The earliest evidence of this instrument comes from Andrew Ellicott who, in 1796, used "a small zenith sector of 20 inches radius" to determine the latitude of the Erie, Pennsylvania (the former French landing at Presqu'Isle). Ellicott used this instrument again in 1796-1800 when he surveyed the southern boundary of the United States, describing it as a "zenith sector of 19
inches radius to be used when the utmost accuracy was not necessary, and where the transportation of the large one could not be effected without great expense and difficulty." 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 Institution in 1898.
Ref: Andrew Ellicott, "Observations made on the Old French Landing at Presqu'Isle, to determine the Latitude of the Town of Erie," Transactions of the American Philosophical Society 4 (1799): 231-232.
Andrew Ellicott, "Astronomical and Thermometrical Observations, made on the Boundary between the United States and his Catholic Majesty," Transactions of the American Philosophical Society 5 (1802): 204.
