704 CLOCKS AND WATCHES end of the spring is attached to the barrel arbor, the exterior portion of which is shown at a, and squared, to admit of winding by a key. The other end of the spring is attached to the FIG. 15. Train of Wheels In a Detached Lever. inner surface of the barrel. The arbor carries a ratchet wheel, which is prevented from turn- ing back by a click. The centre wheel d is driven by the action of the great wheel upon its pinion <*, called the centre pinion. The centre wheel drives the third wheel /, by means of its pinion i, and the third wheel again drives the fourth wheel A, which carries the seconds hand, in a similar manner. The fourth wheel drives the pinion i of the scape wheel _;, whose teeth again alternately lock and impel the pallets / I, which are placed on the pallet arms of the lever. The lever turns upon the pallet arbor i, and by means of the fork gives an impulse to the balance wheel, as has already been described. If the fourth wheel, which revolves once in a minute, has 64 teeth, and the pinion of the scape wheel has 7 leaves, that wheel will turn round once in 6^ seconds; and if it have 15 teeth, each tooth will escape every -^ of a second, and consequently there will be one complete oscillation of the balance wheel every -fa of a second. If the pinion of the fourth wheel contains 8 leaves, and there are 60 teeth in the third wheel, the latter will make one revolution in 71 minutes. Again, if the pinion of the third wheel has 8 leaves, and the centre wheel has 64 teeth, the latter will revolve one eighth as often as the third wheel, or once in an, hour. It is not necessary that these proportions should be fixed, but the num- ber of teeth in the train must be such that there will be a certain ratio between the num- ber of teeth in the centre wheel, which revolves once in an hour, and the number of leaves in the pinion of the fourth wheel, which revolves once in a minute ; and the teeth in the fourth wheel, the leaves in the pinion of the scape wheel, the teeth in the latter, and the vibra- tions of the balance wheel, must have certain relative proportions to each other. The hour hand is moved by a train of two wheels and two pinions, placed on the outer side of the pillar plate, and beneath the dial. The ar- rangement is represented in fig. 16. The can- non pinion is placed on the arbor of the centre pinion, and fits spring-tight, so that it may be moved at pleasure in setting the minute hand. Above the pinion proper there is a barrel upon which the minute hand is placed. If the can- non pinion, which is here hid from view, has 12 leaves, and the wheel into which it pitches has 42 teeth, the latter will revolve once in 4 hours. If, again, the pinion of this wheel has 14 leaves, and the centre wheel has 42 teeth, the latter will revolve one third as often, or once in 12 hours. One of the modern ar- rangements for winding and setting the watch is also represented in this figure. A crown wheel is placed upon the end of a shaft which Fio. 16. Hand Wheels and Stem Winder. passes through the stem. This wheel moves another, which is placed upon a yoke between two other wheels, one of which, the winding wheel, is held in gear by a spring, and the other the setting wheel, thrown into gear at pleasure by the pressure of a button. When one wheel is thrown into gear, of course the other is thrown out, so that the winding of the watch and the setting of the hands are done independently and without interference. An inspection of the figure will afford all the ex- planation that could be given in words. The limits of this article will not allow of a descrip- tion of the striking and alarm parts of clocks and repeating parts of watches, and other de- vices, such as for showing the day of the month, without a sacrifice of more important matter which more strictly relates to time- keeping ; and as these parts can be best under- stood by an actual inspection of the time- pieces, the reader who may wish to become acquainted with their mode of action is advised to study the subject in that way. Excellent watches are now made by machinery in the United States: by the American watch com- pany at Waltham, Mass. j-JE. Howard and com-
