Faraday. 197 



because it appears insoluble. " I said once to Faraday," wrote 

 Stokes to his father-in-law in 1879, " as I sat beside him at a 

 British Association dinner, that I thought a great step would 

 be made when we should be able to say of electricity that 

 which we say of light, in saying that it consists of undula- 

 tions. He said to me he thought we were a long way off that 



yet."* 



For his next series of researches,! Faraday reverted to 

 subjects which had been among the first to attract him as an 

 apprentice attending Davy's lectures : the voltaic pile, and the 

 relations of electricity to chemistry. 



It was at this time generally supposed that the decomposi- 

 tion of a solution, through which an electric current is passed, 

 is due primarily to attractive and repellent forces exercised on 

 its molecules by the metallic terminals at which the current 

 enters and leaves the solution. Such forces had been assumed 

 both in the hypothesis of Grothuss and Davy, and in the rival 

 hypothesis of De La Eive ;+ the chief difference between these 

 being that whereas Grothuss and Davy supposed a chain 'of 

 decompositions and recompositions in the liquid, De La Rive 

 supposed the molecules adjacent to the terminals to be the 

 only ones decomposed, and attributed to their fragments the 

 power of travelling through the liquid from one terminal to the 

 other. 



To test this doctrine of the influence of terminals, Faraday 

 moistened a piece of paper in a saline solution, and supported 

 it in the air on wax, so as to occupy part of the interval 

 between two needle-points which were connected with an 

 electric machine. When the machine was worked, the current 

 was conveyed between the needle-points by way of the 

 moistened paper and the two air-intervals on either side of it ; 

 and under these circumstances it was found that the salt under- 

 went decomposition. Since in this case no metallic terminals of 

 .any kind were in contact with the solution, it was evident that 



* Stokes's Scientific Correspondence, vol. i, p. 353. 



t Exp. Res., 450 (1833). Cf. pp. 78-9. 



