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FACT VS. FANCY IN WEATHER RESEARCH Dr. James E. McDonald Institute of Atmospheric Physics, University of Arizona . The search for more usable water is the West and Southwest has been vigorously pursued for many generations. Pumpage from underground supplies, continued research into desalinization of brackish waters, and strong emphasis upon increasingly more efficient utilization of all water resources has been practiced. In 1946 an additional effort along quite different lines appeared in man's battle with the water problems in the arid West. In 1946 Dr. V. J. Schaefer of the General Electric Research Laboratory made the chance discovery that a supercooled cloud of water drops could be converted into a cloud of ice crystals by addition of very small amounts of dry ice. Since one of the principal mechanisms for the natural production of rainfall in clouds depends critically upon just this conversion of water into ice, this discovery was immediately recognized to open new and interesting possibilities of artificial control of precipita- tion processes. Very shortly after Dr. Schaefer's discovery of the action of dry ice Vonnegut discovered the similar effect of silver iodide crystals. Everyone is now familiar with the way in which these discoveries led to a rapid growth of interest and premature activity in the direction of attempts to seed clouds to increase rainfall. It was almost unfortunate, from a scientific viewpoint, that seeding clouds was so simple a technique, for practice almost immediately outstripped theory and no one really knew at all whether many relatively expensive seeding efforts really led to any economically significant effects. After the first few years of uncontrolled and poorly designed seeding enterprises, a number of scientific efforts to test the efficacy of cloud modification techniques have been begun. The U. S. Weather Bureau, the Canadian government, the Australian government, many universities, and many private businesses have organized fairly carefully designed experiments and there is slowly accumulating a body of experience in this field. Unfortunately, as of 1954, this body of experience contains a still confusing array of favorable and unfavorable results. It is now quite generally agreed that it is indeed possible to alter natural cloud growth processes in discernible ways. It is not yet agreed, however, that these alterations permit man to increase significantly the amounts of precipitation released from clouds. So complex are the internal mechanisms of cloud growth and precipitation development that scientists still work in ignorance of the precise details of the processes - 11 -