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Octant

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probably made in London

Octant
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An octant is a navigational instrument used for measuring angles necessary for determining a ship's position at sea. This wooden example was made around 1760, probably by John Urings, a ship-chandler based in London's Fenchurch Street between 1735 and 1771.

The 16-inch radius mahogany-frame octant has a foresight and backsight with brass fitments. There is an ivory plate stamped 'I. URINGS. Fecit. LONDON.' The inset boxwood scale is divided to 20 minutes, and by transversals to 2 minutes of arc.

An octant is so-called because the scale is one-eighth of a circle, although it can measure 90 degrees using the mirror on the top of the radial arm.

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