The Redwood gazette. [volume] (Redwood Falls, Minn.) 1873-1940, 1877-07-19
Blue-Glass Blindness.

IT is curious to notice in what strange
ways popular mania affects different
people. The believers In, the blue. glass
absurlily have hitherto had monopoly of
wild theories ON that subject, of which
they have invented NO lack, to meet the
various objections raised, but here Is q
blue-glass skeptic grsvely making asser.
tions fully ~ baseless as the errors which
they are aimed to controvert. The skcp-
tic In question Is none other than our
staid contemporary the Eoening Pose, Of
the city; which, In Its anxiety to warn its
readers against an apparent danger inhe.
rent in the blue glass, pefpetfates the fol.
lowings
"T6at blue glass has any curative pfop.
critics remains yet II he proved; but that
glass of that color will concentrate the
lays Of the SUN, in, . lesser degrees, is the
common burning glass does, was known
before Gen. Pleasonton's book was print
ed and made so much OF by the newspa.
pers. A gentleman of Brooklyn suffering
from weakness Of sight was recently led
by the advice of we'll meaning friends TO
use spectaclcs of blue glass, such as Ger.
tain opticians are selling just now. The
result was that his eyes, already too weak tv
be used much in ordinary circumstances,
were exposed to q terrible glare and
heat, which, in less..than a week, entirely
DESTROYED the eyesight of the sufferer. He
is now totally blind. This Is fart. and
the gentleman would doubtless be glad to
have other sufferers from weak eyes know
of his case and draw q moral tkerefrOth.
Another similar instance HAS GoiMe Under
our observation, young lady being in
this case the dupe Of the blue glass enthn-
siasts. It is worth bearing IN mind that
the only property of blue-g that has
been proved is it's power to Concentrate the
rays Of the sun and produce extraordinary
heat"
Neither glass stained blue nor glass of
any other color concentrates the rays Of
the sun as the common burning glass
does" A lens, from the curvature of its
surface or surfaces, has the property of
causing the luminous rays which traverse
it either to converge or to divergc. BY a
burning-gla or double. convex lens, par.
allel rays are conveyed to focus. If
blue glass is made in similar form, it will
act similarly; otherwise it will not.
But, as we have repeatedly pointed out,
blue glass cuts off very large proportion
of the luminous rays, and the light 1t
transmits is nothing but modified SUM-
light, or rather sunlight shaded and re-
duced In intensity; SO that, SO far from
blue glass producing a terrible "glare, -
it transmits an exceedingly mild light.
This property was utilized by photograph.
ers long ago In order to relieve the eyer
Of their sitters while blue spectacles have
been worn by weak eyed people almost
ever since spectacles were contrived.
1t Is not necessary to discuss THE Outs:
ton Of WHETHER blue glass beGothcs hotter
through absorption than clear glass, in the
absence of any authentic experiments on
the subject. 1t is we'll settled that, a.
color teaches us nothing regarding the "a
diatiOn and absorption of non. luminous
heat, any conclusions as to its influence
may well be wholly delusive. The alb.
sorption depends ON the particular alb.
sorptive power of the cOl0ring substance,
and not on its hue. Clear glass is Opaque
to considerable degree to heat rays, and
thcr efore through absorbing them becomes
warmed. The only question, then, i
whether the coloring matter introduced il
capable of producing increased absorb.
ton sufficient to render the glass hot, and
so to cause it to injure the delicate otitel
portion of the eye through Its proximity
thereto. In the absence of any data de-
termining this point, NO positive opinion
can be formed but it seems probable thai
the resulting Inflammation of the orgat
would produce suffering sufficiently in
tense to indicate Its cause to the wearer o1
the glasses and induce him to discard
them before the week had elapsed during
which the lesion became permanently ex
tended to the optic nerve. 1t should b,
understood, however, that if blue-glas!
spectacles arc injurious, It Is because o
the constitution of the glass, and 1t doe.
not necessarily follow in consequence o.
that glass bcing blue.-Scient,fc american