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Inventory no. 38992 - Former Display Label

English PLANISPHERE and QUADRANT
1659

Brass. Signed, 'Henricus Sutton Londini fecit', and dated '1659'.

On the front is a time-telling instrument based on the projection of the heavens invented by Juan de Roias.

The Geminus type of sundial, of which this instrument is a variety, was based on this projection. The scales at the sides served to convert planetary (i.e. unequal) hours found by using the planisphere into ordinary (i.e. equal) hours.

On the back are an alidade and a form of sinical quadrant for finding the azimuth of the sun at its rising or setting. One object of determining these azimuths was to find, by bisecting the angle between them, true North.

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