422 
petitive advantage that seeding may give to one 
cloud in relation to others. 
It is planned for the present to develop fur- 
ther the model that has been proposed here and 
to attempt to bring it to the poimt where ex- 
perimental verification of it can be sought. 
REFERENCES 
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DISCUSSION 
Hovcuton, H. G., Problems connected with the 
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Kraus, E. B., anp P. Squires, Experiments on the 
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Discussion 
Dr. Joanne S. Malkus—I think this is one of 
the best descriptions of tropical clouds. I have 
read Dr. Howell’s paper in some detail, and have 
listened to his lecture, and I like this approach 
on cloud modification very much. I think this 
is because Dr. Howell is not just dumping in 
stuff and making statistical analyses, but he is 
also asking questions concerning the processes at 
work. 
Dr. Bernard Vonnegut—Our observations in 
New Mexico show that at about the same time 
that the cloud suddenly grows and gives precipi- 
tation there is also an extremely rapid buildup 
of electricity. The electric field frequently dou- 
bles every minute or two so that in ten minutes 
it can inerease by two or even three orders of 
magnitude. I think it would be exceedingly inter- 
esting in observations of clouds to observe not 
only the onset of precipitation but also the de- 
velopment of electrification. 
Dr. Walter Hitschfeld—I would like to ask a 
question about the system of organization that 
you mentioned. You started out with a popula- 
tion of small clouds; one of the clouds for some 
reason is able to develop ahead of the others, 
and then somehow is able to organize the devel- 
opment of the remainder of the clouds. What is 
the scale? What is the range over which such an 
organization could be active; and further, have 
you any idea of how it might work? 
Dr. W. E. Howell—First as to scale and range. 
Dealing with impressions rather than measure- 
ments, I would say that clouds approaching the 
critical stage have a depth, typically, of 15,000 
to 20,000 ft, and are roughly the same in diam- 
eter, three miles or so. After passing the critical 
stage they may grow perhaps five times their 
horizontal size and to a depth of perhaps 50,000 
ft, still guessing. This impression was gained from 
