McCook weekly tribune. (McCook, Neb.) 188?-1886, 1884-05-08

and is still taking place on parts of the
earth's SURFACE to-day, visible and
obvious 10 any observer.
Oar inquiry, therefore, is reduced to
this question: What part or parts of
the earth's surface first became suffi-
GENTLY cooled by radiation to be habit
able by plants and animalsp
A supposed case may help us in
reaching correct answer TO this ques-
ton. Let us assume, then, the earth,
| at the time it was a molten mass, had
been and was revolving in an orbit so
near the sun that the amount of heat it
would have been receiving from the sun
would have just equalized the amount
of heat it was losing by radiation. I'm
der these conditions it would have
cooled as the sun cooled-neither fast
er nor slower. This helps us to I'M
derstand that the heat received from
the sun is, and ever has been, an Offset,
so far as it goes, to the heat lost from
the earth by radiation. A statement
of the loss of heat from the earth dur
ing any definite time may be formu-
lated in this way: From the heat lost
from the earth by radiation during a
given period, subtract the heat received
by the earth from the sun during the
same period, and the remainder will be
the earth's net or actual loss of heat.
Sidereal heat received by the earth be-
ing infnitesimal in comparison, is not
here taken into the calculation. But
were it mole considerable, it would not
be important in this connection, for it
falls on all parts of the earth about
equally.
1t is evident from the present con-
ditjpn of the earth's surface, that at
the time it was molten mass, and fol
a long time thereafter, it radiated heat
into space much more rapidly than it
received heat from the sun; but never
theless the heat of the sun is, and al
ways has been, offsetting the loss of
heat from the earth by radia-
ton to the full extent of the
heat which the earth had been receiv-
ing from the sun during the time.
But this sun heat, this Offset to radi-
alton, has not been received by all
parts of the earth equally. The equa-
torial, or torrid zone, has always re-
ceived the most per square foot, or in |
to its area. The two inter- !
mediate, or temperate zones, have re-
ceived the next largest amount per
square foot, or in proportion to their
area, while the polar or frigid zones
have received the least per square foot,
DR. in proportion to their area. If the
amount of sun heat received at the
equator be rated at 1000, then, upon
,he same basis, the average sun heat
throughout the torrid zone should be
'ated at 975, the average sun heat
throughout the temperate zones at 757,
Ind the average sun heat throughout the
rigid zones at 454, or less than one
lalf that of the torrid, and less than
that of the temperate zones.
We speak here, and shall hereafter, of
he geographical zones of the earth for
he sake OF convenience.
The greatest amount of heat received
rom the sun and offsetting radiation
rom the earth, other things being
quail, is, of course, as we have seen at
he equator, and less and less every de-
rec north and south of this line to the
coles. If, then, the frigid zones have
een during all this time receiving the
east heat from the sun-the least offset
o their own loss of heat by radiation
docs it not follow that they were the
rst parts of the earth sufficiently
ooled to maintaia vegetable and ami
nal life? The inference seems inevi-
able.