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tion activities. Five states explicitly claim ownership of water in the atmosphere above their territory, and therefore title to any addition to precipitation from cloud seeding. Recently there has been increased public support of scientific research related to weather modification, especially following publication early in 1958 of the Final Report oj the Advisory Committee. on Weather COlltrol. The National Science Foundation now has a program of study on atmos- pheric physics and other subjects which eventually may lead to greater understanding of the natural processes which weather modification is designed to aller. It is easy to see why there has been so rapid a generation of interest in weather modification. The possibilities for gain are great, and the stakes high. A large proportion of the surface of the United States suffers (rom an inadequate natural water supply, and nearly every part of the United States at some time or other feels the effects of drought or other vagaries of weather. At the same time, the moist air masses moving from the Pacific Ocean eastward across the North American continent go on from the East Coast with more than three-fourths of the moisture they contained originally. The potential for additional precipitation within United States territory thus is immense. In addition, extensive recirculation of water from the land to the atmosphere makes possible the production of precipitation several times, even from the same masses of air and vapor. Even more significant than these estimates of total and re-evaporated supplies of atmospheric moisture is the low "efficiency" of natural precipi- tation. It has been estimated that even a heavy snow precipitates only 0.5 per cent of the overhead moisture in the storm area. If relatively modest increases in this yield of water can be artificially induced, highly rewarding benefits will be obtained. For instance, a 15 per cent increase in total precipitation could mean an additional 1001000 acre-feet of water per year on a I,OOO-square-mile watershed having an annual precipitation of only 15 inches. If this water were to fall in the areas where it is most needed in western and southwestern United States, its monetary value, at $20 per acre-foot, would be $2,000 per square mile in agriculture, or at 15r per thousand gallons, nearly $5,000 per square mile of municipal supply watershed. In addition to moisture redistribution, the prospect o( weather modi- fication has been attractive because of other possible benefits. These include the reduction of hailstorms and resulting damage, decrease in lightning storms and consequent reductions in multimillion-dollar forest fire losses, modification and diminution of hurricane intensity and damage, 21