INDUCED PRECIPITATION 293 
Decay factor of silver iodide freezing nuciei 
O:OOO! 
O:0000I6 30 40 6O 80 100—s«*I2O 140 
Duration of exposure of silver iodide agcroso! to the 
atmosphere (minutes) 
Figure 2. The decay in activity of silver iodide particles from a 
hydrogen burner and a kerosene burner respectively. 
fact a very steep function of air temperature as shown in Figure 
3. While the silver iodide might decay by a factor of 10 in a few 
minutes at ambient temperatures between 20° and 30° C, the 
decay is only a factor of 10 in several days at a temperature of 
Solin 1G, 
This result explains the failure of many ground seeding opera- 
tions which have been carried out at relatively high temperatures 
on flat terrain. What is more important, it suggests the methods 
by which silver iodide might be successfully used for producing 
effects over wide areas. 
