probably made in Paris

Reflecting circle, probably made by Etienne Lenoir

Reflecting circles were used to measure angles necessary for finding longitude. This 'Borda' type brass reflecting circle (pictured here in its wooden box) was made around 1800, probably by Etienne Lenoir (1744-1832), a scientific instrument maker based in Paris.

The telescope, horizon glass and shades are all on one arm, with a separately pivoted index arm with mirror. A series of observations are made, and the mean value found from them. By using the mirror, the time taken to gain a correct reading is less than with a conventional repeating circle.

The repeating circle was 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 of 'reflecting circle'. This form of the instrument was always more popular with European navies than with the Royal Navy.

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Online ID:	000-180-000-899-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.1939.1
Date:	Around 1820
Material:	Brass circle / wooden box. Inscription: No. 229
Dimensions:	11.00" / 6.00" / 12.50" x 12.50" x 3.50"
What:	Reflecting circle / telescope / box / accessory
Subject:	9. NAVIGATION (Departmental Classification) 22. PHYSICS, Light (Departmental Classification)
Who:	Borda (Eponym) Lenoir, Paris (Instrument maker)
Where:	EUROPE: France, Paris
Event:
Description:	Borda reflecting circle, No. 229, by Lenoir, Paris, with brass circle, 6 inch telescope and removable handle, in a wooden box containing a variety of accessories
References:	Daumas, M., Scientific Instruments of the 17th and 18th Centuries and their Makers. London: 1972, pp 129, 183-7, 318-9 Edinburgh Encyclopedia 1830 Vol VI pp 484-92 Turner, A. J. From Pleasure and Profit to Science and Security: Etienne Lenoir and the transformation of precision instrument-making in France 1760-1830. Cambridge: 1989, pp 30, 51-60
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