<h2><SPAN name="EYES" id="EYES"></SPAN>EYES.</h2>
<p class="bq ac">By <span class="sc">W. E. Watt</span>.</p>
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<div class="poetry">
<div class="verse indent6">Why was the sight</div>
<div class="verse">To such a tender ball as th' eye confined,</div>
<div class="verse">So obvious and so easy to be quenched,</div>
<div class="verse">And not, as feeling, through all parts diffused;</div>
<div class="verse">That she might look at will through every
pore?—<span class="sc">Milton.</span></div>
</div></div>
<p class="bq ac">"But bein' only eyes, you see, my wision's
limited."—<span class="sc">Sam Weller.</span></p>
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<ANTIMG class="drop-cap" src="images/initial_t.jpg" width-obs="100" height-obs="93" alt="" /></div>
<p class="drop-cap">THE reason we know anything
at all is that various
forms of vibration are capable
of affecting our organs
of sense. These agitate the brain, the
mind perceives, and from perception
arise the higher forms of thought.
Perhaps the most important of the
senses is sight. It ranges in power
from the mere ability to perceive the
difference between light and darkness
up to a marvelous means of knowing
the nature of objects of various forms
and sizes, at both near and remote
range.</p>
<p>One the simplest forms of eyes is
found in the Sea-anemone. It has a
colored mass of pigment cells and
refractive bodies that break up the
light which falls upon them, and
it is able to know day and night. An
examination of this simple organ leads
one to think the scientist not far wrong
who claimed that the eye is a development
from what was once merely
a particular sore spot that was sensitive
to the action of light. The protophyte,
<i>Euglena varidis</i>, has what seems to be
the least complicated of all sense
organs in the transparent spot in the
front of its body.</p>
<p>We know that rays of light have
power to alter the color of certain
substances. The retina of the eye is
changed in color by exposure to continued
rays of light. Frogs in whose
eyes the color of the retina has
apparently been all changed by sunshine
are still able to take a fly accurately
and to recognize certain colors.</p>
<p>Whether the changes produced by
light upon the retina are all chemical
or all physical or partly both remains
open to discussion.</p>
<p>An interesting experiment was performed
by Professor Tyndall proving
that heat rays do not affect the eye
optically. He was operating along
the line of testing the power of the
eye to transmit to the sensorium the
presence of certain forms of radiant
energy. It is well known that certain
waves are unnoticed by the eye but
are registered distinctly by the photographic
plate, and he first showed
beyond doubt that heat waves as such
have no effect upon the retina. By
separating the light and heat rays from
an electric lantern and focusing the
latter, he brought their combined
energy to play where his own eye
could be placed directly in contact
with them, first protecting the exterior
of his eye from the heat rays. There
was no sensation whatever as a result,
but when, directly afterward, he
placed a sheet of platinum at the
convergence of the dark rays it quickly
became red hot with the energy which
his eye was unable to recognize.</p>
<p>The eye is a camera obscura with a
very imperfect lens and a receiving
plate irregularly sensitized; but it has
marvelous powers of quick adjustment.
<span class="pagenum"><SPAN name="Page_118" id="Page_118">[Pg 118]</SPAN></span>
The habits of the animal
determine the character of the eye.
Birds of rapid flight and those which
scan the earth minutely from lofty
courses are able to adjust their vision
quickly to long and short range. The
eye of the Owl is subject to his will as
he swings noiselessly down upon the
Mouse in the grass. The nearer the
object the more the eye is protruded
and the deeper its form from front
to rear.</p>
<p>The human eye adjusts its power
well for small objects within a few
inches and readily reaches out for those
several miles away. A curious feature
is that we are able to adjust the eye
for something at long range in less
time than for something close at hand.
If we are reading and someone calls
our attention to an object on the
distant hillside, the eye adjusts itself
to the distance in less than a second,
but when we return our vision to the
printed page several seconds are
consumed in the re-adjustment.</p>
<p>The Condor of the Andes has great
powers of sight. He wheels in beautiful
curves high in the air scrutinizing
the ground most carefully and all the
time apparently keeping track of all
the other Condors within a range of
several miles. No sooner does one of
his kind descend to the earth than those
near him shoot for the same spot hoping
the find may be large enough for a
dinner party. Others soaring at greater
distances note their departure and follow
in great numbers so that when the
carcass discovered by one Condor
proves to be a large one, hundreds of
these huge birds congregate to enjoy
the feast. The Condor's eyes have
been well compared to opera glasses,
their extension and contraction are
so great.</p>
<p>The Eagle soars towards the sun
with fixed gaze and apparent fullness
of enjoyment. This would ruin his
sight were it not for the fact that he
and all other birds are provided with
an extra inner eyelid called the nictitating
membrane which may be drawn
at will over the eye to protect it from
too strong a light. Cuvier made the
discovery that the eye of the Eagle,
which had up to his time been supposed
of peculiarly great strength to enable
it to feast upon the sun's rays, is closed
during its great flights just as the eye
of the barnyard fowl is occasionally
rested by the use of this delicate semi-transparent
membrane. Several of
the mammals, among them being the
horse, are equipped with such an inner
eyelid.</p>
<p>One of my most striking experiences
on the ocean was had when I
pulled in my first Flounder and found
both of his eyes on the same side of
his head. All Flat-fish are similarly
equipped. On the side which glides
over the bottom of the sea, the Halibut,
Turbot, Plaice, and Sole are
almost white, the upper side being
dark enough to be scarcely distinguishable
from the ground. On the upper
side are the two eyes, while the lower
side is blind.</p>
<p>When first born the fish swims upright
with a slight tendency to favor
one side; its eyes are on opposite sides
of the head, as in most vertebrates
and the head itself is regular. With
age and experience in exploring the
bottom on one side, the under eye
refuses to remain away from the light
and gradually turns upward, bringing
with it the bones of the skull to such
an extent that the adult Flat-fish
becomes the apparently deformed
creature that appears in our markets
as a regular product of the deep.</p>
<p>The eyeless inhabitant of the
streams in Mammoth Cave presents a
curious instance of the total loss of a
sense which remains unused. These
little fishes are not only without sight
but are also almost destitute of color
and markings, the general appearance
being much like that of a fish with
the skin taken off for the frying pan.
<span class="pagenum"><SPAN name="Page_119" id="Page_119">[Pg 119]</SPAN></span>
The eyes of fishes generally are so
nearly round that they may be used
with good effect as simple microscopes
and have considerable magnifying
power. Being continually washed
with the element in which they move,
they have no need for winking and
the lachrymal duct which supplies
tears to the eyes of most of the animal
kingdom is entirely wanting. Whales
have no tear glands in their eyes, and
the whole order of Cetacea are tearless.</p>
<p>Among domestic animals there is
considerable variety of structure in the
eye. The pupil is usually round, but
in the small Cats it is long vertically,
and in the Sheep, in fact, in all the
cud chewers and many other grass
eaters, the pupil is long horizontally.</p>
<p>Insects present a wonderful array of
eyes. These are not movable, but
the evident purpose is that there shall
be an eye in readiness in whatever
direction the insect may have business.
The common Ant has fifty six-cornered
jewels set advantageously in his little
head and so arranged as to take in
everything that pertains to the pleasure
of the industrious little creature. As
the Ant does not move about with great
rapidity he is less in need of many
eyes than the House-fly which calls
into play four thousand brilliant facets,
while the Butterfly is supplied with
about seventeen thousand. The most
remarkable of all is the blundering
Beetle which bangs his head against
the wall with twenty-five thousand
eyes wide open.</p>
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