probably made in London

Sextant

This type of sextant was designed by Jesse Ramsden (1735-1800), a scientific instrument maker based in London. This brass example (pictured here in its fitted wooden case) was made around 1790, probably by Ramsden.

The first sextants were produced after the reflecting circle was found too cumbersome, while the octant's range of angles was too restricted. A sextant is so-called because its scale is one-sixth of a circle. Sextants were usually constructed of brass and, after the construction of a dividing engine by Ramsden in 1775, the scales were mechanically divided. This allowed smaller arcs to be divided with great accuracy.

A number of methods of combining lightness with rigidity went into the design of the sextant frame. This is one of Ramsden's solutions: the 'bridge' type, with open brass framework at the top which both reinforced the structure and protected the optics.

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Online ID:	000-100-104-233-C
Image Rights Holder:	National Museums Scotland
Project:	0098: National Museums Scotland Project description \| View all records in project
Ref:	National Museums Scotland T.1967.85
Date:	Around 1790 c. 1790
Material:	Cast brass frame; bevelled brass limb; silver scale; brass index arm; wooden handle / mahogany wood case. Inscription: Ramsden London; 1163
Dimensions:	5.00" radius / case 2.50" H x 6.50" radius
What:	Sextant / box
Subject:
Who:	Ramsden, London (Maker)
Where:	England, London
Event:
Description:	Five-inch sextant, in a fitted keystone box, by Ramsden of London, c. 1790
References:	Bennett, J.A. The Divided Circle: A history of instruments for astronomy, navigation and surveying. Oxford: 1987, pp 136-8 For Ramsden, see Clifton, Gloria, Directory of British Scientific Instrument Makers 1550-1851. London: 1995, pp 227-8 Turner, Anthony, Early Scientific Instruments 1400-1800. London: 1987, p 228-9
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