MOTION, a term frequently used in the same sense with automaton.

The most usual movements for keeping time are watches and clocks: the first are such as show the parts of time, and are portable in the pocket; the second, such as publish it by sounds, and are fixed as furniture. Movement, See Horology.

its popular use among us, signifies all the inner work of a watch, clock, or other engine, which move, and by that motion carry on the design of the instrument.

The movement of a clock or watch is the inside, or that part which measures the time, strikes, &c. exclusive of the frame, case, dial-plate, &c.

The parts common to both of these movements are, the main-spring, with its appurtenances; lying in the spring-box, and in the middle thereof lapping about the spring-arbor, to which one end of it is fastened. A-top of the spring-arbor is the endless-screw and its wheel; but in spring-clocks, this is a ratchet-wheel with its click, that stops it. That which the main-spring draws, and round which the chain or string is wrapped, is called the fusey; this is ordinarily taper; in large works, going with weights, it is cylindrical, and called the barrel. The small teeth at the bottom of the fusey or barrel, which stop it in winding up, is called the ratchet; and that which stops it when wound up, and is for that end driven up by the spring, the garde-gut. The wheels are various: the parts of a wheel are, the hoop or rim; the teeth, the crests, and the collet or piece of brass soldered on the arbor or spindle wherein the wheel is rivetted. The little wheels playing in the teeth of the larger are called pinions; and their teeth, which are 4, 5, 6, 8, &c. are called levers; the ends of the spindle are called pivots; and the guttered wheel, with iron spikes at bottom, wherein the line of ordinary clocks runs, the pulley. We need not say anything of the hand, screws, wedges, stops, &c. See WHEEL, Fusey, &c.

Perpetual Movement. Many have attempted to find a perpetual movement, but without success; and there is reason to think, from the principles of mechanics, that such a movement is impossible: for though, in many cases of bodies acting upon one another, there is a gain of absolute motion, yet the gain is always equal in opposite directions; so that the quantity of direct motion is never increased.

To make a perpetual movement, it appears necessary that a certain system of bodies, of a determined number and quantity, should move in a certain space for ever, and in a certain way and manner; and for this there must be a series of actions returning in a circle, otherwise the movement will not be perpetual; so that any action by which the absolute quantity of force is increased, of which there are several sorts, must have its corresponding counter-action, by which the gain is destroyed, and the quantity of force restored to its first state.

Thus by these actions there will never be any gain of direct force to overcome the friction and resistance of the medium; so that every motion being diminished by these resistances, they must at length languish and cease.