Q. Why does not the cold of night always cause rain?
A. When the air is not near saturation (although condensed by the chill of evening), it will still be able to hold its vapour in solution.
Q. Why does a passing cloud often drop rain?
A. Because the cloud (travelling about on the wind) comes into contact with something that chills it; and its vapour being squeezed out, falls to the earth as rain.
Q. Why are rain-drops sometimes much larger than at other times?
A. When the rain-cloud is floating near the earth, the drops are large, because such a cloud is much more dense than one which is more elevated.
The size of the rain-drop is increased according to the rapidity with which the vapours are condensed.
Q. Does not wind sometimes increase the size of rain-drops?
A. Yes; by blowing two or more drops into one.
Q. Why do clouds fall in rainy weather?