PAIR-CASE. The standard form of case for English watches from 1650 to 1800 and beyond. Also widely used on the continent during the earlier years. The inner case, which houses the movement, is generally without decoration unless the watch is a repeater, alarum, or a striking watch when it is pierced and sometimes given minor decoration. The outer case normally is decorated; repousse, engraved, enamelled, or hollowed agate or some other hard stone, or decorated in some other way according to the fashion of the period. Sometimes the outer is left plain, particularly at the end of the period.

PALLET. In particular, the part or parts through which the escape wheel teeth give impulse to the balance. In the club-tooth lever escapement a tooth locks on the outer edge of the pallet after impulse has been given by the preceding tooth. In general, the pallets are jewels and termed 'pallet stones'.

'PARACHUTE'. A device invented by Breguet in which the endstones of the balance staff are supported in short arms of spring steel: hence 'sprung jewels', which give a cushioning effect to the staff pivots should the watch be dropped. It is the earliest form of shock-resisting device. Also suspension élastique.

PASSING CRESCENT. See CRESCENT.

PASSING SPRING. Also known as the 'gold spring', out of which metal it is usually made. It is mounted on a detent in the chronometer escapement. The discharging pallet on the staff unlocks a tooth in one direction. On the return swing it passes the detent without disturbance due to the flexibility of the passing spring.

PEDOMETER WATCH. Sometimes understood to mean a watch and pedometer combined. Ralph Gout took out patent No 2351 for such a watch in 1799.

PEDOMETER-WIND. See PERPETUAL WATCH.

PENDANT. A neck, fitted to the case of a watch, to which the bow (q.v.) is fitted. In a keyless watch, the winding button is at the top of the pendant, the winding button stem passing through the pendant.

PENDULUM WATCH (DIAL). A watch in which a 'mock' or 'false' pendulum (q.v.) appears through an aperture in the dial or is visible through a slot cut in the balance cock or bridge. See also FALSE PENDULUM.

PERPETUAL CALENDAR. A calendar watch which takes into account not only the short months, but leap years, without manual adjustment.

PERPETUAL WATCH. The English translation of the French 'montre perpetuelle' is the name given to a watch which is wound by the oscillation of a pivoted weight during the movements of the wearer. Also called a pedometer-winding watch. Its invention by A. L. Perrelet in about 1770 is generally now accepted. Breguet made a number of such watches. Recordon took out patent No. 1249 for a pedometer-winding watch in 1780.

PILLARS. The pillars of a watch movement are the 'distance pieces' which serve to keep the two plates in their relative positions. The earliest were of plain square section. Later, spiral or round baluster forms were introduced. After about 1600, types became diverse: vase-shape, pyramidical (so-called Egyptian), tulip-form, pierced foliate, lyre-shaped, square section baluster, and finally cylindrical.

PILLARPLATE. The plate, nearest the dial, to which the pillars are fixed. The pillars are merely pinned to the top plate - i.e. that furthest from the dial.

PINION. A small toothed wheel. The 'teeth' are spoken of as 'leaves'. In watch work the wheel is the driver and the pinion is the follower, except in the motion work.

PINCHBECK. An alloy of zinc and copper - named after its inventor, Christopher Pinchbeck, about 1730 - which resembles gold in colour. The term is used rather indiscriminately for gilded brass.

PIN WORK. See PIQUÉ.

PIQUÉ. Or 'pin work'. Pins of gold, silver or brass, the purpose of which is to secure the leather, shagreen or tortoise-shell covering to the outer cases of watches. The practical purpose also served decorative ends in that the heads of the pins were arranged in a decorative pattern, Indeed, more pins were inserted than was strictly necessary in order to form a decoration.

PIROUETTE. A balance staff with integral pinion, thereby causing the balance to swing through a large arc.

PIVOT. The extremity of a rotating arbor on which it is supported.

PIVOTED DETENT. The pivoted detent performs the same function as the blade spring. See SPRING DETENT. John Arnold used this form of detent on his early chronometers. It was favoured more on the continent than in this country.

PLATES. The flat discs between which the wheels and pinions are pivoted. They form the foundation of the movement.

POISE. A balance is in poise if it has no heavy point; if its equilibrium is unaffected by change of position.

P0KER HAND. A minute hand somewhat resembling a poker in form. Usually associated with the beetle hour hand (q.v.).

POSITIONAL ERROR. Changes in the rate of a watch arising from the different positions - i.e. the horizontal and the vertical.

POTENCE. Also spelled 'potance'. A hang-down bracket supporting a pivot; in particular (in watch-work) the underslung bracket supporting the lower pivot of the balance staff in full plate watches. In the early balance spring verge, the verge was pivoted between the balance cock and an extended piece (to give a bearing) of a bracket extending between the movement plates. Later, as a flatter watch became the fashion, this bracket (the potence) was reduced in length and the crown wheel reduced in size. A second extended block on the potence - rather less than mid-way between the top plate and the bearing for the lower pivot of the verge - gave thebearing for the inner pivot of the crown wheel arbor, the other pivot being carried in a second block with an endpiece mounted on the underside and at the edge of the top or potence plate. Julien Le Roy introduced an improvement to make this second block or bearing for the crown escape wheel adjustable as well as the bearing for the inner pivot, i.e. an adjustable potence which enabled the action of the escapement to be adjusted without dismantling the movement. The use of a screwdriver or key will move the inner pivot, and thus the crown wheel across the verge to bring it into beat. The adjustable steel endpiece on the outer pivot enables the depth of the engagement to be varied, and thus the arc of escapement (see Pl. 125).

POTENCE PLATE. An alternative name for the top plate to which the potence is fixed.

POUZAIT ESCAPEMENT. J. M. Pouzait, 1743 - 93, introduced a form of lever escapement in 1786 which has been named after him. It was perhaps the first lever escapement with divided lift (q.v.). The thirty escape wheel teeth stand up from the plane of the wheel. The steel pallets are rather claw-like in appearance and the notch imparts impulse to the balance acting upon a steel impulse pin located on the balance staff. The balance diameter is almost that of the movement plate and the escapement beats seconds. An upright pin on one arm of the lever, acting on the outside of a safety ring on the balance staff in one direction, passes through an opening in the ring in the other direction, then being within the safety ring; this provides the safety action.

PULL-WIND. See PUMP-WIND.

PUMP-WIND. An early form of keyless winding. The watch is wound by moving a shaft, located in the pendant, in and out: a pushing or pulling action. Edward Massey, Viner and Burdess are associated with forms of pump-winding.

PULSE-PIECE. A pin projecting from the edge of a repeating movement and through to a hole in the bottom edge of the case. The finger, held against the pin, receives the blows of the hammer when the watch is striking instead of the bell. Also called a 'deaf-piece' or by the French name 'sourdine'.

PURITAN WATCH. A simple form of English watch, oval in shape, without decoration and usually in silver. They were made between about 1625 and 1650.