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Danish Clocks: A forgotten treasury of magnificent clocks was recognized in Rosenborg and Frederiksborg castles and the Princes Palace in 1953 by H. von Bertele and H. Steisdal. These revealed an early and advanced culture.
Daylight Saving: Introduction of the Summer Time Act of 1925 putting on clocks in summer to give an extra hour of daylight was almost entirely due to William Willett (d. 1915), a London builder. While Britain dallied, Willett's pamphlet on his ideas was translated into French and German and the Germans introduced the system during the First World War from 1914-18 for economy of lighting. The British followed from 1916-18. A sundial memorial to Willett in Petts Wood, Kent, always shows summer time.
De Vick's Clock: One of the earliest known clocks, made by Henry de Vick, of Paris, for King Charles V of France in 1371. It has been heavily restored and is in the wall on a corner of the Palais de Justice.
Dead Beat: Moving in definite jumps without recoiling, as with the seconds hand of a clock with DEAD BEAT ESCAPEMENT, a SLAVE DIAL, or an INDEPENDENT SECONDS watch.
Dead Beat Escapement: More accurate form Of ANCHOR ESCAPEMENT that does not RECOIL. Invented by George GRAHAM in 1715 and still used for REGULATORS and other precision clocks. The PALLETS are often jewelled.
Decimal Time: The French Revolutionaries in 1793 established decimal (or Republican) time as well as decimal weights and measures. A decimal hour was to have 100 minutes. Some clocks and watches with decimal dials were made, but even the zeal of the revolutionaries did not ensure their popularity. A Revolutionary calendar with months of 30 days each and no weeks was also introduced. Each month was named after the weather, e.g. Brumaire (fog) was November, and divided into three periods of ten days called 'decades'.
Decimal Timer: A TIMER calibrated with 100 instead of 60 divisions to the minute. Used for certain industrial purposes where it is more convenient to count in decimals.
Deck Watch: Because a ship's MARINE CHRONOMETER is moved as little as possible to avoid disturbing its RATE, a precision watch is compared with it and used on the deck for observations during NAVIGATION. Such a deck watch is like a large pocket watch, but is kept in a special box, like that for the chronometer, to avoid disturbing it unnecessarily. Originally fitted with a DETENT ESCAPEMENT, but now has a LEVER ESCAPEMENT.
Defroster Time: Switch A TIME SWITCH driven by a synchronous CLOCK motor that switches off a deep freeze refrigerator for I hr. or longer every six hours to keep it defrosted without damaging the contents.
Degree Plate: Small plate marked in degrees, and seconds of a degree, and fixed to the back of a clock case behind a pointer on the end of a pendulum, to show the amplitude or angle of swing. Used on REGULATORS, TOWER CLOCKS, MASTER CLOCKS, and Other PRECISION CLOCKS. VULLIAMY claimed to have invented it. Also called a 'beat plate'.
Demagnetizer: A coil of wire carrying an alternating current from the electric mains and used for demagnetizing watches that have been affected by MAGNETISM. The watch is held in or over the coil and the alternating electro-magnetic field causes rapid reversal of the magnetism in the watch which is reduced to zero as the watch is withdrawn from the influence of the coil.
Dennison, Aaron L.: The pioneer of machine-made watches in Roxburg, U.S.A., in 1850. Later set up at Waltham in 1856, then moved to England where he set up the English Watch Co. The firm of Dennison is now a prominent English maker of watch cases. The original Dennison Watch Collection belonging to the Waltham Watch Co. was sold at Christies, London, for £13,680 in 1961.
Detached Escapement: An ESCAPEMENT in which the oscillating element (PENDULUM or BALANCE AND SPRING) is almost entirely free of the mechanism which it controls, as in the LEVER and DETENT ESCAPEMENTS, and the FREE PENDULUM. Escapements with FRICTIONAL REST are not detached.
Detent: A detente is the 'end of strained relations'. A detent is a lever that holds up a spring or locks something; a pawl is one, for example. Used particularly for the lever associated with the DETENT ESCAPEMENT.
Detent Escapement: An accurate DETACHED ESCAPEMENT in which the BALANCE WHEEL is impulsed in one direction only. During its swing, the balance wheel moves aside a DETENT which releases one tooth of the ESCAPE WHEEL. This tooth gives the balance wheel a push in the direction in which it is going and is then locked. On the return swing of the balance a so-called 'passing-spring' prevents the escape wheel from being unlocked. As the BEAT of MARINE CHRONOMETERS is usually half a second and the escape wheel moves at every other beat, the seconds hand shows DEAD BEAT seconds. Invented for use on ships at sea by Thos. MUDGE, Thos. EARNSHAW, and LE ROY in the early eighteenth century. Also called the 'chronometer escapement'. See Spring Detent.
Dial, Clock: Before about 1400, a clock dial revolved to show the time against a fixed hand. Soon a moving hand became almost universal with a fixed dial of iron, silver, brass, wood, and other materials. Only hours, half hours, and perhaps quarters were shown. Early BRACKET and LONG CASE CLOCKS had rectangular dials of brass with CHAPTER RINGS arid corner SPANDRELS first engraved then as separate parts fixed by screws. As soon as the MINUTE HAND came into use, minute divisions appeared, often prominently marked. The numerals and time divisions were engraved and filled with black wax, and chapter rings often SILVERED, and the dial centres MATTED. In front of the dial was a door with a rectangular glass. The square dial gave way to the BREAK ARCH, and after 1750 a door with a round glass began to be used, which made the square dial behind it appear round and did away with the necessity for spandrels. At the end of that century, the round 'door', comprising just a BEZEL with a glass in it, appeared and has continued to today. Dials also became silvered all over and the separate chapter ring disappeared. Painted dials on sheet metal and also enamelled dials came in at about the same time, although enamelled ones were rare on clocks because of the size. Painted dials with scenes and animals or birds became common on long case clocks after 1800. Dials today are of almost any material, the most common being silvered brass, anodized aluminium, wood, GRAINED brass, ceramic, card or paper on various sheet metals, glass, or plastics with the CHAPTERS painted or printed on, or embossed, or separately made and fastened in place. Dials of TOWER CLOCKS may be of cast iron, copper, aluminium, bronze, concrete, stone, glass, etc.
Dial Painter: Only large dials and special ones are painted today. At one time, many, including enamelled ones, had handpainted hour and minute symbols. Incredible skill was shown on watch dials of a century and more ago, a magnifying glass being necessary to read the fine lettering of the signatures. Painters of TOWER CLOCK dials sometimes employ gold leaf for the numerals; such a painter reckons never to restore the same dial twice as gold leaf lasts more than a generation. Certain painters in the past specialized in decorating dials. See Enamelled Watch, Limoges Enamel and Huaud.
Dial, Watch: Early watch dials were of gilded metal engraved with numerals. Sometimes the numerals were engraved on a separate silver CHAPTER RING. Occasionally the whole dial was silver. ENAMELLED WATCH dials were introduced in the sixteenth century, some painted, others champleve (inlaid enamel). Today dials are silvered or gilded brass, with matt, brushed, polished, or other finish. The numerals or BATONS are printed on, embossed, or metal pieces separately made and applied. There are as many as 40 processes in making a dial. Finest dials are of gold, and for novelty other materials such as leather, veneered wood, and linen have been employed.
Dialling: Mathematical construction of sundials. In the seventeenth century dialling was the basis of many recreational problems such as working out the bounds of land by tree shadows.
Diamond Watch: Any watch of which the case and/or the bracelet is set with diamonds for decoration. Diamonds were once used for JEWEL bearings, particularly END STONES.
Digital Indication: Time indication by figures instead of hands, thus 9.32, as in a TICKET CLOCK Or ELECTRONIC CHRONOMETER. Strictly, digital means in separate steps, so any watch hand is digital, but a SYNCHRONOUS CLOCK hand is not.
Directoire Clock: French style of clock from 1795-99 of various neo-classic designs (also clocks of the period after the Revolution when various experiments were made to show DECIMAL TIME).
Ditisheim, Paul (b. 1865): Fine watchmaker who collaborated with GUILLAUME in developing alloys for precision timekeeping and produced an accurate BALANCE of his own. Also developed modern watch OILS. See Epilame.
Ditisheim Balance: A SOLID BALANCE with small separate BI-METALLIC blades for TEMPERATURE COMPENSATION. Invented by DITISHEIM, of Switzerland, in 1920, for use with a HAIRSPRING Of ELINVAR. This overcame centrifugal troubles of the CUT BALANCE and the magnetic weakness of a steel hairspring.
Diver's Watch: Time intervals are very important to skin divers using limited air supplies and having to be careful of 'decompression times'. Specially WATERPROOFED Watches are made for them. These also have large LUMINOUS numerals and hands and an ELAPSED TIME INDICATION by rotating the BEZEL, which is marked in minutes and quarter hours.
Dollar Watch: Robert Ingersoll sold a number of things for a dollar each, including a printing outfit and a camera, and in 1894 produced his first watch at this low price, 'the watch that made the dollar famous'! In England it was called the 'crown' and sold for five shillings.
Domestic Clock: Any type of clock for the home. The earliest was the HOUSE CLOCK.
Dondi's Clock: First astronomical clock of which complete constructional details are known. Built originally in 1348-64 in Pavia, Italy, it had a 24-hr, dial with fixed hand and elaborate indications, including the first continuous recording of minutes, first dials showing sunrise and sunset, day of the month, annual calendar, conversion of MEAN TIME to SIDEREAL TIME, trajectories of planets, etc. An exact model was made in 1960 by Thwaites and Reed of London, under the instruction of H. Alan Lloyd, for the Smithsonian Institution, U.S.A.
Dormant Jewel: Fraudulent name invented by advertising men to make useless watch JEWELS seem important to gullible buyers.
Double Balance: An early name for the CROSS-BEAT ESCAPEMENT.
Double Summer Time: Introduced in Britain during the Second World War for economy. In winter the clock was one hour in advance of GREENWICH MEAN TIME arid in summer, two hours in advance of it.
Dover Castle Clock: Large iron clock with original VERGE and FOLIOT from Dover Castle, now in the SCIENCE MUSEUM, London. Once thought to have been made in 1348, but possibly made late in the sixteenth or early in the seventeenth century, in fourteenth-century style.
Draw: A LEVER ESCAPEMENT 1S in the locked position most of the time. To keep it so and prevent it from 'tripping', the angle of the PALLETS 1S Set t0 'draw' them into the teeth of the ESCAPE WHEEL when the two are engaged. Invented by Josiah Emery.
Drum Clock: Clock movement in a brass drum-shaped container-like a can of beans-with a glass in the front and lid at the back. The drum fitted into the clock case. Used in many French clocks.
Drum Watch: After the last quarter of the sixteenth century, watches became drum-shaped, like TABLE CLOCKS. The earliest had separate lids, like boxes, but later lids were hinged. Soon the backs and front covers became more domed and the sides of many curved. The drum watch had one heavy hand, no glass, and knobs at the hours for feeling the time in the dark. Also called 'TAMBOUR' or 'cannister'.
Dumb Repeater: A REPEATER WATCH for deaf people. The concussion of the blows could be felt on the case. Made in the eighteenth century.
Duplex: A FRICTIONAL REST ESCAPEMENT probably invented by LE ROY about 1750. Widely used in the best English watches during the first half of the nineteenth century when good timekeeping results were obtained with it. Supplanted eventually by the CHRONOMETER and LEVER ESCAPEMENTS, but continued to be used in some machine-made American pocket watches. The ESCAPE WHEEL has two sets of teeth, one for LOCKING and one for IMPULSE (some Continental versions have two escape wheels). Impulse is given to an impulse PALLET on the BALANCE STAFF. See Chinese Duplex.
Dust Cap: Special cover, usually of brass, which clipped over some eighteenth-century watch MOVEMENTS inside the case.
Dutch Clock: Distinctive style of weight-driven clock standing on a wall bracket. Made in Zaandam and Friesland at the beginning of the eighteenth century. Has elaborate carving around the clock and top of the wall bracket, two hands and no glass. Also the name for a form of clock made in the Black Forest, Germany, 'deutsch' having been mistranslated. The 'staartklok' is another typical early Dutch clock. It hangs on the wall and looks like a HOODED CLOCK, but has a SECONDS PENDULUM in its Case with the weights hanging in front of the case.
Dutch Striking: As well as striking ordinarily at the hour, the clock strikes the next hour on a higher-toned bell every half hour. Found in Dutch and German clocks. Some early TABLE CLOCKS sounded the previous hour at the half hour.
Dutch Wag: Clock without a case hung on the wall. The short pendulum wags quickly beneath it. Also called 'wag on the wall'.