The Pioche weekly record. [volume] (Pioche, Nev.) 1877-1900, 1894-12-13
THE WORK OF DUST,
What Makes the Clear Sky Ap-
pear Blue.
HE FINE MECHANISM OF LIGHT
Without Dust There Would be No Fog
No Clouds. No Rain, No Snow,
No Showers.

Dust has very large share in nearly
all the phenomena of the earth's atmos.
phere. 1t is what makes the clear skv
appear blue; and when we look IN
into the sky we see the dust in the at.
mosphere illuminated by the sun.
There is nothing else before us that can
permit the light to reach the eve.
Light goes invisible, straight through
all gases, whatever their chemical com.
position. The dust catches it, reflects
it in every direction. and SO causes the
whole atmosphere to appear clear, in
the same way that it makes the sun.
beam visible in the darkened room
Without dust there would be no blue
armament. The sky would be as dark
as or darker than we see it in the finest
moonless nights. The glowing disk of
the sun would stand Immediately upon
this dark background, nd the same
sharp contrast would Prevail upon the
illuminated surface of the earth-blind.
ing light where the suns rays fall and
deep black shadows where they do not
Only the light of the moon and the
stars, which would remain visible in
the daytime, would be able to temper
this contrast in slight degree. The
illumination of the earth's surface
would be like that we see with the
telescope on the lunar landscapes; for
the moon has no atmospheric envelope
that can hold floating dust. We then
owe to dust the even moderately tenn
pered daylight, adapted now to our
eyes; and it is that which contributes
much to the beauty of our landscape
scenery.
But if dust makes the sky appear
clear, why is the color of the sky blue
Why does dust, of the different consti-
tuents of white sunlight, reflect the blue
rather than the green, yellow and red
This fact is connected with the size of
the dust particles. Only the finest
dust settles SO slowly that it can be
spread everywhere by means Of the air
currents, and can be fo1nd constantly
in all strata of the atmosphere; and
special Importance can be ascribed only
to these finest PARTICLES The coarse
parts soon fail to the ground. Let us
consider the fine mechanism of light,
the extremely short ether waves which
determine its existence. These waves,
although they are of even less than mi.
croscopic size, are not all equally long.
The shortest are those that give blue
light while all the other colors are
produced by longer waves. The fine
atmosphere dust contains many parti-
Giles which are large enough to reflect
the short blue ether waves, fewer than
can reflect green and yellow, and still
fewer large enough to reflect the long
red waves The red light, therefore,
goes on almost without hindrance,
while the blue is more liable to be
diverted, and thus to reach the eye
A similar phenomenon may be observed
on larger scale on water which is
roughened with waves of different
lengths, and on which ieces of wood
are floating. The j ~ of wood
stand in the same relation to the water
waves as the dust particles to the ether
waves. The great long waves pass the
blocks undisturbed, only rocking up
and down; while the finer ripples of
the water are turned back, as if the
blokcs were firm walls.
The finest dust thus appears blue.
There is much coarse dust in large
towns, when the sky over them is often
gray, while only the finest blue dust is
, carried up in the country. The dust is
also variously assorted at different
heights above the surface of the earth.
The coarser dust will be found at the
lower levels, where it is produced. On
mountains we have most of the dust
beneath us, while the rarefed air can
{ sustain only the finest floating particles.
q Hence the sky on high mountains is
{ clear and deep blue, even almost
black, as if it were without dust. Only
when we look at the lower strata, to-
a ward the horizon, does the color pass
into gray.
Why is the sky in Italy and the
: tropics of SO much deeper blue than
q that of Western Europe? Is the dust
! there finer? 1t is really so; not that a
I finer quality of dust is produced there,
n but because in the moist climate of the
North Sea countries the dust cannot
, float long in the air without being
a charged with water and made coarser,
while in warmer countries water exists
4 in the air as vapor and does not become
{ condensed as a liquid on the dust.
Only when it is carried by the air cur
!. rents into the higher strata and is
cooled there, does it thicken into
i clouds. With this we come " Y =
most important function of dr. / o.
!. atmosphere-the part which % has II,
!. the function Of rain, by reason of
vapors condensing upon it. Itb,be
j.. affirmed with certaint- that. athe
@ water which the sun ca, ,es tovapor-
q ate on the surface of th, sea anon the
d land is condensed aga on dusand
v that no raindrop falls u. it da
!. particle of dust as it's prim4 J. nuc,s.
:. Without dust there would be no ce
. densation Of water in the air-no TO.
/. no clouds, no rain, no snow, no show
@ ers. The only condensing surface
a would be the surface Of the earth itself
@ Thus the trees and plants and the walls
!. of houses would begin to trickle when
i ever cooling began in the air. In win
r ter all would be covered with thick
:, icy crust All the water which we are