HISTORY AND PROGRESS. 



137 



with their south ends in contact with a stout plate, p, of 

 soft iron in the same way as in the transmitter of the 

 magneto-electric pointer telegraph of the same inventors. 

 Between the poles of this system, and oscillated in an angle 

 of a few degrees by means of a handle, H, in the frame be- 

 tween two screw points, is the soft iron armature, as long as 

 the magnet system is wide, 

 cut in deep longitudinal 

 grooves, on opposite sides, 

 as is shown by the sec- 

 tional sketch Fig. 67. In 

 these grooves the coil c 

 of fine insulated wire is 

 wound. The play of the 

 handle is limited by two 

 adjusting screws in the 

 frame A. When at rest, 

 the handle is held against 

 the upper screw by a 

 spiral spring, s, stretched 

 between the handle and front of the triangular piece D on 

 the top. 



One end of the coil of wire on the armature is attached 

 to the screw k, on the terminal K, from which one connec- 

 tion goes to line and another to the screw w, at the foot of 

 the frame A. The other end of the coil is connected with 

 the metal frame supporting the armature, and through the 

 axis/, to the upright support Q, from which a leading wire 

 goes to terminal t and earth. 



"When a current arrives while the instrument is in circuit 

 with the line, it goes from L over R, w, upper adjusting 

 screw in A, through handle H, axis /, Q, t, earth, without 

 traversing the coil. This is the purpose of the connection 

 between R and w. 



When the handle is pressed down, the polarity of the 

 armature is reversed, and a positive magneto-electric current 

 induced in the coil, which circulates also in the line wire, 

 and deflects the tongue of the polarised relay at the receiv- 



Fig. 76. 



