When Sparks Flew

Franklin and his son were the only witnesses to his legendary kite experiment. What really happened?

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MICHAEL ELINS / TIME

THUNDERBOLT: An artist's rendering shows how the electrified kite string bristled with its charge and gave the inventor a famous jolt

It's an iconic moment in American history studied by generations of schoolkids. On a storm-tossed June day in 1752, Ben Franklin, joined by his son William, hoisted a kite with a wire poking out of it high over Philadelphia. As the skies darkened, the kite's hemp string bristled with electricity, like a cat's fur after being stroked. Franklin brought his knuckles close to a brass key dangling from the end of the string. A spark leaped through the air, giving him a powerful jolt--and immeasurable pleasure. No longer could anyone doubt that the small electrical charges created in popular 18th century parlor games and the Jovian bolts thundering from the heavens were one and the same.

But is this oft-told tale another Founders myth, like Washington's confessing to axing his father's cherry tree? The latest skepticism is voiced in a quirky new book, Bolt of Fate (Public Affairs), that calls the whole thing a hoax, echoing the spoofs Franklin confected for Poor Richard's Almanack. But author Tom Tucker's evidence is slim. He makes much of the improbability of flying a kite weighted down by a heavy key, ignoring Franklin's long history of kite flying, and of his delay in publicizing the experiment, though only three months elapsed. More to the point, scientific fraud seems wildly out of character for Franklin. As Harvard chemist and Franklin buff Dudley Herschbach, a Nobel laureate, notes, "It would have been utterly inconsistent with all of his other work in [science] for him to claim he'd done something he had not."

The larger issue, however, is not whether Ben flew the kite, which most scholars agree he did, but how significant his Philadelphia experiment was. In fact, many of his scientific breakthroughs were of great import--and he had a selfless urge to share his new knowledge. When Franklin caught the electricity bug in his 40s, "electrick fire" was a playful if puzzling entertainment. His experiments led him to startlingly modern conclusions. The "fire," he said, is a single "fluid," not the dual "vitreous" and "resinous" electricities postulated by European savants. It exists in two states: plus and minus (terms he coined, along with positive and negative, battery and conductor). Furthermore, he said, if there is an excess of charge in one conductor, it must be precisely balanced, as in double-entry bookkeeping, by a deficit in another. Stated another way, electrical charge is always conserved, an important new principle descended from Newton's conservation of momentum. Finally, he said, when sparks fly between two charged bodies, they instantly restore the equilibrium between them.

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