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 . rawing, in the latter the vertical axis ofthe crystal is in or parallel to the paper, while the crystal is- rotatedi8° 2& to the right and the eye of the observer is supposed to be9° 28 above the top of the crystal. Drawings of crystals are usu-ally clinographic. This method gives solidity and an apparentlytrue perspective. There are also orthogonal projections of crystalsin which there is a plan of the crystal on a horizontal plane, an
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 . rawing, in the latter the vertical axis ofthe crystal is in or parallel to the paper, while the crystal is- rotatedi8° 2& to the right and the eye of the observer is supposed to be9° 28 above the top of the crystal. Drawings of crystals are usu-ally clinographic. This method gives solidity and an apparentlytrue perspective. There are also orthogonal projections of crystalsin which there is a plan of the crystal on a horizontal plane, andan elevation on a vertical plane. Preliminary examination of a crystal may determine its sys-tem, and a free-hand drawing enables the observer to determine thegeneral assemblage of forms, from which a principal one is simple form is completely drawn, a hard pencil being used;in introducing the faces of the other forms on the crystal care mustbe taken to **cut off proportional lengths on all homologous of tetragonal, hexagonal, orthorhombic or isometric crystalscan be readily made, for the faces vertical to the plane (hori-. ^ •=
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectmineral, bookyear1912
