WATCH, any contrivance by which the progress of time is perceived and measured; as a timekeeper actuated by a spring, and capable of being carried on the person. The essential difference between a clock and a watch has been defined to be that the latter will run in any position, but the former in a ver tical position only. Since the invention of the cheap spring clock this definition must be abandoned. Another character istic which was formerly distinguishing was that the watch escapement was al ways controlled by a balance wheel and spring, while the clock escapement was generally governed by a pendulum. Watches are said to have been invented at Nuremberg, about the end of the 15th or beginning of the 16th century. The essential portions of a watch are the dial, on which the hours, minutes, and seconds are marked, the hands, which by their movement round the dial point out the time, the train of wheels, which carry round the hands, etc., the balance,
which regulates the motion of the wheels, and the mainspring, whose elastic force produces the motion of the whole machinery. The works are in closed in a case of metal, usually silver or gold. The shape is now universally circular and flat, so as to be easily carried in the pocket. The early watches had but one hand, and required winding twice a day. The spring was at first merely a straight piece of steel, not coiled. A spring to regulate the balance was first applied by Dr. Hooke, 1658; this was at first made straight, but soon improved by making it of spiral form. A repeating watch, or repeater, has a small bell, gong, or other sounding ob ject, on which the hours, half hours, quarters, etc., are struck on the com pression of a spring. The most perfect form of watch is the CHRONOMETER (q. v.)