Franklin Demonstrates the Electrical Nature of Lightning Summary

  • Last updated on November 10, 2022

By drawing lightning from storm clouds, Franklin’s dangerous kite experiment conclusively demonstrated that lightning was a form of electricity. The experiment also offered further proof of his single-substance theory of electricity and showed that this fluidlike static energy could be passed from one object to another.

Summary of Event

Benjamin Franklin’s kite experiment Science;electricity started with two related questions: What is the nature of electricity? and Is lightning a form of electricity? Franklin indicated in his autobiography that prior to this particular investigation his interest in electricity had been inspired by Adam Spencer. Spencer had lectured on the subject in Boston in 1744 and then later, at Franklin’s invitation, in Philadelphia. Soon after, Franklin attempted various electrical tests, which he frequently reported in letters to his English friend Peter Collinson. Collinson read this correspondence at meetings of the Royal Society of London and eventually assisted in the London publication of Franklin’s letters in Experiments and Observations on Electricity Experiments and Observations on Electricity (Franklin) (1751-1754). Translated into several languages, this three-part work established Franklin’s reputation within the scientific communities of both Europe and the American colonies. [kw]Franklin Demonstrates the Electrical Nature of Lightning (June, 1752) [kw]Lightning, Franklin Demonstrates the Electrical Nature of (June, 1752) [kw]Nature of Lightning, Franklin Demonstrates the Electrical (June, 1752) [kw]Electrical Nature of Lightning, Franklin Demonstrates the (June, 1752) Electricity;and lightning[lightning] Lightning;as electricity[electricity] [g]American colonies;June, 1752: Franklin Demonstrates the Electrical Nature of Lightning[1370] [g]Scotland;June 5, 1755: Black Identifies Carbon Dioxide[1430] [c]Science and technology;June, 1752: Franklin Demonstrates the Electrical Nature of Lightning[1370] [c]Physics;June, 1752: Franklin Demonstrates the Electrical Nature of Lightning[1370] Franklin, Benjamin [p]Franklin, Benjamin;kite experiment Franklin, William

Benjamin Franklin found that lightning was a form of electricity, leading to his invention of the lightning rod.

(Library of Congress)

As early as 1749, Franklin had suspected that lightning was an electrical discharge from storm clouds. In a letter to Collinson, he observed that lightning and electricity shared similarities in color, crookedness of motion, and crackling sounds. If lightning is electricity, Franklin wondered, then how did the clouds obtain this electrical static? He conjectured that salt particles found in oceans rub against water to produce an electrical charge on the surface of the seas. Through evaporation, he further speculated, this charge rises to the clouds, which during certain types of encounters release this charge as lightning.

Franklin also observed that tall objects, such as steeples, trees, or ship masts, can trigger the release of electrical energy from clouds. To protect such structures from fires caused by lightning strikes, he recommended 10-foot-long “upright rods of iron made sharp as a needle” (lightning rods). Extended from the peaks of high structures, these devices would preemptively attract “electrical fire” from the clouds. Although his report on the kite experiment in the October 19, 1752, edition of The Pennsylvania Gazette states that a test of his lightning-rod theory succeeded in Philadelphia, it remains uncertain whether he personally ever conducted such a trial by this date.

On the other hand, it is virtually certain that with the assistance of his twenty-one-year-old son William in June, 1752, Franklin did indeed conduct a kite test of his theory of the electrical nature of lightning. In a letter to Collinson dated October 19, 1752, as well as in the Gazette article published that same month, Franklin reported that during a thunderstorm he flew a kite made of a silk handkerchief tied across cedarwood crosspieces. The kite had a tail, and a foot of wire extended as an antenna from its top end. The lower end of the twine descending from the kite was tied with an insulating silk ribbon, from which an iron key was suspended away from his hand by a cotton string. To keep the silk ribbon and the key dry during the storm, Franklin stood inside a doorway while flying the kite. When he passed his other hand over the key, a spark leaped from the key toward his knuckle. This transfer of energy proved that lightning was electrical in nature.

Franklin’s use of a pointed-tip conductor in the kite experiment also advanced the case for his single-substance (or one-fluid) theory of electricity. Electricity;one-fluid theory of[one fluid theory] At the time of his kite test, the prevalent European theory held that electricity comprised two separate opposing fluids, effluence and affluence. The kite experiment refuted this prominent theory by enabling Franklin to measure the charge of the lower part of storm clouds, which he found to be negative in nature. This reading supported his theory that electricity consisted of a single “electric fluid” that circulates among and through positively and negatively charged materials. Grouping different materials on the basis of their conductivity, Franklin concluded that “A body which is a good conductor of [electrical] fire readily receives it into its substance, and conducts it thro’ the whole to all the parts.”

The kite experiment showed, moreover, that the common substance of lightning’s electric fluid can be passed Electrical conductivity from one object to another. This principle of conductivity and transference so fascinated Franklin that three months after the kite experiment he fashioned an elaborate demonstration utilizing a 9-foot lightning rod that he had attached to the chimney of his home. This rod conveyed electricity through a glass-enclosed wire running down a stairwell to a bell, which was connected by another wire to a second bell. Both bells would ring whenever the lightning rod received an electrical charge. Sometimes so much current passed between the two bells that the entire staircase in Franklin’s home lit up brilliantly, as if “with sunshine, so that one might see to pick up a pin.” Franklin’s wife, legend holds, was not at all pleased by this noisy apparatus or by her husband’s other efforts to convert their home into a laboratory for electrical research.


Benjamin Franklin’s dramatic kite experiment became an instant legend. A recurrent subject for paintings and print illustrations over the centuries, the kite test is now ingrained in the world’s cultural memory of Franklin. As early as 1767, Joseph Priestley, in his History and Present State of Electricity, History and Present State of Electricity (Priestley) described this episode as a “capital” discovery, “the greatest, perhaps, that has been made in the whole compass of philosophy, since the time of Sir Isaac Newton.”

From the standpoint of the history of physics, however, the result of Franklin’s kite experiment with lightning is not considered as significant as Priestley thought. Franklin did not know that in France, a month before the Philadelphia kite test, experimenter Thomas-François Dalibard Dalibard, Thomas-François had already proved the electrical nature of lightning. This French undertaking, it is important to note, was thoroughly indebted to Franklin because it was based on findings Franklin had reported in the first volume of his highly regarded Experiments and Observations on Electricity. Franklin may have been second in proving that lightning was electricity, but it did not matter. His demonstration in Philadelphia was wonderfully theatrical and proved so appealing to a worldwide audience that others in Europe enthusiastically repeated his experiment.

The kite experiment in Philadelphia was, finally, most significant for the evidence it provided in support of two of Franklin’s major contributions to the study of physics: his single-substance theory of electricity and his related invention of the pointed-tip lightning rod, still used today. In 1754, two years after Franklin’s kite project, the Royal Society of London Royal Society, England awarded him the Copley Medal Copley Medal for his electrical research and soon admitted him as a fellow. In spite of initial resistance from the French scientific community, Franklin’s reputation for electrical research likewise quickly spread throughout continental Europe.

In America it was the pointed-tip lightning rod on the kite, more than his single-substance theory, that elevated Franklin’s fame. Franklin’s lightning-rod design, which would become the worldwide standard, was indeed more effective than the European blunt-tipped model. However, its effectiveness when employed to protect buildings from electrical fires resulting from lightning strikes was not its only value for Americans. The strategic foot of wire “made sharp as a needle” and extended skyward from the top of the kite’s wooden crosspieces was the prototype for the lightning rod that would become not only a practical invention but also an “electrifying” cultural symbol for eighteenth century America. Elated because this colonial device was superior to the European version, Americans proudly celebrated the design of Franklin’s lightning rod as a symbol of their new nation’s ingenuity and independence.

Further Reading
  • citation-type="booksimple"

    xlink:type="simple">Cohen, I. Bernard. Benjamin Franklin’s Science. Cambridge, Mass.: Harvard University Press, 1990. Cohen’s work, especially sensitive to Franklin’s Newtonian heritage, also discusses other kite experiments.
  • citation-type="booksimple"

    xlink:type="simple">Hankins, Thomas L. Science and the Enlightenment. New York: Cambridge University Press, 1985. Chapter 3 details the eighteenth century background of Franklin’s work with electricity.
  • citation-type="booksimple"

    xlink:type="simple">Schiffer, Michael Brian. Draw the Lightning Down: Benjamin Franklin and Electrical Technology in the Age of the Enlightenment. Berkeley: University of California Press, 2003. Presents Franklin as a leading figure in eighteenth century electrical research and especially highlights his theory of electricity and invention of the lightning rod.
  • citation-type="booksimple"

    xlink:type="simple">Tanford, Charles. Franklin Stilled the Waves. Durham, N.C.: Duke University Press, 1989. Chapters 2 and 3 feature Franklin’s work on electricity in the context of his other scientific experiments.

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