Page:Popular Science Monthly Volume 3.djvu/429

Rh 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 armature very powerful, and the cam (p) very acute. The same movement of the lever which produces



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 distance corresponding to one letter. The spacing of the words is obtained 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