Manchester Memoirs, Vol. Ix. (1916), No. 11. 



5 



An immense amount of work has been done by a 

 great number of experimenters in attempts to measure 

 and explain the causes of overvoltage, and it is proposed 

 here to give a very condensed account of — 



1. Methods of measuring overvoltage. 



2. The most important phenomena connected with, 



and controlling factors of overvoltage. 



3. The chief theories put forward to account for over- 



voltage. 



4. Suggestions for a more comprehensive theory of 



overvoltage to account for all the observed 

 phenomena as far as at present known. 



1. Methods for Measuring Overvoltage. 



a. By direct measurement of the potential difference 

 between each electrode and a standard electrode while 

 the current is flowing. 



This is the method originally suggested by Caspari, 

 and used by many others. 



A diagram of Caspari's apparatus is given below. 



Text-fig. 1. 



