Cumulus Studies -48- 



different aspect upon the results and had a tremendous influence on the 

 course of future investigations and analysis. This was the effect of ground 

 seeding with silver iodide. 



As usual, close attention was paid to changes in weather conditions, in 

 order to observe any correlation between such changes and the dry-ice seeding. 

 But, although Vonnegut was conducting some silver -iodide seeding on the 

 ground, this was disregarded by Langmuir, who was concentrating on the air- 

 borne dry-ice seedings. Consequently, when he noticed some weather conditions 

 which could not be explained by the airborne seeding, he was puzzled. 



Then he suddenly became conscious of the fact that Vonnegut had been 

 trying to call the ground seeding of silver iodide to this attention, and he im- 

 mediately realized that this might explain the discrepancies he had observed. 

 Further study convinced him that this was, indeed, the case. 



Not only that, but the results of the seeding activities in New Mexico the 

 preceding year were reconsidered in the light of this development. And it 

 appeared reasonable to conclude that the similar widespread effects produced 

 in October, 1948, were the result of the silver-iodide seeding which was done 

 at that time, rather than of the dry-ice seeding, which had been the previous 

 interpretation. 



Langmuir made, as was his habit, an exhaustive analysis of the available 

 data and presented a striking summary of his findings^"' from which the fol- 

 lowing is quoted: 



"I wish particularly in this paper to describe the more wide- 

 spread effects that were produced by the operation of the silver - 

 iodide generator on the ground during July, 1949, near Albuquerque. 

 The first seeding with silver iodide during this stay in New 

 Mexico was on July 15, 1949, but the generator was not run for 

 more than a couple of hours on each day thereafter until the 19th, 

 when it was operated for a short time only, late in the afternoon. 

 On July 20 it was not operated at all, but on the 21st it was op- 

 erated for 13 hours, starting about 5:30 a.m. and using 300 

 grams, or a total of 2/3 pound of silver iodide. 



"Tests made by Dr. Vonnegut have shown that each gram of 

 silver iodide dispersed under these conditions produced 10 16 

 sublimation nuclei that are slowly effective at -5°C but very 

 rapidly effective at -10°C„ 





