136 THE ROYAL SOCIETY OF CANADA 
B, and Bz are storage batteries each having an E.M.F. of about 
2 volts. 

To SPRING 
Figure 1. 
M is a megohm consisting of resistance coils of 100,000, 200,000, 
300,000, 400,000 ohms. 
G is a Broca Galvanometer No. 6964. 
