ELECTRIC TELEGRAPHS. 



415 



duce an actual reversal, but merely that it should weaken the induced 

 magnetism of the cores sufficiently to enable the opposing spring to 

 overpower them. This is one of the most original parts of Hughes's 

 apparatus, and is a main cause of its extreme sensibility. 



The printing-shaft consists of two portions, one of which (I, Fig. 

 14) carries the fly-wheel (V), and turns uniformly under the action of 

 the clock-movement ; the other, which is next the front of the machine, 

 remains at rest when no current is passing ; but, when the armature of 

 the magnet rises, the two parts of the shaft become locked together 

 by means of the ratchet-wheel and click (i i'). 



The portion of the shaft which is thus turned every time a current 

 passes, carries a very acute cam or tooth (p, Fig. 15), which suddenly 

 raises the lever (a b), movable about an axis at one end (T), and, by so 

 doing, raises the paper against the type-wheel, and prints the letter. 

 In order thus to print a letter from the rim of a wheel which continues 

 turning, very rapid movement is necessary. This is secured by making 

 the opposing spring which moves the annature very powerful, and the 

 cam (p) very acute. The same movement of the lever which produces 



Fig. 15. 



Mechanism for Printing. 



the impression, raises the arm (J U), which carries a spring (r) with a 

 click at its extremity. This click, in its ascent, glides over the teeth 

 of the ratchet-wheel (E), but locks into the teeth and turns the wheel 

 in its descent, and, by so doing, advances the paper through the dis- 

 tance corresponding to one letter. The spacing of the words is ob- 

 tained by the help of the blank on the type-wheel. 



The type-wheel should admit of easy adjustment to restore it to 

 agreement with the chariot when accidental derangement may have 

 occurred. For this purpose the shaft (G) is made hollow, its internal 

 and external portions being merely locked together by the click (m), 

 which is held in its place by a permanent current in either direction. 

 On pressing down the button (Q, Fig. 13), the click (m) is raised by the 

 piece E, so as to leave the type-wheel free, and a pin is provided which 



