Page:Encyclopædia Britannica, Ninth Edition, v. 6.djvu/24

14 We may now go to the front (or left hand) of the clock, and describe the dial or &quot; motion-work.&quot; The minute hand fits on to a squared end of a brass socket, which is fixed to the wheel M, and fits close, but not tight, on the pro longed arbor of the centre wheel. Behind this wheel is a bent spring which is (or ought to be) set on the same arbor with a square hole (not a round one as it sometimes is) in the middle, so that it must turn with the arbor; the wheel is pressed up against this spring, and kept there, by a cap and a small pin through the end of the arbor. The consequence is, that there is friction enough between the spring .and the wheel to carry the hand round, but not enough to resist a moderate push with the finger for the purpose of altering the time indicated. This wheel M, which is sometimes called the minute-wheel, but is better called the hour-wheel as it turns in an hour, drives another wheel N, of the same number of teeth, which has a pinion attached to it; and that pinion drives the twelve-hour tcheel H, which is also attached to a large socket or pipe carrying the hour hand, and riding on the former socket, or rather (in order to relieve the centre arbor of that extra weight) on an intermediate socket fixed to the bridge L, which is screwed to the front plate over the hour-wheel M. The weight W, which drives the train and gives the impulse to the pendu lum through the escapement, is generally hung by a catgut line passing through a pulley attached to the weight, the other end of the cord being tied to some convenient place in the clock frame or seat-board, to which it is fixed by screws through the lower pillars. It has usually been the practice to make the case of house clocks and astronomical clocks not less than 6 feet high ; but that is a very unnecessary waste of space and materials ; for by either diminishing the size of the barrel, or the number of its turns, by increasing the size of the great wheel by one-half, or hanging the weights by a treble instead of a double line; a case just long enough for the pendulum will also be long enough for the fall of the weights in 7? or 8 days. Of courso the weights have to be increased in the same ratio, and indeed ratharmore, to overcome the increased friction; but that is of no consequence.

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