The Kite, the Key, and the Storm

In June 1752, according to the fullest surviving account, Benjamin Franklin walked out toward a gathering thunderstorm in Philadelphia with his son William. In his hands was a kite, its apex fitted with a pointed wire, and tied to a length of hemp string. At the string's other end dangled a metal house key, borrowed from a man named Benjamin Loxley. A silk ribbon connected the key to Franklin's hand — dry silk that would not conduct electricity, meant to insulate him from whatever the storm might send down.

The question that drove Franklin into that field had been simmering in Europe for years. In 1749, Jean-Antoine Nollet's speculations had turned the electrical nature of lightning into a prize question in Bordeaux. By 1750 it was a matter of public fascination in France: Denis Barberet won acclaim there for a dissertation proposing a cause resembling what we now call the triboelectric effect, while physicist Jacques de Romas wrote his own treatise with similar ideas. That same year, Franklin abandoned his earlier doubts and began to suspect that lightning truly was attracted to high points — and that it was, in essence, electricity.

In 1752, Franklin proposed an experiment: run a conductive rod up to a great height, connect it to a Leyden jar — an early capacitor — and see if it captured a stroke of lightning. Philadelphia had no spire tall enough for the job. But in France, Thomas-François Dalibard carried out just such an experiment at Marly-la-Ville in May 1752, apparently vindicating Franklin's idea before Franklin himself had managed it. The following year, a Russian scientist named Georg Wilhelm Richmann died attempting to replicate the setup in Saint Petersburg, killed by what was believed to be ball lightning.

Franklin's own solution was more modest and, it turned out, safer: rather than a fixed rod on a spire, why not raise a conductor into the storm on a kite? He described the experiment in a letter to the Pennsylvania Gazette, published on October 19, 1752 — though notably, he never stated plainly that he himself had performed it, or when. That letter was read before the Royal Society in London on December 21, 1752, and later printed in the Philosophical Transactions.

It was left to the chemist Joseph Priestley, writing his 1767 history of electricity, to supply the fullest narrative — details he likely gathered from Franklin himself, who was living in London while Priestley wrote. Priestley described how, sheltering from the rain under an open shed to keep the silk ribbon and key dry, Franklin noticed loose threads of the kite string standing apart and repelling one another, a sign of electrical charge. He touched the key with a knuckle and drew a spark. He touched it to a Leyden jar and charged it.