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 example was made in 1744, probably by Edward Nairne (1726-1806), a scientific instrument maker based in London.

The octant has an ebony frame with an inlaid ivory scale. The scale is divided to 20 minutes of arc and read by the vernier on the end of the brass radial arm to one minute. There is an ivory plate inscribed 'Thomas Hellyer [the owner] 1774/ NAIRNE LONDON'.

An octant is so-called because the scale is one-eighth of a circle. Although this example has the brass arm, it does not yet have a tangent screw as a standard fitting.

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• Online ID: 000-100-104-189-C
• Image Rights Holder: National Museums Scotland
• Project: National Museums Scotland
  Project description   View all records in project
• Ref: National Museums Scotland  T.1909.9
• Date: 1774
  
• Material:
• Dimensions:
• What:
• Subject: 9. NAVIGATION (Departmental Classification)
  
• Who: Nairne, London (Maker)
  
• Where: England, London
  
• Event:
• Description: Octant made by Nairne, London, dated 1774
  
• References:
  • Bennett, J.A. The Divided Circle: A history of instruments for astronomy, navigation and surveying. Oxford: 1987, pp 132-4 
  • For Nairne, see Clifton, Gloria, Directory of British Scientific Instrument Makers 1550-1851. London: 1995, p 196 
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