Why does it rain? Why does water, condensed into droplets, fall from the sky at particular moments, in particular places?
For a long time—until, pretty much, the 19th century—people believed that rain was both caused and impeded by noise. As the journalist Cynthia Barnett writes in her book Rain: A Natural and Cultural History, the Greek essayist Plutarch noted that "extraordinary rains pretty generally fall after great battles; whether it be that some divine power thus washes and cleanses the polluted earth with showers from above, or that moist and heavy evaporations, steaming forth from the blood and corruption, thicken the air." Napoleon, whose loss at Waterloo was helped along by rains that turned his battlefield into mud, was among the military leaders who were convinced in the connection between rainy weather and the blasts of military weaponry.
And as J.C. Lewis wrote in an 1861 letter, later printed in The American Journal of Science and Arts, after witnessing the rains that fell after the battle of Bull Run: “The discharge of heavy artillery at contiguous points produces such a concussion that the vapor collects and falls generally in unusual quantities the same day or the day following.”
Rain, according to this take on meteorology, could also be impeded by noise. In the Europe of the Middle Ages, Barnett writes, bell-ringers would run to church steeples—not to warn villagers of bad weather, but in hopes of weakening the storm. ("Of course," she notes, "clutching the end of a wet rope hung from the tallest point in the village in the days before lightning rods was not the wisest way to ride out a thunderstorm. Prior to the Enlightenment, it was not uncommon for church bell ringers to be killed by lightning.")
All those ideas—the connection between commotion and precipitation—carried on into the 19th century. When the Erie Canal was completed in 1825, thousands of revelers congregated along its path to celebrate the new waterway. The parties were loud; they involved, among other things, a series of 32-pound cannons that had been placed along the canal's wandering route, at every 10 miles or so. They involved what one spectator called "deafening fireworks." They involved artillery companies demonstrating their wares. They involved church bells and marching bands and all manner of human revelry.
The celebrations took place on a crystal-skied Wednesday; they were cut short, on Thursday, by dampening storms that had entered the area. The connection, it seemed to many, was clear: They had made a racket, and the rains had come. The people had summoned the storm.
The United States' first official meteorologist, James Pollard Espy, had a different different take on the theory of storm development. Espy had helped to create a national weather-forecasting network, the first of its kind, via a series of connected by telegraph lines. He was also famous lecturer about weather—people referred to him fondly as the "Storm King"—and had developed a convective theory of rainfall: the idea that storms are driven by warm, humid air that rises in a column. It wasn't the noise of battle and celebration that had summoned the rain, Espy believed; it was the warmth that the ruckus had generated.
It followed, he thought, that if heat brought rain … all you had to do, if you wanted to generate a rain cloud, was to generate some heat of your own. If you wanted to make it rain, you had to start a fire.
Espy, widely respected for his work with the telegraph networks, proposed a bold—some said overly bold—plan to Congress. He wanted the federal government to set aside land that would function as, essentially, a massive timber farm. The farm, he thought, should stretch in a long line, running north to south, from the Great Lakes to the Gulf of Mexico, all along the United States' Western frontier. When farmers needed rain, he thought, the forests could simply be strategically burned—bringing with them, convective heat being what it is, land-quenching moisture.
Espy repeatedly asked Congress to let him start forest fires along a 600-mile stretch of land—the better to test his theory.
The idea did not catch on. His proposal was met, repeatedly, by polite rejections. And though that was in part because Espy's convective theory of storm-making met with disagreement from his fellow scientists—they pointed out that, for example, that organically sparked wildfires could rage without bringing rainstorms in their wake—it was also because of the political situation of the time. Some of Espy's critics, Barnett notes, "did not fear Espy’s plan would fail but that it would succeed—placing the power of rainfall into the hands of the federal government." Antebellum southerners, in particular, feared a government takeover of nothing less than the weather itself. Rain, one South Carolina senator declared in the 1850s, “is a power which none but God can rule with justice. As long as you leave it to the temptation of selfish man, it will go to make the rich richer and the poor poorer.”
Such fears still feel familiar today. Weather remains, for better or for worse, an equalizing, and democratizing, force. None of us control it; which is also to say that all of us are under its control. Senator John Crittenden of Kentucky, responding to Espy's petition for funds in 1838, warned that “he might enshroud us in continual clouds, and indeed falsify the promise that the Earth should be no more submerged." Crittenden added, ominously: "And if he possesses the power of causing rain, he may also possess the power of withholding it.”
This article was originally published at http://www.theatlantic.com/technology/archive/2015/05/the-scientist-who-told-congress-he-could-literally-make-it-rain/392219/
