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Sextant

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probably made in London

Sextant
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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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