Audubon Republican. [volume] (Audubon, Iowa) 1894-1925, 1894-08-09
WHAT DUST Dues IN NATURE.


The Literary Digest has translated
and condensed the following from Die
Gartenlaube: When ray of sunlight
falls through an aperture into a dark
ened room it is rendered visible as far
as it extends. What we actually see,
however, is not the ray of light, but the
particles of floating dust rendered visi-
BILE by it. 1t might appear at first
glance that the part Played by dust
particles in nature is Of 10 great scien-
tilic or general interest; as matter of
fact, however, they play very impor-
tant role. Dust is an important factor
in almost every phenomenon of the
earth's atmosphere. In the first place,
it is due to the dust that the heavens
are blue. When we lift our eyes to the
valued arch above us we see sunlight
reflected by every particle of dust;
there is nothing but the dust between
us and the sun to transmit it's light to
us. Light traverses ali gases, no mat
ter what their chemica! composition,
in straight lines and is Invisible. The
dust intercepts ana reflects it on all
sides, and makes the whole atmosphere
luminous in the same manner as it
makes the track of the suns rays visi-
BILE in darkened room.
Without dust there would be no blue
armament; the heaven would be black
er than we see it on moonless nights.
On this black background the glowing
sun would shine out sharply, and the
same sharp contrast of intense light
and deep shadow would characterize
the surface of the earth There would
be nothing to subdue this sharp con-
trast but the moon and stars, which
would remain visible by day. The il
Illumination of the earth would be SINH
lar to that which we observe when
looking at the moon through tele-
scope; for the moon has no atmospher-
ic envelope and consequently no dust
in suspension. 1t is due entirely to the
dust that we enjoy our soft, uniformly
diffused daylight, for which our eyes
are specially adapted; and it is the
dust which contributes so much to the
beauty of the landscape.
But, while the foregoing explains
how the dust makes the whole vault of
heayen light, it does not explain why
it is chiefly blue rays of the white sun
light that are reflected, and, only to a
small extent, the green, yellow and red
rays. This is dependent on the size of
the dust particles. 1t is only the finest
of them that are borne by the air cur
rents into every stratum of air, and 1t
is only these fine, widely diffused dust
particles that are of any significance
in this connection. Now let us con-
slider the mechanism of light aid the
extreme shortness of the other waves
which constitute it's essence. These
waves, although all microscopically
small, vary considerably in length.
The fine atmospheric dust includes
many particles large enough to reflect
the short blue ether waves, fewer par
ticles capable of rejecting green and
yellow, and still fewer large enough to
influence the long red ethereal waves.
The red light, consequently, passes
through the great majority of the dust
particles, comparatively unhindered;
the blue rays, on the contrary, are in
tercepted and diffused, and so become
visible. This is the reason that the
finest dust-and so, too, the armament
appears blue.
So, then, the finest dust appears blue.
You may observe that the wreath that
curls upward from the burning end of
a cigar is blue, while the smoke drawn
through and exhaled is whitish. The
particles in the latter case have united
and become large enough to reflect
white light. So, too, in the country on
a clear day the sky is blue, but in the
city it appears whitish, because of the
greater number of coarse dust particles
in the air.. 1t is especially on noun
tain heights that the sky is so intensely
blue, because the rarifed atmosphere
supports only the finest dust particles.
at great heights the sky would be al.
most black if there were no dust par
ticleS in suspension, We see it grow
pale as we look at the lower strata of
air toward the horizon.
But why is the sky in Italy and in