Induced Precipitation 
E. G. BOWEN 
Division of Radiophysics, Commonwealth Scien- 
tific and Industrial Research Organization, Syd- 
ney, Australia 
It is assumed that the reader is familiar with the processes of 
inducing rain to fall from clouds by introducing materials like dry 
ice, water, or silver iodide into the clouds at an appropriate stage 
in their development. No attempt will be made to review the 
previous history in this field, but an account will be given of two 
new developments which may have an important bearing on the 
future of weather control. The first of these deals with some new 
discoveries in relation to silver iodide seeding, the second with an 
unexpected contribution from a field of science normally thought 
to be outside the bounds of cloud physics. 
Silver lodide Seeding 
A vast number of seeding operations have been carried out in 
the past few years in which silver iodide has been dispensed into 
the atmosphere from smoke generators on the ground. It is safe 
to say that the net result of these operations has been to produce 
more controversy than they have rainfall, despite the fact that in 
the laboratory, silver iodide is unquestionably a highly efficient 
freezing nucleus. 
Looked at from a physical point of view, and quite apart from 
the question of whether there has been any effect on rainfall, two 
obvious points require checking: (a2) whether the silver iodide 
remains effective as a freezing nucleus when exposed to the at- 
mosphere; and (4) whether it can attain the requisite height, 
which in summer might be of the order of 15,000 or 20,000 feet. 
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