Marine chronometer numbered 987, by Robert Molyneux. A two-day full-plate fusee movement. Four pillars, all fixed with blued steel screws. The fusee, with stop-work and Harrison's maintaining power, has a pipe round the winding square. Earnshaw-type spring-detent escapement. Compensation balance with helical balance spring. The movement is rated to sidereal (star) time.

Mounted in three-tier box (glass missing), with push-catch for lid and lock for upper half. On the front of the upper half is let in an ivory rectangular tablet with no surviving inscription. The box fittings are standard, with surface-mounted handles on the sides, brass gimbals and a winding key. The push-catch is surrounded by a shaped brass insert, while the similar feature round the lock is missing. The top of the lid has a plain brass shield-shaped insert. The underside of the lid has a pasted paper label inscribed in handwriting: 'Loses 3s on sid. time / Gains 233s on mean t. / per diem about" and there is a screwed-on cardboard buffer strip along the hinged edge. The inside of the upper half has a pasted paper label inscribed in handwriting: 'gain or loss of 4m +- 2n s per diem / = do of 1s in (6m -+ 3n s) / Ex. S. Chronr gains 236s on M. T. Clock in 24 hours: / Equivalent to 1s in 6m 6s". The box is lined inside with red paper.

Silvered brass 24-hour dial with Arabic hour numerals from 0 to 24 and Arabic minute numerals every five minutes, with dots marking each minute, also having a large seconds dial having Arabic five-second figures. The dial is inscribed in the centre 'Robt Molyneux / 44 Devonshire Street / Queen's Square / 987'. The chronometer is in good condition.

This chronometer was used by the famous astronomer, John Herschel, at the Cape of Good Hope. In 1834, Herschel moved with his family to Feldhausen near Cape Town in South Africa on a four-year project to plot star clusters in the largely uncharted southern celestial hemisphere. He used this chronometer to time the passage of stars over his 20-foot Reflector.