78 THE ROYAL SOCIETY OF CANADA 



We may treat the electrometer as though it were a simple con- 

 denser in series with a high resistance, neglecting both changes in this 

 resistance and the capacity of the condenser. The arrangement of 

 the discharge circuit is shown in Figure 2. The battery whose emf is 

 E supplies the current I through the resistance Ri and a key Ki, 

 which is one of the keys of a drop chronograph. The two condensers 

 of capacities Ci and C2 are connected as shown and are charged so 

 that the potential difference is I R. R2 is the high resistance of the 

 electrometer whose capacity is C2. L is a self-inductance inserted so 

 that the discharge may be oscillatory. The second key K2 of the drop 

 chronograph may be inserted at x, y or z. When both keys are closed 

 the system is charged and in both condensers the plates are at a 

 common difference of potential I R. If Ki is opened the discharge 

 begins and continues until K2 is opened. If K2 is at x, the oscilla- 

 tion ceases and the two condensers settle down to the same difference 

 of potential. If K2 is at y, the first condenser Ci is left with the 

 charge it had at the instant of opening the key K2. If K2 be con- 

 nected at z, the condenser C2 is left with the charge it had at the 

 instant of opening the key. In any case we may measure the charge 

 by connecting both with a ballistic galvanometer and calculate the 

 potential from the known capacities. Or we may connect to an 

 electrometer and measure the potential. For the case where K2 is at x 

 or z, we may use the capillary electrometer to measure the potential. 

 The first arrangement only was used. 



Suppose plates a and b are charged positively so that when Ki is 

 opened the charge flows from a and h through the system. Let the 

 current in circuit 1 be ii, in circuit 2 be i2, the charge on plate a of Ci 

 be Qi, on plate h of C2 be q2, potential of a be Va and of c be Vc- Let 

 Ri include resistance of L. We may call the capacities of the conden- 

 sers Ci and C2 respectively. 



Then: ,. ,. 



i,R, = V,-Ve-L^ = ^-L^^ 

 ' dt Ci dt 



