The Manitowoc pilot. [volume] (Manitowoc, Wis.) 1859-1932, 1883-11-15
WHOLE NO. 1915.
The Oolored Curtain of the Eve,

InlS rlng-Ilke curtain IN the eye, OF
gray, green, bluish-green, brown, and
other colors, is one among the very
many remarkable contrivances of the
organic world. The eye cannot bear
too much light entering into it, and the
eolored curtain so regulates its own
movements that too much light cannot
enter the eye. The dark circular aper-
ture in the center, known as the pupil,
is consequently for ever altering in size;
on 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 starlight, it is even
bigger than pea.
This colored ring curtain is fixed at
its outer edge. and its inner edge expands
or contracts SO readily and, apparently,
so easily, preserving its circular out
line all the while, that it is quite pro-
voking to the inventor, who has been
trying to invent movable ''stops" or
diaphragm" for years, and after all
his labor cannot even approach it in
perfection, and his despair is complete
when he learns that the movements of
this eye curtain are automatic and quite
independent of the will.
1t is unlike the ordinary window
blind. which is generally of rectangu-
lar shape, and is drawn up or let down
according to the amount of light enter
ing the room. The eve curtain or iris
is of ring shape, and possesses Won
derful 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 eye is
varied. Place yourself before 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 mar
rowly 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 interdependence
between the curtains of the two eyes,
as well as that they are affected by va
riations in the quantity of 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 street these dark
winter nights. A gas-lamp seen at
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 prob
ably formed by optical defects of the
lens within the eye, or by the tear fluid
on the exterior surface of the eye, or by
a combination of all the 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 curtain be drawn
up, then the spokes are long; if the cur
tain be let down, or, in other words, if
the pupil be very small and contracted,
then one cannot see any spokes at all.
Hence, as l look at distant gaslight,
with its radiating golden spokes, | am
looking at something which H,iil give
me a sure indication of any movements
of the eye curtains. | strike match
and allow its light to fall into the eyes;
the spokes of the distant gas-lamp have
retreated into the point of flame as if
by magic; as take the burning match
away from before my eyes the spokes
of the gas-lamp venture forth again.
The experiment may be utilized to see
how much light is required to move the
window curtains of the eyes. Suppose
you are walking toward couple of gas
lamps, A and B; B about fifty yards be-
hind A. Then, if you steadfastly look
at B and at the golden spokes apparent
ly issuing from it, you may make these
spokes test of how soon the light of A
will move your iris. AS you gradually
approach A you come at last TO posi-
ton where its light is strong enough to
make the spokes of B begin to shorten;
title nearer still and they vanish al
together. l have found that about
third of the light which is competent to
contract the pupil very markedly will
serve to commence its movement
RpO7Dlefl1e