Dispersion in Relation to the Electron Theory. 469 

 using 8 for this quantity, may be written 



" 40 X (a + 7 ) 2 + /3 2 ~" («- 7 ) 2 + /3- J ' 



where v is the frequency (angular velocity) of the incident 

 light, and putting v Q for the angular velocity of an electron 

 vibrating with its isolation frequency, and a for the polari- 

 zation constant, 



m 



p _ vg vH 



A more convenient expression has been obtained by 

 (x. H. Livens * which, in terms of the symbols used in 

 the preceding parts of this paper, becomes 



, 2 .,. evK 

 „i-l=_ . 9 ° 



i-x ^ L 



??i(v 1 2 -v-)+ — 



in which the + and — suffixes distinguish the values of n 

 for circularly polarized light of opposite chiralities. 

 Since 



8 =4^G (»--»+)> 



we 



have 



0h = 



2nC 2 



Taking the polarization constant a as 1/3 and writing 



p 2 

 1 - 



we obtain 



2 ^H 



??1(V X 2 -V 2 )+ -jy 



ni-l=— ^± ; ni + 2 = 



* Phil. Mag. August 1913, p. 362. 



