Chro-nom′e-ter.
1. A chronometer is a measurer of time, and this general meaning would include clocks, watches of all kinds, clepsydras, and some other devices, such as hour-glasses and the graduated candles of the beloved King Alfred. The term is, however, applied in a restricted sense to those having adjustments and compensations for the fluctuations of temperature. These have been adapted to the clock and to the watch: in the former the mercurial pendulum of Graham and the gridiron pendulum of Harrison may be cited; and in the latter, the expanding and contracting balance-wheel, depending upon the unequal expansion under changes of temperature of two different metals. With the improvements as adapted to instruments having a balance-wheel this article has to do. The proposition to determine longitude at sea by means of a timepiece and observation for noon was made by Gemma Frisius, in 1530. The attempt did not fail for want of suggestions; Alonzo de Santa Cruz suggested to determine it by the variation of the compass-needle, and by sand-and-water timepieces, wheel-work moved by weights, and by “wicks saturated with oil,” which were supposed to burn equal lengths in given periods of time. During the sixteenth and seventeenth centuries the Spanish, Dutch, French, and English governments had offered rewards for an instrument which should determine longitude within a certain specified degree of accuracy. Sir Isaac Newton suggested the discovery of the longitude by the dial of an accurate time-keeper, and the Parliament of Queen Anne in 1714 passed an act granting £ 10,000 if the method discovered the longitude to a degree of sixty geographical miles, £ 15,000 if to forty miles, £ 20,000 if to thirty miles, to be determined by a voyage from England to some port in America. John Harrison, born in 1693 at Faulby, near Pontefract, in England, undertook the task, and succeeded after repeated attempts, covering the period 1728 – 1761. His first timepiece was made in 1735; the second in 1739; the third in 1749; the fourth in 1755, the year of the great earthquake at Lisbon. In 1758 his instrument was sent in a king's ship to Jamaica, which it reached 5″ slow. On the return to Portsmouth, after a five months absence, it was 1′ 5″ wrong, showing an error of eighteen miles and within the limits of the act. He received the reward of forty years diligence in instalments. He died in 1776. |
| Chronometer. |
2. (Music.) An instrument to indicate musical time. A metronome.
