﻿26S 



Mr. W. Morris Jones : Frictional 



obtained for the other materials rubbed and have been plotted 

 as curves, which show a similar form. 



Table V. 



Specimen. 



Maximum cbarge in E.S.U. when rubbed with 

 Flannel. Silk. Chamois leather 



Quartz 10-950 ( + ) 



Glass 8-818(4-) 



Fluorspar 7-085 ( + ) 



Iceland spar 8-817 ( + ) 



Heavy spar 4*151 ( + ) 



Ebonite 11-022 (-) 



Amber 10707 (-) 



Sealing-wax 9"269 (— ) 



9-761 ( + ) 



7-557 ( + ) 



10-725 ( + ) 



2-212(+) 



11-596(4-) 



1-260 (+) 



11-818(4-) 



1-236(4-) 



11-521 (4-) 



•945(4-) 



7-872 (-) 



4-250 (-) 



7-870 (-) 



4-726 (-) 



6-770 (-) 



4-409 (-) 



Table V. gives the values in electrostatic units of the 

 maximum charges produced on the insulators by friction 

 with the rubbers. It is interesting to note that the trans- 

 parent insulators were positively charged when rubbed with 

 the three materials, and that the opaque substances all 

 became negatively charged. 



The maximum charges produced by friction with flannel, 

 silk, and chamois leather are much greater than those ob- 

 tained by Owen, whose specimens, however, were rubbed 

 with hard materials, viz. slate and copper. This is probably 

 due to the different nature and hardness of the rubbing 

 surfaces. The soft rubbers used in the present experiments 

 allowed a larger area of the specimen to come into contact 

 with the rubber. It is also possible that a hard rubbing 

 surface cuts up or wears away the surface of the specimen. 



Metallic Specimens. 



In the experiments with the metals, the rubber had to be 

 a good insulator and thoroughly dry, otherwise the charge 

 generated leaked away through the rubber to earth as fast 

 as it was produced. For this reason the metallic specimens 

 were rubbed only with silk bands. The insulation of the 

 silk was frequently tested by bringing the cap of a charged 

 electroscope into contact with the band when on the wheel, 

 and observing the rate at which the leaves collapsed. Owing 

 to the hygroscopic nature of the silk, the material had to be 

 kept warm and dry by placing a stove underneath the 

 wheel. The insulation was further improved by having a 

 band of indiarubber between the silk and the slate. 



In rubbing the metals, reversals of the sign of electrifi- 

 cation were frequent, and appeared to be due to several 



