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His G.E. bosses told young Langmuir not to bother about practical applications of his experiments, to look around the laboratory and work on anything that interested him. G.E.'s investment in non-routine research soon paid off. Langmuir became associate director of G.E.'s Schenectady laboratory, worked on such eminently practical things as high-vacuum radio tubes, and the gas-filled light bulb, which, says G.E., saves the U.S. public nearly $1 billion a year in electric bills by lengthening the filament's life.
Langmuir's theoretical work was even more important. Most of it concerned the extraordinary potency of very small things: electrons, molecules, thin films and infinitesimal particles. Over the years Langmuir became an authority on the David & Goliath contests between the very small and the very large, in 1932 won a Nobel Prize for his discoveries in that field.
But, like everyone else, Langmuir did nothing about the weather (except complain about it) until World War II, when he began studying the water droplets in high, cold clouds which freeze into deadly ice on airplane wings. He was drawn away to other urgent war jobs before he found out all he wanted to know about those droplets. But he did not forget them. He suspected that they might answer an important question: Why does it rain?
Ice & Water. The schoolbook explanation of rain is that "clouds condense into raindrops and fall to the ground." It is not quite as simple as that. Unless something special happens to it, a cloud remains a cloud; the droplets in it stay about as they are, too small to fall.
After the war, Langmuir went back to work on the mystery of rain clouds. He knew that the droplets in clouds do not freeze at 0° C. (32° F.). They are supercooled, i.e., are much colder than zero centigrade, the normal freezing point. When an ice crystal comes in contact with supercooled droplets, it can steal water from them, so water vapor moves from the droplets to the ice. The ice crystals grow; the droplets shrink.
Langmuir reasoned, as others had before him, that this process might be a cause of rain and might show a way to make artificial rain. If small ice crystals could be induced to form in a supercooled cloud, they should grow into big snowflakes at the expense of the cloud's droplets, then fall to the ground as snow, or melt into rain.
Langmuir and his brilliant young protégé, Vincent Schaefer, a onetime machinist, settled down in G.E.'s Schenectady lab and began experimenting with a cloud in a test tube. Their "test tube" was an ordinary G.E. home freezer lit by a slanting beam of light and lined with black velvet for better visibility. All they had to do to make a "cloud" was to breathe into the chamber. Making the crystals in the cloud was something else again.
Langmuir and Schaefer tried all kinds of things, with no success. Then, one hot day in July 1946, Schaefer was alone in the laboratory. The cold chamber was not quite cold enough to suit him, so he put in a hunk of dry ice (temp. —79° C., —110° F.). At once he saw bright motes swirling through the light beam. As he watched, they grew into glittering snowflakes and settled to the bottom of the chamber.