Hence 



Effects of Moving Charged Spheres. 

 ^ _ 2irNcq (d cos 6 — c) 



293 



Y[d 2 + b 2 + c 2 -2dccos 0]§ • 



X is the component of the force at P in the direction of the 

 axle due to the sphere at A. V is the ratio of the units. 

 The capacity of the spheres and their potential are measured 

 in electrostatic units. 



Fip\ 4. 



:zzz:z zz_zzrz 



EEEEEEEEEEpE 



Z^_ZZZZZZi:ZZZZZZ 

 ,/ 



Fig. 4 is plotted from this expression, and shows how the 

 force varies with the position of the spheres. The upper 

 curve gives the resultant force at the lower needle due to 

 both sets of spheres, and the lower curve, which is nearly a 

 straioht line, gives the force at the upper needle. Let the 

 mean value of the force at the lower needle obtained by 



Phil. Mag. S. 6. Vol. 2. No. 9. Sept. 1901. X 



