Kite experiment facts for kids

Benjamin Franklin Drawing Electricity from the Sky, an artwork showing Franklin's kite experiment, painted around 1816.

The kite experiment was a famous science test. In this experiment, a special kite with a sharp, metal wire at its top was flown close to thunderclouds. The idea was to collect electricity from the air and bring it down a wet kite string to the ground.

This experiment was suggested by Benjamin Franklin. He might have even done it himself with help from his son, William Franklin. The main goal of the experiment was to learn more about lightning and electricity. Franklin wanted to show that lightning was actually a form of electricity.

Why People Studied Lightning

Before Benjamin Franklin's experiment, many scientists wondered if lightning was related to electricity. In the 1740s, people in France were already discussing this idea. Some scientists, like Jean-Antoine Nollet, thought about it a lot.

By 1750, Franklin, who had been unsure before, started to believe that lightning was indeed electrical. Other scientists, like Jacques de Romas, also had similar ideas around the same time.

Early Lightning Experiments

In 1752, Franklin suggested an experiment using tall metal rods to attract lightning. The goal was to collect this "electric fire" into a Leyden jar. A Leyden jar was an early type of battery that could store an electric charge.

One scientist named Thomas-François Dalibard performed a similar experiment in France in May 1752. Sadly, another scientist, Georg Wilhelm Richmann, was hurt during a similar experiment in Russia in August 1753. This showed how dangerous these early electrical experiments could be. Franklin himself was thought to have done his experiment in June 1752, possibly on top of a church in Philadelphia, but the church spire wasn't built until later.

Franklin's Famous Kite Experiment

Franklin's kite experiment took place in Philadelphia in June 1752. We know about it mostly from a detailed report written by Joseph Priestley in 1767. Priestley likely heard the story directly from Franklin.

This image, called Franklin and Electricity, was engraved around 1860. It was used on $10 banknotes in the United States for many years.

Franklin knew that using tall metal rods could be very risky. So, he chose to use a kite instead. He used a kite made of silk, which doesn't conduct electricity well when dry. He attached a hemp string to the kite, which would become conductive when wet from the rain.

Franklin and his son flew the kite from inside a small shed. This allowed them to keep the bottom part of the kite string, which was made of silk, dry. This dry silk string acted as an insulator, protecting them from the electricity.

A house key was tied to the wet hemp string. This key was connected to a Leyden jar. As the thunderclouds passed over the kite, Franklin noticed that loose threads on the kite string were pushing away from each other. This was a sign that the kite and string were becoming charged with electricity.

Franklin then carefully moved his hand close to the key. He saw an electric spark jump from the key to his knuckle! This spark proved that lightning was indeed electricity. It's important to know that the kite was not hit by a direct lightning bolt. If it had been, Franklin would have been seriously harmed.

What The Pennsylvania Gazette Said

The kite experiment was described in The Pennsylvania Gazette newspaper on October 19, 1752. Franklin wrote about it, but he didn't say that he himself had done the experiment. Here's a simplified version of what he wrote:

"Many newspapers in Europe are talking about the success of the Philadelphia experiment. This experiment uses pointed iron rods on tall buildings to draw electric fire from clouds. It might be interesting to know that the same experiment has worked in Philadelphia, but in a different and easier way. Anyone can try it like this:

Make a small cross from two light cedar sticks. The sticks should be long enough to reach the corners of a large, thin silk handkerchief when it's spread out. Tie the corners of the handkerchief to the ends of the cross. This will be the body of your kite. Add a tail, loop, and string, and it will fly like paper kites. But because it's made of silk, it can handle rain and wind better during a thunderstorm without tearing.

At the very top of the upright stick of the cross, attach a very sharp, pointed wire. This wire should stick up a foot or more above the wood. At the end of the kite string, near your hand, tie a silk ribbon. Where the string and the silk ribbon meet, you can fasten a key.

You should fly this kite when a thunderstorm is approaching. The person holding the string must stand inside a door, or window, or under some cover. Make sure the silk ribbon does not get wet. Also, be careful that the kite string does not touch the door or window frame.

As soon as any thunderclouds pass over the kite, the pointed wire will draw electric fire from them. The kite and all the string will become electrified. You'll see the loose threads of the string stand out in every direction, and they will be attracted to your approaching finger.

When the rain has made the kite and string wet, so they can conduct the electric fire easily, you will find it streaming out strongly from the key when you bring your knuckle close. You can charge a Leyden jar (a 'phial') from this key. And from the electric fire you get this way, you can light spirits and do all the other electrical experiments usually done with a rubbed glass globe or tube. This completely proves that the electric matter from clouds is the same as lightning."

• Philosophical Transactions: A Letter of Benjamin Franklin, Esq; to Mr. Peter Collinson, F. R. S. concerning an Electrical Kite. Phil. Trans. 1751–1752 47, 565–567; (PDF)

See also

In Spanish: Experimento de la cometa de Benjamin Franklin para niños