South Bend news-times. (South Bend, Ind.) 1913-1938, 1917-03-01
Why Snow is White,
That is, as it Falls
From Out of the Skies


is white, and in the second place be-
cause Snow reflects equally all the
waves OF which sunlight is COM
posed so that there is no outstand-
ing color. as there would be il some
Of the waves were absorbed. while
others were reflected. Objects ex-
hibiting a decided color as red,
green. blue. etc, absorb, or extin-
guish some or the waves of light and
reflect only those which produce.
when they fall upon the eve. the
sensation corresponding 10 the par
ticular colors that the objects show
IL all the waves are absorbed. or ex-
tinguished, the object appears black;
if all are reflected it appears white.
The reason why snow reflects
light without color is because il con-
sists Of transparent particles usual
~ in the crystal form, which are ir-
regularly intermixed with globules
OF air The light penetrates a GER
tain distance into the snow and un-
dergoes refractiOn or bending out OF
its course, as it passes from the par
ticles TO the air globules and from
these again 10 the particles. and thus
the waves are sent about in every
direction in the snow. and they find
so many totally rejecting surfaces
that there is no prevailing absOrp-
ton of any Of the color elements of
the light. but on the contrary pre-
vailing reflection of all of them to-
gether. which produces the effect of
whiteness.
Tyndall says: "Wh,teness always
results from the intimate and irreg-
ular mixture of air and a transpar-
ent solid. a crushed diamond
would resemble snow. If we pound
the most transparent rock salt into
powder we have a substance as white
as the whitest culinary salt, and the
colorless glass vessel which holds
the salt would also. If pounded
give a powder as white as the salt
itself"
Foam is white for the same rea-
son. being composed of an irregular
mixture of air and particles of
transparent water. and thus il re-
fleets all the kinds of light-waves.
So. too, a cloud appears white in
the sunshine because it consists of
air and particles OF watery vapor
irregularly intermixed.
But, if you take snow and knead
il into ball Of ice it is nO longer
white. because now the air is eX-
PEELED, and the snow has become
transparent solid, which reflects
the light regularly and only in par
ticular directions. depending upon
the angle of incidence, i. e., the slope
of the impinging light with regard
to the surface.
You may hold the ice-ball up in
such a way that a flash of white
light will come from its surface at
points where the reflection is total.
but there are mo such points distrib-
uted through the ball. Where the
reflection occurs the ice acts like a
mirror. If you look into a mirror
you do not see the glass, or the mer-
curry film that backs it. but only
your face. apparently behind it, be-
cause in this case the reflection Is so
perfect that the solid producing it is
not visible, but is. so TO speak, con-
Gtdltu ny tic ItAANNAAOAA-
Still, there are circumstances in
which snow instead of appearing
white shows, or gives rise to, the
most brilliant and exquisite tints of
blue. This is best seen. according
TO Tyndan, who made many obser-
vations of the phenomenon in his
Alpine scrambles, in the finely gran
ulated snow high on the mountains.
/ When d hole is made in such snow
with a staff il sometimes looks as if
it were filled with an azure vapor.
The effect. Tyndall thought. is
probably due TO a sitting process
undergone by the light as il is re-
\ Elected from side TO side of the cav
\ ty. the short blue waves finally pre-
vailing as the longer ones are elimi-
mated. lie made an interesting eX-
! pertinent to test his idea. Digging
a cOnical hole in the snow, three
| feet deep and a foot wide at the
mouth. he saw il filled, like a cup,
with blue light. But when he placed
his staff in the axis of the hole. thus
cutting off the cross-fire of light
from the walls of the cavity the
blue color disappeared, only to re-
appear. in all its beauty, when the
staff was withdrawn.
The blue color of the sky is an
example of the effect of the scat
tering OF light-waves. This scatter
ling is produced either by excessive
Inv fine particles of dust, or by par
ticles of watery vapor. or even by
the molecules Of the air itself. In
this case the repeated reflections &c
which the scattering is due are not
made. as in ordinary reflection, from
surfaces large in comparison With
the Hght-waves, but from particles
comparable in diameter with the
lUght-waves. and even smaller thar
some OF the waves.
The particles that scatter the blue
light through the sky, i. e, the up
per air. are so small that they act
effectively only on the blue waves
which are near the short end of the
gamut OF light. The longer waves
are relatively little scattered. and
so an outstanding blue color is the
result.