164 Prof. J. J. Thomson on the 



Substituting the above values for a and ft, and remembering 

 that 



v 4-7T v 47T 7 47T, 



we get 



47T, d^Jt 



K h= 'Hz- 



Putting 1/K = V 2 , where V is the velocitv of light through 

 the dielectric, and remembering that 



d l + d$ +— =0. 

 dx dy dz 



rf^ 2 + dy 2 + V VV ^ 2 



we get 

 which, if 



*i = 



V V 2 / 



may be written as 



o^jr d^f d^Jr =Q 



dx 1 dy 1 dz\* ~~ 



The solution of which is 



, _ A 



Since 



And since 



V»A= * d ±. 



47r dz 



when the integration is extended over a sphere of radius a 

 concentric with the moving sphere, and e is the charge on 



