1876.] L. Schwendler — On the General Theory of Duplex Telegraphy. 5 



K=f + a + c 



e 



r 



v = - 

 1 



Rigid fulfilment of the two functions S = o and D = o. 



For finite quantities these two functions can only become zero if A = 

 o, i. e., 



B sj a — R X v \/ b = o. 



which is the balance equation for the compensation method. 



To fulfil this equation permanently, no matter what the special cause 

 of disturbance may be, we can again adopt two essentially different modes 

 of re-adjustment, viz. :- — 



Either leave the two coils a and b or their armatures stationary, and 

 adjust balance by altering the resistance in one or both of the two circuits, 

 or leave the resistances constant and alter the relative position of the two 

 coils or their armatures with respect to a given magnetic pole. These two 

 methods of re-adjusting balance shall be considered separately. 



a. Re-adjustment of balance by altering resistances. 



In order to have immediate balance it will be clear that the alteration 

 of resistance must be restricted to the compensation circuit, which is elec- 

 trically independent of the line circuit. The total resistance in the compen- 

 sation circuit consists of three different resistances, namely b, a, and d. 

 Neither b nor a, considering their nature, can conveniently be made adjust- 

 able in practice ; hence the alteration of resistance in the compensation 

 circuit is restricted to d, which must therefore consist of increments of the 

 proper size. The adjustment of d should be quick and convenient. 



In addition to this adjustment, A. = — may be made adjustable by va- 

 rying TJ in increments of one cell. Such an adjustment is however not fine 

 enough for ordinary use. The E. M. E. of one cell is too large a quantity in 

 comparison with the total E. M. r. used in the compensation circuit. If the 

 variation of the line current becomes very great, it might perhaps be found 

 convenient to alter TJ, but as an ordinary mode of adjustment it must be 

 dispensed with.* 



* During the period of low insulation of the line it might be advisable and practi- 

 cable to make E larger than during the period of high insulation of the line (wet and 

 dry season). 



