p. 482 : by D. A. Goldhammer, Ann. d. Phys. xlvi (1892), 

 p. 71 ; xlvii (1892), p. 345; xlviii (1893), p. 740; 1 (1893), p. 772 : by P. Drude, 

 Ann. d. Phys. xlvi (1892), p. 353; xlviii (1893), p. 122; xlix (1893), p. 690; 

 lii (1894)) p. 496 : by C. H. Wind, Verslagen Kon. Akad. Amsterdam, 29th Sept., 

 1894 : by Reiff, Ann. d. Phys. Ivii (1896), p. 281 : by J. G. Leathern, Phil. 

 Trans, cxc (1897), p. 89; Trans. Camb. Phil. Soc. xvii (1898), p. 16: and by 

 W. Voigt in many memoirs, and in his treatise, Magneto- und Elektro-optik. 

 Larmor's report presented to the British Association in 1893 has been already 

 mentioned. 



In most of the later theories the equations of propagation of light in magnetized 

 metals are derived from the two fundamental electromagnetic equations 



curl H = 4?rS, - curl E = H ; 



the total current S being assumed to consist of a part (the displacement-current) 

 proportional to E, a part (the conduction -current) proportional to E, and a part 

 proportional to the vector-product of E and the magnetization. 



Various mechanical models of media in which magneto-optic phenomena take 

 place have been devised at different times. W. Thomson (Proc. Lond. Math. Soc. 

 vi (1875)) investigated the propagation of waves of displacement along a stretched 

 chain whose links contain rotating fly-wheels : cf . also Larmor, Proc. Lond. Math. 

 Soc. xxi. (1890), p. 423 ; xxiii (1891), p. 127 ; F. Hasenohrl, Wien Sitzungsberichte 

 cvii, 2a (189S), p. 1015 ; W. Thomson (Kelvin), Phil. Mag. xlviii (1899), p. 236, 

 and Baltimore Lectures ; and Fitz Gerald, Electrician, Aug. 4, 1899, Fitz Gerald's 

 Scientific Writings, p. 481. t Journal de Physique (3) i, pp. 205, 345. 



