(331) The screw has fixed upon it, at its lower extremity, a small bevel pinion, gearing with a similar one placed loosely on the short shaft forming the centre for the arm. During the oscillation of the arm the pinion moves with it, and it is clear that if both remained in this position only this alternate action would occur, and no rotation of the screw would be made. If, however, the pinion on the short shaft be rotated it communicates its motion to the screw =P=, and thus traverses the nut. This is what takes place, and the precise method of effecting it will be described in detail at a little later period. The nut engages with the screw and originally had an eye or hook formed in it, to which the end of the winding chain or band =C= was fastened. The attachment is now made in a different manner, a frame =A= being fixed to the nut along with which it can slide. At the upper end of the frame a small drum is carried, round which the winding chain is wrapped, passing over a small bowl =D= at the lower end of the frame. The other end of the chain or band =C= is fastened to the drum or scroll =X^{ 1}= which is mounted on a shaft =X= carried in suitable bearings in the square. On the same shaft a spur wheel is geared which engages with a pinion loose upon the tin roller shaft, which it revolves by special mechanism afterwards described in detail. The use of a scroll is intended to accelerate the revolutions of the spindles during the latter part of the fallen traverse. This, like the winding arm, is a modified application of the fusee, and it will be easily understood that when the chain is being unwound from the larger diameter of the scroll, the number of revolutions given to the scroll will be less than when it is being taken off the smaller diameter.
(332) It has been previously shown that the diminishing diameter of the spindle causes it to be necessary that, as the cop is built higher upon it, a correspondingly higher rotary velocity shall be given to it, in addition to the increased terminal velocity produced in the manner described. The most usual method of doing this has been to provide at the end of the quadrant arm a bracket carrying a pin known as the “nosing peg.” The object of this device is to shorten the chain by deflecting it from a straight line about the time when the carriage nears the end of its inward run. This is equivalent to a sudden shortening of the chain, and gives a sudden acceleration to the winding drum. In some cases an automatic arrangement is fitted by which the peg is brought into contact with the chain at an earlier point every stretch, so that the acceleration of the spindle takes place sooner, as the nose of the cop is formed higher up the spindle. It is not difficult to obtain a clear notion of the action of the nose peg if a short length of string be held at one end and attached to a sliding piece at the other. If then the string be pressed down by a rod at the same point, but a little further every time, it will be seen that the sliding piece is moved to a greater extent with each depression.