History of Science Museum: Collection Database Search


Raising the equator

Early English equinoctial dials have a feature which forces the semi-circular support of the chapter ring to be raised at right angles to the main body of the dial. This support needs to be vertical so that the latitude quadrant which sets the inclination of the chapter ring operates correctly.

The device is visible in inv. 54727. The semi-circular support has two hinge parts which project beyond the main body of the instrument when it is closed. When the lid is opened it engages with these two projections and lifts the support up the vertical. Slots are cut in the edge of the lid to accommodate the projections properly.

However, both inv. 36259 (Elias Allen) and 44225 (Charles Whitwell) have been altered or have had the support replaced at some point in their history. Both have the slots to accommodate the projections, but the hinge projections are not there. This makes it very difficult to use the instrument as intended.

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