Time & Clocks Dictionary
Abbot Horne Collection: Collection of over 70 SAND-GLASSES presented to the SCIENCE MUSEUM, London, in 1952.
Accumulator Watch: Swiss ELECTRIC WATCH driven from an accumulator in the back of the case. The accumulator lasts nine months and can be recharged in a few hours from an ordinary torch battery by using a special connector to a plug on the wrist-watch.
Accuracy of Clocks: Timekeeping of mechanical clocks with VERGE and FOLIOT or bar BALANCE made around 1500 varied by about 1/2 hr. or more daily. This was brought down to I hr. by the hog's BRISTLE REGULATOR arid to about 30 sec. a day by the CROSS BEAT ESCAPEMENT in special clocks after 1586. The BRACKET CLOCK with VERGE and BOB PENDULUM (after 1657) would keep to ±20 sec. daily over short periods. The SECONDS PENDULUM with ANCHOR ESCAPEMENT (after 1671) increased accuracy to ± 10 sec. a day and, if well regulated, to less than +3 sec. a week. A modern factory electric MASTER CLOCK Will hold about + 1/2 sec. a week. A MARINE CHRONOMETER will hold about 0.3 sec. a day. A RIEFLER CLOCK will keep to about 1/100th sec. a day. A FREE PENDULUM observatory clock is accurate to 1 sec. a year. The QUARTZ CLOCK is accurate to the equivalent of a second in 30 years, and the ATOMIC clock to the equivalent of 1 sec. in 3,000 years.
Accuracy of Watches: Watches are inherently less accurate than clocks because they are moved about, which causes positional ERRORS. Early VERGE watches could not be relied upon within quarter of an hour. The HAIRSPRING brought accuracy down to minutes. Modern precision pocket watches should go within 5 to 10 sec. a day and precision wrist-watches to within 10 to 20 sec. Cheap watches should be within 3 to 5 min. for pocket and 5 to 10 min. for wrist. See Rate and Rating Certificate. The accuracy of timekeepers is taken for granted. Yet one that is 10 sec. a day fast or slow is 99.99 % accurate. Speedometers are commonly 5 % out, which with a clock would mean an error of 8 hr. 24 min. in a week!
Act of Parliament: Clock Name given to COACHING or TAVERN CLOCKS when a TAX was put on timekeepers in the eighteenth century. Villagers thought it cheaper to use the inn's coaching clock-but it was not always so, as landlords employed their clocks to attract custom! (Fig. 29). Adjusted Some watches have this word engraved on their MOVEMENTS. It means that they are high grade and have been corrected for TEMPERATURE ERRORS arid for POSITIONAL ERRORS. An adjusted pendulum clock is corrected for temperature error only.
Adjuster: Highly skilled man who can regulate watches to very fine limits by manipulating the HAIRSPRING, BALANCE, and parts of the ESCAPEMENT.
Ahaz, Dial of: Sundial (probably the shadow of a pillar that moved up steps as the sun rose) mentioned in the Bible, II Kings, Chap. 20, verse 11.
Air Almanac: Airman's equivalent of the NAUTICAL ALMANAC, giving star positions every ten min. to obtain 'fixes' for finding his position with the aid of a CHRONOMETER. Published by H.M. Stationery Office. See Navigation.
Airy, George Biddell: The ASTRONOMER ROYAL from 1835-81. Discovered that if a PENDULUM Or BALANCE AND SPRING 1S IMPULSED briefly in the mid-point of its swing, this will have least effect on its timekeeping. If the impulse is given before dead centre, the pendulum or balance will go faster, and if given after dead centre, it will go slower. There is no need to impulse at every swing. He was inventor of the ESCAPEMENT Of a SIDEREAL CLOCK by Dent, for GREENWICH OBSERVATORY in 1872. Also introduced the TAPE CHRONOGRAPH to Greenwich.
Alarm: Clock that can be set to ring a bell at a given time. Alarms, or 'alarums', were made as early as the fourteenth century, and many early CHAMBER CLOCKS have alarm mechanisms. Manufacture of alarms today is highly automated; one of the Scottish factories can turn them out at the rate of one every two and a half sec., automatically adjusted to an accuracy finer than many scientific instruments. Common alarms have THIRTY-HOUR MOVEMENTS. TRAVELLING CLOCKS have EIGHT-DAY alarm movements. There are modern alarms with adjustable loudness, MUSICAL ALARMS, arid REPEATER ALARMS.
Alarm Watch: Modern wrist-watch that incorporates an alarm mechanism for reminding the wearer of appointments, or waking him. The first was the 'Cricket'. There is a separate button for winding and setting the alarm. Some models are scaled as ELAPSED TIME INDICATORS for car parking. Others, on watches for skin divers, indicate safe underwater time limits.
Albion: 'All-by-one'-all made by one man. Name falsely given to an astronomical clock made by Richard of Wallingford and placed in the south transept of 5t Albans Abbey in the fourteenth century. Actually a geometrical instrument he constructed.
Altitude Sundial: Type of PORTABLE SUNDIAL showing the time by the height or altitude of the sun in the sky. (The shadow of an upright post is shortest at noon when the sun is at its highest.)
American Clock: English, Dutch, French and other clockmakers were among early emigrants to North America and their own styles merged into others that became peculiarly American. See Banjo Clock, Terry, U.5.A. Horological Industry, Waggon Spring Clock.
American Watchmakers Institute: Organization of all watchmakers in the U.S.A. formed in 1960 by the amalgamation of the Horological Institute of America and the United Horological Association of America. Official journal: The American Horologist. Address: 10525 Puritan Avenue, Detroit 38, Michigan.
Ammonia Maser: An ELECTRONIC CLOCK, in which the timekeeping element is the vibration of the ammonia molecule, developed particularly in the U.S.A. and Switzerland. Not inherently as accurate as the ATOMIC CLOCK. 'Maser' means Microwave Amplification by Simulated Emission of Radiation.
Anagram: In earlier centuries scientists established claims to discoveries and inventions by concealing them in anagrams. HOOKE'S law of the BALANCE SPRING, 'as the tension is, so is the force', was concealed as 'c e i i i n o s s s t t a v', the letters comprising the Latin version 'ut tensio, sic vis'. Galileo, Newton, Huygens and others used anagrams. Sir Christopher Wren's anagram for FINDING THE LONGITUDE, still held by The Royal Society, has never been cracked!
Anchor Escapement: Clock control, probably invented by Robert Hooke or William CLEMENT of London about 1671 Supplanted the VERGE ESCAPEMENT and made really accurate clocks possible. Used on most pendulum clocks today. An anchor-shaped piece of steel is swung to and fro by the PENDULUM to release a tooth of the ESCAPE WHEEL at each swing, or BEAT. At the same time, the escape wheel IMPULSES the pendulum through the anchor escapement to keep it swinging. Also called the 'RECOIL ESCAPEMENT'.
Anne Boleyn Clock: Clock of lantern type, said to have been given to Anne Boleyn by King Henry VIII on their wedding in 1532, now in the library at Windsor Castle. The elaborate copper gilt case and bracket on which it stands are excellently preserved. The MOVEMENT was replaced in mid-sixteenth century. On top of the case is a model lion with the arms of England. The two weights are engraved with the initials 'H' and 'A' and true lovers' knots. The clock was later given to Horace Walpole and was bought after his death by Queen Victoria.
Anniversary Clock: Another name for a YEAR CLOCK.
Antiquarian Horological Society: Formed in 1953 to assist and stimulate original research and preserve records and fine examples of clock and watchmaking and DIALLING. Holds regular meetings and visits to places of horological interest. Address: 35 Northampton Square, London, E.C.1.
Apparent Time: Another name for SOLAR TIME, or time as indicated by the SUNDIAL.
Appointments Clock: Device for jogging the memory. One of the earliest was Davidson's memorandum clock of 1891. There was a drum on top with slots marked in hours into which the owner put ivory tablets on which he had written his appointments. The clock delivered each tablet into a little box at the appointed hour and rang an alarm bell. A modern version is a desk pad with hours marked down one side. A built-in clock moves an indicator down the list of appointments.
Apprentice: The CLOCKMAKERS COMPANY indentured apprentices from 1631. They had to serve seven years before becoming JOURNEYMEN. A MASTER clockmaker could take a second apprentice only after the first one had served five years. The Company has published a list of apprentices which helps to trace makers. Today the BRITISH HOROLOGICAL INSTITUTE handles most indentures.
Arabic Numerals: Introduced to Europe after the more literate Crusaders found Arabic numbers much more convenient than Roman, in the twelfth century, but not common on clocks until recent times.
Arbor: Horological name for a shaft or axle in a clock or watch. That for the BALANCE is called the 'Staff'.
Arc: The full angle through which a PENDULUM Or BALANCE swings. For a precision pendulum this is usually less than 1 1/2 (see Circular Error). Short pendulums may have arcs as wide as 30°. A balance normally swings through 1 1/2 to Q turns, but this falls off to about 1 1/4 turns after the MAINSPRING POWER OUTPUT has fallen when the spring has run for 24 hours (see Positional Errors). Good balance action is called 'long arcs' and poor action 'short arcs'.
Arch Dial: Square clock DIAL with an almost semi-circular arch in the top. The space in the arch was first used for the maker's name, or decoration, and later for AUTOMATA, or a phase of the MOON DIAL. In fashion from about 1720. Correctly a 'broken arch dial' as the arch does not extend to the edges of the dial.
Architectural Clock: Style of case based on architectural of buildings. Earliest wooden BRACKET and LONG CASE clock CASES were made in this style.
Armillary Sphere: Fixed model of the Universe made of metal rings in use from over 2,000 years ago. There is one in Pickering Court, off St James's Street, London, S.W.1. The emblem of the BRITISH HOROLOGICAL INSTITUTE.
Arnold, John (1736-99): Gunsmith who became a fine watchmaker. Made one of the world's SMALLEST WATCHES, a RING WATCH, for King George III. Later devoted himself in London to pocket and MARINE CHRONOMETERS, patenting a BALANCE SPRING that was ISOCHRONOUS arid a DETENT ESCAPEMENT. Made about 1,000 timekeepers, mostly marine, and never two alike. Business enemy of EARNSHAW. His son J. R. Arnold, who was apprenticed to BREGUET, continued the business and went into partnership with E. J. Dent, who later made 'BIG BEN'.
Artificial Clock: Early name for a mechanical clock to differentiate it from a natural 'clock' such as the sun or moon.
Ashmolean Museum Collection: This is at Oxford and includes fine examples of early watches (including the REPEATER invented by Daniel Quare), clocks, and the earliest ASTROLABE known.
Astrolabe Elaborate: ALTITUDE DIAL for finding the time in TEMPORAL Or EQUAL HOURS, probably invented by the Greeks.
Astronaut's Clock: Extremely accurate timekeeper that is unaffected by fierce acceleration and varying gravity for space travel. Among those so far developed are the SATELLITE TIMER, QUARTZ CLOCK, and the EARTH PATH INDICATOR. For ground control systems, QUARTZ and particularly ATOMIC CLOCKS are suitable. See Time.
Astronomer Royal: First appointed for FINDING THE LONGITUDE by astronomical observation. Responsible today also for TIME DETERMINATION and TIME DISTRIBUTION. John FLAMSTEED was the first. Of others, Bradley discovered NUTATION, set up the TIME BALL, and started a time distribution service, AIRY improved clock accuracy. Dyson adopted the FREE PENDULUM, and Spencer-Jones adopted the QUARTZ CLOCK. See Greenwich Observatory. There are separate Astronomers Royal for England (Herstmonceux), for Scotland (Edinburgh), and Northern Ireland (Armagh), Australia, and South Africa.
Astronomer's Pendulum: Early astronomers used a weight which swung on a cord to measure time, before the PENDULUM CLOCK was invented. The time of swing was calculated by GALILEO and HUYGENS. See Observatory Clock.
Astronomical Clock: Clock with astronomical indications, such as SIDEREAL time and the movements of the Earth, Moon, and planets, on dials or by models. Earliest mechanical clocks were astronomical. Famous makers were DONDI, who designed the first of all, BURGI, BALDEWIN, HABRECH'T, RAINGO, and JANVIER. See also Globe Clock, Orrery and Strasbourg Clock. The latest large astronomical clocks made in England are one in York Cathedral, another in the Financial Times building in Cannon Street, London, E.C.4, and a replica of DONDI'S CLOCK.
Astronomical Ephemeris: Tables which include EQUATION OF TIME figures. Since 1960, published jointly by the Royal GREENWICH OBSERVATORY and the United States Naval Observatory. Incorporates the original NAUTICAL ALMANAC and the American Nautical Almanac.
Atmos Clock: Automatically-wound Swiss table clock. An aneroid bellows is pressed out by a rise in temperature to operate a mechanism that winds the mainspring. Has a TORSION PENDULUM.
Atomic Clock: The radio frequencies emitted by atoms and molecules at low pressures are fixed and unchanging with time. They can therefore be used to control a radio oscillator itself controlling a QUARTZ CLOCK. The most accurate atomic clock or frequency standard ever made employs as its 'pendulum' the vibration of the caesium atom, which is at 9,192,631,770 cycles a second. It was developed by Louis Essen and J. V. L. Parry at the NATIONAL PHYSICAL LABORATORY. Their first model, C. 1, of 1955, for checking the quartz clocks at the laboratory and the Post Office standard frequency broadcasts from the Rugby Radio station, was the world's first atomic clock to go into service. See Radio Time Signal. The latest version, C.3, is accurate to the equivalent of one second in 3,000 years and has shown that the Earth's rotation is slowing down by about two MILLISECONDS a year after making other corrections for PRECESSION OF THE EQUINOX arid NUTATION. See Ammonia Maser.
Atomic Time: An ATOMIC CLOCK, using as its standard of frequency the vibrations of atoms of the element caesium, is much more accurate than any other time standard, such as the Earth, and the QUARTZ CLOCK. Therefore Atomic Time will probably replace ephemeris TIME. A network was set up in 1961 using atomic clocks in the U.K. and U.S.A. to provide time signals accurate to half a MILLISECOND over a large part of the Earth's surface for checking artificial satellites, etc.
Automatic Clock: Winding System used on many new TOWER CLOCKS, in which an electric motor is automatically switched on and off to wind up the weight every quarter of an hour or so. Many old tower clocks are being converted from hand winding, which took an hour or more daily. A Huygens ENDLESS CHAIN is used which provides MAINTAINING POWER. Automatic winding is employed in most domestic BATTERY CLOCKS, an electro-magnet rewinding a small mainspring every few minutes. The arrangement for driving ELECTRIC MASTER CLOCKS is also a form of automatic winding. See Atmos Clock and Light Clock.
Automaton: Animated mechanical figure or scene. Earliest were Egyptian, followed by Greek and Roman gods which pointed to 'chosen' kings or leaders. Early automata worked by mechanical clocks were called JACKS. Later, joustingknights, waterfalls, windmills, ships at sea, animals playing musical instruments, acrobats, etc., were worked by the clockwork and often associated with MUSICAL CLOCKS. A famous one was Bridge's Microcosm (now in the British Museum). James Cox was a renowned maker in the eighteenth century. Watches were also made with automata (occasionally of erotic scenes which were concealed until operated by a secret PUSH PIECE). One of the most recent large clocks with automaton is the GUINNESS CLOCK. The word 'automation' is derived from this.
Auxiliary Compensation: Additional form of temperature compensator for a COMPENSATION BALANCE in order to avoid MIDDLE TEMPERATURE ERROR. A great variety of such compensations were invented in the nineteenth century. Best solutions were the GUILLAUME, DITISHEIM, arid OVALIZING BALANCES for MARINE CHRONOMETERS and high-grade watches.