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This theodolite belonged to John Johnson (1771-1841), the surveyor general of Vermont. Its basic form-with the telescope mounted on the open side of a semicircle-derives from the design that Jonathan Sisson introduced in London in 1737. The horizontal circle and vertical arc are graduated every degree and read by vernier to 10 minutes. The vertical arc has a second scale marked "LINKS of CHAINS" that correlates angle of elevation with horizontal distances, to be used when surveying sloping ground. The level vial on the compass face seems to be original with the instrument; the vial outside the compass may be a later addition.
The "J. Gilbert Tower Hill LONDON" inscription refers to either the John Gilbert who worked in London in the years 1719-1750, or his son of the same name who worked in London in the years 1751-1791.
Ref: Gloria Clifton,Directory of British Scientific Instrument Makers 1550-1851 (London, 1995), p. 112.
"John Johnson" in Abby M. Hemenway, ed., The Vermont Historical Gazeteer (Burlington, Vt., 1868), vol. 1, pp. 596-599.
"John Johnson" in National Cyclopaedia of American History, vol. 17, pp. 290-291.
Currently not on view
Object Name
Gilbert, John
Gilbert, John
place made
United Kingdom: England, London
horizontal circle: 10 in; 25.4 cm
overall: 8 1/2 in; 21.59 cm
needle: 3 1/4 in; 8.255 cm
telescope: 12 1/2 in; 31.75 cm
hanging level: 4 in; 10.16 cm
overall in case: 11 3/8 in x 15 5/8 in x 11 3/4 in; 28.8925 cm x 39.6875 cm x 29.845 cm
ID Number
accession number
catalog number
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Medicine and Science: Physical Sciences
Measuring & Mapping
Surveying and Geodesy
Data Source
National Museum of American History
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