Mahogany and brass octant.

Octant made by John Gilbert, London, 1764

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Octant made by John Gilbert, London, 1764
Science Museum Group
© The Board of Trustees of the Science Museum

Octant made by John Gilbert, London, 1764. Mahogany frame, limb, and index arm; the lower end of the arm is of brass, brass fittings, a brass stop for the index arm; an inlaid ivory plate in the crossbar. Signed on the inlaid plate: Made by In.o Gilbert on Tower Hill | LONDON | For Iere.h Beale, Feb.ry 27: 1764. Inlaid ivory scale from -5° to 95° every 20', measuring to 90°. Ivory vernier to 1', zero at the centre. There is no tangent screw; the clamping screw is on the back of the index arm (its brass pressure plate is broken). Three socket shades (two red, one green), from another instrument. Index-glass (broken and separated from the instrument) adjustment by screw; adjustment of the horizon glass by a fixed milled screw and a lever, worm gear and a milled clamping screw. The sight vane has one pinhole. No box.

Details

Category:
Navigation
Object Number:
1981-846
Materials:
ivory, brass (copper, zinc alloy) and mahogany (wood)
type:
octant
credit:
Wellcome Trust