120 Mr. L. Schwendler on the General Theory 



The resistance of the b branch in each station can now be 

 easily calculated from the balance equations and the values given 

 for g' and g 11 . 



The value of the b branch must be calculated in order to be 

 able to ascertain that maximum part of b which will have to be 

 made variable in increments for the purpose of adjusting balance ; 

 and to this interesting question we shall revert further on. 



The general solution of the problem might now be considered 

 complete if it were not for the currents which produce the sig- 

 nals, of which we do not know as yet with certainty that we have 

 the maxima in the solution given above. It must, however, be 

 understood that this solution represents the only true one from 

 our physical point of view, and that, if it should not be identical 

 with that giving the maxima currents when considered generally 

 by themselves from the beginning, the solution would not be 

 thereby invalidated, but only the duplex method in question 

 would prove to be not quite so perfect as could be desired. The 

 sequel, however, will show that the relation a=d=g=f repre- 

 sents also the maxima currents that are possible under the cir- 

 cumstances. As this investigation is of great importance in 

 forming a correct opinion of the value of the method, it will be 

 fully gone into. 



Maxima Currents. — When considering the question of cur- 

 rents for any telegraphic circuit, the two conditions which inva- 

 riably should be fulfilled are : — 



First. Greatest possible constancy of current. 



Secondly. Maximum current. 



How far these two conditions can be fulfilled simultaneously 

 depends clearly on the special circuit and the special arrange- 

 ments adopted ; but so much is certain, that, from a practical 

 point of view, the first condition (constancy of current) will 

 always be of far greater importance than the second, inasmuch 

 as the required strength of currents can be obtained by employ- 

 ing cells efficient in kind, sufficient in number, and properly 

 arranged to suit requirements. 



Thus in our case, when we consider the currents which pro- 

 duce the signals in duplex telegraphy, before going to the condi- 

 tion of maximum current we must ascertain first the condition 

 of greatest possible constancy of current. 



Now it has been proved before that immediate balance in each 

 station is requisite in order to make the effect of any disturbance 

 on the receiving instrument as small as the circumstances will 

 allow of. But as these disturbances were considered with 

 respect to one and the same instrument (i. e. independently of the 

 magnetic moment), these disturbances are then simply due to 

 the disturbances in the signalling current ; from which it follows 





