Catching Lightning

On June 10, 1752, in Philadelphia, Benjamin Franklin flew a kite in a thunderstorm with a metal key tied to the string. When lightning charged the atmosphere, sparks jumped from the key to his knuckle. He had proved lightning was electrical, not divine. The experiment was reckless -- others who tried similar demonstrations died. But Franklin stood inside a shed, kept the string dry except for a conducting section, and made sure he was not the path of least resistance.

Franklin had been studying electricity since 1747, experimenting with Leyden jars and proposing that electricity behaved like a fluid with positive and negative charges. The kite tested whether lightning was the same phenomenon as laboratory static. When it worked, it confirmed sky and laboratory were connected.

engraving depicting franklin's kite experiment, in which he demonstrated the electrical nature of lightning. source: wikimedia commons

The immediate application was the lightning rod. A grounded metal rod attracted strikes and channeled charge safely into the earth. Some clergy called it blasphemy. Franklin pointed out that people built roofs to keep out rain, also sent by God. Lightning rods became standard. Buildings stopped burning. Ships stopped losing masts. Franklin never patented the design. He believed useful inventions should be shared freely.

His work influenced Faraday and Maxwell. His terminology -- positive and negative -- endures. His concept of electrical grounding became fundamental to engineering. The kite and the key were not the point. The point was that nature could be understood, knowledge could be applied, and a man with a piece of string and a question could change how we see the sky.