﻿M. W. von Bezold's Investigations on the Electrophorus. 219 



or its surfaces are influenced. Moreover my entire theory may 

 be altered so as to fit in with Poggendorff's point of view, and a 

 decision between the two does not seem possible as long as we 

 have no clear conception of the manner in which electricity passes 

 to an insulating- surface. 



The experiment on which Eiess"^ bases his assumption of the 

 three layers in the electrophorus-cake is the following : — 



If a resin (shellac or ebonite) disk held in the hand be rubbed, 

 when tested by an electroscope it will exhibit negative electricity 

 on both surfaces. If, however, the disk be rubbed while it is placed 

 on a metal plate, the rubbed surface (A) will indicate negative 

 electricity, but the lower (B) none at allf. If now the nega- 

 tive electricity of the rubbed surface (A) be removed by passing 

 it through a flame, the positive electricity of the lower surface 

 (B) can be at once recognized, and the upper surface (A) will 

 appear unelectrical. If the lower surface (B) be then passed 

 through the flame it will be unelectrical, and the upper one 

 negative. By repeating this, first one and then the other sur- 

 face may be alternately made unelectrical. 



These experiments are quite correct, and may be very beauti- 

 fully repeated with the powder-mixture ; we shall subsequently 

 revert to them, when all the experiments relating to the theory 

 of the electrophorus have been described in their due connexion. 



To complete this series of experiments, it must be added 

 that, instead of laying the cake while it is rubbed upon a metal 

 plate, it may just as well be held in the hand and the unrubbed 

 surface afterwards passed through a flame. From these experi- 

 ments, Riess concludes that there are three electrical layers in 

 an electrophorus-cake rubbed while it is held in the hand. This 

 assumption is quite superfluous. Remembering the well-known 

 fact that the action of electricity at a distance is the less altered 

 by the interposition of an insulator the more perfect this insu- 

 lator, it is intelligible that a cake of such a material, after elec- 

 trifying one side, must exhibit exactly the same phenomena, even 

 if no other force is at work than that action at a distance. 

 For while by applying the rubbed side A the negative electricity 

 produced by friction passes directly to the electroscope, by ap- 

 plying the surface B the positive electricity excited by induction 

 in the electroscope will pass to B, and the electroscope will 

 therefore also diverge with negative electricity. 



If the disk lies during the rubbing upon a metal plate, in 

 consequence of the action at a distance exerted by this rubbed 

 surface, in this plate the electricity is separated, and positive elec- 



* Die Lehre von der Reibungselektricitat, vol. i. p. 294. 

 t This, however, is only the case if the rubbing was strong enough. 

 When feebly rubbed the disk acts just as if it were merely held in the hand. 



