Pocket Watches. — A pocket-watch is very similar in principle to a good clock, except that the regulation of the former is by a ba lance and spring, hnd that of the latter by a pendulum. It would be a matter of some dif ficulty to determine what artist first reduced the portable spring-clock to the dimensions of a watch to be worn in the pocket. The small clocks prior to the time of Ilnyghens and Hooke were very imperfect machines ; they did not even profess to subdivide the hours into minutes and seconds until the invention of the balance-spring, which is to the balance what gravity is to the pendulum, and its intro duction has contributed as much to the im provement of watches as did that of the pen dulum to clocks. The honour of this inven tion was warmly contested by the last-named individuals previous to 1658 ; but, so far as priority of publication is concerned, the honour is due to Hooke.
When clocks and watches had acquired a certain degree of accuracy in their perform ance, the time lost in winding up (especially when it had to be done every twenty-four hours) became a matter of importance, and there have been several inventions to remedy this evil. By Huyghens the clock was kept going while winding up by means of an end less cord. The forcing spring gives another plan, in which a lever is so adjusted as to allow the wheels free movement, while the spring barrel is being acted on by the key. But Hartison's contrivance for the same pur pose is the one now in general use, both in clocks and watches, and is admirably adapted to the purpose, as it requires no attention from the person who has to wind up the ma chine, but is always in its place, and ready for action the moment the operation of winding is commenced. It is generally called the going fusee, but a better name for it is maintaining power. The principle of its action depends On the mode in which the fusee is fixed into a socket connected with the main wheel, so as to allow the wheel and the fusee to rotate independently of each other when required.
The word escapement is a term applied to a combination of parts in a clock or watch, which has for its objcot the conversion of the circu lar motion of the wheels into a vibratory mo tion, as exhibited in the pendulum. The component parts include the scape-wheel, the pallets with their arbor or axis, and a bent lever attached thereto, called the crutch, which last piece maintains the motion of the pendu lum. In a watch this combination consists of the scape-wheel, together with all those parts lying between it and the balance, and which are concerned in converting the circular mo tion of the wheels into the alternating one of the balance. The pallets act upon or between the pointed teeth of the scape-wheel by a reci procal or oscillatory motion.
In a common Vertical Watch, the barrel containing the spring is near one edge; and next to it is the fusee. The spring within the barrel, formed by a narrow strip of highly tem pered steel, is fastened at one end to the in terior of the barrel, and at the other to the axis or arbor of the barrel. A fine steel chain
runs from the exterior of the barrel to the ex terior of the fusee ; and, when the watch is wound up by the application of the watch-key to the arbor of the fusee, the chain is drawn from off the cylindrical surface of the barrel, and wound on the grooved surface of the fusee In this process the spring within the barrel becomes coiled round very tightly; and, it is the recoil or resistance of the spring which slowly pulls the chain back again to the and causes the fusee to rotate. The fusee is concentric with a toothed wheel, whose teeth act upon those of a second wheel, and those upon a third, and so on throughout the deli cate machine : one wheel rotating with such a velocity as to enable an index hand upon its axis to mark hours, another minutes, another (in a seconds-watch) seconds, and another to act upon the regulating or pendulum appa ratus.
One of the chief distinctive features in watches, and the one by which the name or designation is often determined, is the nature of the escapement. The duplex escapement so named from a French watchmaker, is much more intricate than the escapement of a com mon vertical watch. A vertical watch has the escapement perpendicular to the face of the watch, while a horizontal watch has the escape ment so formed parallel to the face of the watch. A lever watch has an escapement dif fering from all the others, which is preferred to those of either the vertical or horizontal watch. Earnshaw's detached escapement, in tended chiefly for chronometers, is considered to excel all others for the accuracy of its per formance.
The term repeater, or repeating watch, is ap plied to those watches which, in addition to showing the time on the dial, are supplied with mechanism for giving audible indication of the time when required. In an eight day spring clock, the number of blows given by the hammer to the bell corresponds with the hour denoted by the hand of the clock ; and there is an arrangement by which the pulling of a string may be made to denote the hour last struck. But, from the peculiar mechan ism involved, there are about ten minutes in every hour during which this repeating could not be produced. The filling up of this defi ciency is an object in a repeating watch or clock. Some of these watches strike only the hours and quarters ; while others, called minute repeaters, strike the minutes also. In a common watch, the wheels and pinions which are placed between the frame-plates constitute the going train ; while the wheels and pinions placed between the uppermost Nrame-plate and the dial, serving to communi cate the motion from the centre wheel to the index hands, constitute the ; but, in addition to these a repeating watch has another system of mechanism, called the re peagqg train, for the purpose of transmitting the movement frb,.„ ... motion-work to the hammers which are'to strike the hours and quarters.