The Washington times., 1894-07-08
THE USE OF DUST.
To 1t We Owe the Blue of tho Sky and
Other Pleasant Sights.

| To It We Owe the Blue of tho Sky auG
Other Pleasant Sights.
| from the Leipsic Gartenlaube.I
Without dust there would be no blue lrma
ment; the heaven would be blacker than we
see it on moonless nights. On this blac!
! background tie glowing sun would shine ou
sharply, and the same sharp contrast of in
tense light and deep shadow would charac
terize the surface Of tine earth. There woult
be nothing to subiue this sharp contrast bu
the moon and stars, which would remair
visible by day. The illumination Of the earti
would be similar TO that which we observe
when looking at the moon through q teie
scope; for the moon has no atmospheric
envelope, and, consequently. no dust in sus-
pension.
1t is due entirely to the dust that we enioy
our soft, uniformly diffused daylight. 70.
which are eyes are specially adapted: and il
is the dust which contributes SO much 20 the
beauty OF the landscape. But. while the fore
going explains how the dust makes the whol,
vault OF heaven light. ii does not explain why
il is chiefly the biue rays OF the white sunligh,
that are reflected and only to a small extent
the green. yellow, and red rays. This is de-
pendent Oh the size of the dust particles. II
IN cuty lsit uiAcSk y! tntfu tQaI are Dpfut ss
the air currents into every stratum of air, and
it is only these fine. widely diffused dust
particles that are OF any significance in this
connection.
Nov let us consider the mechanism oil
Light and the extreme shortness of the ether
waves which constitute its essence. These
waves, although all microscopieully small,
vary considerably in length. The dne at
mospberic dust Includes many particles large
enough TO reject the short blue ether-waves,
fewer particles capable OF refiecting green and
yellow, and still lever large enough to in
fuence 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 intercepted and diifused, and SO become
visible. This is the reason that the finest
dust-and so, too, the acknowledgements
blue.
So, then. the finest dust appears blue. You
may OIL erye that tie wreath that curls up
ward from the burning end OF cigar is blue,
while the smoke drawn through and exhitlei
is whitsh. The PARTICLES in the latter case
have united and become large enough to re-
fleet 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 grea,er num-
ber OF coarse dust particles in the air. 1t is
especially on mountain heights that the sky Is
so intensely blue, because the rarehed at
mos?here supports only the finest dust par
ticles.
At grea. height the sky would be aimos.
black II there were no dust particles in sus-
pension. 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
US? Is the dust finer there? As u fact, it
really is. Not that finer dust rises there, but
in our climate the dust particles are soon
CnfTN ut.al with
them coarser. In warmer regions however.
the vaDor retains Its wafer character, and
does not condense ON the floating dust Il is
not until the aerial currents have borne it to
higher and colder regions that it is con-
densed to clouds.
Without dust we would have no fog, no
clouds, no rain, no snow, no briliant-hued
sunsets, no ceruIean SKY. The surface OF the
earth itself. the trees. the houses, along with
man and beast. would be the only objects on
which the vapor could condense, and these
would begin TO drip whenever the air was
cooled sufficiently. In Winter everything
would be covered with crust OF ice Our
clothes would become saturated with water
condensinS upon them. Umbrellas would be
of no avail. The vapor-laden atmosphere,
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 parti-
cles in a given space. In London and in
Paris. at the surface. cubic centImeter hus
been found TO contain nearly n quar.er OF a
million particles: on the top OF the EitIel
Tower there are about half as many: while in
the high Alps there are only about 200 parti-
cles 10 the eentimeter. 4 great deal OF the
drst at high attitudes is cosmie dust. consist
Ing, like tine meteorites, of carbon and iron.