Characteristics of striæ in optical glass . Fig. io.—Top: Rolled dense fluit vici^cd edgewise. Bottom: Rolled window glass viewed edgewise Figs. 13 and 14 show the striae in a rolled plate through polishededges and through the polished faces, respectively. This is clear-white, rolled crown glass, and shows very clearly that for glassof this sort an examination through the flat faces offers no cri-terion as to the quality of the glass, unless it is to be used with theline of sight perpendicular to the Fig. II.—Rolled window plate of Fig. 10 viewed flatwise4. STRI^ AND DEFINITION The eff
Characteristics of striæ in optical glass . Fig. io.—Top: Rolled dense fluit vici^cd edgewise. Bottom: Rolled window glass viewed edgewise Figs. 13 and 14 show the striae in a rolled plate through polishededges and through the polished faces, respectively. This is clear-white, rolled crown glass, and shows very clearly that for glassof this sort an examination through the flat faces offers no cri-terion as to the quality of the glass, unless it is to be used with theline of sight perpendicular to the Fig. II.—Rolled window plate of Fig. 10 viewed flatwise4. STRI^ AND DEFINITION The effect of striae upon definition of an image produced by anoptical system in which they are present is an important question,to which it is difficult to give a definite answer. In general, it isobvious that striae which are sufficiently heavy and dense will iSm«^^] ^^^^^ ^^ Optical Glass 83 injure the definition, and a mere glance edgewise through thewindow plate of Fig. 10 or through the plate of Fig. 13, at a straightedge, makes it evident that such irregular refraction as is exhibitedby these plates seriously blurs the image. The effect of suchstriae is shown in Fig. 15, which presents images of an artificialstar, as seen first without (a) and then with the plate interposed.
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Keywords: ., bookcentury1900, bookdecade1920, bookidcharacterist, bookyear1920
