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Jefferson's interest in a machine for measuring force went hand in hand with his development of the moldboard plow. Early in 1809, he received a spring-operated dynamometer from France, the invention of Edme Regnier (1751-1825). It was stolen when Jefferson's goods were shipped from Washington to Virginia in March of that year. Some time after April 1810, he was able to borrow a dynamometer from Robert Fulton and to measure mathematically the force necessary to pull a plow fitted with his own "mathematically perfect" moldboard. Not only the plow was tested, as Edmund Bacon states: "He had a machine for measuring strength. There were very few men that I have seen try it that were as strong in the arms as his son-in-law, Colonel Thomas Mann Randolph; but Mr. Jefferson was stronger than he."[1]

Thomas Jefferson and Robert Fulton

Primary Source References[2]

1796 May 20. (William Strickland to Jefferson). "I have enquired after and seen the machine for ascertaining the resistance of Plows; and am told it answers with the purpose intended; the plan is extremely simple, consequently the price, which is five guineas is too great...It is invented and sold by Winlaw..."[3]

1808 May 1. (Jefferson to David Baillie Warden). "I read in the Memoirs du societe d'Agriculture de la Seine (but in what part of them I have this moment made a fruitless search to find) some experiments on the resistance, of ploughs by a machine which measured the degree of resistance, of ploughs & consequently the comparative force necessary to draw them."[4]

1808 October 14. (Thomas Mann Randolph to Jefferson). "I have received the French Dynamometer, it is a light & beautiful contrivance depending on a spring, & a good deal in the way of the powder eprouvette which I showed you..."[5]

1809 December 31. (Jefferson to Joel Barlow). "I therefore imported their dynamometer in order to prove mine with Guillaume's. I am now engaged in this work, but have lost my dynamometer. I think you have one. could you do me the favor to lend it to me for this experiment..."[6]

1810 January 24. (Jefferson to Joel Barlow). "...I am disconsolate on learning my mistake as to your having a dynamometer. my object being to bring a plough to be made here to the same standard of comparison by which Guillaume's has been proved..."[7]

1810 April 10. (Jefferson to James Madison). "...I have at the same time recieved [sic] an offer from mr Fulton to lend me his dynamometer, mine having been lost...I have certainly never seen a plough do better work or move so easily, still the instrument alone can ascertain it's merit mathematically..."[8]


  1. Bear, Jefferson at Monticello, 71.
  2. Please note that this list should not be considered comprehensive.
  3. PTJ, 29:105.
  4. Library of Congress.
  5. Massachusetts Historical Society.
  6. PTJ:RS, 2:111.
  7. Ibid., 2:176.
  8. Ibid., 2:333-334.


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