deliberate introduction into clouds of various substances that act as condensation nuclei or ice nuclei in an attempt to induce precipitation. The first experiments with cloud seeding were conducted in 1946; since then seeding has been performed from aircraft, rockets, cannons, and ground generators. Many substances have been used, but solid carbon dioxide and silver iodide have been the most effective; when used in supercooled clouds (composed of water droplets at temperatures below freezing), they form nuclei around which the water droplets evaporate. The resulting water vapour deposits into ice crystals, which build quickly as water droplets attach themselves. Attempts have been made to use these substances to minimize damage to crops and buildings from hailstones.