The First American: The Life and Times of Benjamin Franklin (40 page)

In February
1750 Franklin responded to William Watson’s query about killing turkeys. “Please to acquaint him that we made several experiments on fowls this winter,” Franklin wrote Collinson. Recounting the details of charging the apparatus, he reported that a full charge sufficed to kill chickens outright. “But the turkeys, though thrown into violent convulsions, and then lying as dead for some minutes, would recover in less than a quarter of an hour.” Not to be denied, Franklin linked several electrical jars together, which jointly succeeded. “We killed a turkey with them of about 10 lb. wt. and suppose they would have killed a much larger. I conceit that the birds killed in this manner eat uncommonly tender.”

In the process of electrocuting birds, Franklin nearly electrocuted himself. The experience was enlightening, if jolting.

I found that a man can without great detriment bear a much greater electrical shock than I imagined. For I inadvertently took the stroke of two of those jars through my arms and body, when they were very near full charged. It seemed an universal blow from head to foot throughout the body, and was followed by a violent quick trembling in the trunk, which gradually wore off in a few seconds. It was some moments before I could collect my thoughts so as to know what was the matter; for I did not see the flash though my eye was on the spot of the prime conductor from whence it struck the back of my hand, nor did I hear the crack though the by-standers say it was a loud one; nor did I particularly feel the stroke on my hand, though I afterwards found it had raised a swelling there the bigness of half a swan shot or pistol bullet. My arms and back of my neck felt somewhat numb the remainder of the evening, and my breastbone was sore for a week after, as if it had been bruised. What the consequence would be, if such a shock were taken through the head, I know not.

Yet he could guess. From time immemorial humans had speculated on the nature and cause of lightning. That it was a form of fire—indeed, the first fire, the
fulmen fulminis,
as it came to be called—had seemed clear at least since the Greeks sang of Prometheus stealing fire from the heavens. The sulfurous smell that often accompanied lightning reinforced this view. As to the cause of lightning and the accompanying thunder, for long centuries most mortals were willing to account it supernatural. The gods were angry and in their anger hurled thunderbolts at each other or at the earth. The elder Pliny, one of the few ancients to look for a natural explanation, called thunder an “earthquake of the air”—which did not advance the discussion very far, since no one knew what caused earthquakes. The sulfurous smell of lightning reinforced this—spurious—connection, in that sulfurous flames were associated with Hades and the nether regions of the earth.

Not until the early eighteenth century, apparently, did anyone draw a connection between lightning and electrical phenomena. In 1716 Newton described an experiment in which a needle was brought close to a piece of amber that had been rubbed with silk. “The flame putteth me in mind of sheet lightning on a small—how very small—scale,” he wrote. As electrical investigators learned to generate larger charges, and larger sparks, the similarity between the discharges in the heavens and the discharges in the laboratory grew more compelling. By the time Franklin took up the study of electricity, the notion that lightning was electric was commonplace among the cognoscenti.

But plenty of history’s commonplace ideas—from the flatness of the earth to the faster falling of heavy objects—had proven, on closer examination, to be wrong; what remained in the puzzle of the lightning was for the electrical conjecture to be tested. This was precisely what Franklin proposed to do.

In April 1749 Franklin wrote a long letter to John Mitchell, a colleague of Peter Collinson and likewise a fellow of the Royal Society. In this letter he put forward a complex theory of lightning with a fairly simple essence: that particles of water in thunderclouds became electrically charged by their wind-borne jostling, and that lightning was nothing more than the discharge of the pent-up electrical force. This theory supported certain recommendations, which in turn comported with
observation. For instance, a person caught out in a thunderstorm ought not to seek shelter beneath a lone tree, for the tree would tend to channel the electrical discharge to the ground—and to whoever happened to be at the base of the tree. “It has been fatal to many,” Franklin noted. The unlucky person caught by the storm should remain in the open for a second reason. “When clothes are wet, if a flash, in its way to the ground, should strike your head, it will run in the water over the surface of your body; whereas if your clothes were dry, it would go through the body. Hence a wet rat can not be killed by the exploding electrical bottle, when a dry rat may.”

Upon their arrival in London, these results won Franklin further praise from the Royal Society. “Your very curious pieces relating to electricity and thundergusts have been read before the Society,” Peter Collinson reported back, “and have been deservedly admired not only for the clear intelligent style but also for the novelty of the subjects.”

Franklin was delighted to hear this, as the piece was his most ambitious venture into the theory of electricity. The encouragement prompted him, during the next few weeks, to offer an exceedingly practical recommendation that followed from his theory. One aspect of the theory involved “points”: sharp metal objects that could draw off electrical charges before they reached alarming levels. “The doctrine of
points
is very curious,” Franklin told the Royal Society, through Collinson, “and the effects of them are truly wonderful; and from what I have observed on experiments, I am of opinion that houses, ships, and even towns and churches may be effectually secured from the stroke of lightning by their means.” Customarily church spires and weathercocks were topped by round balls of brass or wood; these allowed the charge to build excessively. Let them be replaced by “a rod of iron, 8 or 10 feet in length, sharpened gradually to a point like a needle, and gilt to prevent rusting, or divided into a number of points, which would be better—the electrical fire would, I think, be drawn out of a cloud silently, before it could come near enough to strike…. This may seem whimsical, but let it pass for the present, until I send the experiments at large.”

The experiments were designed to test aspects of Franklin’s theory; the one that proved most important dealt directly with the fundamental question of whether lightning and electricity were the same. “To determine the question, whether the clouds that contain lightning are electrified or not, I would propose an experiment to be tried where it might be done conveniently.” That is:

On the top of some high tower or steeple, place a kind of sentry box big enough to contain a man and an electrical stand. From the middle of the stand let an iron rod rise, and pass bending out of the door, and then upright 20 or 30 feet, pointed very sharp at the end. If the electrical stand be kept clean and dry, a man standing on it when such clouds are passing low, might be electrified, and afford sparks, the rod drawing fire to him from the cloud.

Franklin saw little danger in this test, but for apprehensive persons he suggested that the observer in the box hold a grounded wire by insulated handles; from time to time he could bring the wire close to the iron rod, drawing off any sparks without endangering himself.

By now Franklin was well known among the small community of English electricians; when Collinson published this paper and Franklin’s letters on electricity in 1751, Franklin’s circle of scientific admirers expanded swiftly. The circle encompassed King Louis of France, whose curiosity had progressed beyond dancing guardsmen and leaping monks. The monarch’s interest inspired two intrepid French experimenters, Messieurs d’Alibard and de Lor, to put Franklin’s conjecture to his test. In May 1752 d’Alibard reported just such sparks as Franklin had predicted; a week later de Lor recapitulated the test, with similar results.

Apparently both men eschewed the precautions Franklin prescribed for the faint of heart; by their good luck the storms they encountered were quite mild. At least three English experimenters were similarly fortunate, as, evidently, was an electrician in Berlin. In 1753, however, a Swedish scientist in St. Petersburg, Georg Wilhelm Richmann, suffered a fatal shock while conducting Franklin’s experiment in a more severe storm.

Perhaps ironically, perhaps understandably, Richmann’s death simply enhanced Franklin’s growing fame. It demonstrated, if demonstration were necessary, that electricity was no mere plaything. It underscored the utility, indeed necessity, of Franklin’s lightning rods. And it made Franklin out to be braver, in the pursuit of science, than he actually was.

Yet he was no coward. In June 1752, after the French trials were successfully performed but before the news of them reached America, Franklin himself conducted a variant of his experiment. He would have done so earlier had he not believed that the tower or steeple he spoke of needed to be quite tall—taller than anything in Philadelphia. As it happened, the vestrymen of Christ Church had decided to erect a new steeple; Franklin was waiting for the construction to be completed.
(Perhaps with an eye toward asking permission to tempt heaven from the steeple, nonmember Franklin was one of the first contributors to the construction fund. He subsequently managed a lottery to complete the fund-raising.)

Meanwhile, however, he conceived another route to the heart of the storm. Likely recalling the kite he had employed to pull himself across the Mill Pond in Boston, he proposed to fly another, this mounted with a miniature lightning rod. The kite would be made of silk rather than paper. “Silk is fitter to bear the wet and wind of a thunder gust without tearing,” he explained. Hemp twine would run from the kite to the ground. Dry, hemp conducted electricity moderately well; wet, it would “conduct the electric fire freely.” At the ground a large key was to be tied to the twine; this would absorb the electric charge that ran down the string. Lest the kite-flyer—Franklin himself—be jolted, a silk ribbon should be attached to the string at the bottom. This must be kept dry (the kite-flyer would stand in a doorway); if it was, it would insulate the flyer’s hand from the wet twine and key.

Although Franklin could discern no flaws in the design of the experiment, he was insufficiently sure of himself to risk a public demonstration. So he surreptitiously enlisted William as his aide and found a lonely field, with a shed and the requisite doorway, where the two of them might hazard their lives but not their reputations.

Summer brought thunderstorms and the opportunity to test both his theory and his experimental design. A promising storm blew up one afternoon, with thunderheads rising high. Franklin and son launched their kite; it soared toward the base of the cloud. But nothing happened. The key gave no indication of absorbing an electrical charge. Franklin could not understand where he had miscalculated. Joseph Priestley, to whom Franklin related the afternoon’s events, described what happened next:

At length, just as he was beginning to despair of his contrivance, he observed some loose threads of the hempen string to stand erect, and to avoid one another, just as if they had been suspended on a common conductor. Struck with this promising appearance, he immediately presented his knuckle to the key, and (let the reader judge of the exquisite pleasure he must have felt at that moment) the discovery was complete. He perceived a very evident electric spark. Others succeeded, even before the string was wet, so as to put the matter past all dispute, and when the rain had wet the string, he collected electric fire very copiously.

Franklin
appreciated the recognition that came with his growing scientific reputation, but there were times when he preferred anonymity. This preference had given birth to Silence Dogood; so also to Martha Careful and Caelia Shortface. None of these worthy women, however, became as famous as Polly Baker, who in the late 1740s embarked on a transatlantic career that for a time outshone Franklin’s own.