Late Georgian Treen Domed Sundial & Compass

English-made. Original domed glass, with treen domed, hinged top. Early 19th Century. Magnetic dial for 51 degree latitude. In the lid of the box is a table of corrections for the equation of time. Circa 1865.

Featured in the Royal Greenwich Museums.

Magnetic dial for latitude 51° North. It has a paper dial card with an outer circle of 32 compass points; North indicated by a fleur-de-lys. The hour ring is divided clockwise with a sunface at the South point, and a simple brass gnomon is set on the dial-plate. A glass plate is set over all and is held in place by the metal of the case. A magnetic bar attached to the underside of the card orientates the dial correctly and it is set for a magnetic variation of 19° West of North. The dial has a round wooden case with a domed top, brass hinge and hook fastener.

In the lid of the box is a table of corrections for the equation of time. Printed in the centre of the table is the legend 'FAST MEANS THAT THE CLOCK SHOULD BE FASTER THAN THE DIAL. SLOW, SLOWER.'. While the dial-plate/ compass card is similar to other magnetic dials, the highly domed case and the inclusion of the equation of time are unusual, as the small dial-plate hinders the reading of adjustments to mean time. Dial was set for a permanent magnetic variation, therefore while still in functioning order, the readings are slightly askew due to change in Earth's magnetic field.