Time-Piece, a term including clocks, watches, and other contrivances, for measuring the propress, or ascertaining the duration, of time.

The ancients were not acquainted with other time-pieces than the common sun-dial, and water-clocks, or vessels filled with any liquid, which was allowed to descend in drops, so that the portion thus disengaged, in an imperfect manner indicated the length of time, which had elapsed: for these contrivances, hour-glasses were afterwards substituted.

The present mechanical timepieces with the pendulum, were probably invented in Italy, towards the end of the 13th, or beginning of the 14th century ; but the smaller machines, called watches, were not known in Europe till the middle of the 17th century, when the steel spring was employed as a substitute for weights, and the spiral or regulating spring, instead of the pendulum. The merit of this invention is claimed by the city of Nirnberg, whence Oliver Cromwell was furnished with an oval watch, that is still shewn among the curiosities deposited in the British Museum. In England, these useful chronometers were first made by Dr. Hooke ; and in Holland, by Huygens ; but the name of their original inventor is consigned to oblivion. Since that period, numerous improvements have been made by Tompion, Sully, Le Roi, Berthoud, Gray, Graham, and other artists, whose names we decline to register.

From the extensive utility of time-pieces, in measuring with exactness the periodical revolutions of planetary bodies, it was farther conjectured, that such machines might be advantageously employed for the purpose of ascertaining the longitude at sea. Various experi-ments have, by order of the British Government, been instituted with this design ; but the most correct Instrument, was that constructed by the late Mr.Harrison, and denominated a Time-keeper ; for which the Commissioners of the Board of Longitude, in 1764, awarded him the sum of 10, 000l., being one half of the premium which was promised by an act of parliament, passed in 1714, to the artist whose mechanical contrivance might be calculated to find the longitude at sea. Mr. H.'s admirable work did not vary more than 43" of time in a voyage from England to Jamaica: it was afterwards improved; and a time-piece, constructed on his principles, was sent out with Capt. Cook, in 1772; which, during the space of three years, did not differ more than 14 1/2 seconds per diem ; the remaining sum of 10, 0001. was consequently paid to the inventor. Our limits not permitting us to enter into the rationale of its mechanism, the reader is referred to the Principles of Mr. Harrison's Time-Keeper, etc. (4to. 1767, 5s. Nourse), in which its construction, as well as its application, are fully stated, and illustrated with plates.

Another time-keeper for ascertaining the longitude, was invented, a few years since, by Mr. Arnold, and which during a trial of 13 months differed only 6.69" during any two days. Its greatest vari-ation would not have exceeded one minute of longitude, which might thus be computed with the same accuracy as the latitude can be determined. We understand, however, that this contrivance has not been introduced into the Navy.