Richmond dispatch. [volume] (Richmond, Va.) 1884-1903, 1894-07-29
THE HUMAN EYE.
II Seems to BE Adapted Ia All Require
ments-fiews.

tBDiWldr Stl"l'ft MDuSliA.l
The approach 70 perfection in modern
telescopes and microscopes Is wonf2rl u
indeed: but as PSYCHOLOGISTS have adj
vanced the knowledge Of vision The So
c4llel irnperffcti0ns Of the eye have been
steadily disappearing, ana even now ther;
IS not much u learn. Viewed merely es
an optical instrument an apparatus con-
tanned I'm a globe lcs5 than an inch IN Ill
ameter. in which is produced an image
practically perfect ~ form ara Color
which car BE- accurately adjusted almost
Instantly for every distance fr1m hVe
inches TO inhnity. is movable in every dl-
rcctlon. has an area fOr The detection OF
IN. most minute details. ard ~ the same
tine a sufficient appreciation or large
objects. f. double but the images IN either
eye exactly cyiucding, enables Us 10 sea
all shades Of color, estimate distances
s1nlity and 20 some extent the con'is-
t,nc- 81 0bjecr. the normal human eye
nay well be called perfect. The more III
a., cd. thu eye H. studied in detail the more
thoroughly does one appreciate its per-
fiction a. an optical apparatus.
We receive the impression Of single
object. although there are two images
one in either eye-but & Is necessary that
the images be- made upon corresponding
points In the retina. lf the angle or
vision In one eye be deviated, even 70
slight degree. by pressing on one CLONE
with the finger We see two images. one
can appreciate how exactly these points
must correspond, when II IS remembered
that the two rays OF light appear as
one only when the distance between
them is one thirty-6ye hundreds Of an
inch Not the least Of the wonders Of the
eye are connected viii the appreciation OF
images made upon thf retina by certain
parts of the brain.
II is literally true Sat a person may
see and vet not percelvt II has happened,
in certain injuries OF the brain, that a
person sees and reads the words In a
book. and yet does not perceive their
Significance This is called Wori-blndnesS.
In a. certain portion Of the brain Is a part
which enables us 70 recognize the fact that
we see an object YET this object conveys no
idea. There are two Of these sO-cdlled
centres of Vsion-one on either side
and their action is partly crossed. When
the centre is destroyed on one side. the
inner half Of one eye and the outer hall
Of the other eye are blinded. Further
back in the brain, however, IS centre
which enables Us TO perceive or under
stand what IS seen.
When this centre IS destroyed We see
objects, and may avoid Obstacles In walk
INK but persons. words, .etc., are not re-
cosnized. This centre etists only on the
left side of the brain.
An impression. however short, made
upon the retina Is perceived. The letters
are on printed page, are distinctly sen
when ilumined by an electric spark. the
duration Of which Is only forty bll.Jnth
OF second; but the impression re-
mains much longer. Anything IN motion
appears 10 US in way quite different
from the single impression that Ne should
have from an electric spark. In pic
turs representing an animal In motion,
as II appears in an Instantaneous photo
graph, the positions seem absurd ana
ike nothing we have ever seen.
In looking at a horse in action, the I'M
uresslons made by the different positions
Of the animal run into each other, and art
should represent as nearly as possible the
sum. or average Of these impressions. II
is also true that Impressions are dii-
fused in the retina ibeyoni the points
upon which they art directly received.
This is called irradiatDn; and the impress
SION is diffused farthe! for white or light
colored than for bla:< or dark objects.
1t IS well known tat a white square
locks considerably larger than dark
square exactly the same size; or the
hands in white gloves look larger than IN
black gloves.
The whole question Of the appreciation
OF colors and blindness IS still
wrapped in mystery. We know that
some persons cannot distinguish between
certain colors. but the reason OF this Is
obscure Perfect sight can exist only
when the eye is perfect. The form and
color OF objects may be distorted so that
an inaccurate image is formed upon the
retins. ana this image. however imper'
feet IL may be. is what Is perceived BY
the brain. In hearing the case Is dlf'
ferent
The waves OF sound. II they be con.
Quoted to the internal ear, and II the
nerve or hearing. with ,lts examinations
be normal, cannot be mo1ned In the course
OF transmission. Sound@ are always APP
precated at their exact value, except as
regards intensity. Enough has been safe
about the eye, think, TO show that II
Is perfectly adapted 10 all requirements
and whatever defects II may seem &
have. viewed as an optical instrument
render II more useful TO us than II these
apparent defects did not exist.