﻿272 Mr. W. Morris Jones : Frictional 



Additional Experiments. 



Some of the insulators and metals were rubbed in strong- 

 magnetic and electric fields, but no change in the maximum 

 charge produced was noticed. The influence of temperature 

 on the maximum charge was also investigated, and in this 

 case also no effect was observed. In some experiments the 

 rubbing wheel was driven by a motor, and the influence of 

 pressure between rubber and specimen and that of velocity 

 of the rubbing surface were investigated. From the results 

 obtained, it appears that the maximum charge is independent 

 of the pressure and of the velocity*. 



General Conclusions. 



It has often been supposed that frictional electricity is of 

 the nature of contact electricity, the frictional work being 

 expended in bringing the surfaces into closer contact f. It 

 should, however, be noted that in Owen's experiments, mere 

 contact without rubbing did not in any case produce the 

 slightest evidence of charge on his specimens, and the same 

 result was found in the course of the present experiments. 

 Frictional electricity appears, therefore, to be an effect of 

 a different order from that of contact electricity, and it is 

 worth while considering whether the facts cannot be accounted 

 for on some other hypothesis. 



Let us assume that the rubbing friction has the effect of 

 removing electrons from either the rubber or the specimen 

 at a rate proportional to the rate of working. Then if e is 

 the total quantity of electricity liberated by a quantity of 

 work w, we may write 



de dw 



dt dt 



fl) 



where a is a factor depending on the nature of the materials 

 and also upon the normal thrust between the bodies; a is a 

 constant during any one experiment. 



We now assume that during a rub, leakage of electricity 

 takes place at a rate proportional to the total charge present, 

 Q, and to the rate at which fresh surface of the rubber is 

 coming into contact with the surface of the specimen, the 

 total leakage being e' . The velocity of the rubber is pro- 

 portional to the rate of working, so that this law of leakage 



* This result was slated by Peclet. 



t Helmholtz, Wissenschaftliche Abhandlunrjen, Erster Band, p. 860. 



