296 Mr. E. P. Adams on the Electromagnetic 



Then the charge on any sphere is given by 



where the odd subscripts refer to spheres of the same set, and 

 even subscripts to spheres of the other set. 



Numerous determinations have shown that the potential of 

 the individual cells making up the battery averages almost 

 exactly two volts when freshly charged. On this basis, 

 assuming perfect insulation, the potential of the 10,000 cells 

 was 20,000 volts. It was thought best, however, to get a 

 closer estimate of the potential, since the insulation was not 

 perfect. This was measured by means of a guard-ring 

 electrometer. If the radius of the movable disk is R, the 

 inside radius of the guard-ring R ; , D the distance between 

 the movable disk and the fixed disk, W the weight required 

 to balance the attraction of the two disks, and g the acceler- 

 ation of gravity *, 



P=4D 



W 



R 2 + R' 2 



R = 5-933 

 R' = 6033 



g =980 



The following determinations were made : — 



D. G. P. 



3-0 2-078 64-0 



2-5' 2-780 62-0 



2-0 4-505 63-0 



These values of the potential are in electrostatic units. To 

 convert into volts, multiply by 300, and the potential as 

 measured by the electrometer is 18,900 volts. 



As a further check the maximum sparking distance between 

 two metallic spheres was measured. With polished brass 

 spheres, 2'6 cms. in diameter, this distance was found to be 

 0*58 cm. According to the observations of Bailie f, this 

 corresponds to a potential 



P = 63. 



* Maxwell, vol. i. section 217. 



f J. J. Thomson, Recent .Researches, p. 77. 



