8 L. Scliwendler — On the General Theory of Duplex Telegraphy. [No. 1, 



With respect to the variation of the three quantities K, R, and A., the 

 function S may therefore be expressed in three different forms. 



5 1 = e q 3-2" when K varies only. 



5 2 = e q — — 8-S when R, i. e., a varies only. 



5 3 = e q — ^ — S A when A., i.e.^JE or e or both are varying only. 



R 



These three different disturbances of balance may act singly or conjointly, 

 and it is clear that they are independent of each other, at all events as far 

 as this investigation is concerned. Consequently the safest plan will be to 

 make each influence as small as the circumstances will allow it. 



The disturbance S x for any constant eq X v \/b, and any given 8 K 

 will obviously become smallest the larger R K is selected. Supposing 

 R -f- K constant, whatever that value finally may be, R K has a maximum 

 for R = K, and the very same condition will obviously make the disturb- 

 ance S 2 smallest. 



$ 3 offers no best condition, this expression only shews that it has an 

 absolute maximum with respect to b, namely as 



R = a -f- d -f- &> for b = a + d. 



Thus we are informed that whatever relation between b and a -f- d may 

 be finally chosen, b = a -f d should not be selected, as otherwise any 

 given variation of A would have the greatest possible disturbing effect on 

 the balance. But b = a + d being the condition for the maximum mag- 

 netic effect in the compensation circuit, it is hereby established that for the 

 sake of regularity of signals, which under all circumstances is to be consi- 

 dered of paramount importance in Duplex Telegraphy, the magnetic effect 

 in the compensation branch must not be achieved in the most economical 

 manner, but quite the reverse. This, as the compensation circuit has actu- 

 ally to produce wholly or partly the duplex signals, is a testimonium pau- 

 pertatis for the compensation method, and proves it in this respect inferior 

 to both the double balance and the differential method. 



R = K 

 is the regularity condition for the compensation method, i. e. 



In order to make the disturbance of balance by a variation of the resis- 

 tance in both the circuits absolutely as small as possible, the total resistance 

 of the compensation circuit should be equal to the total resistance of the 

 line circuit.* 



* This result is against the adopted view, for Dr. Glutei as well as others after him 

 have always treated the compensation circuit as a kind of local circuit, i. c, giving to it 



