This compass was made by Benjamin Rittenhouse working in partnership with his nephew, Benjamin Evans, in Worcester Township, Pennsylvania, around 1798-1801. It has a variation arc on the south arm that extends 15 degrees either way; the "folded" vernier is moved by rack and pinion and reads to 5 minutes. John Johnson (1771-1841), the Surveyor-General of Vermont, used this compass in 1817-1820 while surveying of the boundary between Maine and
Canada. His notes refer to it as "a Circumferentor of 2.5 inches Radius made at Philadelphia by Rittenhouse and Evans and graduated to every 5 Minutes by the help of a nonius."
Ref: "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
Johnson's report on the Maine-Canada boundary survey, in University of Vermont Library.
