The Stourbridge Observer, Cradley Heath, Halesowen & District Chronicle.
Stourbridge, West Midlands, England, 1883-12-29 00:00:00

THE FORMATION OF RAIN DROPS.

Various theories have been advanced to account for
the formation of rain drops, but the most satisfactory
explanation is that proposed by Professor Osborne
Reynolds. The minute particles of which clouds are
composed are moving downwards in consequence of the
attraction of gravity ; but, by reason of the resistance
which the air offers to their descent, they are only
moving very slowly. Since, however, the resistance
offered to the passage of large drops is much smaller in
proportion to their weight than that offered to small
drops, it follows thr.t the large drops will descend
faster than the smaller ones, and will overtake them,
comiug into collision with any which are in the direct
line of their descent. When two drops collide they
will unite to form a larger drop, which will descend
with increased velocity, sweeping up all smaller drops
in its path, and thus increasing in size until it emerges
from the cloud. Since many clouds are several miles
in thickness It is easy to see that a particle descending
from the upper part of the cloud may become a rain
drop of considerable size before it emerges from the
cloud. In their passage from the cloud to the earth
the larger rain drops will overtake the small ones in a
precisely similar way; at the same time the size of the
drops may be slightly increased by the condensation of
water from the air through which they are falling, or
may be slightly diminished by partial evaporation from
the eurfaooe of the drops. A falling rain drop descends
with a velocity which increases until the acceleration is
balanced by the resistance of the air, after which the
drop descends with uniform velocity. It is, of course,
well known that large clouds may exist without any
rain falling from them. In some cases rain is actually
formed, but evaporates and is again converted into
va.,our before it can reach the ground; in many cases
the non-formation of rain is possibly due to the fact
that under certain unknown atmospheric or other con-
ditions the particles forming the clouds do not unite
when they collide. As an agent of geological change,
rain is of the greatest importance. It plays a largo
part in the disintegration of rocks and the formation of
soils, washes the smaller particles into streams and
rivers, and is ia fact one of the most important of the
various denuding agents. Indeed, since rain is the
ultimate source of all our brooks, rivers, Sec., it may be
said to be the principal agent of geological change on
the earth's surface. The amount of the rainfall varies
very considerably in different countries, and in different
par!s. of the same country, depending on geographical
position, the conformation of the surface of the
ground, the proximity of large lakes and the sea, etc.
Toe heaviest annual fall of rain occurs in the zone of
calms over the equatorial region of the Atlantic and
Pacific Oceans, and on the Weet coasts of the British
Isles, India, Norway, North and 6outh America, and
New Zealand. In all these latter districts the wet
wind blows over a large tract of ocean and becomes
heavily charged with moisture, which it deposits when
forced upwards by the action of the mountains on the
coasts. The driest districts in the world are the deceit
regions of Africa and Asia. The amount of rain which
falls in single showers is sometimes enormous, especi-
ally in the Tropics. In the British Isles one of the
heaviest falls on record is a fall of 5.36 inches in
twenty.four hours in Monmouthshire, July 14th, 1875.
On October 25, 1836, at Gibraltar there was a fall of
30•11 inches.—Cassell's Ccmcise Cyclopcedia.