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XLIL On Frictional Electricity. By Morris Owen, B.Sc, 

 Isaac Roberts Student of the University College of North 

 Wales, Bangor *. 



IN a celebrated memoir in the Annates de Chimie et de 

 Physique for 1834 f, Peclet describes a long series of 

 experiments in which he measured the intensity of electri- 

 fication produced by friction under various conditions as to 

 the nature, pressure, and velocity of the rubbing surfaces. 

 The results of the measurements are given as deflexions of a 

 pendulum electrometer connected to a metallic comb placed 

 near one of the rubbed surfaces : they indicate that in each 

 case the surface (if insulating) acquires, after a sufficient 

 amount of friction, a constant surface-density which is 

 independent of the pressure applied during the friction. 



Since Peclet' s experiments very little attention appears to 

 have been directed to the measurement of the charge pro- 

 duced bv the friction of solid bodies, and as it seems desirable 

 to obtain measurements in absolute units the following- 

 experiments were arranged with this object and, in particular, 

 to study the electrical charges produced by small amounts of 

 rubbing. 



(1) The Rubbing Apparatus. 



It was thought that the best way of stating the results 

 of these experiments would be to obtain curves showing 

 the charge produced by various amounts of work. The 

 apparatus was therefore arranged so as to enable simul- 

 taneous measurements to be made of the work done against 

 friction and the total charge produced on one of the rubbed 

 surfaces. 



The rubber consisted of a wheel, of considerable moment 

 of inertia, whose axle turned in fixed bearings and to which 

 a known amount of kinetic energy could be imparted bv 

 allowing a weight mg falling through a measured height h to 

 set it into rotation. The weight was attached to a cord 

 which passed over a fixed pulley in the ceiling of the room 

 and was wound round a pulley on the same axle as the wheel. 

 Neglecting the small amount of frictional work at the axles 

 of the pulleys, the kinetic energy communicated to the 

 wheel is then mgh — hnv 2 or mh (g—f), where / is the 

 acceleration of the falling weight and v the velocity with 

 which it reaches the floor. The acceleration f was small and 

 was measured by observing the time taken by the weight in 



* Communicated by Prof. E. Taylor Jones. 



t Ann. de Chimie et de Physique, lvii. (1834) p. 337. 



