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Theodolite

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probably made in London

Theodolite
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A theodolite is a surveying instrument for measuring horizontal and vertical angles. This brass example was made around 1770, probably by Jesse Ramsden, a scientific instrument maker based in London.

The theodolite's telescope is supported by two brackets above an 180 degree arc which is adjusted against the vernier scale by rack-and-pinion. This is mounted over a horizontal circle which contains a central compass, engraved 'Ramsden, London'. The whole is on a raised column above four levelling screws.

Jesse Ramsden (1735-1800) is credited by George Adams with the innovation of permanent double 'A' frames on the horizontal circle of the theodolite. This is clearly a slightly less mechanically-stable precursor to that design.

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