80 THE ELECTRIC TELEGRAPH. 



A commutator is sometimes employed for directing the 

 arriving currents, at pleasure, through the indicator or 



through the alarm ; but, more usually, the alarm is inserted 

 in the same circuit, and when it is not required to give notice 

 of the arrival of a current, its coils are short-circuited by a 

 contact peg inserted in a hole between the terminals s s' of 

 the electro-magnet coils. 



The plan according to which two such instruments are 

 connected up for two stations is shown in Fig. 43, where the 

 line L is connected at each station to an alarm, A, which can 

 be short-circuited at s, if required ; the other side of the 

 alarm is connected with one side of the coils of the indicator 

 i by a wire, w ; thence a connection, ?*/, leads to the coil of 

 the transmitter or inductor T, and to earth. 



On turning the handle of the transmitter, the currents 

 pass, first of all, through the indicator of the home apparatus, 

 the pointer of which turns correspondingly with the handle ; 



