Astronomical and navigational instruments, Celestial navigation

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Hoppe's Improved Sextant

NAV1235
Astronomical and navigational instruments

Object connections:

Collection Astronomical and navigational instruments, Celestial navigation
ExhibitionsShips, Clocks & Stars: The Quest for Longitude
User collections The Board of Longitude by Richard_Dunn
Gallery locationNot on display
PeopleProvenance: Gardener, Vivien (Jnr. D
Provenance: Gardener, Vivien (Snr)
Provenance: Monks

Object details:

Object ID NAV1235
Description The sextant has a polished brass diamond-pattern frame with two polished limbs, two index arms, and a wooden handle. The tangent screws and clamping screws are positioned on the back of both index arms. The sextant has four 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 worm screw operated by a capstan screw. The swivelling arm of the lower magnifier is broken, the magnifier is missing and the upper magnifier is on a 45mm swivelling arm. Attached to the sextant is a threaded telescope bracket with perpendicular adjustment made by a rising-piece and a milled knob. The telescope is 162 mm in length with an inverted image. A second telescope is 92 mm with an erect image. The sight-tube is 86 mm with a red shaded eyepiece, an adjusting pin and a screwdriver. The sextant is contained in a wooden keystone box. The lower inlaid silver scale is from -2° to 144° by 15 arcminutes, measuring to 125°; the upper inlaid silver scale is from 143° to 0° to 137° by 20 arcminute, measuring to 102° and 116°. Lower vernier to 15 arcminutes, zero at the right; upper vernier to 10 arcminutes, and zero at the centre. Hoppe’s improvement consists of an index glass that can be rotated by a short index arm that moves over the second scale mounted on top of the frame. By this the theoretical range of the instrument is increased to 265 degrees, but in practice probably not over 160 degrees.
Date made circa 1805

Artist/Maker Hinde, John
Place made London, England
Credit National Maritime Museum, Greenwich, London
Materials mahogany handle, lignum vitae; metal: silver:; metal: brass
Measurements Overall: 120 x 360 x 340 mm; Radius of the lower arc: 222 mm; Radius of the upper arc: 76 mm
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