Benjamin Franklin's Kite Experiment

The famous story about Benjamin Franklin flying a kite on a stormy day and accidentally discovering electricity is widespread, yet not necessarily accurate. His discoveries did lead to many advancements regarding electricity, the most famous invention being the lightning rod, used even today to prevent lightning-caused fires. For a long time, Franklin hypothesized that electricity and lightning are the same things. Unfortunately, he had no way of proving it, as his surrounding area was too flat and the Philadelphia church - the only building high enough for his ideas, was still undergoing construction. It all changed once he realized that there is another way to get closer to clouds - by using a kite. In this article, we'll dive into the history and logistics of Benjamin Franklin's Kite Experiment.

Benjamin Franklin's Kite Experiment Period and Background

In 1750, the electrical nature of lightning became a public debate in France, with many scientists of the day such as Denis Barbaret, Jacques de Romas and Jean-Antoine Nollet all investigating the nature of electrical charge around this time. Across the Atlantic, Benjamin Franklin was also investigating electricity and by the end of 1749 had found many similarities between lightning and electricity.

Benjamin Franklin Drawing Electricity from the Sky, Wikimedia Commons

In 1752, Franklin presented an experiment in which one end of a conducting twine was connected to a Leyden jar (a type of primitive capacitor) and the other end to a kite, to demonstrate that lightning was an electrical phenomenon. Franklin himself said that he first conducted the experiment in June 1752, reportedly on the roof of the Christian Church in Philadelphia. Still, there are doubts about where and how the experiment was actually carried out, as it was not independently observed.

A similar experiment was carried out by Thomas-François Dalibard in Marly-la-Ville in northern France in May 1752. Trying to imitate the experiment, Georg Wilhelm Richmann died in Saint Petersburg in August 1753, thought to have been struck by a lightning bolt.

Benjamin Franklin's Kite Experiment Hypothesis

As we have already established - Franklin did not discover electricity. Although it was a well-established scientific concept with some practical applications, electricity wasn't fully understood until long after Franklin's death in 1790. Based on the available knowledge of electricity at the time, Franklin noticed many similarities between electricity and lightning. Mainly, he observed that both phenomena:

1. created light;

2. were followed by loud crashes;

3. had a very distinct smell; and

4. were attracted to metals.

So, the main aim of this experiment was to prove the connection between the two concepts, as Franklin hypothesized that lightning is a form of electricity.

Benjamin Franklin's Kite Experiment Story

The main idea of Franklin's experiment was fairly simple - collect the electrical charge created in the Earth's atmosphere during a storm, just before a bolt of lightning strikes. Contrary to popular belief, Franklin wasn't hit by a lightning bolt, as that would probably be deadly.

The actual experiment was supposedly conducted on a rainy day in a field. The kite was launched into the stormy sky, while both Franklin and his son were waiting in a safe, dry place. Soon after, Franklin noticed hanging threads on the string standing upright and recognized similarities between this behavior and other experimental observations made when using a conductor.

The same thing happens in the string, as the current is directed through it and similar charges repel each other, resulting in the "hairs" on the rope to raise. This observation alone indicated that Franklin's hypothesis was correct; however, he went a step further and touched a metal key tied to the string. As a result, he experienced a light electric shock and observed a spark. He then went on to "collect" the electric charge using a Leyden jar (in modern terms, it was being charged), to perform further studies.

Benjamin Franklin's Kite Experiment Diagram

The experimental setup used by Franklin was quite straightforward. A detailed diagram of the setup used is visible below.

Each component of this kite, has a purpose, especially when it comes to the materials chosen. The base of the kite is made of two perpendicular sticks, with a silk handkerchief stretched over it. Silk was chosen deliberately, as in contrary to paper, it is sturdy enough to withstand the harsh weather conditions. A hemp rope is attached to the base of the kite, extending all the way to the ground. When soaked by the rain, this rope becomes a good conductor of electricity. At the bottom of the rope, a metal key is attached using a string made of silk. As described earlier, Franklin remained inside a dry space to avoid becoming conductive himself!

Benjamin Franklin and Electricity

There was a practical reason as to why Franklin was so fascinated by lightning. As a politically active member of society, he was concerned about the sheer amount of lightning-caused fires in his homeland. Once Franklin had successfully performed the Kite Experiment, his next idea was to achieve a similar effect of collecting electricity from storm clouds using a metal rod.

Lightning rods

As a result, lightning rods were invented and became a regular addition to buildings to steer lightning strikes directly into the ground. A diagram displaying a house equipped by a lighting rod is visible below.

Lightning rods protect buildings from lightning bolts by redirecting the electricity directly into the ground through a wire attached to it, Wikimedia Commons

This system is a great conductor, allowing the current to be diverted into the ground without causing any significant heat damage. Essentially, the metal rod becomes the highest point for the lightning to strike. The cable connected to the rod needs to have a very low resistance to prevent it from heating up too much when conducting the energy of a lightning strike.

Franklin bell

Franklin also developed something known as the Franklin bell. It was an extension to his lightning rods combined with Andrew Gordon's original invention of "electric chimes".

It was the first-ever instrument to convert between electrical and mechanical energy. A diagram of the first Franklin bells mentioned in literature is visible below.

Franklin bells - an alarm system used in the 18th century to warn about upcoming lightning storms, Wikimedia Commons

The basic principle of this device is as follows. One of the bells is connected to the lightning rod, another one - to a grounded rod. During a storm, the metal bell attached to the lightning rod accumulates charge that eventually attracts the bell clapper. Once the clapper and the bell come into contact, their charges become identical, causing them to repel. The bell connected to the ground now has an opposite charge to the bell clapper, causing them to attract and repeat the same process as before. Subsequently, the system will create noise as long as the thunderstorm is going on.

Vocabulary

In addition to practical inventions, Benjamin Franklin has also contributed greatly to introducing and describing crucial definitions and concepts in the study of electricity. For instance, terminology such as conductors, batteries, and charge are all of his imagination. Franklin believed that all objects contain "a single fluid", and depending on whether there is a surplus or shortage of said fluid, the object is positively or negatively charged, respectively. While this theory may not have been entirely correct, the terminology used by Franklin himself is still in widespread use today.