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Postcard of Chronometer.
© National Museums Scotland


A marine chronometer was a portable clock, which kept extremely accurate time, and was used in finding a ship's longitude at sea, by comparing the clock's standard time (set to that at Greenwich) with the ship's local time. This example was made around 1850 in Edinburgh by Robert Bryson (1778-1852), one of the most important Scottish clock and instrument makers of the 19th century.

After the major breakthrough in horological design by John Harrison and the production of the marine chronometer, the instrument was further developed by the London makers John Arnold and Thomas Earnshaw. This example, made by Bryson, is a two-day marine chronometer with an Earnshaw-type spring detente escapement. The clock face is inscribed 'ROBT. BRYSON EDINBURGH 34', and is housed in a brass-bound mahogany box, slung in gimbals.

When this chronometer was 'rated' by the Greenock instrument makers D. McGregor, who were appointed by the Admiralty, in 1880 it was gaining five-tenths of a second per day; and by 1932 gaining four-tenths of a second per day. It is not clear when this example ceased to be used at sea.

Record details

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Online ID: 000-180-001-173-C
Image Rights Holder: National Museums Scotland
Project: 0504: National Museums Scotland Part 2
Project description | View all records in project
Ref: National Museums Scotland  T.1981.2
Date: 1840-1850
Around 1850
Material: Brass with Mahogany case.
Dimensions: 180x180x125mm(Case)
What: Chronometer
Subject: 20. Time Measurement chronometers (Departmental Classification)
Who: Robert Bryson, Edinburgh (Maker)
The Jean Bain Bequest
Where: Scotland, Edinburgh
Description: 2-day marine chronometer, signed 'Robert Bryson Edinburgh 34' with Earnshaw type spring detent escapement. Boxed c.1850
  • For improvements to the chronometer, see Jonathan Betts, 'Arnold and Earnshaw: the practicable Solution,' in W.J.H. Andrewes (ed.), The Quest for Longitude, Harvard, 1996, pp 311-28 
  • For Robert Bryson, see T.N. Clarke et al., Brass & Glass: Scientific Instrument Making Workshops in Scotland, Edinburgh, 1989, pp 112-22 
  • J.A. Bennett, The Divided Circle: a History of Instruments for Astronomy, Navigation and Surveying, Oxford, 1987, pp.184-187. 
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