Silver Iodide and dry ice are used to seed clouds, which
is a type of weather modification. The practice is usually
to create rain or snowfall where needed, such as over an
area of drought or ski area, or to modify or suppress other
weather conditions such as hail and fog, such as around
an airport.
Cloud seeding was first discovered in 1946 and has been
experimented with for many decades over many areas of the
world creating various results and controversies. The principle
is to introduce ice nuclei into the atmosphere to attract
moisture until the weight is such that it falls as snow
or rain. Currently, the most active country seeding clouds
is China.
