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Caesium clock:
( Pic )     The first caesium atomic clock was built in 1955 by Dr. Louis Essen and J.V.L. Parry of the National Physical Laborator. Earlier work in the United States had resulted in the National Bureau of Standards building the first atomic clock based on the ammonia molecule. Its accuracy, although an improvement on that of the quartz-crystal clock, did not justify further development when the caesium clock appeared. The caesium atom has an extremely accurate natural viberation of 9,192,631,770 cycles which is used to control a radio frequency generated by a quartz-crystal oscillator and multiplier. The output may be fed through frequency-reducing circuits and used to drive a clock.

Calendar aperture:
( Pic )     A slot in a dial which shows the day of the month engraved on a flat ring or annulus, toothed on the inner edge and moved every 24 hours by a pin in a 24-hour wheel geared to the hour wheel.

Calendar clock:
( Pic ) ( Pic ) ( Pic )   Between 1860 and 1875 several patents were granted for mechanisms indicating the day of the week, the day of the month and the month of the year on a seperate dial below the time dial in the same case as the clock mechanism. The earliest patent was issued to Hawes of Ithaca, New York, on the 17th of May 1853, but it did not compensate for leap-year, although adjusting for the varying lengths of the months. Atkins & Burritt of Ithaca, New York, were granted a patent September 19th, 1854 for the first true perpetual-calendar mechanism. The mechanism was improved by the Mix Brothers, and purchased by the Seth Thomas Clock Company in 1864.

Calendar Work:
( Pic )     The function of a calendar work is to indicate the date, and in some clocks the day and month. A wheel rotating once in 24 hours carries a pin which engages with ratchet teeth on the calendar wheel or ring.

Calipers:
( Pic )     Pivoted calipers are brass or steel instruments with two pivoted legs adapted to point inwards or outwards accordking to type of need. They are used for taking external or internal comparative measurements, particularly of curved surfaces or bores. Sometimes they have a locking screw and means of making fine adjustments, as when fitted with a geared quadrant.

Calotte:
A modern traveling clock which folds into a leather case; also called a threefold or portfolio clock. Calotte (French for skull cap) properly refers only to the circular metal case of the clock.

Cam:
Usually a disc or cylinder of irregular profile, contacted by a lever which follows the contour of the disc.

Candle clock:
Tradition has it that King Alfred utilized the idea of marking a candle in divisions, each of which would take approximately one hour to burn. This is really not a clock but simply an interval timer, like a sand glass, and could be used for dividing the day or night into convenient parts. The principle is the same as that of an oil lamp clock; in both cases the flame has to be protected from drafts to avoid uneven burning.

Capucine:
( Pic )     A type of late 18th and early 19th-century traveling clock, predecessor of the true pendule de voyage, also sometimes called a foncine or lantern clock. These rectangular brass clocks, surmounted by an open bell and stirrup handle, stand up to 12 inches high and were made with leather-covered traveling cases. Their tall thin shape suggests Gothic chamber clocks, which may be in their pedigree as they seem to have originated in the St. Claude district of France. The name may derive from the hooded appearance of the clock. Capucines had eight- or 15-day movements, alarms, hour and half-hour striking and sometimes pull-repeat.

Carborundum Wheels:
( Pic )     An abrasive disc or wheel of artificial stone mounted on a machine spindle and rotated at speed for grinding. Carborundum wheels are obtainable in many diameters, widths, spindle sizes, shapes and grades. The material is quick-cutting and useful for shaping steel clock parts and tools, though care must be taken not to overheat the work. As with buffs and mops, when using a Carborundum wheel the eyes and body should be protected. A tool rest is also necessary.

Carillon:
A set of bells, musically tuned and hung in a tower, played by a pin barrel or by hand. The carillon is occasionally associated with domestic clocks, and in both types two hammers are sometimes provided for each bell, lifted by separate pins, to increase the striking rate of one note.

Carriage clock:
( Pic )     Some horologists consider the coach watch a very large watch usually of outstanding design and workmanship and often incorporating repeating work sounding on bells, to be the first carriage clock. Thomas Tompion made a few trveling clocks incorporating both pendulum and balance wheel control, the latter for use during the journey. The direct precursor of the carriage clock is the pendule d'officier of about 1775, though the originator of the true carriage clock was the famous Abraham-Louis Breguet. In its common form the carriage clock consists of a gilt-brass case with glass-panelled sides and top, hinged carring handle and separate platform escapement; it often has alarm and repeating mechanisms, more rarely grande-sonnerie striking. It is the most popular of all clocks and is still manufactured today.

Cartel clock:
( Pic )     A decorative wall clock which had its origin in France during the 18th century. It was essentially a clock for the boudoir or salon and was frequently a ptimepiece without a striking mechanism. French cartel clocks had circular drum movements, round dials with glazed bezels, and ornate ormolu cases. Earlier examples are rococo in style, while more balanced lyre shapes, adorned with bows and ribbons, appeared during the French neoclassical periof of Louis XVI. English cartel clocks, while following the style of the French circular dial, were usually set in carved and gilded wooden mounts or cases. They often had asymmetrical rococo designs, some in the Chinese taste, and were frankly designed as wall ornaments as well as clocks.

Caryatid:
( Pic )     Architercturally, a carved or modelled half-length female figure, which serves as a pier or pilaster. According to legend, the Caryatids were the women of Caria who attempted to betray the Greeks to the Persains and for their treachery were condemned to be walled up alive. Similar figures, sometimes full or three-quarter length, were carved in wood on a smaller scale as decorative features in Renaissance wood panelling. Caryatids were occasionally used as ornaments on Louis XIV clock cases, and they occure as gilded cast-metal decoration on the front corners of some large late 19th-century bracket clocks.

Ceramic Clock Case:
The use of pottery and porcelain for clock cases goes back to about the middle of the 18th century. many examples are simply metal cases with enamelled porcelain plaques set into mounts or perhaps porcelain flowers or figures as ornament. Enamelled porcelain introduces bright, clear color into case design and the porcelain factories of Meissen in Germany and Sevres in France supplied decorative details of this kind as well as vases to complete a garniture de chemin'ee with a clock. The neoclassical period of the late 18th century produced many fine ceramic cases, sometimes using the new jasperware of Josiah Wedgwood from circa 1775. Parian porcelain, developed from biscuit (unglazed) porcelain, was a splendid material for decorative cases, somewhat resembling marble, and the 19th century saw fine ceramic cases from firms such as Minton, Doulton and Charles Meigh of Stoke-on-Trent, as well as many cheap ones from standard mass-produced movements.

Chime Gongs:
( Pic )     Early clocks and watches all chimed on bells, but this made striking watches very thick. In the last quarter of the 18th century, when the fashion changed to thinner watches, a steel-wire open ring was fitted around the band of the movement and fixed to it at one end. When struck near the fixed end, a good bell-like sound resulted. Wire gongs were later made with many turns in sprial form, to give a low-pitched sound. With their advantge of occupying only a small volume, they have been extensively used in clocks of many kinds since the early 19th century.

Chime Rods:
( Pic )     Modern clocks often strike on metal rods which, like gongs, must be fitted to a substantial metal block attached to a sounding board to give their best effect.

Chime Tubes - Bells:
( Pic )     Late in the 19th century, musical and chiming longcase clocks were made fitted with tubes from 1 to 1 1/2 inches in diameter and to varying lengths, which were suspended at one end in the back of the case. Tubular bells in this form give a mellow, bell-like sound and make a decorative feature at the back of the case when finished in brass or nickel plate.

Chops:
Jaws of wood, fibre or soft metal placed in a vice to protect work being held there from being marked by the vice.

Chuck Box:
( Pic )     The chuck box is used for holding work during turning. The box chuck consists of a hollow cylinder fitted with radial screws which grip the work to be turned. This type of chuck is particularly useful for mounting work eccentrically.

Chuck Collet:
( Pic )     This type of chuck is often called a split chuck. It consists of a hollow spindle, usually threaded at one end, the forward end being accurately drilled or broached and split, and able to close on and grip the work being turned as it is tightened into the hollow driving spindle of the lathe headstock, using the draw bar or draw screw. It is mostly used for comparatively small work and sets of variously sized split chucks are available for a given lathe. Being hollow it has the advantage that it can accommodate long lengths of wire, and for this reason it is often called a 'wire chuck'.

Chuck, Lantern:
This is a specialised chuck for holding parts such as screws, and is used with the screwhead or screwpoint polishing tool.

Chuck, self-centering:
( Pic )     A useful chuck adaptable to many sizes of work. It has three or more radial jaws which close together on the work held by means of a screw or scroll inside the chuck, in such a way as to center the work automatically as they close. This chuck is widely used on engineers' lathes as well as for clockmaking.

Chuck, step:
( Pic )     The step chuck is similar in operation to the split chuck or collet chuck except that it has a stepped face, with concentric steps or rings which are suitable for holding small clock wheels or similar parts. Like split chucks they are available in a range of sizes, with different diameters of steps.

Click:
( Pic )     The pivoted bar which allows movement in one direction only of a ratchet wheel. In engineering, the term 'pawl' is generally used for the part which horologists call a 'click'

Cock, Clock Plate :
( Pic )     A bracket with one foot, often used for pivoting clock arbors outside the plates, as in the case of a balance or escape cock.

Cushion Top:
( Pic )     The name given to the shaped tops of hoods of longcse clocks towards the end of the 17th century, when carved cresting went out of fashion. Cushion tops appeared in a variety of shapes, such as a simple ovolo moulding surmounted by a small platform, or in the style of the wooden basket top to be found on the bracket clocks of the period. In more ornate clocks the cushion top might even appear as a double inverted bell. The cushion top was often ornamented with a pair of turned and gilded ball-shaped finials or similar ones in a spiral, flame-like form. It was usually veneered and decorated in the same way as the rest of the case and was a favorite hood top for taller, arch-dial longcase clocks, lasting until the introduction of the pagoda top about 1740.