Southern standard. (McMinnville, Tenn.) 1879-current, 1881-11-05
Solar Problems.

In considering the quantity and in
tensity of the light emitted by the sun,
we are again lost in the bewildering
magnitude of numbers. The amount
can be measured and proved and stated
in familiar terms, but the result can not
be mentally grasped. Though the
source of illumination is $1,000, 900 miles
away, its light would quickly disorgan-
lze and destroy the eye exposed to it.
Sunlight is the intensest radiance at
present known. 1t so far surpasses the
brightness of the calcium light, and
even the most powerful electric arc, that
iteither OF these lights is interposed be-
tween the eye and the surface of the sun
it appears like black spot upon the
disk. An ordinary gas burner consum-
ing five feet of gas hourly gives as much
light as sixteen standard candles, and
the total light of the sun is computed to
be about equivalent to four hundred
billion billion of such gas-jets. The in
tensity of the light ct the solar surface
is estimated to be 10000 times greater
than the average brightness of the can
die flame. 1t is LAG times more brilliant
than the calcium light, and probably
about four times as intense as the cleo
trio light. Prof. Langley compared the
brightness of sunlight with the binding
brilliancy of the molten metal in Bes-
semer converter. But the dazzling
stream OF melted iron was deep brown,
compared with the solar radiation, and
presented contrast like that of dark
coffee poured into white cup. No al
lowance being made by the absorption
OF the suns rays by passing through the
smoky air of Pittsburgh, they came out
$500 times brighter than the dazzling
radiance of the incandescent metal. But
the solar light is much feebler at the
SUMS border than at the central region
of the disk, which is accounted for by
the absorption of portion of the rays
by the solar atmosphere. La Place
maintained that this absorption of light
by the SUMS atmosphere amounts to
eleven-twelfths of the whole, and Secchi
agrees with him. But other authorities
make it less, and say that the sun with
out its atmosphere would be about four
times as bright as we now see it.
All the suns rays are lines of force
manifested and measured by material
changes. They are all believed to be of
the nature of waves or pulses which ex-
pend themselves in the production of
motions. The luminous rays to which
we have just referred impress the nerv-
GUS matter of the eye and thus give rise
to vision. The actinic rays produce
chemical decompositions, and the Their
mai rays give rise to expansion, but all
the waves of solar radiation are carriers
of energy, and when intercepted do
work. The measurement of solar heat
is more satisfactory than that of solar
light, rs thermometers are more ac-
curate than photometers with candle
power units.
But there is a preliminary difficulty
from the absorption of heat by the
earth's atmosphere. A considerable
part of it is thus intercepted and can
not be measured. "Speaking loosely,
it may be estimated that at the sea level
in fair weather, neither excessively
moist or dry, about 30 per cent. of the
solar radiation is absorbed when the sun
40 ob tho nonith, and AT leosb TO per
cent. at the horizon. Of the rays strik-
ing the upper surface of our atmos-
phere, between 40 and so per cent,
therefore, are generally Intercepted in
the air, even when there are no clouds.n
OF course, this heat is not lost to the
earth; but when we come to measure
the actual amount received upon q
square foot of the earths surface, it
must be remembered that it is but little
more than half of that which has been
emitted by the sun.
The amount of solar heat actually re.
ceiyed upon given areas of the earth's
SURFACE has been determined in various
ways, which need not be here described.
If we express the result in terms of pow
er, and take the whole surface of the
earth, the average energy received from
the sun on every thirty square feet of
the earth's surface is equal to one con-
tlnuous horsepower. 1t is assumed the
sun radiates equally in all directions, so
that If he We're surrounded by a sphere
as large as the earth s orbit, or 1876, 0OU,-
900 miles in diameter, his radiations
would give dynamic effect of perpet-
ual horsepower upon each thirty square
feet OF this enormous surface. OF the
total solar radiation, the earth receives
only fraction of inconceivable minute
ness, but one twenty-two-hundred-mil-
lionth of the whole. Yet this inlinitisi-
nal fraction of solar power is the great
capital of terrestrial energy: wind pow
er, electric power, steam power, and the
power of all living organisms.
Herschel has given the great result in
terms of melting ice. A shell of ice an
inch thick and 1856, 100000 miles in di-
ameter, surrounding the sun, would be
melted in two hours and thirteen min
utes, A shell of ice enclosing the sun
at his surface, mile in thickness,
would be melted in the same time.
HerSchel continues, that if cylinder of
ice forty-five miles in diameter were dart
ed into the sun with the velocity of
light, the suns heat, if concentrated
upon it, would melt it as fast as
1t came; or, in other words, if
q solid column of ice two and quarter
miles in diameter and 93,00O,0 900 miles
long, that should span the ABYSS from
the earth to the sun, could be acted upon
by the total solar heat, it would be melt
cd in single second, and in seven Sec
onds more it would be dissipated in
vapor. 1t has, again, been computed
that the heat streaming from the sun
into space would be sufficient to boil
ZOO, 900, 600 cubic miles of ice-water each
hour. The burning glass by which the
solar rays are concentrated produces an
effect which is equivalent to moving the
object in its focus n certain distance
Il L l. =.