CHAP. IV.] 



ELECTRIC TELEGRAPHY. 



601 



the motions of the pendulum of the departure and arrival station. 

 Not only must their oscillations be isochronous, but they must have 

 amplitudes perfectly equal, in order that the styles may move at the 

 two stations simultaneously and have at the same instant the same 



FIG. 392. Caselli's pantelegvaph. 



velocities. This result is obtained by the following arrangement. At 

 each extremity of the .arc which is described by the mass of iron of 

 the pendulum-bob is an electro-magnet, in the same direction as the 



