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Calendar: Many centuries ago, Emperors employed astronomers to fix their own calendars. Julius Caesar carried out a drastic reform, resulting in our present calendar, because officials were altering dates to suit themselves. Augustus Caesar changed leap year to every four years instead of three and the name of the month Sextilis to Augustus (August). Pope Gregory made the final change by introducing 97 leap years in 400 years instead of 100. The Gregorian calendar was accepted by Catholic countries in 1582. England did not come into line until 170 years later, thinking this a Popish plot.

Calendar Reform: The present calendar wastes time and money because of the varying lengths of months and different days on which festivals occur. The League of Nations proposed a reform and so has United Nations. Neither has been accepted. The U.N. World Calendar gives 26 working days in each month and 91 in each quarter. Days of months would always fall on the same dates. This leaves an odd day at the end of the year without a number to be called World Day (or New Year's Day). Leap Year's Day would fall similarly between 30 June and 1 July, and be unnumbered.

Calendar Clock: One showing the date, sometimes the month, and even the day of the week. Most have to be corrected at the end of months of less than 31 days. Self-correcting versions are called PERPETUAL CALENDARS. A pin on a wheel turning once in 24 hours operates the mechanism around midnight.

Calendar Watch: Wrist- or pocket watch showing the date through an aperture in the dial. On some the date can be reset by moving the minute hand back and forth across 12 o'clock (midnight). On others the hands have to be twirled through 24 hours to move each date.

Calotte: Travelling clock which folds into leather case or portfolio. 'Calotte' actually refers to the circular metal case of the clock itself.

Camera Timer: Special clock with DIGITAL RECORDING built into cameras used for aerial surveys, etc. Each picture then gives on the edge a miniature record of the time at which it was taken. Camera timers of a different design are made for horse racing, athletics, and other sporting events, to give 'photofinishes'. The camera faces along the winning line. The film moves past a slit, which acts as the camera aperture, the speed being appropriate to the speed of the contestants. Thus the camera records a series of events on one film. It also shows, on the edge, the timing of the competitors; the timer is set going by a starting gate or breaking of a light ray, at the beginning of the race.

Candle Clock: Candle with bands marked on it to indicate passing time, said to have been invented by King Arthur.

Canonical Hours: Seven periods known as Matins, Prime, Tierce, Sext, Nones, Vespers, and Compline into which early monasteries divided the day, to control working and prayer times. Froissart, in his Chronicles, refers to Canonical Hours before 1377 and a.m. and p.m. after that date.

Canterbury Cathedral Clock: There is a record of the first clock being erected here in 1292, four years after the first WESTMINSTER PALACE CLOCK may have been erected.

Cap: Separate dustproof cover inside the case to cover a watch MOVEMENT, common from about 1750. Superseded by the Borgel screwed-up case and others more dustproof up to today's WATERPROOF CASE.

Captain Cook's Watches: This famous sailor tested many of the earliest timekeepers for FINDING THE LONGITUDE including those made by HARRISON, MUDGE, ARNOLD, and KENDALL.

Captain Scott's Watch: A DECK WATCH by S. Smith and Sons recovered from Captain Scott's body in the Antarctic and used again by Dr Fuchs on the Trans-Antarctic Expedition in 1957. Stolen at London Airport in 1961.

Carriage Clock: Smallish portable clock, spring-driven with BALANCE. The earliest are like very large pocket watches (Plate 7). French ones have a rectangular brass case usually with glass sides and top, and with a handle on top; each has a PLATFORM ESCAPEMENT, often strikes, sometimes chimes, or is a REPEATER. See Sedan Clock.

Cartel Clock: Ornate French wall clock in cast bronze or carved wood with a gilt finish and half-seconds PENDULUM, of Louis XV period.

Case, Clock: The earliest clocks known had no cases, but soon metal panels were used between vertical corner posts to keep out dust, as in the LANTERN CLOCK. Even today TURRET CLOCKS rarely have protective cases. Decorative cases go back four centuries when elaborate engraving, repousse and carving on brass or precious metals, and rock crystal were employed. Almost every material available has since been used, from reinforced concrete to cardboard. Today most common materials are wood, brass, ceramics and plastics for domestic clocks of which current designs have developed from GOTHIC, LANTERN arid BRACKET CLOCKS.

Case, Watch: Earliest watch cases were ball shaped (wrongly called NUREMBERG EGGS) and made of gilded brass. Gilded bronze was common in the sixteenth century. The ball was rapidly superseded by the DRUM shape which became rounded at the edges after about 1575, when octagonal shapes also appeared. Oval shapes were introduced just before 1600 (see Puritan Watch). There were no glasses and the single hand was read through the pierced decoration of the cover, although rock crystal was sometimes used as a 'glass'. The case was hinged below the PENDANT, the MOVEMENT being hinged on the same line, but held in the bottom of the case by a small catch. The PAIR CASE increased in popularity after mid-seventeenth century (see Cap). Considerable decoration was applied from this time, of rock crystal, ENAMEL, chasing, chiselling, and REPOUSSE. The FORM WATCH also appeared. Gold, silver, brass, and PINCHBECK were used and outer pair cases were sometimes of leather (see Pinwork), SHAGREEN, or PIQUE. Modern wristwatch cases are of gold alloy, stainless steel, or (for cheap ones) aluminium alloy. They are machined from solid shaped bar, or formed from sheet by press tools by specialist manufacturers. The fine finish on gold is obtained by diamond tools. Modern cases are three-piece, two-piece, or one-piece (which is 'opened' by removing the UNBREAKABLE GLASS). See Waterproof Case.

Cassiobury Clock: A TURRET CLOCK from Cassiobury Park, Hertfordshire, still with FOLIOT made about 1600.

Centre of Oscillation: The time of swing of a PENDULUM depends on its length (only) from the centre of SUSPENSION to the centre of oscillation, which is also called the 'centre of percussion'. The latter is an imaginary point within the BOB related to the centre of gravity. This explains why adding a weight above the bob makes the clock go faster; it raises the centre of oscillation and makes the pendulum 'shorter'.

Centre Seconds Hand: Seconds hand of a watch or clock pivoted in the centre of the dial. Also called 'sweep seconds'.

Certificate: See Rating Certificate, Kew 'A' Certificate and Craftsmanship Test.

Chamber Clock: Earliest form of domestic clock. Made of iron by blacksmiths like the first TOWER CLOCKS. Driven by weights and hung on a wall in the hall which was the centre of the medieval home, so that its striking could be heard all round. Also called a 'house clock'. See Lantern Clock.

Chapter Ring: The circle on which the hours are marked. On antique clocks this is often a separate brass ring engraved with the numerals, etc., the engraving being filled with black wax, and the ring SILVERED and LACQUERED.

Chapters: The hour marks of a clock.

Chatelaine Watch: Watch with an ornamental, and often enamelled, chain with trinkets attached. A true chatelaine was the chain holding the keys, worn by the mistress of the medieval castle; it became popular again in Victorian times as an ornament.

Chelsea Clock: Another name for SHIP'S BELL CLOCK, as many are made by the Chelsea Clock Co., U.S.A.

Chemical Clock: Device using chemical cartridges for timing periods of electric current flow. The current 'eats up' the cartridge, the reduced length showing the time on a scale.

Chess Clock: Special TIMER for chess players with two MOVEMENTS and two dials, one showing the accumulating time occupied by one player in his moves, and the other the time of the other player. As each player makes a move, he presses a knob on the clock which stops the hands of his dial and starts those of his opponent's dial.

Chime: Simple melody on bells or gongs at the quarter or half hours and preceding the hour. The earliest was the TING TANG on two bells. Most are on four bells, but there are others on any number. The WESTMINSTER CHIME is a four-bell. Notre Dame in Paris is an eight-bell. The Whittington chime of Bow Church, London, is on eleven bells, but is sometimes modified so that it can be played on fewer.

Chiming Clock: Clock that CHIMES. TOWER CLOCKS and some antique clocks chime on bells. Modern domestic clocks usually have the WESTMINSTER or modified Whittington chime on rod GONGS. The hour note is produced by hitting several gongs simultaneously. A turning chime BARREL with pins or cams operates GONG HAMMERS to produce the tune. In such clocks there are three separate MAINSPRINGS or BARRELS and trains of wheels for timekeeping, striking, and chiming.

Chinese Clocks: The Chinese produced the transitional clock between the old inaccurate WATER CLOCK and the mechanical clock. A monk I-Hsing probably invented the first ESCAPEMENT in A.D. 725. The Chinese had no part in the development of the mechanical clock, but the present regime has introduced clock and watchmaking industries. Many clocks (and watches) of special design were made in the eighteenth and nineteenth centuries by English and Swiss makers for the Chinese market. See Su Sung's Clock.

Chinese Duplex: Swiss watch with a special kind Of DUPLEX escapement made for the Chinese market in mid-nineteenth century. This made the CENTRE SECONDS HAND appear to be DEAD BEAT, and move every second. Such watches were usually made in pairs. The MOVEMENTS had elaborately engraved and scalloped-edged BRIDGES, which could be seen through an inside glass cover.

Chippendale Case: Clock case based on the designs of Thos. Chippendale in his book of furniture designs, 1754. Usually in mahogany.

Chronograph: A timepiece that can be started and stopped to measure short time intervals. Usually a watch for timing only is called a TIMER or STOPWATCH and one that shows the time of day as well is- called a 'chronograph'. Wrist chronographs often have special scales such as TELEMETER and TACHYMETER. There are also chronographs for technical and scientific uses. The recording chronograph was invented in 1807 by Thomas Young, who used a revolving drum on which a pencil marked the beginning and end of the time interval. The electro-magnetic chronograph was invented by Wheatstone, or the younger BREGUT. Washington Observatory was the first to use a chronograph for measuring star transits in 1849. See Transit Instrument. Chronographs for very short time intervals are sometimes electronic and to confuse the name still more, the makers called them CHRONOMETERS.

Chronographer (or chronopher): Apparatus controlled by a clockwork CONICAL PENDULUM used from 1852 by the Electric Telegraph Co., railway companies, and the General Post Office, to send TIME SIGNALS from GREENWICH OBSERVATORY by wire t0 some 1,000 towns and to railway stations. Work at telegraph offices was stopped a few minutes before 10 a.m. and before 1 p.m. to receive the 'time current', which moved the telegraph (galvanometer) needles to one side, then flicked them to the other exactly at the hour. 'BIG BEN'S' timekeeping was originally checked by chronographer.

Chronometer: Originally a name for a metronome, but applied to a precision timekeeper in 1714 by Jeremy Thacker. Now a general name for a non-pendulum precision clock or a watch, although purists insist that it means a timepiece with a DETENT ESCAPEMENT, such as the MARINE CHRONOMETER. Makers of electronic instruments call their timekeeping devices ELECTRONIC CHRONOMETERS. The Admiralty names high precision LEVER WATCHES 'chronometers'. In Switzerland since 1951, no manufacturer has been allowed to call a watch a 'chronometer' unless it has obtained an official RATING CERTIFICATE from one of the testing bureaux.

Chronometer Escapement: Another name for the DETENT ESCAPEMENT.

Chronoscope: Name usually given to a continuously running timepiece for recording short time intervals by engaging and disengaging a hand. Invented in 1840 by Wheatstone, whose instrument was accurate to 1/60th sec. HIPP made one a few years later accurate to 1/1,OOOth sec. Today the very much more accurate QUARTZ CRYSTAL CLOCK, AMMONIA MASER, Or ATOMIC CLOCK is used. See Timer.

Church Clock: The oldest clocks in England are usually in the towers of cathedrals and churches, although some were placed in the church itself. On the Continent many were in separately built towers. In Langford Church, Oxfordshire, is a large VERGE clock still working, with its original stone WEIGHTS. See Salisbury Cathedral Clock.

Circular Error: To remain accurate regardless of the angle it swings through (ISOCHRONOUS), a pendulum should swing in a CYCLOIDAL CURVE. It actually swings in an arc, and takes longer to swing in a large arc than a small one. The circular error is the loss in time caused by swinging in a circular path. At an arc of 10 it is about -40 sec. a day. Christiaan HUYGENS discovered this and invented CYCLOIDAL CHEEKS to eliminate it. Accurate clock pendulums are designed to swing through a total arc about 1 1/2 so that the error is negligible. The recoil of an ANCHOR ESCAPEMENT tends to compensate for the circular error for ordinary purposes. See Escapement Error.

Cleaning: Misleading term used by watch and clockmakers for servicing, which actually involves stripping, examination, cleaning of individual parts by CLEANING MACHINE, perhaps with ULTRASONIC unit, reassembling, oiling, readjustment, and regulation by RATE RECORDER. OIL dries out after about two years and forms a soap which may act as a grinding paste with dust. After removal of this and re-oiling and greasing, the watch usually has a different RATE.

Cleaning Machine: Old craftsmen used to, and still do, clean clocks and watches by hand, starting with cleaning fluids, then a paste of powdered chalk brushed on and off, and finally finishing the PIVOT holes with PEGWOOD, and the pivots with PITH. Now machines are usually employed, especially for watches, which are stripped and the main parts put in a gauze basket which is oscillated in a series of special cleaning fluids and dried in a drying chamber. Some machines are automatic. See Ultrasonic Cleaning.

Clepsydra: A WATER CLOCK; literally, 'stealer of time'.

Clerkenwell: Traditional home of watch and clock manufacturing in London, although many early clockmakers, such as TOMPION, GRAHAM, and MUDGE, were in Fleet Street. Now there is no major manufacturing in Clerkenwell, except for one firm of tower clock makers in Bowling Green Lane, and many watch and clock traders have joined the diamond dealers in Hatton Garden. The peak of Clerkenwell's manufacture Of ENGLISH LEVERS was in the first half of the nineteenth century when 20,000 craftsmen were employed.

Click: Traditional horological name for the pawl of a pawl and ratchet mechanism. See Recoiling Click.

Clock: From clokka, a bell. The first mechanical clock of which there is definite evidence was put up in 1335 on the church of Beata Vergine (now San Gottardo), Milan. It struck a bell at every hour up to 24, having no dial, and may have been the first public clock. The first printed illustration of a MOVEMENT was in a book by Girolamo Cardan (inventor of the cardan joint) in 1557. Earliest references to 'clok' and 'clocke' are in 1371 and 'clokkemaker' in 1390.

Clock Manor Museum: Museum at Manor Heights, Bergen Park, Colorado, USA,, of wide range of clocks from many countries. Founded by Orville R. Hagans, 1961.

Clock Star: The rotation of the Earth, and therefore time, can be more accurately measured from one or more of the 'fixed stars' than from the Sun, so such stars are called 'clock stars'. See Transit Instrument, Sidereal Time and Time Determination.

Clock-Watch: Early watch that strikes like a clock. Some had repeater mechanisms, but with an extra TRAIN of wheels that had to be wound separately. A REPEATER WATCH also strikes, but only when required to.

Clock Winder: Man who winds and looks after clocks, either domestic ones in large houses or TOWER CLOCKS, which often take many hours to wind after climbing hundreds of steps. Most tower clocks now have AUTOMATIC CLOCK WINDING Or are being converted to it.

Clockmaker: Once a maker of clocks and watches who was recognized by his craft guild. Now a clock repairer. Clockmaking requires skills and knowledge different from watchmaking.

Clockmakers Company: The Worshipful Company of Clockmakers is No. 61 in the City of London craft guilds, its Charter having been granted on 22 August 1631. First Master was David RAMSAY. All famous past craftsmen were Freemen or Liverymen. Its Charter enabled the Company to enter any premises in and around London City to seize and destroy any faulty work, or work not done by someone who had not served his APPRENTICESHIP. Foreigners could only work with Company members, and foreign timepieces and sundials had to be approved before sale. It no longer controls the trade, but is advisory and social, has a fine library, and the GUILDHALL MUSEUM COLLECTION. It publishes lists of past apprentices and awards the TOMPION MEDAL. Those appointed to the Livery still include well-known horologists. Address: Candlewick House, 116 Cannon Street, London, E.C.1.

Club Tooth: Special shape of ESCAPE WHEEL TOOTH employed with the LEVER ESCAPEMENT to increase the length of IMPULSE while decreasing wear.

Coaching Clock: Wall timekeeper with large dial, round or hexagonal, 2 to 3 ft. in diameter, used by coaching inns in the eighteenth century, for the benefit of travellers. Also called a TAVERN CLOCK, and later an ACT OF PARLIAMENT CLOCK. The dials were usually black or green with gold numerals and had no glass. Usually there was a SECONDS PENDULUM. Many are still in existence in inns south of London. One inn opposite Canterbury Cathedral has two.

Cock: A metal bar which carries one or more PIVOT bearings and is fixed at one end only. Looks like half a BRIDGE.

Cocktail Watch: Fancy watch for women. Usually the UNBREAKABLE GLASS is thick and lens-like and called a 'cocktail glass'.

Coin Watch: A gold coin, usually a Napoleon or a Marie Louise, with an extremely thin watch movement and dial concealed inside it. The coin is hollowed out and hinged, and opened by a hidden catch. Wonderful technical achievements by several Swiss manufacturers.

Cole, James Ferguson (1799-1880): One of the finest of English clock and watch makers, and one of the last who could make every part of the MOVEMENT and CASE himself, even to engraving. Sometimes called the 'English BREGUET' because he exchanged ideas with Breguet. At the Five Centuries of British Timekeeping Exhibition in London, 1955, there was a special pocket CHRONOMETER he made when he was under 21, and a special LEVER WATCH made when he was 72.

Collections: In England the main collections of clocks and watches that are on exhibition are those of the ASHMOLEAN MUSEUM, Oxford; BRITISH MUSEUM; Fitzwilliam Museum, Cambridge; Gershom Parkington, Bury St Edmunds; GUILDHALL MUSEUM; Museum of the History of Science, Oxford; NATIONAL MARITIME MUSEUM; Royal United Service Museum; SCIENCE MUSEUM; Basingstoke Museum; and WALLACE COLLECTION. Abroad there are collections: In Austria-Kunsthistorisches Museum, Technisches Museum, Schatz des Deutschen Rittordens, Oesterreishes Museum fur Angewandte Kunst, Uhren Museum der Stadt (Vienna Clock Museum), all in Vienna, and the Steirisches Landesmuseum, Graz; In Denmark -Rosenborg Castle, National Museet, both in Copenhagen. In France-the Louvre, Conservatoire Nationale des Arts et Metiers, Musee des Arts Decoratifs, all in Paris, and the Musee de Besangon. In West Germany-Bayerisches National Museum, Munich; Germanisches Museum, Nuremberg; Wurttembergisches Landesmuseum, Stuttgart; Hessisches Landesmuseum, Kassel; Mainfrankisches Museum, Wurzberg; Kienzle Museum. In East Germany-the Staat. Math. Phys. Salon, and Zwinger, Dresden. In Holland-Rijksmuseum, Gemeentemuseum, both in Amsterdam; Rijksmuseum voor de Geschiedenis der Natuurwetonschappen, Leiden. In Switzerland-Musee d'Art et Histoire, Geneva; Historisches Museum, Basle; Musee d'Horlogerie, La Chaux de Fonds. In the U.S.A. -Metropolitan Museum of Art, New York; Columbia Museum of Horological Antiquities, Pa.; CLOCK MANOR MUSEUM, Colorado; American Museum of Clocks and Watches, New York 53; Franklin Institute, Pa.; U.S. National Museum (Smithsonian), Washington 25; California Academy of Sciences, San Francisco 18; Berenice Bishop Museum, Honolulu.

Columbus Clock: Souvenir clock made almost entirely of wood, but imitating a fifteenth-century VERGE and FolioT iron clock. Probably first made in the Black Forest, Germany, for the Chicago Exhibition of 1892 to commemorate the 400th anniversary of the landing of Columbus and later mass produced in the U.S.A. A picture of Columbus and the date 1492 which are embossed on the wooden dial have misled gullible 'antique' buyers. There are variations, some with Mozart's picture, and others with a fir tree and the date 1640.

Column Clock: Clock with a base like an architectural column. See Pillar Clock.

Compass Sundial: Type of PORTABLE SUNDIAL, similar to a fixed SUNDIAL, which was set up by a compass and then showed SOLAR TIME by the position east or west of the sun in the sky.

Compensation Balance: A BALANCE designed to correct TEMPERATURE ERROR, when used with a particular type of HAIRSPRING. The earliest attempts at TEMPERATURE COMPENSATION were by controlling the force of the hairspring. First to compensate the balance was LE ROY, who fixed to it two mercury thermometers, expanding inwards. At higher temperatures a balance goes slower; the thermometers made it tend to go faster as temperature rose. He improved on this by using a balance wheel rim of two semicircular BI-METALLIC strips, each carrying a weight one end and being fixed to the balance arm at the other. This is called a 'cut balance' (Fig. 5) and was much improved in the EARNSHAW BALANCE. In heat, the ends of the bi-metallic strips moved the weights towards the centre of the balance. The compensation, however, introduced a MIDDLE TEMPERATURE ERROR which attempts were made t0 eliminate by AUXILIARY COMPENSATION. This error is only serious on timepieces like MARINE CHRONOMETERS submitted to extremes of temperature. Most successful was the GUILLAUME BALANCE, which has the rim made of a special bi-metallic strip to give almost perfect compensation with a steel hairspring. Other forms are the DITISIIEIM BALANCE and the OVALIZING BALANCE, also for use with special hairsprings. The cut balance used in high-grade watches has screws round the rim which act as weights and can be screwed in or out to adjust temperature compensation, timekeeping, and POISE. Introduction of the alloy ELINVAR simplified the entire problem by enabling the hairspring to be effectively compensated, so that a plain uncut brass balance could again be employed. Since 1930, various other hairspring alloys such as Metalinvar, NIVAROX, Isoval, Durinval, and Nispan-C have been invented to give excellent compensation with plain uncut balances of nickel, or a beryllium alloy such as GLUCYDUR. Many millions of cheap watches, however, are still made with useless dummy compensation balances, which is fraudulent.

Compensation Curb: The second attempt at TEMPERATURE COMPENSATION Of a BALANCE and SPRING by HARRISON in mideighteenth century. A BI-METALLIC strip effectively shortens the length of the hairspring by moving two CURB PINS along it as temperature rises.

Compensation Pendulum: A PENDULUM that has been compensated for TEMPERATURE ERROR. In 1721, GRAHAM made a pendulum with a jar of mercury of particular size for its BOB. The mercury expands upwards to compensate for the rod expanding downwards. This was followed by HARRISON's cheaper version of steel and brass rods, the GRIDIRON PENDULUM. Another combination of metals is zinc and steel (see Riefler Clock). Pendulum rods are also made of wood, such as Fir, dried out and varnished, as its expansion coefficient is small. Perfect compensation, however, was not achieved until GUILLAUME discovered INVAR, a metal alloy that remains the same length at different temperatures. See Temperature Error.

Complicated Watch: Watch with COMPLICATED WORK. The most complicated watch in the world is said to be one, still existing, made by LE ROY in 1896. It has a PERPETUAL CALENDAR giving date, day, month, and year for 100 years, phases and age of the moon, seasons, solstices, equinoxes, and EQUATION OF TIME; there 1S a CHRONOGRAPH with FLY BACK, minute and hour counters, and UP-AND-DOWN DIAL: it will strike GRANDE SONNERIE, or ordinarily, or be silent; there 1S a MINUTE REPEATER On three notes; SIDEREAL gearing operates ASTRONOMICAL DIALS for Paris and Lisbon (where the first owner lived) and LOCAL TIMES are given for 125 of the world's towns; sunrise and sunset times for Lisbon are shown, and a thermometer, hygrometer, barometer, and compass are incorporated. The watch can be regulated without being opened (Plate 4). Only about three manufacturers still make really complicated watches, which can cost over 3,000 each.

Complicated Work: Any mechanism other than simple time-of-day in a clock or watch, such as ASTRONOMICAL, CHRONOGRAPH, arid REPEATER. Watches with SELF-WINDING work, simple CALENDAR Or ALARM, are so common today, however, that they are not regarded as complicated.

Compound Pendulum: A pendulum which has a weight on each end of its rod and is suspended near the centre. It swings very slowly. Used in the metronome and very rarely in clocks.

Comptoise Clock: Alternative name for a MORBIER CLOCK, after the district where the village Morbier is situated.

Condensation: A watch case that is not completely air-tight or WATERPROOF, will 'breathe' as its temperature changes. If it draws in perspiration from the wrist, or other moisture, a drop in temperature will make this condense inside the glass and on the steel parts, causing rust. The air in a waterproof watch contains so little moisture that sudden chilling can only produce a milky haze on the glass. The answer to this is to seal the watch in very dry air, although one Swiss maker produces vacuum-sealed watches.

Congreve Clock: A ROLLING BALL CLOCK in which the ball is the timekeeper, invented by Wm. Congreve in 1808. The ball runs down a zigzag track on a metal table (indicating seconds by passing under bridges). The table is tilted the opposite way every half-minute to send the ball back to the other end. Tilting is effected by clockwork, released by the ball striking catches at each end of the track. Hours and minutes are shown on dials. It has been calculated that the steel ball rolls about 12,500 miles a year.

Conical Pendulum: Pendulum that swings in a circle, invented by Jost Bodeker in 1587. Used as a speed governor by Siemens and AIRY for training a telescope on a moving star. Also used for novelty clocks, one of which has the MOVEMENT in, and dial on, the ball-shaped pendulum BOB. A disadvantage is the large CIRCULAR ERROR.

Conical Pivot: Elementary cone-shaped PIVOT used in alarm clocks, cheap watches, and meters. Runs in a CUP BEARING and usually employed for the BALANCE Only in timekeepers. Wear of these pivots often explains why an alarm will only run dial downwards.

Constant Force Escapement: An ESCAPEMENT designed to give exact measured IMPULSES to a BALANCE arid SPRING or a PENDULUM, and thus avoid changes in RATE caused by variations in the driving force. See Remontoire and Gravity Escapement.

Contrate Wheel: Cup-shaped wheel with its teeth cut in the rim of the cup so that they are at right angles to the wheel. Used with normal PINION (gear) to drive through a right angle. Simple alternative to a bevel gear. Used with the modern PLATFORM ESCAPEMENT arid on some VERGE clocks arid watches.

Conversion: As each improvement to timekeeping was invented, such as the PENDULUM, ANCHOR ESCAPEMENT, HAIRSPRING, LEVER ESCAPEMENT, etc., many older timepieces were converted. This often makes it difficult to date antique pieces. As accurate modern timepieces are so plentiful, it is considered vandalism to convert an antique. Yet people still commit the heresy of removing an antique MOVEMENT in favour of a synchronous electric one.

Cordless Clock: American name for a BATTERY CLOCK.

Cotehele Clock: Ancient TOWER CLOCK with iron wheels set in a row in a vertical iron frame fixed to a wooden post, with the VERGE and FOLIOT at the bottom. It is in the chapel of Cotehele House, near Calstock, Cornwall, which belongs to the National Trust. See Vertical Frame.

Count Down: Method of announcing time still available before an event, particularly the firing of a rocket, by counting backwards first in hours, minutes, then seconds until the last '3, 2, 1, fire', using a large special TIMER.

Count Wheel: Correct name for what is usually called the LOCKING PLATE since it counts the strokes of striking.

Coventry: One of the centres of the earlier BRITISH HOROLOGICAL INDUSTRY, with CLERKENWELL arid PRESCOT. Watchmaking started here in the early eighteenth century and up to 1860 a big trade was carried on with the U.S.A. RAW MOVEMENTS came from Prescot, and went through the hands of the 'first half doer', the 'escapement doer', the 'finisher', the 'timer', and the 'examiner'. The Coventry trade was killed in the late nineteenth century by the craftsmen refusing to accept machine finishing methods and only one firm still thrives there, although it gave up making watches when the factory was blown up in World War Two. Coventry watchmakers were once easily recognized in the street by their top hats, white aprons rolled up to the waist, and eyeglasses hanging round their necks.

Cox, James (1760-88): English clock and watchmaker who specialized in COMPLICATED WORK and in exporting to oriental countries. He ran a museum of SINGING BIRDS, unusual clocks with AUTOMATA, and mechanical toys, in London.

Craftsmanship Test: A performance test for watches carried out by the NATIONAL PHYSICAL LABORATORY. It replaced the KEW 'A' CERTIFICATE tests. See Rating Certificate.

Cratzer, Nicholas: Henry VIII'S ROYAL CLOCKMAKER, who made the ANNE BOLEYN CLOCK. A letter of 12 October 1520, to Cardinal Wolsey, suggested using Cratzer as a spy in Germany.

Cromwellian Clock: Another name for a LANTERN CLOCK.

Cross-Beat Escapement: A more accurate VERGE ESCAPEMENT having two springy balance arms swinging across each other on nearly the same centre. Invented by Jobst BURGI about 1586, but only 'rediscovered' in 1953 (by Dr H. von Bertele). Also called a 'double balance'.

Crown Wheel: The ESCAPE WHEEL Of a VERGE ESCAPEMENT, which is therefore also called 'crown wheel escapement'. It is a form of CONTRATE WHEEL with pointed teeth, which give it the appearance of a king's crown. It lasted in clock and watch escapements for 400 years until the ANCHOR ESCAPEMENT made it unnecessary in clocks and the CYLINDER and other escapements ousted it from watches.

Crucifix Clock: Clock combined with a model of the Christian crucifixion; made in seventeenth century.

Cruciform Watch: Watch with a case the shape of a cross, i.e. a FORM WATCH (Plate 4). Crutch Connecting member between the ESCAPEMENT of a clock and its PENDULUM, allowing domination by the pendulum. Invented by Christiaan HUYGENS in 1657.

Crystal: An unbreakable watch GLASS.

Ctesibius: Mathematician of 200 B.C. who was first to design a water clock to show hours of varying duration (TEMPORAL HOURS) during the year.

Cuckoo Clock: Clock in which a wooden cuckoo calls the hours by popping out of a door at the hour, its call being imitated by pipes and air bellows. The earliest extant of about 1775 is of wood with a VERGE ESCAPEMENT and pendulum in front of the dial. It strikes half hours on a glass bell. The inventor may have been Anton Ketterer, of Schonwald in the Black Forest, some 40 years earlier. Later ones have carved wooden cases, metal MOVEMENTS, short pendulums, two metal 'fir cone' weights, and run for 30 hours. Cuckoo clocks are often but quite wrongly supposed to be Swiss in origin and make.

Cuckoo-Quail Clock: A CUCKOO CLOCK which also imitates the sound of the quail. Another version has a trumpeter as well as a cuckoo.

Cup Bearings: Cone-shaped depressions in the end of a steel screw or plug, associated with the CONICAL PIVOTS Of the BALANCES Of 3O-hr. alarm clocks and cheap watches. For electric supply and other meters, the cup bearings are often of synthetic ruby.

Curb Pins: To make small changes in the RATE of a watch, the outer end of the HAIRSPRING runs between two closely spaced 'curb pins' on the INDEX, so that moving the index in effect alters the length of the hairspring.

Cut Balance: A temperature COMPENSATION BALANCE with a BI-METALLIC rim. The rim is cut to form two semicircles, each being fastened at one end to the arm of the balance wheel. Larger cut balances which carry weights on the ends of the arms tend to be affected by the weights trying to swing outwards under centrifugal force, so that they are not truly ISOCHRONOUS.

Cycloidal Cheeks: Curved plates each side of the suspension of a PENDULUM to make it swing in a cycloid instead of an arc, thus avoiding CIRCULAR ERROR. Invented by HUYGENS.

Cylinder Escapement: Form of ESCAPEMENT perfected by George GRAHAM in 1725 with a half cylinder on the BALANCE STAFF which releases and 1S IMPULSED by the ESCAPE WHEEL teeth. It replaced the VERGE ESCAPEMENT, and came into its own again in the nineteenth century for machine-made cheap watches and clocks, until replaced by the PIN LEVER. Also called the 'HORIZONTAL ESCAPEMENT'.

Cylindrical Spring: POCKET CHRONOMETERS (except Swiss ones) and MARINE CHRONOMETERS have BALANCE SPRINGS that are HELICAL in shape with incurved ends (instead of being flat spirals) because early makers found these had better RATES. First patented by ARNOLD in 1775. The present Mercer marine chronometer has a helical balance spring made of an alloy of the precious metal palladium. Springs of quartz glass have also been made. The FLOATING BALANCE is suspended from a helical balance spring half of which is wound clockwise and half anti-clockwise to prevent the balance from rising and falling. A few pocket watches have also been made with cylindrical MAINSPRINGS.

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