Benjamin Franklin is probably best known for two things in popular culture: his portrait on the $100 dollar bill, and flying a kite in a lightning storm to capture electricity.
In fact, we do not know for sure whether he himself ever conducted the experiment with the kite. (According to the Franklin Institute, he probably did.) What we do know for certain is that Ben Franklin’s inventions include the first practical electrical device, and that he was the first scientist to explain electricity in terms we still use today, including current, positive and negative, and even battery.
Spark of an Idea
In the 1750s, decades before his role in the American Revolution earned him a place on the $100 bill, Benjamin Franklin was already a leading inventor and scientist. His ideas and research were famous across Europe as well as what were then still the British colonies in America.
One of the many subjects that drew his interest was electricity. Some awareness of electrical phenomena, says Practical Physics, goes back to ancient times. Rubbing cloth on amber, a semiprecious material used for jewelry, will produce a static charge. In fact, the Greek word for amber, elektron, gave its name to electricity and all related terms.
According to the Library of Congress, electrical phenomena were drawing the attention of scientists by the 1750s, but otherwise were only useful for parlor tricks such as producing sparks. Nor did scientists yet have a theory of electricity that could explain the phenomena they observed.
Ben Franklin’s inventions related to electricity started out with one dramatic insight: that a lightning bolt was an enormous electrical spark.
Key to a New Technology
To test this theory, says the Franklin Institute, he proposed a test in which a metal object, elevated above its surroundings, would attract the electric charge that Franklin correctly believed was present in the atmosphere during a lightning storm. The metal target would be connected to a Leyden jar, an early device for storing an electric charge.
Our fullest account of Franklin’s efforts, per the Franklin Institute, comes not from Ben Franklin himself, but from British contemporary and scientist Joseph Priestley, who discovered oxygen. According to Priestley, Franklin originally planned to try the experiment in a church spire. Then he came up with the kite as a more convenient way to carry the metal target up into a stormy sky.
In October 1752, a Philadelphia newspaper published Franklin’s own account of the experimental procedure, using a key as the target and a kite to carry it aloft. The experiment, he wrote, conclusively demonstrated “the Sameness of the Electric Matter with that of Lightning.”
Franklin never specifically says that he performed the experiment himself, so we can’t be absolutely sure, but he explained electricity and its connection to lightning.
The First Electrical Safety Device
Ben Franklin was a great believer in practicality, as noted by the Library of Congress. So for him it was not enough to explain electricity — he also wanted to find practical uses for it. And that was exactly what he did. He did not yet have a way to make electricity do useful work, but he could prevent electricity (in the form of lightning strikes) from doing something dangerous: starting fires.
Franklin realized that his original proposed version of an electricity-capturing device, connected to the ground rather than a Leyden jar, could be set on top of a building to protect it from lightning strikes. Lightning would be drawn to the metal target, a pole, instead of the building, and the wire would conduct the current safely to ground.
Franklin’s lightning rod, as the new practical version was called, was the first electrical device to have a function other than entertainment or experimentation. It also allows us to include on the list of Ben Franklin’s inventions the first electrical safety apparatus.