Octant

An octant is a navigational instrument used for measuring angles necessary for determining a ship's position at sea. This ebony example was made in England in 1755. It is unsigned.

The octant has backsights (for measuring angles of more than 90 degrees) and diagonal scales. There is an ivory plate inscribed with the date, 1755, and the owner's name, 'George Harris'. The name has been obliterated, probably when the octant changed hands.

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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