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Franklin's sentry box experiment. AIP Niels Bohr Library
A self-educated, amateur scientist, Franklin was fascinated by the so-called "electric fluid," and independently investigated charged objects and how sparks jumped between them using an electricity tube given to him by his friend Peter Collinson. He concluded that lightning was merely a massive electric spark, similar to those produced from charged Leyden jars. Based on his observations, he proposed an experiment with an elevated rod or wire to "draw down the electric fire" from a cloud, with the experimenter standing in the protection of an enclosure similar to a soldier's sentry box.
Before Franklin could put his proposal into practice, Frenchman Thomas Francois D'Alibard used a 50-foot long vertical rod to draw down the "electric fluid" of the lightning in Paris on May 10, 1752. One week later, M. Delor repeated the experiment in Paris, followed in July by an Englishman, John Canton. But one unfortunate physicist did not fare so well. Georg Wilhelm Reichmann attempted to reproduce the experiment, according to Franklin's instructions, standing inside a room. A glowing ball of charge traveled down the string, jumped to his forehead and killed him instantly - providing history with the first documented example of ball lightning in the process. To add insult to injury, Russian chemist Mikhail Lomonosov successfully performed the same experiment a few days later.
As for Franklin, he was apparently unaware of these other experiments when he undertook his own version during a thunderstorm in June 1752, on the outskirts of Philadelphia. Unlike Reichmann, he quite sensibly stood under a shed roof to ensure he was holding a dry, non-conducting portion of the kite string. Impressed with lightning's power and potential danger, he went on to develop the lightning rod as a protective measure, as well as a device called "lightning bells" that would jingle when lightning was in the air. His observations laid the groundwork for later scientists, including Michael Faraday and Thomas Edison, to further explore the mysterious properties of electricity.
Birthdays for May:
May 11 — Richard Feynman (1918)
May 15 — Pierre Curie (1859)
May 21 — Andrei Sakharov (1921)
May 23 — John Bardeen (1908)
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