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<br />and reduction in frequency and severity of floods. The fact that the <br />prt'sent scientific basis for expecting such results is meager does not nec- <br />essarily mean that the longer-range prospects are negative, for examina- <br />tion of the problems has just hegun. <br />Cloud seeding in some instances can be done at a cost of only a few <br />cents an acre, with possible returns a hundred times as great. It there- <br />fore has something of the aspects of a treasure search, with possibilities <br />of a rich strike, or even a bonanza, on relatively low expenditures. But <br />the likelihood of return, as in the case of a mineral strike, is not e\'ery- <br />where the same. The probability of return, the extent of results and the <br />area of their incidence therefore are matters not only of scientific interest, <br />but of great practical significance. <br /> <br />There have been four differing opinions regarding the success of weather <br />modification efforts. On the one extreme are claims of the weather modifi- <br />cation contractors to the effect that their activities have directly caused <br />heavy increases in precipitation. A.t the other extreme are conservative <br />meteorologists who feel that there are insufficient data for appraisal of <br />the results, or that if there are any effects, they must be small. The views <br />of the groups employing the "rainmakersll range between these extremes, <br />most of them apparently feeling that some beneficial results have been <br />secured. Still another position is held by some of the pioneering physicists <br />in this field, who claim that major cyclical changes in preciphation patterns <br />over thousands of miles have been due to cloud-seeding experiments. <br />Just as evaluation of the early experiments was hampered by the <br />extreme natural variability in weather conditions, it has been difficult to <br />distinguish effects which might be due to commercial cloud-seeding efforts. <br />Although much cloud seeding has been performed during the past ten <br />years, only a small fraction has been for the particular purpose of obtaining <br />scientific data on which to base conclusions of its effectiveness. However, <br />several experimental projects devoted specifically to determining the ef- <br />fectiveness of cloud seeding have been undertaken by the United States <br />\Veather Bureau and others in the United States, and abroad. <br />Few scientific efforts in modern times have been accompanied by 50 <br />much controversy as weather modification. No doubt this has been fed <br />by the understandable professional optimism of the commercial rain- <br />makers. Public interest became so intense that an objective group, the <br />Advisury Committee on Weather Control, was established by act of Con- <br />gress in 1953 to make "a complete study and evaluation of public and <br />private experiments in weather control," and report upon it. <br />From an analysis of the results of the research studies mentioned above <br />and many commercial cloud-seeding projects, the Advisory Committee <br /> <br />, <br /> <br />~ <br /> <br />22 <br />