Page:The American Cyclopædia (1879) Volume IV.djvu/713

 CLOCKS AND WATCHES 701 The oldest watch escapement was the verge and crown wheel, and had the train of wheels for the going part, as well as for turning the hour and minute hands, arranged in the same way as they were in the clock of Huygens. Fig. 8 represents the old-fashioned English rerge escapement watch. At a is shown the barrel containing the main spring; at 6 the fusee around which the chain is wound, con- structed in the form of a conical spiral to in- crease the leverage, as the spring diminishes in power by uncoiling ; c is the centre wheel, FIG. 8. Old English Verge Escapement. turned by the great wheel on the fusee by the centre pinion c' ; d is the third, and e the fourth wheel, which drives the crown and scape wheel f. The pallets p, p, moving to and fro upon the verge 0, which is the staff of the balance wheel A, regulate the time of escapement of the teeth. The minute hand i is placed upon the cannon pinion, and the hour hand j upon the barrel k of the hour wheel I. The arrange- ment for turning the hands is the same as that shown in fig. 16. The original lever escape- ment was invented in France by Hautefeuille about 1722, and differed much in its action from the detached lever now in general use. It is known as the rack and pinion lever, and is represented in fig. 9. The lever a has a rack, r, having the segment of a cog wheel at one end and pallets, A, A, at the other, and turning upon a pivot called the lever arbor, which is placed in the centre of the circle of which the rack is a segment. The bal- ance wheel <Z, by its vibrations, causes the pinion to carry the rack backward and forward, and conse- quently moves the pallets at the other end of the lever in about the same way they are moved by a pendulum. As, however, the arc through which the balance wheel moves is subject to considerable variation on account of the motion given to the watch in carrying, the differences in the extent of the vibrations of the pallets, and the constant lug between the rack and the pinion, caused an imperfection in the movement which was ob- viated by a modification invented by Mudge, which was called the detached lever, because the end of the lever which formerly carried FIG. 9. Rack and Pinion Lever of Hautefeuille. the rack, but which now was made in the form of a crotch or fork, was detached during certain parts of its oscillation. Fig. 10 represents the invention of Mudge, with several modifications in form which have since been devised. He placed the pallets one on each side of the lever arbor, instead of placing them at one end, opposite the fork, as in this figure. A pin in the roller which is placed over the arbor of the balance wheel, and a notch in the bottom of the fork, are so arranged that an alternate locking and detachment takes place at every escape of a tooth in the scape wheel. This detach- ment relieves the parts of the constant lug which existed in the rack and pinion, and allows the pallets to make perfectly equal vibrations, whether the balance wheel does or does not. This kind of lever is the one now in common use, and likely to be for a long time to come, as it is difficult to imagine any device better calculated to produce uniform motion in the train of wheels of a watch which is intend- ed to be worn in the pocket. The top of the scape wheel s is moving to the right, with a constant force derived from the main spring. The pallets a and b have been moved to the left, so that & is out of range, and a within range of the teeth. The tooth c has locked upon the dead surface of the pallet a. The balance wheel is now moving in the same direction as the scape wheel, its top to the right, and its lower part, which is cut away, to the left; the pin upon the roller of the balance wheel has entered the notch in the fork; as soon as it strikes the side below FIG. 10. Modern Detached Lever Escapement.