WATCH-MAKING. The wheels in apring-clocks, and in watches, are urged on by the force t5 a spiral spring, con tained in a hollow cylindrical barrel, or box, to which one end of a cord or chain is fixed, and lapping it round the barrel, for several turns outside : the other end is fixed to the bottom of a solid, shaped like the frustrum of a cone, known by the name of the fusee, having a spiral groove cut on it : on the bottom of this cone, or fusee, the first or great wheel is put. (See FIIBEE.) The arbor, on which the spring-barrel turns, is so fixed in the frame that it cannot turn when the fusee is winding up : the inner end of the spring hooks on to the barrel arbor, and the outer end hooks to the inside of the barrel. Now, if the fusee is turned round in the proper direction, it will take on the cord or chain, and, consequently, take it off from the barrel. This bends up the spring ; and, if the fusee and great wheel are left to themselves, the force exerted by the spring in the barrel, to unbend itself, will make the barrel turn in a contrary direction to that by which it was bent up. This force of the spring unbending itself,' being communicated to the wheels, will set them in motion, and they will move with considerable velocity.
Their time of continuing in motion will depend on the number of turns of the spiral groove on the fusee, the num ber of teeth in the first or great wheel, and on the number of leaves in the pinion upon which the great wheel acts, &c.
The wheels, in any sort of movement, when at liberty, or free to turn, and when impelled by a force, whether it is that of a weight or of a spring, would soon allow this force to terminate ; for, as the action of the force is constant from its first commencement, the wheels would be greatly accelerated in their course, and it would be an improper ma chine to register time or its parts. The
necessity of checking this acceleration, and making the wheels move with a uni form motion, gave rise to the invention of the escapement, or 'scapement, as it is commonly called. To effect this, an al ternate motion was necessary, which re quired no small effort of human ingenuity to _produce.
The escapement is that part of a clock or watch, connected with the beats which we hear it give ; and these beats are the effects of the moving power, carried for ward by means of the wheels in the movement to the last one, which is call ed the awing-wheel in a pendulum clock, and the balane,e-wheel in a watch.
The teeth of this wheel act on the pallets or verge, which are of various shapes, and which form the most essen tial part in a scapement ; they drop from each tooth of the swing or balance-wheels, on their respective pallets, giving one beat or impulse to the pendulum or bal ance, in order to keep op or maintain their motion ; and, were it not for the pallets, which alternately stop the teeth of the swing or balance-wheels, the mo tive-force would have no check.
• Hence it is, that, by this mechanism of the Neapement, the wheels in the move ment are prevented from having their revolutions accelerated.