It would be a waste of time to describe the nature of wheels and pinions, as this kind of machinery is now so generally known. It may be sufficient to remark, that a clock or a watch movement is an assemblage of wheels and pinions, contained in a frame of two brass plates, connect ed by means of pillars, the first or great wheel of which, in an eight day clock movement, has concentric with it a cylindrical barrel, having a spiral groove cut on it. To this cylinder is attached one end of a cord, which is wrap ped round in the groove, for any determined number of turns, and to the other end of the cord is hung a weight, " " which constitutes a power or force to set the wheels in mo tion. Their time of continuing in motion will depend on the height through which the weight has to descend, on the number of teeth in the first or great wheel, and on the number of teeth or leaves of the pinion upon which this wheel acts, &c. The wheels in spring clocks and in watches are urged on by the force of 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 frustum 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. 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 con sequently take it off from the barrel. This bends up the spring ; and if the fusee and great wheel are left to them selves, the force exerted by the spring in the barrel to un bend itself, will make the barrel turn in a contrary direc tion 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 conside rable velocity. Their time of continuing in motion will depend on the number of turns of the spiral groove on the fusee, the number of teeth in the first or great wheel, and on the number of leaves in the pinion upon which the great wheel acts, Ste. The wheels in any sort of move ment, 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 ac tion of the force is constant from its first commencement, the wheels would be greatly accelerated in their course, and it would be an improper machine to register time or its parts. The necessity of checking this acceleration, and making the wheels move with an uniform motion, gave rise to the invention of the escapement, or 'scapement, as it is commonly called. To effect this, an alternate motion was necessary, which required no small effort of human ingenuity to produce.
On the Escapenzent,or 'Scapement.
THE escapement is that part of a clock or watch con nected with the beats which we hear them give ; and these beats are the effects of the moving power, carried forward by means of the wheels in the movement to the last one, which is called the swing wheel in a pendulum clock, and the balance 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 essential part in a 'scapement ; the drop from each tooth of the swing or balance wheels, on their respective pallets, giving one beat or impulse to the pendulum or balance, in order to keep up or maintain their motion ; and were it not for the pallets which alternately stop the teeth of the swing or balance w heels, the motive force would have no check. Hence it is, that, by this me
chanism of the 'scapement, the wheels in the movement are prevented from having their revolutions accelerated, which would take place to such a degree, as to make the machine run down in a minute or two ; ‘yhereas, from the resistance opposed by the pallets, it is kept going for twenty-four or thirty hours, for a week or a month, or even for twelve months. In the clocks or watches, however, which as a matter of curiosity have been made to go so long, it was not possible to have an accurate measure of tine.
No part of a clock or watch requires so mtn h skill and judgment in the contrivance of it, and so much care and nicety in its execution, as that of the 'scapement ; none of the 'scapements of the present day require this more than the ancient crown wheel and verge 'scapement, which, when nicely executed, upon the proper principle, does ex tremely well for a common pocket watch. But this is a thing hardly now to be met with. From the time of Dr Hooke, and during the last century, many ingenious con trivances for 'scapements were suggested ; but the num ber of them adopted in practice is very limited. The crown wheel and verge 'scapement is represented in Plate CCC. Fig. 2, where V is the verge, and C the crown wheel. p, p the pallets, and B B the balance. It is the old est that is known, and must have been the only one used in clocks, for several centuries, previous to the middle of the seventeenth, or towards the end of it. Although it has been so long in use, and so well known to every clock and watch-maker, that its merits are now overlooked, and held in little estimation, )et, if it is duly considered, it will be found to have been a very masterly and ingenious device. The crown wheel and verge are of such an odd shape, that they resemble nothing that is familiar to us. Yet some ancient artist had contrived it for the purpose (and it cer tainly was an ingenious thought) to give an alternate mo tion to a plain wheel, or cross, which he had suspended from the upper end of its axis by a string, or which at first might rest on the lower end of the axis or foot pivot. This plain wheel was like the fly of our common kitchen jack. In place of this circular rim, or plain wheel on the axis, there were some of them that had two arms upon it, forming something like a cross; on these were made a sort of notches, concentric to the axis, in which were hung a small weight on each arm, which, by shifting more or less from the centre, the clock was made to go slow or fast. From the weightiness of this kind of balance, and the rude execution of the work, the ft iction on the end of the foot pia 01 would be so great, that it is probable there was some ditfietnty to make the clock keep going for any length of time. R, course was then had to suspend the balance by a small cord. so that the end of the lower pivot should not rest on the foot of the potence. This ingenious idea has in modem times been adopted both by Berthoud and Le Roy, who have had the balances in some of their marine time-keepers suspended by a very small wire, or a very de licate piece of watch pendulum spring wire. The me chanism of the movement of these old clocks is exactly the same as has been frequently made for an alarm. To construct this, and apply it to a clock, there was hardly a step to go ; and therefore in all probability the invention of the alarm part took place before that of the striking part, though sonic have thought otherwise. The contrivance of the striking part was a more complex process, and less likely to take place * The alarm•clock is represented in Plate CCC. Fig. S.