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Plain Surveying Compass

Plain Surveying Compass View Interactive Version ]

Although no references to the English 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 1827.1

Jefferson almost certainly owned and used a plain surveyor's compass—in England it was known as 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 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 $54.2


Artist/MakerJohn Bleuler
Created1791-1829
Origin/PurchaseEngland
Object TypeScientific Instruments
Materialsbrass, steel, glass
Dimensions15 1/2 x 2 in.
LocationCabinet

Footnotes

  1. John Hartwell Cocke to Thomas Jefferson Randolph and N. P. Trist, 20 January 1827, Nicholas P. Trist Papers.
  2. 27 March 1786 and 12 December 1805, James A. Bear, Jr., Jefferson's Memorandum Books; Thomas Jefferson to Thomas Freeman, 16 November 1805, The Thomas Jefferson Papers, Library of Congress; list of "Mathematical Apparatus", Bedini, 501.

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