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Physical Sciences Collection - Surveying and Geodesy

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Theodolite - click to enlarge

Theodolite - click to enlarge

Click photos to enlarge.

Theodolite

Catalogue number:
PH*309596

Dimensions:
height 7.5 inches; horizontal circle 5.5 inches diameter; needle 2.5 inches; telescope 7.5 inches long

Discussion:

This theodolite was probably made in London in the mid-18th century. Its basic form--with the telescope mounted on the curved side of a semicircle--derives from the design that Thomas Heath introduced in 1725. The horizontal circle and vertical arc are graduated every degree and read by verniers to 10 minutes. The words "Diff: Hypo & Base" on the telescope support and the scales labeled "Feet" and "Links" on the vertical arc are used to correlate angle of elevation or depression with horizontal distances when surveying sloping ground. In addition to the telescope, there is a pair of open sight vanes. A level vial is mounted above the telescope.

This theodolite belonged to Orange Warner Ellis, a surveyor who lived in Odelltown, a village along the Richelieu River, just a few miles north of New York State. Odelltown was settled by Joseph Odell, a Loyalist from Poughkeepsie who moved from the United States to Lower Canada in 1788, in order to remain under British rule. Odelltown would later be seen as a Britannic outpost in a Francophone region of Quebec.

Ref: J. A. Bennett, The Divided Circle (Oxford, 1987), pp. 86, 146-147.

Further Information:

Theodolite

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