20 ELEMENTS OF STATIC ELECTRICITY. 



It will also be noticed that the approach of either 

 electrified body while the other lies on the disc causes 

 the leaves to converge, while its withdrawal produces 

 divergence. 



There is often a slight divergence of the leaves when 

 both bodies are in contact on the disc, due to the diffi- 

 culty of producing perfect adjustment of contact, and 

 also to the fact that the electric condition of one body 

 may change more rapidly than that of the other, from 

 imperfect insulation or other cause. 



The amount of divergence is also liable to vary, the 

 removal of one body producing greater divergence than 

 the removal of the other. This difference is also easily 

 accounted for by difference of mass, of conductivity, or 

 other cause. 



Hence we deduce the following rule : When electricity 

 is generated on two bodies by their mutual friction, the elec- 

 tricity of each is neutralized by the presence of the other. 



The effect of the mutual friction of the two bodies is 

 to create a difference of potential by the transfer of 

 electric energy from one to the other. As one gains 

 what the other loses, the amount of energy on the two 

 is not changed so long as they remain in contact, and 

 hence the potential of the electroscope is not disturbed. 



But let one of the bodies be removed ; suppose it to 

 be the one to which energy has been transferred, the 

 potential of the remaining body being negative, there is 

 instantly a transfer of energy to it from the disc and 

 leaves, which thus become negative also. 



The leaves, being both at the same potential, diverge 

 by mutual repulsion ; and that potential being less than 

 zero, the divergence is increased by attraction from the 

 higher potential of the glass and surrounding objects. 



