The octant has an ebony frame and limb with a brass index arm, fittings, a wooden handle, and an inlaid ivory plate on the crossbar. The tangent screw and clamping screw are located on the back of the index arm. The octant has four socket shades, three red and one green, and three horizon shades, two red and one green. Index-glass adjustment is made by a screw and on the horizon glass by a square-headed screw, a detached key, a lever, worm gear and a milled clamping screw. Attached to the octant is a magnifier on an 85mm swivelling arm, as well as a threaded telescope bracket without adjustment. The telescope is 82 mm in length and has an erect image. The sight-tube is 82 mm in length and has a red shaded eyepiece, a milled adjusting key, and a magnifying glass, which is missing. The octant is contained in a polished mahogany box, containing a Henry Hughes and Son Ltd certificate of examination, dated 1937.

The instrument has an inlaid ivory scale from 0° to 109° by 20 arcminutes, measuring to 90°. The octant has an ivory vernier measuring to 1 arcminute, with zero at the right.

Object Details

ID: NAV1335
Collection: Astronomical and navigational instruments
Type: Octant
Display location: Not on display
Creator: Stebbing, Joseph
Date made: circa 1850
Exhibition: Ships, Clocks & Stars: The Quest for Longitude
People: Molony, Edward
Credit: National Maritime Museum, Greenwich, London
Measurements: Overall: 110 mm x 300 mm x 250 mm
Parts: Octant

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