Franklin, testing his theory that lightning was simply electricity, flew a kite topped with a metal wire during a storm and connected a key to the wet string, drawing a charge he could feel and store. Though the exact date is disputed, the experiment — recounted by Franklin and his associate Joseph Priestley — became one of the era's most famous demonstrations, directly inspiring the lightning rod.
Franklin had proposed the identity of lightning and electricity in letters to the Royal Society before he tested it himself, and other experimenters in France had already verified the theory using tall grounded rods weeks earlier, news of which had not yet crossed the Atlantic. Franklin's version, involving a kite, his son William, and a Philadelphia field, became the far more famous telling, largely through Joseph Priestley's later account published in 1767.
The setup was elegantly dangerous: a silk kite with a pointed wire attached to the string, flown into a gathering storm, with a metal key tied near the ground end and Franklin holding a dry silk ribbon insulating his hand. As the storm approached, loose threads on the string stood up, and when Franklin touched the key he felt a spark — evidence that the string had conducted an electrical charge down from the clouds.
Whether Franklin risked direct electrocution or, as some historians argue, merely detected charge in the surrounding air rather than a direct strike, remains debated. What's undisputed is the consequence: Franklin went on to invent the lightning rod, a simple grounded metal spike that could protect buildings from fire, a genuine and immediately useful piece of Enlightenment science born from a genuinely reckless afternoon.
Key people: Benjamin Franklin, Joseph Priestley