Ellsworth American. [volume] (Ellsworth, Me.) 1855-current, 1902-05-14
THE DUST In THE AIR.
IT'S FUNCTION IN THE MECHAN-
ISM OF a SUNSET.
COLOR EFFECTS OF TIE MICROSCOPIC
PARTICLES THAT IMPRoGNATE
TIE ATMOSPHERE.

| Most people IL they were asked to state
| the color of the sun would say that II
was orange, and they would as confident
iy assert that the color of the atmosphere
| was blue. Recent researches and irTes-
| legations, however. point to the conclu-
sion that the real color of the sun Is blue.
while that OF the atmosphere surrounding
the earth is orange. Commonly the
earth's atmosphere appears so transpar-
ent and translucent that 1t Is hard to re-
alize the fact that II has as much effect
on the light and heat coming from the
sun as II ii were roof of thick glass.
| But the atmosphere is very far from be-
Ing as colorless as it seems to be, and the
best way Of discovering its true tint Is
not to gaze Immediately overhead, but to
look away toward the horizon. By 80
\ doing the atmosphere will be seen, as 1t
! were. in bulk, fdo overhead there Is only
small accumulation of 1t compared
with the many miles Of thickness through
| which the vision travels when the eye
looks toward the horizon.
The atmosphere surrounding the earth
| then may be likened to a screen of an
orange color, and it will be readily under
stood that any light passing through this
! screen will experience some remarkable
notifications. Vow, as already stated,
! 1t appears highly probably that supposing
any one could see the sun from a position
outside the earth's atmosphere the light
coming from this central luminary would
} be seen to be not white, but blue. This
/ blue is of course not pure monochromat-
| ic blue, and the expression really means
+ that it sums up the dominant note in the
color scheme. What, therefore, the at
mosphere may be considered to do is to
stop out or absorb all the colors at the
blue end of the spectrum, the residue FL
/ tering through to the earth as white light.
When the rays of light first left the sun,
I the blue rays were the strongest. but
very soon after they entered the earth's
atmosphere their progress was impeded.
J and of all the rays journeying from the
sun they quickly became the weakest.
On the other hand, the red rays, which at
/ first were inconspicuous. had the facility
| of penetrating the earth's atmosphere
and were the most in evidence at the end
of their long journey.
The first step, accordingly, to be taken
when investigating a sunset is to realize
F., that the white light from the sun which
Is commonly supposed to be composed of
the seven primary colors should rather be
tuDukul VI us u Etsiuut Va the Oiibiuut
radiations. A further important point is
| to bear in mind that all radiations of
light are of different wave lengths. This
fact indeed is at its very foundation, so
/ to speak, of all sunsets. and it is tho
prime agency by which their flaming,
gorgeous tihts and colors are produced.
| 1t is due to this fact, for instance, that In
the neighborhood of large towns the sun
nearly always appears to set as red
| ball of fire. The rays of light at the red
| end of the spectrum are Of much longer
wave length than any of their fellow
| rays, and so are the best qualified for
| penetrating the dense bank of haze which
| so commonly floats over all large towns
| and cities In such localities. as the sun
\ sinks TO rest, the green rays are first
| absorbed by this bank of haze, and then
the yellow. and. lastly. the orange and the
red, the latter. more often than not, be-
| ing the only ones TO get through at all.
| A careful observation of sunset will re-
veal the fact that the colors fade in the
| above mentioned order, and the reason
| they do so is that they are of different
wave lengths.
| Now, the color In the sky may, as it
| WERE be painted on the clouds, or on the
hazy air. or on the open sky itself. As
regards the latter. the color that is most
| conspicuous is of course the blue, and in
| seeking for the origin of this tint it will
| be found that the search leads to an ex-
| PLANTATION of many of the other colors.
| On looking up into the sky on cloudless
sunny day. when the swallows, perhaps,
| are flying SO high that they appear but
| as tiny specks in the dome of blue. it
| seems almost impossible to think of the
| atmosphere as being otherwise than
| perfectly clear and translucent. 1t is.
| however. in reality charged with minute
dusty particles. which have always been
found in myriads whenever the atmos-
/ phere has been tested either over the
| open sea or at the top of high noun
| tains. These particles of dust, it will be
seen, are the agents principally RESPONSE
| bic for tinting the atmosphere blue and
| for fltering out the gorgeous hues of
sunset.
| In the lower strata of the atmosphere
! the coarser particles of dust not only
/ scatter the waves of light, but they also
reflect them. so that at these lower levels
| the blue tint is diluted by white light and
| is accordingly not so intense as when
| seen, say from the top of a high noun
! tain. AT this elevation only the finer va
I rieties of dust are floating, and there is
| little reflection of the light. but much
scattering. and hence it is here that the
blue attains its greatest intensity. In
4 that part of the sky nearest the sun the
rays of light come in direct line to the
| eve of the observer, and the scattering OF
the light does not appear so great as
when one looks across the path of the
| beams. and il is due to this circumstance
that the sky near the sun is not of so in
tense a blue as portions of the sky far
Their away. A similar kind of thing hap
| pens in respect to the clouds, where dust
| readily accumulates and, rejecting the
| light, produces their brilliant wilderness.
At the edges of the clouds. moreover. the
| atoms of dust are busily engaged in re-
fracting the beams of light. and TO this
cause is due that brilliant fringe of
brightness which so often adorns many
of the largest clouds. Not only therefore
does the atmospheric dust filter out of
the blue light that tints the sky, but it
alec fahr;aotaa tho moments that color