The Hawaiian star. [volume] (Honolulu [Oahu]) 1893-1912, 1895-01-14
LIGHT, COLOR AND THE EYE.
Ngai,n-Sn Int.rastlnr Exparip,auAs

Extraordinary Differences In the Power Of
yision-Some Interesting Experiments.
While the eyesight of many persons is
defective, a still greater number have eyes
which are unlike each other In seeing power.
In fact, many practically make use Of one
eye only; the other, having been originally
a little defective, was by degrees called on
for duty less and less and accordingly de.
generated.
One gentleman could see with his right
eye the figures on the face Of clock five
zig tbs Of I'm inch high ut IL feet, while he
.n'l see them AS clearly with the left eye
at "!eht inches distance, and curiously
tluIsh this extraordinary difference in the
lowers of vision of both eyes was not de-
tected by him until he had reached middle
age. Many people are unable to keep one
eye shut and the other open ut the same
time.
This is especially common with children,
but less frequent with adults, and it will
be readily understood that in such cases
considerable differences in the powers of
the eyes may exist without being suspect
ed. Sir John Herschel mentions the case
of an elderly person who by chance made
the unpleasant discovery that he was alto
gether blind in one eye.
Some simple and easily performed eX-
perments give interesting glimpses into
| the constitution of the eye. Go into dark
room with a candle. Looking ut the wall,
which should be of uniform dark tint, on
moving the candle up and down close to
the outer side of one eye, so that the light
falls very obliquely onto it, one of what
are called "Purkinje's figures" will be
seen. This is an appearance of a celles of
diverging and branched red lines on II dark
field, in the interspace of two or three of
which is sort of cup shaped disk.
These lines are the blood vessels OF the
retina, and the disk is the yellow spot" OF
most sensitive part of the eye. In the same
situation, looking still at the dark wall aud
keeping the eve fixed on one point, hold
the candle at arms length and move it tc
and fro for distance of about two inche:
on level with the point toward which the
eye is directed and little to the right OF
left of it, when "A faint light may be seer
moving in the opposite direction to the can
die and on the lower side of the point looked
at.
This light, if more nearly inspected, il
seen to be an inverted image of the candl,
flame, equal in size to it, but very faint
and is, in fact, the light of the candle TT
flecred from the lens of the eye. Other in
ternal parts of the eye also reflect some o
the light that falls into it, but the image
formed by them are not so easily seen.
1t is well known that the pupil contract
mechanically in bright light and expand
in faint light, but it has been found tina
to some extent this change is under the con
troll of the will. A scientific observer writ
/. ing on this subject says that when fronting
81 window or other light he can make til
pupil expand or contract at the desire O
any one looking into his eyes
The pupil is contracted while he steadil
- looks at the light, and when he wishes t
expand it all that is necessary is to take hi
attention away from the eye and fix it Of
some other part of the body without NOV
!, ing his eyes. This he does, say, by bit
ing his tongue, pinching his arm or il
some such way. The sensitiveness of tn
retina is diminished by this means, and tn
pupil dilates. 1t contracts again when tn
mind is once more recalled to the eye an
the bright light.-Tit-Bits,