An astronomical longcase regulator by Dent of London, number 587, featuring G.B. Airy’s ‘Remontoir Dead-beat’ escapement, circa 1842

Catalogue description — Royal Museums Greenwich

This clock was originally intended for the observatory in Pulkova, near St. Petersburg, the movement fitted with the dead-beat remontoir at Airy’s suggestion in order to over come the problems associated with running a clock in extremes of temperature. Dent wrote the Russian astronomer, Professor F.G.W. Struve (1793-1864), to inform him that this and other clocks were to be shipped aboard the ‘Jupiter’ steamer on 2 October 2 1842 but owing to a problem with the maintaining power, Dent 587 would not be included in the shipment. It appears that this clock was never sent to the observatory at Pulkova and instead remained at the Dent premises until it was sold at auction in 1977. Item 31 in Edward John Dent’s listing for the Great Exhibition of 1851 reads: ‘A superior astronomical clock, with a remontoire dead-beat escapement, invented by G. B. Airy, Esq., Astronomer Royal (see paper in "Royal Astronomical Society's Monthly Notices," Nov. 11, 1842, by Mr. Airy.)’ and the clock can be seen in a contemporary engraving produced for the Illustrated Exhibitor. The four-wheel movement is enclosed by substantial rectangular brass plates, which have a curled and lacquered finish. The wheels have six straight crossings and are driven by a cylindrical brass cased weight, which is suspended on a barrel cut with 16 turns. The barrel carries the great wheel, Harrison’s maintaining power and stopwork. The escapement is mounted on the back plate and features two co-axially mounted wheels, which are connected by a helical remontoire spring. The innermost wheel is fixed to the escape arbor and is fed through a pair of locking pallets. The second wheel is the true escape wheel which is runs freely on jewelled bearings around the escape arbor and interacts with a pair of dead-beat pallets. The two pairs of pallets are mounted to the same arbor and each has fine adjustment via hand screws. There are also two detents that can be used to lock the escape wheel to adjust the set up of the remontoir without handling the wheels. The movement is screwed to ornate and substantial gilt brass scroll brackets and has a 12 inch circular silvered dial with integral sight ring. The dial is laid out in typical regulator fashion and is inscribed ‘DENT, LONDON, Clockmaker to the Queen’ and bears the number, 587, within the 24 hour subsidiary dial. The sight ring is further inscribed ‘The Escapement Invented by G.B. Airy Esq. Astronomer Royal’. The mercury type temperature compensated pendulum is visible through the glazed front and sides of the beautifully carved mahogany case. The pendulum swings in front of a silvered scale, used for regulation of the clock by means of a sliding weight on the pendulum rod. A silvered scale with mercury thermometer is mounted to the panelled back board.