Gilbert Theodolite

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" signature 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
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
place made
United Kingdom: England, London
ID Number
accession number
catalog number
Measuring & Mapping
Surveying and Geodesy
See more items in
Medicine and Science: Physical Sciences
Surveying and Geodesy
Data Source
National Museum of American History, Kenneth E. Behring Center
maker referenced
Clifton, Gloria and Gerard L. E. Turner. Directory of British Scientific Instrument Makers 1550-1851
owner referenced
Hemenway, Abbey Maria. Vermont Historical Gazetteer
Additional Media

Visitor Comments

Add a comment about this object

**Please read before submitting the form**

Have a comment or question about this object to share with the community? Please use the form below. Selected comments will appear on this page and may receive a museum response (but we can't promise). Please note that we generally cannot answer questions about the history, rarity, or value of your personal artifacts.

Have a question about anything else, or would you prefer a personal response? Please visit our FAQ or contact page.

Personal information will not be shared or result in unsolicited e-mail. See our privacy policy.

Enter the characters shown in the image.