CLOUD SEEDING IN THE AMERICAN TROPICS 
Fie. 3—Towering Cumulus in tropical air over land, showing umbrella of 
cirrus recently separated from top of a Cumulus tower which has since dis- 
sipated 
under circumstances such as these precipitation 
does become well established in one cloud, it is 
hard to avoid the impression that a marked in- 
crease in the rate of growth of the cloud is often 
connected with the onset of precipitation, ac- 
companied by the degeneration of other clouds 
in the vicinity. New towers rise from the top of 
the precipitating cloud to much greater heights 
than formerly and take on the aspect of Cumulo- 
nimbus; the cloud base darkens; and the im- 
pression of roiling, tumbling growth-and-dissi- 
pation activity is replaced by one of swift 
organization of a large-scale convective cell. The 
ensuing rainfall, while sometimes heavy, is likely 
to be much more spotty than that accompanying 
Sequence I. 
Both sequences, together with gradations be- 
tween them, were observed during our seeding 
activities in Cuba. After the first season’s work 
we drew daily isohyetal maps [Howell Associates, 
1952] and examined them for connections be- 
tween the pattern of rainfall and the pattern of 
seeding. It was immediately noticed that about 
a third of the maps showed good correspondence 
