Horizontal sun and moon pedestal dial for 51° North. The brass dial-plate is square shaped and has a rotatable hour-circle to enable it to be used as a moondial. On the rotatable disc is an hour-circle numbered clockwise with a central sunface decoration. The disc is turned by three knobs (at both ends of the VI line and at the southern XII). On the main dial-plate is a scale which represents the difference in hours between sun time and moon time. Engraved around this circle are the words 'Nosce Cupis Varios Solis Lunceque Labores' (Thou wouldest know the different toils of sun and moon). The spandrels are decorated with scrolled leaf patterns and one contains the arms of 'La Bistrate of Flanders', ennobled in 1682. On the coat of arms is, among other things, a crowned helmet and two greyhounds. 'HOROLOGIUM SELENIACUM' (moon dial] is marked in opposite corners on banners. The gnomon is triangular and plain brass.

This instrument was made for the family of La Bistrate, whose arms appear on the dial. The main dial-plate carries a scale giving the difference in hours between solar time and lunar time as well as the lunar-age scale. Thus the conversion can either be made arithmetically or mechanically. Mrs Gatty (Eden and Lloyd, 1900) mentions that a brass dial with a moveable plate for lunar hours was seen in a shop in London. It is possible that this is the same instrument.

For more information regarding this dial please refer to the OUP & NMM catalogue, 'Sundials at Greenwich'.