Early History -10- 



"Curt flew into the cloud and I started the dispenser in 

 operation. I dropped about three pounds (of dry ice) and then 

 swung around and headed south. 



"About this time I looked toward the rear and was thrilled 

 to see long streamers of snow falling from the base of the cloud 

 through which we had just passed. I shouted to Curt to swing 

 around, and as we did so we passed through a mass of glistening 

 snow crystals!.... We made another run through a dense portion 

 of the unseeded cloud, during which time I dispensed about three 

 more pounds of crushed dry ice..... This was done by opening 

 the window and letting the suction of the passing air remove it. 

 We then swung west of the cloud and observed draperies of snow 

 which seemed to hang for 2-3000 feet below us and noted the 

 cloud drying up rapidly, very similar to what we observe in the 

 cold box in the laboratory.. ...While still in the cloud as we saw 

 the glinting crystals all over, I turned to Curt and we shook hands 

 as I said 'We did it!' Needless to say, we were quite excited. 



5 'The rapidity with which the C0 2 dispensed from the window 

 seemed to affect the cloud was amazing. It seemed as though it 

 almost exploded, the effect was so widespread and rapid.. .'„.... 



"When we arrived at the port, Dr. Langmuir rushed out, enthu- 

 siastically exclaiming over the remarkable view they had of it in 

 the control tower of the G.E. Lab. He said that in less than two 

 minutes after we radioed that we were starting our run, long 

 draperies appeared from the cloud vicinity." 



This first seeding flight was of tremendous significance. Not only did 

 it show that the laboratory experiments and calculations were justified, but 

 it also contributed new material to the rapidly accumulating store of know- 

 ledge. For example, it suggested that the veil of snow that first appeared 

 immediately below the cloud could not have been produced by snow falling 

 from the cloud but rather was produced directly by the action of the dry 

 ice pellets falling into a layer of air below the cloud which was saturated 

 with respect to ice but not with respect to water. 



Subsequent experiments proved that it was also frequently possible to 

 seed a supercooled cloud by flying just below it and dropping dry ice. The 

 thickness of the layer in which such seeding is possible is about 10 meters 

 for each degree C below the freezing point at the cloud base. The ice crys- 

 tals thus formed may be carried up into the cloud if the cloud is actively 

 growing by convection. 



