Sounding sextant

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A sounding sextant is essentially an ordinary nautical sextant but adapted to measure horizontal angles, and usually with a wide field telescope. It is used in hydrographic surveys to fix the boat's position relative to shore stations. This example was made around 1800, probably by Thomas Jones (1775-1852), a scientific instrument maker based in London's Charing Cross.

The sextant is used horizontally, although it works on the same principles as an ordinary nautical sextant. Its optical components take a more extended field of view and it is built upon more robust principles. This sextant has an Admiralty mark 'HO 62', and is inscribed on the ivory scale 'THOMAS JONES/ [62...Charing Cross]'. It lacks the microscope over the vernier.

Thomas Jones held the instruments made for the Hydrographic Office from early 1826, but in February 1828 these were returned to that department and marked with various letters. Unfortunately, it has not been possible to identify which instruments went on particular voyages of discovery.

Record details

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• Online ID: 000-180-001-168-C
• Image Rights Holder: National Museums Scotland
• Project: National Museums Scotland Part 2
  Project description   View all records in project
• Ref: National Museums Scotland  T.1910.91
• Date: Around 1800
  c. 1800
  
• Material: Inscription: HO 2 [Admiralty mark]
  Specimen / nautical instrument / sextant, marine / box
  
• Dimensions:
• What: Specimen / nautical instrument / sextant, marine / box
  
• Subject:
• Who: Admiralty (Owner)
  Jones, London (Instrument maker)
  
• Where: England, London
  
• Event:
• Description: One of a group of nautical, astronomical and drawing instruments - a marine sextant, telescope for reading vernier missing, Admiralty mark "HO 2", in a box, made by Jones, London, c. 1800
  
• References:
  • For marine surveying, see J.A. Bennett, The Divided Circle: a History of Instruments for Astronomy, Navigation and Surveying, Oxford, 1987, pp 206-7 
  • For the marking of instruments for the Hydrographic Office, see Stimson, A.N., 'Some Board of Longitude Instruments in the Nineteenth Century' in De Clercq, P.R., Nineteenth Century Scientific Instruments and their Makers, Amsterdam and Leiden, 1985, App 
  • Stanley, W. F., Surveying and Levelling Instruments, London & New York: 1901 
• Translations:
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