Astronomical and navigational instruments, Celestial navigation

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octant with artificial horizon

NAV1296
Astronomical and navigational instruments

Object connections:

Collection Astronomical and navigational instruments, Celestial navigation
User collections Longitude punk'd by hfinch-boyer
Gallery locationNot on display

Object details:

Object ID NAV1296
Description This unusual sextant incorporates an early attempt to solve the problem of taking a sight when the horizon is not clearly visible. The sextant has an anodized brass frame in two sections joined at the apex with the limb at the top (rather than the bottom, as was more common) and an octagonal wooden handle at the bottom. It has a horizon glass, sight vane, spirit level, vernier and a static shade. The limb and the index glass are on the movable part of the frame. The sextant has one red index shade and no horizon shades. Index- and horizon-glass adjustment is made by screws. The sight vane has one pinhole. The artificial horizon consists of a brass tube containing a spirit level. It is based on the principle of the double reflected image of the celestial body being alongside the reflection of the level. The instrument is held limb uppermost by the handle, similar to a hand mirror. The instrument has a brass scale from -5° to 115° by 15 arcminutes, measuring to 115°. The sextant has a brass vernier measuring to 15 arcseconds, with zero at the left.
Date made circa 1780

Artist/Maker Unknown
Place made England
Credit National Maritime Museum, Greenwich, London, Caird Collection
Materials glass; wood; brass
Measurements Overall: 60 mm x 380 mm x 190 mm
Parts
  • octant with artificial horizon (NAV1296)
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