HARRISON, JOHN—An English mechanician born at Faulby in Yorkshire in 1693. He made many improvements in the mechanism of clocks, the greatest of which was the compound pendulum. He won in 1761 a reward offered by Parliament in 1714 for an instrument that would determine longitude within thirty marine miles. Harrison's chronometer gave it within eighteen miles. He invented the going fusee, the gridiron compensation pendulum and suggested the idea for the compensation balance, afterward worked out by other watchmakers. Died 1776. HAUTEFEUILLE, JOHN—(Abbe.) Born 1647. Died 1724. He disputed successfully Huyghens' claim to a prior invention of the steel balance spring. He is also credited with the invention about 1722 of the rack-lever escapement. [Illustration] HEART-PIECE—The heart-shaped cam on the center-seconds wheel of a chronograph, which causes the hand to fly back to zero. HELE, PETER—(See _Henlein, Peter_.) Some historians credit invention of first watch to Peter Hele. There is no doubt, however, that Hele and Henlein were one and the same. Preponderance of authority favors "Henlein" as the correct spelling of the name. HELICAL—Following the course of a helix or spiral. HELIOTROPION—See "_Polos_." HEMICYCLE—Form of sun-dial in which the shadow of a vertical pointer or "gnomon" is cast upon and moves around the inner surface of a half globe or sphere. Supposed to have been invented about 350 B. C. (See _Sun-Dial_). Vitruvius, the Roman Engineer, ascribes invention to the Babylonian priest and astronomer, Berosus. HENLEIN, PETER—Sometimes called Peter Hele. A clockmaker of Nuremberg, who is believed to have made the _first_ portable (pocket) clock or _watch_ sometime early in the sixteenth century. Born 1480. Died about 1540. His clock was round, driven by a spring and had small wheels of steel. It was much larger than present day watches. HOLLOW PINION—A pinion bored through the center. The center pinion in many watches is hollow. "HON-WOO-ET-LOW" OR COPPER JARS DROPPING WATER—A form of clepsydra at Canton, China, said to be between 3000 and 4000 years old. It consists of four copper jars arranged on steps. Each jar drops water into the one below it until the last one, in which a bamboo float, indicates the time in a rude way. HOOKE, ROBERT, M. D.—An English physician-philosopher born on the Isle of Wight in 1635. His accomplishments were numerous. He claimed to have discovered the isochronism of the balance spring and its application to watches, though this was also claimed by Huyghens. He invented a pendulum timekeeper for finding the longitude at sea; devised the first wheel-cutting engine about 1670; and he invented the anchor escapement for clocks. His studies and inventions covered a wide field. He died in 1702. HOROLOGE, (OROLOGE), (HOROLOGIUM)—A general term applied indiscriminately in old writings to any mechanism for measuring time.