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# Primary Sources in the Science Classroom: Thomas Jefferson’s Proposed System of Weights and Measures

This post was co-written by Trey Smith, the Library of Congress 2015-16 Science Teacher in Residence, with Sally Mitchell and Donna Volkmann, 2015-16 Albert Einstein Distinguished Educator Fellows.

Special thanks to Julie Miller in Manuscript Division at the Library of Congress for her help with Jefferson’s papers.

Most of us know Thomas Jefferson as the primary author of the Declaration of Independence. Fourteen years later, on July 4, 1790, Jefferson followed up with another revolutionary document, a report on weights and measures.

The House of Representatives had asked Jefferson, then the Secretary of State under George Washington, to submit a report on establishing a standardized system of weights and measures for the new nation.

 Page 4 from “On Weights, Measures and Coins” report, January 10, 1791. Page 5 from “On Weights, Measures and Coins” report, January 10, 1791.

Introduce students to Jefferson’s ideas about measurement by facilitating an analysis of page 1 from a published excerpt from the report. Withhold details about the document at first to encourage students to speculate:

• What do the tables show?
• What are the mathematical relationships among tables 1 – 4? (Students might notice that “Superficial Measure” [or area], “Measures of Capacity” [or volume], and “Weights” are each derived from “Measures of Length”.)
• Which units in the tables are familiar and unfamiliar?

The tables illustrate Jefferson’s recommendation that a system of weights and measures could be related by powers of ten. This decimal-based system was the second of two options Jefferson presented: The first was to standardize the existing jumble of weights and measures that differed from state to state. Students might consider why a standardized system in general, and a decimal-based system in particular, would be useful and desirable both then and today.

Jefferson’s interest in a logical system of measurement grounded in natural laws reflected the Enlightenment philosophies of the time. Provide students with a cropped image from page 2 of Jefferson’s handwritten report to introduce Jefferson’s recommendation for obtaining a standard measure of length upon which the rest of the system could be built.

Jefferson argued that a pendulum should be used to mark consistent lengths.

• Why does Jefferson think a pendulum is a solution to reliable measurements?
• What other problems does a pendulum introduce? What solutions to these problems does Jefferson propose?
• What method is used today for measuring length in the International System of Units?

Before issuing his report, Jefferson shared drafts with peers. David Rittenhouse, a member of the American Philosophical Society in Philadelphia, wrote Jefferson on June 21 and June 25, 1790, suggesting that a physical rod might be easily lost and raising questions about Earth’s presumed uniform motion.

• What other scientific ideas does Rittenhouse address in his letters to Jefferson?
• What evidence do you see that Jefferson incorporated Rittenhouse’s ideas into his final report?

Students today might take for granted—or be frustrated by—the two systems of measurement used in America today, one for everyday life and the other for scientific pursuits. Jefferson’s papers reveal key ideas about the importance and practice of establishing a coherent system for describing and quantifying things and phenomena.

If Jefferson saw measurement in America today, how might he react?