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Tabernacle Clock: Miniature TOWER CLOCK six to nine inches high, made in the sixteenth and seventeenth centuries. The MOVEMENT was similar to that of a LANTERN CLOCK, but driven by a MAINSPRING and FUSEE instead of a weight.

Table Clock: Most common form of early clock of the late sixteenth and seventeenth centuries, being DRUM shaped, or later, square, or hexagonal, with feet. Separate ALARM mechanisms were common on early ones. Hexagonal table clocks, in particular, were made in Germany well into the eighteenth century.

Tachometer: Scale sometimes combined with a wrist-chronograph, to show speed over a given distance, such as one mile or one kilometre marked on the dial. Timing a motor-car, say, over this distance records the speed in m.p.h. or k.p.h.

Tact Watch Montre: A tact made by BREGUET for blind people. The watch cover had fixed studs to mark the hours, and a movable pointer, which, when turned clockwise by the wearer, was stopped at the correct time. It was a cheaper alternative to a REPEATER.

Talking Clock: Clock which 'speaks' the time, the most common being the telephone voice TIM. The earliest were made about 1914, comprising a clock MOVEMENT, speech record on a band, acoustic head, gramophone needle, and horn.

Tambour (or Tambourine Watch): Another name for a DRUM WATCH or canister watch, the case being like a round tin with the perforated rim and the MOVEMENT hinged to it.

Tape Chronograph: Instrument for comparing the RATES of clocks, CHRONOMETERS, and STAR TRANSITS. In the simplest instrument, a timekeeping mechanism moves a paper tape under two pens which draw straight lines on the paper. Each pen can be given a jerk by an electro-magnet connected to a clock or TRANSIT INSTRUMENT. Therefore humps in the lines compare the rates. More elaborate versions, such as the Belin chronograph, are used by observatories.

Tavern Clock: Another name for a COACHING CLOCK Or ACT OF PARLIAMENT CLOCK (although they were in use well before the TAXES ON TIMEKEEPERS).

Taxes on Timekeepers: In 1797, William Pitt introduced a tax of 5 shillings a year on every clock, 10 shillings each on gold watches, and 2s 6d on silver watches. Clock and watch makers had to take out licences. This increased the popularity of the tavern clock, which became known as the ACT OF PARLIAMENT CLOCK. At the same time there was a 'plate tax' existing on gold and silver watch cases. Both Acts were repealed in 1798.

Telemeter: Scale sometimes combined with a wrist CHRONOGRAPH to record the distance of an event seen and heard, such as a thunderstorm. The recording hand is released when lightning is seen and stopping when the thunder is heard, the hand then indicating the distance away of the storm.

Telephone Timer: A special ELAPSED TIME INDICATOR for use with telephones on the Subscriber Trunk Dialling system. Some 'ping' every three minutes and give the cost of the call.

Telleruhr: Literally a 'plate clock'. Made in the sixteenth and seventeenth centuries in Germany (particularly in Augsburg) and Austria. Usually hung on the wall but occasionally stood on a pedestal. The flat metal DIAL with elaborately shaped edges has a sometimes silver or pewter CHAPTER RING. In some, the short pendulum hangs over the front of the dial. The hands are usually elaborately pierced. See Trophy Clock.

Tell-Tale Clock: Alternative name for a WATCHMAN'S CLOCK.

Temperature Compensation: Method of avoiding timekeeping variations (ERROR) at different temperatures, which affect PENDULUMS, BALANCE AND SPRINGS, QUARTZ CRYSTALS, and most other time standards. COMPENSATION PENDULUMS are designed to keep the lengths invariable. A balance and a hairspring are affected separately, and differently, by temperature changes, which is a complication. IIARRISON first applied compensation to hairsprings-by employing an arrangement like GRIDIRON PENDULUM to vary the tension Of CYLINDRICAL HAIRSPRINGS; then by developing a COMPENSATION CURB for spiral springs. Many developments have been made in COMPENSATION BALANCES for use with hairsprings of differing metals and alloys.

Temperature Error: Timekeeping error caused by variations in temperature. A PENDULUM with a steel rod will expand in length and become slower by 21 sec. a day for a rise of 10'F (51'C). A COMPENSATION PENDULUM Can eliminate this error. The effect is more complicated with a BALANCE AND SPRING. For the same temperature rise, a brass balance wheel will expand and swing slower by about 5 sec. a day; much more important, the spring will become weaker and lose 1 min. a day. So the balance and spring together lose 65 sec. a day for a rise of 10'F. A good COMPENSATION BALANCE with special hairspring commonly reduces this error to 510 sec. per day for a 1'C rise in TIMEKEEPING TRIALS.

Temporal Hours: Before the fourteenth century, when there was hardly any artificial illumination, daylight was split into a number of hours, usually 12, and so was the night. A daylight hour was therefore different from a night hour and both varied at different times of the year, but not by much in the Mediterranean areas where most early civilizations thrived. Early sundials show temporal hours. See Mean Time, Equal Hours and Japanese Clocks.

Testing: See Rating Certificate, Timekeeping Trials, Kew 'A' Certificate and Quality Standards.

Thermal Dial: Used on a TIME SWITCH to make or break electric contacts at a given time or at a preset temperature.

Thin Long Case Clock: A LONG CASE CLOCK 6 ft. or more high with a trunk only about 8 in. wide. Some are eighteenth century, but these cases were also made from about 1840 to take the MOVEMENTS Of LANTERN CLOCKS, usually with BOB PENDULUM and ALARM. Such lantern clocks originally had arched dials and spiked feet.

Thinnest Watch: Thin watches are elegant and fashionable. They were made as early as the start of the eighteenth century by Daniel QuARE. The thinnest in quantity production is 1.18 mm. thick (slightly over 4/100 in.). A SELF-WINDING WATCH only 2.5 mm. (1/16TH in.) thick is also made in Switzerland. Extra thin movements are sometimes made into COIN WATCHES.

Thirty-Hour Clock: Clock which runs at least 30 hr. at one winding. Intended to be wound daily. A few early LANTERN CLOCKS ran for only 12 hr. or so. Later clocks went for EIGHT DAYS or more, and cheaper ones, 30 hr. The principle applies today for clocks. Some watches will run as long as 45 hr. at a winding. This also improves timekeeping as the MAINSPRING POWER is then more constant when the watch is wound daily.

Thousand-Day Clock: Small, battery-operated pendulum clock with TRANSISTOR switching which runs for 1,000 days on one cell.

Tic Tac Escapement: A small ANCHOR ESCAPEMENT which extends over only two teeth of the ESCAPE WHEEL. Used on French and some early English clocks with BOB PENDULUMS.

Tick: Sound made by the release and arrest of a TRAIN Of gears by the ESCAPEMENT, made up by as many as 40 different sounds in a watch. Ticks vary from 'tocks' because alternate PALLETS arrest the ESCAPE WHEEL and different parts of the MOVEMENT resonate. The sound of a tick lasts about 15 MILLISECONDS.

Tick Amplifier: The sound of a watch tick can indicate many different faults. Watch repairers sometimes use amplifiers to diagnose them.

Ticket Clock: Rather like a circular CARRIAGE CLOCK, but shows the time in figures on celluloid tickets, of which there are two sets, one above the other, for hours and minutes. The tickets are like leaves of a cylindrical book which flip round at the minutes and hours. Invented in 1903. Also called a 'flick leaf clock' or 'Plato clock'.

Tidal Dial: Indication on some eighteenth century LONG CASE CLOCKS of high and low tides, often shown on the MOON DIAL. Another version was a rising and falling plate representing the sea, operated by a cam, invented by James Ferguson. They were useful in times when rivers and coastal waters were the principal means of transport. Tidal dials on modern TIME SWITCHES control the flow of sewages or factory effluent into the sea by opening a valve when the tide goes out.

Tide: The Saxons divided a day into eight tides, shown by their SUNDIALS. We still use 'noontide' and 'eventide'. The tides were: Morgan 4.30 a.m. 7.30 a.m.; Daeg-mael 7.30 a.m.10.30 a.m. ; Mid-dag 10.30 a.m.-1.30 p.m. ; Afanverth dagr 1.30 p.m.-4.30 p.m.; Mid-aften 4.30 p.m. 7.30 p.m.; Ondverth nott 7.30 p.m.-10.30 p.m.; Mid-niht 10.30 p.m.-1.30 a.m.; Ofanverth nott 1.30 a.m.-4.30 a.m.

TIM THE SPEAKING CLOCK: Of the British Post Office which speaks the exact time when 'TIM' is dialled by the telephone and is accurate to 0.1 sec. It was inaugurated in 1936. The apparatus is controlled by a FREE PENDULUM and the voice announcements are built up from a series of recordings on glass discs. Paris was the first city to have a speaking clock, in 1933. The latest models are controlled by QUARTZ CRYSTAL CLOCKS.

Time: No one knows exactly what time is. It is a concept of mind, representing a change from order to disorder. It is not absolute. According to the Theory of Relativity (Einstein) the RATE of a clock depends on the situation of the observer. In practice this means that a clock in an artificial satellite approaching the speed of light goes at a slower rate measured from the Earth than measured from the satellite. Passage of time is measured by referring to a recurring phenomenon, such as the rotation of the Earth, vibration of a PENDULUM, BALANCE, QUARTZ CRYSTAL, MOLECULE Or ATOM. Living things have a built-in 'HUMAN CLOCK'. Two kinds of time are in ordinary use: (1) Time of day and (2) Duration of time interval. For (1), rotation of the Earth has to be used. For (2), ATOMIC TIME 1S more accurate. It would be more practical to base both on Atomic Time for convenience.

Time Ball: The world's first accurate TIME SIGNAL, which was installed at GREENWICH OBSERVATORY in 1833 by John Pond for shipping in the Pool of London. The ball was a wooden frame 5 ft. in diameter, covered with leather. It was wound halfway up to the top of a mast on the north-east turret, at 12.58, and dropped down the 15 ft. mast at exactly 1 p.m. by a trigger release. After 1852 the ball was released automatically by an electric signal from an OBSERVATORY CLOCK. Time balls became popular and were erected in the Strand, London (for CHRONOMETER makers) and at Deal, Devonport, Portsmouth, Portland (for shipping), and elsewhere. The present Greenwich ball is of aluminium on a 30 ft. mast and is still operated, but by the National Maritime Museum. Superseded by TIME SIGNALS.

Time Determination: This is the duty of the ROYAL GREENWICH OBSERVATORY in Britain and the National Bureau of Standards in the U.S.A. It means determining exact points in time as accurately as possible for TIME DISTRIBUTION. The fundamental unit of time is the period of time the Earth takes to rotate on its axis, which is a day. This can be measured by timing the Sun from noon on one day to noon on the next, as with a SUNDIAL, but the days are found to vary in length (see Solar Time). It is more accurate to observe a CLOCK STAR instead, to obtain SIDEREAL TIME. This is done by taking an observation with a TRANSIT INSTRUMENT and comparing the going of the Earth with the going of the OBSERVATORY CLOCKS by means of a TAPE CHRONOGRAPH. Clocks have proved to be the more accurate timekeepers, showing up wobbling (and other irregularities in the Earth's rotation. Mean sidereal time is sidereal time corrected for these irregularities and can be converted to mean solar time for general use. However, time is now even more accurately determined from observation of the Earth's orbit, which is converted to mean solar time for TIME DISTRIBUTION for public consumption .

Time Distribution: After TIME DETERMINATION, the ROYAL GREENWICH OBSERVATORY -distributes time to the Post Office, B.B.C., NATIONAL PHYSICAL LABORATORY, and other main users. Earlier in the century other distributors of time were the Post Office (by their chronographer); and the Standard Time Co. of London; the Self-Winding Clock Co., of New York, and Normallzeit Gesellschaft, of Berlin, who set up electric wires to railway stations, CHRONOMETER makers, and elsewhere, through which a synchronizing signal at a certain time forcibly corrected clocks on the spot.

Time Gun: Gun fired as a TIME SIGNAL, such as that on Edinburgh Castle. Not as accurate as a TIME BALL because of the sound delay. The earliest were fired by the Sun's rays to give a SOLAR TIME signal.

Time Lock: Special safe or strong-room lock that enables the door to be opened only after a certain time. Invented by James Sargeant in the U.S.A. in 1872. The time lock is wound with a clock key when the door is open and set for a certain period of time. When the door is shut and the bolts thrown, the time lock blocks the bolt mechanism until the time has elapsed. Usually two or more clock mechanisms are used in case one should stop.

Time Recorder: Clock which gives a permanent record of certain events. The first was the WATCHMAN'S CLOCK. In 1885, an American, Bundy, invented a clock that printed the time when keys were inserted, to 'clock in' employees. The modern factory version is controlled by a MASTER CLOCK and automatically stamps cards with the time at which they are inserted, being used for job costing as well as employee control. Another version used on lorries records the periods of time that they are in motion.

Time Signal: Indication of a specific time, usually by a visual or aural signal. See Radio Time Signal, Time Ball, TIM and Time Gun.

Time Stamp: A rubber date stamp which also prints a dial and hand showing the time of stamping. It incorporates a timepiece. Some have DIGITAL INDICATION. Can be self-contained or be controlled by a MASTER CLOCK.

Time Switch: Electric or mechanical switch operated by a clock mechanism, used for street lighting (usually with a SOLAR DIAL), factory heating, shop window lighting, radio switching, refrigerator switching, time bombs, etc. See Gas Controller.

Time Zone: If countries employed LOCAL TIMES, time of day would change with the smallest journey east or west. 5o in 1884 the world was split into 24 time zones of 15 each. The principal one is 71 each side of Greenwich to which G.M.T. applies. Each zone successively west became an hour earlier and each zone east an hour later. The centre of the zone on the side of the world opposite Greenwich is the DATE LINE. Countries which fall in two zones declare for one or the other, and big countries may have several STANDARD TIMES. There are also other local variations including DAYLIGHT SAVING. See World Time Dial.

Timer: A pocket watch, or clock, for measuring short time intervals. The earliest, in the eighteenth century, had an arm which pressed against a wheel in the mechanism to stop it. The first watch in which the hand returned to zero was shown by Nicole and Capt at the London Exhibition of 1862. The push button of a pocket timer is pressed once to start the hands, again to stop them, and a third time to return them to zero. The accuracy depends on the BEAT of the balance. One beating 1/5th sec. is accurate approximately to that. For greater accuracy, balances beating up to , o sec., and occasionally more, are used. See Sports Timer, Pulse Meter, Tachometer, Telemeter, Split Seconds Timer, Decimal Timer, Production Timer and Chronograph. A clock timer can also have hands that return to zero. See Process Timer, Interval Timer, Elapsed Time Indicator and Time Switch. For sportsmen, skin divers, airline pilots and others needing to judge time intervals, there is an accurate watch with a CENTRE SECONDS HAND, which has an extra set of minute markings reading anti-clockwise on the BEZEL. The bezel can be rotated and is turned so that the time interval, say 20 min., is opposite the minute hand. The minute hand then moves towards zero on the bezel, always showing the remaining minutes. If the bezel is set opposite the centre seconds hand, remaining seconds are indicated.

Timekeeper: Any form of TIMEPIECE, CLOCK, CHRONOMETER, TIME SWITCH, or other device showing time of day. Also a person responsible for timekeeping for any purpose such as recording times in sports events, or at a factory. See Sports Timing.

Timekeeping Trials: Special competitions for performance of timekeepers under strict conditions, including tests in differing positions, ovens, and refrigerators. In the eighteenth and nineteenth centuries the most important ones were run by the ROYAL GREENWICH OBSERVATORY for MARINE CHRONOMETERS. Today the most important trials are controlled by the Geneva and Neuchatel Observatories, and the prizes are monopolized by Swiss makers and ADJUSTERS.

Timepiece: Strictly, a clock or watch showing time of day only and not striking or chiming.

Timing Machine: Another name for a RATE RECORDER.

Timing Screws: Screws around the rim of a CUT BALANCE. Also called 'MEAN TIME screws'. There are four to adjust the RATE, since the balance swings slower when they are screwed outwards. They are placed at 90 to each other starting from the ends of the arm of the balance. Other screws in the rim are adjusted for TEMPERATURE COMPENSATION arid POISE.

Timing Washers: Tiny washers placed under the screws in the rim of a BALANCE to adjust the RATE at which it swings and also to correct POISE errors.

Ting Tang: Most ancient form of chime on two bells, sometimes struck by two QUARTER BOYS giving one blow on each at quarter past, doing this twice at half past, three times at a quarter to, and four before the hour. The first bell has a higher note. HAMPTON COURT CLOCK is ting tang. The system is also used in REPEATER WATCHES.

Tipsy Key: Winding key for watches with a ratchet so that it could not be turned backwards. Also called a BREGUET key.

Tompion, Thomas (1639-1713): Usually regarded as the most famous of all English clock and watchmakers. Born at Ickwell Green, Northill, Bedfordshire, and trained as a blacksmith, but went to London and became a clockmaker, setting up at 'The Dial and Three Crowns', Water Lane, Fleet Street. Made the first clocks for GREENWICH OBSERVATORY in 1676, the first EQUATION CLOCK, now in the ROYAL COLLECTION, arid a YEAR CLOCK as Well as the 'RECORD' ToMPION for King William III. Invented a forerunner of the CYLINDER ESCAPEMENT for watches with BARLOW and Wm. Houghton. Became famous in his own time, particularly for watches, of which he produced about 5,500. He made about 650 clocks and also barometers and other instruments. Buried in Westminster Abbey. Succeeded by George GRAHAM. See Bath Clock and Plate 1.

Torsion Pendulum: Pendulum that twists on its SUSPENSION SPRING instead of swinging to and fro. Has a Slow BEAT, therefore consuming small power so that it is used for FOUR HUNDRED DAY CLOCKS. Invented by Robert Leslie in 1793. Also used in the ATMOS CLOCK.

Tortoise Clock: Bowl of water, with hours marked round the rim, in which a metal 'tortoise' floats, to indicate the time. The tortoise is moved round the edge by a magnet turned by clockwork in the base. Invented by GROLLIER. Should be 'turtle clock'! A recent version has a duck in a tiny pond. Also called a 'magnetic clock'.

Tourbillon: A watch ESCAPEMENT has POSITIONAL ERRORS. TO even out some of these, and improve the RATE, BREGUET invented in 1801 an arrangement for pocket watches in which the entire escapement was mounted on a platform which revolved, usually once a minute, which he called a 'tourbillon'. See Karrusel.

Tower Clock: General name for a large public clock, although many early ones were in the body of churches, not in the tower or turret. First made in the thirteenth century (see Salisbury Cathedral Clock). The frames were then heavy wrought-iron cages which degenerated to BIRDCAGE and BEDPOST forms. Others had a VERTICAL FRAME. The FLAT BED form, invented in France, is now universal. Most modern tower clocks have a GRAVITY ESCAPEMENT, a LONG PENDULUM and AUTOMATIC WINDING, which avoids a long chute for the weights and the need for a CLOCK WINDER. Some are electric, operated from a MASTER CLOCK; others are SYNCHRONOUS electric, although this is not ideal for public clocks because such clocks stop during power cuts. Also called 'turret clock'.

Tower of Babel Clock: Famous ROLLING BALL CLOCK representing the famous tower, made by Hans Schlottheim for Emperor Rudolf II between 1595 to 1604. A crystal ball ran round a spiral track in a minute to unlock the ESCAPEMENT and was restored to the top by a spring-operated conveyor belt.

Train: Series of engaging gears as used in a timepiece; thus timekeeping train, striking train, and chiming train. The gear ratio is very high, being stepped up in mechanical clocks and stepped down in SYNCHRONOUS. A watchmaker identifies a train by the number of ticks per hour (the BEAT), men's watches usually having an '18,000 train'. Also referred to as 'a count of 18,000'.

Transistor: Miniature electronic switch replacing the mechanical switch in some battery-operated clocks and watches. See Electronic Watch and Clock.

Transit Instrument: Special telescope rigidly fixed in an eastwest direction, but capable of being swung north-south. It is adjusted to point to a CLOCK STAR each time the Earth rotates. Hence intervals between seeing the same star are 24 hours of SIDEREAL TIME. The astronomer turns a handwheel to move a 'wire' (actually made from spider's web) across the eyepiece in time with the apparent star movement (Fig. 28). This operates electric contacts which make blips on the moving paper tape of a TAPE CHRONOGRAPH, which also records seconds from the OBSERVATORY CLOCK for comparison. Very accurate observations can be taken of some clock stars by an instrument called the 'photo zenith tube', which is connected to the observatory's SIDEREAL CLOCK and photographs star transits and clock records.

Travelling Clock: Spring-driven non-pendulum clock for travelling. Formerly a CARRIAGE CLOCK which fitted into a special case, or a SEDAN CLOCK. Now a CALOTTE and usually an alarm.

Travelling Watch: Large watch for carriage use. Also called a CARRIAGE CLOCK.

Trophy Clock: Another name for PLATE CLOCK or TELLERUHR, as these had name plates on each side of the dial surround for engraving, when used as prizes in Germany.

Trumpeter Clock: Of similar origin to the CUCKOO CLOCK but the bellows blow trumpets instead of cuckoo notes. Some operate drums as well at the hours.

Tubular Chime: Chime on lengths of tube in a LONG CASE CLOCK.

Tulip Decoration: Decoration, such as finials and ENGRAVING on English clock MOVEMENTS and CASES in the seventeenth and early eighteenth centuries, often included tulips because of the Dutch influence.

Tulip Tompion: Famous bracket clock made by THOMAS TOMRIORR about 1680 and so called because the FINIALS on top of the case are like tulips.

Turns: Elementary form of lathe used by watch and clockmakers for centuries. It comprises two fixed points, the 'centres', between which the work is fixed. A bow of cane rotates the work, the gut 'string' being given a turn round it. The watchmaker holds his cutting tool with one hand and 'bows' with the other. Very accurate. Almost entirely displaced by the watchmaker's lathe, except in non-industrial countries.

Turret Clock: Another name for a TOWER CLOCK.

Two-Seconds Pendulum: A pendulum BEATING two seconds, which is about 13 ft. 4 in. long. Thomas Tompion used them in his clocks for GREENWICH OBSERVATORY. Clocks by other makers with 2-seconds pendulums are 'BIG BEN'; St Paul's Cathedral; Birmingham University; Lisburn Cathedral, Co. Down; and over a dozen more over the country. See Long Pendulum.

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