HISTORY AND PROGRESS. 167 



nent magnets M, M 1 . c is a switch, the terminals a, b, and c 

 of which are respectively connected with the transmitter, 

 receiving instrument, and line. One end of the coil i, i 1 is 

 in permanent connection with the centre c of the contact- 

 lever L, and the other end with the terminal a of the switch. 

 The contact-point 2, against which the lever L, L 1 plays, is to 

 earth ; and, lastly, the side b of the switch is connected by a 

 wire to the coils of the polarised Morse, and thence to earth. 

 If the inductor i be turned round between the poles of the 



Fig. 90. 



permanent magnets M, M 1 , whilst L 1 rests against the insulated 

 point 1, and the arm of 'the switch c is on a, the currents in- 

 duced in the wire will meet with an infinite resistance between 

 L 1 and 1, and no impulse will be transmitted through the 

 line ; but if L be lifted up, and the contact between L 1 and 

 2 established, the currents will pass from the coils i, I 1 (c, 

 L 1 , 2) to earth, and on the other side from i, i 1 (a, c, I) to 

 line, and at the distant station, through the Morse instru- 

 ment, to earth. 



When the arm c is put on b, the transmitter is cut out of 

 circuit, and the currents arriving pass from line (7, c, 5, A) 

 to Morse and earth. 



The types, which are set up in a composing-rule in order, 

 like printing-types, are made of- thin pieces of metal cut in 

 teeth, in forms resembling those shown in Fig. 92, represent- 



