The times. [volume] (Richmond, Va.) 1890-1903, 1894-06-24
DUST's PART NATURE.
An Important Factor In Most A,mosph eric
Ph.nomens.

~
Ph.nomens.
When ray OF sunlight falls through an
aperture into darkened room II is rem
dered visible as far as 1t extends. What
we actually see, however, IS not the ray
OF hght, but the particles OF floating du.I
rendered visible by it. IL might appear,
at Hrst glance that the part played by
dust particles In nature is Of no great
scientific or general interest. as mat
ter OF fact, however. they play very
important role. Dust Is an important
FACTOR in almost every phenomenon OF
the earth's atmosphere. In the first
place IL Is due TO the dust that the heay-
ems are blue. When we lift our eyes 10
the Vaulted arch above us we see sun
nSnt reflected By every particle or dust;
there Is nothing but the dust between US
ana the sun TO transmit its light to Is.
Light traverses all gases. no matter
what their chemical composition. in
straight lines, and Is Invisible The dust
intercepts and reflects IL on all sid s,
ana makes the whole atmosphere lumi-
nous In the same manner as II makes the
track Of the suns rays visible IN a dark
ened room.
without dust there would be no blue
ornament; the heaven would be backer
than we see Il 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 70
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
telescope, for the moon has no atmOs-
pheric envelope and consequently no dust
in suspension. II IS dine entirely to the
dust that we enjoy our soft, uniformly
dtffused daylight. for which our eyes
are especially adapted: and II IS the dust
which contributes 50 much TO the beauty
OF the landscape.
But, while the foregoing explains how
the dust makes the whole vault of heav-
en- light, IL does not explain why it Is
chiefly the 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. IL is only the finest OF
them that are borne by the air currents
into every stratum Of air. and IL is only
these fine. widely diffused dust particles
that are Of any significance In this con-
nection. Now let us consider the me-
chanism Of light ar1 the extreme short
ness Of the ether waves which consti-
tute its essence. These waves, although
all microsccpically small. vary consid-
erably in length. The fine atmospheric
dust includes many particles large
enough 10 reflect the short blue ether
waves, fewer particles capable Of re-
ilectng green and yellow and sull fewer
large enough TO influence the long red
ethereal waves. The red light COnse-
quently, passes through the great ma
iority " the dust particles, compa rativc-
ly unhindered; the blue rays. on the
contrary are intercepted and dlifused,
and so become visible. This Is the rea-
son that the finest dust-and so. too the
acknowledgements 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 whtish. The par
ticles 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. II IS especially on mountain heights
that the sky is so Intensely blue. be
cause the rarefied atmosphere supports
only the finest dust particles. At great
heights the sky would be almost black
II there we're no dust particles in sus-
pension. We see IL grow pale as We look
at 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 so much finer
there As n fact. 1t really is. Not that
finer dust rises there but in our climate
the dust particles are soon saturated
with water vapOr, which makes them
coar.ser In warmer regions, however
the vapor retains its watery character
and does not condense on the floating
dust. Ii is not until the aerial currents
have borne it to higher and colder re-
giors that it is condensed to clouds.
This brings us to the most important
role played by dust I'm our atmosphere;
its influence I'm determining rainfall. due
to the fact that yapor fiuidifeS upon the
dust particles.
1t may be accepted as beyond question
that, of all the water evaporated by
the sun from the surface Of land and
sea, not one drop returns which has not
condensed upon a particle OF dust as 4
nucleus. This is easily demonstrated.
We I'LL a large flask with air which has
been filtered through cotton waddings
until all the original dust is driven out
and the flask is full Of dustless air
Into this dustless air turn current OF
steam from a kettle, and you will find
II transparent. and, therefore. Invisible
Not a trace OF the cloudy appearance
we associate with steam. The only
thing noticeable is that the inner walls
of the flask begin to drip; the vapor
condenses here as II cools. because there
Is nothing else for It to condense on.
But blow ordinary dust-laden air into
the flask and the VapOr at once as
sumes the familiar cloudy appearance
due to its condensation on the dusLpartl-
cles; and II begins TO rain In the mask.
The reason for this Is that the Vapor
condenses on the dust particles ana
drops -.
no fog. no clouds no rain, no STOW, no
brilliant-hued sunsets. no cerulean sky
The surface Of the earth Itself, the trees
the houses along with nan 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 a crust OF Ice.
Our clothes would become saturated with
water condensing upon them. Umbrellas
would be Of no avail The vapor-laden
atmosphere. moreover. would penetrate
10 our rooms and condense upon the
walls and furniture. In short, the
world we live in would be quite another
world II there were no dust.
Since scientists began 10 realize the
important part played by dust In the
economy OF nature. measures have been
taken TO count the particles in given
space. In London and in Paris. at the
surface. a cubic centimeter has been
found to contain nearly a quarter OF a
million particles; on the top or the
Eiffel Tower there are about halt as
many. while in the high Alps there are
only about 200 particles TO the ntlmeter.
great deal Of the dust at high aIutudes
is cosmic dust, consisting. Ike the Inste-
frnV1