Benjamin Franklin: An American Life (20 page)

Also, by pouring out the water and metal inside a charged Leyden jar and not being able to elicit a spark, he found that the charge did not actually reside in them; instead, he correctly concluded, it was the glass itself that held the charge. So he lined up a series of glass plates flanked by metal, charged them up, wired them together, and created (and gave a name to) a new device: “what we called an electrical battery.”
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Electricity also energized his antic sense of fun. He created a charged metal spider that leaped around like a real one, he electrified the iron fence around his house to produce sparks that amused visitors, and he rigged a picture of King George II to produce a “high-treason” shock when someone touched his gilded crown. “If a ring of persons take the shock among them,” Franklin joked, “the experiment is called The Conspirators.” Friends flocked to see his shows, and he reinforced his reputation for playfulness. (In one of the weirder scenes in Thomas Pynchon’s novel
Mason & Dixon,
Franklin lines up some young men in a tavern to jolt them from his battery, shouting “All hold hands, Line of Fops.”)

As the summer of 1749 approached and the rising humidity made experiments more difficult, Franklin decided to suspend them until the fall. Although his findings were of great historical significance, he had yet to put them to practical use. He lamented to Collinson that he was “chagrined a little that we have hitherto been able to discover nothing in the way of use to mankind.” Indeed, after many revised theories and a couple of painful shocks that knocked him senseless, the only “use discovered of electricity,” said the man who was always trying to tackle his own pride, was that “it may help make a vain man humble.”

The end of the experimenting season gave an occasion for a “party of pleasure” on the banks of the river. Franklin described it in a letter to Collinson: “A turkey is to be killed for our dinners by the electrical shock; and roasted by the electrical jack, before a fire kindled by the electrified bottle; while the healths of all the famous electricians in England, France and Germany are to be drank in electrified bumpers, under the discharge of guns from the electrical battery.”

The frivolity went well. Though turkeys proved harder to kill than chickens, Franklin and friends finally succeeded by linking together a big battery. “The birds killed in this manner eat uncommonly tender,” he wrote, thus becoming a culinary pioneer of fried turkey. As for doing something more practical, there would be time for that in the fall.
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In the journal he kept for his experiments, Franklin noted in November 1749 some intriguing similarities between electrical sparks and lightning. He listed twelve of them, including “1. Giving light. 2. Color of the light. 3. Crooked directions. 4. Swift motion. 5. Being conducted by metals. 6. Crack or noise in exploding…9. Destroying animals…12. Sulpherous smell.”

More important, he made a connection between this surmise about lightning and his earlier experiments on the power of pointed metal objects to draw off electrical charges. “Electrical fluid is attracted by points. We do not know whether this property is in lightning. But since they agree in all particulars wherein we can already compare them, is it not probable they agree likewise in this?” To which he added a momentous rallying cry:
“Let the experiment be made.”

For centuries, the devastating scourge of lightning had generally been considered a supernatural phenomenon or expression of God’s will. At the approach of a storm, church bells were rung to ward off the bolts. “The tones of the consecrated metal repel the demon and avert storm and lightning,” declared St. Thomas Aquinas. But even the most religiously faithful were likely to have noticed this was not very effective. During one thirty-five-year period in Germany alone during the mid-1700s, 386 churches were struck and more than one hundred bell ringers killed. In Venice, some three thousand people were killed when tons of gunpowder stored in a church was hit. As Franklin later recalled to Harvard professor John Winthrop, “The lightning seems to strike steeples of choice and at the very time the bells are ringing; yet still they continue to bless the new bells and jangle the old ones whenever it thunders. One would think it was now time to try some other trick.”
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Many scientists, including Newton, had noted the apparent connection between lightning and electricity. But no one had declared “Let the experiment be made,” nor laid out a methodical test, nor thought of the practicality of tying this all in with the power of pointed metal rods.

Franklin first sketched out his theories about lightning in April 1749, just before his end-of-season turkey fry. The water vapors in a cloud can be electrically charged, he surmised, and the positive ones will separate from the negative ones. When such “electrified clouds pass over,” he added, “high trees, lofty towers, spires, masts of ships…draw the electrical fire and the whole cloud discharges.” It was not a bad guess, and it led to some practical advice: “Dangerous therefore it is to take shelter under a tree during a thunder gust.” It also led to the most famous of all his experiments.
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Before he tried to conduct his proposed experiments himself, Franklin described them in two famous letters to Collinson in 1750, which were presented to the Royal Society in London and then widely published. The essential idea was to use a tall metal rod to draw some of the electrical charge from a cloud, just as he had used a needle to draw off the charge of an iron ball in his lab. He detailed his proposed experiment:

Franklin’s one mistake was thinking that there would be no danger, as at least one European experimenter fatally discovered. His suggestion of using a wire held with an insulating wax handle was a smarter approach.

If his suppositions held true, Franklin wrote in another letter to Collinson, then lightning rods could tame one of the greatest natural dangers people faced. “Houses, ships and even towns and churches may be effectually secured from the stroke of lightning by their means,” he predicted. “The electrical fire would, I think, be drawn out of a cloud silently.” He wasn’t certain, however. “This may seem whimsical, but let it pass for the present until I send the experiments at large.”
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Franklin’s letters were excerpted in London by
The Gentleman’s Magazine
in 1750 and then published as an eighty-six-page booklet the following year. More significant, they were translated into French in early 1752 and became a sensation. King Louis XV asked that the lab tests be performed for him, which they were in February by three Frenchmen who had translated Franklin’s experiments, led by the naturalists Comte de Buffon and Thomas-François D’Alibard. The king was so excited that he encouraged the group to try Franklin’s proposed lightning rod experiment. As a letter to London’s Royal Society noted, “These applauses of his Majesty having excited in Messieurs de Buffon, D’Alibard and de Lor a desire of verifying the conjectures of Mr. Franklin upon the analogy of thunder and electricity, they prepared themselves for making the experiment.”

In the village of Marly on the northern outskirts of Paris, the Frenchmen constructed a sentry box with a 40-foot iron rod and dragooned a retired soldier to play Prometheus. On May 10, 1752, just after 2 in the afternoon, a storm cloud passed over and the soldier was able to draw sparks as Franklin had predicted. An excited local prior grabbed the insulated wire and repeated the experiment six times, shocking himself once but surviving to celebrate the success. Within weeks it was replicated dozens of times across France. “M. Franklin’s idea has ceased to be a conjecture,” D’Alibard reported to the French Royal Academy. “Here it has become a reality.”

Though he did not yet know it, Franklin had become an international sensation. An ecstatic Collinson wrote from London that “the Grand Monarch of France strictly commands” that his scientists convey “compliments in an express manner to Mr. Franklin of Philadelphia for the useful discoveries in electricity and application of the pointed rods to prevent the terrible effects of thunderstorms.”
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The following month, before word of the French success reached America, Franklin came up with his own ingenious way to conduct the experiment, according to accounts later written by himself and his friend the scientist Joseph Priestley. He had been waiting for the steeple of Philadelphia’s Christ Church to be finished, so he could use its high vantage point. Impatient, he struck on the idea of using instead a kite, a toy he had enjoyed flying and experimenting with since his boyhood days in Boston. To do the experiment in some secrecy, he enlisted his son, William, to help fly the silk kite. A sharp wire protruded from its top and a key was attached near the base of the wet string, so that a wire could be brought near it in an effort to draw sparks.

Clouds passed over to no effect. Franklin began to despair when he suddenly saw some of the strands of the string stiffen. Putting his knuckle to the key, he was able to draw sparks (and, notably, to survive). He proceeded to collect some of the charge in a Leyden jar and found it had the same qualities as electricity produced in a lab. “Thereby the sameness of electrical matter with that of lightning,” he reported in a letter the following October, was “completely demonstrated.”

Franklin and his kite were destined to be celebrated not just in the annals of science but also in popular lore. Benjamin West’s famous 1805 painting,
Franklin Drawing Electricity from the Sky,
mistakenly shows him as a wrinkled sage rather than a lively 46-year-old, and an equally famous nineteenth-century Currier and Ives print shows William as a little boy rather than a man of about 21.

Even among scientific historians, there is some mystery about Franklin’s celebrated kite flying. Although it supposedly took place in June 1752, before word had reached him of the French tests a few weeks earlier, Franklin made no public declaration of it for months. He did not mention it in the letters he wrote Collinson that summer, and he apparently did not tell his friend Ebenezer Kinnersley, who was lecturing on electricity in Philadelphia at the time. Nor did he publicly report his kite experiment even when word reached him, probably in late July or August, of the French success. His
Pennsylvania Gazette
for August 27, 1752, reprinted a letter about the French experiments, but it made no mention that Franklin and his son had already privately confirmed the results.

The first public report came in October, four months after the fact, in a letter Franklin wrote to Collinson and printed in his
Pennsylvania Gazette.
“As frequent mention is made in the public papers from Europe of the success of the Philadelphia Experiment for drawing the electric fire from the clouds,” he wrote, “it may be agreeable to the curious to be informed that the same experiment has succeeded in Philadelphia, though made in a different and more easy manner.” He went on to describe the details of constructing the kite and other apparatus, but in an oddly impersonal way, never using the first person to say explicitly that he and his son had carried it out themselves. He ended by expressing pleasure that the success of his experiments in France had prompted the installation of lightning rods there, and he made a point of noting that “we had before placed them upon our academy and state house spires.” The same issue of the paper advertised the new edition of
Poor Richard’s Almanack,
with an account of “how to secure houses, etc., from lightning.”

A more colorful and personal account of the kite flying, including the details about William’s involvement, appeared in Joseph Priestley’s
The History and Present State of Electricity,
first published in 1767. “It occurred to him that, by means of a common kite, he could have a readier and better access to the regions of thunder than by any spire whatever,” Priestley wrote of Franklin, and “he took the opportunity of the first approaching thunder storm to take a walk into a field, in which there was a shed convenient for his purpose.” Priestley, a noted English scientist, based his account on information directly from Franklin, whom he first met in London in 1766. Franklin supplied Priestley with scientific material and vetted the manuscript, which ends with the flat declaration: “This happened in June 1752, a month after the electricians in France had verified the same theory, but before he had heard of anything they had done.”
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The delay by Franklin in reporting his kite experiment has led some historians to wonder if he truly did it that summer, and one recent book even charges that his claim was a “hoax.” Once again, the meticulous I. Bernard Cohen has done an exhaustive job of historical sleuthing. Drawing on letters, reports, and the fact that lightning rods were erected in Philadelphia that summer, he concludes after forty pages of analysis that “there is no reason to doubt that Franklin had conceived and executed the kite experiment before hearing the news of the French performance.” He goes on to say that it was performed “not only by Franklin but by others,” and he adds that “we may with confidence conclude that Franklin performed the lightning kite experiment in June 1752, and that soon after, in late June or July 1752, it was in Philadelphia that the first lightning rods ever to be erected were put in service.”
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