Franklin's lightning experiment. Illustration of the US scientist Benjamin Franklin (1706-1790) and his son William, performing their famous lightning experiment. On 15 June 1752 they flew a kite during a thunderstorm, with a metal wire on the kite attracting a lightning strike. Electricity flowed down the string to a key, charging a Leyden jar (capacitor). This experiment proved that lightning was an electrical phenomenon, and supported Franklin's invention of lightning rods. Some scientists died repeating the experiment.