The morning news. [volume] (Savannah, Ga.) 1887-1900, 1894-07-15
THE USE OF DUST.
To 1t We Owe the Blue of the Sky and
other Pleasing Sights.
From the Leipsig Gartenlaube.

OLDeG HleaSlnR S1BuLSs
From the Leipsig Gartenlaube.
Without dust there would be no blue
armament; the heaven would be blacker
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 or
the earth. There would be nothing to
subdue this sharp contrast but the moon
and stars, which would remain visible by
day. The illumination of the earth
would be similar to that which we OBJ
serve when looking at the moon through
a telescope; for the moon has no atmos-
pheric envelope, and, consequently, no
dust in suspension.
1t is due entirely to the dust that we
enjoy our soft, uniformly ditfused day
light, for which our eyes are specially
adapted and it is the dust which con-
tributes so much to the beauty of the
landscape. But, while the foregoing ex-
plains how the dust makes the whole
vault of heaven light, it does not explain
why it is chiefly the blue rays of the
white sunlight that are reflected and only
to 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 currents
into every stratum of air, and 1t is only
these fine, widely diffused dust particles
that are of any significance in this con-
nectiOn.
Now, let US consider the mechanism of
light and the extreme shortness of the
other waves which constitute its essence.
These waves, although all microscopically
small, vary considerably in length. The
fine atmospheric dust includes many par
ticleS large enough to reflect the short
blue ether-waves, fewer particles capa-
BILE 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 compare
lively unhindered; the blue rays, on the
contrary, are intercepted and diffused,
and so become visible This is the rea-
son that the finest dust-and so, too, the
tirmament-ap appears blue.
So, then, the finest dust appears blue.
You may observe 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 mountain nights that the
sky is so intensely blue, because the
rarefied atmosphere supports only the
finest dust-particleS.
At great hight the sky would be al
most black if there were nodust-partic
in suspension. We see it grow pale as we
turn our eyes to the lower strata of air
toward the horizon. But why is the sky
in Italy and in the tropics so much deeper
blue than with us2 Is the dust finer
therel AS a fact, it really is. Not that
finer dust rises there, but in our climate
the dust-particles are soon separated with
water vapor, which makes them coarser
In warmer regions, however, the vapor
retains its watery character, and does
not condense on the floating dust. 1t is
not until the aerial currents have borne
1t to higher and colder regions that it is
condensed 20 clouds.
Without dust we would have no fog, no
clouds, no rain, no snow, no brilliant
hued sunsets, no cerulean sky. The sur
face of the earth itself, the trees, the
the houses. along with man and beast.
would be the only objects on which the
vopor could condense, and these would
begin to drip whenever the air We're cooled
sufficiently. In winter everything would
be covered with crust of ice. Our clothes
would become saturated with water con-
densing upon them. Umbrellas would be
Oh no avail. Inc VdpOr-ldQGn atmOS-
phere, moreover, would penetrate to our
rooms and condense upon the walls and
furniture.
In short, the world we live in would
be quite another world if there were no
dust. Since scientists began to realize
the important part played by dust in the
economy of nature, measures have been
taken to count the particles in a given
space. In London and in Paris on the
SnTf9Hp a pIJhia
found to contain nearly a quarter of a
million particles; on the top of the Eiffel
tower there are about half as MANY;
while in the high Alps there are only
about 200 particles to the centimeter. 4
great deal of the dust at high attitudes is
cosmic dust, consisting, like the meteor
ties. of carbon and iron.