The Manning times. [volume] (Manning, Clarendon County, S.C.) 1884-current, 1914-06-24
LIGHT OF The sun
In Its Pure State We on the Earth
Have Never Seen It.
SOME RAYS DO NOT REACH US.
II They Did They Would Probably De-
stroy Life as 1t Exist: on Our Planet.
Daylight and Sunlight Differ Almost
a. Much as Do Wine and Water.

a. Much as Do Wine and Water.
las clear as daylight expresses In
ordinary language maximum Of plain
ness and obviouSness. Nevertheless
daylight is one of the most complicat-
ed 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
it does not say that daylight and sun
light are identical. In fact, they diff
fer almost as much as do water and
wine.
But the degree Of difference varies.
Daylight Is q mixture Of two kinds OF
light, and its quality IS continually
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 On open sky,
with the sun high in the heavens. day
light, says Professor Nichols Of Cor
nell, IS almost entirely sunlight A
white surface exposed to an unobscur-
ed sky receives directly from the sun
IS per cent OF the light that illuminates
it and only Is per cent from other
parts Of the sky dome.
This other part Of the illumination
is called skylight. and it consists OF
light, nearly all Of which came orig
tnaI!y 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
remains Is no longer the same thing
as before.
Ca 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
daylight are surprisingly great. The
intensity Is on the average ten times
as great in midsummer as In midwin-
ter, but this average comes far from
expressing the utmost difference that
can exist, for investigation has shown
that between the clearest summer day
and the darkest day Of winter the ra-
tio Of the intensity of daylight may be
as great as 800 to 1.
Besides, the quality Of daylight Is
continually changing OF account OF the
variations in the relative amounts OF
the different rays Of the spectrum that
are mingled IN 1t. The spectrum Of
Hight is q 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-
duce variations Of color and Of intensi-
ty of color, as well as Of the quantity
Of invisible radiations present, and
these variations are not the less real
and important because the eye IS not
always fully aware Of them.
AS to pur sunlight. We never see 1t
on the earth. The light that arrives to
US from the sun has neither the color
nor the intensity that it possesses be-
fore it enters the atmosphere. The
ultraviolet rays especially are almost
completely screened of by the atmos-
phere, and If they reached Us in their
full force it is probable that life rs
now organized on this planet would be
destroyed by them.
Every different world has Its own
daylight. although all may be iliumt
mated by the same sun. Not only does
relative distance affect the intensity OF
daylight on different planets, but the
constitution Of their various Amos
pheres has IN equally great effect
Venus has q daylight twice as intense
as ours; Mars ore-half as intense. On
Jupiter the intensity Is l-25 Of that on
the earth; on Saturn, $50; on Nep-
tune, 1900.