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Theodolite

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Theodolite
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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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