the Capacity of Gold-leaf Electroscopes. 24 1 J 



shown in the diagram. The gold-leaf system was insulated 

 in the usual way by a bead of sulphur inside the case, and 

 potentials are put on it bv means of a metal charger mounted 

 on a plug of amber. It is necessary to distinguish between 

 c the capacity of the gold-leaf system itself and c that of the 

 charger including the mercury cup mounted on its end. 



Method. 



The following method is used : — 



(i.) The capacity of the quadrant system K as far as the 

 connecter is determined, as shown later, using a stardardised 

 Gerdien condenser. 



(ii.) c', the charger only, is charged to V volts and shared 

 with K. The resulting potential v is measured by the 

 deflexion produced. 



c is given by the equation 



c'V=*= (K-hc'> 



••• "' = K vi, a> 



(iii.) c* -f c f , the gold-leaf system plus the charger, charged 

 to V volts and shared with K. The resulting potential v' is 

 measured as before. Then 



i 

 or c + r ' = K yZv ( 2 ) 



Subtracting (1) from (2) the capacity of the gold-leaf 

 system is obtained. 



(iv.) To determine the capacity of the gold-leaf system 

 at different voltages, a sliding condenser is added to the 

 quadrant system and the value of K adjusted so that the 

 resulting potential alter sharing with the quadrant system is 

 not far from one volt. 



Discussion of Errors* 



The equation from which c', the capacity of the charger, is 

 computed is 



<' = K V-,' 



where K, V, and v are independent variables. 



Phil. Mag. S. 6. Vol. 38. No. 2'U. Aug. 1919. S 



