Time & Clocks Dictionary
Pair Case: Extra detachable case round early highly decorated watches for protection. Some had a plain silver or gold inner case into which the MOVEMENT was hinged, then a separate decorative case, then a third, protective, case. The ordinary pair case of the eighteenth century had a plain inner and single outer case to keep out the dust, but some were ENAMELLED or otherwise decorated.
Pallet: The part of an escapement that intercepts the teeth of the ESCAPE WHEEL. Jewelled pallets made of synthetic ruby are better for watches and clocks than PIN PALLETS made of steel.
Parachute Index: Combined SHOCK ABSORBER and regulation INDEX for watch BALANCE WHEELS invented by BREGUET. Forerunner of the modern shock absorber.
Parliament's Clocks: Clocks for the House of Commons, which was restored after damage during the Second World War, were the gift of Northern Ireland. One hundred and seventy-two SLAVE DIALS, split into six groups, are operated from a MASTER CLOCK through a control panel in the switch room. For timing divisions of the House, the Speaker has a special INTERVAL TIMER. The tower clock is popularly called 'BIG BEN'.
Pavement Clock: Clock set flush in the pavement or sidewalk with a heavy glass dial. There is one near Windsor Castle.
Pedometer Watch: The first SELF-WINDING WATCH was a pocket watch with a weighted lever, like that in a pedometer, which jerked when the wearer moved and wound the MAINSPRING. Made also by BREGUET.
Pegwood: Stripped twig of boxwood sharpened at the end like a pencil and used to clean out the PIVOT HOLES of clocks and watches.
Pendant: The 'hanging' part of a pocket watch, i.e. the part to which the 'bow' or loop is fixed. Since KEYLESS WINDING, the 'pendant position' of any watch is where its WINDING BUTTON (also called the 'crown') is fitted. The expression is used when checking POSITIONAL ERRORS, i.e. 'pendant right'.
Pendulum: A weight swinging under the influence of gravity. First it was hung from a thread and the swings counted for astronomical time measurements. GALILEO discovered that the swing or BEAT depended only on the length of the thread or pendulum rod, not the angle of swing or weight of the BOB. HUYGENS proved this was only true if the pendulum swung through a cycloidal curve instead of the arc of a circle, the difference being CIRCULAR ERROR. Of several applications of a pendulum to clock mechanisms, that by Huygens was most successful. The RATE of a pendulum is altered by the different forces of gravity in different parts of the world. The formula is: time of swing in seconds equals the square root of the length in inches divided by 32, which gives approximately 39 in. (a metre) for a SECONDS PENDULUM. This measurement is made from the point Of SUSPENSION t0 the CENTRE OF OSCILLATION Of the BOB. The pendulum controls the RATE of a clock MOVEMENT and is kept swinging by IMPULSES from the ESCAPEMENT. See Rating Nut, Conical Pendulum and Torsion Pendulum.
Pendulum Rod: Rod holding the BOB, made of brass, steel, varnished wood such as fir (which is not so much affected by temperature). COMPENSATION PENDULUM rods are made from INVAR or composite materials.
Pendulum Watch: After the application of the PENDULUM to clocks, watchmakers who did not truly appreciate its theory tried to apply it to watches. A pendulum replaced the BALANCE and the watch was set in gimbals so that it would always stay upright. The case was therefore ball-shaped. This did not work well, so a counterbalance was added to the pendulum and it really became a DUMBELL BALANCE again. Most so-called pendulum watches were made after about 1700 and are false, being designed as a 'sales stunt' of the time to take advantage of the reputation of the pendulum. A disc was attached to the balance and could be seen oscillating through a slot in the dial, like the MOCK PENDULUM Of a clock.
Perpetual Calendar: Calendar worked by a clock which corrects for months of different lengths (and sometimes for leap year also). Occasionally incorporated in COMPLICATED WATCHES.
Perpetual Watch: Name for the SELF-WINDING WATCHES made by BREGUET.
Phillips Curve: A special curve or OVERCOIL of the outer end of a HAIRSPRING towards the centre to improve ISOCHRONISM, worked out mathematically by Edouard Phillips, a Frenchman, in 1860. The curves were further improved by another mathematician, Lossier of Geneva, around 1907. See Breguet Spring.
Phonic Motor: An elementary motor which can be kept in step with an alternating electric current, like a SYNCHRONOUS CLOCK. Its consumption of electricity is so low that it can be driven from a radio valve; it is therefore commonly used to drive the hands or DIGITAL counters of a QUARTZ CLOCK.
Photographic Timer: A switching device connected to a photographic enlarger. The dial is set to the time of printing exposure. A switch is pressed which sets the timer going and switches on the enlarger light. The light is switched out automatically at the end of the time set. A simpler form is a TIMER Or ELAPSED TIME INDICATOR that rings a bell.
Picture Frame Clock: The round DIAL is set in velvet in a picture frame, with brass SPANDRELS. Made from about 1875 to 1900 in France with green, blue or red velvet.
Pierpont Morgan Collection: Magnificent collection of watches now in the Metropolitan Museum, New York. A superb catalogue of this in a limited edition of 46 copies was produced. One is in the ILBERT LIBRARY at THE BRITISH HOROLOGICAL INSTITUTE.
Pigeon Clock: Special TIME RECORDER for pigeon racing. Birds are taken to the starting place and released. On each bird's arrival at its particular 'home' an identification ring from its leg is placed in a pigeon clock there. This records the time on a paper chart in hours and minutes and seals rings in a storage magazine in order of insertion. There are several devices to prevent the clock from being 'fiddled'.
Pillar Clock: French DRUM CLOCK with round movement and dial on four vertical pillars standing on a round base. The pendulum hangs in the middle of the pillars. Made in marble, ormolu, and wood in the nineteenth century. Also a special form of JAPANESE CLOCK showing time by a pointer moving along a linear scale, or any clock on a pillar.
Pillars: The riveted or screwed rods which fasten the PLATES together to make a clock FRAME or early watch frame. Formerly they were carved or turned in fancy shapes.
Pinion: One of the small solid, and usually steel, gear wheels in a clock or watch. The large gears are called 'wheels'. Formerly 'pinion wire' with the cross section of a gear, could be bought for cutting into pinions. The teeth are called 'leaves'. See Wheel and Lantern Pinion.
Pin Lever: Alternative name for a PIN-PALLET Watch.
Pin-Pallet: An ESCAPEMENT with steel pins instead of jewelled PALLETS, used in cheap, particularly ROSCOPF, watches. The action is very similar to the LEVER ESCAPEMENT, and it is sometimes called 'pin lever'. Also the BROCOT ESCAPEMENT for clocks, which was not designed for cheapness.
Pin Wheel Clock: ESCAPEMENT popular in France. Also employed in TURRET CLOCKS on the Continent. The teeth of the ESCAPE WHEEL are replaced by pins. A swinging pair of levers attached to the PENDULUM allows the pins to 'escape' one by one, and this also IMPULSES the pendulum. It is accurate and needs only a small pendulum arc. Invented by Amant in 1741.
Pinchbeck, Christopher (1651-1713): Inventor and maker of musical clocks, which gained world-wide repute, and of the metal alloy still called 'Pinchbeck'. Worked in Fleet Street, 'at the sign of the Astronomico-Musical Clock'. The 'curious secret of new-invented metal which so naturally resembles gold' was four parts copper to three zinc. His eldest son, also Christopher, made an ASTRONOMICAL CLOCK for King George III, which is still in the ROYAL COLLECTION.
Pinwork Watch: PAIR CASE of leather, studded with silver pins. Pique Tortoiseshell inlaid with a decoration of silver or gold, used for watch PAIR CASES in the eighteenth century.
Pith: Used by watchmakers for cleaning delicate watch parts.
Pivot: The small end of a shaft or ARBOR that runs in a bearing hole. As special shape is necessary for BALANCE STAFF pivots that run in jewels, CONE PIVOTS are employed for cheap watches, alarm clocks, and many meters.
Pivoted Detent: A form of DETENT ESCAPEMENT (as used on early MARINE CHRONOMETERS). The lever or detent which releases the ESCAPE WHEEL turns on a PIVOT. Now replaced by the SPRING DETENT.
Planetarium: Representation of the night sky on a dome by complicated sets of projection lenses driven by clockwork. The only British one is at Madame Tussauds, in London, but another is to be built at GREENWICH OBSERVATORY.
Plate: A front and a back plate of brass are joined by turned PILLARS to make a clock FRAME. In early watches top and bottom plates were similarly employed. Early clocks had elaborate engraved decoration, such as TULIP, over the backplate. Plates of MARINE CHRONOMETERS are usually SPOTTED. Those of some watches and small clocks are matted and GILDED, and of some machine-made clocks PRINKED.
Plate Clock: See Telleruhr.
Platform Escapement: An ESCAPEMENT (usually LEVER) on a small separate platform, usually across the PLATES of a clock. Usually driven by a CONTRATE WHEEL.
Plato Clock: American name for a TICKET CLOCK.
Pocket Chronometer: A high grade pocket watch with a DETENT ESCAPEMENT arid CYLINDRICAL HAIRSPRING, made particularly over the end of the eighteenth and throughout the nineteenth century (even after the LEVER ESCAPEMENT became general). PIVOTED DETENTS were incorporated before about 1780 and SPRING DETENTS afterwards. The pocket chronometer is liable to POSITIONAL ERRORS and particularly affected by shock, reasons why it was surpassed by the LEVER. The seconds hand has DEAD BEAT action. Principal makers included the ARNOLDS, EARNSHAW, Dent, BEREGUET, COLE, Jump, and Frodsham. The Swiss definition is a pocket watch, with lever or other escapement, that has gained a RATING CERTIFICATE.
Pocket Watch: Watch introduced after the invention of the pocket in the first quarter of the seventeenth century and very popular after 1675, when the waistcoat became fashionable. Now largely superseded by the WRIST-WATCH, except for men's dress wear and precision timekeeping, as a pocket watch is more accurate because of its larger size and reduced liability t0 POSITIONAL ERRORS, being kept in a vertical position most of the time. A TOURBILLION Or a KARRUSEL practically eliminates errors in vertical positions. See Pair Case.
Point of Attachment: Usually the point at which the inner end of the HAIRSPRING IS fixed to the BALANCE. Also called the 'pinning point'. It is impossible to fix this end on the exact axis of the BALANCE STAFF. As the end is therefore slightly out of centre, this causes movement of the centre of gravity of the HAIRSPRING and therefore small changes in RATE. Manipulation of this end of the balance is one of the fine ADJUSTMENTS carried out by watch ADJUSTERS.
Poise: Watchmaker's name for being in 'balance', or more exactly in 'static balance'. A BALANCE WHEEL is poised by adjusting the weight around the rim, either by removing metal, screwing screws around the rim in or out, or altering washers under the screws. An 'out-of-poise' balance causes increased POSITIONAL ERRORS.
Portable Sundial: Since a normal sundial had to be fixed in a certain and permanent position, portable sundials were valuable to military leaders and others before the portable clock was invented. There are two types, COMPASS DIAL and ALTITUDE DIAL. One of the earliest known is a silver and gold Saxon pocket sundial of label shape on a chain of the tenth century found in 1939 in the soil of the Cloister Garth of Canterbury Cathedral. It is an altitude dial showing TIDES.
Positional Errors: A watch runs at different RATES in different positions owing to ESCAPEMENT ERROR, lack of ISOCHRONISM, changes in the centre of gravity of the BALANCE arid HAIRSPRING owing to the fact that the inner end of the spring cannot be fixed in the exact centre, and so on. The rate in wear is an average of these errors and therefore varies with different wearers. A good wrist-watch is tested and regulated in six positions, dial up, dial down, button up, button down, button right, button left. Worst errors are kept to the button left position, which occurs rarely with the watch on the outside of the left wrist. (A precision watch on the inside of the left wrist will give its worst performance.) A good watch which is a few seconds fast can be brought to time by leaving it on edge overnight, as it loses slightly in this position. Cheap wristwatches are checked and regulated in two positions. Positional errors do not have so much effect on POCKET WATCHES and none at all on clocks.
Postman's Alarm: Alarm wall clock, with long PENDULUM and weights hanging below it, two brass bells on top, and outside hands. Made in Germany, modified in England, and popular up to 1939. Potence Form of COCK used as a lower bearing.
Prague Town Hall Clock: One of Europe's finest astronomical clocks built in 1490, renovated in 1866, destroyed in the Second World War and reconstructed after it.
Precession of the Equinox: Effect caused by the Earth turning like a dying top so that the axis has a slow conical motion. This causes a day of SIDEREAL TIME to be 9 MILLISECONDS shorter than the true period of rotation of the Earth. Discovered in 130 B.C. by Hipparchus. NUTATION is another disturbance in rotation. In addition, it was discovered in 1953 by QUARTZ CRYSTAL CLOCKS and confirmed by the ATOMIC CLOCK, that the Earth is slowing down.
Precision Clock: Any clock made for very accurate timekeeping, such as a REGULATOR, FREE PENDULUM CLOCK, electric MASTER CLOCK, QUARTZ CLOCK Or CHRONOMETER clock with CONSTANT FORCE ESCAPEMENT Or DEAD BEAT ESCAPEMENT, OBSERVATORY CLOCK, etc.
Precision Watch: Quality watch which has been individually adjusted arid holds a RATING CERTIFICATE. See Chronometer.
Prescot, Lancashire.: Once a centre of the BRITISH HOROLOGICAL INDUSTRY, especially about 1850, making most parts of watches (and the best files in Europe) by hand methods for assemblers in COVENTRY, CLERKENWELL, etc. Two watchmakerinventors, John Wycherley and T. P. Hewitt, caused a revival later, then the Lancashire Watch Co. (1888) and Prescot Watch Factory were opened, but hand craftsmen resisted the trend and the trade went to Switzerland.
Prime Meridian: The zero MERIDIAN LINE which passes through GREENWICH OBSERVATORY and on which the world's time measurements and TIME ZONES are based. The Observatory is now in Sussex and not on the meridian, so corrections have to be made for this in TIME DETERMINATION.
Prinked: A prinked clock PLATE has small dots impressed in rows on it to harden the surface.
Process Timer: Clock for timing a manufacturing process. Sometimes a separate large TIMER, at others an ELAPSED TIME INDICATOR, or TIME SWITCH, which actually controls the process.
Production Timer: A TIMER used to measure the time of making a single article. The hand then indicates the rate of production per hour.
Programme Controller: Large cam which turns under the control of a MASTER CLOCK and rings bells, such as for school lessons changes, or operates switches to carry out some other programme. Programme times can be completely changed or varied on different days of the week.
Pull Repeater: A REPEATER CLOCK with a cord from each side which is pulled to make it sound the time. Useful for nights before matches were invented.
Pulse Meter: TIMER calibrated to give pulse rate per min. by timing 30 beats.
Pump Winding: Early form of KEYLESS WINDING by 'pumping' a knob on the watch which wound the MAINSPRING through a ratchet mechanism.
Puritan Watch: Oval shaped pocket watch with rounded edges and plain case only about 2 in. long, commonly made in England in the seventeenth century.
Push Button Regulator: Modern watch with a small push button in the case to alter the regulation without opening the case. One version has a button which puts the watch to time on the TIME SIGNAL arid REGULATES it automatically at the same time. See Sympathetic Clock.
Push Piece: A press button on a watch case for operating additional mechanisms such as a CHRONOGRAPH, AUTOMATON, SPLIT SECONDS HAND, etc.