Product images of Mechanical equinoctial dial
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Mechanical equinoctial dial
Mechanical equinoctial dial for latitudes 0-90 North. The dial has a circular base with three turned feet. Set into the centre of the base is a silvered compass. On the base-plate, there is a circular bubble level and the equation of time is marked. The main part of the dial has a thick ring set in the plane of the meridian. This consists of two rings, the inner one to be adjusted for latitude. Pivoted within this ring is a further ring carrying a shaped alidade. It comprises two lenses and a circle whose centre is marked and on which the light falls after passing through the lenses. On the axis of the declination ring, and within the ring itself, is an hour dial, which does not move with the ring but remains fixed. The action of turning the declination ring until the sun's rays fall through the two lenses of the alidade on to the centre of the bottom circle causes the hands on the hour dial to turn and indicate the correct time.
- Image reference: D7733
- National Maritime Museum, Greenwich, London, Gabb Collection