72 THE ELECTRIC TELEGRAPH. 



The wheel commutator R, the tongue d, and contact anvil x, 

 are provided to regulate the interruptions of the currents. 

 The wheel has on its circumference thirty teeth, which, in 

 the course of one revolution, lift the hammer, therefore, 

 thirty times from its contact with the anvil. 



When the armature of the electro-magnet is attracted to 

 the poles, a tooth of the wheel R lifts up the hammer from 

 the anvil, and interrupts the circuit, the electro-magnet 

 immediately becomes demagnetised, and the armature falling 

 off again, depresses the fork of the escapement, and allows 

 the scape-wheel to advance six degrees together with the 

 wheel commutator, R. By this means, contact is re-established 

 between d and x y the tooth which separated them passing by, 

 and the end of the hammer d falling into a space. 



The electrical circuit is shown in the figure by wires, and 

 in following the motions of the scape- wheel, contact- wheel, 

 R, &c., it is necessary to imagine a battery inserted between 

 T' and m. The current, then, goes from the + pole of the 

 battery, following the arrows along the circuit T', n t d, x y 5, 

 coils of M, to the > pole of the battery. 



In this way the pointer keeps on running round the dial 

 as long as the maintaining power of the clockwork lasts. 

 The motion may be arrested either by breaking the battery 

 circuit, in which case the armature falls off, and the fork- 

 escapement rests on the upper surface of the scape- wheel, or 

 by arresting the pointer itself. The latter is the method 

 employed in telegraphing ; the key over the dial, corres- 

 ponding to any letter, on being pressed down, interposes a 

 peg which bars the further progress of the pointer, and, 

 in this respect, resembles the arrangement of Siemens and 

 Halske's pointer telegraph. 



When it is wished to advance or to put back the pointer 

 on the dial, at any station, without the assistance of the 

 current, this is done by pressing on the button of the lever 

 T > P> <I> which presses the armature against the electro- 

 magnet, and lifts the fork. 



54. An alarm used with this telegraph is rung by the release 

 of a soft iron armature from the poles of an electro-magnet. 



