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  DURING THE CALM DAYS on the second half of the Samson’s voyage, Priestley would stand at the stern of the ship and lower a thermometer attached to a rope into the sea to record the temperature of the water at different depths. Such exact measurements would have been impossible at the beginning of the century; the sealed mercury thermometer had been invented in 1714 by Gabriel Fahrenheit, who also devised a scale for his contraption, establishing 32 degrees as the freezing point. As is so often the case in the history of science, an increase in the accuracy of measurement led to a fundamental shift in the perception of the world. Marking changes in the temperature of ocean water enabled navigators to identify and exploit a pattern in the ocean’s currents that they had blindly stumbled across in centuries past: a river of warm water that runs from the tropics all the way up the coastline of North America, and then makes a sharp right turn toward Europe as it passes Cape Cod. Sailors had long tapped the energy of that oceanic river in their travels along the eastern seaboard, but its continued passage across the North Atlantic had gone largely undetected by all but the most experienced seamen.

  The first precise measurement of that oceanic flow came indirectly through a pattern detected in the flow of information. In 1769, the Customs Board in Boston made a formal complaint to the British Treasury about the speed of letters arriving from England. (Indeed, regular transatlantic correspondents had long noticed that letters posted from America to Europe tended to arrive more promptly than letters sent the other direction.) As luck would have it, the deputy postmaster general for North America was in London when the complaint arrived—and so the British authorities brought the issue to his attention, in the hope that he might have an explanation for the lag. They were lucky in another respect: the postmaster in question happened to be Benjamin Franklin.

  Franklin would ultimately turn that postal mystery into one of the great scientific breakthroughs of his career: a turning point in our visualization of the macro patterns formed by ocean currents. Franklin was well prepared for the task. As a twenty-year-old, traveling back from his first voyage to London in 1726, he had recorded notes in his journal about the strange prevalence of “gulph weed” in the waters of the North Atlantic. In a letter written twenty years later, he had remarked on the slower passage westward across the Atlantic, though at the time he supposed it was attributable to the rotation of the Earth. In a 1762 letter he alluded to the way “the waters mov’d away from the North American Coast towards the coasts of Spain and Africa, whence they get again into the Power of the Trade Winds, and continue the Circulation.” He called that flow the “gulph stream.”

  When the British Treasury came to him with the complaint about the unreliable mail delivery schedules, Franklin was quick to suspect that the “gulph stream” would prove to be the culprit. He consulted with a seasoned New England mariner, Timothy Folger, and together they prepared a map of the Gulf Stream’s entire path, hoping that “such Chart and directions may be of use to our Packets in Shortning their Voyages.” The Folger/Franklin map was the first known chart to show the full trajectory of the Gulf Stream across the Atlantic. But the map was based on anecdotal evidence, mostly drawn from the experience of New England-based whalers. And so in his voyage from England back to America in 1775, Franklin took detailed measurements of water temperatures along the way, and detected a wide but shallow river of warm water, often carrying those telltale weeds from tropical regions. “I find that it is always warmer than the sea on each side of it, and that it does not sparkle in the night,” he wrote. In 1785, at the ripe old age of seventy-nine, he sent a long paper that included his data and the Folger map to the French scientist Alphonsus le Roy. Franklin’s paper on “sundry Maritime Observations,” as he modestly called it, delivered the first empirical proof of the Gulf Stream’s existence.

  So as Joseph Priestley dipped his thermometer into the waters of the Atlantic, he was retracing the steps that Franklin had taken almost twenty years before. The sight of those four waterspouts would also have brought back fond memories of his old friend. In his letter to le Roy, Franklin had speculated that North Atlantic waterspouts likely arose out of the collision between cold air and the warm water of the Gulf Stream. There is no direct evidence in the historical record, but it is entirely probable that it was the waterspout sighting that sent Priestley off on his quest to measure the temperature of the sea, trying to marshal supporting evidence for a passing conjecture his friend had made a decade before. Franklin had been dead for nearly four years, but their intellectual collaboration continued, undeterred by war, distance, even death.

  Priestley’s retracing of Franklin’s 1775 journey went far beyond the scientific experiments they each performed en route. Franklin, too, had been a hunted man in his final days in London, driven from England by scandal and the first stirrings of war. Twenty years later, Priestley was making the same voyage, facing the same threat. While their religious beliefs differed, their scientific and political views were remarkably harmonious. In his intellectual sensibility, Franklin was closer to Priestley than he was to any of the American founding fathers. This was the bleak irony of their parallel voyages across the Atlantic: the ideal of Enlightenment science had instilled in them a set of shared political values, a belief that reason would ultimately triumph over fanaticism and frenzy. But now the vortex had swallowed them both.

  All around Priestley immense forces of energy surged: the tight spiral of the waterspout, the vast conveyer belt of the Gulf Stream, the liberated energy of the British coal fields that had helped send him into exile. One of Priestley’s greatest scientific discoveries involved the cycle of energy flowing through all life on Earth, the origin of the very air he was breathing there on the deck as he watched his thermometer line bob in the waters of the Atlantic. Together, all those forces converged on him, as the Samson struggled against the current, bearing west to the New World . . .

  BENJAMIN FRANKLIN AND THE KITE

  CHAPTER ONE

  The Electricians

  December 1765

  London

  THE LONDON COFFEE HOUSE LAY IN St. PAUL’S churchyard, a crowded urban space steps from the cathedral, bustling with divinity students, booksellers, and instrument makers. The proximity to the divine hadn’t stopped the coffeehouse from becoming a gathering place for some of London’s most celebrated heretics, who may well have been drawn to the location for the sheer thrill of exploring the limits of religious orthodoxy within shouting distance of England’s most formidable shrine. On alternating Thursdays, a gang of freethinkers—eventually dubbed “The Club of Honest Whigs” by one of its founding members, Benjamin Franklin—met at the coffeehouse, embarking each fortnight on a long, rambling session that has no exact equivalent in modern scientific culture. (The late-night bender at an industry conference probably comes closest: the sharing of essential, potentially lucrative information while stimulated by the chemical cocktail of caffeine, alcohol, and nicotine.) Boswell visited the “Honest Whigs” on occasion, and he had this to say of the experience:

  It consists of clergymen, physicians and some other professions . . . (including) Mr Price who writes on morals . . . we have wine and punch upon the table. Some of us smoke a pipe, conversation goes on pretty formally, sometimes sensibly and sometimes furiously: At nine there is a sideboard with Welsh rabbits and apple-puffs, porter and beer.

  On December 19, 1765, Joseph Priestley sat down at a coffeehouse table, there in the shadow of St. Paul’s, and began a conversation that would transform his life. London had dazzling sights, and shops full of the latest scientific equipment, and Royal Societies devoted to pioneering research. But like so many young men and women since, Priestley had come to the great city with one driving objective: he had a book idea to pitch. That was why he found himself, for the first time, in the good company of the Honest Whigs.

  Priestley was thirty-two, an affable and freethinking minister and schoolteacher whose career to date had been somewhat stymied by a persistent stammer. (
His first trip to London, ten years earlier, had been to spend a month with a speech therapist, a Mr. Angier, who promised to “cure all defects of speech” and made his clients take an oath not to reveal his technique.) Born in 1733 in a small town called Fieldhead, about six miles outside of Leeds, Priestley belonged to an extended family of religious nonconformists, at a time of intense political and theological battles between the Church of England and religious dissenters. Even in that unorthodox milieu, Priestley managed to push the boundaries: at nineteen, he was denied membership in the Independent Chapel of Heckmondwike, in Yorkshire. Exiled from the strict Calvinism of his family, he spent his twenties preaching to small dissenting congregations in Needham and Nantwich, offending a few parishioners along the way with his maverick theories on the divinity of Jesus Christ.

  The congregation in Nantwich numbered only sixty regular attendees, which left Priestley with plenty of spare time to start a small school in the town, where he instructed thirty boys six days a week. He began writing in that period, drafting short treatises on theological matters—the supernatural distortions of the Apostle Paul was a favorite subject—showing them to a few mentors and then burying them in his drawer for later revision. And while those essays would eventually find their way to a mass readership, his first published book was an equally radical take on a seemingly less contentious subject, The Rudiments of English Grammar, one of the first attempts to systematically map the structure of the English language with the rigor that scholars had long applied to Latin and Greek. (Priestley’s combination of innovative linguistics scholarship and firebrand political writing would chart a path followed two centuries later by Noam Chomsky.)

  Rudiments helped Priestley land the post of tutor at Warrington Academy, a prominent dissenting school in Yorkshire. Originally hired to teach languages (he was fluent in six), Priestley quickly introduced courses in modern history and politics—a cutting-edge curriculum in an educational regimen still devoted to conjugating the verbs of dead languages. His first year at Warrington, Priestley wed Mary Wilkinson in Wrexham, Wales, where Mary’s industrialist father ran the Bersham Ironworks. In his memoirs, Priestley would later write of his marriage: “This proved a very suitable and happy connexion, my wife being a woman of an excellent understanding, much improved by reading, of great fortitude and strength of mind, and of temper in the higher degree affectionate and generous; feeling strongly for others, and little for herself.”

  During his years at Nantwich, Priestley had developed an amateur’s passion for science. Though barely able to make ends meet, by the late 1850s he had cobbled together enough savings to buy an air pump and an “electricity machine.” Together with a well-calibrated scale, these three contraptions were at that time the state-of-the-art essentials of a scientific toolkit. (They would, each in their different ways, help support the great tower of scientific innovation that Priestley would build in the coming years.) By the time he got to Warrington, Priestley had the science bug. He had become, to use the terminology then in vogue, a dabbler in “natural philosophy.”

  Like many of his peers, his first love was electricity. To understand the importance of electricity in the imagination of the educated classes in the mid-1700s, one has to understand the unusual convergence that made it so fascinating. In most cases when a fundamental force in the universe is first formally understood by science, there is a lag between that understanding and the emergence of popular technologies that depend on the science for their existence. Newton’s law of universal gravitation didn’t immediately spawn a craze for gadgets built on his equations. Even in today’s accelerated world, it took at least two generations for Watson and Crick’s discovery of DNA to engender mainstream technologies such as DNA tests. But with electricity, the two phenomena overlapped: you had the discovery of one of nature’s most fundamental forces, and you had an immediate flood of mesmerizing parlor tricks. You had awe-inspiring scientific genius, and you had gadgets, all in one swoop.

  Until the 1740s, electricity had been thought of as two separate fluids, with the relationship between them poorly understood. After conducting an ingenious run of experiments—many of which involved literally shocking his houseguests with a machine designed to generate static electricity—Benjamin Franklin hit upon a series of fundamental insights about electricity that remain unchallenged to this day. Franklin first suggested that electricity was composed of a single fluid, with two inseparable charges, which he called “positive” and “negative.” He discovered, likewise, that the two charges interacted in predictable ways; the current would reliably attempt to flow from a positively charged body to a negatively charged one. From this, Franklin deduced the general principle known as the “conservation of electrical charge”—the idea that electricity can neither be created nor destroyed, but instead is merely passed from one conducting object to another. (His biographer Walter Isaacson suggests that this insight may have originated in the many years Franklin spent poring over balance sheets as he built up his publishing business in Philadelphia.)

  That basic model of electricity survives to this day, along with the vocabulary Franklin built to describe it. (“Battery,” “charged,” and “conductor” were all his coinages.) The gadgets, however, have not fared as well. Consider this drawing:

  As bizarre as it looks, scenes like this were regular appearances in the drawing rooms and fairgrounds of the mid-seventeenth century. They were the special effects of Enlightenment popular culture. In this case, a young boy suspended in the air with silk ropes is positively charged by a machine that generates static electricity. First the boy’s hair spikes up. Then, as the onlookers gasp in amazement, he reaches to touch a small girl, and sparks shoot between their fingertips. Willing volunteers were regularly pulled out of the audience to experience the voltage firsthand. The early explorers into this magical realm, scientists and showmen alike, were known by a name that also persists to the present day, though it has a somewhat different connotation now. They were called the Electricians.

  The most transformative gadget to come out of the Electricians’ cabinet of wonders was the lightning rod, also a concoction of Franklin’s. (The quick jump from conceptual breakthrough to practical application was a hallmark of Franklin’s science, as it would be of Priestley’s.) Humans had long recognized that lightning had a propensity for striking the tallest landmarks in its vicinity, and so the exaggerated height of church steeples—not to mention their flammable wooden construction—presented a puzzling but undeniable reality: the Almighty seemed to have a perverse appetite for burning down the buildings erected in His honor.

  Franklin first suggested the idea of taming that “electrical fire” in a letter to his friend Peter Collinson, written in 1750:

  There is something however in the experiments of points, sending off, or drawing on, the electrical fire, which has not been fully explained, and which I intend to supply in my next. For the doctrine of points is very curious, and the effects of them truly wonderfull; 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 lightening by their means; for if, instead of the round balls of wood or metal, which are commonly placed on the tops of the weathercocks, vanes or spindles of churches, spires or masts, there should be put a rod of iron 8 or 10 feet in length, sharpen’d 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. . . .

  Word of Franklin’s hypothesis quickly spread, as his ideas circulated through the periodicals and coffeehouse networks, even crossing the Channel in a French translation. In 1752, the lightning-rod theory was first successfully put to the test (in France, as it turned out—the beginnings of Franklin’s storied relationship with the French). Within five years of his speculative note to Collinson, lightning rods had become a common sight on church
steeples throughout Europe and America. Franklin’s biographer Carl Van Doren aptly describes the astonishment that greeted these events around the world: “A man in Philadelphia in America, bred a tradesman, remote from the learned world, had hit upon a secret which enabled him, and other men, to catch and tame the lightning, so dread that it was still mythological.”

  Thus it is no great surprise that when Joseph Priestley took up the hobby of natural philosophy, it was electricity that first captured his fancy. No other field had generated so much scientific and practical innovation in such a short amount of time. But Priestley the writer had detected a missing piece in the growing science of electricity: no one had written a popular account of these world-changing discoveries. And so he had set off to London, hoping to meet the Electricians in the flesh, and to persuade them to let him tell the story of their genius.

  PRIESTLEY ARRIVED in London armed with a letter of introduction from John Seddon, the rector at Warrington Academy, addressed to John Canton, a member of the Royal Society and a leading electrician himself. “You will find [Priestley] a benevolent, sensible man, with a considerable share of Learning,” Seddon wrote. He added a postscript: “If Dr. Franklin be in Town, I believe Dr. Priestley would be glad to be made known to him.”

  Dr. Franklin did, in fact, prove to be in town, and so when Canton brought Priestley to the London Coffee House, the young, stammering schoolteacher from Warrington found himself seated across the table from the world’s most celebrated electrician. They were joined by the Welsh moral philosopher and mathematician Richard Price, who would become one of Priestley’s great friends and allies in the coming years.