Rensselaer Union, Volume 9, Number 43, Rensselaer, Jasper County, 12 July 1877 — Blue-Glass Blindness. [ARTICLE]

Blue-Glass Blindness.

It is curious to notice in what strange ways a popular mania affects different people. The believers in the blue glass absurdity have hitherto had a monopoly of wild theories on that subject, of which they have invented no lack, to meet the various objections raised, but here is a blue-glass skeptic gravely muking asser. tions fully as baseless as the errors which they are aimed to controvert. The skeptic In question is none other than our staid contemporary the Evening Poet, of the city; which, in its anxiety to warn its, readers against an apparent danger inherent in the blue glass, perpetrates the following: “ That blue glass has any curative properties remains yet to be proved; but that glass of that color will concentrate the rays of the sun, in a lesser degree, as the common burning glass does, was known before Gen. Pleasonton’s book was printed and made so much ot by the newspapers. A gentleman of Brooklyn suffering from weakness cf sight wa9 recently lea by the advice of well-meaning friends to use spectacles of blue glass, such as certain opticians are selling just now. The result was that his eyes, already too weak to lie used much In ordinary circumstances, were exposed to a terrible glare and heat,'/which, in less.than a week, entirely destroyed the eyesight of the sufferer. He is now totally blind. This is a fact, and the gentleman would doubtless be glad to have other sufferers from weak eyes know of liis case and draw a moral therefrom. Another similar instance has come under our observation, a young lady being in this case the dupe of the blue glass enthusiasts. It is worth bearing in mind that the only property of blue-glass that has been proved is its Dower 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 diverge. By a burning-glass or double-convex lens, parallel rays are conveyed to a 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 a very large proportion of the luminous rays, and the light it transmits is nothing but modified sunlight, or rather sunlight shaded and reduced in intensity; so that, so far from blue glass producing a terrible “glare,” it transmits an exceedingly mild light. This property was utilized by photographers long ago in order to relieve the eyes of their sitters; while blue spectacles have been worn by weak-eyed people almost ever since spectacles were contrived. It is not necessary to discuss the question of whether blue glass becomes hotter through absorption than clear glass, in the absence of any authentic experiments on the subject. It is well settled that, as color teaches us nothing regarding the radiation and absorption of non-luminous heat, any conclusions as to its influence may well be wholly delusive. The absorption depends on the particular absorptive power of the coloring substance, and not on its hue. Clear glass is opaque to a considerable degree to heat rays, and therefore through absorbing them becomes warmed. The only question, then, is whether the coloring matter introduced is capable of producing increased absorption sufficient to render the glass hot, and so to cause it to injure the delicate outer portion of the eye through its proximity thereto. In the absence of any data determining this point, no positive opinion can be formed; but it seems probable that the resulting inflammation of the organ would produce suffering sufficiently intense to indicate its cause to the wearer of the glasses and induce him to discard them before the week had elapsed during which the lesion became permanently extended to the optic nerve. It should be understood, however, that if blue-glass spectacles are injurious, it is because of the constitution of the glass, and it does not necessarily follow in consequence of that glass being blue. —Scientific American.