The Savannah morning news., 1901-08-11
WHEN AND WHY 1T RAINS.
Nothing About Next Weeks weather
but an EpitOme of Observed Facts.

Nothing About Next Weeks Weather
but an Epitome of Observed Facts.
From the London Standard.
The distribution Of rainfall is the
subject of a very interesting mono
graph written by DIR. A. ]. Herbertson
and published the other day by Mr..
John Murray. The amount of the rain
fall depends on a variety of causes.
First among them are heat and cold.
All the rivers, says the preacher. ran
into the sea, yet the sea Is not full.
With good reason, because the sun
pumps the water up into the air, from
which 1t is again sent back by the
cold of space; as the air cools. 1t be-
comes less capable of retaining vapor.
so the water reappears, first as clouds,
and then as rain. Thus the amount
Of rain Is often greatest in tropical
countries at any rate near an ocean,
while in polar regions it is compare
lively small-and often comes down as
snow. But the continents and oceans,
the dominant winds, which are partly
dependent on them, and the differences
OF level In the ground. all affect the
rainfall Of a district, both as regards
its total amount and its distribution
over the year. 1t may range from
Desert of Cobb. a zone In Northern
Africa-including the Sahara, and ex-
tending eastward across Aabia to-
ward Afghanistan--and a narrow strip
of South America, west of the Peru
Wan and Chilean Andes, are rainless;
while the other extreme is represented
in the Khasia Ghauts, where the an
nual fall sometimes reach 600 inches.
the greater part of which comes down
in about half the year. In our own
country we think four to five inches
in twenty-four hours a record, but
at one station in these Ghauts nearly
forty-one inches fell on a June day
in 1876. In our islands the eastern
coasts are much drier than the west
ern, and the lowlands than the up
lands. Winds blowing from the At
lantic come to our shores laden with
vapor, and on these II is condensed.
Rising ground hastens the process;
the air is cooler there. for the Their
mometer falls about one degree for
each 300 feet of ascent, and the hills
themselves. like big stone in the path
of stream, force the vapor-laden cur
rents up into yet colder regions. Owing
to the first cause, while about two feet
of rain falls annually in London, al
most half as much again Is measured
on the Lancashire coast. For the sec
ond reason, the fall is about So inches
at the Woodhead reservoirs, and al
most So at those on Rivington Pike,
whence Manchester and Liverpool once
drew their chief supplies. But the wet
test spot in the British Isles is near
the head of Borrowdale, where about
$50 inches are registered every year.
Apart from these variations, the rain
fall, DR.. Herbertson tells us, is distri
buted in seven belts girdling the earth.
a G a which
is bounded by two tropical dry belts;
the temperate zones are wet, and are
succeeded by dry polar caps. But this
system, as might be anticipated, is not
fixed in position for to a certain ex-
tent, as seen from the excellent maps
with which this volume is supplied. 1t
follows the sun. For instance, July is
a wet month over Central America,
in the northern part of the southern
continent. in Africa between the equa-
tor and the Sahara, over all India, ex-
cept the extreme south, Burma, the
southern half of China, with the Malay
archipelago and adjoining islands to
some little distance south of the equa-
tor In that month also much of North
America, Central and Northern Europe
and a broad belt extending through
Central Asia are moderately rainy, the
latter fact being indirectly connected
with the former. But in January all
this region, with the exception of East
ern North America. is comparatively
dry, while the more rainy region in
cludes much of South America and of
Africa south of the equator, the north
ern part of Australia, and the islands
as before. Not only are the facts stat
ed. but the scientific explanations OF
them are also given in this pleasantly
learned essay,