The chemist Irving Langmuir had already won a Nobel Prize, but he'd never screamed in delight during an experiment before. It was November 13, 1946. He was standing in a control tower at the Schenectady, New York, airport, watching a small prop plane go buzzing overhead. Fourteen thousand feet above him, his assistant was leaning out the plane's window, tossing pellets of dry ice into a cloud. Seconds later, the cloud “began to writhe as if in torment,” one witness recalled. Within five minutes, the cloud had disappeared, transformed into rain. Even before the plane landed, he raced off to telephone a reporter. Mankind, he shouted into the receiver, had finally learned to control the weather.