The National tribune. [volume] (Washington, D.C.) 1877-1917, 1890-02-27
THE WEATHER.
Some OF the Effects of The Suns Heat on Our At
mOsphere.
BY LIEUT.. J. p. FINLEY, U. s. SIGNAL SERVICE.

Correspondence invited suggestions desired,
and information cheerfuily furnished. Every ef-
fort ploycd to make this Bureau of practical use
TO the readers of The NATIONAL TRIBUNE All
communications should lie addressed-W Weather,
THE NATIONAL TRIBUNE Office. Washington, ID. q. ]
The sun is the original source of all heat
which exerts an influence upon the atmosphere.
This heat which proceeds from the distant
lumnary is subject TO various notifications in
accomplishing certain effects upon the atmOs-
phere. Sir William Thomson finds that the
average quantity of heat received by tho earth
from the sun, as determined by Pouillet and
Herschel aud converted by J0ues unit, IS for
an area of one square foot, exposed perpendicu-
lary to the direction of the solar rays, SO foot
pounds per second. This number relates 10 the
heat received at the outer surface of our atmos-
phere. The quantity of heat absorbed by the
atmosphere will depend upon the chemical
constitution or the mechanical purity of the
air Mt that place, and upon the thickness Of the
stratum of air traversod by the solar rays. This
thickness depends principally upon the latitude
of the station aud the apparent altitude of the
sun above the horizon. In general it may
be concluded that on the driest, clearcst
days 10, but on ordinary days % per cent. of
the solar heat is absorbed by the atmosphere
before the rays reach the earth, the sun being
supposed in the zenith. 1t is believed by some
that the quantity of heat received from the
other Investigations show that there are sensi
BILE hourly changes in the intensity of solar
radiation. In ordinary discussions of meteor
illogical problems these slight changes may be
neglected
1t is important for US to bear in mind that
the effect Of solar radiation in determining
the temperature of the air is manifested gem
orally in three different ways, viz, l. BY the
direct rays Of tho sun, the atmosphere directly
absorbing the solar heat passing through it, 2.
The absorption of heat reflected and radiated
from the earth and clouds 8. BY mere contact
with the warmer earth.
The effect of the direct rays Of the sun and
of radiation or reflection from objects on the
earth's surface, is shown in Winter. when the
ground is covered with snow. In the vicinity
of trees aud posts the snow disappears more
rapidly than it does where the surface of the
snow is entirely uubrokeu. This arises from
the fact that the rays of the sun are absorbed
by the dark surface Of the trees more readily
than they are by the snow. Thus the trees are
warmed and these in their turn send out rays
of heat by which the adjacent snow is melted.
If body be placed in the presence of other
bodies some colder and some hotter than itself,
IL will from this mutual interchange of tenn
peraturo receive more heat from the hotter
bodies thas it radiates TO them, and thus be-
come warmer; but it will receive less heat from
the colder bodies than 10 radiate5 TO them, aud
consequently Will become colder. This rs the
condition in which the earth is placed regard
ing the sun. When its surface is to,cayd the sun
il receives more heat than is radatcd from it
but when it is turned from the sun toward the
cold regions Of space, it gives out more heat
than 1t receives. In the formation OF clouds in
Nil the processes Of evaporation and condensa-
| ton, in tho violence Of local atmospheric
| changes, aud in the priH,tn mobile Of the winds
is seen tho mighty. all pervadiug and rrcsisti-
bic influence OF the solar heat Upon it all the
other forces concerned in atmospheric move
mcnts and conditions are dependent for their
! efficiency.