26 



Inaiigural Address by the President. 



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E 



Fij 



In Figure 2 D represents an ordinary Voltaic cell — a plate of 

 copper and one of zinc connected and immersed in an oxidizing 

 electrolyte. A current flows with the arrows, round the circuit 

 copper, zinc, electrolyte, copper. 



Now, if we cut this circuit at a point in the copper, as shown 

 at E, we get a difference of potential between the copper ends 

 at the division, positive iri the part next the immersed portion 

 of the copper, negative in- the other end. Similarly if we cut 

 the zinc as at F, we get- tHe positive end above towards the 

 contact, negative end below, and if we divide through the 

 electrolyte as at G we have still the same effect, positive at the 

 side in which the zinc is immersed, negative in that containing 

 the copper. Now supposing we let this dividing diaphragm 

 through the electrolyte be composed of air, and let it gradually 

 increase so as to occupy so much of the space between two metal 

 plates that only a mere film of the electrolyte is left on each metal 

 surface, we have at once the whole effect as observed in the 

 Volta condenser experiment or in the contact experiment of 

 Lord Kelvin. I have shown this to be the case experimentally" 

 and, further, if instead of merely dividing a single electrolyte, 

 we use two electrolytes^" such as a layer of copper sulphate 

 solution on the copper, and zinc sulphate solution on the zinc^ 



15. Phil. Mag. VII., p. 110, 1879. 



16. Proc. Roy. Soc, XLI., p. 306, 1886, 



