Frictional Electricity. 465 



ebonite specimens have all been reduced so as to give read- 

 ings corresponding to a specimen of 2*15 cms. in width. 

 Curves I., II., III., IV. show the quantities of electricity 

 produced on specimens of equal width in the friction of 

 ebonite and slate, ebonite and copper, glass and slate, glass 

 and copper. The same pressure was applied between the 

 rubbers in each case. 



The curves show that with a sufficient amount of frictional 

 work the charge produced reaches a constant maximum 

 value ; that this maximum is independent of the pressure 

 applied during the rubbing, but that the maximum is 

 reached with a smaller quantity of work the greater the 

 pressure. 



The view generally held as to frictional electricity is that 

 due to Helmholtz *, viz., that it is of the nature of contact 

 electricity, the frictional work being expended in bringing 

 the surfaces into closer contact. This view appears to be 

 borne out by the observation noted above, that after a number 

 of recent rubs the maximum deflexion may be obtained with 

 quite a small amount of frictional work, an amount much 

 less than that required to give the maximum charge with 

 the first rub. During the three or four hours' rest it might 

 be supposed that the surface of the specimen goes through a 

 process of slow elastic recovery of its original uneven form, 

 or that during this time the surface becomes tarnished by 

 the atmosphere, so that after this period the first contact is 

 not a good one. 



It should be noted, however, that in no case, whether after 

 recent rubs or not, did mere contact of wheel and specimen 

 without rubbing produce even the slightest evidence of charge 

 on the specimen. 



All the experiments described above were carried out in 

 the Physical Laboratory of the University College of North 

 Wales ; and, in conclusion, I desire to acknowledge my 

 great obligation to Professor E. Taylor Jones for the interest 

 he has taken in the work, and also for much valuable help, 

 and advice. 



Wissenschaftliche Abhandlungen, Erster Band, p. 860. 



Phil Mag. S. 6. Vol. 17. No. 100. April 1909. 2 K 



