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For all his achievements as a statesman, inventor and scientist, Ben Franklin etched himself into the popular imagination as a man who dared fly a kite in a thunderstorm. The idea was to prove that clouds could be electrified and that mankind could exert some control over lightning. And yet, Franklin never wrote up the results of his most famous experiment beyond a vague newspaper account, which didn't make clear whether he or someone else actually channeled electriharges from the sky to his famous key.
And so, more than 250 years after the fact, Franklin remains himself a lightning rod for controversy among historians. Some say he was much too smart to have tried such a foolhardy, death-defying stunt. Others say Franklin was much too honest to have falsely reported that he pulled it off.
But historians and scientists agree on one thing — whether he did or didn't fly that kite, Franklins' achievements as a scientist were enormous and under-appreciated. If he hadn't been so famous as an inventor and founding father, "Franklin would be recognized as the greatest scientist of his age," said physicist and Franklin enthusiast Shawn Carlson, founder of the Society for Amateur Scientists and, more recently, the LabRats Science Education Program.
Science for curiosity's sake
As Franklin's thoughts went from laboratory experiments to lightning rods, he also tipped the scales in a debate that still rages today over the value of basic, curiosity-driven science. The benefits of basic science had been extolled more than 100 years before Franklin's day by British thinker Francis Bacon. "The idea was that if we understood enough about how the world works we could find ways to manipulate nature to make a better world," said Carlson.
Early on, Franklin didn't seem to know how his study of electricity would lead to anything practical. "He started to say he was feeling guilty with all the pleasure he was getting from working with electricity, and he wished he could do something useful with it," said Rutgers historian James Delbourgo, author of A Most Amazing Scene of Wonders: Electricity and Enlightenment in Early America. The lightning rod was, Delbourgo said, "an afterthought."
In his book, Benjamin Franklin's Science, historian I. Bernard Cohen describes how, in the mid 1700s, electricity was used in shows that combined entertainment with science lectures. Such spectacles usually involved young people coming onstage, getting charged with static, and then shocking one another.
Franklin, keeping with tradition, put on his own public shows. And he wrote that he threw dinner parties in which he used electrical devices to kill, tenderize and cook turkeys. But amid all the fun, he also observed predictable patterns in the way some materials conducted electricity and others "insulated" or blocked its flow. He observed the phenomenon of grounding. And then he devised a theory that explained what he observed.
He saw electricity as a fluid that sought equilibrium, so that objects that were depleted in it would want to draw it in, and those charged with an excess, to give it up. He understood that a charged object would repel charges on one side of nearby objects — a phenomenon known as induction. "Franklin's understanding is our modern understanding," said physicist Carlson. "He invented modern electrostatics."
The historians say our modern description of electric currents and positive and negative charges harks back to Franklin and those scientists who went on to make batteries built on his work.
The world had to wait a few decades for batteries, but Franklin did think of a practical invention that could be used right away — the lightning rod. The idea rested on Franklin's understanding of electrical behavior along with an untested assumptions that clouds held electric charge and lightning was just a scaled-up version of sparks.
Being the scientific thinker that he was, he devised an experiment to test the electrical nature of clouds and lightning. He proposed the construction of a long iron rod that would stick up in the air and channel charges from a cloud down to a room where a scientist could observe its behavior. According to Cohen's book, Philadelphians started to build such an experiment at Christ Church, but two things happened before that was finished. First, the French heard of Franklin's idea and carried out a similar experiment successfully, and Franklin realized that the concept could be tested more easily with a kite.
Debating that kite flight
Cohen, who died in 2003, maintained that Franklin really flew the kite. He took at face value a subsequent account of the experiment, published in 1767 by English scientist Joseph Priestley. Priestley wrote that Franklin carried it off in June of 1752, accompanied by only his 21-year-old son. According to that account, the kite was never struck by lightning, but Franklin was able to channel current from clouds down the string. At the bottom, in Priestley's version, Franklin included an apparatus called a Leiden jar, commonly used to collect static electricity. By using the jar, he could show that the cloud's electricity acted just like electricity generated in laboratory experiments.
But that account leaves several mysteries, said Alberto Martinez, a historian of science at the University of Texas and author or the book Secret Science. In August of 1752 Franklin published an account of the French iron rod experiment in his own newspaper, the Pennsylvania Gazette, but he never mentioned anything about the kite. Then in October of that year he described a kite experiment done in Philadelphia but didn't say he did it himself. Franklin wrote that such an experiment was easy, said Martinez, despite the risk of death by lightning strike.
In his book, Martinez recounts an episode of the television show Mythbusters, in which a mock-up of the experiment is set up, lightning strikes the kite and fries a dummy of Franklin. But neither Franklin nor Priestley ever said he was struck, and other experiments showed that kites and iron rods can pick up charges off the atmosphere.
In the end, Martinez said he doesn't see enough evidence to determine whether Franklin flew that kite, but he said he wouldn't be outraged if it did turn out to be a hoax. After all, Franklin was right to realize that clouds were electrically charged and lightning rods really could protect buildings and ships.
Franklin first proposed that lightning rods would prevent lightning by helping relieve the imbalance between clouds and the ground, but he amended himself later to say that if lightning struck the rods, it would be safely conducted to the ground.
But then, even lightning rods became lightning rods for controversy, with naysayers claiming they only added danger by drawing lightning to buildings. Others had faith-based objections, including a preference for the existing lightning-deflection technique, which was to ring church bells.
One of Franklin's rivals, Abbe Nollet of France, wrote that "It is impious to ward off God's lightning as for a child to resist the chastening of the rod of the father" — a sentiment that Franklin countered by pointing out that lightning was no more an act of God than rain, and yet we put roofs on our houses. He also asked people to consider the most common victim of lightning and asked what God could possibly have against trees.