H

Hairspring :
A slender hair-like coil that controls the regular movement of the balance wheel in a clock.

Halfpenny Moon or Halifax Moon :
A form of auxiliary lunar dial of circular shape which was adapted for use on square-dial clocks. Although halfpenny moons were occasionally used by London makers as early as 1735, the vast majority of examples are to be found on the clocks of Lancashire and Yorkshire makers later in the 18th century. An alternative to the halfpenny moon on a square-dial clock was the segmented moon opening, like the usual moon movement in an arch dial but here inverted, the moon's disc descending to full moon then ascending, instead of the climbing and descending path followed in an arch dial.

Hammer :
The clock part that hits the bell or gong to indicate time.

Hammer Tail :
The part of the hammer arm which extends below its pivot and is moved by the lifting pins in the pinwheel.

Hands :
The time indicators that mark the hours, minutes, and seconds on a clock dial.

Hanging Clock :
Gothic weight-driven clocks needed to be positioned so that the weights had room to fall. This was usually done by standing the clock on a bracket or hollow pillar. A simplification was to provide a hanging loop at the back of the clock and spurs to grip the wall and keep the clock in position. This idea was often used on English lantern clocks, but the method is less practical and even dangerous the heavier the clock becomes. The hanging clock therefore is usually limited to the lighter type such as the south German or Austrian Telleruhr. (A hooded clock is not a hanging clock, which inplies that the clock movement itself hangs, not its case.) Sometimes small spring-driven clocks in the shape of Gothic clocks or table clocks of tower form were hung from a small chain fastened above the cupola.

Hanging-Ball Clock :
A clock devised in the mid 17th century which enclosed a balance-controlled mechanism in a metal sphere to indicate the time by means of a band rotating on its circumference past a fixed pointer. The weight of the clock itself was the driving force, and it was suspended from a cord wound round a barrel inside the clock, the clock gradually descending as the hours passed. Winding was accomplished by raising the clock to the top of the cord, and a spring inside the barrel caused the latter to rotate and wind it up. The fusee of conventional clocks was eliminated but a barrel and spring still had to be provided.

Hanging Shelf Clock :
A wall clock with a shelf-like base that makes it appear as if it is resting on a shelf.

Hardening :
The term used to describe any of the hot or cold methods of hardening metal. It is frequently followed by tempering. Some metals, like brass, can only be hardened by a cold working operation, while a heat treatment is used for steel. Mild steel cannot be hardened, except in instances when it can be case-hardened, converting the metal skin into a harder steel. Carbon steel, containing various amounts of carbon, is affected by the temperature to which it is raised, the time it remains at this temperature, the rate at which it is cooled, and the atmosphere in which the work is carried out. Specialist manufacturers of steel tools and parts use carefully controlled methods of heating and cooling the steel, while clockmakers in small workshops acquire considerable skill in judging the correct temperature of the steel before plunging it into water, or oil, or otherwise cooling it to ensure the correct hardness.

Hardening, Hammer :
Brass, copper, gold, silver and certain other metals or alloys are hardened and made more resilient or springy by hammering them in a cold state on an anvil or stake. Hammer hardening produces a change in the microstructure of the metal, making it more suitable for certain needs. The same effect can be produced by rolling the cold metal through pressure rollers. Clockmakers harden brass by these methods for clock plates, wheels (especially escape wheels), and for making springs. Surface hardening of metal can be achieved by burnishing.

Hipp-toggle :
A mechanism developed by Matthaus Hipp to maintain a pendulum in oscillation electrically (also called 'Hipp's butterfly switch'). The pendulum rod carries a free-swinging vein or trailer which passes over a notched block mounted on the upper pair of contacts. When the pendulum amplitude falls sufficiently, the lower edge of the vein enters the notch, and on the return swing of the pendulum, the contacts close. Mounted on the lower end of the pendulum is an iron bar, which passes close to an electro-magnet, which is energized on closure of the contacts in a phase relationship to the pendulum, so as to maintain the pendulum's amplitude. Alternatively, the same system may be used to energize, whenever the amplitude of the pendulum falls, a coil mounted on the lower end of the pendulum, swinging over a fixed magnet.

Hodometer :
A device which can be coupled to the wheels of a carriage to record the number of revolutions made by the wheel, from which the distance traversed along the road can be inferred.

Hog's Bristle :
Prebalance-spring clocks sometimes had an adjustable arm carrying two hog's bristles positioned to bank the foliot or balance arms. They allowed finer adjustments of rate than were possible by altering the mainspring set-up.

Hollow column Clock :
E. & G. Bartholomew, casemakers at Bristol, Connecticut, introduced the hollow column Connecticut shelf clock for 30-hour wooden movements c. 1830. This Empire-style case had a moulded cornice with 3 in. diameter hollow columns on each side at the front, about two-thirds the length of the case, to accommodate the cast-iron weights. The bottom section of the case had veneered side panels and a framed door, containing a painted glass tablet or looking glass. A double panelled door was mounted in the upper section with the dial glass and either a painted tablet or mirror. While not common, this style of case was made for other firms who marketed and manufactured clocks both at Bristol and other Connecticut locations, and even as far west as Ohio. The veneer on the columns was applied as strips about 3 in. wide, wound helically. Modifications of this style were made with carved top splats and carved feet. The case was in vogue until c. 1840 and a few examples are known containing 30-hour brass movements.

Hood, Slide-off :
The most common method of removing the hood of a longcase clock to gain access to the movement. An overlapping strip of wood runs in a groove on either side of the case itself so that the hood does not tip forward when sliding off. The slide-off hood was introduced shortly before the end of the 17th century. It is normally fitted with a glazed, hinged door.

Hood, Slide-up :
The first longcase clocks had hoods which were lifted vertically to gain access to the hands or movement. The slide-up hood moved in wooden grooves on the upper part of the backboard of the case and was locked in position by a spring catch known as a spoon, which had to be depressed to allow the hood to be raised. This was a satisfactory method of fitting the hood when longcase clocks were little more than 6 ft. in height, but as the design of clock cases developed their height increased, and towards the end of the 17th century slide-up hoods became inconvenient. The slide-up hood was glazed but had no door, and because the hood had to be slid upwards to wind the clock hinged doors came to be fitted in most instances.

Hooded Clock :
A type of wall clock in which only the movement and dial are enclosed by a hood and the weights and pendulum hang down below. This is a considerable disadvantage as the pendulum may easily be disturbed and stop the clock. Sometimes a lantern clock designed to hang on a hook was provided with a wooden bracket and a wooden hood to act as a dust cover, but most hooded clocks were designed as such. By 1700 they were often made with elaborate marquetry hoods. Most were of the single-hand variety, with simple country-made fruitwood cases, but clocks with minute hands are also known. Hooded clocks continued to be made throughout the 18th century but were eventually replaced by the English dial clock with its eight-day spring-driven fusee movement.

Horologium :
The term was used in medieval manuscripts to denote any sort of timekeeper, were it a weight-driven clock or a water clock or a sundial. Consequently the researcher has to be wary of the term. The word was also used by the Dutch scientist, Christiaan Huygens, in the title of his work, written in 1658, describing the use of a pendulum to control a clock.

Horology :
The science of measuring time or making timepieces.

Hour Wheel :
The wheel in a clock which carries the hour hand and forms the last member of the motion train, usually rotating twice in 24 hours.

Hourglass :
A device containing sand that flows from the upper to the lower globe to indicate the passing of a certain amount of time.

Hour-glass Clock :
A very rare American 30-hour clock movement designed by Joseph Ives, c. 1840, mounted in a figure-of-eight shaped laminated wood case of late Empire design. The case was mounted on a base board, flanked on each side by turned columns with finials. A full-length door contained the dial glass and a painted tablet. The brass movement was powered by a horseshoe-shaped thin steel strip, secured inside at the top. Fusee barrels attached to the great wheel arbors of the time, and striking trains had cords to each end of the spring; this may have been the earliest spring-driven Connecticut clock. It is among the few known direct fusee-operated mechanisms, and although the label within the case stated 'patent brass clocks manufactured by Joseph Ives', the specific patent covering features of this movement is unknown.

Hours, Babylonian :
A system of hour reckoning in which the whole day-and-night period was divided into 24 equal parts with the numbering starting at sunrise. The system was used in Bohemia and Hungary between the mid 14th and the late 16th centuries, and some pin-gnomon dials of that period indicate Babylonian hours.

Hours, Great and Small :
Sets of hour lines on German sundials of the 16th and 17th centuries are sometimes entitled 'Grosse Uhr' and 'Kleine Uhr'. These terms refer to the Italian (1 - 24) and the normal 2 X 12 equal-hour systems respectively.

Hours, Italian :
In Italy from the 14th to the 18th centuries a system of time reckoning was used in which the whole 2 X 12-hour period was numbered 1 - 24 in a succession of equal hours starting from zero half an hour after sunset. Thus the first eight hours are always in darkness and so do not appear on sundials; noon varies from 16 to 20 hours. Italian sundials made during this period usually show only Italian hours; many clocks and sundials made in south Germany have provision for indicating them. The odd half-hour at sunset is often ignored, but it is shown on precision instruments.

Hours, Japanese :
The Japanese system of dividing the day, which was similar to that used in Europe in the Middle Ages, continued in use until 1873. The daylight period, including a considerable amount of twilight, was divided into six equal parts, and the period of darkness also into six parts. These hours were numbered, from midnight to noon, 9, 8, 7, 6, 5, 4, and again in the same sequence from noon to midnight. Japanese clocks were therefore designed to indicate and strike on this system. The length of twilight included in the Japanese day may be judged from the fact that some clock dials show that (in approximately 35º latitude) 'day' and 'night' were of about equal length in winter while in summer 'day' was over twice as long as 'night'.

Hours, Jewish :
Identical with temporal hours.

Hours, Nuremberg :
During the late 16th and 17th centuries a special system of hour reckoning was employed in the Nuremberg area differing from that of the rest of Europe. It used equal hours, but numbered the daylight hours from 1 onwards and the night hours similarly. Very few clocks using this principle have survived, two important examples being a 14th-century iron wall clock, formerly in St. Sebaldus Church, Nuremberg, and a table clock of c. 1500, both now in the Germanisches Museum, Nuremberg. The dial of the latter has a set of concentric rings of hour figures and a single hour hand graduated according to the date of use.

Hydrogen Clock :
A version of the hydrogen clock, also known as the gas-operated clock, is in the Clockmakers' Company Museum in London; it was designed by Pasquale Andervalt in Italy c. 1835. It consists of an open-centered dial exposing the mechanism, with a pin-pallet escapement and ornate gilt pendulum bob, the clock movement being mounted on supports fixed to a large red glass cylinder. Above the movement is a coiled spiral brass tube holding balls of zinc which, as the driving weight nears its lower position, are released one by one to fall into a solution of dilute sulphuric acid in the red glass jar. Hydrogen gas is generated and the resulting pressure lifts the entire mechanism behind the dial, winding the going weight, the larger of the two visible. The smaller weight is used to maintain the clock in motion whilst the larger is wound, the winding process being quite slow. On completion of the winding the hydrogen gas is released in preparation for the next cycle. These clocks are rare; hydrogen is a most inflammable gas and perhaps the majority have exploded in use.