In the eleventh verse of Surat az-Zukhruf, rain is defined as water
sent down in "due measure". "It is He (God) Who sends down water in
due measure from the sky" (Qur=92an, 43:11)
Indeed, rain falls on the earth in an unerring measure.
The first of the measures related to rain is its speed of descent.
When dropped from a height of 3937 feet, an object having the same
weight and size as a rain-drop would continuously accelerate and fall
on the ground at a speed of 347 miles/h. The average speed of
raindrops, however, is only 9.3-12.4 miles/h.
The reason for this is that the raindrop has a special form that
increases the frictional effect of the atmosphere and helps it fall on
the ground more slowly. A glance at the figures below is sufficient to
understand the disaster the earth would face every time it rained if
rain raindrops were in a different form, or the atmosphere did not
have the quality of friction.
The minimum altitude of rain clouds is 3937 feet. The effect caused by
a single drop falling from that height is equal to a 1 kg object
dropped from 5.9 inches. There are also rain clouds at altitudes of
32808 feet. In this case, a single drop would have an effect equal to
a 1 kg object dropped from 43.3 inches.
It is estimated that in one second, approximately 16 million tons of
water eva****ate from the earth. This number is equal to the amount of
water that drops on the earth in one second. In one year, this figure
amounts to 505x1012 tons. Water continuously circulates in a balanced
cycle according to a "measure".
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