602 THE APPLICATIONS OF PHYSICAL FORCES. [BOOK v. 



arc, and having its armatures opposite the mass of iron when it arrives 

 at the end of each oscillation to the right or to the left. At this 

 moment a current introduced by a regulating chronometer seen on 

 the left at the top of Fig. 392 excites the electro-magnet and its 

 armature, which attracts the mass of the pendulum, retains it for an 

 instant, and consequently draws it out, at each oscillation, to the same 

 distance. The interruption of the current is made by the motion of 

 the pendulum of the chronometer, which at each double oscillation 

 separates a little spring and opens the circuit. The commutator, 

 whose business it is to open and close the circuit, also receives its 

 motion from a piece stiffly jointed to the rod of tlu pendulum. 



FIG. 393. Transmitter and indicatoi of Caselli's pantelegraph. 



In this way the regulation of the two pendulums at the departure 

 and arrival stations depends on the concordance of the movements of 

 the chronometer pendulums that accompany them. These regulating 

 chronometers, whose pendulums move with double the velocity of the 

 pantelegraph pendulum, are regulated separately as exactly as possible. 



The chemical paper on which the messages are printed must be 

 prepared with care and kept tolerably moist. The quality of the 

 paper itself is important. The metallized sheets on which the 

 messages are written in a particular kind of ink, are made of 

 white paper, carefully silvered and pressed, and having wide 

 margins. They have three boundaries one being the line from 



