Cumulus Studies -53- 



"The total amounts of rain that fell in the state on the 

 two days as a result of seeding were found to be 800 million 

 tons on October 14, 1948 and 1600 million tons on July 21, 1949. 

 If these units are not so familiar to you, I may say that on 

 October 14, 1948, the total amount of rain resulting from seed- 

 ing was 160 billion gallons and on July 21, 1949, 320 billion 

 gallons. 



"Dr. Vonnegut has measured the number of effective sub- 

 limation nuclei produced by the type of silver-iodide smoke 

 generator used in our New Mexico experiments for each gram 

 of silver iodide used.... One thus finds that, to get a 30-percent 

 chance of rain per day within a given area in New Mexico, the 

 cost of the silver iodide is only $1. for 4000 square miles. 



"If similar conditions prevailed over the whole United 

 States, the cost per day to double the rainfall would be only 

 of the order of a couple of hundred dollars. This verified an 

 estimate that I made in November, 1947 in an address before 

 the National Academy of Sciences that e a few pounds of silver 

 iodide would be enough to nucleate all the air of the United 

 States at one time, so that it would contain one particle per 

 cubic inch, which is far more than the number of ice nuclei 

 which occur normally under natural conditions.' Such a dis- 

 tribution of silver -iodide nuclei 'in the atmosphere might 

 perhaps have a profound effect upon the climate.' " 



The report then discusses a new theory which Langmuir had devel- 

 oped of the rate of growth of snow crystals in supercooled clouds contain- 

 ing known numbers of sublimation nuclei. After a brief exposition of the 

 basis of this theory, he says: 



"From the probability theory of the growth of showers 

 from artificial nucleation, one obtains the result that the 

 total amount of rain produced by operating a ground generator 

 increases in proportion to the square of the amount of silver 

 iodide used. Thus, with three times as much silver iodide 

 one would get nine times the rainfall. The intensities of the 

 showers would be no greater, but they would extend over a 

 greater area. 



"An analysis of the July 1949 rainfall in New Mexico, 

 Arizona, Colorado, Oklahoma, Kansas, and Texas gives evidence 

 that a band of heavy rain progressed in an easterly direction 

 during the period of July 20 to July 23 from southern Colorado 

 across the southern half of Kansas, where it gave 3 to 5 inches 



