1897.] 



Contact Electricity of Metals. 



521 



WEEKLY EVENING MEETING, 

 Friday, May 21, 1897. 



Sm Edward Frankland, K.C.B. D.C.L. LL.D. F.R.S. 



Vice-President, in the Chair. 



The Right Hon. Lord Kelvin, G.C.V.O. D.C.L. LL.D. F.R.S. M.B.I. 



Contact Electricity of Metals. 



§ 1. Without preface two 95 years old experiments of Volta's were, 

 one of them shown, and the other described. The apparatus used 

 consists of : (a) a Volta-condenser of two varnished brass plates, of 

 which the lower plate is insulated in connection with the gold leaves 

 of a gold leaf electroscope, and the upper plate is connected by a 

 flexible wire with the sole plate of the instrument ; (6) two circular 

 discs, one of copper and the other of zinc, each polished and unvarnished, 

 I hold one in my right hand by a 

 varnished glass stem attached to it, 

 while on my left hand I hold the 

 other, which is kept metallically con- 

 nected with the sole plate of the 

 electroscope by a thin flexible wire. 

 To commence the experiment I 

 place one disc resting on the other, 

 and lift the two till the upper touches 

 a brass knob connected by a stiff 

 metal wire with the lower plate of 

 the Volta condenser. I break this 

 contact and then lift the upper plate 

 of the condenser ; you see no diver- 

 gence of the gold leaves. This 

 proves that no disturbing electric 

 influence sufficient to show any per- 

 ceptible effect on our gold leaf 

 electroscope is present. Now I re- i i^.. 1. 



peat what I did, with only this 



change — I hold the lower disc with the upper disc resting on it two or 

 three centimetres below the knob. I then with my right hand lift 

 the upper plate of the Volta-condenser ; you see a very slight diverg- 

 ence between the shadows of the gold leaves on the screen. I can just 

 see it by looking direct at the leaves from a distance of about half 

 a metre. Still holding the lower plate firmly in my left hand in 

 the same position, and holding the upper plate by the top of its 

 glass stem in my right, at first resting on the lower plate I lift it and 



