Ellicott Transit and Equal Altitude Instrument

Andrew Ellicott (1754-1820) was the leading geodetic surveyor in the United States in the early years of the Republic, and he aimed to produce surveys that compared favorably with those done by the best Europeans in the field. In his words, the transit and equal altitude instrument was "the most perfect, and best calculated for running straight lines." Moreover, "when the different verifications are carefully attended to, [it] may safely be considered as absolutely perfect."
Ellicott made this instrument, and used it to run the western boundary of New York in 1789, the boundaries of the District of Columbia in the early 1790s, the southern boundary of the United States in 1796-1800, and the boundary between Georgia and North Carolina in 1811. Ellicott took this instrument with him to West Point, when he became professor of mathematics at the U.S. Military Academy in 1813. A descendant, Andrew Ellicott Douglass, deposited it with the Smithsonian in 1898.
This instrument, marked "Andw Ellicott Philadelphia," is modeled on the transit and equal altitude instrument that had been made by John Bird in London, purchased by Thomas Penn in 1763, and used by Mason and Dixon for their survey of the boundary between the colonies of Maryland and Pennsylvania. Ellicott had used this English instrument in 1784, when he was part of the team of American surveyors who extended the Mason-Dixon line to the western edge of Pennsylvania.
Ref: Andrew Ellicott, "A Letter to Robert Patterson," Transactions of the American Philosophical Society 4 (1799): 32-51.
Andrew Ellicott, "An Account of the Apparatus used on the Boundary between the United States and His Catholic Majesty," Transactions of the American Philosophical Society 5 (1802): 204-208.
Silvio Bedini, "Andrew Ellicott, Surveyor of the Wilderness," Surveying and Mapping (June 1976): 113-135.
Currently not on view
Object Name
transit and equal altitude instrument
Ellicott, Andrew
overall: 18 1/4 in; 46.355 cm
axis: 16 in; 40.64 cm
place made
United States: Pennsylvania, Philadelphia
ID Number
catalog number
accession 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
Credit Line
Andrew Ellicott Douglass
American Philosophical Society. Transactions of the American Philosophical Society
American Philosophical Society. Transactions of the American Philosophical Society
American Congress on Surveying and Mapping. Surveying and Mapping
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