Savannah courier. (Savannah, Tenn.) 1885-1979, 1888-10-18

the area OF his image in the visual
field is no larger (indeed aieasur-
ably smaller) than when he is high
above the horizon
How is 1t, then, the reader may here
ask, that the apparent enlargement of
the setting sun and moon varies with
the condition of the ARP 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 1t 10 not capable of do
ing. The explanation of the effects of
thick aif 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 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 instiu.
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 small pro-
portion of those who read these lines
have ever noticed the sky surface look
ing fiat. have observed the appear
ance myself three or four times during
my life, but then / have been always
on the lookout for 1t, this particular
illusion having long had great interest
for me. The occasions when the fiat
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 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 a 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
fairness 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 |
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 fat though really part
of the inner surface of an immense
spherical shell.
There is converse allusion familiar
only to balloonists which is to be ex-
planned in the same way. Rising high
above the earth surface in d balloon,
we see the surface of the earth be-
Htdtu dTCutu 1ubO bllO lOIln vi dill lll-
mense bowl or basin. The mind re-
fuses to admit the thought that the ex-
ceedingly minute depression of the Wis
ible 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 height
of half a 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 il
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.
Among illusions affecting color some
of the most important and interesting
are those which painters have to take
into account in producing with opaque
tints, the effects of sunlight or moon
light, the CLEAN of metals and kindred
illusions. A painter who should strive
to represent sun-illumined lily by
simply using the strongest white tints
at his command would fail utterly
BY using dark tints he obtains the
effect of brightness, where by using
bright tints he only obtains dirty
looking white. So with metallic effects
which are often admirably caught il
paintings.
1t is related of the French painter
Delaroche that he had tried again ani
again to produce fair imitation o
cleaning gold in one of his historical
paintings Giving up the attempt il
despair, he sent for fiacre to take
him to the gallery OF Luxembourg