History of the Typewriter

—305— It is maintained under a constant and even tension by means of two toothed wheels, one at each edge of the paper, the paper being pressed down upon the serrated periphery of the wheels by two small pressure rollers. The toothed wheels, are maintained under constant tension by means of a winding gear, which is operated by a magnet acting through an arm. As this arm oscillates a knife edge on its upper end strikes a small pinion at the foot of the shaft, on which is a flywheel, and causes it to spin, a worm above the pinion on said shaft engaging the worm wheel, and winding up the shaft on which this worm wheel is journaled. Upon the shaft, between the toothed wheels, are two helical springs, which are wound upon the shaft with sufficient friction to cause the rotation of said shaft to exert a. rotational effect upon said toothed, wheels, thus preserving a constant tension upon the paper. This tension is resisted by two pawls, which engage a toothed wheel, keyed firmly upon the steel shaft that carries the roll of paper. The pawls are operated by the pulsations of the magnet, and are brought into play whenever a new line is to be commenced, the releasing of the wheels allowing the paper to be unwound a quarter of an inch, which is the space between two successive lines. This escapement is provided with ingenious mechanism to compensate for the decreasing diameter of the roll of paper ; for it is obviously necessary that the escapement wheel should rotate through a larger arc when the roll is nearly exhausted than it does when the roll is full ; otherwise an even feed of a quarter of an inch could not be maintained at all times. The compensating gear consists of a curved wire, one end of which rests upon the roll of paper, while the other is attached to a vertical sliding bar, at the centre of which is carried 3. horizontal stop-piece. When the paper is to be drawn forward, one stop is released and another engaged, the amount of rotation of the escapement wheel being determined by the distance between the inclined face of the arm, which carries the escapement pin, and the opposing face of the stop-piece. By this arrangement it will be seen that as the roll decreases there is an equiva- lent increase in the amount of rotation of the escapement wheel at each release. The type-wheel is a small disc of brass with the alphabet cast in soft rubber around its periphery. This wheel is capable of rotation, oscillation and lateral or transverse motion. The ink roller, is carried on an arm of the carriage, and is inked every time it passes the ink-brush of the ink