Moving Charged Spheres. 165 



y R 2 + R' 2 



R = 5-933 

 R' = 6-033 

 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 meas- 

 ured by the electrometer is 18,900. 



As a further check the maximum sparking distance between 

 two metallic spheres was measured. With polished brass 

 spheres, 2'6 cm in diameter, this distance was found to be 0*58 cm . 

 According to the observations of Bailie,* this corresponds to a 

 potential : 



P = 63 



Bailie's observations were with spheres of different sizes. In 

 the region of a spark-length of this magnitude, he found that 

 spheres of 3 cm diameter gave nearly the same results as spheres 

 l cm in diameter, so that his results for spheres of 3 cm diameter 

 can be used with very small error for spheres 2*6 cm in diameter. 

 From these determinations, the value 



P = 63 



in electrostatic units is taken as the potential of the spheres. 

 The great advantage in using a storage battery as the source 

 of electricity is that one measurement is sufficient to determine 

 the potential. The battery when used was always freshly 

 charged, and the variations in its potential from one experi- 

 ment to another were very small. 



Substituting the following numerical values : 



Radius of spheres = 1*35 



we find 



c 



= 20-38 



d 



= 22-91 



d' 



= 29-28 



b 



= 8-16 



X 



= 19-30 



h 



= 2-55 



A-B 



= 1-541 



C-D 



= 0-000232 



9. 



= 1-38 X 63 



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



