Cumulus Studies -47- 



than 40,000 square miles as a result of the seeding—about a quarter of 

 the area of the State of New Mexico. And substantially all of the rain for 

 the whole of New Mexico that fell on October 14 and 15 was the result of 

 the seeding operations near Albuquerque on October 14. "The odds in 

 favor of this conclusion as compared to the assumption that the rain was 

 due to natural causes are many millions to one." 



An early estimate by Langmuir was that about 100,000,000 tons of 

 rainfall was produced. Later, using the rain reports from 330 stations 

 given in a U. S. Weather Bureau publication, he concluded that the orig- 

 inal estimate was unduly conservative.'^) s a i^ he: "The evidence in- 

 dicated that the rain started from near the point of seeding shortly after 

 the time of seeding and then spread gradually at a rate which at no place 

 exceeded 22 miles per hour, over an area of at least 12,000 square miles 

 north to northeast of Albuquerque with an average of about 0.3.5 inches. 

 This corresponded to about 300,000,000 tons." 



SILVER IODIDE AT NEW MEXICO 



So satisfactory were the tests conducted at Albuquerque in 1948 that 

 it was decided to make a further study of cumulus clouds at that location 

 in the middle of July the following year. Much more elaborate plans were 

 made for this second expedition; for example, not one but a number of 

 airplanes took part, and virtually all the members of the Research and 

 Operations Groups went along. 



Previous to the arrival of the main body of the project, Langmuir 

 and Schaefer investigated the general cloud situation in the various moun- 

 tain regions nearby and decided the cloud systems along the Rio Grande 

 Valley near Albuquerque were superior for their purpose to anything 

 they could find in other parts of Arizona and New Mexico. In addition, 

 the excellent radar, photographic, and shop facilities of the Experimental 

 Range of the New Mexico School of Mines appeared to be ideal for carrying 

 out the operations planned. 



Eetween July 13 and July 22 a total of ten flights was conducted, on 

 eight of which two or three planes participated. Excellent co-operation 

 was enjoyed in every phase of the operation, and an extensive mass of 

 data was obtained both in the air and at the ground stations which were 

 set up. Seeding operations with varying amounts of dry ice and the 

 ground operation of a silver-iodide generator were the subjects for the 

 flight studies J 18 ) 



Again the dry-ice seeding was successful, and the results of the 

 various airborne seeding operations was quite satisfactory. Eut a new 

 factor was introduced into this second expedition which put an entirely 



