Theodolite

A theodolite is a surveying instrument for measuring horizontal and vertical angles by the way it is mounted on a special levelling head at the top of a tripod (now missing). This brass example was made around 1750, probably by John Yeaman, a scientific instrument maker based in Edinburgh.

This simple theodolite has two fixed sights and two moveable sights on a bar called an alidade. In the centre of the instrument is a compass with a silvered dial, marked around its edge in degrees. The compass has eight cardinal points. The instrument is signed inside the graduated degree scale around its brass edge 'J. Yeaman Edinr'.

John Yeaman (?1716-c.1780) was apparently a clock and watchmaker recorded between 1734 and 1749 outside Edinburgh's city wall in the Burgh of Canongate, where he described himself from 1745 as a 'mathematical instrument maker'. John Miller (1746-1815), subsequently one of Scotland's most important instrument makers of his generation, was probably apprenticed to Yeaman at some point. Both businesses were renowned for the quality of the surveying instruments.

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