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XXX. Frictional Electricity on Insulators and Metals. By 

 W. Mokris Jones, B.Sc, Research Student of the University 

 of Wales *. 



IN a recent paper Morris Owen f describes a series o£ 

 experiments, in which he obtained absolute measure- 

 ments of the charges produced on solid bodies by known 

 amounts o£ frictional work. In particular, he rubbed 

 ebonite and glass with slate and copper under various con- 

 ditions as to pressure, and found that with a sufficient 

 amount of frictional work the charges reached a constant 

 maximum, and that this maximum was independent of the 

 pressure applied during the rubbing, but was reached with a 

 smaller quantity of work the greater the pressure. 



As there seems to be. but little known about frictional 

 electricity, the investigations described below were under- 

 taken with the object of discovering new facts which might 

 be of assistance in forming a quantitative theory. In these 

 experiments, after the method adopted by Owen, measure- 

 ments were made of the charge produced on a surface by 

 friction and of the frictional work spent in generating it. 

 Apart from any theory of the phenomenon, this seems 

 the most convenient way of stating the results of the 

 experiments. 



Apparatus. 



The apparatus employed was essentially the same as that 

 used by Owen, but there were several improvements. The 

 rubbing apparatus consisted of a slate wheel round the rim 

 of which rubbers of various soft materials were placed. The 

 wheel, of moderate moment of inertia and *8 cm. thick, 

 turned in bearings fixed in a wooden framework, and could 

 be set into rotation by a known weight falling through a 

 measured height. The weight was attached to a cord passing- 

 over a light pulley in the ceiling and wound round a wooden 

 drum fixed on the wheel. A vertical pole graduated up- 

 wards in decimetres gave the distance through which the 

 weight fell. In later stages of the work the wheel was 

 driven by an electric motor of variable speed. 



The specimens rubbed were usually disks about V2 cm. 

 in diameter, and were of various insulating and metallic 

 materials. They were mounted with an insulating cement on 



* Communicated bv Prof. E. Taylor Jones, 

 f Phil. Mag. xvii. p. 457 (1909).' 



