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St Mark's Clock: Magnificent astronomical clock with AUTOMATA in St Mark's Square, Venice. It has tablet numerals.

St Paul's Cathedral Clock: May have been England's first public clock. Records show that in 1286 the clock keeper Bartholomo Orologiario' was entitled to a loaf of bread daily. This clock was probably inside the nave. It was replaced in 1344. Such clocks had no dials or hands, but JACKS which struck bells. They were lighted with candles for services. The present clock was installed in 1893 and strikes on GREAT TOM, having been designed as a rival to 'BIG BEN'.

Salisbury Cathedral Clock: The oldest clock (1386) still working. It was originally in a thirteenth century bell tower in the Close, and re-installed in the cathedral in the eighteenth century when the bell tower was demolished. Replaced by a new clock in 1884, it was 'lost' until discovered by T. R. Robinson in the tower in 1928, and cleaned and put on show in 1931. Many years ago it had been converted to pendulum. In 1956 it was restored to FOLIOT, with 4-sec. ticks, and set going again inside the cathedral. There is no dial. The frame and wheels are of wrought iron, the frame being held together with mortice and tenon joints with wedges like early furniture.

Salomons' Collection: Famous collection, mainly of BREGUET'S work, by the late Sir David Salomons.

Salt Cellar Clock: The container holding salt was often large and of gold or silver in the seventeenth century and an important item in state banquets unimportant people being put 'below the salt'. A clock was occasionally incorporated in it.

Sand-Glass: Early interval TIMER, comprising a glass globe, with a narrow waist, partly filled with sand (often powdered inside the church egg shell). When up-ended, the sand passes from the top to the bottom globe in a fixed time. If the time is an hour, the device is an hour-glass. Developed after WATER CLOCKS, having the advantage of not freezing. The earliest have two open glass bulbs with a pierced brass diaphragm between them. Sand was placed in one and the parts sealed by wax and bound with thread round the joint. The next type was introduced in the late seventeenth century and has two bulbs blown and drawn in one piece, one left with a hole at the top for insertion of the sand. The hole is stopped by a cloth-covered cork. Many have a copper diaphragm pressed into the waist. A third type, from early nineteenth century, is similar but the hole has been sealed by the glass blower. Some were constructed in batteries of three or more with different time intervals. Large ones were commonly stood on pulpits in the past to time sermons and called 'sermon glasses'. Used too, on ships, as late as 1839 even in the British Navy, to calculate speeds. For this a float or 'chip' at the end of a long line with knots at intervals was thrown over the side. The number of knots that ran out as timed by the sand-glass gave the speed in knots. The House of Commons has a 2-min. glass formerly employed for timing division bells calling Members to vote.

Satellite Timer: Time switch for switching on and off the radio transmitter and receiver and other instruments in artificial satellites. If a radio operated by a solar battery were not switched off it might transmit indefinitely, unnecessarily blocking useful channels. In American satellites the basis of the timer is the ELECTRONIC WATCH.

Science Museum Collection: The most interesting of all collection of timekeepers for the mechanically minded, covering not only a comprehensive historical range of instruments and inventions, but the history up to recent developments in electric clocks, MASTER CLOCKS, TIME SWITCHES, and GAS CONTROLLERS, TIME RECORDERS, STOP-WATCHES, QUARTZ CRYSTAL and ATOMIC CLOCKS, etc., not shown by other collections. At South Kensington, London, S.W.7.

Scratch Dial: Primitive SUNDIAL scratched on church walls from the twelfth to fifteenth century. See Mass Dial.

Screw: Metal screws came into use on clocks about 1500 on the Continent, but not until nearly a century later in England. Previously, slots and wedges (as in early wooden furniture) were employed to make temporary joints, and permanent joints were usually fire welded.

Second: The International Committee of Weights and Measures defines the second as one 31,556,925.9747th part of the year 1900. This is based on EPHEMERIS TIME. A second measured by the ATOMIC CLOCK is now known to be more accurate and may in future be adopted. It equals 9,192,631,770 vibrations of the caesium atom. The word was originally a 'second minute', i.e. the second division into 60.

Seconds Hand: Hand of a clock or watch showing seconds. One of the earliest is on BURGI'S rock crystal clock made just after 1600, but they did not come into general use on clocks until the LONG PENDULUM was invented and on watches until the CYLINDER ESCAPEMENT. See Centre Seconds.

Seconds Pendulum: A PENDULUM taking a second to swing from one side to the other and therefore theoretically 39.14 in. long.

Secret Signature: Because BREGUET's watches were faked, he put a secret signature on many as an indication of authenticity. This is a very tiny signature under the 12 on enamel dials and on either side of 12 on metal ones, on which it can be spotted by looking across the dial towards the light.

Sedan Clock: Small clock with a VERGE watch movement and often a circular wooden case about 6 in. across, for hanging in a sedan chair. Made in the late seventeenth and early eighteenth centuries.

Self-Correcting Chimes: Automatic arrangement on most domestic chiming clocks by which the chimes, if out of sequence, are held up at the hour and released when again in step.

Self-Winding Clock: Perhaps the first was driven by a fan in the kitchen chimney, as recorded by Gaspar Schott in 1664. Very many types have been invented. See Light Clock, Atmospheric Clock, Automatic Winding and Battery Clock.

Self-Winding Watch: Watch wound by the movements of the wearer. Also called 'automatic', 'pedometer watch', and jerkwinding watch'. Perrelet or Recordon invented the self-winding pocket watch about 1780, and it was made in some numbers by BREGUET. An eccentric weight in the watch, as in a pedometer, oscillated with movements of the wearer and wound the mainspring. LE ROY invented a ROTOR winding system about the same time. The self-winding wrist-watch was invented by an Englishman, John Harwood, in 1923, who also invented a system by which the watch strap moved the LUGS of the watch to wind it. In another system, the Rolls by Hatot of Paris, the whole watch oscillated in its case to wind the spring. Currently a number of Swiss factories make only self-winding watches, mostly with rotors which wind when turning in either direction and have a clutch to prevent overwinding. An automatic watch is more accurate than an orthodox one because the mainspring is kept at a more constant tension. There are usually 40 to 50 hours reserve power. Some have UP-AND-DOWN DIALS. The button is for hand setting only.

Sermon Glass: A SAND-GLASS once used on pulpits to time sermons. Loquacious clerics in full spate would sometimes say, 'Let us take another glass . . .

Serpentine Hand: Clock minute hand which is wavy instead of straight. Introduced about the middle of the eighteenth century.

Set Hands: The clutch mechanism in every timepiece that allows the hands to be set to a new time without damaging the MOVEMENT.

Set in Beat: See Out of Beat.

Seth Thomas: American clockmaking pioneer born in Wolcott, Connecticut, in 1785. Joined TERRY and Hoadley after being apprenticed as a carpenter and joiner, afterwards making a fortune on his own with factories producing clocks, brass and wire. Set up Seth Thomas Clock Co. in 1859 in Plymouth. Perfected the SHELF CLOCK.

Setting-Up: Pre-tensioning a spring, i.e. fixing the lowest tension to which it can run down. In early spring-driven timepieces, the MAINSPRING could be set up to different tensions to adjust the power output and therefore the timekeeping. With the FUSEE, the mainspring has to be set up to keep the gut taut. STOP WORK is necessary with such mechanisms.

Sextant: An instrument for measuring angles used in NAVIGATION for finding LOCAL TIME by star observations. The height of a star is found by turning a knob of the marine sextant so that an image of the star is brought down to the horizon. A scale then gives the angle. The bubble sextant, which has an artificial horizon, is used for aircraft.

Shagreen: Shark skin used for nineteenth century watch cases. Imitated also by other fish skins and leather dyed green.

Sheepshead Clock: A LANTERN CLOCK with a particularly large DIAL, supposed to make it look like a sheep's head.

Shelf Clock: American pendulum clock with a tallish case up to about 4 ft. which stood on a shelf. Some looked like cut down LONG CASE CLOCKS.

Shepherd's Dial: Early kind of portable ALTITUDE SUNDIAL Of cylinder shape from which the GNOMON protrudes horizontally. A vertical line on the cylinder, corresponding to the HOURS Of the month, is held facing the Sun and end of the shadow shows the hour on a horizontal scale.

Ship's Bell Clock: Clock striking on the ship's bell system (see Ship's Time). An unusual one was in the Royal withdrawing room at the Festival of Britain. The glass bell was also the clock case.

Ship's Time: Three systems of time are used on board ships. A sailor's day is reckoned from noon and divided into a series of 'watches'. Each is of four hours except the two Dog Watches of two hours each. During a watch the SHIP'S BELL is struck once at the end of the first half hour, twice at the second, up to eight times at the end of the four hours. A passenger's day is a normal 24 hours, as shown on SLAVE CLOCKS on the ship operated from a MASTER CLOCK, which is advanced or retarded at night, according to whether the ship is going west or east, to adjust approximately to LOCAL TIME. The third time reckoning 1S GREENWICH MEAN TIME shown by the ship's CHRONOMETER. This, compared with local time obtained by a SEXTANT and the NAUTICAL ALMANAC from the Sun, Moon or stars, gives the ship's longitude for navigation.

Shock Absorber: Arrangement to protect the delicate PIVOTS Of a jewelled BALANCE WHEEL from damage if a watch is knocked.The JEWELS are carried in special self-centering, spring-loaded seats which will absorb blows from various directions. The first was Breguet's PARACHUTE. Present systems are more precise and efficient.

Shortt Clock: The most accurate form of pendulum clock ever made. Invented by W. H. Shortt in 1921 for use as an OBSERVATORY CLOCK. See Free Pendulum Clock.

Sidereal Clock: Clock keeping SIDEREAL TIME, used in observatories for star observations and TIME DETERMINATIONS. Some clocks show MEAN TIME as Well as SIDEREAL.

Sidereal Time: The time of rotation of the Earth as measured from a CLOCK STAR, instead of from the Sun. This is more accurate but ignores daylight, giving a day of 23 hr. 56 min. 4.1 sec. It is thus impractical for ordinary use, but is employed in TIME DETERMINATION. OBSERVATORY CLOCKS are made t0 show sidereal time. See Nutation, Precession of the Equinox and Transit Instrument.

Signatures: The actual makers of old clocks and watches engraved their names on the dial and back PLATE. In the eighteenth century, they continued to do so because they were the designers and finishers although much work was put out to makers of parts, called 'chamber masters'. In the late eighteenth and nineteenth centuries more and more clockmakers, including famous ones, bought complete MOVEMENTS and sometimes complete clocks from specialist manufacturers in CLERKENWELL and elsewhere for their regular 'lines' but still signed them. The same makers sometimes supplied to retailers who had their names engraved as makers. Some such clocks even bear customers' names. So the true maker is sometimes not the person named on the dial. There may be a punch mark somewhere in the movement revealing the real maker.

Silent Escapement: The noisy ticks of the VERGE ESCAPEMENT was an objection to NIGHT CLOCKS, so Joseph KNIBB attached short lengths of springs to the PALLETS to absorb the shock of the CROWN WHEEL and noise. Justin VULLIAMY in mid-eighteenth century, mainly for NIGHT CLOCKS, introduced lengths of taut gut to replace the metal PALLETS. Some modern ALARMS have a form of silencing. The MAGNETIC ESCAPEMENT is also silent.

Silk: Suspension Method of suspending a PENDULUM from a loop of silk thread, the PENDULUM rod having a hook at the top. Timekeeping is adjusted by winding up the thread. Often seen in earlier French clocks.

Silvering: Matte silver finish of the brass CHAPTER RING of most antique clocks. Before the invention of silvering, about 1660, decorative clock parts and chapter rings were sometimes in solid silver.

Singing Bird: Clockwork mechanism with bellows imitating bird songs, usually associated with AUTOMATA Of birds. Some are in snuff boxes, which reveal a miniature 'bird' when opened, others are life-sized 'birds' in cages which move and sing so realistically it is difficult to believe they are not alive. Made by early English clockmakers such as PINCHBECK and later in large numbers from mid-eighteenth century by the Swiss, French and Germans, until the 1920s. Famous makers were the Brugiers family (c. 1770-1886), Jacquet-Droz, the Rochat family, Lami, Jean David and Auguste, and the Maillardet brothers, all of Geneva; and the firm Of LE ROY, and Blaise Bontemps, of Paris.

Sinking Bowl: Bronze bowl with a hole in it which sinks in a given time when floated in water; used by the Saxons as a WATER CLOCK, or more accurately, a TIMER. Still used today in Algeria to time irrigation of land.

Six Pips: The familiar RADIO TIME SIGNAL originated from a talk on the B.B.C. given by HOPE-JONES on 21 April 1923, the year after the DAYLIGHT SAVING ACT, when he vocalized the last six seconds to the hour. The electrically produced 'pips' started in August 1923. They are correct to within 0.1 sec. and normally within 0.05 sec.

Size: American system of watch measurement originated by A. L. DENNISON, based on thirtieths of an inch. 0 size is the basis, equalling 35/30ths in. 1 size is a thirtieth larger, i.e. 36/30ths, and so on. 1/0 size is a thirtieth smaller, i.e. 34/30ths, and so on. See Ligne.

Skeleton Clock: Spring-driven clock in which the PLATES, DIAL, and other parts are 'skeletonized', i.e. elaborately pierced. Usually under a glass dome. Very popular from about 1860. Occasionally the MOVEMENTS of weight-driven LONG CASE CLOCKS and REGULATORS were skeletonized

Skeleton Watch: Watch in which the PLATES or EBAUCHE, COCKS, BRIDGES, BARREL, DIAL, and so on, are pierced like fretwork. An early version was by Thos. MUDGE, in the eighteenth century. A few skeleton pocket watches are still made in Switzerland.

Skull Watch: Watch made in the seventeenth century in the form of a skull, sometimes of silver or wood. Read by opening the jaw. See Mary Queen of Scots' Watch.

Slave Dial: A clock dial in which the hands are operated by an electro-magnet from the electric impulses sent every half minute from a MASTER CLOCK elsewhere. Also called an 'impulse dial'.

Smallest Watch: Small watches for their time, such as PURITAN WATCHES, have been made since early days. An amazingly small and complicated RING WATCH was made by John ARNOLD for King George II. He refused to make another for the Empress of Russia. The smallest watch in quantity production is made by Jaeger Le Coultre. The MOVEMENT has 74 parts including 15 jewels and measures just over I in. by just under 5 in. In the first half of the nineteenth century, the Swiss made some small watches of pocket watch style, I in. and less in diameter, with CYLINDER Or LEVER ESCAPEMENTS.

Smith, Sir Alan Gordon (1881-1951): Principal founder of the reborn BRITISH HOROLOGICAL INDUSTRY, W110 turned his father's jeweller's shop in the Strand, London, into almost an entire clock and watch industry.

Smuggling: Watch smuggling is caused by high import duties, taxes, and quotas, which make it profitable. Many thousands of watches are smuggled yearly by well-run organizations into the U.K. from Switzerland and sold by agents in factories and public houses. Many are inferior watches with imitation JEWELS which are in fact dear at the price asked, but others are good. Snail Diamonds are smuggled out to pay for them. The U.S.A., Italy, India, various countries in Africa, etc., are also badly affected. It is illegal to possess a smuggled watch.

Snail: A cam shaped like a snail's shell. Used particularly for the hook holding the end of the MAINSPRING to the ARBOR of the BARREL, which thus avoids breakage by following the spiral of the spring.

Snailing: Curved lines radiating from the centre of the polished steel winding wheels in a watch, or the steel small end (the 'cap') of a FUSEE, used for decoration.

Solar Dial: The 24-hr. DIAL Of a TIME SWITCH Or GAS CONTROLLER which switches street lights on and off and adjusts the switching times according to the time of year. The dial carries two cams to operate the on and off switches and is revolved by a clock. The position of the cams is altered daily by an ingenious automatic indexing arrangement.

Solar Time: Time measured by a SUNDIAL. A solar day is from the Sun's highest point (MERIDIAN) on one day to its meridian on the next. Solar days vary in length throughout the year. To simplify timekeeping, the average solar day over the year, called the 'mean solar day', is taken as a standard and divided into EQUAL HOURS. Mean solar time at Greenwich is GREENWICH MEAN TIME. See Equation of Time.

Solid Balance: Straightforward BALANCE WHEEL normally made of a single metal, and therefore without BI-METALLIC COMPENSATION. Not a CUT BALANCE. TEMPERATURE COMPENSATION 1S usually effected by making the HAIRSPRING Of NIVAROX or a similar alloy.

'Solunar' Dial: Daily tidal times, as shown on some wrist CHRONOGRAPHS and used in conjunction with 'solunar table's (J.. Alden Knight) to forecast feeding times of fish and game for sportsmen. Can be set for different places. See Tidal Dial.

Spade Hand: Hand with an end like the Ace of Spades.

Spandrel: English BRACKET CLOCKS have a circular CHAPTER RING on a square DIAL, the corners of which were at first engraved but very soon were filled with triangular ornaments of cast brass, called 'spandrels'. The earliest, from about 1660, had cherubs' heads and were finely chiselled. Later they became less well finished. The cherub persisted for about 100 years, but many other designs, particularly leaf and scroll, were popular. Brass spandrels were given a coat of GILDING; occasionally they were made entirely of silver.

Spherical Watch: Probably the earliest form made (see Musk Ball Watch). Small spherical or BALL WATCHES for women are still made to be used as a FOB WATCH or on a chain round the neck.

Spiral Hairspring: A HAIRSPRING of spiral form. The earliest, of untempered steel, had 1 1/2 to 2 turns; by mid-eighteenth century there were 4 to 5 turns; modern ones have about 12 turns. The inner end is fixed by a collet to the STAFF (axle) of the BALANCE WHEEL. The outer end is fixed to a stud on the BALANCE COCK, or may be curved inwards as an OVERCOIL. See Regulator and Index.

Split Seconds: A TIMER with two CENTRE SECONDS HANDS, one over the other, and an extra push button. The main push button starts, stops, and returns both hands to zero. After the hands are started, the second push button will stop the 'split hand' only and when pressed again, cause it to catch up the other hand. Useful for timing both first and second places in athletic events.

Sports Timer: A TIMER of pocket watch shape which is calibrated in 1/5 to 1/100 sec., for athletics, or in a special way for other sports (see Split Seconds). For boxing, 3 min. rounds with 1 min. intervals are shown by the minute hand; for football, j hr.; for hockey, 35 min. and ice hockey 20 min.; for water polo, 7 min. with an interval of 5 min.; and for yacht races, the 5 min. interval before the starting gun is indicated. With a sculling timer, ten strokes are timed and the hand then indicates the strokes per minute. See also Tachometer, Telemeter and Chronograph.

Sports Timing: For this, the TIMERS and CHRONOMETERS used are certified. (The BRITISH HOROLOGICAL INSTITUTE checks them for the Auto Cycle Union which controls motor and motorcycle racing and Road Time Trials Association controlling bicycle time trials. The NATIONAL PHYSICAL LABORATORY has more elaborate tests for these and others.) The man who is the TIMEKEEPER usually has to pass tests, also. The Amateur Athletics has carried out such tests at Motspur Park since 1949. Checked over 100 to 220 yards races against a man considered a master timekeeper, a candidate has to score 90, 80 or 70 % accuracy to be graded 1st, 2nd or 3rd class. Average reaction time to starting and stopping signals is 0.02 seconds. Actual error depends partly on the form_ of TIMER used.

Spotting: Decoration used for the brass PLATES of clocks and MARINE CHRONOMETERS, used inside watch cases, rows of spots being produced by a small circular polishing tool.

Spring: See Mainspring and Hairspring.

Spring Detent: The now universal DETENT ESCAPEMENT for MARINE CHRONOMETERS, invented by BERTHOUD, ARNOLD and EARNSHAW. The detent or lever which releases the ESCAPE WHEEL is mounted on a spring instead of a PIVOT, which eliminates variations caused by wear of the pivot and the necessity to oil it.

Stackfreed: Device on earliest German watches to improve poor timekeeping. The crude MAINSPRING lost power rapidly as it ran down. To make power output more even, the mainspring also turned a cam, on the edge of which a roller was pressed by a spring. This caused extra friction, which decreased as the mainspring ran down. The turns of the mainspring were also limited by STOP WORK for the same reason.

Stadium Timer: Large TIMER dial, usually operated electrically, for sports audiences. Calibrated according to the sport concerned.

Staff: Watchmaker's name for the axle of the BALANCE.

Stainless Steel: Nickel-chromium steel commonly used for entire watch cases and the backs of ROLLED GOLD or GOLDPLATED cases, as it resists the acids from the skin.

Standard Time: Time applying in a particular TIME ZONE, or country if this overlaps zones. In Britain, Standard Time is G.M.T. Canada has five standard zones an hour apart as the country spreads over five zones. They are: Atlantic, Eastern, Central, Mountain and Pacific Times.

Star Transit: The time at which a star crosses the MERIDIAN. Star Wheel Star-shaped wheel used to give positive movements of CALENDAR and other dials of clocks or watches. A v-shaped spring, called a 'jumper', causes the star wheel to jump swiftly from one indication to the next. See illustration overleaf.

Steuart Corrector: Arrangement of an electric motor controlled by a pendulum invented by Alexander Steuart to control the public clocks in Edinburgh, the TIME GUN at the Castle, and the TIME BALL on Cotton Hill, from the Royal Observatory at Edinburgh.

'Stopper': Watchmaker's name for a watch that stops at infrequent intervals for reasons difficult to trace.

Stop-Watch: A TIMER in pocket watch form for recording time intervals. See Production Timer, Sports Timing and Split Seconds.

Stop Work: Arrangement to prevent a mainspring from being over-wound, when the spring coils may bind together and stop the timepiece. Used also on very early watches and clocks and on musical boxes to prevent the mainspring from running down too much, thus causing bad timekeeping (or slow music).The most common form on the modern watch is the RECOILING CLICK to prevent overwinding.

Strap, Watch: A leather strap to hold a watch to the wrist, invented by an Englishman, A. E. Pearson, for soldiers who wanted WRIST-WATCHES during the First World War. An early strap had a leather cup to hold the watch. Then loops were soldered to the watch case to take loops in the strap. LUGS are most common today. A spring-loaded bar between a pair of lugs passes through a loop in the strap. Straps are often padded and have turned-in edges, being sewn with thread or nylon and/or glued. Leathers, pigskin, crocodile and other skins are used as well as fabric and nylon cloth.

Strasbourg Clock: Elaborate ASTRONOMICAL and AUTOMATA CLOCK in Strasbourg Cathedral, France, first erected in 1354, reconstructed by Isaac and Josias HABRECHT in 1575, and redesigned and rebuilt by J. R. Schwilgue in 1842. It incorporates a mechanical globe and a mechanical cock that crows three times at noon.

Striking Clock: Clock that sounds the hours on a bell or GONG. Very early clocks did this without indicating the time on a dial. The striking TRAIN is separate from the GOING TRAIN of gears, being released by it at the hours by a system of pins and levers incorporating a LOCKING PLATE or RACK. See Chiming Clock.

Style: Another name for GNOMON.

Su Sung's Clock: A MONUMENTAL CLOCK made in 1088 by a Chinaman, Su Sung. It had one of the first known ESCAPEMENTS, a water wheel controlled by two steelyards or weigh-bridges. The clock was 30 to 40 ft. high. On top was a huge powerdriven ARMILLARY SPHERE of bronze and inside a room with an automatic CELESTIAL GLOBE. A 5-storey pagoda on the front had doors through which JACKS appeared every quarter hour ringing bells and holding tablets to indicate the hours. The clock consumed half a ton of water in 9 hours, and also contained the earliest endless chain, oblique gearing, long transmission shafts, cup bearings, and 'telescope drive'.

Subscription Watch: The famous watchmaker BREGUET never made two watches alike except for a series known as 'subscription' which were claimed to be the cheapest very high quality watches made. They were produced in batches and subscribed for in advance. They have large enamelled dials and single hands.

Sully, Henry (1680-1728): Clever but unlucky maker who travelled on the Continent after his apprenticeship and became friendly with Julien LE ROY. He took 60 English watchmakers and their families to Versailles and later St Germain to improve French standards of craftsmanship, but was unlucky financially and in health. Invented the OIL SINK and a marine timekeeper. French revolutionaries removed most of the inscription on his memorial in St Sulpice Church, Paris, which gave him credit for helping the French industry.

Summer Time: STANDARD TIME which has been advanced by one hour in the U.K. See Daylight Saving. Sun and Moon Watch Watch with an unusual dial, which appeared about 1700. The minute hand is normal. Hours are shown by an image of the Sun travelling round a semicircular slot marked from 6 a.m. to 6 p.m. An image of the Moon follows, showing the hours from 6 p.m. to 6 a.m.

Sun Ray Clock: Wall clock with a case like a 'sunburst' with rays of gilded metal, wood, or, in contemporary styles, of wire.

Sundial: Method of showing time by shadows cast by the Sun according to its direction (COMPASS SUNDIAL), or height (ALTITUDE SUNDIAL), in the sky. The earliest were probably Egyptian and spread to the Roman Empire (about 290 b.c.) and Grecian Empire. A popular early type was the HEMICYCLIUM. England's earliest sundials are Saxon, and on Bewcastle Cross, Cumberland (c. A.D. 670), and Kirkdale Church, Yorkshire (c. 1060). PORTABLE SUNDIALS Were also made from early times. Early sundials showed TEMPORAL HOURS. From mid-fourteenth century they began to show EQUAL HOURS after an Arab mathematician, Abu'l Hassan, calculated that the GNOMON should be parallel to the Earth's axis. After mechanical clocks were introduced, the sundial remained in use as a master by which to set them. During the seventeenth and eighteenth centuries, portable sundials were supplied with the best clocks.

Suspension: Flexible or pivoted mounting of a pendulum, usually a SUSPENSION SPRING. Early VERGE clocks had knife edge suspension (like a weighing-machine). SILK SUSPENSION is another form.

Suspension Spring: Short length of clock spring on which a pendulum hangs, Invented by WM. Clememt.1671, or Robert Hooke earlier.

Sweep Seconds: American name for CENTRE SECONDS.

Swiss Horological Industry: Geneva goldsmiths of the sixteenth century were the first Swiss watchmakers and in the next centuries they specialized in ENAMELLED WATCHES. When the Huguenots were driven from France in 1685, many watchmakers went over the mountains into Switzerland. The chief workers were the 'cabinotiers', who turned their own homes into workshops. The Swiss soon adopted the GOING BARREL instead of the FUSEE and mechanization (see Ingold), particularly in the Neuchatel area, which started them towards becoming the world's biggest and finest watchmakers. Now the industry is divided into four groups under the Swiss Chamber of Horology:

1. The Swiss Watch Federation of over 500 manufacturers and finishers of JEWELLED LEVER WATCHES. 2. Ebauches S.A., a group of 18 factories making parts for jewelled lever watches. 3. Union des Branches Annexes de 1'Horologerie, makers of all parts except EBAUCHES. 4. Roscopf Association, 44 factories making cheaper ROSCOPF-type watches. There are several watch-testing stations and compulsory quality control was also introduced in 1962. Output of watches is about 40 million yearly. Jewelled lever travelling and alarm clocks are also made in quantity. The industry is almost entirely in the Valley of the Loire and the Jura Mountains.

Sympathetic Clock: Amazing time-controlling arrangement invented by BREGUET in 1805-10. It comprised a clock and watch. The watch was placed in a clip in the clock at night and the clock, at a fixed hour, not only reset the watch to the correct time, but also REGULATED it according to its gaining or losing RATE. This incorporated the principle of feedback, the basis of automation.

Synchronous Clock: Electric clock dial operated from the main supply frequency, invented by H. E. Warren of the U.S.A. in 1918. The 'clock' is actually a synchronous electric motor which keeps in step with the generators at the power station, which are themselves kept in step with G.M.T. by a FREQUENCY COMPARISON METER. The frequency in the U.K. is 50 cycles a second and in the U.S.A. 60.

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