Satinwood cased eight-day bracket timepiece with gravity escapement and centre-seconds

Description — British Museum

Bracket timepiece; eight-day; gravity escapement; round silvered-metal dial with centre-seconds; satinwood case with moulded arched hood; glazed panels to front and sides surmounted by brass flaming vase finials. Train-count: Gt wheel 180 2nd wheel 144/12 3rd wheel 144/12 4th wheel 60/12 Escape wheel 10/10 Motion work. 2nd whl pinion 24 driving Min whl pinion 48 driven Minute wheel 120 Minute pinion 32 Hour wheel 80 Canon pinion 25.

Curator's comments — British Museum

Text from 'Clocks', by David Thompson, London, 2004, p. 126. William Nicholson Table regulator London, 1797 Height 57 cm, width 30.75 cm, depth 17.3 cm The first gravity escapement was invented by Alexander Cumming (1732-1814) in 1774. This revolutionary escapement for precision regulators is based on the principle of using weighted arms which always fall through the same distance to impulse the pendulum. Consequently, every impulse given is equal in magnitude, giving a more constant rate of oscillation. Cumming's escapement was followed very shortly by Thomas Mudge's, and then a number of other important makers, amongst them William Harvey, introduced their own versions. The advantage of these escapements is that the impulse to the pendulum is constant and not affected by the variations in power from the driving force. Little is known of William Nicholson who was born in 1753 and lived and worked in London until his death in 1815. This clock, signed on the dial 'Wm Nicholson f. 1797', is a unique piece with Nicholson's own form of gravity escapement invented in 1784. Interestingly, however, he may have involved the clock and watchmaker William Hardy in its production because Hardy's name and address are scratched on the back of the dial 'Harday Copice Row' (Hardy's address was 28 Coppice Row, Clerkenwell). The spring-driven movement has Harrison's form of maintaining power to keep the clock going during winding. The clock is unusual in appearance in that the movement is mounted on a massive steel block to provide stability and the pendulum is not suspended from the back of the movement. Instead, two substantial gilded supports rise up from the base and meet at the top to provide a suspensions point for the pendulum. At the top of the supports is Nicholson's unusual form of temperature compensation: a bimetallic block which, as temperature changes, alters its shape to raise or lower the top suspension block and in so doing changes the effective length of the pendulum suspension spring. Another unusual feature is the coiled wire spring which is placed around the pendulum bob to secure it when the clock is being moved. The elegant satinwood-veneered case has glazed panels at the top, sides and front which reveal the movement from all sides. The case stands on four turned feet and is surmounted by a large urn and flame finial with acanthus decoration. The clock is an interesting example of a rather unassuming case which in reality conceals a movement of a most unusual and interesting design. Ilbert Collection.