Most of us grew up with a general idea that Benjamin Franklin “discovered” electricity. As adults we realize that can’t be entirely true. So just what does Benjamin Franklin have to do with electricity? And what’s with the kite?
In Franklin’s day, electricity was understood no better than it had been in ancient times. Entertainers and pranksters used static electricity to shock people for laughs, and that was about it.
In 1747, Franklin received from a fellow tinkerer a device for generating static electricity. Entranced by the object, Franklin commissioned a local glassblower and silversmith to make more such gadgets. He used them to collect electric charges and conduct experiments.
His first great discovery was that the generation of a positive charge is accompanied by the generation of an equal negative charge. This concept, known as the law of conservation of charge, was a major scientific breakthrough. Before Franklin’s discovery, scientists believed that electricity involved two independently-created fluids, known as vitreous and resinous; Franklin’s findings instead demonstrated the single-fluid theory of electricity.
Franklin’s single-fluid theory and his law of conservation of charge have now withstood over 250 years of practical application.
Franklin needed to invent some new terms in order to explain his findings to the scientific community. In a letter to a colleague he wrote: “We say B is electrised positively; A negatively: or rather B is electrised plus and A minus… These terms we may use until your philosophers give us better.” In fact, no better terms were needed; we use Franklin’s to this day. His other neologisms include neutral, condense, and conductor.
Franklin experimented with capturing and storing electrical charges using a device called a Leyden jar, which was a primitive form of capacitor. These experiments led to his invention of a new device, also still in use today, which he named the electrical battery.
Another important Franklin discovery was the fact that metal points draw electrical charges more readily than do blunt pieces of metal. This led to his most famous experiment and one of his most indispensable inventions.
More background is needed here. In Franklin’s day, lightning was feared as one of the most destructive of natural forces. Scientists did not understand the phenomenon; it was generally explained as a supernatural occurrence, an expression of God’s wrath. In the 13th century, St. Thomas Aquinas had declared that the sound of church bells would repel lightning strikes; 500 years later, church bells were still being rung at the approach of a thunderstorm.
This was a singularly bad idea. During one 35-year period in Germany, 386 churches were struck and more than 100 bell ringers killed. In Venice, lightning struck a church where gunpowder was being stored, and three thousand people lost their lives.
Franklin believed it was time to try another solution.
In November of 1749 he recorded in his journal the strange similarities he had noticed between lightning and electrical sparks. Both gave off the same color of light; both were swift and had the same crooked shape, and made the same type of noise; both were conducted by metals, could kill animals, and were accompanied by a sulfurous smell.
Since there were so many similarities between lightning and electricity, might there not be yet another similarity? Might not lightning, like electricity, be drawn to a metal point?
If this supposition were true, then it might be possible to tame one of the greatest natural dangers known to mankind.
This is what he set out to prove by his famous experiment.Using a silk kite with a sharp wire attached to the top and a metal key suspended near the end of the string, he was able to draw off sparks from a passing storm cloud. It is remarkable that he did not kill himself in the process. But by this means he proved that lightning could indeed be deliberately drawn off by the use of a lightning rod.
Few scientific discoveries have provided such an immediate practical benefit to humanity. By proving that electricity and lightning were the same thing, Franklin transformed a deadly supernatural force into a scientific phenomenon that could be controlled. Within the year, lightning rods were being installed all over Europe and the colonies, and Franklin was suddenly a famous man.