. Precious stones, a popular account of their characters, occurrence and applications, with an introduction to their determination, for mineralogists, lapidaries, jewellers, etc. With an appendix on pearls and coral. Precious stones; Pearls; Corals. DOUBLE REFRACTION OF LIGHT 49 Now every facet at the front of a cut transparent gem forms with any facet at the back (provided they are not parallel) a prism ; and through every such pair of facets can be seen, when viewed in the proper direction, an image of a small flame. As a matter of fact, a large number of such images will be seen, since for
. Precious stones, a popular account of their characters, occurrence and applications, with an introduction to their determination, for mineralogists, lapidaries, jewellers, etc. With an appendix on pearls and coral. Precious stones; Pearls; Corals. DOUBLE REFRACTION OF LIGHT 49 Now every facet at the front of a cut transparent gem forms with any facet at the back (provided they are not parallel) a prism ; and through every such pair of facets can be seen, when viewed in the proper direction, an image of a small flame. As a matter of fact, a large number of such images will be seen, since for any one facet at the front of the stone there will be several at the back, each of which may form with the front facet a prism and give rise to an image. The images given by singly refracting stones are single, as in Fig. 19, while doubly refracting stones give two images very close together, as shown in Fig. 25. This difference enables us to distinguish a singly refracting from a doubly refracting stone. For this purpose the stone should be held with the largest front facet, namely, the table, close to the eye, and a small flame viewed through it. On turning the stone about, a position will be arrived at when numerous coloured images of the flame become visible, each being single if the stone is singly refracting, or double if it is doubly refracting. Each image, whether double or single, has originated by refraction through a prism formed by one of the facets at the back of the stone and the table at the front. The images seen through a doubly refracting stone are shown in Fig. 26a, while those seen tlirough a singly refracting stone are shown in Fig. Fig. 25. Path of light through a doubly refracting prism. (Perspective view.). Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Bauer, Max, 1844-1917; S
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