258 PLEASANT WA YS IN SCIENCE. 



message, writing, or picture, is spread. As the swing of the 

 pendulum begins, a similar pendulum at the receiving station 

 begins its swing; the same break of circuit which (by de- 

 magnetizing a temporary magnet) releases one, releases the 

 other also. The latter swings in an arc of precisely the 

 same range, and carries a precisely similar style over a 

 similar cylindrical surface on which is placed the prepared 

 receiving paper. In fact, the same pendulum at either 

 station is used for transmitting and for receiving facsimiles. 

 Nay, not only so, but each pendulum, as it swings, serves in 

 the work both of transmitting and recording facsimiles. As 

 it swings one way, it travels along a line over each of two 

 messages or drawings, while the other pendulum in its 

 synchronous swing traces a corresponding line over each of 

 two receiving sheets; and as it swings the other way, it 

 traces a line on each of two receiving sheets, corresponding 

 to the lines along which the transmitting style of the other 

 is passing along two messages or drawings. Such, at least, 

 is the way in which the instrument works in busy times. It 

 can, of course, send a message, or two messages, without 

 receiving any.* 



In Caselli's pantelegraph matters are so arranged that 

 instead of a negative facsimile, like Fig. 9, a true facsimile is 

 obtained in all respects except that the letters and figures 

 are made by closely set dark lines instead of being dark 

 throughout as in the message. The transmitting paper is 

 conducting and the ink non-conducting, as in Bakewell's 

 original arrangement ; but instead of the conducting paper 

 completing the circuit for the distant station, it completes a 

 short home circuit (so to speak) along which the current 

 travels without entering on the distant circuit When the 

 non-conducting ink breaks the short circuit, the current 



* It is to be noticed, however, that the recording pointer must 

 always mark its lines in the same direction, so that, unless a message is 

 being transmitted at the same time that one is being received (in which 

 case the oscillations both ways are utilized), the instrument works only 

 during one half of each complete double oscillation. 



