Marshall County Republican. (Plymouth, Ind.) 1856-1878, 1857-03-05

II mc .McCmdnISnl Oh the Eve.
There is most learned and able articl,
on The Sight and How to See,'. in a late
rumber of the North British leeuieu. w,
will endeavor to present an abstract of SONS
Of the new and leaiing ideas embraced il
it, they being Of deep and practic interes
T. every human teing, a BON
Of all the FIVE senses-seeing, hearing.
smelling tasting. and feeling-~by which
we acquire our knowledge Of the external
world, the sense Of sight is the most i'm
poitant. The eye surpasses all the other or
gans OF sense in the extent of its range, anc
it can p.rctrve the rays of lighs which may
! have proceeded from distant s.ar, even a.
ter the orb.had been blotted out of space
This power of observation does not depend
on the magnitude of the epeball or any o.
It's parts; the minutest animal-requirine
a microscope to makeit visible-contain.
/ the image of the external world painted or
It's resina as distinctly as that of a man, OF
an elephant, The human eve has been ad-
mired for the beauty of its form, and the
range and ouickness Of its movements; and
varied mechanism has excited the wonder
of philosophers. The eyeball is nearly
globular, being of q spheroidal form, like
an orange-its smallest diameter being that
which we direct TO objects to see them. 1t
moves in socket elegantly prepared for
| IT'S reception, and is fabricated by a pecu-
liar secretion, which entirely removes the
friction of its 1incessant motions. Bys
means ofsix muscles attached to it, with
out moving the head, it can direct itself to
almost every point of a hemisphere, but
with the motion of the head combined. it
commands "a panorama of everything
around it. The ball of the eve, which is
about 9-10 of an inch, In diameter. has a !
tough and. Opaque external membrane, !
called the schlerotic coat, which forms the
white portion. Into this, and in front os |
the ball, slightly raised above it, is insert |
ed a circular transparent portion, like a
small glass, called thc cornea Although |
ii is as transparent as glass, it is. like the
/: llerotic coat, very tough Il is compos-
OF several firmly adhering layers of equal !
thickness, and is nearly half an inch in d.
ameter. Within the cornea, and in con-
tract with it, is the aqueous humor trans
parent fluid. 1t has the form of plano
convex lens, the curved side being the inner
surface of the cornea, and the plane side
the visible surface of the iris, which is COL
pred circular fat membrane, with an aper-
turc its center called the pupil 1t has
he remarkable property Of contracting
The size of the pupil from one-fourth to
one-eight of an inch under strong light, and
again when the light is dimin-
she'd This membrane divides the eye in
o two very equal parts-the anterior and
chambers. The anterior which is
! front of the iris, contains the aqueous hu-
nor; the posterior, behind it, contains the
'itreous humor, and the crystalline lens
(he vitreous humor resembles the white of
IN egg, fills up great portion of the eve
,all, and keeps it descended, like an india
ubber bag filled with water. 1t is divided
nto several cells, the humor occupying each
Ike honey In honey comb. The crystalline
ems occupies the front of the vitreous hu-
nor;s ID is double convex-more convex
ehind than beforehand is placed in thin g
ag Immediately behind the iris-the pupil
T opening of the iris being opposite the
entral part of the lens. q
The crystalline lens is beautiful piece of
In its perfec. state it is
transparent as drop of water, aud yet it
onsists of great number Of coats, like an :
Mon, each coat composed of an immense
lumber of fibers, with teeth on one side
Ike those of saw-thc teeth of one fiber
ltering into the hollows of the adjacent
bers, so as to bind them together-t).
hese fbers are of equal length, taper from
lch end to the their middle, and SO COM
med, that the lens is most dense at its GEN.
r, and least so towards its circumference.
/ the crystalline lens, fourteenth of an inch
diameter, ola Goldfish, there are FIVE mill
ms of teeth, exhibiting mechanism
hich may well excite the profoundest sd- C
Behind the vitreous humor, and lining =
Q inner surface of the schlerotic, is the
oroid coat,--a delicate membrane cover
on its posterior surface with black pig
ent, and Immediately within this pigment
the retina, the innermost coat of all, and +,
ing next to the vitreous humor 1t isa Y
licate REGULATED membrane, consisting :,
several layers of different structures, the y
act use0 which has not yet been determ- U
"a. although the membrane which they
nm is that which receives the images of
fernal objects, like the gray glass in the =
mera obscura. A line drawn through
: center of the pupil and the crystalline m
IS, is called ''the axis of vision" or the
teal axis of the eye, and che extremity :
this axis is that point where it touches
. retina. About one-tenth of an inch
m the extremity of this axis-in hori- Z
ntal direction--the retina is slightly rais- u
this is the place where the optic ncrve
m the brain enters the schlerotic coat,
1 expands into the retina At the ex- &c
nifty Of the axis. is a small spot with &c
low margin, which is more transparent :
N the rest of the retina; this spot exists
v in man Monkeys and some lizards, -
/ Is about from the fifteenth to the thir-
b o. an inch in diameter. "a - cas-
This general description of the eye and
mechanism shows how wonderfully tits :
de, and how infinitely it surpasses in
icacy and refinement, the most skilfnll is