INDUCED PRECIPITATION 299 
It implies that the fundamental rainmaking process in the atmos- 
phere is a seeding process and that the atmosphere is much more 
free from rain-forming nuclei than has previously been supposed. 
Conclusion 
These results suggest that the arrival of dust in the upper 
atmosphere and its descent to the ground might turn out to be 
one of the most important factors controlling rain formation. It 
focuses attention on several broad fields of study which would 
be important in this regard: 
1. The study of meteors in all their aspects, particularly the 
neglected field of meteoric dust. 
2. The physics of dust falling through the atmosphere. 
3. The properties and distribution of freezing nuclei in the 
lower atmosphere. 
From the point of view of artificial weather modification, it 
suggests: (a) that the effects might be very much greater than 
was otherwise supposed; (4) that the most effective seeding opera- 
tions might be those which are designed to influence the weather 
on a continent or hemisphere wide basis, rather than operations 
intended to cover a few square miles of territory only. 
REFERENCES 
1. Bolton, J. G., and N. A. Qureshi. 1954. The effects of air tempera- 
ture and pressure on the decay of silver iodide. Bull. Am. Met. 
Soc., 35, 395-399. 
2. Smith, E. J., and K. J. Heffernan. 1954. Quart. F. Roy. Meteorol. Soc., 
80, 182-197. 
eepomich b) |. Ke - Hefernan, and Ba Ke Seely. 1955. dhe decay, 
of ice nucleating properties of silver iodide in the atmosphere. 
F. Meteorol., 12, 379-385. 
