in 1946 when Vincent Schaefer and Irving Langmuir demonstrated that 

 it was possible to initiate precipitation by dropping pellets of carbon 

 dioxide from an airplane into a cloud composed of water droplets at 

 below-freezing temperatures. This dramatic development led to Project 

 Cirrus, a broad theoretical and field program intended to establish a 

 strong scientific basis for cloud modification. Perhaps the most important 

 scientific finding was that silver iodide crystals were as effective as dry 

 ice in transforming supercooled clouds into ice-crystal clouds, and thence 

 to rain. More spectacular — and more controversial — were ( 1 ) an experi- 

 ment with seeding a hurricane off the east coast, with inconclusive re- 

 sults and (2) experiments by Langmuir that convinced him (but very 

 few others) that periodic seeding of the atmosphere with silver iodide 

 in the southwestern United States produced corresponding periodicities in 

 the rainfall 2,000 miles to the east. 



Enough interest was stimulated by Project Cirrus to set in motion two 

 other agency projects. The first was the Cloud Physics Project under the 

 auspices of the U.S. Weather Bureau, the Air Force, and the National 

 Advisory Committee for Aeronautics, conducted from 1948 to 1951. The 

 second was a 5-year Department of Defense project which began in 1952. 

 These serious efforts yielded inconclusive results because of their brevity, 

 the primitive state of the art of instrumentation, and partly because the 

 design of the experiments was not sufficiently sophisticated to filter out 

 the natural variability of the atmosphere. 



Meanwhile, a determined band of meteorological entrepreneurs moved 

 in and succeeded in placing nearly ten percent of the land area of the 

 country under commercial seeding, from strategically located silver iodide 

 generators, at an annual cost of between 3 and 5 million dollars. The 

 movement spread to 30 other countries. 



Sufficient interest and controversy were generated by these results that 

 Congress established in 1953 an Advisory Committee on Weather Control to 

 study and evaluate the results of private and public experiments. Its report 

 issued in 1958 was cautiously optimistic, concluding that increases of 10 

 to 15 percent in rainfall were induced by seeding spring and winter storms 

 in the mountainous areas of the western United States. More long-term 

 research was recommended with special responsibilities being assigned to 

 the National Science Foundation. The Advisory Committee report was 

 subjected to considerable attack, primarily on statistical grounds. How- 

 ever, the NSF did mount a modest but sound program of fundamental re- 

 search and field experimentation, which laid an important basis for the 

 next decade. As a result of extravagant claims and questionable practices 

 by a few commercial cloud seeders, and controversy on statistical inter- 

 pretation of experimental results, the field did not flourish during the 

 early 1960's. 



A two-pronged study was initiated in 1963 and 1964, by the National 



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