填空题

Rainmaking Scientific rainmaking was started by Vincent J. Schaefer after the year of (1) . A lucky (2) brought him to success. Schaefer was hired, during World War II, by Dr. Irving Langmuir to study how and why (3) forms on the wings of airplanes. The two went to New Hampshire because (4) were common and cold winds often blew. In New Hampshire, they were surprised to learn that the temperature of the clouds surrounding them was far below the (5) , and yet ice did not form there. After the war Schaefer went on the experiment. One morning a friend asked him to go for lunch. He went and left the (6) of the freezer up. When he returned from lunch, he found the temperature of the freezer was (7) than that required for ice crystals to remain solid. There were two choices now. He could wait for the freezer to lower the air temperature or he could add (8) ice. He chose the latter. Then when he did this, he happened to (9) a large amount of air. Suddenly he saw (10) were formed. He did the experiment again and succeeded in making a tiny snowstorm in the laboratory.