The first sign of a waterspout forming is a dark stain on the surface of the sea, like a circle of black ink. Within a matter of minutes, if atmospheric conditions are right, a spiral of light and dark streaks begins to spin around the circle. Soon a ring of spray rises up into the air, water molecules propelled aloft by the accelerating winds at its periphery. And then the spout surges to life, a whirling line drawn from sea to sky, sustained by rotational winds that have been measured at up to 150 miles per hour.
Unlike land-based tornados, waterspouts often form in fair weather: a vortex of wind, capable of destroying small vessels, that appears, literally, out of the blue. While it is not nearly as dangerous as a traditional tornado, the waterspout was long a figure of fear and wonder in mariner tales of life on the open sea. In the first century B.C., Lucretius described "a kind of column [that] lets down from the sky into the sea, around which the waters boil, stirred up by the heavy blast of the winds, and if any ships are caught in that tumult, they are tossed about and come into great peril." Sailors would pour vinegar into the sea and pound on drums to frighten off the spirits that they imagined lurking in the spout. They had good reason to be mystified by these apparitions. The upward pull of the vortex is strong enough to suck fish, frogs, or jellyfish out of the water and carry them into the clouds, sometimes depositing them miles from their original location. Scientists now believe that apocryphal-sounding stories of fish and frogs raining from the sky were actually cases where waterspouts gulped up a menagerie of creatures straight out of the water, and then deposited them on the heads of bewildered humans when the spout crossed over onto land and dissipated.
A waterspout sighting is a meteorological rarity, even in the tropical waters where spouts are most often seen. Ships in the colder waters of the North Atlantic, particularly during early spring, almost never encounter them. So it was more than a little surprising that, on one extraordinary day in the spring of 1794, the hundred-odd passengers en route to New York aboard the merchant ship Samson caught sight of four distinct waterspouts simultaneously drifting their way across the sea.
Most passengers onboard the Samson would have viewed the looming spouts not as statistical anomalies but as sinister omens, if not outright threats. No doubt some passengers aboard the Samson ran below decks in fear at the first sighting, while others stared in wonder at the four spouts. But we can say with some confidence that one passenger aboard the Samson rushed to the deck at the first hint of a waterspout sighting, and stood transfixed, observing the spray patterns and cloud formations. It is easy to imagine him borrowing the captain's telescope and peering into the vortex, estimating wind velocity, perhaps jotting down notes as he watched. He would have known that the lively scientific debate over spouts—started in part by his old friend Benjamin Franklin—revolved around whether spouts descended from clouds, as tornados do, or whether they propelled themselves upward from the ocean surface. The idea of witnessing four waterspouts on a North Atlantic voyage would not have been a sign of foreboding or an imminent threat for him. It would have been a stroke of extraordinary good luck.
This was Joseph Priestley, formerly of Hackney, England, en route to his new home in America. At sixty-one years old, he was among the most accomplished men of his generation, rivaled only by Franklin in the diversity of his interests and influence. He had won the Copley Medal (the Nobel Prize of its day) for his experiments on various gases in his late thirties, and published close to five hundred books and pamphlets on science, politics, and religion since 1761. An ordained minister, he had helped found the dissenting Christian sect of Unitarianism. He counted among his closest friends the great minds of the Enlightenment and the early Industrial Revolution: Franklin, Richard Price, Josiah Wedgwood, Matthew Boulton, James Watt, Erasmus Darwin.
But while Priestley's luminous career had established an extensive base of admirers in the newly formed United States, he had booked passage on the Samson thanks to another, more dubious, honor. He had become the most hated man in all of Britain.
Transatlantic voyages in the late eighteenth century were perilous affairs, even when the vessel avoided the substantial risk of being "lost at sea." One of the most ghastly accounts of sea travel from that period—Gottlieb Mittelberger's Journey to Pennsylvania— described the scene onboard the ship Osgood as it made its way from Rotterdam to Philadelphia in the summer of 1750:
But during the voyage there is on board these ships terrible misery, stench, fumes, horror, vomiting, many kinds of seasickness, fever, dysentery, headache, heat, constipation, boils, scurvy, cancer, mouth-rot, and the like. . . . Add to this want of provisions, hunger, thirst, frost, heat, dampness, anxiety, want, affl ictions and lamentations, together with other trouble, as . . . the lice abound so frightfully, especially on sick people, that they can be scraped off the body. . . . The water which is served out on the ships is often very black, thick and full of worms, so that one cannot drink it without loathing, even with the greatest thirst. . . . Towards the end [of the Osgood's voyage] we were compelled to eat the ship's biscuit which had been spoiled long ago, though in a whole biscuit there was scarcely a piece the size of a dollar that had not been full of red worms and spider's nests.
It was not exactly the Queen Mary, to say the least. A nice clean shipwreck might have started to seem appealing after a few days dining on black wormwater and spider's eggs. On the Samson, the drunken captain and his first mate argued so violently with each other that the water casks were neglected and caused much "suffering" among the steerage passengers, according to Priestley's somewhat ambiguous account. Mary Priestley, Joseph's wife, labored through three weeks of constant seasickness in the heavy seas that the Samson met upon leaving England.
To embark on such a journey at the age of sixty-one took a particular mix of fearlessness and optimism. Priestley had both qualities in abundance. Nearly every extended description of the man eventually winds its way to some comment about his relentlessly sunny outlook. He was almost pathologically incapable of believing the threats that arrayed themselves against him. Here is Priestley giving his account of the voyage of the Samson, in a letter written to a friend upon landing in New York:
We had many things to amuse us on the passage; as the sight of some fine mountains of ice; water-spouts, which [are] very uncommon in those seas; flying fishes, porpoises, whales, and sharks, of which we caught one; luminous sea-water, &c.
The storm that nearly sunk the ship merits two brief sentences, amid all the amusements:
We had very stormy weather, and one gust of wind as sudden and violent as, perhaps, was ever known. If it had not been for the passengers, many of the sails had been lost.
Mary Priestley was less sanguine about the storm ("It was a very awful night") and struggled to strike a similar note of enthusiasm in her description of the passing diversions of the voyage:
Our voyage at times was very unpleasant, from the roughness of the weather; but as variety is charming, we had all that could well be experienced on board, but shipwreck and famine.
It's not hard to hear a hint of gritted teeth or gentle satire in that "variety is charming" line, as though she's mimicking a discourse from her beloved "Dr. P" on the latest sighting of "luminous sea-water" or some other fascination—a speech she had heard a few too many times during those three weeks of seasickness.
But however severe the peril that confronted them in setting sail for America, in that spring of 1794, Mary and Joseph Priestley had little choice but to book passage on the Samson. The open rage and violence that had rained down on them made the decision to flee inevitable. Priestley had spent weeks shuttling from safe house to safe house, as the newspapers and pamphleteers and cartoonists called for his head. His persecution had caused many to compare him to Socrates. (Before Priestley's departure, then vice president
John Adams wrote in a letter to Priestley, "Inquisitions and Despotisms are not alone in persecuting Philosophers. The people themselves, we see, are capable of persecuting a Priestley, as another people formerly persecuted a Socrates.") In contemporary terms, Priestley had become the Salman Rushdie of Georgian England: a world-famous intellectual whose political and theological musings had planted a bull's-eye on his back. America was the logical way out.
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 fl owing 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 . . .
Reprinted from THE INVENTION OF AIR: A Story of Science, Faith, Revolution, and the Birth of America by Steven Johnson by arrangement with Riverhead Books, a member of Penguin Group (USA), Inc., Copyright © 2008 by Steven Johnson.