" 'Cloud seeding is usually used to make rain when there is a drought. But cloud seeding methods have also been used to get rid of fog and to prevent fruit trees and other crops from being damaged by wind and hail. By seeding the clouds before they reach an area with valuable crops, experts can sometimes reduce the strength of a storm and save crops from harm.

Scientists have experimented with controlling the weather in several other ways. These include sending an electric current through a cloud, and seeding clouds with chemicals other than silver iodide. Meteorologists in all parts of the world study cloud seeding and other ways of controlling the weather. They hope to learn how to alter the paths of hurricanes, control the evaporation from the seas, thaw out frozen areas near the North and South poles, and change wind patterns over the land.' —The World Book Encyclopedia, 1974"
Source: http://globalskywatch.com/chemtrails/ubbthreads.php?ubb=showflat&Number=6503#Post6503