Theodolite

A theodolite is a surveying instrument for measuring horizontal and vertical angles. This brass example was made around 1750, and retailed by London optician Benjamin Martin (1704/5-1782).

This instrument consists of a compass, with two spirit levels, and has both fixed and movable sighting vanes on a graduated circle. It could be used if attached to a ball-and-socket levelling head and tripod (neither shown here), to take readings in both vertical and horizontal planes.

Martin was a much respected designer of scientific instruments and had a shop at the sign of 'Hadley's Quadrant and Visual Glasses' in Fleet Street in London. He was also a prolific writer and gave lectures on Natural Philosophy illustrated with his instruments.

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Online ID:	000-100-044-570-C
Image Rights Holder:	National Museums Scotland
Project:	0098: National Museums Scotland Project description \| View all records in project
Ref:	National Museums Scotland T.1971.87
Date:	Around 1750
Material:
Dimensions:
What:	Circumferentor / compass
Subject:	5. CARTOGRAPHY, Surveying (Departmental Classification)
Who:	B. Martin, London (Maker)
Where:	England, London
Event:
Description:	Circumferentor and compass by B. Martin of London
References:	For an explanation of the evolution of the theodolite, see Bennett, J.A. The Divided Circle: A history of instruments for astronomy, navigation and surveying. Oxford: 1987. pp 145-9 Millburn, John R., Benjamin Martin author, instrument-maker, and country showman. Leyden: 1976, pp 224-5 Millburn, John R., Retailer of the sciences: Benjamin Martin's scientific instrument catalogues, 1756-1782. London: 1986, p 24
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