118 



THE ELECTRIC TELEGRAPH. 



arm so as not to be in metallic contact with the key. 

 circuit of the switch is made between a and b. 



The 



Fig. 63, 



The switch is shown in Fig. 64. It consists of a bent 

 metal beam, e e, supported by the uprights ef, and makes 

 contact at one end with the screw u, at the other by means 

 of a spring, /, with the screw w. The beam is held in its 



position of rest by the spiral spring s, and is deflected by 

 the attraction of a soft iron armature, a, to the poles of the 

 electro-magnet m. On the upright n is a tooth-wheel, w, 

 engaging with a pinion. On the axis of the latter is a fly, 

 and round that of the former passes a cord with a weight at 

 one end, the other end being attached to the extremity of 

 the beam. By this means the extremity of the beam may 



