In Benjamin Franklin’s 1752 kite experiment, what did the electrical sparks indicate about lightning?

Benjamin Franklin’s 1752 kite experiment indicated that lightning is electrical.

Franklin proposed that a thundercloud might carry electrical charge and designed a kite experiment to test the idea. According to the account published by Joseph Priestley, Franklin’s son William helped fly the kite during a storm, and Franklin drew a spark from a key attached to the wet kite string. This showed that storm clouds could produce electrical effects similar to those observed in laboratory experiments.

Franklin did not attract a lightning strike directly, which would have been extremely dangerous. The experiment is often retold as though the kite were struck, but the reported observation involved induced charge and sparks from the apparatus.

The work helped connect atmospheric electricity with lightning and contributed to Franklin’s invention of the lightning rod. Historians continue to discuss the precise details of the event, but the electrical nature of lightning was the central conclusion.