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An 18th-century ebony, brass and ivory octant
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An 18th-century ebony, brass and ivory octant

BY BENJAMIN MARTIN WITH IVORY SCALE BY JESSE RAMSDEN, 1771-1782

已結束2008年4月23日

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GBP 5,000

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An 18th-century ebony, brass and ivory octant
by Benjamin Martin with ivory scale by Jesse Ramsden, 1771-1782
18¼in. (46.5cm.) radius index arm signed MARTIN Inv.t et fecit Londini, with double pin-hole sight and slide shades, back sight, mirrors with screw attachment, three interchangeable filters, inset ivory plaque on 'T' bar, the inlaid ivory scale graduated 2°-0°-99° divided every 20', the framed vernier scale providing measurements to the minute of arc, the scale engraved with I R either side of an anchor, reverse with inset ivory plaque and three brass bun feet; in later case with 6 engraver's tools (key missing).
19¾in. (50cm.) long in box

專家說明

A FINE OCTANT BY MARTIN WITH A SCALE BY RAMSDEN. Jesse Ramsden (1735-1800), who used the anchor trade mark, invented a machine for accurate scale division in 1771, which won him an award of £300 from the Commissioners of Longitude in 1777, and 'became one of the key inventions of the industrial revolution' (ODNB). Benjamin Martin (bap. 1704/1705-1782) would have paid Ramsden to make this scale, and his death in 1782 dates this instrument -- which unites two of the leading British instrument-makers of the 18th century -- to 1771-1782.