Chronometer

Chronometer, any instrument for measuring time, but especially a watch-like instrument for measuring it with great regularity and exactness in order to facilitate the taking of astronomical and nautical observations. Accuracy is attained by exceeding delicacy of mechanical workmanship, and by various compensating devices which counteract the effect of the contraction or expansion of particular parts under the influences of heat and cold. This accuracy is not, however, absolute; and a ship at sea, therefore, commonly carries several chronometers, and her captain also takes care to ascertain before sailing the rate of losing or gaining of such chronometers as he takes with him. It is obvious that, if a chronometer, set to the meridian of Greenwich and going at mean time, be carried elsewhere, the observer may very easily discover, by comparing his Greenwich time with the observed time of his new position, in what longitude he happens at the moment to be. The invention of the chronometer is of somewhat ancient origin, but the modern chronometer dates from the time of the great improvements of Pierre Leroy, and of Arnold, Earnshaw, Barraud, Hatton, and other makers of the early part of the present century.