The Hartford republican. (Hartford, Ky.) 18??-1926, 1914-04-17
LIGHT OF The sun
In Its Pure State We on the Earth
Have Never Seen 1t.
SOME RAYS DO NOT REACH US.
" They Did They Would Probably De-
stroy Life as It Exists on Our Planet.
Daylight and Sunlight Differ Almost
as Much as no Wine and Water.


Daylight and Sunlight Differ Almost
as Mueh as no Wine and Water.
las clear as daylight" expresses in
ordinary language Il maximum of plain
ness and obviousness. Nevertheless
daylight is one of the most complicat-
cd and capriciously variable of all nat
ural phenomena.
Almost everybody you meet will tell
you that daylight and sunlight are diff
ferent names for the same thing. They
think they know that much of astron-
omy anyway. But astronomy does not
teach anything of the kind. Astronomy
simply tells us that the sun is the pri-
mary cause or source of daylight, but
il does not say that daylight and sun
light are identical. In fact. they diff
fer almost as much us do water and
wine.
But the degree of difference varies.
Daylight is n mixture of two kinds Of
changing. as everybody who has ever
had anything to do with photography
knows. The proportions of the two
kinds of light that make daylight are
not the same from hour to hour and
hardly from minute to minute.
In clear weather. under an open sky,
with the sun high in the heavens. day
light, says Professor Nichols of Cor
nell. is almost entirely sunlight y
white surface exposed to an unobscur
IS per cent of the light that Eliminates
it and only IL per cent from other
parts of the sky dome.
This other part Of the illumination
is called skylight. and it consists Of
light, nearly oil of which came orig
inally from the sun. but which has
been changed in quality by reflection
from the earth. from the clouds and
from dust and vapor in the air. Many
Of the rays that characterized the orig
inal sunlight have been absorbed by
the rejecting substances. so that what
is no longer the same thing
as before.
On a completely overcast day there
Is no sunlight. properly so called. but
only skylight. Whether the sky is
overcast or not the intensity of day
light varies with the hour Of the day
and with the season. This Is due to
differences in the elevation of the sun.
These variations in the intensity Of
a In yl;rh< ORC cnrpris;nOlv tvroof Tho
is on the average ten times
as great in midsummer as in midwin-
ter, but this average comes far from
the utmost difference that
can exist. for investigation has shown
that between the clearest summer day
and the darkest day of winter the ra-
ito of the intensity of daylight may be
rs great as 800 to /.
Besides. the quality Of daylight is
changing on account Of the
variations in the relative amounts Of
The different rays of the spectrum that
ire mingled in it. The spectrum Of
light is gamut Of vibrations. and the
result of the selective action exercised
by the substances and vapors, from
which the light has been reflected and
through which it has passed is to pro-
luce variations of color and of intensi-
" of color. as well as Of the quantity
If invisible radiatiOns present. and
hese variations are not the less real
md important because the eye is not
always fully aware of them.
A. IN 10Th n
IN the earth. The light that arrives to
is from the sun has neither the color
nor the intensity that it possesses be-
'Ore it enters the atmosphere. The
rays especially are almost
screened off by the atmos-
)here. and If they reached us in their
'ull force it is probable that life as
now organized on this planet would be
destroyed by them.
Every different world has its own
daylight. although all may be illumi-
lated by the same sun. Not only does
'elative distance affect the intensity of
daylight ON different planets. but the
constitution Of their various atmOs-
there's has an equally great effect.
Venus has daylight twice as intense
is ours; Mars One-half as intense. On
Jupiter the intensity is los of that on
he earth; on Saturn, 100; ON Nep-
une. 1000.
But each OF these planets has an at
nosphere peculiar to itself, and thus
he differences Of daylight upon them
ire made still more remarkable. This
S one Of the first things to be taken
nto account in all speculations about
he Availability Of those other worlds.
Garrett p. Serviss In Spokane Spokes-