392 Telephone Systems of the Continent o/ Europe 



the test wire T (fig. 134), to forty ohms. When a ringing current 

 arrives from line and traverses the coil i, the armature K is attracted 

 and the lever L attached to it lifted, releasing in the ordinary way 

 the heavy iron shutter o turning on the pivot M. The shutter 

 falls, however, only a short distance, about five millimeters, just 

 far enough to strike against a small projection on the aluminium 



FIG. 13 



plate P, which is cocked up to a horizontal position by the shock 

 and discloses the number on the shutter o which it had pre- 

 viously covered. In the back of the shutter o is a hole into 

 which the projecting and sloping end of the core of the electro- 

 magnet j fits when o is upright. It does not fall far enough to 

 remove it from the attractive influence of j, so that when a plug is 



