472 



REPORT 1884. 



(this is not to be confused with Volta's summation or series law, which is 

 only applicable to metals), viz., that the total E.M.F. of a closed circuit 

 of any number of substances may be reckoned by adding up the Volta 

 forces observed electrostatically for every pair of substances in contact. 

 This law is, it seems to me, for reasons given later (7), very probable 

 theoretically, but still it was quite essential to have it experimentally 

 established, especially as they point out that it is often called in question 



Fig. 5. — End view of Ayrton and Perry's Apparatus. 



without good ground. The establishment of this law is, I say, perhaps 

 their main work in this matter, besides the observation of the Volta effect 

 for various difficult substances, especially liquids and liquids. 



Clifton arrives at the same conclusion with regard to summation, and 

 gives handy diagrams, reproduced in ' Jenkin's Electricity,' of tbe contact 

 force at the different junctions. My own opinion is that the intended 

 and obvious significance of these diagrams is theoretically wrong, but 

 they embody certain experimental results conveniently, and they can 

 be interpreted properly. 



Both Clifton and Ayrton and Perry appear to believe in the great 

 constancy of the value Zn/Cu. Clifton gives it as -8516 Volt. (' Quelle 

 precision ! ' somewhat sarcastically ejaculates Pellat, who himself finds it 

 to vary between '63 and - 92). Ayrton and Perry assert that it is more 

 constant than a Daniell. I believe that both Professor Clifton and Pro- 

 fessors Ayrton and Perry have made several experiments besides those 

 recorded in their communications to the Royal Society, but as they have 

 not been published I can give no account of them. 



Among the Theses presented to the Faculty of Science in Paris in 

 1881, we find an important memoir by Pellat, 1 which reviews the whole 



1 Theses presentees a la Faculte des Sciences de Paris, pour obtenir ie Grade de 

 Docteur-es-Sciences Physiques, par M. II. Pellat, Professeur de Physique au Lycee 



