CHAP, in.] ELECTRIC TELEGRAPHY. 557 



Henley's needle telegraph has for its moving agent a magneto- 

 electric machine. An electro-magnet is made to turn in front of the 

 poles of a strong permanent magnet in the form of a horse-shoe : by 

 means of a little ivory knob which is pressed by the finger, an induced 

 current may be set up, which circulates in the line and the indicator, 

 and as soon as the finger is raised, a second current passes in the 

 opposite direction. The indicator is itself an electro-magnet provided 

 with two pieces of soft iron at its two poles, and between these two 

 pieces, which are in the form of a horse-shoe, is placed a magnetized 



FIG. 357. Manipulator of Foy and Breguet's needle telegraph. 



needle whose deflections are repeated by an indicating needle mounted 

 parallel to it on the same axis. The signs in Henley's telegraph are 

 similar to those of Morse's as described further on. 



Toy and Breguet have invented a needle telegraph, reproducing 

 the signals of Chappe's air telegraph. This system has been worked 

 since 1845 between Paris and Eouen (145 kilometres), and has given, 

 as it appears, excellent results. Like Wheatstone's two needle tele- 

 graph it required two lines of wire but the inventors have constructed 

 apparatus with a single needle only which require but one line and 

 still give from 100 to 120 signals a minute. 



