Gilt full plate movement with four baluster square-based pillars from the top plate, the bottom-plate pinned and signed Tho. Mudge 1777, with a screwed dust exclusion pipe for the winding square, fine pierced and foliate engraved balance bridge, additionally decorated with a griffin and scallop shells, the recessed dial plate screwed to the top-plate, slot-aligned in the outer case and held by two screws.
The reverse 7-turn chain fusee, with Harrison’s maintaining power, the fixed barrel with ratchet set up, over-hung outer piece for chain and rotation, fine polished wheels with 6 arm crossings, great wheel with 100 teeth, centre wheel with 120 teeth and 20 leaves on the pinion, third wheel with 120 teeth and 16 leaves on the pinion, the contrate wheel with 120 teeth and 15 leaves on the pinion, also with a wheel for the seconds of 45 teeth driving a reversing wheel of the same count, escape wheel with a pinion of 12 leaves and 15 escape wheel teeth.
The constant force escapement, 15 tooth escape wheel with no lift, polished steel arbors and pivots, hard stone pallets shaped for lift and locking, both pallets with constant force blued spiral springs, all running in jewels with endstones, held in adjustable potance.
The polished brass flat rim balance with fine three arm crossing and counterpoise weight, cranked balance staff with pins for impulse, two matched blued steel spiral balance springs, the balance pivots run between roller wheels to minimize friction which are held by pillared plates, diamond endstone for the balance bridge and ruby endstone for the balance potance.
The separate temperature compensation mechanism is mounted on the back plate comprising two straight bi-metallic springs acting on a lever, which is pivoted and at the other end has two curb pins that act on the outer end of the bottom balance spring, the other end is formed into a long cranked tail protruding from under the balance guard (visible above the signature), fine adjustments are made by the sliding movement of the bi-metallic springs through adjustment screws mounted either side of the balance guard.
Regulation is by curb pins acting on the top balance spring, the adjustment is through a square mounted on the balance bridge with a sliding brass assembly held in tension by a swan neck spring and indexed on a semicircular plate and indicated by a blued steel pointer.
Thought to have been lost at sea, but by 1950, the horologist Charles Allix had discovered that it had survived and was with a European collector;
Christie’s Geneva, 8 November 1976, lot 240;
The Time Museum, Rockford, Illinois, USA, inventory no.1303;
Sotheby’s, Masterpieces from the Time Museum, 13 October 2004, lot 672, sold for £1,240,000;
John C Taylor collection, inventory no.132
Mudge & von Brühl, A reply to the answer of the Rev. Dr. Maskelyne, astronomer royal, to a narrative of facts, relating to some time-keepers constructed by Mr. Thomas Mudge, for the discovery of the longitude at sea, 1791;
Thomas Mudge Jr, A Description with Plates of the Timekeeper Invented by the Late Thomas Mudge, London, 1799 (reprinted London 1977);
Gould, The Marine Chronometer, Its History and Development. London, 1923, reprinted 1989, p.107-125;
Pioneers of Precision Timekeeping, 1965, Good, ‘The Mudge Marine Timekeeper,’ (Monograph No.3), p.75-91;
Rees, Clocks, Watches and Chronometers, Extracts.London, reprinted 1970;
Antiquarian Horology, Spring 1978, Hutchinson,‘Some Observations on the Timekeepers of Thomas Mudge’, p.715-719;
Chamberlain, It’s About Time, 1978, p.337-339;
Antiquarian Horology, 1981, Daniels, ‘Thomas Mudge: The Complete Horologist,’ p.150-173;
Britten, Old Clocks, Watches and Their Makers, Ninth Edition, 1982, p.128a-b, 192-193;
Randall & Good, Catalogue of Watches in the British Museum, VI Pocket Chronometers, Marine Chronometers, and other Portable Precision Timekeepers, 1990, p.181-185;
Randall, The Time Museum Catalogue of Chronometers, 1992, front cover illus. & exhibit no.118;
The Time Museum Brochure, reprinted from Invention & Technology, 1992, Garver, ‘Keeping Time’,p.11;
Quest for Longitude, edited by Andrewes, 1993, Penney, ‘Thomas Mudge and the Longitude: A Reason to Excel’, p.294-308, pl.18;
Horological Journal, January 2006, Randall, ‘Thomas Mudge and the Swiss contribution to his inventions’, Lecture synopsis, p.16-17;
Dunn & Higgit, Ships, Clocks, and Stars, the Quest for Longitude, 2014, p.162 illus. p.164-166;
Betts, Marine Chronometers at Greenwich, 2018, p.48 & 228