The American journal of science and arts . s surprised to observe the whole ofits surface covered with parallel lines or veins, some of which re-flected the light more powerfully than others, so as to have theappearance of a striped ribband, somewhatresembling the rude sketch here given,which shows that the plane surface of thediamond, in a space of less than one-thirtiethof an inch, contains many hundred veins orstrata of different reflective and refractivepowers, as if they had been subjected to va-riable pressures, or deposited under the influ-ence of forces of aggregation of variable inten
The American journal of science and arts . s surprised to observe the whole ofits surface covered with parallel lines or veins, some of which re-flected the light more powerfully than others, so as to have theappearance of a striped ribband, somewhatresembling the rude sketch here given,which shows that the plane surface of thediamond, in a space of less than one-thirtiethof an inch, contains many hundred veins orstrata of different reflective and refractivepowers, as if they had been subjected to va-riable pressures, or deposited under the influ-ence of forces of aggregation of variable intensity. If, Sir Davidobserved, the planes of these different strata had been perpen-dicular to the axis of the diamond lens, their difference of refrac-tive power would produce no sensible effect injurious to the per-fection £>f the image ; but if these strata are parallel to that axis,as they are in the lens under consideration, each stratum musthave a different focus, and consequently produce a series of par-tially overlapping British Association for the Advancement of Science. 39 The results of this experiment in restoring the diamond to itsvahie as an optical material, in so far as it enables us to cut it ina proper direction, and select proper specimens, and its connectionwith some delicate researches of Profs. Airy and Maccullagh, onthe superficial action of diamond upon polarized light, possessconsiderable interest, but the fact of a mineral body consisting oflayers of different refractive powers, and consequently differentdegrees of hardness and specific gravity, is remarkable. Therewere several minerals, such as Apophyllite^ Chabasie, and others,in which Sir David said that he had found different degrees ofextraordinary refraction in different parts of the crystal; but thisvariation of property depends upon a secondary law of structure •and he believed that there was no crystal, either natural or artifi-cial, in which the properties of ordinary refraction,
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