Ashland tidings. [volume] (Ashland, Or.) 1876-1919, 1914-04-02

stroy Life as IL Exists on our Planet.
Daylight and Sunlight Differ Almost
as Much as Do Wine and Water.
LAS clear as daylight" expresses in 4
ordinary language maximum OF plain
ness and obviOusness. Nevertheless /
daylight is one of the most compicat
ed and caprlciously variable of all nat
uraI 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- |
0my 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 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
bad 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
neil, is almost entirely sunlight. A
white surface exposed 10 an unobscur-
ed sky receives directly from the sun
S5 per cent Of the light that illuminates
1t 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 thar characterized the orig
. inal sunlight have been absorbed by
the rejecting substances. so that what
remains is 10 longer the same thing
as before.
On completely overcast day there
Is no sunlight. properly SO called. but
only skylight Whether the sky is
o2ercast 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, f1r 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 800 to I.
Besides. the quality OF daylight Is
continually changing on account OF the
r variations in the relative amounts OF
!. the different rays OF the spectrum that
s are mingled in it. The spectrum of
g light is a gamut of vibrations, and the
: result of the selective action exercised
n by the substances and vapOrs. from
which the light has been reflected and
!, through which II 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 pure sunlight, we never see IL
on the earth. The light that arrives to
US from the sun has neither the color
q nor the intensity that It possesses be
N fore IL enters the atmosphere. The
!, ultraviolet, rays especially are almost
i. completely screened OF by the atmos-
phere. and II they reached US in their
e full force it is probable that life as
1. now organized ON this planet would be
Is destroyed by them.
Every different world has its own
daylight, although all may be iliumi
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 au equally great effect
Venus has daylight twice as intense
q as ours; Mars ODe-half as intense. Or
Jupiter the intensity Is i-25 Of that or
the earth; Cd Saturn. 100; Oh Nep
tune. 1900
But each OF these planets has an at
mOspbere peculiar 10 itself. and thus
a the differences Of daylight upon then
IL are made still more remarkable. Thi,
is one OF the FIRST things to be taker
into account in all speculations about
the babitabillty OF those other worlds
Garrett =. Serviss In Spokane Spokes
n man. Review.