Prof. Thomson on the Mechanical Theory of Electrolysis, 431 



of the earth's magnetic action on the current through it, will 



be expressed by the integral / coz.Y.r^dz; as is easily proved, 



whether the current be supposed to pass directly between the 

 centre of the disc and the point of its circumference touched by 

 the fixed wire, or to be, as it in reality must be, more or less 

 difiused from the direct line, on account of the lateral^extension 

 of the revolving conductor. Hence we have 



W=|r2F7a). ...... (3) 



5. Let E denote the quantity (in units of matter, as grains 

 for instance) of one of the elements concerned in the chemical 

 action, which is electrolysed or combined in the unit of time, and 

 let denote the quantity of heat absorbed in the chemical action 

 during the electrolysis or combination of a unit quantity of that 

 element. Then we have 



e = ^.E (4) 



M=J.6>E (5) 



Now it has been shown by Faraday, that in electro-chemical 

 action of any known kind, produced by means of a continuous 

 current, the amount of the action in a given time is approxi- 

 mately if not rigorously proportional to the strength of the cur- 

 rent ; and all subsequent researches on the subject have tended 

 to confirm this conclusion. The only exception to it which, so 

 far as I am aware, has yet been discovered, is the fact established 

 by Faraday, that various electrolytes can conduct a continuous 

 current, when the electro-motive intensity is below certain limits, 

 without experiencing any continued decomposition*; but from 

 it we may infer as probable, that in general the quantity decom- 

 posed with high or low electro-motive intensities is not quite 

 rigorously proportional to the strength of the cm-rent. 



This non-electrolytic conducting power is, however, at least 

 in the case of water, found to be excessively feeble ; and it is 

 not probable that when electrolysis is actually going on in any 

 ordinary case, the quantity of electricity conducted by means of 



* It is probable that when an electromotor of an intensity below a cer- 

 tain limit is put in connexion with two platinum electrodes immersed in 

 water, there is at the first instant no electrolytic resistance ; and a decora- 

 posing current passes which gradually falls off in strength, until the elec- 

 trodes are, by the separated oxygen and hydrogen, put into a certain state, 

 such that with the water between them, they exert a resisting electric force 

 very nearly equal to that of the electromotor; after which a uniform cur- 

 rent of excessively reduced strength passes without producing further de- 

 composition. I hope before long to be able to communicate to the Maga- 

 zine an account of some experiments I have made to illustrate these cir^ 

 cumstances. 



2G3 



