Cumulus Studies -52- 



Tn fact, this decrease followed quite accurately equations (2) 

 and (3), which indicated that the rain fall depended on the con- 

 centration of nuclei, and this, in turn, varied inversely in pro- 

 portion to the distance from the source. 



"This analysis makes it possible to separate the effects 

 of the artificial silver -iodide nuclei from that- of the background 

 of sublimation nuclei that were' already present in the atmosphere. 

 The analysis gave proof that C = 0, so that there was no appreci- 

 able background on each of these two days. We must conclude 

 that nearly all of the rainfall that occurred on October 14, 1948 

 and July 21, 1949 was the result of seeding. 



"The agreements between the intensity of the average rain- 

 fall in separate regions and the theoretical equations were so 

 good in each of the four sectors on October 14 and July 21 that 

 the probability factors for each sector ranged from 10 2 to 10 3 . 

 Taking all the octants together, the probability factor rose to 

 about 10 8 to 1. 



"For each of the eight octants that gave appreciable rain, 

 the rain started progressively later as the distance from the 

 source of the silver iodide increased. The advancing edge of 

 the rain area thus moved from Albuquerque on July 21 at a 

 velocity of about 15 mph and on October 25 at a speed of about 

 25 mph. These velocities agree well with the wind velocities 

 observed at various altitudes. 



"The method of correlation coefficient can be applied to 

 the relation of the time of the start of the rain to the distance 

 from Albuquerque. This indicates that there is another prob- 

 ability factor which is the order of 10 8 to 1. 



"Taking these results altogether, it seems to me we may 

 say that the results have proved conclusively that silver -iodide 

 seeding produced practically all of the rain in the State of New 

 Mexico on both of these days. 



"I have not mentioned what happened on the other days. 

 The results, although somewhat more complicated due to the 

 overlapping of the effect of seeding on successive days, are 

 almost as striking as those of Flights 45 and 110, in which we 

 used silver -iodide seeding. Very high probability factors are 

 found, which help confirm the results indicated by the analysis 

 of Flights 45 and 110. 



