Characteristics of striæ in optical glass . with one-half second and doubling the timefor each successive one until the eighth exposure was for 64 seconds. Smith, Bennett,!Merritt J StricE in Optical Glass 87 In the case of prisms 3 and 4, the one-half-second exposure wasunintentionally omitted. It is apparent from these reproductions that the damage doneto the image by the prisms 4, 5, and 6, is hardly noticeable. Inthe case of prisms 2 and 3 the scattered light is pronounced, butit is apparent from the figure that the central spot is relativelymuch more intense than the streamers of scattere
Characteristics of striæ in optical glass . with one-half second and doubling the timefor each successive one until the eighth exposure was for 64 seconds. Smith, Bennett,!Merritt J StricE in Optical Glass 87 In the case of prisms 3 and 4, the one-half-second exposure wasunintentionally omitted. It is apparent from these reproductions that the damage doneto the image by the prisms 4, 5, and 6, is hardly noticeable. Inthe case of prisms 2 and 3 the scattered light is pronounced, butit is apparent from the figure that the central spot is relativelymuch more intense than the streamers of scattered light. Thisis, without doubt, the explanation of the fact that the observeddefinition in these cases is very fair. Only in the case of prism iis the scattered light not of relatively small intensity, and in thecase of this prism the definition was noticeably poor on a visual test. II. INDEX OF REFRACTION As already stated, the scattering of light by striae is due to thedifference between the refraction of the striae and that of the sur-. ^A//re ^^<?.f Fig. 18.—The Pulfrich refractometerThe knife-edge serves to cut off the oblique rays, and thus gives lines in the observing telescope rounding glass. In testing the index of refraction of opticalglass produced by this Bureau at its Pittsburgh branch it wasnoticed that some of the test prisms for the spectrometer andsome of the test slabs for the Pulfrich refractometer gave multi-ple lines in the field, and also that these samples contained heavystriae. The spectrometer, dealing with transmitted light, offersno simple interpretation of the difference in deviation; but case of the Pulfrich refractometer, where the magnitudesdepend upon the critical angle of total reflection, the conditionsare simpler. With the latter instrument the position of the edgeof the illuminated field indicates the refractive index of the lowersurface of the test slab where it is in contact with the monobromo-naphthaline lying between it and t
Size: 2411px × 1036px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1920, bookidcharacterist, bookyear1920
