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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Franklin's electrostatic machine | 2/3 | https://en.wikipedia.org/wiki/Franklin's_electrostatic_machine | reference | science, encyclopedia | 2026-05-05T09:37:04.008946+00:00 | kb-cron |
== Electrical principles == Franklin's experiments with Leyden jars progressed to connecting several Leyden jars together in a series, with "one hanging on the tail of the other". All of the jars in the series could be charged simultaneously, which multiplied the electrical effect. A similar apparatus had been created earlier by Daniel Gralath. Franklin called this device an "electrical battery", but that term later came to have a different meaning, referring instead to a set of one or more galvanic cells. At that time, the word "battery" was a military term for a group of cannons. Franklin was the first to apply the terms "positive" and "negative" to electricity. Through his research, Franklin was among first to prove the electrical principal of conservation of charge in 1747: a similar discovery was made independently in 1746 by William Watson. Franklin wrote detailed letters and documents about his experiments with the electrostatic machine and Leyden jars. In 1749, Franklin made a list of several ways in which lightning was similar to electricity. He concluded that lightning was essentially nothing more than giant electric sparks, similar to the sparks from the static charges produced by his electrostatic machine. He referred to static electricity as "electric fire", "electric matter", or "electric fluid". The term "electric fluid" was based on the idea that a jar could be filled and refilled when it became empty. That led to the revolutionary idea of "electrical fire" as a type of motion or current flow rather than a type of explosion. Several 18th-century electric terms were derived from his name. For example, static electricity was known as "Franklin current", and "Franklinization" is a form of electrotherapy where Franklin shocked patients with strong static charges, to treat patients with various illnesses.
== Lightning rod invention ==
Franklin invented the lightning rod based on what he learned from experiments with his electrostatic machine. Franklin and his associates observed that pointed objects were more effective than blunt objects at "drawing off" and "throwing off" sparks from static electricity. This discovery was first reported by Hopkinson. Franklin wondered if this discovery could be used in a practical invention. He thought something could be made to attract the electricity out of storm clouds, but first he had to verify that lightning bolts really are giant electric sparks. He wrote Collinson and Cadwallader Colden letters about this theory, and he described the kite experiment in the October 19, 1752 issue of the Pennsylvania Gazette. (Tom Tucker of the Isothermal Community College doubts the account, however, because of ambiguities in the account and points that out in his book Bolt of Fate: Benjamin Franklin and his Electric Kite Hoax. Others disagree with this view, arguing that Franklin would not make up such a fake story because he valued the integrity of the scientific community.)
To test his theory, Franklin proposed a potentially deadly experiment, to be performed during an electrical storm, where a person would stand on an insulated stool inside a sentry box, and hold out a long, pointed iron rod to attract a lightning bolt. A similar but less dangerous version of this experiment was first performed successfully in France On May 10, 1752, and later repeated several more times throughout Europe, though after a fatality in 1753 it was less frequently tried. Franklin declared that this "sentry-box experiment" showed that lightning and electricity were one and the same. Franklin realized that wooden buildings could be protected from lightning strikes, and the deadly fires that often resulted, by placing a pointed iron on a rooftop, with the other end of the rod placed deep into the ground. The sharp point of the lightning rod would attract the electrical discharge from the cloud, and the lightning bolt would hit the iron rod instead of the wooden building. The electric charge from the lightning would flow through the rod directly into the earth, bypassing the structure, and preventing a fire. Franklin's friend Kinnersley traveled throughout the eastern United States in the 1750s demonstrating man-made "lightning" on model thunder houses to show a how an iron rod placed into the ground would protect a wooden structure. He explained that lightning followed the same principles as the sparks from Franklin's electrostatic machine. These lectures by Kinnersley were widely advertised, and were one of the ways Franklin's lightning rod was demonstrated to the general public.
== Legacy ==