The Republican. [volume] (Oakland, Md.) 1877-current, 1877-04-28

operation the next day. Persons who
are thus affiicted-for it is an affection,
though often they do not actually know
of the defect to which they are subject
may possess in every other way the
keenest eyesight; and it by no means
follows that man who is color blind
has in any other way less perfect eye
sight than an artist or any other person
whose calling requires nicely Of dis
tinction in the matter of Colors and
hues. The question occurs, to what is
color blindness due? In certain cases,
to want of education of the eye in this
particular service; but the more gener-
ally to local causes and diseases, and to
hereditary defect. Instances occurring
under the first-named class are not real
cases of color blindness. 1t is really no
more true to say that man is color
blind because he calls red "green," or
blue yellow" persistently, and with a
/ perfect appreciation of the difference,
| simply because he has never been taught,
/ than it is to call a man blind who calls
oval "round" because he has learned no
I better. But in the other instances the
| color blindness is a true defect In
Egypt, China, and other countries
where ophthalmia is prevalent, color
blindness is common; and the peculiar
light which exists in certain localities
where there is large expanse of fiat,
sandy soil, and which is known to be
very trying to the eyesight, is very often
found to produce this defect where it
does not otherwise impair the vision.
Hereditary cases of colorbl1ndness are
common. The painter Turner has been
said by some of his critics to have been
color-blind and we believe that one Of
his sisters had a defect of vision which
caused her to confuse one color with
another in such way as to prevent her
from describing accurately a picture
placed before her. If a person of per-
feet sight will look steadily for few
moments at any object of one or three
primary colors, whether lamp or any
thing else, and then close the eyes and
watch, so tospeak, with his closed eyes, he
will find the object reproduced in a kind
of cloudy representation, or rather re-
tanned on the eye; but its color will be
changed from the primary to its CORE
spending Complementary secondary
color. Thus the impression ofared object
will present itself as green; yellow as pur-
pie, and blue us orange. Vice 0ersd, if the
object is one of those secondary colors,
the reproduction on the retina will be Of
the corresponding primary color. In
this way, it is quite possible for man
, who has been looking for any length of
time at red light on a railway at night
to remove his eyes for moment or two
and, on looking again at the lamp, 10
. find that-in the course of the natural
relief afforded by the impression on the eye
resolving itself into the secondary color
| his sight is for Il moment impeded by
the floating image (nOw green instead Of
I red) before his eyes, and the actual lamp
i (still red covered, as it were, by the re-
) tanned figure, so that it appears to be
green. This curious effect is no faultssof
vision, and might easily mislead an
5 engine-driver who, having first actually
seen the red light, has, after withdraw
ing his eyes, Immediately afterward
imagined it changed to green or white,
; an indication of the removal of the OBJ
: staCle to the progress of his train. In
/ this way, by continual straining of the
c eye in search of particular signal, es-
O roUi"lly at night, win no light beyond
q that of the glazing furnace of the engine
= in itself detrimental to the cyes-it is
quite possible that color blindness NAV
> be acquired, and that a man who was
( once perfectly able to distinguish the
most delicate tints may become insensi-
= bic to the effects of widely different
e colors.-Chdm6erS' Journal.