provided that the freezing takes place in a shorter time than its
fall. The nearer to the earth, and the more suddenly, this process
takes place, the more violent is the rain that results and the
larger the raindrops and the hailstones because of the shortness of
their fall. For the same reason large raindrops do not fall thickly.
Hail is rarer in summer than in spring and autumn, though commoner
than in winter, because the air is drier in summer, whereas in
spring it is still moist, and in autumn it is beginning to grow moist.
It is for the same reason that hailstorms sometimes occur in the
late summer as we have said.
The fact that the water has previously been warmed contributes to
its freezing quickly: for so it cools sooner. Hence many people,
when they want to cool hot water quickly, begin by putting it in the
sun. So the inhabitants of Pontus when they encamp on the ice to
fish (they cut a hole in the ice and then fish) pour warm water
round their reeds that it may freeze the quicker, for they use the ice
like lead to fix the reeds. Now it is in hot countries and seasons
that the water which forms soon grows warm.
It is for the same reason that rain falls in summer and not in
winter in Arabia and Ethiopia too, and that in torrents and repeatedly
on the same day. For the concentration or recoil due to the extreme
heat of the country cools the clouds quickly.
So much for an account of the nature and causes of rain, dew,
snow, hoar-frost, and hail.
Let us explain the nature of winds, and all windy vapours, also of
rivers and of the sea. But here, too, we must first discuss the
difficulties involved: for, as in other matters, so in this no
theory has been handed down to us that the most ordinary man could not
have thought of.