36 



Mr. E. M. Wellisch on the Motion of 



fraction / of the total time ; this fraction can be determined 

 experimentally. Under these conditions the mobility k of 



the ion under consideration is given by k = y^~> where wis- 



the number of complete alternations per second, d is the 

 distance between the gauze and the electrode e, and V is the 

 critical potential, i. e. the value of x which is just sufficient 

 to enable the ions to reach the electrode e before the field is 

 reversed. 



Fie-. 2. 





The diagram of connexions is exhibited in fig. 2. As in 

 the previous experiments, two commutating disks were em- 

 ployed : one of these had 20 fibre segments while the circum- 

 ference of the other was half fibre and half metal. The 

 motor was worked generally on 110 volts which afforded 

 approximately 42 revolutions per second. 



The double-pole double-throw switch S, when thrown to 

 the right, completed the connexions as exhibited graphically 



