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Earnshaw, Thomas (1749-1829): Famous maker born in Ashton-under-Lyne, partly self-taught. Developed the MARINE CHRONOMETER and claimed ARNOLD stole his DETENT ESCAPEMENT. Made pocket chronometers and some clocks.
Earnshaw Balance: A BI-METALLIC BALANCE Of brass fused on to steel, invented by Thos. EARNSHAW.
Earth Path Indicator: An astronaut in a space capsule orbiting the Earth at 17,000 to 18,000 m.p.h. has to know where he is to make a safe descent. The Earth Path Indicator made for the U.S. Mercury Man in Space project is a clock which shows a model of the Earth as it appears to revolve below him.
East, Edward (1602-97): Maker of fine clocks and watches. Probably born at Southill near TOMPION'S birthplace. Followed David RAMSAY as Royal watchmaker to Kings Charles I and II. Lived in Pall Mall near the King's tennis courts. May have introduced NIGHT CLOCKS to England.
Ebauche: Unfinished watch MOVEMENT. In Switzerland most of these are produced by special factories. Other specialist factories make mainsprings, escapements, dials, hands, etc. A third group, the 'watch factories', are FINISHERS and design and manufacture watches based on the parts they purchase. There are still factories which make a watch from start to finish, but they are few. See Lepine Calibre.
Eight-Day Clock: Clock intended to be wound once a week. The extra day is for reserve.
Elapsed Time Indicator: A TIMER scaled from, say 30 minutes to 0, instead of 0 to 30. The hand is turned to 0 and moves back to 30, showing the time elapsed. See Telephone Time.
Electric Clock: General term for SYNCHRONOUS, electric MASTER CLOCK, BATTERY and other clocks powered by electricity.
Electric Watch: Wrist-watch operated by a small battery in the case. The first practical one was produced by the Hamilton Watch Co., U.S.A., in January 1957. There is no MAINSPRING and fewer gear WHEELS than in mechanical watch. It is an excellent timekeeper. The battery is the size of an acid drop and lasts up to 18 months. Atomic batteries lasting up to five years are being developed. There are French, German, and Swiss versions. The Hamilton has a tiny coil of wire fixed to the BALANCE arid a miniature switch operated by it sends a current of electricity through the coil for a few thousandths of a second. This causes a magnetic field around the coil which reacts with two small fixed magnets to give the balance a push every time it swings in one direction. Since the balance has a normal HAIRSPRING attached, it is kept swinging to and fro. The balance drives the hands by a simple ratchet system. The 'winding button' is for setting the hands and switching off the battery during storage. Although so small, the coil has 230 ft. of wire in it. Swiss and French versions have the coils fixed and they attract the arm of the swinging balance. Some Swiss watches have accumulators which can be recharged by clipping a watch to a torch battery. Consumption is under 14 micro-amps.
Electronic Chronometer: A QUARTZ CLOCK for measuring short time intervals, usually with DIGITAL INDICATION. See Chronometer.
Electronic Clock: The rather exaggerated name for a BATTERY CLOCK with pendulum and TRANSISTOR instead of mechanical switch. Correct for a QUARTZ CLOCK and an ELECTRONIC CHRONOMETER.
Electronic Watch: Newest development in accurate timekeeping, announced by the Bulova Watch Co., U.S.A., in 1960. Invented by a Swiss, Max Hetzel. Timekeeping is guaranteed to a minute a month. A tuning fork, about one inch long, is kept vibrating at 360 cycles a second by coils of 16,000 turns of wire and a miniature battery all within a normal-sized watch. A tiny pawl on the tuning fork drives a wheel of less than 1/10 in. diameter with 300 teeth, which turns the hands, without apparent jerks. There is no tick, but a high-pitched hum, and only 12 moving parts against 19 in an ordinary and 26 in a SELF-WINDING WATCH. Power consumed is 8 millionths of a watt. Also used for TIME SWITCHES in artificial satellites. There are still small, but fixed, POSITIONAL ERRORS in two positions of up to 5 sec. a day.
Elinvar: Alloy for HAIRSPRINGS invented by Dr GUILLAUME arid named from 'elasticite invariable' because its elasticity does not vary at different temperatures like that of spring steel. Revolutionized watch adjustment by eliminating MIDDLE TEMPERATURE ERROR and also enabled the BALANCE AND SPRING t0 be made NON-MAGNETIC. See Compensation Balance and Temperature Compensation.
Ellicott, John (1706-72): Son of a fine clockmaker of the same name, he became even greater than his father, making many CYLINDER watches and clocks. Invented a form of COMPENSATION PENDULUM. Had an observatory in his private house at Hackney.
Empire Clock: French gilt clock of Greek or Egyptian style made from about 1800 to 1815. Second Empire clocks are cheap reproductions of these and were made from about 1850-70.
Enamelled Watch: Coloured enamels were used as watch decoration from earlier than 1550 in champleve style-hollows filled with enamel. Painting in different coloured enamels was employed in Limoges from 1500-1600. The only Limoges watches now existing are in the METROPOLITAN MUSEUM, New York. Painting in colour on white enamel, which was then fired and given a transparent coat, was invented about 1630 and became supreme in Blois, France, where the best early work was done, then in Geneva, Switzerland, where it is still carried on. Finer examples are in the BRITISH MUSEUM, VICTORIA AND ALBERT MUSEUM, the LOUVRE, Paris. See Huaud.
End-to-End Striking Clock: Ancient arrangement, particularly for TOWER CLOCKS and LANTERN CLOCKS, of having the driving BARRELS for the timekeeping and striking end to end, instead of side by side, as in modern weight and spring clocks.
Endless Rope or Chain: Arrangement to provide MAINTAINING POWER for weight-driven clocks. Invented by HUYGENS about 1656. Used particularly on 30 hr. LONG CASE CLOCKS, and modern TOWER CLOCKS with AUTOMATIC CLOCK WINDING. The driving weight pulls on the left hand line to drive the clock. The right hand line raises the driving weight. The small weight is merely to keep the rope taut.
End Stone: Flat circular bearing jewel to take the end-thrust of a PIVOT. Used particularly for watch BALANCES. Made of synthetic ruby or, in the past, diamond or natural gemstone, because of their hardness. See Shock Absorber.
English Dial: Fine hanging wall clock, made at the beginning of the nineteenth century, in round or octagonal wooden case, the clock looking 'all dial' with a FUSEE MOVEMENT and sometimes a small box below for the PENDULUM. Often used as office or kitchen clocks.
English Lever: General name for the English watch made in the nineteenth century with a pointed toothed ESCAPE WHEEL (as opposed to the Swiss CLUB TOOTH) and LEVER ESCAPEMENT. Regarded at the time as the 'Rolls-Royce of watches'. See British Horological Industry.
Engraving: All apprentices were once taught engraving, so that they could cut dials and decorate clock and watch parts, but gradually work was put out to specialist engravers. Back PLATES of clocks were once elaborately engraved, as were the dials, bottom plates, and COCKS of watches.
Ephemeris Time: Time calculated from the orbits of the Earth round the Sun (as alternative to the rotation of the Earth). In 1956 the International Committee of Weights and Measures adopted the SECOND of Ephemeris Time as the fundamental unit of time, instead of the second of Mean SOLAR TIME. It is obtained in practice from the orbital motion of the Moon round the Earth, then made available for general purposes by QUARTZ CLOCKS, ATOMIC CLOCKS, etc. See Time Determination.
Epilame: After parts of a watch have been submitted to ULTRASONIC CLEANING they are so chemically clean that oil may spread, so they are given a coating of a patent 'epilame' (stearic acid) to prevent this, a treatment devised by Dr Woog of Paris and Paul DITISHEIM before ultrasonic methods were invented.
Equal Hours: After about 1350-1400, TEMPORAL HOURS were replaced by equal hours, each hour being of the same length whether by night or day. Mechanical clocks coming into use during this time in Europe and showing equal hours were responsible. JAPANESE CLOCKS were made to show temporal hours, however, until 1873. SUNDIALS were also made to show equal hours.
Equation Dial: An extra dial on a clock showing the EQUATION OF TIME, so that a SUNDIAL could be used to set the clock to MEAN TIME. First made by TOMPION and by QUARE about 1695. It was only the accuracy of the ANCHOR ESCAPEMENT that made the difference between sundial and clock apparent.
Equation of Time: The difference between SOLAR TIME (i.e. sundial time) and mean solar time (i.e. time shown by clocks), the sundial sometimes appearing fast and sometimes slow according to the clock. Before TIME SIGNALS, accurate clocks and watches had to be set by the SUNDIAL, so the Equation of Time had to be known. This was often a printed table stuck inside the clock or watch case. Expensive clocks, such as the BATH CLOCK, had an EQUATION DIAL showing how much the sundial should be fast or slow compared with the clock. The year's equation figures are published in the ASTRONOMICAL EPHEMERIS. They vary between about 16 1/2 minutes and -14 1/4.
Escape Wheel: The last wheel in a GOING TRAIN, controlled by the ESCAPEMENT.
Escapement: The rate-controlling mechanism of a timekeeper. The first recorded, made by I-Hsing, a Chinese monk, in A.D. 725, was called the 'celestial balance' and was employed to control a WATER CLOCK. The earliest mechanical escapement was the VERGE and FOLIOT probably invented in the fourteenth century. Many thousands have since been invented. Most common are the ANCHOR for PENDULUM clocks, the LEVER for clocks and watches with BALANCES, and the DETENT ESCAPEMENT for MARINE CHRONOMETERS.
Escapement Error: AS soon as a PENDULUM Or BALANCE 1S given a push to keep it swinging, its timekeeping is usually interfered with, this difference in RATE being called 'escapement error'. It was analysed by AIRY. It and CIRCULAR ERROR are sometimes opposite and tend to cancel each other.
Essen Ring: Quartz crystal cut to ring shape and used for high accuracy QUARTZ CRYSTAL CLOCKS. Developed by Louis Essen of the National Physical Laboratory. At the Post Office Research Laboratories in Dollis Hill in North London one was buried 20 metres down in London clay in a sealed canister in 1955 and is used as a standard of frequency.
Eureka Clock: Electric BATTERY CLOCK, invented in 1906, which has a very large BALANCE WHEEL driven by an electromagnet.
Examinations: Every year the BRITISH HOROLOGICAL INSTITUTE holds four grades of examinations in centres in the U.K. and abroad, for success in which diplomas and other awards are made.
Exeter Cathedral Clock: Ancient iron TOWER CLOCK Of vertical construction now restored and in the north transept of the cathedral (see Vertical Frame). Has large astronomical dial almost identical to another in Ottery St Mary Church, Devon. Both are claimed to be fourteenth century, but are much later.
Expanding Bracelet: Sometimes called a 'flexible bracelet' although these are not always expanding. Early versions were made from expanding spring links; current ones usually have a spring scissors action. A good expanding bracelet is precision made and may have over 100 parts. Some have latches for removing single links for length adjustment. Often made of gold or ROLLED GOLD Or GOLD PLATED base metal with stainless steel backing.
Explorer's Watch: Watertight English pocket watch made by Dent with a DENNISON case at the end of the last century for use of explorers. The winding button and the dial were covered by screw-on caps with cork washers; this was the first successful WATERPROOFING,