162 



THE ELECTRIC TELEGRAPH. 



pressed down, the current of c is sent through the line, and 

 passes through the coils of relays I and n to earth. Helay i 

 is unaffected, but relay 11 is put in action, and the Morse M I 

 in the local circuit (E t z, relay n, 3, 2, M 1? c, &c.) prints 

 whatever signals are given by K. 



When K' is depressed at the sending station, current Si is 



Fig. 89. 



transmitted, and the tongue of relay i deflected against the 

 local contact. Thus two local circuits are closed ; the first is 

 that including the battery E 2 , R, and the extra coils of relay 

 n, by which the action of the line current in this relay is 

 counteracted, and the tongue held still against the insulated 

 contact ; therefore M! does not respond to these stronger cur- 

 rents. The second local circuit is that of the Morse M and 

 battery E^ 



The intensity of the counteracting battery E 2 , whose mag- 

 netic effect upon the armature of relay n we will call S 3 , is 

 regulated by the interposed resistance R until it balances the 

 magnetising power of the line current sent by K'. 



The third case is that in which, during the manipulation 

 of the two keys, both happen to be pressed down together. 

 When this occurs the current S 2 of the whole battery goes 

 through both the relays I and n. Relay i is put in action 

 as before, and closes its printing circuit, and that of the 



