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Backstaff
The backstaff is made from a lignum vitae frame with boxwood arcs and a boxwood inlaid plate on the main strut, with brass rivets, and no vanes. Small decorative stars are stamped at the ends of the arcs. Three modern replacement vanes have been added.
The transversal scale on the thirty degree arc is from 0° to 25° by 5 arcminutes, and reads to 1 arcminute. The graduation on the sixty degree arc is from 0° to 65° by 1°, and on the outer edge has a scale for correcting for the Sun’s semi-diameter.
The transversal scale on the thirty degree arc is from 0° to 25° by 5 arcminutes, and reads to 1 arcminute. The graduation on the sixty degree arc is from 0° to 65° by 1°, and on the outer edge has a scale for correcting for the Sun’s semi-diameter.
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Object Details
| ID: | NAV0034 |
|---|---|
| Collection: | Astronomical and navigational instruments |
| Type: | Backstaff |
| Display location: | Not on display |
| Creator: | Unknown |
| Date made: | 1700-1750 |
| Credit: | National Maritime Museum, Greenwich, London, Caird Collection |
| Measurements: | Radius of the thirty degree arc is 609 mm and that of the sixty degree arc 192 mm. Overall length of the instrument is 635 mm. |
| Parts: | Backstaff |