Lightning and thunder were tokens of divine displeasure: so common view had it. Catholic philosopher and theologian Thomas Aquinas wrote “It is a dogma of faith that demons can produce winds, storms, and rains of fire (lightning) from heaven.” And no less a luminary than Thomas Jefferson professed in one letter his discomfort at the experiments with thunderstorms by his friend. “He began to go on about the presumption of erecting iron rods to draw the lightning from the clouds. He talked of presuming upon God, as Peter, attempted to walk upon the water…” Jefferson’s wrote about Benjamin Franklin, who hypothesized that lightning was scientific phenomenon, not a divine one.

On this day, June 15, in 1752, Franklin went out into a thunderstorm with his kite in an attempt to prove the lightning was electrical in nature. To the top of the kite he affixed an iron point and to its string he attached a small key, hypothesizing that lighting would be attracted to the iron on top of the kite, and travel down the length of the string to the key.

Franklin did not publish his famous experiment; nor do any contemporary accounts exist. The earliest mention comes from Franklin’s friend and fellow scientist Joseph Priestley, who also described what happened next: “…[A] considerable time elapsed before there was any appearance of its being electrified. … at length, just as he was beginning to despair of his contrivance, he observed some loose threads of the hempen string to stand erect, and to avoid one another, just as if they had been suspended on a common conductor. Struck with this promising appearance, he immediately presented his knuckle to the key, and (let the reader judge of the exquisite pleasure he must have felt at that moment) the discovery was complete.”