418 



THE POPULAR SCIENCE MONTHLY 



be produced which will be the exact reproduction of the broken line 

 of the dispatch traversed by the style. Accordingly, when the style 

 of M has described a series of lines close together and covering the 

 sheet, R will be covered with a series of points or lines forming a copy 

 of the dispatch. The tracing point is carried by a lever turning about 

 an axis near its lower end. To this lower end is attached, a connect- 

 ing rod, jointed at its other end to the pendulum (Fig. 17). While 

 the pendulum swings in one direction, the style traces a line in one 

 direction on the sheet. At the end of this stroke, an action occurs 

 which, besides advancing the style, raises it, so that it does not touch 

 the sheet during the return-stroke. 



The synchronism of the pendulums at the two stations, which is 

 absolutely necessary for correct working, is obtained by means of two 

 clocks which are separately regulated to a given rate, the clock-pen- 

 dulums making two vibrations for one of the telegraphic pendulum. 

 The bob of the latter consists of a mass of iron, and vibrates between 

 two electro-magnets, which are made and unmade according to the po- 

 sition of the clock-pendulum, as the latter makes and breaks the circuit 

 of a local battery. The mass of iron is thus alternately attracted by 

 each of the two magnets as it comes near them, and is prevented from 

 gaining or losing on the clock. 



Fig. 18. 



Fig. 19. 



.^^K*3\\ 





"^^SSSij^^^e-z 



FAo-sraniiE op Dispatch. 



Copt on Tin-foil. 



It is evident that the Caselli telegraph may be applied to copy not 

 only letters, but a design of any kind ; hence the name of pantelegraph 

 which has been given it. Fig. 18 represents a copy thus obtained 

 upon Bain's paper. Fig. 19 represents a copy, obtained at the same 

 time upon a sheet of tin-foil, such as is usually placed beneath the 

 paper. The current decomposes the moisture of the paper, and the 

 hydrogen thus liberated reduces the oxide of tin, of which a small 

 quantity is always present on the surface. If the foil be then treated 

 with a mixture of nitric and pyrogallic acid, the traces are developed, 

 and come out black. 



The Caselli system has been used for some years on the telegraphs 



