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made in England

Postcard of Octant.
© National Museums Scotland


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.

Record details

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Online ID: 000-100-104-273-C
Image Rights Holder: National Museums Scotland
Project: 0098: National Museums Scotland
Project description | View all records in project
Ref: National Museums Scotland  T.1981.21
Date: Around 1750
c. 1750
Material: Mahogany, boxwood. Inscription: G T ABS 1796
Who: G.T. Abs (Inscribed on the object)
Description: Mahogany and boxwood 18" radius octant, inscribed 'G.E. Abs, 1796', English, c. 1750
  • Bennett, J.A. The Divided Circle: A history of instruments for astronomy, navigation and surveying. Oxford: 1987, pp 132-4 
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