Effects of Moving Charged Spheres. 297 



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

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

 that spheres of 3 cms. diameter gave nearly the same results 

 as spheres 1 cm. in diameter, so that his results for spheres 

 of 3 cms. diameter can be used with very small error for 

 spheres 2*6 cms. 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 deter- 

 mine the potential. The battery when used was always 

 freshly charged, and the variations in its potential from one 

 experiment to another were very small. 



Substituting the following numerical values : 



Radius of spheres . . 1*35 



c 20-38 



d 22-91 



d' 29-28 



b 8-16 



x 19-30 



h 2*55 



we find : 



A-B 1-541 



C-D 0-000232 



q 1*35x63 



Below are given the successive equilibrium positions of 

 the needle in six series of reversals, as an illustration of the 

 results that have been obtained : 



No- 1. No. 2. No. 3. 



63 165 130 



60 66 172 178 109 122 



64 76 188 223 122 130 



71 79 200 220 112 130 



69 76 213 121 140 



69 146 156 



164 171 

 162 



