The Hood River glacier. (Hood River, Or.) 1889-1933, 1914-04-02
LIGHT OF THE sun
In It's Pure State We on the Earth
Have Never Seen Il.
SOME RAYS DO NOT REACH US.
n They Did They Would Probably De.
stroy Life as II Exists on Our Planet.
Daylight and Sunlight Differ Almost
as Much as Do Wine and Water.

w ihey Oto iney Woulo rrocabiy be-
stroy Life as IL Exists on Our Planet
Daylight and Sunlight Differ Almost
as Much as Do Wine and Water.
As clear as daylight" expresses in
ordinary language a maximum Of plain
ness and obyiousness. 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 dif-
ferent names for the same thing They
think they know that much OF astrou-
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
II 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 a 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 an 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
S5 per cent OF the light that illuminates
it and only 10 per cent from other
parts Of the sky dome.
This other part Of the illumination
is called skylight. and 1t consists of
light. nearly all 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
remains is no longer the same thing
as before
On 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-
ito Of the intensity OF daylight may be
as great as 300 to |.
Besides, the quality OF daylight is
continually changing on account OF the
variations In the relative amounts OF
the different rays of the spectrum that
are mingled in 1t. The spectrum Of
light is a 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 1t has passed is to pro.
duce variations of color and of intensi-
ty of color, as well as of the quantity
Of Invisible radiatlons present, and
these variations are not the less real
and important because the eye Is not
always fully aware Of them.
AS to pure 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 ii possesses be-
fore it enters the atmosphere The
ultraviolet rays especially are almost
completely screened off by the atmos'
phere. and II they reached us In their
full 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-
mated by the same sun. Not only does
relative distance affect the Intensity of
daylight on different planets, but the
constitution OF their various atmos-
pheres has an equally great effect
Venus has a daylight twice as Intense
as ours; Mars one-half as intense. On
Jupiter the intensity is 1875 of that on
the earth; on Saturn, 100; on Nep-
tune, 1900.
But each Of these planets has an at
mosphere peculiar to itself, and thus
the differences Of daylight upon them
are made still more remarkable. This
is one OF the first things to be taken
into account In all speculations about
the habitabilty OF those other worlds.
Garrett +. Serviss in Spokane Spokes-
man-Revlew.