CHAP, iv.] ELECTRIC TELEGRAPHY. 599 



thrown into the circuit A B c D, which offers a much more feeble 

 resistance than the line-wire, whose length is relatively considerable^ 

 and the current passes to the ground at the sending station. The 

 indicator is not influenced, and receives nothing. 



When, on the contrary, the style of the manipulator touches the 

 insulating parts, that is, rests on the marks of the writing or drawing 

 of the message, the circuit in A B c D is closed, but it is open in the 

 line, and a current is sent into the style s' of the indicator. Under 

 the influence of this current the point on the cyanurated paper 

 through which the current passes on its way to the ground is acted on 

 chemically ; a decomposition of the cyanide takes place, with a pro- 

 duction of Prussian blue, and its impression on the paper. This 

 impression is produced every time the style of the manipulator 

 encounters the parts marked with insulating ink, and the number of 

 marks and their length on each of the lines passed over at the same 

 time by the two styles will be identical at the receiving and sending 

 stations. The message will be identically reproduced on the cyanurated 

 paper in blue marks. The only difference from the original consists 

 in the successive lines not being in absolute contact, and the marks in 

 the message reproduced not being therefore rigorously continuous. 

 The effect is analogous to that produced by the very fine parallel lines 

 with which the engraver in a wood engraving in relief covers all the 

 surface left in relief on the wood. Figure 391 gives a very exact idea 

 of this difference, but we see that the general form of the original 

 message is not at all altered, and that this telegraph has a good right 

 to be called the autographic telegraph. 



The telegraph whose principle we have just described is M. Caselli's. 

 Since there is nothing to prevent the reproduction in this way of all 

 sorts of writing, drawings, or any kind of signs, provided they are 

 traced on the proper metallic paper, we can understand the reason of 

 the name pantelegrapli given to the apparatus of this system. 



We may now enter somewhat into detail on the manner in which 

 the preceding arrangements are realized, and on the mechanism of 

 the indicator and manipulator. 



The motive power in Caselli's pantelegrapli is a pendulum, whose 

 metallic rod of two metres length is suspended from a solid iron frame- 

 work, the bob being a rectangular mass of soft iron weighing eight 

 kilogrammes. In the middle of the rod two cranks are fixed for 



