Hacke'IT — The Ionic Theories of Mtujne to-optic Rotation. 21 

 where 



= = 1 + 2 -^i. 



\2 



II. 



Drudc writes for the rotation on the hypothesis of the Hall-cfEect 

 S=--i:?-', [p. 438.] 



where 



^/ = charge on ion in electrostatic units, 

 e, = charge on ion in electromagnetic units. 



Transformation 



Using the same notation as before, we have 



= e, = ce„ - — j = ri", — = — . — , 



47r^./ ej ire m. 



since 



6, -i-rre/ m,0, 4:7re,c ^ 47r . e,c X,^ e, A.,'- 



(?/ m, ' 471 e/'^ m, ' 47r'^c- ttc 



Therefore 



V = TTC . 1/ = 7r6' 2, — = Z 



Hence 



^ -zll.TTCv' -ZII.V 



