Jefferson, weather, and the temperature on July 4, 1776

Page from Thomas Jefferson's Weather Memorandum
Book showing his temperature observations for
the first two weeks in July 1776
(Library of Congress)

A little Independence Day Weather Trivia for you:

Thomas Jefferson, it turns out, was one of the most avid weather observers of his time. For more than 50 years, he kept careful, systematic records of temperature and other meteorological conditions, not only at his home in Monticello, but wherever he travelled. On July 1, 1776, while in Philadelphia for the Second Continental Congress, Jefferson purchased a thermometer from a local merchant, John Sparhawk, for £3–15 (the equivalent of more than $300 today). On July 4, 1776, Jefferson awoke to record a temperature of 68°F at 6:00 a.m. By 1:00 in the afternoon—about an hour before a final agreement on the Declaration of Independence was reached - the temperature had risen, most appropriately, to 76°F. It would cool down only two-and-a-half degrees by 9:00 p.m. Although local lore tends to recount the day as hot and sweltering, thanks to Jefferson we know that was not the case.

Jefferson continued his study of weather and climate, recruiting friends such as James Madison to take observations for comparison. (Both men lamented at the loss of their barometers to the hands of the British—Jefferson's was broken, and Madison's was stolen, along with his thermometer.) Jefferson’s efforts to establish a network of amateur weather observers laid the foundation for the current National Weather Service Cooperative Observer Program (Coop), and one of the most prestigious awards NWS presents to local observers each year bears Jefferson's name.

Jefferson made his final entry in his weather memorandum book just six days before his death, which occurred on July 4, 1826—half a century to the day after he took perhaps his most famous temperature readings ever.

(Excerpt from: Weatherwise Magazine, "Retrospect: July 4, 1776: The Declaration of Independence," by Sean Potter)