﻿228 L. Schwendler — 0)i the General Theory of Duplex Telegraphy. [No. 4, 



The resistance of tlie h branch in each station can now be easily cal- 

 culated from the balance equations and the values given for g' and g\ 



The value of the h branch must be calculated to enable as to 

 ascertain that maximum part of 5 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 signals, 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 general- 

 ly 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 shew that 

 the relation a =: d = g =y represents also the maxima currents that are 

 possible under the circumstances. As this investigation is of great impor- 

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

 fully gone into. 



Maxima Cuerents. When considering the question of currents, for 

 any telegraphic circuit, the two conditions which invariably should be ful- 

 filled are : 



Firstly. — 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 arrangements adopted ; but so 

 much is certain, that from a practical point of view, the first condition (con- 

 stancy 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 produce the 

 signals in Duplex Telegraphy, before going to the condition of maximum 

 current, we must ascertain first the condition oi 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 dis- 

 turbances were considered with respect to one and the sajjie 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 at 

 once that the fulfilment of the immediate balance condition is required also 



