Southwest-sentinel. [volume] (Silver City, N.M.) 1883-189?, 1892-08-02

rain Is o change from heat TO cold,
OF vice versa. Into a mas of
heated air, a mass or current of
cold air falls or is injected, or sim
liar phenomena occur with a mass
Of warm air, and there is a conden-
sation Of the moisture which al
ways exists in the atmosphere with
a fall of rain. Sometimes the air
Of higher OF lower temperature is
brought by a wind of more or less
violence, and the rainfall is more
or less copious. When an upper
stratum of cold air falls upon a
lower stratum the change usually
proceeds slower and the rain is
more moderate at first, with pros
pect of longer continuance. In
these atmospheric notifications
electricity plays a part, but wheth-
es as cause or effect is not as yet
and perhaps never will be fully
determined. Mountain ranges or
isolated mountain peaks affect the
local rainfall, or modify it to such
an extent that the entire character
of certain countries is changed by
these agencies. When there is a
range of lofty mountains like the
Sierra Nevada, at no great distance
from the sea the passage of the
moist currents of air toward the
interior of the continent is inter
rupted. Nearly all the rain falls
on the seward side and the inter
ior becomes a comparative desert,
as in North America, depending
for the scanty amount of moisture
furnished it on other natural
causes. In great deserts like the
Sahara rain only falls in the vicin-
ity of mountains, where the storms
are often violent, but brief. The
climatology of the tropics has been
imperfectly studied, but the rains,
which are much more abundant,
depend in the equatorial belt, as
in the temperate zones, on changes
of temperature. Droughts occur
in Hindostan and in Central Afri-
ca, but it is to be remarked that
great desert regions like those of
Northern Africa and Central Asia
are only found at a considerable
distance north and south of the
equator.
The laws hat regulate rainfall
are even more general than this
statement of facts would seem to
intimate, since they depend in a
great asu on the trade winds
and the secondary air current
called monsoons, which these gen.
crate. The monsoons diverge to-
ward the north and south, and are
modified by the form of The seas
and continents. AS the equatorial
winds tend toward the poles great
currents of air are constantly flow
ing toward the equator to supply
the void they leave. Were there
no other elements in the calculation
winds would flow during long
periods of time in the same direc-
ton with a regularity that would
be monotonous. To prevent this,
heat comes in as a new factor. In
summer, the air heated in great
valleys and vast spaces of level
country rises and cold air falls
from above or rushes in from the
lateral spaces to supply its place.
Ocean currents like the so-called
Japan current or the Gulf stream
modify the climate along thous-
ands of miles of seacoast, extending
their effects often far into the in.
terror. All these causes, it viii be
observed, are of a general nature
and far beyond the control of man
Still they are purely terrestrial
and our climate is dependent OIL
the sun, which has its changes anc
Irregularities. If the heat it fur.
nishes the earth were a constant
quantity and it SO exerted its at
tractiye power on this planet as t
keep the polar axis at the same
angle TO the ecliptic, our seasons
would always present the same
variation of heat and cold. Blu.
we have to account with spots OF
l the surface Of the sun, whose intiu
ence is not precisely understood
but is supposed to be malign, anC
with change in the relative posi-
ton of the poles, which has already
, had some effect on the earth's at
/ mosphere, though this cannot ye
be proved.