INTERMITTENT CURRENTS. 467 



charging currents, and in the second by discharging currents. If the 

 plate makes n double vibrations in a second with a battery of electro- 

 motive force E, the current is nEC. Measuring the deflection a of 

 the needle, and the deflection 8 which the current of the same 

 battery would give through a resistance R, the deflections being 

 reduced by the graduation, we have again 



EC = -5a, E^R^S; 



(jr Lr 



consequently, 



If the resistance R is chosen so that the current is the same in 

 both cases, we have simply ^ ^ 



C L 

 ~nR' 



We thus obtain the value of the capacity relative to a time of dis- 

 charge determined by the duration of the contacts. 



1056. By means of a rocking commutator we may arrange the 

 experiment in such a way that the charging and discharging currents 



Fig. 222. 



successively traverse the galvanometer in the same direction. The 

 galvanometer G (Fig. 222) being placed in the circuit of the battery 

 which terminates at the binding screws P and N of the commutator, 

 the armatures of the condenser C are connected with the terminals 

 A and B. When the commutator is worked backwards and forwards, 

 the charge of the condenser is alternately C, and at each operation 

 the quantity of electricity which traverses the galvanometer is equal 

 to 2EC. If there are n reversals per second, the mean intensity 

 of the current is 2nEC. If p is the resistance of the circuit which 

 would give the same permanent current, we have 



P 



H H 2 



