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Theodolite

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Peter Jefferson, active for many years as a county surveyor, almost certainly gave his older son some instruction in surveying. For a few months Thomas Jefferson filled the position of Albemarle County surveyor once occupied by his father, apparently carrying out his duties entirely through deputies. When he resigned in 1774, he did not let his surveying skills decay. He used them for the rest of his life to map his lands and measure his landscape.


Dozens of Jeffersonís plats survive of his lands in both Albemarle and Bedford counties. In 1793, with theodolite and Gunterís chain, he revised the boundaries of his fields at Monticello to fit his crop-rotation schemes. In 1806 he surveyed a new entrance road from the Rivanna River to the house. He also enjoyed passing on the secrets of surveying to apt young men; at age sixty-six he was running lines on the rugged slopes of Monticello, while instructing a grandson.


In 1778 Jefferson purchased from mathematician Robert Andrews perhaps the most sophisticated surveying instrument then available, a telescopic theodolite made by Jesse Ramsden.1 In one of several tributes to this celebrated instrument maker, Jefferson wrote that "the measure of angles, by the wonderful perfection to which the graduation of instruments has been brought by a Bird, a Ramsden, a Troughton removes nearly all distrust from that operation."2


Since this "most excellent" instrument could be used for measuring both horizontal and vertical angles and was equipped with telescopes, Jefferson employed his theodolite for far more than land surveying.3 In the months after he bought it, he made observations on the variation of the needle, fixed the true meridian of Monticello, calculated the position of features of the Monticello landscape and surrounding mountains, and may have used it in his observation of the solar eclipse in June 1778. In 1815, in one of his most elaborate trigonometric exercises, he used the theodolite to determine the elevation of the Peaks of Otter in the Blue Ridge Mountains.



Artist/MakerJesse Ramsden
Created1735-1800
Origin/PurchaseLondon, England
Object TypeScientific Instruments
MaterialsBrass, copper; case: mahogany
Dimensions14 x 7 3/4 x 6 3/4 in.
LocationCabinet

Footnotes

  1. 12 January 1778James A. Bear, Jr., Jefferson's Memorandum Books.
  2. Thomas Jefferson to Alden Partridge, 2 January 1816, American Memory Project - The Thomas Jefferson Papers.
  3. Thomas Jefferson to David Rittenhouse, 19 July 1778, Julian Boyd, The Papers of Thomas Jefferson, 2:202.

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