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Print shows Thomas Jefferson, full-length portrait, facing slightly right, standing beside a table; he is lifting from the table the Declaration of Independence with his right hand and pointing to it with his left hand; there is a bust of Benjamin Franklin on the table, as well as several books. On a small table to the right is a single-disc electrostatic generator and beneath that, resting on the floor, is a globe.
Portrait of Thomas Jefferson with Declaration of Independence and scientific instruments. Engraving by Cornelius Tiebout, after a painting by Rembrandt Peale, ca. 1801. Prints and Photographs Division, Library of Congress.

Counting the Miles: Thomas Jefferson’s Quest for an Odometer

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Today’s post is guest authored by Julie Miller, historian of early America in the Library’s Manuscript Division. Julie has written for Inside Adams before- see her post on “The President and the Parsnip: Thomas Jefferson’s Vegetable Market Chart (1801-1808).”

Thomas Jefferson included this drawing of an odometer mounted on a carriage wheel in his letter to Benjamin Vaughan, July 23, 1788. Thomas Jefferson Papers, Manuscript Division, Library of Congress. Detail from page 6.
Thomas Jefferson included this drawing of an odometer mounted on a carriage wheel in his letter to Benjamin Vaughan, July 23, 1788. Thomas Jefferson Papers, Manuscript Division, Library of Congress. Detail from page 6.

Thomas Jefferson, who liked to count and measure everything, coveted an odometer. While in Paris as the United States minister to France, he learned that he could buy one in London, and asked American artist John Trumbull, who was there, to investigate for him. Early in 1788 he wrote Trumbull: “Enquire if a triangular odometer is to be bought in London, and at what price.” (Memorandum for John Trumbull [February, 1788] ). Trumbull replied, warning Jefferson that odometers were custom-made to fit the “exact diameter of the wheel to which they are to be applied,” and they were expensive (Trumbull to Jefferson, February 26, 1788). “I find the Odometer too dear,” Jefferson, disappointed, replied, “and therefore will not order one” (Jefferson to Trumbull, May 18, 1788).

Jefferson must have changed his mind about giving up, since that summer he asked another friend, British diplomat Benjamin Vaughan, to look again, (Jefferson to Vaughan, July 23, 1788). Vaughan confirmed what Trumbull had already told him (Vaughan to Jefferson, August 2, 1788), and Jefferson returned to the United States the following year without an odometer.

Finally, in September, 1791, while he was living in Philadelphia as Secretary of State, Jefferson bought a pendulum odometer from a Scottish-born Philadelphia clockmaker Robert Leslie. Jefferson learned about Leslie’s work with pendulums as he worked on the “Report on Weights and Measures” that he submitted to Congress on July 4, 1790. In the report he suggested using a vibrating rod, or rod pendulum, as a reliable way to determine a standard unit of measure. Jefferson credited Leslie, who he called “the most ingenious workman in America” for this idea (Jefferson to William Short, September 1, 1791).

Robert Leslie's advertisement in the Federal Gazette and Philadelphia Evening Post, February 26, 1790.
Robert Leslie’s advertisement in the Federal Gazette and Philadelphia Evening Post, February 26, 1790.

Today an odometer is the instrument in a car that records the distance driven. In the eighteenth century odometers were mounted on the wheels of horse-drawn carriages, and the pendulum odometer, the type Jefferson bought from Leslie, was commonly used. The pendulum odometer’s triangular shape allowed it to be mounted between the spokes of a carriage wheel, where it counted each of the wheel’s revolutions. To calculate the distance a carriage had traveled, the driver multiplied the wheel’s circumference by the number of its revolutions. In his July 23, 1788 letter to Benjamin Vaughan, Jefferson explained that the odometer’s pendulum “always keeps its vertical position while the wheel is turning round and round,” and he included a drawing to show what he meant. To represent the carriage wheel in motion, Jefferson drew several odometers, each attached to a different spoke of the wheel, each with its pendulum dangling downward.

On September 2, 1791, the same day Jefferson paid Leslie ten dollars for the odometer, he and his friend and fellow Virginian James Madison, then a congressman, set off on a trip home with the odometer strapped to the wheel of Jefferson’s phaeton (a type of carriage). On the way they stopped at Georgetown to meet with the commissioners who were planning what would soon be the District of Columbia, next Jefferson dropped Madison off at Montpelier, and finally he reached his home, Monticello, near Charlottesville. As he often did, Jefferson made an itinerary of the trip, in which he recorded his observations of the road and the places where he ate and slept, and, using his new odometer, distances. (The 1791 itinerary is in one of Jefferson’s memorandum books at the New York Public Library. It is published in: Bear and Stanton, Jefferson’s Memorandum Books, II:832-835.)

Robert Leslie may have been ingenious, but his odometer was not perfect. Jefferson had to have it mended on the road on September 3, the day after he and Madison left Philadelphia, and then it failed again on September 12, just before he got home. Once at home he discovered a larger mistake, one that he had made himself, the same one that John Trumbull had warned him about in 1788. Jefferson had calculated that 360 revolutions of the phaeton’s wheel constituted one mile. The distances he recorded as he and Madison traveled from Philadelphia to Virginia, he wrote, “were on the belief that the wheel of the Phaeton made exactly 360 revolns. [revolutions] in a mile, but on measuring it accurately at the end of the journey its circumference was 14 f.[feet] 10 ½ I. [inches] and consequently made 354.95 revolns. in a mile.” Jefferson had mismeasured his wheel: when he measured it again he found that it was a little bigger than he had thought, and as a result he had miscalculated the number of revolutions it made per mile, and, therefore, the distance he had traveled.

After traveling to Washington from Monticello in September, 1807 with Clarke’s odometer strapped to his carriage wheel, Jefferson realized that the wheel was too large to get a correct reading. See his calculations on lower left. Itinerary, Monticello to Washington DC, with Distances, September 30, 1807, Thomas Jefferson Papers, Manuscript Division, Library of Congress. Transcription is at: Founders Online, Early Access at

In the years to come Jefferson remained interested in odometers, buying at least one more, and working on ways to improve their design. In 1807, when he was president of the United States, he learned that Virginia inventor James Clarke had designed and made an odometer, and asked Clarke if he could borrow and copy it (Jefferson to Clarke, May 22, 1807). Clarke, evidently thrilled at such a request from the president, gave Jefferson one of his odometers. Jefferson was happy with this odometer, which he used for many years. He liked the bell that rang after every mile. (Jefferson to Clarke, September 5, 1820). He also liked the way the odometer divided the miles into units of ten, because it justified his enthusiasm for the decimal system, which he had advocated in his 1790 “Report on Weights and Measures.” When he wrote his autobiography years later he was still hoping the United States would adopt a decimal system, and used Clarke’s odometer as an example of its merits: “I use, when I travel, an Odometer of Clarke’s invention which divides the mile into cents [hundredths], and I find every one comprehend[s] a distance readily when stated to them in miles & cents; so they would in feet and cents, pounds & cents, &c.” (Jefferson, Autobiography, Fragment, 1821).

But even Clarke’s odometer was not perfect; once again, the problem had to do with getting a carriage wheel of the correct size to fit it. On September 30, 1807 Jefferson recorded a trip from Monticello to Washington using Clarke’s odometer. The odometer, he wrote, “is made for a wheel of 16 f [eet] circumference,” but his phaeton had a wheel that measured 16 feet and 5/8 inches. As in 1791, the carriage wheel was too big for the odometer (Itinerary, Monticello to Washington, September 30, 1807).

Today we celebrate Thomas Jefferson as a scientist and inventor, but we forget the patience and effort he expended on projects over many years. We forget that Jefferson didn’t work alone, but in collaboration with others, such as Robert Leslie and James Clarke, who combined science with invention and practical mechanics. All of them knew that these endeavors, like many others, are about planning, testing, trying, failing, fixing, trying a different way, failing again, and then, maybe, succeeding – and having a good time along the way.

Learn More About It

Primary Sources, Manuscript:

The documents linked to above (with a few exceptions) are in the Thomas Jefferson Papers in the Manuscript Division of the Library of Congress.

You can find transcriptions for most of them on Founders Online, National Archives.

Primary Sources, Published:

James A. Bear, Jr and Lucia C. Stanton, eds. Jefferson’s Memorandum Books. 2 Vols. Princeton, NJ: Princeton University Press,1997.

Thomas Jefferson. Report of the Secretary of State, on the Subject of Establishing a Uniformity in the Weights, Measures, and Coins of the United States. New York: F. Childs and J. Swaine, 1790. The text of this report is online at the Avalon Project: Documents in Law, History, and Diplomacy, Yale Law School.

Secondary Sources:

Silvio A. Bedini. Jefferson and Science. Charlottesville, VA: Thomas Jefferson Foundation, 2002.

Silvio A. Bedini. “Thomas Jefferson, Clock Designer.” Proceedings of the American Philosophical Society 108 (June 22, 1964): 163-180. Documents Jefferson’s collaborations with Robert Leslie.

“Odometer,” in Robert Bud and Deborah Jean Warner, eds. Instruments of Science, an Historical Encyclopedia. New York: Garland, in association with The Science Museum, London, and the National Museum of American History, Smithsonian Institution, Washington DC, 1998.

“Odometer,” in Thomas Jefferson Encyclopedia

Comments (5)

  1. Very nice story, many twists and turns (and how many miles?). Thank you!

  2. This post would be great as a beginning unit on measurement. Students could be engaged in how the process of measurement has changed over time. Give them both ends of the spectrum- Jefferson’s odometer and today’s fitbits and the like. Ask the overarching question about how each of these technologies work and what technologies were developed along the way to give us fitbits and such! Thanks for the post.

  3. The early roads were measured in miles and mile markers established. How were these distances measured?

  4. Wonderful reading. Robert Leslie was a great inventor who was largely lost to American history due to the 1836 patent office fire that destroyed his records. For those interested in Robert Leslie, who’s firm also made the “Great Clock” that is at Jefferson’s Monticello, the National Association of Watch and Clock Collectors ( has research and a Leslie made watch in its impressive clock & watch museum collection.

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