Butler citizen. [volume] (Butler, Pa.) 1877-1922, 1883-10-31
The Colored Curtain in the Eye.

This ring-like curtain in the eye, o
gray, green, bluish-green, brown, ant
other colors, is one among the very
many remarkable contrivances of the
organic world. The eye cannot beal
too much light entering into it, anC
the colored curtain so regulates its owr
movements that too much light can
not enter the eye. The dark circular
aperture in the center, known as the
pupil, is consequently for ever altering
in size on a bright, sunshiny day
out in the open, it may be only the
size of pins head, but at night, when
there is no light stronger than star
light, it is ever bigger than pea.
This colortd ring curtain is fixed al
its outer edge, and its inner edge ex
pands or contracts so readily and, ap.
parently, so easily, preserving its cir
cular outline all the while, that it is
quite provoking to the inventor, who
has been trying to invent movable
"stops" or "diaphragms" for years,
and after all his labor cannot even ap-
proach it in perfection, and bis des-
pair is complete when he learns that
the movements Of this eve curtain
are automatic and quite independent
Of the will
1t is unlike the ordinary window
blind, which is generally of arectangu-
lar shape, and is drawn up or let
down according to the amount of light
entering the room. The eye curtain
or iris is of ring shape, and possesses a
wonderful power of expanding itself so
as to diminish the area of the pupil,
and of shrinking in, so as to enlarge
the area of the pupil. Its movements
may be watched in variety of ways,
some of which we shall describe.
The common way of watching the
movements of the iris is to regard it
closely in looking glass while the
amount Of light entering the eyes is
varied Place yourself before a look
ing glass and with your face to the
window Probably the iris will be ex-
panded, and there will only be very
small opening or pupil in the center.
Now shut one eye suddenly, while
narrowly watching the other in the
glass all the time At the moment
the light is cut off from one eye, the
iris of the other contracts or is drawn
up so as to enlarge the pupil. This
shows that there is remarkable in
terdependence between the curtains OF
the two eyes, as well as they are af,
fected by variations in the quantity ol
light falling on them.
Perhaps one of the most interesting
ways of watching the movements Of
these sympathetic eye curtains is one
which may be followed while you are
out walking on the streets these dark
winter nights. A gaslamp seen at o
distance is, comparatively speaking, a
point of light, with bars of light ema
mating from it in many directions
These bars, which give the peculiar
spoked appearance to star, are proba-
bly, formed by optical defects of the
lens within the eye, or by the teal
fluid on the exterior surface of the eye
or by a combination of all these causes
Be that as it may, the lengths of the
spokes of light are limited by the inner
margin of the eye curtain if the cur
tain be drawn up, then the spokes are
long if the curtain be let down, or
in other words, if the pupil be very
small and contracted, then one cannot
see any spokes at oil Hence, as
look at distant gaslight, with its
radiating golden spokes, / am looking
at something which will give me a
sure indication of any movements O
the eve curtains. | strike match and
allow it's light to fall into the eyes
the spokes of the distant gaslamp have
retreated into the point of flame as il
my magic; as | take the burning
match away from before my eyes The
spokes of the gaslamp venture forth
again.
The experiment may be utilized tc
see how much light is required to move
the window curtains of the eyes. Sup
pose you are walking toward couple
of gaslamps, A and b b about fifty
yards behind A. Then, if you stead
fastly look at B and at the COLDER
spokes apparently issuing from it, you
may make these spokes test of how
soon the light of A will move your
Tres. AS you gradually approach A
you come at last to q position where
its light is strong enough to make the
spokes of B begin to shorten ; little
nearer still and they vanish altogether
| have found that about third of the
light which is competent to CONTRACT
the pupil very markedly will serve tc
commence its movement.