Results in Hawaii -43- 



This was an important development. Although Langmuir had given 

 some thought to the effects of seeding nonsupercooled clouds, he hadn't 

 done much about it, and this new work caused him to restudy theoretical 

 calculations he had prepared in 1944 in connection with the work at Mt. 

 Washington^ U > 



He now had a new approach to the subject of weather modification: 

 the growth of rain. 



RAIN CHAIN REACTION 



The result was Langmuir's chain-reaction theory of rain production, 

 in brief, as follows: A typical large drop of water grows in size as it falls 

 through the cloud, growing faster and faster until it gets so big that it 

 breaks up, producing smaller droplets. If there are rising air currents, 

 the little droplets will be borne aloft into the cloud again, growing in size 

 as they go, until they get so big that they start falling again. This process 

 continues in a chain reaction, causing the whole cloud to go over into heavy 

 rain. Under the right circumstances, according to this theory, seeding 

 with water would be just as good as with dry ice. (13) 



The outgrowth of this, in turn, was considerable work by Project 

 Cirrus to test Langmuir's theory and apply some of its principles in prac- 

 tice. For example, to determine the validity of several of the important 

 phenomena which his theory postulated, laboratory studies were initiated 

 of the growth of water droplets and of the behavior of droplets floating in 

 the air.*- ' These studies continued for a considerable period in the 

 laboratory, and some very interesting observations were made and data 

 collected. Later, the Research Group did considerable work in the study 

 of the drop size and size distribution of various types of precipitation. (2,3) 



As another approach to the subject, an extensive series of exper- 

 iments was conducted to explore the possibility of inducing precipitation 

 or other modification in growing cumulus clouds by water seeding. (21) 



The complete exposition of the theory by Langmuir was a beautiful 

 example of theoretical analysis and mathematical calculation. (13) Among 

 other things, it reviewed the knowledge of cloud physics which had al- 

 ready been gained in the light of the new theory, summing up the probable 

 behavior of both stratus and cumulus clouds. It went so far as to suggest 

 that the chain reaction could, under the right conditions, be started by 

 introdicing even a single drop of water into a cloud, although the action 

 would be most rapid when many large drops were introduced near the 

 top of the cloud. It outlined the probable behavior of self -propagating 

 storms. It postulated that the phenomena that occur in artificial seeding 



