Thomas County cat. [volume] (Colby, Kan.) 1885-1891, 1888-10-25

lance, is judged to be larger.
So it is with the setting sun. The
eye sees that the sun is far of, and
SO judges him to be large, though
the area of his image in the visual
field is no larger Gndeed measur-
ably smaller) than when he is high
above the horizon.
How is it, then, the reader may here
ask, that the apparent enlargement Of
the setting sun and moon varies with
the condition of the air? The setting
or rising moon. in particular, looks
much larger when the air is thick.
Does this not prove that the retroactive
action of the air is in question? The
effects of the retroactive action of the air
being perfectly well known no phenom::
ena whatsoever can prove that that
action does what tits not capable of do
ing. The explanation of the effects OF
thick air is very simple. The sugges-
ton of increased distance, already
strong when the sun at noon is low, is
strengthened if the air is thick. For
the sun and moon then look fainter,
and the mind recognizes in a fainter
aspect an apparent effect of distance.
Here nature uses apparatus and makes
her conjuring so much the more eff
fctive.
We have in what is called Gloom
ing" an illusion depending on the
effects of thickened air. A sailor will
tell you that ship really looks larger
when she looms through fog than when
the air is clear. But if her distance is
known and her apparent size measured
with a sextant or other suitable instru-
ment, it will be found that she looks
no larger than she should look,
whether the air be clear or thick The
mind is simply deceived into thinking
the ship is farther away than she
really is, and so judges that she looks
larger.
The illusion of deeply arched in
stead of nearly fat sky is occasion
ally broken. Probably but a small pro-
portion of those who read these lines
have ever noticed the sky surface look
ing fiat. l have observed the appear
ance myself three or four times during
my life, but then l have been always
on the lookout for it, this particular
illusion having long had great interest
for me. The occasions when the fat
ness of the under surface of the cloud
sky can be recognized are those when
the clouds lie actually in long paral-
lei beds of tOlerably uniform breadth
and separated from each other by toll
erably equal distances and lying in the
same general level-the sun being near
the horizon, so as to illuminate the
cloud-bands underneath. At such
times, as also when instead of uniform
bands a kind of network of clouds COW
ers the sky towards the place of the
horizon sun, an effect of fOreshOrtening
is produced which brings out the hori-
zOntality of the cloud surface-that is,
not of the surface of individual clouds,
but of the general layer.
remember one occasion when / was
travelling across the Western prairies,
towards the time of sunset. that as the
sun in his descending motion passed
from above to below layer of clouds
uniformly reticulated, the golden tinge
along an edge of each of the cloud
streaks so distinctly indicated the rela-
tive positions of the different parts of
the network of clouds, that the true
flatness of the surface was as strongly
forced on me as usually the incorrect
arched form is impressed on the mind.
For the first and only time in my life 1
was not only able Gas on three or four
other occasions) but actually forced to
feel what an immense globe this earth
world of ours is. For there was the
widely-spanning surface of cloud look
ing perfectly fiat though really part
of the inner surface of an immense
spherical shell.
There is a converse allusion familiar
only to balloonists, which is to be ex-
planned in the same way. Rising high
above the earth's surface in q balloon.
We see the surface of the earth be-
meath arched into the form of an inn
mense bowl or basin. The mind re-
fuses to admit the thought that the ex-
ceedingly minute depression of the Wis
IDLE horizon corresponds to the SEEM
ingly immense depth Immediately be-
low the aeronaut. Or one may say
(though in reality it is saying the same
thing) that the mind can not admit the
thought of the immensely of the dis
lance of the horizon. From a height
of half mile the horizon is some
forty miles away. or eighty times
further than the earth's surface below,
but the mind sets the horizon only
three or four miles away Cat least if
the air is clear), and consequently the
surface. which (regarded as a whole)
is really slightly convex below the OBJ
server, appears to be markedly con-
cave.
an