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Backstaff
The backstaff consists of an ivory frame and arcs, with brass rivets; an ivory sight vane, horizon vane and shadow vane. The sight vane and shadow vane slide in grooves cut in the outer edge of the arcs instead of being clamped against the arcs by the usual brass pressure plates. Floral decorations are found on all parts of the instrument’s frame. A decorative mermaid and merman flank the signature in French.
The transversal scale on the thirty degree arc is from 0° to 30° by 10 arcminutes, and reads to 1 arcminute along the fiducial edge of the sight vane. The graduation on the sixty degree arc is from 0° to 60° by 1°.
Probably not meant for use on board a ship. Part of a presentation set including a cross-staff (NAV0505), two Gunter’s scales (NAV0108 and NAV0107) and a sector (NAV0166) all fitted in a lyre case. The inscription may point towards an original French owner. The shadow vane is a modern replacement.
The transversal scale on the thirty degree arc is from 0° to 30° by 10 arcminutes, and reads to 1 arcminute along the fiducial edge of the sight vane. The graduation on the sixty degree arc is from 0° to 60° by 1°.
Probably not meant for use on board a ship. Part of a presentation set including a cross-staff (NAV0505), two Gunter’s scales (NAV0108 and NAV0107) and a sector (NAV0166) all fitted in a lyre case. The inscription may point towards an original French owner. The shadow vane is a modern replacement.
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Object Details
| ID: | NAV0040 |
|---|---|
| Collection: | Astronomical and navigational instruments |
| Type: | Backstaff |
| Display location: | Display - Tudor and Stuart Seafarers Gallery |
| Creator: | Tuttell, Thomas |
| Date made: | circa 1700 |
| Credit: | National Maritime Museum, Greenwich, London, Caird Collection |
| Measurements: | Radius of the thirty degree arc is 686 mm and that of the sixty degree arc 229 mm. Overall length of the instrument is 689 mm. |
| Parts: | Backstaff |