Changing the Weather.

In 1943 earth scientists began to investigate the possibility of weather modification. Working at the General Electric Research Laboratory, Irving Langmuir and Vincent Joseph Schaefer began collaborating in a study of how cold temperature and humidity combine to form rime, a thin coating of ice, on all objects exposed to the weather. After observing the way ice forms on airplanes as they pass through cold clouds, Langmuir and Schaefer moved to broader research on clouds and the causes of precipitation.

Human-Made Rainfall.

After months of experimentation, Schaefer determined that precipitation is caused in supercooled clouds — clouds at or below freezing in which ice crystals and water drops both exist; the ice crystals grow bigger as the water droplets become smaller, until all the moisture is gone or the ice crystals are heavy enough to fall from the cloud. If the temperature...