Effects related to the Ball Effect. 251 



Hence 



We¥L 2 GTS „ , 

 Ibirm T 



where S is the effective area of the disk. 

 Thus the torque on the disk is 



dW = aH' CTS ^ 



The existence of this torque was shown, but not measured, 

 by Corbino in the case of bismuth. Its measurement would 

 furnish another means of calculating the free time of an 

 electron. 



The third effect, the induction of a radial current in the 

 disk on exciting a normal magnetic field, is also easily 

 explained. At any instant during the rise of the magnetic 

 field let E be the radial electromotive force and c the radial 

 current. Then 



^W_-^ = ecS d , 

 dt lijTrm 



Ec'=-^^^(H 2 T). 

 at v 



We assume that T is a function of the magnetic force. 

 Therefore : 



lbirm dt y J 



The resistance of the disk is 



R= 



2r>d 



log- 2 , 



Hence the whole quantity of electricity that flows radially 

 during the setting up of the magnetic field is : 



e$ 



On comparison with the theory of these effects given by 

 Professor Corbino, we see that his " differential moment of 

 the ions/' E", is to be replaced by 



1 eT 



2 m* 



For the field strength 3700, Professor Corbino determined 



