Sextant (detail)

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This is a detail of a brass sextant made around 1790, probably by Jesse Ramsden, a scientific instrument maker based in London.

The detail shows the signature on the sextant. It reads 'Ramsden London'. Jesse Ramsden was the instrument maker who devised a method of mechanically division of scales by building a successful dividing engine in 1775. The sextant is also numbered, in the centre of the scale, no. 1163. Ramsden's business made more than 1400 sextants.

Ramsden's dividing engine reduced the time required to graduate a sextant scale, and reduced costs. Mechanisation meant greater precision than that allowed by the human hand. Greater precision meant better measurements, and a more accurate scientific method.

Record details

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• Online ID: 000-190-002-058-C
• Image Rights Holder: National Museums Scotland
• Project: National Museums Scotland
  Project description   View all records in project
• Ref: National Museums Scotland  T.1967.85
• Date: Around 1790
  c. 1790
  
• Material: Cast brass frame; bevelled brass limb; silver scale; brass index arm; wooden handle / mahogany wood case. Inscription: Ramsden London; 1163
  Sextant / box
  
• Dimensions: 5.00" radius / case 2.50" H x 6.50" radius
  
• What: Sextant / box
  
• Subject:
• Who: Ramsden, London (Maker)
  
• Where: England, London
  
• Event:
• Description: Five-inch sextant, in a fitted keystone box, by Ramsden of London, c. 1790
  
• References:
  • Bennett, J.A. The Divided Circle: A history of instruments for astronomy, navigation and surveying. Oxford: 1987, p 136-8 
  • For Ramsden, see Clifton, Gloria, Directory of British Scientific Instrument Makers 1550-1851. London: 1995, pp 227-8 
  • Turner, Anthony, Early Scientific Instruments 1400-1800. London: 1987, p 228-9 
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