The article, marking 250 years of American independence, opens with a vivid historical detail: Thomas Jefferson bought a thermometer from Philadelphia merchant John Sparhawk on the morning of July 4, 1776. He used the device for decades, recording temperatures at his Monticello estate, in Washington, D.C., and in Paris during his ambassadorship. That Thursday, he noted a mild 20°C at dawn and 23°C in the evening, as the Continental Congress moved toward adopting the Declaration of Independence.