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<br />I BACKGROUND <br /> <br />.' <br /> <br />Probably the first rain stimulation proposal having any reason- <br /> <br />able scientific basis was that made by James P. Espy. In the <br /> <br />AprilS, 1839 issue of, the National Gazette and Literary Regis- <br /> <br />ter of Philadelphia, Espy proposed that large fires be built to <br /> <br />generate updrafts. He felt that in a humid atmosphere, cumulus <br /> <br />clouds would develop and eventually produce rain. There are no <br /> <br />records that indicate the scheme led to any field trials and it <br /> <br />was not until the 1880's that congress appropriated $10,000 to <br /> <br />conduct some field experiments based ,on a very old idea that <br /> <br />"it always rains after a battle". Explosive charges were car- <br /> <br />ried aloft by balloons and the tests were followed by optimistic <br /> <br />reports. The work of T. Bergeron and W. Findeisen in the 1930's <br /> <br />~~ . <br /> <br />developed the concept of supercooled water clouds, crystallizat- <br /> <br />,L <br /> <br />1 '. <br /> <br />" <br />ion, and "warm rain" and "cold rain" process. <br /> <br />Modern scientific weather modification had its serious begin- <br /> <br />nings in the 1940's at the General Electric Laboratories in <br /> <br />Schedectady, New York. Dry ice and silver iodide were the strong <br /> <br />candidates, used by Irving Lamgmuir, vincent Schafer, and Bernard <br /> <br />Vonnegut during these early laboratory and field trials. Nuclea- <br /> <br />ting agents have changed very little over time and the materials <br /> <br />used by Western Kansas Weather MOdification as well as most of <br /> <br />the other projects throughout the world are silver iodide, in <br /> <br />various forms, and dry ice. <br />