Dipleidoscope dial for latitudes 0°-90° North. It has a square base of oxidised brass set on three small feet. Set on to the base are two bubble levels and the compass. The compass has a white metal inside, a raised degree scale and its cardinal and quadrantal points named in English initials. At the South end of the instrument, two pillars support a horizontal rod with a screw end to allow an adjustment for latitude. The latitude scale is mounted on the West pillar. At the South end of the unit is an engraved white metal hour scale. A brass marker attached to the axis indicates the time. The dial has an optical unit consisting of a squat cylinder, in the upper face of which is a blue glass aperture, behind which are set two mirrors. On a hinged arm on the West side of the unit is a brass telescope viewing tube, which is free to rotate.
Unlike AST0183 and AST0243, this dipleidoscope can be used in all northern latitudes. It also has a telescope for more accurate observation of the conjunction of the solar images. The number '1357' is stamped on the base of the instrument and is probably its serial number. 'E.I. DENT LONDON PATENTEE' is engraved on the hour-scale. A similar instrument is in the Whipple Museum (accession no. Wh: 0472); it is marked with the serial number '1660'. An instrument in the MHS, Oxford (new inventory no. 33826) carries the number '1592' scratched on its base.
For more information regarding this dial please refer to the OUP & NMM catalogue, 'Sundials at Greenwich'.
Credit: National Maritime Museum, Greenwich, London