Benjamin Franklin's Kite Experiment: The Discovery of Electrical Nature

Benjamin Franklin’s famous kite experiment of 1752 is one of the most iconic episodes in the history of science. The experiment demonstrated that lightning was a form of electricity, and it helped to establish the foundation of the modern science of electricity. This article examines the context, the method, the results, and the lasting influence of the experiment.

The Context of the Experiment

By the middle of the eighteenth century, electricity was one of the most exciting areas of scientific research. Experiments with static electricity, generated by rubbing various materials together, had produced a series of surprising phenomena, and several European scientists had developed theories about the nature of electricity. The American colonies were somewhat peripheral to this research, but Franklin, who was an active member of the Royal Society and a correspondent of many of the leading European scientists, was well aware of the latest developments.

Franklin had developed a theory of electricity that held that electricity was a single fluid that existed in all matter, and that the various electrical phenomena were the result of the presence or absence of this fluid. Lightning, in Franklin’s view, was the discharge of this electrical fluid from the clouds, and it could be studied using the same methods that had been developed for the study of static electricity.

The theory predicted that lightning should have the same properties as the electrical sparks that could be generated in the laboratory. If the theory was correct, then it should be possible to draw electricity from a thunderstorm using a pointed conductor, and to use this electricity to perform the same kinds of experiments that could be performed with laboratory electricity.

The Method of the Experiment

Franklin proposed a method for testing his theory in a letter to his correspondent Peter Collinson in 1750. The method involved erecting a pointed metal rod on a tall building or in an open field during a thunderstorm, and observing whether the rod would draw electricity from the storm. If the rod did draw electricity, then lightning and electricity were the same phenomenon.

Some of Franklin’s European correspondents performed the experiment before he did. In 1752, the French scientist Thomas-François Dalibard successfully performed the experiment in France, using a pointed rod erected in a field. The experiment produced the expected result: the rod drew electricity from a passing thunderstorm, and the electricity could be used to perform the usual experiments.

Franklin, who had been planning to perform the experiment himself, decided to use a different method. The kite experiment was his response to the difficulty of obtaining a tall enough building or other structure to perform the original experiment. The kite allowed him to reach a sufficient height with minimal equipment.

The experiment was performed in June 1752, during a thunderstorm in Philadelphia. Franklin, accompanied by his son William, flew a kite made of a silk handkerchief and a hempen string, with a metal key attached to the string near the bottom. A silk ribbon, held by Franklin, connected to the key and provided insulation from the ground.

When the kite was caught by the storm, Franklin observed that the loose fibers of the hempen string stood on end, as if they were repelling each other, and that his hand, placed near the key, produced a spark. He had successfully drawn electricity from the storm, and the experiment confirmed his theory that lightning was a form of electricity.

The Results of the Experiment

The kite experiment produced several important results.

First, it confirmed Franklin’s theory that lightning was a form of electricity. The experiment demonstrated that the electrical fluid could be drawn from a thunderstorm using a pointed conductor, and that the electricity thus obtained had the same properties as laboratory electricity.

Second, it led to the development of the lightning rod. Franklin’s practical invention, the lightning rod, was a pointed metal rod erected on a building and connected to the ground by a wire. The lightning rod would draw the electrical discharge from a thunderstorm and conduct it safely to the ground, preventing damage to the building.

The lightning rod was rapidly adopted throughout Europe and America, and it became one of the first practical applications of scientific research. It was a powerful demonstration of the practical value of the new science, and it helped to establish the credibility of the scientific enterprise.

Third, it helped to establish the international reputation of American science. Franklin’s experiment was widely reported in the European scientific literature, and he was elected to the French Academy of Sciences and was awarded the Copley Medal of the Royal Society. The experiment helped to establish the American colonies as a serious participant in the international scientific community.

The Legacy of the Experiment

The kite experiment has had a lasting influence on the development of the modern science of electricity. The experiment is one of the most famous episodes in the history of science, and it is taught in schools and universities throughout the world. The image of Franklin, flying his kite in a thunderstorm, has become an iconic representation of the scientific enterprise.

The experiment also represents an important model of the scientific method. Franklin’s theory made specific predictions, the predictions were tested by experiment, and the experiment confirmed the theory. The procedure is a model of the proper relationship between theory and experiment in the natural sciences, and it has been an important inspiration for the subsequent development of the scientific method.

Further Reading

• The Stanford Encyclopedia of Philosophy (plato.stanford.edu), relevant entry
• The Cambridge Companion to [Thinker] (Cambridge University Press)
• Isaiah Berlin, Four Essays on Liberty (1969)