Thomas 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 Edmé Régnier (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, Col. Thomas Mann Randolph; but Mr. Jefferson was stronger than he."[1]

Thomas Jefferson and Robert Fulton

Primary Source References

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 well 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 ...."[2]

1808 May 1. (Jefferson to David Bailie Warden). "I read in the Memoires du societé 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, & consequently the comparative force necessary to draw them."[3]

1808 October 11. (Jefferson to Thomas Mann Randolph). "I have recieved 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 shewed you."[4]

1809 December 31. (Jefferson to Joel Barlow). "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 ...."[5]

1810 January 24. (Jefferson to 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 ...."[6]

1810 April 16. (Jefferson to James Madison). "... I have at the same time recieved 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."[7]


  1. ^ Hamilton W. Pierson, Jefferson at Monticello: The Private Life of Thomas Jefferson (New York: Charles Scribner, 1862), 70. See also Bear, Jefferson at Monticello, 71.
  2. ^ PTJ, 29:105. Transcription available at Founders Online.
  3. ^ Thomas Jefferson Papers, Library of Congress. Transcription available at Founders Online.
  4. ^ Thomas Jefferson Papers, Library of Congress. Transcription available at Founders Online.
  5. ^ PTJ:RS, 2:111. Transcription available at Founders Online.
  6. ^ PTJ:RS, 2:176. Transcription available at Founders Online.
  7. ^ PTJ:RS, 2:333-34. Transcription available at Founders Online.