The sextant has a polished brass frame and limb, with a four-legged brass section on the back for the belt pole mounting. The detachable belt pole is made of brass and wood. The tangent screw and clamping screw, which are modern replacements, are fitted to the limb on a separate shoe, to the left of the index arm. It also has three red socket shades. Index-glass adjustment is made by a screw and on the horizon glass by a lever moved by a milled worm screw, and a milled clamping screw. The sight-tube is a modern replacement. The sextant has no box.

The instrument has a polished brass scale from -13° (marked 77) to 128° by 20 arcminutes, measuring to 122°. The sextant has a brass vernier measuring to 1 arcminute, with zero at the centre.

Object Details

ID: NAV1177
Collection: Astronomical and navigational instruments
Type: Sextant
Display location: Not on display
Creator: Bird, John
Date made: 1757; circa 1758
Exhibition: Time and Longitude; Ships, Clocks & Stars: The Quest for Longitude
Credit: National Maritime Museum, Greenwich, London
Measurements: Overall: 130 x 800 x 560 mm; Radius: 464 mm

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