Materials: brass, steel, glass; case: wood (probably pine), paper
Dimensions: L: 39.4 (15 1 /2 in.); H: 5.1 (2 in.); 17.8 (7 in.) with sights; dial: D; 15.2 (6 in.); Depth: 2 (3/4 in.); case: 29.4 x 17.1 x 6.7 (15 1/2 x 6 3/4 x 2 5/8 in.)
Location: Monticello's Visitor Center
Provenance: John Hartwell Cocke; by descent to John Page Elliott; by gift and purchase to the Thomas Jefferson Foundation in 1992
Accession Number: 1992-4-3
Historical Notes: Although no references to the English instrument maker John Bleuler appear in Jefferson's records, this instrument may have been his, as John Hartwell Cocke purchased other surveying equipment from Jefferson's estate in 1827.
Jefferson almost certainly owned and used a plain surveying compass (in England it was known as a circumferentor). It would have been his major surveying tool before he acquired his Ramsden theodolite in 1778. He later expanded his surveying equipment by purchasing more portable circumferentors-called graphometers in England. While in London in 1786 he bought "a pocket graphometer by Cole," and in 1805 he asked Thomas Freeman, leader of the Red River exploring expedition, to buy him "an accurate compass for surveying, with two pair of sights moving concentrically, an outer graduated circle with a Nonius to take angles accurately without regard to the needle, with its ball and socket and staff." He reflected the still-present confusion in terminology when he added that he believed "they are called Circumferentors, but is not certain." He added it to his instrument list as "a common Theodolite or Graphometer," eight inches in diameter and costing $54.37.
↑ John Hartwell Cocke to T.J. Randolph and N.P. Trist, January 20, 1827, Nicholas P. Trist Papers, Library of Congress.
↑ Jefferson, March 27, 1786, in MB, 1:616 and December 12, 1805, in ibid., 2:1170; Jefferson to Thomas Freeman, November 16, 1805. Thomas Jefferson Papers, Library of Congress. Polygraph copy available online.