of Duplex Telegraphy. 529 



method, quite immaterial whether the same or opposite poles 

 of the two line-batteries are connected to earth. As pointed 

 out, it is preferable to connect the same poles, i. e. the nega- 

 tive poles, of the line-batteries to earth. 

 Assuming this case, we have 



p' =AW-BV, 



Q'^A'-iTK-BV. 

 Substituting now for A', W, and <&' their values, and re- 

 membering that 



&=^ WT , 



_ J > approximately, 

 n' =r' s/b' J 



3S 



i 



n =r \/b r 

 we get the following general expressions for the two functions 



and 



D' = 



e' 



B/K' 



A f 

 pi sfa~i 



S"= 



A" 

 e"a" , 



D"= 



e " . 



K' 



A! 4 



r 



for station I. 



R"K' 



s/a" 



for station II., 



where 



A = R\/rt— K\v*/b, 



K=/+a + c, 



e 



v= -• 

 9 



Rigid fulfilment of the two functions S = and D = 0. 

 For finite quantities these two functions can only become 

 zero if A = 0, i. e. 



which is the balance-equation for the compensation method. 



To fulfil this equation permanently, no matter what the spe- 

 cial cause of disturbance may be, we can again adopt two 

 ess entially different modes of readjustment, viz. : — 



Either leave the two coils a and b or their armatures sta- 

 Phil. Mag. S. 5. No. 7. Suppl Vol. 1. 2 N 



