CHRONOMETER

, is any instrument or machine used in measuring time; such as dials, clocks, watches, &c.

The term is however more particularly used for a kind of clock, so contrived as to measure a small portion of time, even to the 16th, or the 40th part of a second; one of this latter kind I have seen, made by an ingenious artist; but it could not be stopped to the 10th part of the proposed degree of accuracy. There is a description of one also in Desaguliers's Experimental Philosophy, invented by the late ingenious Mr. George Graham; which might be of great use for measuring small portions of time in astronomical observations, the time of the fall of bodies, the velocity of running waters, &c. But long intervals of time cannot be measured by it with sufficient exactness, unless its pendulum be made to vibrate in a cycloid; for otherwise it is liable to err considerably, as is the case of all clocks with short pendulums that swing in large arches of the circle.

Various other contrivances, besides clocks, have been used for measuring time for some particular purposes. See a musical chronometer described in Malcolm's Treatise of Music, pa. 407.