Even before the Evans map, Franklin had been thinking about Atlantic storms for some time. He had intended to explain them to Jared Eliot, a Connecticut clergyman and physician, another in Franklin’s expanding network of correspondents. In a letter of 1747, Franklin told Eliot that storms along the Atlantic coast moved southwest to northeast (up the coast of North America) even though the prevailing winds blew northeast to southwest, “i.e. the Air is in violent Motion in Virginia before it moves in Connecticut” even as the wind itself seemed to move in the opposite direction. There were exceptions, he noted, but the pattern was frequent, and the worst storms were always leeward rather than windward. Franklin promised to give Eliot “Reasons for this Opinion” in his next letter but then became too entranced by electricity to do so.11
Eliot waited almost two years before he learned Franklin’s “Reasons.” In 1750, Franklin finally related how he had wanted to observe a lunar eclipse several years earlier. He was foiled by a sudden storm that, blowing northeastward, drew clouds over the moon. He was then surprised to learn that the eclipse had been visible in Boston—why, if the storm came from the northeast, had it not obscured skies in Boston earlier than in Philadelphia? By questioning travelers and correspondents, he found that this was “a constant Fact, that N East Storms begin to Leeward; and are often more violent there than farther to Windward.” The reason, he believed, lay far to the south, in the Gulf of Mexico and the Florida straits. There, air was “heated by the Sun,” and being thus “rarified,” it drifted northward, where it met the “chill’d and condens’d” air over the British colonies. The collision sent the warm air still higher even as the cool draft sank, with each current tending in the opposite direction, warm to the north and cold to the south. This created a whirling corkscrew, with cooler eddies that curled under, slinking northeast to southwest.12
These descriptions of Atlantic storms betray their intellectual ancestry. Both Franklin’s 1726 observation of drifting gulfweed and his experiments with heat had primed him to see storms as products of thermal variation and circulation. Franklin’s letter to Eliot even compared windflow along North America’s coast to the way in which “a Fire in my Chimney” created an upper outflow of heat that eventually met a cooler, lower “Current of Air constantly flowing from the Door to the Chimney.” Like a Pennsylvania fireplace, North America channeled currents of air. The Appalachian range, running from northeast to southwest and parallel to the coast, helped propel winds alongside the “Continent.” Again, Franklin had generated universal principles from local observations.13
Perhaps Atlantic storms might reveal more general properties of nature, particularly when they produced electricity. How did storm clouds become electrified? When they were, did they tend to carry a positive or a negative charge? If clouds could carry a charge, Franklin reasoned, electricity must exist in the atmosphere. Lightning, which certainly looked like a spiky electrical discharge, was just that.
Friction explained everything. In the early 1750s, Franklin explained to several correspondents that atmospheric electricity made sense if one assumed, as he did, that matter was made of particles. The sea clouds that seemed to generate electricity were, for example, constituted of water and salt; the particles of each coexisted without transforming one another. “The separate Particles of Water” were like “hard Spherules, capable of touching the Salt only in Points” where their outside curves touched. (See his “Fig. VI” on the plate of illustrations that accompanied his Experiments and Observations. ) The friction they created had to produce atmospheric electricity, Franklin theorized, much as the friction between a revolving glass “Globe” and a “Cushion” produced static electricity. Saltwater thus had “constituent Particles of Salt and Water (as in a Sea of Globes and Cushions).” Franklin realized that this finding meant “there must be Interstices” within any form of matter, “yet the Mass incompressible.” In 1753, he would portray air, which conducted electricity, as doing so through its “Particles,” which “in hard Gales of Wind,” friskily rubbed themselves against things like trees and houses “as [if] so many minute electric Globes, rubbing against nonelectric Cushions.”14
So Franklin had a hypothesis. What he needed next was an experiment to demonstrate that electricity did occur in the atmosphere, most dramatically as lightning. He would propose elevating a pointed metal rod into the clouds to conduct atmospheric electricity downward, where its properties could be verified.
Electrical points, made in Philadelphia. Benjamin Franklin, New Experiments and Observations on Electricity (1754). HOUGHTON LIBRARY, HARVARD UNIVERSITY.
In July 1750, Franklin suggested an experiment “on the Top of some high Tower or Steeple.” There, an investigator would stand on an insulated floor within a “Sentry Box” (see Franklin’s “Fig. IX” above) that supported an ascending metal rod with a point. The pointed rod would, like an experimental bodkin (“Fig. VIII”), draw electricity down in a particulate stream, making the sentry equally (but not fatally) “electrified” with the atmosphere.15
Collinson had this protocol read to the Royal Society—further evidence that Franklin’s work mattered in the metropolis. Then, Edward Cave published all of Franklin’s electrical letters in April 1751 as Experiments and Observations on Electricity, Made at Philadelphia in America, by Mr. Benjamin Franklin . . . , edited and introduced by London physician John Fothergill, Fellow of the Royal Society (FRS), who seems to have done so at Collinson’s request. After this edition appeared in London, it was translated into French and published in Paris in 1752. These printed instructions invited (or perhaps dared) interested men of science to try Franklin’s experiments, including the sentry box test.16
Who would risk it? Several Frenchmen, as it turned out, were willing to do so. Franklin had the good fortune to be caught up, perhaps unwittingly, in a distant battle between French Cartesians and Newtonians. The Cartesians blocked acceptance of Newtonianism in France. They ridiculed universal gravitation and championed instead their master’s assertion that vortices in elementary bits of matter explained everything. A few, including Pierre Louis Moreau de Maupertuis, defended Newton, arguing that gravitation must create a shortening of the earth’s axis, resulting in the earth’s fattening at the equator and flattening at the poles. Two geodesic expeditions, one to Peru in 1735 and the other to Lapland in 1736, set out to measure the earth. Charles-Marie de La Condamine went on the expedition to Peru that measured several degrees of the meridian near the equator, and Maupertuis led the venture that did the same in Arctic Lapland. Their measurements confirmed a shortening of the earth’s axis.17
But the Cartesians fumed and refused to yield ground, insisting on their superior attention to mechanical causes—such as those underpinning the Abbé Nollet’s theories of electricity—as opposed to vague Newtonian forces. The stalemate continued. The Newtonian Georges Leclerc (later Comte de Buffon) and the Cartesian Antoine Ferchault de Réaumur, who was Nollet’s patron, had been sandbagging each other for years. Then, in 1751, Buffon read Franklin’s essays and discovered something wonderful: a mere colonial, in far-off Philadelphia, had devised a convincing theory of electricity that supported Newton’s claims. (Note the timing. War between France and Britain had ended in 1748—it was, politically, an uncontroversial moment for a Frenchman to sing the praises of a Pennsylvanian.) Buffon made sure an ally, Jean François Dalibard, translated Franklin’s book. Then, in 1752, Buffon and Dalibard showed Franklin’s indoor experiments to the king. This was a direct rebuke of Nollet, who was the king’s official experimenter.18
In May 1752, Dalibard instructed an assistant to perform “the Philadelphia experiment” at Marly, outside Paris. The attempt worked: a pointed metal rod conducted atmospheric electricity down to the earth. A later experiment by a still-unidentified man named “Delor” in Paris confirmed the finding. Nollet sputtered and pointed out problems with Franklin’s theory, including the odd concept of electrical atmospheres. What were these? What did they explain, anyway? Rega
rdless, Dalibard and Delor published their results immediately, and Franklin was now famous in a place (and a way) he had never expected to be. Translated, the two French reports appeared in two London newspapers. June’s Gentleman’s Magazine featured a letter from a convert in Paris, who confessed how “we ridiculed Mr Franklin’s project for emptying clouds of their thunder” and “could scarce conceive him to be any other than an imaginary Being.” In August, the London Magazine version of the reports appeared in the Pennsylvania Gazette, Franklin’s former paper. After a celebrated tour of Europe, the Philadelphia experiment had come home.19
What did Franklin think of the Descartes-Newton debate, the one that had made him a success? He didn’t give a fart. He said so in 1780, when living in France. When he read some philosophical questions the Royal Academy of Brussels had just proposed, offering medals for the best replies, Franklin hooted at what he perceived as the preciousness of the mathematical question. It reminded him of the kind of sterile academic debate that had consumed the French Cartesians and Newtonians for almost half a century. So Franklin wrote a bagatelle, a slight and amusing essay, purporting to address “the Royal Academy of * * * * *” on the problem of human flatulence. “What Comfort can the Vortices of Descartes give to a Man who has Whirlwinds in his Bowels! The Knowledge of Newton’s mutual Attraction of the Particles of Matter, can it afford Ease to him who is rack’d by their mutual Repulsion, and the cruel Distensions it occasions?”20
For decades, Franklin kept his indifference to the theories of his French detractors to himself, but then, he finally let it out. This gaseous essay is Franklin’s only mention of Descartes, ever. Was he Newtonian? Yes. Was he anti-Cartesian? No, not really. Then, was he pro-Franklin? Ah, that was the whole point, the reason never to acknowledge criticism, starting with Nollet’s.
Remember again Poor Richard’s advice: make haste slowly. Franklin cared only for his own success, not the theories, objections, or resentments of others. He did seem to know something about the Cartesian-Newtonian debate. He followed the geodesic expeditions that, by measuring the flattening of the earth, indicated the force of gravity. He requested the account of Maupertuis’s expedition from James Logan in 1748, and when he commented on Indians’ susceptibility to smallpox in 1750, he cited La Condamine. He had followed the triumphs of these Newtonians just as he himself was making an impact in France.21
But he knew better than to claim a place in the debate. As he had learned as clerk in the Pennsylvania Assembly, passionate and prolonged argument on one side of a question could make enemies. The republic of letters expected its citizens to be sociable and to use wit and persuasion, not angry denunciation or guile. (This expectation was sometimes honored in the breach, as Buffon and Nollet had made very clear.) So Franklin carefully crafted his statements on nature, then let them fare for themselves, whatever detractors might say. He started to compose a letter to Nollet in 1754 but never sent it—hence his belated (and coded) comment on the Newton-Descartes debate in 1780, the closest he ever came to a response to Nollet.22
Yet given how much he wanted to promote himself, it must have been frustrating for him to contemplate, in 1752, that he could not even execute his own experiment, sticking a pointed probe into the clouds. Philadelphia, vexingly, lacked any site high enough for Franklin to do the demonstration, even when the city crackled with thunderstorms—the Pennsylvania Gazette for 1752 snapped with references to lightning and thunder.23
So Franklin thought of another method, his kite experiment. In two elegant paragraphs, he told readers of the Pennsylvania Gazette in the fall of 1752 how to build, from wood, cotton, silk, and metal, an electrical apparatus. “Make a small Cross of two light Strips of Cedar,” he advised, and then knot to the frame a silk handkerchief and attach a wire point. This kite would conduct electricity down a cotton string terminating in a silk ribbon tied to a metal object, the famous key. The experimenter was to watch for a promising set of rumbling clouds and then send up the kite. The critical moment had arrived when the kite-string’s fibers would “stand out every [which] Way”—it was electrified. The experimenter should then calmly allow the rain to wet the kite and string but not the ribbon and key, so that when the ribbon was lashed to the kite-string, “the Electric Fire” would “stream out plentifully from the Key on the Approach of your Knuckle.”24
If this protocol seems sketchy, maybe that is because Franklin had forgotten to mention one very important element: an assistant (and witness). Twenty years after the Pennsylvania Gazette description of his kite had appeared, Franklin would assure electrical experimenter Joseph Priestley that he had flown one shortly after Dalibard’s assistant had done the sentry box version but before news of this got back to him. When he made this claim, Franklin finally remembered to note that his son, William, had “assisted him in raising the kite.”25
So we have to think of the experiment as a two-person operation, involving William (or “Wet”) Franklin (WF) and Benjamin or (“Bone-dry”) Franklin (BF). WF went out with the kite, set it aloft, watched for the prickling of fibers on its string, and then got everything thoroughly wet. Consequently, WF got soaked but could have contemplated his father’s cheerful assertion that “a wet Rat can not be kill’d” by electricity “when a dry Rat may.” Meanwhile, BF, the dry rat, stood inside some kind of shelter, keeping the ribbon and key dry. After WF sloshed inside, tugging the kite behind, BF attached the ribbon and key and presented a knuckle. Keep in mind that, in addition to an assistant, Franklin had something else he did not bother to explain: an almanac maker’s keen awareness of the local weather. Trade knowledge mattered. How else could anyone decide whether clouds promised a thunderstorm that would stay at the right distance and height?26
Quickly, imitators of the two forms of the Philadelphia experiment generated multiple verifications that electricity existed in the atmosphere. As far as Franklin was concerned, this was indirect evidence that, if friction created static electricity, the same might be true of its atmospheric form. Again, he was addressing questions about the general nature of matter and the presence of electricity throughout the material creation. Here, however, his belief that indoor laboratory results could explain outdoor natural forces was beginning to strain the evidence.
From his indoor experiments, Franklin argued that, if pointed conductors drew electricity better than blunt ones, then they could drain electricity from clouds. This topic addressed a real problem—when lightning struck, it could cause terrifying and fatal damage. Franklin recommended the erection of pointed lightning rods atop buildings and ships. He first described these rods in Poor Richard for 1753. There, Richard Saunders dismissed any religious doubts that humanity should defy natural disaster. Indeed, he hinted at a divine revelation of lightning rods. “It has pleased God in his Goodness to Mankind,” he preached, “at length to discover to them the Means of securing their Habitations and other Buildings from Mischief by Thunder and Lightning.”27
Instructions followed. Alongside each building, an iron rod should be planted “three or four Feet in the moist Ground” and “six to eight Feet above the highest Part of the Building.” That was a lot of costly metal, but Saunders added that the readily available lengths of iron that builders cut into nails were perfectly acceptable. Each should be topped by “a Foot of Brass Wire, the Size of a common Knitting-needle, sharpened to a fine Point.” The same principle would protect a ship if a shorter rod was secured to its topmast and then an attached wire was run down into the water, which grounded it.28
Whenever atmospheric electricity ominously rumbled, pointed metal rods would discharge it. Individual houses or ships would be protected, and multiple rods in towns and cities provided collective benefit; together, they might prevent electricity in the atmosphere from building up in the first place. Franklin’s insistence that lightning could be managed by ordinary building materials, familiar to anyone who paid the least attention to everyday items (“the Size of a common Knitting-needle”), showed his hope that hi
s invention could serve anyone.
Franklin had demonstrated that atmospheric electricity existed and had recommended a way to limit its threat to life and property. But he found it harder to answer his other philosophical question: Did clouds carry a positive or negative charge? The answer would shed light on the formation of electricity and its interaction with other forms of matter. Was a positive or negative charge associated with the genesis of electricity? Franklin thought clouds were “most commonly in a negative State.” But the electricity drawn from actual clouds was inconclusive. So he went back to indoor experiments. He had read of a way to generate vapors for experiments. He placed a brass plate on an electrified metal stand, heated the plate, and then sprinkled it with water. Franklin expected that the resulting steam would also be electrified. It never was, so he never satisfied himself as to whether clouds, when first generated, tended to be more frequently positive or negative in charge.29
Again, the underlying problem was the assumption that experiments indoors were analogous to nature outside. Franklin had, for instance, used the concept of an atmosphere, usually applied to the larger natural world, to explain electrical phenomena indoors. But these electrical “atmospheres” were, as the Abbé Nollet had pointed out, rather puzzling. In his first letter on his first electrical experiment, Franklin had asserted that an invisible force had to surround a charged body, as rosin smoke had revealed when it settled around a charged piece of iron shot.
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