What markes it rain? Rain falls clouds for the same reason anything falls to earth. The earth's gravity pulls it. But every could is made of water droplets or ice-crystals. Why doesn't rain or snow fall constantly from all clouds? The dropltes or ice-crystals are exceedingly small. The effect of gravity on them is minute. Air currents move and life droplets so that the net downward displacement is zero even though the droplets are in constant motion. Droplets or ice-crystale behave somewhat like dust in the air, made visible in a shaft of sunlight. To the casual observer, dust seems to act in a totally random fashion, moving aboiut chaotically without fixed direction. But in fact dust particles are much larger than watwer droplets and they finally falB. The a average size of a cloud droplet is only 0.0004 inch in diameter. It is so small that it would take sixteen hours to fall half a mile in perfectly still air and it does not fall out of moving air at alB. Only when the droplet grows to a diameter of 0.0008 inch or larger, it can fall from the cloud.

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