WATCH, in the art of war, a number of men posted at any passage, or a com pany of the guards who go on the patrol.
At sea the term watch denotes a mea sure or space of four hours, becadse half the ship's company watch and do duty in their turn, so long at a time ; and they are termed starboard watch and larboard . watch.
WATcir is also used for a small porta ble movement or machine for the measur iug of time, having its motion regulated by a spiral spring. Watches, strictly ta ken, are all such movements as show the parts of time ; as clocks are such as publish it, by striking on a bell, &c. But commonly, the name watch is appropriat ed to such as are carried in the pocket, and clock to the large movements, whe ther they strike or not. See CHRONOME• TER, CLOCK, HOROLOGY• The several members ofthe watch part are, I. The balance, consisting of the rim, which is its circular part ; and the verge, which is its spindle, to which belong the two pallets, or levers, that play in the teeth of the crown wheel. 2. The potence, or pottance, which is the strong stud in pock et watches, whereon the lower pivot of, the verge plays, and in the middle of which one pivot of the balance-wheel plays ; the bottom of the potence is called the foot, the middle part the nose, and the upper part the shoulder. 3. The Cock, which is the piece covering the ba lance. 4. The regulator, or pendulum spring, which is the small spring in new pocket watches, underneath the balance. 5. The pendulum, whose parts are the verge, pallets, cocks, and the bob. 6. The wheels, which are the crown-wheel in pocket pieces, and swing wheel in pen. dulums, serving to drive the balance or pendulum. 7. The contrate-wheel, which is that next the crown-wheel, &c. and whose teeth and hoop lie contrary to those of other wheels ; whence the name. 8. The great or first wheel, which is that the fusee, &c. immediately drives : after which are the second wheel, third wheel, &c. 9. Lastly, between the frame and dial-plate is the pinion of report, which is that fixed on the arbor of the great wheel, and serves to drive the dial-wheel as that serves to carry the hand.
Plate Watch represents the parts of a watch the proper size: fig. 1, is a plan of the wheel work, the upper plate (fig. 2) being removed to expose them ; fig. 2 is the upper plate, the cock, F, (fig.5) being taken away to show the balance ; fig. 3, the wheel work beneath the dial ; fig, 4, a detached part ; fig. 5, a general eleva tion of the whole, being supposed to be set out at length to show the whole at one view ; fig. 6, the great wheel ; fig. 7, the under side of the fusee; fig. 8, the main spl•ng, barrel, &c.
The essential difference between a clock and a watch consists in two par ticulars : first, it is moved by a spring in lieu of a weight ; and, secondly, its motion is governed by a balance instead of a pen dulum. The balance is a small wheel, n, (fig. 2 and 5, Plate Watch) fixed on an arbor, or axis, called the verge, and turn ing freely upon pivots at the ends of the arbor. To the axis of the balance the in ner end of a very elastic spiral spring, a, called the pendulum spring, is fastened, and the outer end of the spiral is made fast to some fixture, r: in this state the balance will have a position of rest, which will be when the spiral spring, o, is in,that position which it would assume when de tached from the balance, and perfectly at liberty : now if the balance is turned round on its pivots by any external force in either direction, it will wind up or unwind the Spiral spring, which will (when the exter nal force is removed) return the balance to its state of rest ; and as this is done with considerable velocity, the momentum the balance acquires by its motion will carry it beyond the point of rest on the other side. This again alters the spring, which returns the balance, throwing it beyond the point of rest t and in this manner the balance will vibrate, until the friction of the pivots and the resistance of the air destroys the original impulse. All vibrations of such a balance, which pass through eqnal spaces, will be performed in equal times.