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Colby's Horizon Instrument
The sextant has a black-lacquered circular brass plate, with the upper segment cut away, and a wooden handle. A spring-loaded pin locks when the observation is made. Attached to the sextant is a fixed bracket with a 53mm sight-tube at both ends, and a spirit level centred between the two. The object end of the sight-tube has cross wires and two shades in red and green.
The horizontal line of reference is established by an arc-shaped pendulum, pivoted at the centre of the instrument, and hanging freely during the sighting. The pendulum is then locked by a trigger mechanism before the sextant is read.
The instrument has a brass scale to 105° on either side of 0° by 1 arcminute, measuring to 92°. The sextant has two verniers, one for altitude measuring to 1 arcminute, with zero at the centre, the other for zenith distance measuring to 1 arcminute, with zero at the right.
The sextant is contained in a square fitted wooden box.
Hall Colby of New York patented ‘Colby’s altimeter or self-adjusting quadrant or sextant’ (no. 1200 of 1854 and no. 1736 of 1855) and in the USA (no. 100,119 of 1870).
The horizontal line of reference is established by an arc-shaped pendulum, pivoted at the centre of the instrument, and hanging freely during the sighting. The pendulum is then locked by a trigger mechanism before the sextant is read.
The instrument has a brass scale to 105° on either side of 0° by 1 arcminute, measuring to 92°. The sextant has two verniers, one for altitude measuring to 1 arcminute, with zero at the centre, the other for zenith distance measuring to 1 arcminute, with zero at the right.
The sextant is contained in a square fitted wooden box.
Hall Colby of New York patented ‘Colby’s altimeter or self-adjusting quadrant or sextant’ (no. 1200 of 1854 and no. 1736 of 1855) and in the USA (no. 100,119 of 1870).
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Object Details
| ID: | NAV1128 |
|---|---|
| Collection: | Astronomical and navigational instruments |
| Type: | Sextant with artificial horizon |
| Display location: | Not on display |
| Creator: | Colby, Hall; Unknown |
| Date made: | circa 1870 or later |
| Credit: | National Maritime Museum, Greenwich, London, Adams Collection |
| Measurements: | Overall: 108 x 203 x 235 mm; Radius: 89 mm |
| Parts: | Colby's Horizon Instrument |
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