﻿22G L. Schwendler — On tie General Theory of Duflex Telegrajphy. [No. 4, 



which expression has a maximum with respect to both g' and g" considered 

 as independent variables, and such indeed according to the nature of the 

 problem they really are. 



Thus, differentiating P with respect to / and /', we get 



and 



But as the same kind of instruments are employed in both the stations, 

 we require evidently also the same force in both to produce the signals, no 

 matter what the state of the line may be. 



Thus we must put* 



p/ ^ p" 



or 



JE^ ^V g" 



". . . ^^ ~^-^' 



Substituting this value for the proportion of the e. m f., we get 



and 



but 



ana 



^,=/ + ^" + ^ 



^,^f + i' + i 



Substituting these values in the above equations and reducing ; and, 

 further, dividing the first equation by Z' -f * and the second by r -{- i, we 

 get at last 



and 



= 



* This supposition in" tlie case of a perfect line is fulfilled Idj itself, since then the 

 two instruments are not only of the same kind, hut absolutely identical. 



