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Sounding sextant

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probably made in London

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.

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