Glasses for protecting eyes from injurious radiations[3rd ed.] . transmission of a sample which had but littleabsorption in the visible spectrum, while in the infra-red the ab-sorption differs but little from that of white crown glass of thesame thickness (E, in Fig. 2; thickness = mm) and having asimilar silicate composition. Curve B gives the transmission of adark sample of this same kind of glass. Here the increasedabsorption of the coloring matter extends to 3/x, beyond whichthere is a slightly higher transparency. Such a variation in trans- 7 Kindly furnished by the American Optical
Glasses for protecting eyes from injurious radiations[3rd ed.] . transmission of a sample which had but littleabsorption in the visible spectrum, while in the infra-red the ab-sorption differs but little from that of white crown glass of thesame thickness (E, in Fig. 2; thickness = mm) and having asimilar silicate composition. Curve B gives the transmission of adark sample of this same kind of glass. Here the increasedabsorption of the coloring matter extends to 3/x, beyond whichthere is a slightly higher transparency. Such a variation in trans- 7 Kindly furnished by the American Optical °—19 2 s Technologic Papers of the Bureau of Standards mission was previously observed in red The absorptionband a i coincides with that of neodymium. This sample(Bt Fig. 2, and D, Fig. 12) transmits about 54 per cent of the infra-red radiation from a furnace heated to 10500 C. This is not a verymarked absorption when compared with the sage-green glass justdescribed. For the effectiveness in absorbing the ultra-violet, seeTable ^cc Crookc-ss glasses: A, light (t= mm); B, dark (t= mm); C, ferrous , sage-green(t= mm).D, Schotts black glass (t= mm). E, white crown glass (t= mm). F, blue-green glass (A. O. No. 59; t= mm). (A and B are Crooksess neutral-tint glass.) Other glasses were produced by Crookes which have a highabsorption in the infra-red. They are pale blue, bluish green, orsage green in color. In fact, as will be noticed presently, glasseswhich absorb highly in the infra-red have either a low transmissionthroughout the visible spectrum or have the transmission bandshifted into the green or blue. 6 Coblentz, Publication No. 97, Carnegie Institution of Washington, 1908. Glasses jor Protecting the Eyes 9 IV. VARIOUS GLASSES FOR ABSORBING THE INFRA-REDGOLD-PLATED GLASSES Metals are the most opaque substances known for infra-redradiations, while in,the visible spectrum (as is well known to allwho have h
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