Equinoctial dial

Universal equinoctial dial for latitudes 0°-90° North. The base consists of a brass ring supported by four feet and quartered by brass struts at its outer end. Engraved on the front of the base is the maker’s signature, ‘JOHANN MICHAEL UOGLER IN ELLINGEN FECIT’. The compass is mounted on the outer end of one of the struts and its cardinal points are marked in German. The magnetic variation is marked by a scratched line at 12° West of North

The latitude arc is attached to the centre of the base. Two turned pillars stand at the East and West points of the base and pivoted between these is a circle marked with 16 points of the compass (also in German). This circle is screwed to a perpendicular semicircular support which holds the semicircular hour plate. The hours are marked VI-XII, I-VI and a scale for the equation of time is displayed graphically as a figure of eight in the centre. Outside this is a zodiacal scale marked by symbols. Across the North-South diameter of the wind ring is a brass wire carrying a bead at its centre. The shadow of the bead at midday gives the declination and the equation of time. An inscription along the North side of the hour-plate reads, ‘A new horological invention from the tables of Lord Johann, philosopher of Wurtzelbau indicates the equation of time during the course of the day on the meridian of Nuremberg, latitude 49°’.

This equinoctial dial is unusual in having a wide hour-plate rather than the thin ring more usually found on such dials. This allows the mean time to be displayed at midday by the shadow cast by the bead, which acts as the gnomon. The figure of eight of the analemma on the hour-plate causes the dial to display the position of the sun in the ecliptic at midday. It is possibly the earliest known example of a sundial carrying the analemma and so displaying a mean time at midday. That the analemma was then a recent creation is certified by the use of the phrase ‘a new horological invention’ on the hour-plate.

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

Object Details

ID: AST0368
Collection: Astronomical and navigational instruments
Type: Equinoctial dial
Display location: Display - ROG
Creator: Vogler, Johann Michael
Date made: early 18th century
Credit: National Maritime Museum, Greenwich, London, Caird Collection
Measurements: Diameter: 176 mm; Maximum height: 180 mm

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