366 Prof. 0. Lodge on the Controversy 



separated : and let z' be the distance between the same sur- 

 faces at the instant when the hypothetical moist or liquid 

 connexion is likewise last broken : then in the dry case the 

 resultant charge is inversely proportional to c, being in fact 



9 



/'■- 



of the order 9()) , electrostatic units, for the usual case of 



circular disks ; whereas in the moist case z! must be sub- 

 stituted for c. 



Xow a very minute drop of liquid pulls out before it snaps 

 into a column ir tenths of a millimetre long, which then repre- 

 sents z' ; whereas the dry c may be a tenth or even a hundredth 

 of this magnitude, with well-made plates and careful mani- 

 pulation. 



I have emphasised this to negative any possible idea that I 

 regard moisture as an adverse fetish, acting discontinuous! v. 

 It is better away ; but, if it exists, its detrimental effect is a 

 mere arithmetical affair. 



Xo one. I hope, can now suppose that I imagine that 

 moisture is essential to the success of the experiment, though 

 in his Friday evening discourse to the Royal Institution. 

 May 1897, reprinted in the Phil. Mag. (July 1898), Lord 

 Kelvin says that there are signs in my British Association 

 Report (Phil. Mag. 1885) of a tendency to fall back upon 

 De la Rive's old [and utterly discredited] hypothesis that 

 the Yolta effect was due to oxidation of the zinc by moisture 

 from the air. He means, I expect, that I attach too much 

 importance to the action of oxygen (which may be true : a 

 word on that later), but never have I imagined it to be 

 needed in the form of moisture, nor have I ever wanted the 

 zinc to be actually oxidised. If it be perceptibly oxidised, 

 the Yolta effect is diminished. 



I say once more — in accordance, I believe, with everybody: — 



(1) Two metals connected wholly or partly by liquid are in 

 approximately the same electrical condition as if connected 

 wholly or partly by air. They do not become oppositely 

 charged unless they are at one (or more) point metallically 

 connected: then they do : and in order to be able fully to 

 display this charge on separation, the persistently-connecting 

 medium must be insulating, that is must be dry. i.e. free 

 from liquid. It must also be free from high-frequency 

 tetherial radiation or other ionising influence. 



(2) If the metals are connected both metallically and electro- 

 lvtically. metallically at one place and eleetrolytically at 

 another, we have a common voltaic cell and a continuous 

 current. 



(3) To complete the statement : — If the metals are con- 



