Old Passion's Clock Dictionary

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

G

Gadget Clock :
A clock with accessories.

Gallery Clock :
An eight-day or electric clock, usually round, with a simple case and a dial usually eight inches orlarger designed to hang on a wall in a public place.

Gauge, Mainspring :
A fine gauge similar to a pivot gauge, used for measuring the thickness of mainsprings. Another mainspring gauge is used to measure the height of the spring, and is known as a 'width' or height' gauge. It consists of a flat plate with graduated slots on its edges, each slot being marked with numbers or measurements to check the height of a given spring. These gauges are used for small clocks only.

Gauge, Micrometer :
A type of gauge for accurate measurement of small parts to thousandths of an inch, obtained by turning a precision, fine-pitched, threaded screw a known number of revolutions, or parts thereof, from a fixed datum position. This movement is indicated by a rotating scale against a fixed scale. Micrometers are made in many shapes and sizes, adaped to many different measuring needs.

Gauge, Pinion :
A gauge similar to a slide gauge, used to measure the distance between the plates of a clock or the length of a pinion from shoulder to shoulder, showing both measurements at the same time. The name is also applied to a caliper-type of instrument with legs adjusted by a nut on a screw to take pinion measurements. A further type is like a wire gauge and measures the diameter of a pinion; it is particularly useful when measuring a pinion with an odd number of leaves.

Gauge, Pivot :
A gauge for measuring the diameter of clock pivots. It consists of two flat steel plates fastened together by strips of metal at their ends to form a tapered slot between the inner plate edges. The size of the gap between the edges at any point is given on scales marked out on the plates. By inserting the pivot at the wide end of the slot and moving it along, its diameter can be determined.

Gauge, Sliding :
A name applied to numerous measuring tools which have a jaw, or jaws, adapted to slide along a bar or beam, and set in position on it. It is also an old name for sliding calipers. The beam is usually provided with a scale and, in vernier instruments, with a secondary scale on the jaw sliding box. Sliding height gauges are designed with a heavy base for placing on a flat surface, and the sliding jaw is moved up the vertical column to check the height of work, also on the flat surface. Sliding calipers have many uses and may be fitted with two pairs of jaws and a depth probe for taking external, internal and depth measurements in one operation. Dial calipers have a dial and pointer and are rapidly read, without a vernier.

Gauge, Vernier :
Many measuring instruments are fittd with a vernier, a subsidiary scale for making subdivisions of the main measuring scale. For subdividing a main scale in units of ten the vernier has ten equal divisions totalling the length of nine of the main scale, and the reading is taken from the vernier where alignment takes place on the divisions of both scales. Some vernier gauges are made which can be read to 0.01 mm; a vernier protractor divides degrees of a circle into minutes.

Gauge, Wire :
A steel plate with a range of graduated round holes or slots, accurately gauged to a standard legalized in 1883. Each hole is marked with the standard wire-gauge number, and the equivalent imperial or metric size may be added; some firms retained their own gauge sizes for many years. The tool is used to measure the diameter of wire or sheet metal.

Gears :
Gearing is the basis of clockmaking and the ability to calculate the necessary ratios is a fundamental clockmaking skill. To reduce pivot frictional losses, high gear ratios are necessary, leading in turn to losses in the gearing. Ratios above 10 to 1 require very high-numbered wheels to achieve a smooth gear action. The shape of gear teeth is carefully selected so that one tooth rolls on another - ideally, eliminating sliding friction. In clocks this is normally achieved by making the acting parts of wheel or pinion teeth of epicycloidal form (the curve generated by a point on the circumference of one circle rolling around another). In general engineering, the involute tooth shape is more generally used (the curve traced by a point on the diameter of a circle rolling on a plane). This tooth shape is used because of its strength and because it is possible to generate pinions or wheels of any number, using only one cutting hob. Involute pinions of less than 20 leaves cut with normal cutters have seriously weakened tooth roots, making involute gearing unsuitable for most clockmaking applications. Epicycloidal pinions have teeth with radial sides, giving stronger roots, and can be made with as few as five leaves. The best clocks have high-numbered pinions, with more than eleven leaves, but to obtain the necessary ratios they are more expensive to manufacture.

Gears, Helical :
Charles McDowell, a Yorkshireman, pioneered the use of helical gearing in clocks early in the 19th century. Helical gearing allows more uniform transmission of power, even using high ratios, allowing pinions to be made with only one long spiral leaf.

Gears, Wolf-tooth :
A buttress-shaped gear profile, sometimes used in the winding work of high-class clocks. It is stronger than the normal symmetrical tooth shape, which allows power transmission in both directions.

Gears, Worm :
Large ratios may be obtained using a form of helical gearing in which the driving wheel is in the form of a cylindrical screw, cut with a single or multistart thread and meshing at right angles with the plane of the worm wheel. worm gearing is occasionally found in the calendar work of clocks, and commonly encountered in the reduction train of synchronous electric clocks.

Gilding :
The process of coating a base metal such as brass with a very fine layer of gold, much used in watch-movement finishing. For clocks it is largely confined to decorative external details such as spandrel mounts for dials. Because gold does not oxidize or tarnish it makes a good finish and gives an attractive appearance. The early gilding process was known as 'fire', or 'mercurial' gilding; in simple terms, the gold surface was obtained by rubbing it with a mercury-gold amalgam and heating until the mercury evaporated away, leaving a layer of pure gold behind. After this treatment the gilding was washed and finished by burnishing to bring up the bright quality of the metal. This method was highly injurious to workers because of the toxic effects of mercury, and in the 19th century it was replaced by electrogilding.

Gilding, Parcel :
Partly gilding. Normally, a term used in connection with partially gilded domestic objects made of silver, it also applies to parcel-gilt clock dials and in some instances decorative metal clock cases.

Gilt :
A gold-colored coating.

Gimbal :
A support used to keep a clock level.

Gingerbread :
The name used to describe the elaborate designs pressed into a clock's wooden case.

Girandole Clock :
A distinctively American clock which derives its name from the similarly shaped mirror with convex glass and gilded balls surrounding the frame. Somewhat similar to the banjo clock, though larger, the bottom frame is circular rather than rectangular and the base piece below (bracket) has carved acanthus leaves rather than the scrolled pediment of the presentation banjo form. They were made as eight-day timepieces having a pendulum 2in. longer than the Willard patent. The case is somewhat larger and gold leafed, usually with an ornately carved eagle. By many this is regarded as the most handsome clock case ever designed in America. Exceedingly rare, there are believed to have been only 50 originals produced.

Globe Clock :
The earliest globe clocks were mechanically turned globes with clock dials made in 16th-century Europe. Another type has a globe with an inscribed revolving hour band and a fixed indicator to show the time, usually made to stand on a table. The more modern globe clock, early 20th century, takes the form giving the time at any point on earth in addition to local mean time. In the United States two types were made, the Timby and the Juvet. The movement was an eight-day timepiece with jewelled balance. The case supported a rotating globe, showing the time of sunset on any part of the globe. A separate dial indicated the time, which could be adjusted for a specific meridian. Apparently the manufacturer was never able to produce this mechanism to the inventor's patent, and it remained merely a novelty. A 30-hour solar timepiece, consisting of a 12in. diameter globe mounted on a stand, turning every 24 hours, was manufactured at Canajoharie, New York, 1879-86. A large floor model had an 18in. diameter globe. Manufacture ceased when a fire destroyed the factory on 18th October 1886. Both Timby and Juvet timepieces have become rare collectors' items.

Globe, Celestial :
A representation of the starry heavens, imagined as projected on to a sphere from the center of the Earth and viewed from outside the sphere. Some form of celestial globe must have been constructed by the Greeks, but the earliest surviving example is the Farnese globe of marble dating from the 2nd or 3rd century BC, now in the Museo Nazionale in Naples. It is almost entirely decorative and of little use for measurement. Small Islamic bronze globes of the 11th and 12th centuries survive, but it was not until the 16th century that an interest in them developed in Europe; they were then made of gilded copper or painted wood. An outstanding example, was made in Vienna by Hans Dorn under the supervision of Martin Bylica; it is dated 1480. The magnitudes of the stars are shown by the number of rays radiating from each. A further fine example, of painted wood is signed and dated Johann Stoffler, 1493. One of the functions of the great water clocks of China of the 10th and 11th centuries was to drive a celestial globe, and clock-driven globes appeared in Europe during the Renaissance.

Globe, Terrestrial :
A representation on a small scale of the main features of the Earth's surface, either purely geographical, showing continents, seas, islands, etc., or political, showing national boundaries also. The construction of such a globe implies an affirmation that the Earth is a sphere, or almost spherical, and although vague references to globes appear in Greek and Latin authors it was not until the Renaissance that their existence in Europe is certain. The earliest which has survived is the so-called Erdapfel of Martin Behaim. It was made in 1492 of papier-mache covered with parchment, with 1,100 localities marked on it. The well-known Jagellonian globe in Cracow, probably made by Hans Dorn of Vienna, consists of an armillary sphere surrounding a clock-driven brass terrestrial globe. It dates from c. 1507 and bears the word 'Amerika'. The great geographical discoveries of the 16th century stimulated interest in terrestrial globes.

Globular or Rotating Moon :
This is probably the most realistic reproduction of the changes in the moon's phases which has ever been contrived for use with clockwork. It consists of a sphere, half white and half black, rotating vertically in a circular opening in the arch of a dial, driven from the main movement by a bevel gear. As the 29 1/2 days of the lunar month pass, the moon turns imperceptibly, showing an approximately true visual image of the moon at any given time. One of the earliest clockmakers, Ahasuerus Fromanteel, who worked in London during the reign of Charles II, knew of the principle of the rotating moon.

Gnomon :
The shadow-casting part of a sundial. The actual edge or point which casts the shadow is called the 'style', the gnomon being the whole structure. If the style is parallel to the earth's axis, the gnomon is called a 'polar' gnomon. A gnomon may be a thin piece of sheet metal. a pin, or a tautened string.

Gold Leaf :
An extremely thin sheet of solid gold sometimes applied as a decoration on columns, tablets, or other parts of a clock case.

Gothic Case :
A case shaped like a Gothic arch; also called a beehive clock because its sloping sides give it an appearance similar to a beehive.

Gothic-on-Frame Clocks :
As small spring-driven shelf clocks became popular, Birge & Fuller of Bristol, Connecticut, introduced c. 1844 an eight-day movement powered by Joseph Ives's patented 'accelerating lever spring' (wagon spring), housed in a modified sharp-Gothic-on-frame case. This style is often referred to as 'steeple-on-steeple' or 'double-decker steeple'. There are two distinct styles, each produced in two sizes. The earlier, offered only by the Birge firm, had long candle-style finials on each side of the case, mounted on top of the lower frame. The large case for eight-day movements had double finials, and the smaller 30-hour movement case had single finials. The other style had the conventional finials found on the regular sharp Gothic case, with two mounted each side on top of the lower frame and two on top of the upper frame.

Grandfather Clock :
The name for a floor standing clock in a tall, upright case; originally called a long-case or tall-case clock.

Grandmother Clock :
A smaller, floor-standing version of a grandfather clock.

Graver :
A cutting tool of hardened steel, square or lozenge-shaped in section and of varying thickness. One end has a tang for fitting in a handle and the other is ground off at an angle to obtain the cutting point or face. A graver may be used by hand for turning in the lathe or turns, or as a hand-engraving tool. The cutting face is sharpened on a fine oilstone and finished on an Arkansas stone.

Gravity Clock :
Any clock which is driven by its own weight. The earliest appeared in the mid 17th century. They had a bracket in the form of an arm attached to the wall, the hand holding a chain on which the clock, in the form of a globe, hung. To wind the clock it was lifed, a spring retracted the chain inside the clock and, when released, the clock descended. Maurice Wheeler described on of his devising in 1684, the clock descending an inclined plane. A pivoted weight inside the clock provided the power to the train as it tried to assume a vertical position, though the actual power came from the clock descending the inclined plane. Hours and minutes were indicated on the clock, the days of the week on the plane. Nowadays the term more often refers to the silent keyless clock made in the early 1900s. This has a base carrying two columns with a toothed rack in one which engages a wheel in the clock movement. The clock is raised to the top of the columns by hand, thereupon its own weight drives it; the escapement is visible and impulses a short pendulum. These clocks, also called rack clocks, were popular for a limited period only.

Great Wheel :
The first and usually largest wheel in a clock train. The wheel mounted on the line or spring barrel in going-barrel clocks, or on the fusee arbor in fusee clocks.

Greenwich Time :
Greenwich Mean Time or its modified form, British Summer Time, is the legal standard time of the United Kingdom. Greenwich Royal Observatory was set up in 1675, and one of its main objectives was to establish a standard of time in connection with the determination of longitude at sea. Its famous Octagon Room, designed by Sir Christopher Wren, was equipped in 1676 with two 'great' clocks by Thomas Tompion, both with 13 ft. pendulums and a year's going time. The two Tompion year clocks, fitted with dead-beat escapements of a type first proposed by Richard Towneley of Burnley, were later somewhat modified by Tompion and eventually succeeded by clocks with the Graham type of dead-beat escapement and mercury-compensated pendulums. From 1872 to 1925 the standard timekeeper was a Dent clock with G.B. Airy's modification of the spring-detent escapement, zinc-and-steel compensation pendulum and barometric compensation. This was followed in 1925 by a Shortt free-pendulum clock with its pendulum swinging almost entirely freely in a case at constant air pressure, served by a slave pendulum which impulsed the free pendulum and was afterwards synchronized by a signal from it. The error of the Dent clock was about 0.01 seconds per day, and of the Shortt clock a few thousandths of a second. The Shortt clock was superceded in 1942 by a group of quartz-crystal vibrating at 100 kilocycles per second, electronic gearing reducing this to 50 cycles per second, the final time indication being a continuously rotating hand. Before 1955 the Greenwich timekeeper was checked against the stars by a transit instrument and since then by a photo-zenith tube. A new precision method of measuring time, developed between 1945 and 1955, was the atomic clock, in which the timekeeping element is a molecular or atomic vibration. The caesium atomic clock, brought into practical use by Louis Essen and J. V. L. Parry at the National Physical Laboratory, Teddington, in 1955, was accurate to one part in 10 to the tenth power, equivalent to an error of one second in 300 years. This clock is not free-running, but is used to synchronize a system of quartz-crystal clocks. Greenwich Mean Time has been based on the atomic clock since 1967. A second National Physical Laboratory atomic clock of 1959 was seven times more accurate than the first, and was later improved still further to an accuracy of one part in 10 to the twelfth power, corresponding to an error of one second in 30,000 years. Accuracy of this order, when combined with astronomical observation, makes it possible to detect variations in the rotation of the Earth itself, revealing an annual fluctuation together with a slow drift. By 1967 the atomic clock had been shown to be a more accurate timekeeper than the Earth itself, which led to an international decision to base the unit of time, i.e. the second, not fundamentally on the rotation of the Earth but on an atomic vibration, and the General Conference on Weights and Measures thus defined the second as the period of 9,192,631,770 vibrations of an atom of caesium 133 in zero magnetic field. The work of Greenwich Observatory was gradually transferred to Herstmonceux, Sussex between 1946 and 1958, but Greenwich Mean Time remains the time of the meridian of Greenwich itself. From 1st January 1972 the world time signals broadcast from many countries have been based on atomic time and converted in steps to Universal Time to allow for the slowing down of the Earth's rotation.

Return To Top