An eight-day sidereal regulator, mounted within a stone block at the southern end of the Airy transit circle by William Hardy, London, circa 1811

Catalogue description — Royal Museums Greenwich

An eight-day sidereal regulator, mounted within a stone block at the southern end of the Airy transit circle by William Hardy, London, circa 1811. This regulator is significant as it was the first of Hardy’s regulators with spring pallet escapement to be built. Prior to its commission in 1809 William Hardy submitted a longcase regulator fitted with his own spring pallet escapement for testing at the Royal Observatory. Pleased with its performance the then Astronomer Royal, Dr Nevil Maskelyne (1732-1811), recommended that the board of ordnance commission Hardy to manufacture an exceptional astronomical regulator to accompany Troughton’s ten-foot transit instrument (the mural circle) which was already being constructed. Hardy set to making the regulator with great enthusiasm sparing no expense or effort. It appears that he ordered the unfinished movement from Leyland of Prescot to whom he supplied the cutters to provide truly epi-cycloidal teeth. Hardy’s method of producing the cutters is described in Gill’s 'Machinery Improved' which was published in 1839. Today the gearing still runs very smoothly when the escapement is removed; in a fitting testament to its quality Charles Frodsham remarked in volume XXVIII of the 'Horological journal' ‘wheelwork in Hardy’s regulators is among the best in England, and the shape of the wheels and pinions makes the most perfect gearing I ever witnessed’. Dr Maskelyne died before the clock was delivered to the Royal Observatory and his successor, John Pond (1767-1836), questioned the £325 bill referring it to the Royal Society for scrutiny. Various clockmakers were consulted including the eminent retired clockmaker, Alexander Cumming, who interviewed Hardy. In the end Hardy accepted payment of £200 but as Cumming had suggested in his letter to W.H. Wollaston, dated 19 January 1812, the prestige in making such an important timekeeper led to further commissions. Two regulators of the same design were purchased in 1812 by F.R. Hassler for use in the American coastal survey. The regulator was initially used in the circle room until 1823 when it was moved to the transit room. Hardy’s escapement performed extraordinarily well in the short term. However, for the escapement to function properly good lubrication is critical and if allowed to run dry the escapement will not function consistently and the rate will become erratic. About 1830 the Astronomer Royal sent for Hardy to attend to the clock but for reasons unknown Hardy did not respond quickly and the clock was entrusted to E.J. Dent who replaced the spring pallet escapement with a deadbeat escapement and also added his own name to the clock dial. Hardy was mortified that Dent should be allowed to alter the clock in this way and complained to the Royal Society. In 1850 the regulator was removed from its case and housed within the stone block at the southern end of Airy’s transit pit; four years on Dent installed the electrical contacts connecting the movement to his galvanic chronograph. The jewelled dead beat escapement has deliberately large drops; the electrical impulses are given during the moment of drop so as to reduce any chance of the contacts interfering with the rate of the pendulum. The movement is now in the same form as it was when it was used by the Sir George Biddell Airy. The Hardy transit clock continued to be used for observations until the observatory was relocated in Herstmonceux in 1957. The movement has exceptionally thick (7mm) arched brass plates are united by five heavy pillars riveted to the backplate and secured by domed blued steel screws with shouldered brass washers. The finely constructed six-wheel train is driven by brass cased weight with integral pulley and triple pulley system to compensate for the short drop of the pendulum chamber. The double line runs on a turned barrel with a sprung C-shaped stop iron mounted to the front flange with a chamfered push piece lying across the nineteenth turn. The barrel is also fitted with Harrison’s maintaining power, a great wheel and a second wheel driving the large hour wheel. All wheels have six straight crossings and are of light construction. The dead-beat escapement with jewelled brass pallets is mounted on the backplate; a sixty-tooth contact wheel with one blank division is mounted to escape wheel arbor between the frontplate and the dial with corresponding view aperture cut into the dial plate. The half-second and minute galvanic impulses were recorded on a drum chronograph to meter the astronomer’s observations recorded by a hand-held push button. The seconds beating zinc tube type temperature compensated pendulum has a knurled and graduated rating nut and is suspended from a Troughton frame mounted to the cast iron seatboard. The twelve inch circular painted dial is signed “Willm. Hardy Inv. et Fecit, New Dead-Beat escapement by Dent”. The outer minute track having arabic five-minute markers enclosing a seconds subsidiary dial with observatory marks and shuttered viewing aperture for the electrical contacts over a twenty four-hour subsidiary. Both subsidiary dials have painted steel counterpoised hands alongside a tapering minute hand.