UTILIZING WATER RESOURCES OF AIR 317 
formation of rain and necessary supporting data, most evaluations 
on rain-making to date have been statistical in nature and insensi- 
tive in detecting changes of less than about 20%. When used 
properly these methods can be powerful tools in extracting infor- 
mation from the data, but they cannot make good data out of poor 
data. It is unfortunate that nearly all the rain-making evaluations 
have been made on commercial cloud-seeding operations, which 
are not primarily designed as experiments for the purpose of ob- 
taining scientific information. 
Data on the natural distribution of condensation and freezing 
nuclei should also be useful to those engaged in commercial cloud 
seeding. As mentioned earlier, there is evidence that the natural 
supply of nuclei is variable (7). At the present time most commer- 
cial cloud seeders operate on the assumption that the natural 
supply is inadequate, and attempt to overcome this deficit by 
adding more. Suggestions have been made that adding too many 
artificial nuclei to the atmosphere may result in “‘overseeding”’ 
and inhibit rainfall. In view of the possibly large fluctuations in 
the concentration of natural nuclei due to variations of wind blown 
dust, volcanic ash, meteoritic dust, sea salt, etc., it may be reason- 
able to ask how Nature knows the optimum concentration for 
rain and how she prevents ‘‘overseeding.”’ Obviously this leads 
one to speculate on the interesting possibility that there may be 
some situations in which rainfall would be increased by removing 
nuclei from the air. 
The data discussed above should also be useful in determining 
the economic value of weather modification in the arid lands. The 
monetary value of a rain-increasing project will depend upon the 
additional water resources available in the air and the cost of 
putting some of this water on the ground. If this cost is relatively 
low and if there is a reasonable chance of success, an intensive 
effort is justified. In this country, President Eisenhower has ap- 
pointed an Advisory Committee on Weather Control which plans 
to give particular attention to the economic implications and 
scientific basis of weather modification in their report, which is 
expected to be available in 1956. On the international level, the 
World Meteorological Organization’s Committee on Aerology (10) 
