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eleven western states. (See table on page 24.) Eighty-eight per cent of this would fall within the five states of \Vashington, Oregon, California, Idaho, and Colorado. Moisture additions from increased precipitation, however~ depend upon the presence of clouds. They accordingly cannot be depended upon as solutions to any specific drought problem in a given season. The results suggested are only to be expected as a long-time average. The major potential benefits from cloud seeding by present commercial methods thus appear to be much more sharply regionalized than is popularly understood at the present time. At the same time, since much of the area where seeding is applicable is in need of additional water for irrigation, municipal supply, and industrial use, increased precipitation and runoff can be highly valuahle, Although there appears to be little promise of substantial effect on precipitation outside of the western one-fourth of the United States, there may be some indirect benefits in adjacent areas through augmentation of stream flow on the eastern slope of the Rockies. Increased withdrawal for irrigation, municipal supply, and industrial use in states downstream might thus be possible. Another regional benefit in the western states would be to agriculture not under irrigation. Additional precipitation, particularly in the winter and spring, would have substantial benefit in the value of increased agricultural yield. Here again, this supply of water would not be depend- able, because of highly variable atmospheric conditions. Although prob- ably no improvement can be realized in the driest years and little if any advantage can be gained in the wettest years, benefits should be obtainable under the more 'lnormal" conditions. In the wheat-growing areas of the Northwest, for example, a unt~.inch increase in precipitation, obtained at. times when most needed, might produce a yield improvement of one to five bushels per acre. However, much western dry farming is in regions relatively unfavorable for artificial cloud seeding, since the mountainous terrain needed to deflect upward the moisture-laden clouds-the orographic influence in other words-is not close at hand. Hence, the prospects for precipitation increase in a locality must be appraised by examination of the conditions in that particular area. In individual watersheds the possible effects of artificial cloud seeding on the supply of water can range from zero to perhaps a 15 per cent increase. Suc.h extremes could be found, respectively, from the aTid or semidesert climates of southern Arizona and New Mexico, to the ridges of the Sierra Nevada, the Cascade l\:lountains, and the Rocky Mountains, where ideal orographic conditions exist. In the planning of water develop- ment and use in the years ahead, consideration of the potentialities of artificial cloud seeding and weather modification in each particular area 25