At about 5 pm on 19 June 1835, a violent tornado tore past New Brunswick in the state of New Jersey, leaving a 30-kilometre-long trail of devastation in its wake. Entire houses were tossed into the air, their roofs and rafters torn off and scattered hundreds of metres away. Hats, books and roof tiles were flung out in a band 8 kilometres wide, with some even landing on the tip of Staten Island.
Picking carefully through the wreckage in the aftermath was James Espy, a teacher from Philadelphia. He noted the position of fallen trees, and a house where blasting winds had opened fissures in the walls. 鈥淚n one crack was thrust a lady鈥檚 handkerchief,鈥� he reported, 鈥渁nd in the other a sheet, which had been taken up from a bed in the room.鈥� Other houses had walls blown completely outwards 鈥渁s if by an explosion鈥�. Espy was convinced he could explain the forces behind this fearsome weather 鈥� and, incredibly, that he could summon them up himself.
THE 鈥淣ew Brunswick spout鈥� was a tornado that made a big impression. Not only was it dramatically devastating, it had also hit within easy travelling distance of nearby cities. As soon as the tornado had run its course, every major figure in early American meteorology promptly turned up with surveying equipment to catalogue the wreckage. But James Espy was rather keener than most: he believed that the direction in which the fallen trees were pointing would prove his contention that heat caused storms to rush centripetally inwards from all directions, like air sucked up a chimney.
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The unlikely birthplace of Espy鈥檚 theory was the small backyard of his home in Philadelphia. According to one visitor, the whitewashed plank fence around the house was 鈥渟o covered with figures and calculations that not a spot remained for another sum or column鈥�. This impromptu notebook enclosed a garden littered with vessels of water and thermometers dedicated to determining the dew point, the temperature at which atmospheric water vapour condenses. These tumblers of cold water were a simple but powerful tool, 鈥渢he lever with which the meteorologist was to move the world鈥�, wrote Espy.
Espy was convinced that the heat and condensation his simple apparatus measured were the driving force behind storms. As the sun warmed air near the ground, he noted, this air rose. As it pushed upward through cooler air, water vapour condensed out, causing the rising air column to expand and rise even higher 鈥� sucking in more air from below 鈥� until it finally dried out and was exhausted of its energy. In the process, the condensed water vapour fell as rain or hail.
Drawing on his backyard calculations and a century鈥檚 worth of data on dozens of deadly tropical hurricanes recorded in ships鈥� logs, Espy set down his convection theory in his great opus The Philosophy of Storms, published in 1841. The leading French physicist of the day, Fran莽ois Arago, was impressed. 鈥淓ngland has its Newton, France its Cuvier, and America its Espy,鈥� he proclaimed.
Indeed, convection is now one of the basic premises of meteorology. But Espy鈥檚 model did not explain as many phenomena as he had imagined: he rejected, quite wrongly, the notion of hurricanes and tornadoes swirling in a rotary form, a sight now familiar to anyone watching satellite images on news reports. And not all his ideas were received with the warmth he thought they deserved. In January 1842, Espy called on Congressman 鈥� and former US President 鈥� John Quincy Adams. Espy had exasperated Adams. 鈥淭he man is methodically monomaniac,鈥� Adams wrote in his memoirs. 鈥淎nd the dimensions of his organ of self-esteem have swollen to the size of a goitre by a report from a committee of the National Institute of France, endorsing all his crack-brained discoveries.鈥�
Most contemporaries reading Adams鈥檚 memoirs would have known exactly what those 鈥渃rack-brained discoveries鈥� were. Espy had travelled from Maine to Mississippi giving lectures on how he could alter the country鈥檚 weather at will 鈥� most particularly, how he could create rain. 鈥淎ny cause which produces an up-moving column of air, whether that cause be natural or artificial, will produce rain,鈥� he asserted. All you needed was a calm day, a low dew-point, and a source of heat. A volcano would do the trick. As Espy pointed out, a violent eruption in Iceland in 1821 was followed by terrible storms and floods as far away as Italy. In times of drought, he suggested, a more controlled method might bring a more moderate and useful rainfall.
The press dubbed Espy 鈥淭he Storm King鈥�, and some journalists even expressed cautious hope for his plans. 鈥淗e will be deserving of the Homeric epithet of the cloud-compelling Jupiter,鈥� ventured the New York Express after one of his lectures. 鈥淚f Professor Espy can do what he thinks can be done, make a storm, at once, man is almost a master of the world.鈥� And just how was he going to achieve this? Well鈥e might, say, deliberately set a forest fire.
鈥淚f I should be encouraged to go on with the experiment, I mean to have a large mass of combustibles prepared ready for use,鈥� Espy promised in the final pages of The Philosophy of Storms. 鈥淚f any gentleman intends to clear from twenty to fifty acres of woodland this spring, or early in the summer, in the western or north western parts of Pennsylvania, will he please to inform me of the fact as soon as is convenient.鈥�
Espy had good reason to appeal to his readers for help, for he looked unlikely to get any from the government. The US Senate had already thrown out a bill to grant Espy $50,000 to create enough fire-induced rain to make the Ohio river navigable from Pittsburgh during the summer. One newspaper had condemned the plan as 鈥淢agnificent Humbug鈥�. His colleagues quietly wished Espy would get off his embarrassing hobby-horse, for his other work was perfectly respectable. Throughout the 1840s he was regarded highly enough to be given scientific appointments in Washington DC, compiling weather reports for the army, the navy and the Smithsonian Institution. Espy effectively became the US鈥檚 first national meteorologist. He rigged up fans to demonstrate miniature waterspouts to members of Congress, and even used his understanding of airflow to create ventilation systems for the chambers of the US Senate. But he simply would not drop his wild rainmaking scheme.
Espy was quick to point out to doubters that his idea was not an entirely new one. In England in 1636, the Earl of Pembroke wrote to the high sheriff of Staffordshire requesting that, as King Charles I was about to pass through the county, no farmer should burn his fields lest it bring rain down on the royal procession. Espy also had correspondents from Pennsylvania to the Pampas attesting to local customs of fire-induced rains, and he reprinted their accounts in his book. He admitted, 鈥淕entlemen have made their puns on this project and had their laugh鈥�. But he insisted an experiment in rainmaking could withstand any scrutiny.
He was fortunate that this scrutiny never really came. It was years before he finally carried out a trial, torching 5 hectares of woods in Fairfax County, Virginia in July 1849. The event passed unnoticed, not the least because it didn鈥檛 rain. But could it have worked? The answer is a resounding yes. Vast forest fires are notorious for creating their own weather in the form of pyrocumulus clouds, which whip up storms in the manner Espy described. But you need the right set of weather conditions, and even if you succeed, you may regret it: pyrocumulus columns can collapse, sweeping fire outwards at high speeds. Would-be rainmakers are liable to incinerate themselves.
Still, Espy鈥檚 efforts in Washington didn鈥檛 come to naught. Like many meteorologists, he was intrigued by the potential of the newly strung telegraph lines for collecting data and giving early warnings of bad weather. On 1 May 1857, this unsigned item appeared in the Washington Evening Star: 鈥淵esterday there was a severe storm south of Macon, Ga; but from the fact that it was still clear this morning at that place and at Wheeling, it is probable that the storm was of a local character.鈥� In other words, it would not be hitting elsewhere. The report 鈥� the first weather forecast in US history 鈥� is thought to have been penned by Espy and his colleague at the Smithsonian, Joseph Henry. And even if Espy himself hadn鈥檛 created the weather, that hasn鈥檛 stopped people blaming the weatherman ever since.