HAIRSPRING. A common name for the balance spring (q.v.).

HALF PLATE. See FULL PLATE.

HALF-QUARTER. A repeater which, in addition to repeating the hours and quarters, also gives an additional single stroke if 7- minutes or more have elapsed since the last quarter. Introduced in about 1695.

HALLMARK. The mark made by punches on gold or silver, consisting of the standard mark, the mark of the Hall (e.g. the Goldsmith's Hall, London, the Birmingham mark, etc.), the quality of the metal, the date letter and the maker's mark. Other countries have assay marks.

HAND-SETTING. Also set-hand mechanism. Mechanism for altering the position of the hands. In the earliest watches this was done by pushing the hour hand directly to the right time. With two-hand watches, this was first done by fitting the key on to the hand-set square (the arbor carrying the hands). With the introduction of keyless work (q.v.) the hands can be set through the winding button. Also see MOTION WORK.

HANGING BARREL. See STANDING BARREL.

HEART PIECE. A heart-shaped cam used in chronograph work to cause the chronograph hand to fly back to zero. Patented by A. Nicole in 1844, No 10348.

HELICAL SPRING. See BALANCE SPRING.

HOG'S BRISTLE. A bristle or flexible hair. Found on early German watches, where two upright, short bristles mounted on a pivoted arm act as banking pins to limit the supplementary arc of the foliot or balance, each end of the foliot striking against a bristle in turn. By moving the pivoted arm a degree of regulation can be effected, a shorter arc giving a faster rate and vice versa. A much rarer form is where a long bristle, fixed at one end, is flexed at its free end by two pins standing upright on the rim of the balance; reducing the length of the bristle causes a faster rate. Both forms give a certain amount of elasticity to the action of the balance.

HOOKE'S LAW. Hooke's Law relating to springs. See BALANCE SPRING.

HORIZONTAL ESCAPEMENT. See CYLINDER ESCAPEMENT, which is the alternative and now more usual name.

HORNS. The horn-shape extremity of the fork in the lever escapement. The two 'prongs' extend on each side of the notch.

HOUR RACK. Part of the striking mechanism that is moved one tooth for each hour. The rack - which is a pivoted toothed sector - has a tail which drops on to the snail (q.v.) and its position in relation to this determines how many teeth are to be gathered by the gathering pallet (q.v.) which in turn determines how many hours are struck. A quarter rack acts similarly for the quarter-hours. Rack striking was invented by Edward Barlow in 1676.

HOUR WHEEL. The wheel which carries the hour hand.

HUNTER. A watch the case of which has a front as well as a back cover, thus affording protection to the glass. The front is opened by means of a push-piece. A half-hunter has a small thick glass (a 'pebble glass') fitted into the front cover allowing a portion of the dial and hands to be seen.