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This instrument 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. 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, 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 was later seen as a Britannic outpost in a Francophone region of Quebec.
Ref: J. A. Bennett, The Divided Circle (Oxford, 1987), pp. 86, 146-147.
Currently not on view
place made
United Kingdom: England, London
overall: 7 1/2 in; 19.05 cm
horizontal circle: 5 1/2 in; 13.97 cm
needle: 2 1/2 in; 6.35 cm
telescope: 7 1/2 in; 19.05 cm
overall: 8 1/8 in x 7 1/4 in x 5 7/8 in; 20.6375 cm x 18.415 cm x 14.9225 cm
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Medicine and Science: Physical Sciences
Measuring & Mapping
Surveying and Geodesy
Data Source
National Museum of American History