How do they make rain?

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Got this from "How do they do it?" book. Just want to share with you!In 1946 Vincent Schaefer and Irving Longrnuir started their work at the General Electric Research Laboratories in Schenectady, New York, which proved that rain clouds could be artificially, encouraged to produce showers. Clouds are made up of billions of particles of water too small to fall as rain. Only when the droplets grow to a quarter of a millimeters or more will they fall as a fine drizzle. Smaller droplets evaporate before reaching the ground. One way the droplets grow is by freezing to form particles of ice. In a cloud containing some ice particles and some water droplets, the ice particles grow rapidly as the droplets evaporate and the vapor is transferred to the ice. Since the temperature of clouds is often below freezing it might be expected that the droplets would freeze easily. But the water can be 10 or 20 degrees below freezing (super cooled) without actually freezing. The reason for this is that the water in clouds is absolutely pure, without any dust or other contaminants which can form the centre of an ice crystal. If tiny particles are provided, the droplets freeze, grow quickly until they are large enough to fall, and then melt as the temperature rises, reaching the ground as rain. Schaefer and Longtnuir proved that small particles, usually of silver iodide, added to super cooled clouds could create rapidly growing ice crystals. These particles have been dropped from aircraft, carried by rockets or even released at ground level for air currents to carry them aloft. In the Soviet Union, 70mm artillery guns have been used to fire silver iodide particles into clouds, exploding at the right height to disperse the chemical. As long as the clouds are super cooled the technique may work - increasing rainfall by up to a fifth. But since it is impossible to know how many rain would have fallen anyway there are still question marks over the method’s economic effectiveness.