Most Americans are familiar with the story of Benjamin Franklin and his famous 18th-century experiment in which he attached a metal key to a kite during a thunderstorm to see if the lightning would pass through the metal. That's largely due to many iconic illustrations commemorating the event that found their way into the popular imagination and became part of our shared cultural lore. But most of those classic illustrations are riddled with historical errors, according to a new paper published in the journal Science and Education.
Franklin's explorations into electricity began as he was approaching 40 years old after his thriving career as an entrepreneur in the printing business. His scientific interest was piqued in 1743 when he saw a demonstration by scientist/showman Archibald Spencer, known for performing various amusing parlor tricks involving electricity. He soon started a correspondence with a British botanist named Peter Collinson and began reproducing some of Spencer's impressive parlor tricks in his own home.
He would have guests rub a tube to create static and then have them kiss, producing an electrical shock. He designed a fake spider suspended by two electrified wires so that it seemed to swing back and forth of its own accord. And he devised a game dubbed "Treason," whereby he wired up a portrait of King George so that anyone who touched the monarch's crown would be shocked. And he once infamously shocked himself while trying to kill a turkey with electricity.
Among his many insights into the phenomenon, Franklin noted how sparks jumped between objects and concluded that lightning was merely a massive electric spark, similar to those produced from charged Leyden jars. To test his theory about the nature of lightning, Franklin published a paper proposing an experiment with an elevated iron rod wire to “draw down the electric fire” from a cloud, with the experimenter standing on insulated ground in the protection of an enclosure similar to a soldier’s sentry box. Franklin reasoned that an electrified cloud passing over the pointed rod would pull electricity from the cloud, such that if the man moved the knuckle of his finger closer to the metal rod, there should be sparks.
There's no record of Franklin performing his sentry-box experiment, per Breno Arsioli Moura, a science history educator at the Federal University of the ABC in Brazil who authored the new paper. But a Frenchman named Thomas-Francois D’Alibard did. D'Alibard read Franklin's published paper and used a 50-foot-long vertical rod to perform his version of the sentry-box experiment in Paris on May 10, 1752. Others across Europe soon followed suit. It was a rather dangerous experiment, as evidenced by the unfortunate Georg Wilhelm Richmann. He also attempted to reproduce the experiment, but a glowing ball of charge traveled down the string, jumped to his forehead, and killed him instantly—perhaps the first documented instance of ball lightning.
It seems Franklin didn't know about these attempts when he devised his simpler kite experiment along similar conceptual lines. The established account goes something like this: Anticipating a thunderstorm in June 1752, on the outskirts of Philadelphia, Franklin built a kite out of two strips of cedar nailed together in the shape of a cross or “X,” with a large silk handkerchief forming the body, since silk could withstand the wet and wind of a thunderstorm. He attached a wire to the top of the kite to serve as a makeshift lightning rod. Hemp string was attached to the bottom of the kite to provide conductivity and attached to a Leyden jar by a thin metal wire. Also attached to the hemp was a silk string held by Franklin. Joining the hemp and silk strings was a metal key.
Next, Franklin stood under a shed roof to ensure he held a dry portion of the silk string to keep it from becoming conductive. Franklin’s son, then 21, assisted him in raising the kite, and they settled down to wait. Eventually, Franklin observed the loose filaments of twine “stand erect,” indicating electrification. He pressed his knuckle to the key and was rewarded with an electric spark. This proved that lightning was static electricity. Contrary to popular myth, Franklin wasn't struck by lightning; if he had been, he likely would not have survived. The spark resulted from the kite/key system being in a strong electric field.
According to Moura, there are two primary historical sources for the aforementioned details about the kite experiment. One is a short letter written in October of that same year by Franklin to Collinson, reproduced in The Philadelphia Gazette (with some textual differences). The other account was written 15 years later by Franklin's friend and colleague, Joseph Priestley, in the latter's 1767 treatise, The History and Present State of Electricity.
Franklin's letter focused primarily on describing the kite, and he never confirmed in the text whether the experiment was performed. Priestley's account contained more specific details on the experimental setup and noted that Franklin conducted the experiment with the help of his son. Most historians assume that since Priestley consulted with Franklin (who was in London at the time) while writing his treatise, this account is probably largely accurate, though Franklin may have misremembered some of the details more than a decade later.
But there are some notable differences between the two accounts, per Moura. For instance, Franklin emphasized the importance of taking shelter to keep the silk ribbon and key from getting wet, while Priestley mentions the shelter but not why it was necessary. The implication is that Franklin conducted the experiment in an open field. Priestley also offered a clearer description of the precise role of the silk ribbon: to insulate the system. And while Franklin insisted that no lightning should strike the kite, Priestley writes of lightning "descending" the string, with the sparks charging the Leyden jar.
Moura notes that neither of these primary accounts contained any illustrations of the kite experiment. In fact, while scouring various online databases and archives, he found none produced in the 18th century; most were dated from the 19th century. (He did find a few 18th-century illustrations of others performing the experiment.) For this study, Moura selected seven representative illustrations: four published in books, one that appeared in a magazine, one Currier and Ives lithograph (see top image), and one vignette by an artist named Alfred Jones produced by the Bureau of Engraving and Printing.
Most included details that suggested the artists were heavily influenced by Priestley's 1767 account, but Moura found multiple historical errors in these illustrations. For instance, several depict Franklin's son as a boy, even though William Franklin would have been 21 at the time. Many also depict Franklin performing the experiment in the open air rather than taking shelter to avoid electrocution. The Leyden jar is also conspicuously absent in these illustrations.
“In most cases, the kite is being struck by lightning, or lightning bolts are very near it, although Franklin did not want to draw a lightning strike down upon himself," said Moura. "Most illustrations don’t show the silk ribbon that was meant to insulate the kite. Franklin simply holds the string. If that had been the case, he would have earthed the kite and ruined the experiment. One illustration shows Franklin holding the key near or on the string, which isn’t warranted by any account.”
Granted, these were all popular illustrations by artists with little to no scientific background and were never intended for educational purposes. But according to Moura, their inaccuracies still matter precisely because they were so influential, coloring our perception of the famous kite experiment even centuries later.
"An accurate remake of the illustrations based on this study might allow students and teachers to have a better comprehension of the design of the experiment as originally proposed by Franklin, both regarding the elements of the kite and how it worked," Moura concluded. "We must look carefully at the pictures portraying science scenes before considering them as actual and precise representations."
DOI: Science and Education, 2023. 10.1007/s11191-023-00421-y (About DOIs).
