554 THE APPLICATIONS OF PHYSICAL FORCES. [BOOK v. 



in the two. The signals sent are thus reproduced at the same 

 instant. 



The two needle telegraph of the same inventors is based on the 

 same principle as the preceding. The two apparatus of the sending 

 and receiving stations are each composed of a double galvanometer 

 and a double manipulator, independent of each other. The clerk who 

 works them, takes, in his two hands, the two handles which move the 

 manipulators to the right and left, he then turns them in one direction 

 or the other, separately or simultaneously, so as to produce the signals 

 which constitute the alphabet and the figures of which Fig. 353 is 

 the table. 



FIG. 353. Vocabulary of the two needle telegraph. 



At the top of the apparatus (Fig. 352) is the alarum which 

 announces the sending off of a message. On the side are two 

 metallic bands which put the alarum in communication with the 

 current in the line. The receiving clerk, as soon as warned, replies by 

 a concerted signal that he is ready to receive he then turns the 

 handle seen at the side of the apparatus, so as to stop the communica- 

 tion with the alarum, and interrupt the ringing during the time the 

 message is being received. 



The dial placed below the handles of the manipulators is provided 

 with a needle, which, according to its position on the dial, cuts off 

 such and such stations on the line from the action of the current, 

 or divides the line into two independent parts. This is called the 



