The Camden chronicle. (Camden, Tenn.) 1890-current, 1893-12-22
LIGHT AND COLOR.
Extraordinary Differences in the
Power of Vision.
Results Of Some Simple and In
teresting Experiments.

have eyes which are unlike each other
in seeing power. In fact, many prac-
tically make use of one eye only; the
other, having been originally little
defective, was by degrees called on for
duty less and less, and accordingly de-
generated. One gentleman, mentioned
by It'd Bits, who could see, with his
right eye, the figures on the face of o
clock fve-eighths of an inch high at
twelve feet, while he could see them as
clearly with the left eye at only eight
inches distance, and, curiously enough,
this extraordinary difference in the
power of vision of both eyes was not
detected by him until he had reached
middle age. Many people are unable
to keep one eye shut and the other
open at the same time. This is espec-
tally 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
suspected. Sir John Herschel men
tions the case of an elderly person
who by chance made the unpleasant
discovery TIT he was altogether blind
in one eye.
Some simpl, and easily performed
experiments give interesting glimpses
into the constitution of the eye. Go
into dark room with candle. Look
ing at the wall, which should be of a
uniform dark tint, on moving the can
die up and down, close to the outer
side Of one eye, so that tho light falls
very obhquely onto it, one of what
are called "Purkinje's figures" will be
seen. This is an appearance of q
celles of diverging and branched red
lines on o dark field, in the interspace
of two or three of which is q sort of
cup-shaped disk. These lines are the
blood vessels of the retina, and the
disk is the 'yellow spot" or most SEN
sitiye part of the eye. In the same
situation, looking still at the dark wall
and keeping the eye fixed on one
point, hold the candle at arms length
and move it to and fro for distance
Of about two inches on a level with the
point toward which the eye is directed
and little to the right or left of it,
when faint light may be seen NOV
ing in the opposite direction to the
candle and on the lower side of the
point looked at. This Light if more
nearly inspected, is seen to be an in
verted image of the candle flame
equal in size to it, but very faint, ant
is, in fact, the'light of the candle re
hected from the lens of the eye
Other internal parts of the eye also
reflect some of the light that falls into
it, but the images formed by then
are not SO easily seen.
1t is well known that the pupil con
tracts mechanically in bright and ex
pands in faint light; but it has beef
found that, to some extent, this chang
is under the control of the will.
scientific observer, writing on thi
subject, says that when fronting win
dow or other light he can make tn
pupil expand or contract at the desir
of anyone looking into his eye. TIL
pupil is contracted while he steadil
looks at the light, and when he wishe
to expand it all that is necessary is t
take his attention away from the ey
and fix it on some other part of tn
body without moving his eyes. Thi
he does, say, by biting his tongue
pinching his arm or in some such way
The sensitiveness of the retina is din
inished by this means and the pup.
dilates. 1t contracts again when tn
mind is once more recalled to the ey
and the bright light.
A Beech Tree is Safest.
The danger of taking refuge III