Too Much Rainmaking

Dr. Irving Langmuir, high priest of scientific rainmaking, sounded a solemn warning last week: those who sow too many rainstorms may reap nothing but droughts. Speaking at the School of Mines in drought-threatened New Mexico, Langmuir denounced the commercial rainmakers, many of them woefully ignorant of the art, who are seeding the atmosphere with silver iodide throughout the dry Southwest. "Some of them," he said, "are using hundreds of thousands of times too much. No more than one milligram [.000035 oz] of silver iodide should be used for every cubic mile of air."

According to Langmuir's theory, silver iodide particles in the right amount will turn a cloud of supercooled (below freezing) water droplets into snowflakes. The flakes sink to warm lower levels, melt and fall as rain. But if there are too many iodide particles competing for the moisture in the water droplets, the snowflakes formed are too small to fall. They may even rise, drifting off as thin cirrus clouds that never yield any rain.

In much of the Southwest, power companies, water districts, even farmers and cattlemen are hiring rainmakers to seed the reluctant clouds. Langmuir presented evidence that such overenthusiastic use of silver iodide has already prevented rain in certain areas.

Another danger of the current rainmaking boom in the Southwest is that the silver iodide particles, invisible and almost undetectable, may drift to the humid eastern part of the country (which often has too much rain) and cause damaging floods. Langmuir cannot prove that this has happened; the new technology of "meteorological engineering" is still too young to draw such definite conclusions.

But he believes that "there ought to be a law," or at least a voluntary agreement, controlling the amount of silver iodide to be fed into the atmosphere.

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