ELECTRIC TELEGRAPHS. 



409 



it away from g, and interrupts the current. The electro-magnet is 

 thus demagnetized, and the armature springs back against g, so as to 

 allow a fresh current to pass. The armature is thus kept in continual 

 vibration ; and a hammer (K), which it carries above, produces re- 

 peated strokes on a bell (T). 



Morse's apparatus, first tried in America about 183 V, is now per- 

 haps the most extensively used of all. 



His receiving instrument, or indicator, in its primitive simplicity, 

 consists (Fig. 9) of an electro-magnet, a lever movable about an axis, 

 carrying a soft-iron armature at one end, and a pencil at the other, 

 and a strip of paper which is drawn past the pencil by a pair of 

 rollers. 



Fig. 9. 



Morse's Telegraph. 



As the pencil soon became blunt, and was uncertain in its marking 

 a point, which scratched the paper, was substituted. This has now, 

 to a great extent, been superseded by an ink-writer, which requires 

 the exertion of less force, and at the same time leaves a more visible 

 trace. 



Fig. 10 represents Morse's indicator as modified by Digney. A 

 train of clock-work, not shown in the figure, drives one pair of rollers 

 {n m), which draw forward a strip of paper (p p) forming part of a 

 long roll (K). The same train turns the printing-cylinder (H), the sur- 

 face of which is kept constantly charged with a thick, greasy ink by 

 rolling-contact with the ink-pad (L). The armature (B B') of the 

 electro-magnet (A) is mounted on an axis at C, and carries a style at 

 its extremity just beneath the printing-cylinder. When a current 

 passes, the armature is attracted, and the style presses the paper 

 against the printing-cylinder, causing a line to be printed on it, the 

 length of which depends on the duration of the current, as the paper 

 continues to advance without interruption. The lines actually em- 



