572 THE APPLICATIONS OF PHYSICAL FORCES. [BOOK v. 



order of the corresponding letter on the dial. Underneath each key 

 is a tooth, which when the key is pressed down juts against a corre- 

 sponding peg as soon as the angle of rotation corresponding to the 

 latter is described. At this moment the motion stops, and the number 

 of transmissions and interruptions of the current effected is, as ,we 

 have seen, dependent on the order of the key or the letter. The needle 

 of the indicator has then passed over the same number of divisions, 

 and is then stopped at the letter sent. The key being let go the catch 

 e is lowered the tooth of the wheel B is held again until another key 

 being pressed down disengages it, and starts a fresh rotation and fresh 

 stoppage. 



FIG. 370. Froment's dial telegraph ; manipulator. 



Above the key-board is a dial whose needle moves with the trans- 

 mitter and serves as a check to the clerk who sends off a message. 



M. Eroment has constructed apparatus on this system which work 

 without clockwork movement. Those which possess this mechanism 

 for motion are constructed for working long lines. But all of them 

 according to the unanimous testimony of competent judges, work 

 w r ith surprising precision. Whatever may be the movements, says 

 M. Du Montcel, which are executed on the key-board, in whatever way 

 the keys are pressed down, as soon as the ringer rests on one of them 

 the corresponding letter appears on the dial. 



