THE BALLISTIC GALVANOMETER 123 



The total quantity of electricity discharged through a shunted 

 instrument which is slightly damped is 



Q = Qo - * l+ 5 r 'i ^arly enough. 



Considering the damping to be electromagnetic and that the 

 shunted galvanometer is used on an open circuit, 



C Z T . 

 But ~p is practically constant. Therefore when the damping is 



not large, the multiplying power to be used with ballistic throws 

 may be obtained by considering the galvanometer resistance to 

 be increased by a certain constant amount which depends upon 

 the construction of the instrument. The effective multiplying 

 power of the shunt is 



This is Latimer Clark's method of correction. The quantity A 

 may be determined experimentally. Suppose a condenser to be 

 charged to V\ volts and discharged through the shunted instru- 

 ment; then 



When the condenser is charged to V 2 volts and discharged 

 through the unshunted galvanometer, 



Q 2 = K *',, = CF 2 



A practical difficulty met with when applying shunts of the ordi- 

 nary sort to a moving-coil ballistic galvanometer is that the range 

 of the instrument cannot be greatly extended before the damping 

 becomes excessive. 



In open-circuit work, that is, in measurements upon condensers 



