made in Paris

Reflecting circle (detail), known as Borda circle

The reflecting circle was used to measure angles necessary for finding longitude, and originally devised in the 1750s by the German astronomer Tobias Mayer (1723-62). A number of improvements to the instrument were published by the Chevalier de Borda (1733-1799) and gave it its alternative name, 'Borda circle.' This is a detail of a brass and silver example made around 1810 in the Parisian workshop of scientific instrument maker Francois-Antoine Jecker.

This Borda-type circle is divided on its scale, with sighting, direction and index arm verniers reading to 1 minute of arc. It lacks its shades. The inscription across one of the spars reads 'No 41 Jecker a Paris'.

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Online ID:	000-180-001-177-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
Date:	Around 1810
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References:	Daumas, M., Scientific Instruments of the 17th and 18th Centuries and their Makers. London: 1972, pp 203, 279-80, 320-1, 336 For the 'Borda circle', see A.J. Turner, From Pleasure and Profit to Science and Security: Etienne Lenoir and the Transformation of Precision Instrument-Making in France 1760-1830, Cambridge, 1989, pp 51-60 See article 'Circle', ch. 1 'On the Reflecting Circle', in the Edinburgh Encyclopaedia, edited by David Brewster, Edinburgh, 1830, vol VI, pp 486-92
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