The hands, G H, are moved by the cerf tral arbor which projects through the lower plate, E, (fig. 5) and receives a pinion of twelve teeth fixed on the end of a tube which fits tight upon the arbor, but will slip round easily to set the hands when the watch is wrong : the other end of the tube is square, and receives the minute hand, H, which points out the minutes on a circle of sixty upon the dial plate, M M; the pinion on the tube turns a wheel, L, of forty-e ight (seen in plans in fig. 3) on whose arbor is a wheel of six teen, turning another wheel, K, of forty eight, the arbor of which is a tube fitting on the other tube, and has the hour hand, G, fixed upon it ; by this arrangement the minute hand, H, turns round twelve times for one revolution of the hour band, G.
As the time the balance takes to per form a vibration depends upon the arc it passes through, the least increase of force in the main-spring would alter the rate of the watch ; therefore the fusee is cut into a spiral, diminishing from top to bottom, as the spring draws the chain with greater force when wound up than when it is more released. The chain acts upon a shorter lever when the spring is wound up, and upon a longer when it is down, so as to regulate the unequal ac tion of the spring to a perfectly regular force upon the wheel work.
As it will most probably happen that a watch will not always keep the same time, it is necessary' to have an adjustment that may cause it to move faster or slower :. this can be done by two ways, either by increasing or diminishing. the force of the
main-spring, a, which increases or dimin ishes the arc the balance describes ; or it may be done by strengthening or weaken ing the pendulum spring, a o, which will cause the balance to move quicker or slower. The first is done by turning the rachet wheel, b, (fig. 5 and 3) on the end of the arbor of the mainspring, thereby winding up or letting down the spring without turtling the fusee ; but as this is a very coarse adjustment, it is never used but by the maker, and recourse is had to the pendulum spring, a, (fig. 2) which is fixed to a stud, r, upon the plate, E, by one end, and the verge of the balance by the other : pis a small piece of metal, call ed the curb, having a notch in it to re ceive the spring : the acting part of the spring is from p to the centre ; and as the culb,p, is moveable, the acting length can be altered : the curb is cut into teeth, and turned by a pinion, v, (fig. 4) which represents the piece, asses, detached from the plate, E, and turned up : the pi nion, q, has a small dial, divided into thir ty, fixed to its arbor on the upper side of the plate, 8 a, by which it can be set so as to regulate the watch to the utmost nicety : t ce t (fig. 1) are four pillars, by which the two plates, E E, of the watch are held together ; and t tit (fig. 2) re present the heads of the' same pillars coming through the upper plate, and small pins put through to keep the plate down.