Elements of mineralogy, crystallography and blowpipe analysis from a practical standpoint .. . With Convergent Light and Crossed Nicols. In sections normal to the optic axis with monochromatic light,sections not too thin will show the dark cross with arms parallel tothe vibration planes of the nicols. The arms will be either indis-tinct near the center, or in thicker sections will not reach thecenter, Fig. 363. The first ring will be some distance out, beyondthis there will appear the alternate dark and light rings. With white light the central circle will have the color tint whichis obtained
Elements of mineralogy, crystallography and blowpipe analysis from a practical standpoint .. . With Convergent Light and Crossed Nicols. In sections normal to the optic axis with monochromatic light,sections not too thin will show the dark cross with arms parallel tothe vibration planes of the nicols. The arms will be either indis-tinct near the center, or in thicker sections will not reach thecenter, Fig. 363. The first ring will be some distance out, beyondthis there will appear the alternate dark and light rings. With white light the central circle will have the color tint whichis obtained over the entire field when parallel light is used. The Direction of Rotation may be ascertained in convergent lightby: (a) The widening of the arcs when the analyzer is turned in thedirection of rotation. (b) A quarter undulation mica plate inserted diagonally abovethe plate converts the rings and cross into two interwound spirals,which start near the center and wind in the direction of rotation,* * A plate of left and another of right-handed substance give a fourfold spiral inwhich the di
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Keywords: ., bookcentury1900, bookdecade1900, bookpublishernewyorkdvannostran
