52 



THE ELECTRIC TELEGRAPH. 



gently upwards against the contact-screw c at the other end, 

 and that an electric circuit is established, as is represented 

 in the figure, in which the positive pole of the battery v 

 is connected by a wire, w, with one end of the wire-coil 

 of the electro-magnet E, the other end of the wire-coil being 

 connected with the contact-screw c, by a wire, w', whilst a 

 third connection- wire, uf', joins the axis of the armature A, 

 with the negative pole of the battery. It is obvious that the 

 current circulates in the coils of the electro-magnet, magnetises 

 them, and causes the armature to be attracted to the poles, 

 leaving the contact- screw c, and thereby interrupting the 

 battery circuit. The instant this occurs, and the battery cur- 

 rent ceases to circulate in the coils, the soft iron cores of the 

 electro-magnet lose their magnetism, and have no longer the 

 power to retain the armature which is consequently lifted up 

 again by the spring s. On reaching its position of rest, it 

 makes contact again with c, and re-establishes the battery cir- 

 cuit. This is followed by an immediate interruption ; and the 

 same play must necessarily be repeated, the armature being 



Fig. 26, 



always re-attracted to the poles of the electro-magnet, break- 

 ing thereby the circuit, and being again let go, and making 

 the circuit again, and so on ad infinitum. 



The manner in which Dr. Siemens applied this method of 

 interruption to the service of his telegraph system will be 

 easily seen from the accompanying plan, Fig. 26. 



If we were to take the apparatus just described and attach 

 to the end of the armature, in any way, a continuation with 



