Cumulus Studies -40- 



If , on the other hand, the cloud was seeded just above the freezing level, 

 heavy rain might be produced. Similarly, water seeding by means of water - 

 filled balloons released from airplanes might dissipate a cloud and produce 

 rain at low altitudes, but it seemed that in such instances dry-ice seeding 

 would be much more effective. 



April 18, 1949 . The results of the flight on this day, with Langmuir 

 accompanying Silverthorne aloft, were so outstanding as to merit detailed 

 comment. ^1J The following is extracted from an account of the flight by 

 Langmuir in the Project Cirrus report to the government of July 30, 1951: 



"We flew up to Point Sal and found a mass of dry air above 

 the moist air coming from the sea at an altitude of about 6000 

 or 7000 feet.... From a height of about 8000 feet, looking South, 

 a whole panorama of high cumulus clouds could be seen rising 

 above the smoke, which extended up to about 11,000 or 12,000 

 feet further inland, although it was much lower than this near 

 the sea. 



"A large cloud was found which rose, I believe, to a height 

 of about 25,000 feet, and we seeded it by making a series of short 

 passes into the cloud at an altitude of approximately 21,000 feet- 

 two pellets* about one inch cubed being dropped into the cloud 

 at 50-second intervals during these passes. The whole circuit 

 of the cloud was made, and then the plane moved off a short 

 distance, enabling us to see the effect produced. 



"A band around the cloud, perhaps 500 or 1000 feet high, 

 was observed which obviously consisted of ice crystals and 

 which ultimately detached itself from the lower part of the 

 cloud and floated off as a huge mass of ice crystals that could 

 be seen for a long time. 



"After the top of this cloud had turned to ice crystals 

 and had detached itself, there was left under this cloud 

 nothing but a group of lower clouds that reached only about 

 14,000 feet, which was below the freezing level. Later we 

 flew down among these clouds and found that cloud bases 

 had gone down from 12,000 feet to about 7,000 feet. It was 

 difficult to see whether any rain was falling because of the 

 smoke, but from the lowering of the cloud base we concluded 



*Dry ice. 



