As dawn broke in Philadelphia on July 4, 1776, the weather was a pleasant 68 degrees. The temperature crept up to 72.25 degrees at 9 a.m., reaching a balmy 76 by 1 p.m. before dipping slightly to 73.5 at 9 p.m.
We know this because on the day that the Continental Congress adopted the final wording of the Declaration of Independence, severing ties with Britain’s King George III in an act of rebellion that would create the independent United States of America and reverberate around the globe for centuries, Thomas Jefferson measured and recorded the temperature four separate times.
While Jefferson’s drafted thoughts about how “all men are created equal” were being certified as the voice of a brand-new nation, the man himself was evidently focused on the weather. According to the meticulous memorandum books in which he logged his personal expenditures, on July 4, he purchased a thermometer from John Sparhawk, an apothecary and bookseller on Second Street who also apparently sold meteorological instruments, for three pounds and 15 shillings. It was part of something of a spending spree, as the day also saw him buying seven pairs of women’s gloves for 17 shillings. He further reported giving one shilling and six pence to charity.
