Snow Is Predicted

Meteorologists, like other people, deplore the weather, but some of them have designs on it. General Electric Co. scientists recently announced a discovery which might turn weathermen into active weathermakers.

The U.S. winter air is apt to be full of "supercooled" clouds (below the freezing point). These clouds might, with help, be converted into snow. If it works, G.E.'s effort' to manufacture snowstorms might appreciably affect the U.S. climate.

The first step was taken when G.E.'s Vincent J. Schaefer turned a cloud into snow by pelting it from an airplane with pellets of dry ice (TIME, Nov. 25). G.E. then discovered that dry ice is not necessary.. A child's popgun shot into a supercooled cloud works almost as well. The air expanding out of the gun starts snowflakes forming. One night not long ago, G.E.'s Dr. Bernard Vonnegut walked out of his front door into a below-freezing fog. He fired his popgun once. For 30 feet the fog turned into snowflakes.

Stop the Fog. But dry ice and popgun explosions are shortlived instruments. What G.E. snowmen wanted was something that would hang around in the air waiting for a supercooled cloud. They discovered in the laboratory that snowflakes form more readily if they have something like ice to crystallize on. So they tossed all sorts of powdered substances into the fog in their laboratory "cold chamber." Silver iodide did the trick magnificently, turning the fog to snow. Silver iodide crystals are hexagonal, as snow crystals are. Apparently snowflakes recognize the kinship and are fooled into hanging on. An infinitesimal whiff is enough. In the presence of iodine vapor a single electric spark will knock enough silver out of a dime to start a snow flurry. Burning a cotton string impregnated with silver iodide makes enough crystalline smoke to cause a sizable snowstorm.

The snowmen have not yet tried their silver iodide treatment on full-sized, outdoor clouds, but they intend to soon, with the help of the U.S. Air Forces. In the meantime they have done some figuring. The silver iodide particles need be only one-millionth of an inch in diameter. A billion billion of them will fit in an eggshell. About 200 pounds of silver iodide may be enough to seed the entire atmosphere of the U.S. at the rate of 100,000 nuclei per cubic foot. Adding one pound per hour will keep it seeded.

Stop the 'Hail. G.E. does not plan to tinker with the whole U.S. atmosphere, but it has its eye on hailstorms, which do enormous damage to crops in certain parts of the country. Hail is formed when raindrops are sucked into rising currents in a thundercloud. They freeze high in the air, collide with supercooled water droplets, and grow into crop-slashing hailstones. Dr. Irving Langmuir proposes to charge the thunder-threatening air with silver iodide particles. Sucked up into the cloud, they will turn the supercooled droplets into snow before they can build up hailstones.

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