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Backstaff
The backstaff is made from a mahogany frame with boxwood arcs, brass rivets, and no vanes. There is an inlaid boxwood plate in the main strut and decorative fleurs-de-lis (stamped) are found at the ends of the arcs.
The transversal scale on the thirty degree arc is from 0° to 25° by 10 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 10 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: | NAV0032 |
|---|---|
| Collection: | Astronomical and navigational instruments |
| Type: | Backstaff |
| Display location: | Not on display |
| Creator: | Gilbert, John; National Maritime Museum |
| Date made: | circa 1740 |
| Credit: | National Maritime Museum, Greenwich, London |
| Measurements: | Radius of the thirty degree arc is 601 mm and that of the sixty degree arc 191 mm. Overall length of the instrument is 635 mm. |
| Parts: | Backstaff |