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XXXI. The Contact Theory of Voltaic Action. By W. E. 

 Ayrton and John Perry, Professors of the Imperial College 

 of Engineering, Tokio, Japan. 



To the Editors of the Philosophical Magazine and Journal. 



The Imperial College of Engineering, 

 GENTLEMEN, Tokio, Japan, December 14, 1877. 



WHEN contributing his paper, " On the Difference of 

 Potential produced by the Contact of Different Sub- 

 stances." to the Royal Society on May 22, 1877, Professor 

 Clifton, of Oxford, seemed to be quite unaware of the elaborate 

 series of experiments on exactly the same subject made by us 

 in the winter of 1875, a fall account of which was communi- 

 cated in a paper on " The Contact Theory of Voltaic Action, 

 Paper No. I.," to Professor Sir William Thomson, May 6, 

 1876, who at the British- Association Meeting at Glasgow of 

 that year gave a public account of the method employed by 

 us and the results we obtained, reserving our complete paper 

 for the pages of the Proceedings of the Royal Society. 



If the investigation in question had been of merely ordinary 

 importance, we should not have deemed it necessary to point 

 out the priority of our experiments to those of Professor 

 Clifton ; but when the fact is remembered (a fact not very 

 evident from Professor Clifton's paper) that a series of expe- 

 riments such as we performed clears up the long-standing 

 discrepancies between the chemical and contact explanations 

 of voltaic phenomena, and so is of extremely great importance 

 in the science of energy, we trust we may be pardoned for 

 claiming the priority due to us. Much of the ordinary original 

 work performed in physical laboratories must, of course, be 

 undertaken nearly simultaneously in different countries ; and 

 our great distance from Europe necessarily places us in tl e 

 unfortunate position of being some months in time behird 

 other men who publish papers in the same societies as our- 

 selves ; but in this particular case the work was not of an 

 ordinary kind, and we have not to ask for the indulgence of 

 scientific men in making allowance for our residence in Japan, 

 seeing that, first, our paper reached England exactly one year 

 before Professor Clifton's communication was made to the 

 Royal Society, and, secondly, Sir W. Thomson was so kind 

 as to give an account of our method and results to the 

 British Association several months before Professor Clifton 

 appears to have commenced his earliest experiments on the 

 subject. 



The method of experimenting employed by this gentleman 

 is essentially the same as that used by ourselves, with this im- 



