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Octant

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made in England

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 in England around 1750. It is unsigned.

The octant has diagonal scales and is fitted for taking backsights (angles of more than 90 degrees) as well as fore-sights (angles up to 90 degrees). There is an ivory plate inscribed 'G.E. ABS., [the initials of a later owner] 1796'.

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. This example has a second pinhole sight and second horizon glass, allowing measurements greater than 90 degrees.

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