In Benjamin Franklin’s 1752 kite experiment, Franklin’s apparatus showed lightning to be electricity.
Franklin proposed testing whether thunderstorms carried the same electrical phenomenon produced by laboratory machines. He described flying a kite with a pointed wire during a storm, using a silk insulating cord and a metal key as part of the setup. Sparks reportedly jumped from the key when a finger approached it, indicating an electrical charge.
The experiment supported Franklin’s broader theory that lightning and ordinary electrical sparks were related. It also helped motivate the development of lightning rods, which Franklin designed to provide a safer path for electrical discharge from buildings.
The famous account should be treated carefully. Franklin did not necessarily fly the kite directly into lightning, and a direct strike could have been fatal. Some historians also debate details of the episode because the best-known description appeared later. The experiment’s scientific point was the electrical character of storm clouds, not the production of lightning itself.