A popular guide to minerals : with chapters on the Bement Collection of minerals in the American Museum of Natural History, and the development of mineralogy . ly these axes of elasticity vary with rays of different col-ored light, so that in such crystals there may not only be a dif-ferent degree of refraction in the three different axes of elasticity,but these three different degrees may vary for different coloredrays of light as well. Supplementary details of elucidation of the foregoing general-ized paragraphs follow. When the observer begins his examination of the physical prop-erties of
A popular guide to minerals : with chapters on the Bement Collection of minerals in the American Museum of Natural History, and the development of mineralogy . ly these axes of elasticity vary with rays of different col-ored light, so that in such crystals there may not only be a dif-ferent degree of refraction in the three different axes of elasticity,but these three different degrees may vary for different coloredrays of light as well. Supplementary details of elucidation of the foregoing general-ized paragraphs follow. When the observer begins his examination of the physical prop-erties of minerals he at once sees that a crystallized body has aconsistent and rigidly controlled texture, that its properties havefixed relations to direction and structure, that as Prof. Miers haswritten, from the physical point of view a crystal is very differentfrom the uncrystallized substance, just as a regiment is a very dif-ferent thing from a crowd of men; the material may be the same,but it is differently arranged. The varying intensity or characterof any of these physical properties may be graphically shown asconditioned by planes or axes of Fig. 261 Fig. 262 Fig. 263 Hardness; tests with a sclerometer (the teacher should de-scribe this instrument and if possible improvise and use one in theclass-room) show a changing hardness over the face of a crystalin different directions which when plotted give a symmetrical
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectmineral, bookyear1912
