Richmond dispatch. [volume] (Richmond, Va.) 1884-1903, 1888-09-23
NATURES C0NJURING.
PROFESSOR PROCTOR SAYS THAT SEE
ING Is NOT BELIEVING.
The Apparent size Of the sun at the Zenith
and ct the Horizon-xtfsct OF the
Contrast Of celors.
rri..sbarrh Dispaich.l

by false impressions oven wnen we1noW
the real state of the case, 30 that nature
may In some sense be compared with a
coniurer who explains the trick he IL
about 10 play, YET he deceives the eve MS
perfectly as though We knew nothing
about the manner Of bis performance.
We know that handkerchief which We
rave him to experiment upon has not
been cut in half, yet we saw him cut It
In half; we know be has not pounded
our gold watch in a mortar, yet that is
what We saw him do.
Here is nature about TO perform her
daily conjuring trick making the sun as
he sets look larger than he really IS l
say nothing Of his looking out OF shape
because nature uses apparatus to produce
that illusion. and the eye really does see
correctly. But she makes the sun look
swollen and huge without apparatus.
though again and again we find her clever
performance explained in that way. The
refracting power Of the air really does
make tho sun look eRg-shapod. (he
is tho original Humpty- Dumpty that
sat on a vall-the horizon-and got a
great fall-&c.. &c common hen
laid egg answers that Old World conun-
drum1 and so the kindly instructive per
sons who wrote "Sandford and Merton
for the confusion of intelligent child
hood, carefully explain that 1t Is the re-
fracting power of the air which enlarges
the setting sun. even as the refractlDg
power of water in a glass bottle eDlarges
letters seen through it. But the refract-
ING mower OF the air has nothing TO DO
with the apparent enlargement oil the
sun. IL does affect the suns apparent
size. but the other way, making nm
look smaller, not lsrger-in Just such de-
gree as it apparently congresses HIM
from q globe 10 an egg.
HOW WE AXE DECEIVED.
Nature simply takes us in when she
makes rs believe that the setting sun
looks larger than the snn in the mid
hoavcns. Perhaps ought rather TO say,
for that indeed Though il has mover vet
been noticed in the books IS the true
feature Of the illusion. Nature doceiyes
us hy making US think the sun IN the
mid heaven looks smaller than when near
the horizon. Perhaps the reader thinks
hostatementsido Butthey are not
We are nearer the truth when we Judge
the suns size as he he nears the horizon
than when We estimate it from hls APP
pearance high above that circle. The
reason is obvious. When the sun is low
We can sec the aspect of the landscape,
that he is much farther away than Won
der house or hill or tree, when he is ac-
tnallv on the horizon. We see that he
is behind those objects; and thus we
cannot imagine him to be merely foot
or ward IN diameter between which
lengths lie all the estimates OF the suns
diameter which the mind unconsclOusly
forms when DE IS high in the sky. 30 he
seems to be much larger when low.
But lust here the thoughtful reader
will perhaps urge that the eye ought still
10 be able to Judge whether the image OF
the sun in the visual field Is really nc
larger when he is low. The eye, how
ever. knows nothing about Its visual
field. The mind judges Of what the eye
sees in quite other ways. Here Is a sim
pie experiment TO show this
In good black ink draw a capital let
preferably round O-in strong
black type OH white card. Now. sitting
facing a wall of uniform tint, hold or fix
the card steadily IN an upright position
at about arms length. and contemplate
that black o as steadily rs possible
"while ore with moderate haste may
count a hundred" Now let the care
drop and look at the wall with as little
interruption in time and as little change
in the diameter of vision as possible
There is seen rs usual the compile
mentary image Of the letter, but Il
has grown much larger. If. for instance
the o il an inch in diameter and the
wall is twelve times as far away as tn,
card had been, the letter seen will be ap
parently a foot in diameter. The minC
is not able 10 persuade itself that the let
ter has not grown suddenly larger. Ye
in reality the image in the visual field Il
precisely the same now as 1t had beer
before. The mind is simply deceived b!
the effect of diStance-the same oblec
seen of the same apparent size but sup
posed to be at a greater distance, i
judged TO be larger.
EXPLAINING SOME ILLUSIONS.
So tits with the setting sun. The eye
sees that the sun is far OIL. and so Judge
HIM to be large, though the area OF hi
image in the visual field is no larger Tin
deed measurably smaller) than when h'
is high above the horizon.
How is it, then, the reader may herr
ask, that the apparent. enlargement o
the setting sun and moon varies with th'
condition Of the air? The setting o.
rising moon, in particular, looks mucl
larger when the air is thick. Does no
this prove that the refractiye action o
the air is in question The effects o
the refractive action of the air being per
fecty well known no phenomena what
soever can prove that the action doe
what it is not capable of doing. HI
explanation of the effects Of thick air i
very simple. The suggestion OF in
creased distance, already strong vhel
the sun or moon is low, is strengthened
if the air is thick. For the sun and moor
then look fainter. and the mind recog
nizes in fainter aspect an apparent et
feet of distance. Here nature uses ap
paratus and mekes her conjuring S,
much the more effective.
We have in what is called blooming
an illusion depending on the effects o
thickened air. 4 sailor will tell you tina
ship really looks larger when sine loom
through fog than when the air is clear
But if her distance is known and her APP
parent size measured with sextant o
other suitable instrument it will b
found that she looks no larger than sh
should look, whether the air be clear o
thick. The mind is simply deceiye'
into thinking the ship is farther ava.
than she really is, and so judges that sh
looks larger.
There Is an illusion which affects ever,
one at all times-or 50 nearly atall time
that man may count on his fingers Tn
few occasions when BIO has been able 4
recognize what he knows TO be TIA
reality.
Look at the sky when it is clouded
and the effect produced is that OF THEM
terror OF vast hollow done-shaped Gov
eriDg. nearer overhead than toward th
horizon. The real cloud surface has
shape quite different from this Instea'