DENNISON, AARON L.—Born in Freeport, Me., in 1812. Died Birmingham, England, January 9, 1898. At eighteen he was apprenticed to a watchmaker. Later in working at the trade, he was impressed with the inaccuracies which existed in the best handmade watches. This, with a visit to the Springfield Armory, gave him his idea of machine-made watches with interchangeable parts. He interested Edward Howard in the project, and having found the needed capital they started in the business and laid the foundation of what is now the Waltham Watch Company. Dennison has been called the "father of American Watchmaking" tho there seems ground for the claim that he shares that honor with Edward Howard. DEPTHING—The technical name for the proper adjusting or spacing of the gearing in a watch. DETENT—The device which halts, and releases, at the proper instant the escapement of a clock or chronometer. See: _Escapement_. DE VICK, DE WYCK, OR DE WIECK, HENRY—A German clockmaker who, in 1364, made the first turret clock of which reliable information and description remains. The clock was made for Charles V. See: _Clocks, Interesting Old—De Vick's_. DIAL—Commonly called the face of the watch—made of gold or silver or other metal or of enamel, with the required figures—in the United States one to twelve upon it in a contrasting color. See also, _Sun-dial_. DIAL FEET—Short wires soldered to the back of the dial of a watch or clock which hold it in place by fitting into holes in the pillar plate. DIAL OF AHAZ—A sun-dial belonging to Ahaz, King of Judea 742-727 B. C., mention of which occurs twice in the Scriptures—II Kings, XX: 9-11, and Isaiah XXXVIII: 8. It is believed that one of his Babylonian astrologers constructed it for him. DIAL PLATE—See _Lower Plate_. DIAL, SUN—See _Sun-dial_. DIAL WHEELS—The wheels constituting the motion work of a watch. DIURNAL—In an astronomical sense, pertaining to a period covering a mean solar day. See: _Solar Time_. DOG SCREW—A screw with an eccentric head used to attach a watch movement to a dome case. DOG-WATCH—A nautical term for two daily two-hour periods of watching aboard ship. The first begins at 4 P. M., the other at 6 P. M. DOLMEN—A sacred instrument used for astronomical purposes at certain critical periods of the year; formed of four stones at the cardinal points and a leaning stone crossing diagonally and forming with the east stone a sacred "creep-way." The solar hours were indicated by the shadow of the leaning stone touching various prominent points or edges. One at Camp, England, is prehistoric. DOME—The inner case of a watch which snaps on the band of a case. DOME-CASE—A case in which the inner case or dome snaps to the band of the case. DONDI, GIACOMO—Born at Padua, Italy, in 1298. In 1344 he set up at Padua a famous clock which became a model for later clocks and which earned for him the surname, "Orologio."