84 HENRY A. ROWLAND 



Eliminating / between this equation and (1), we find 



At first sight this equation will appear to be the same as that of Max- 

 well; but on further examination we see that it is more general in the 

 value of q. 



Equation (3) is the correct equation to use in this case, and reduces 

 to that of Kohlrausch when L = 0. 



To see how this error will affect Kohlrausch's results, we must re- 

 member that he uses this equation to find the constant of his galvano- 

 meter, on which his whole experiment depends; and the error is so 

 interwoven with all his results .that an entire recomputation is neces- 

 sary, provided the data for calculating the coefficient of self-induction 

 of the galvanometer coils and earth inductor can be obtained. 



The equation 



t* tl 



* 2 + / 2 - 2 + /S 



does not hold when self-induction is considered ; and so his fundamental 

 equation (1) is not correct, containing a twofold error. 



The linear differential equation (3) is easily solved; but as the results 

 are complicated, it is hardly worth while at present, until a recalcula- 

 tion can be made. I prefer to solve it on the supposition that L is 

 small, and thus merely obtain a correction to Kohlrausch's equation 

 connecting t and t , after which equation (15) or (17) (Maxwell's ' Elec- 

 tricity/ art. 762) can be used when made more general by substituting 

 q for Om. 



As far as I have had time to go at present, the correction seems to 

 be in the direction of making Kohlrausch's determination more nearly 

 coincide with that of the Committee on Electrical Standards of the 

 British Association. Other engagements occupy my attention at pres- 

 ent ; but I hope to see these corrections made to an otherwise excellent 

 determination of this most important unit. 



London, August 4, 1875. 



