The Somerset herald. [volume] (Somerset, Pa.) 1870-1936, 1872-06-26
The Eye.

There Is no optical instrument max
or who does not succeed in construct
ing an apparatus much more perfect
in many points than the cvc-that
marvellous organ-which we are in
clined to regard as the masterpiece of
vital and organic architecture. on ac-
count of the great service il renders
To man
This sense of sight, which is SO far
reaching that it gives us the power to
penetrate infinite space and appre-
hcnd the universe, at the same time
makes us familiar with the minntcst
objects; this sense which is the free
est and most uncirciImscribcd in il,
actions-for our sense Of touch is
limited by the length of our arms,
hearing To few thousand feet, the
senses of smell and taste having still
greater limitations-this sense. | say.
acts through an agent apparently so
impcrfcctlv adapted to its purpose,
that investigations stand amazed ut
the idea how by it we receive anv in
tclligible impressions. That we do is
an evidence of the independence Of
the mind, and lis power to make use
fnl these necessary and imperfect
means of contact with the outer
world, and proves the necessity of ed
ucating this sense to quick and pre-
else perceptions in order to correct its
faults and perfect the great work
which Nature has designcdly left i'm
perfect.
The eve has the defect of what in
physics is called the "abcrration of
sphericity :" that is, the RAYS that
pass through the centre of the lens
have common focus, but rays which
pass certain distance from the cen.
tire do not converge Mt the same point
but pass beyond. The nearer they
come to the circumference, the great
cr tine focal distance, if the lens is rig
orously spherical. In good optical
instrument, this defect is scarcely per
ccptiblc, the RAYS being centralized bv
flattening the lens. The eve is not
spherical, but has an elliptical curve.
This was for some time thought to be
an advantage, but the contrary is the
truth. And this curve is not even
well ''centcred," that is, placed sym-
mctrically to the visual axis like
lens, but is changed and twisted in
every direction. From this results
what has been called the '.astigmat-
ISM of the eye, which consists in not
being able to see at the same distance
vertical line with the same distinct
ness as one that is horizontal. This re-
Gently discovered phenomenon has at
tracted the attention of all oculists, as
1t sometimes constitutes disease of
the eye. Again, the rctina of the
eye has spots where it is entirely
blind to impressions of light. But is
this eve, which is unsymmetrical, bad
Y centred, blind in spots, at least per-
fectlv translucid Not at all. The
cornea and crystalline lens of the eve
are not absolutely limpid, as appears
when examined through an intense
blue or violet light, which renders il
fuorescent. This phenomenon is due
TO the traces of Il substance analogous.
to quinine, body which possesses in
the highest degree the property of flu
orcscence, that is, of emitting light
of its own, under the excitement of
blue or violet lights. The chrvstaline
lens, itself, is not of a homogeneous
composition, but has crystalline
structure of six branches. This is
the cause of the stars appearing to Us
with rays. All attempts to explain
this phenomenon were vain, until it
was found to be. in the visual organ
itself 1t is for this reason that the
crescent of the moon, when it is very
thin, seems to be double or triple to
some persons.
These facts are enough to show any
Dne how prone the unframed eve
must be to error and self-dcception,
and that seeing Is not physical, but
4 mental act. In infancy, the eve is
aided by the hands or touch to ae-
luire experience of the nature and
of things; later in life,
he eve asserts its superiority by in
the hands to perform ingen-
Gus and cunning work. The two
senses seem thus to continue mutually I
o assist and act upon each other
rouch lends to sight material aid and
support. The eve relines and gives ;
tC the material sense of I
ouch, so that, when sight is wanting )
ouch takes its place and performs it,
iuties.
The eve in its direct and steady
ook embraces but small compass of
Ictual sight; in fact, we clearly see
nut Il small point, which comes just
n the focus of the eye; and it is ow-
ng to quick vibratory movement of
he eye that we are able to see large l
'xtents apparently at the same time.
-Professor John H. Neimeyer. ;
THE surprising feats executed this !
summer by Prof H. Greeley and his
mall but select troupe of political