Page:The American Cyclopædia (1879) Volume V.djvu/539

CRYSTALLINE LENS CRYSTALLOGRAPHY 535 thon's son-in-law and zealous disciple, was im- prisoned for 12 years. In 1586, on the elector's death, his son Christian I. was induced to favor Calvinism. After his death again the duke Frederick William of Saxe-Weimar suppressed Philippism, even putting Crell to death in 1601. See Heppe's GescMchte des deutschen Protes- tantismm (1852); Giseler's "Church History" (English translation, New York, 1861); and Hagenbach's " History of Doctrines " (English translation, New York, 1861-'2). CRYSTALLINE LENS, a lenticular transparent body, placed between the aqueous and vitreous humors of the eye in vertebrate animals, at about its anterior third ; it is about four lines in diameter and two in thickness in man, and its axis corresponds to the centre of the pupil. The curvature of the lens is in proportion to the density of the medium in which the eye is habifually placed, being very flat in birds of the highest flight, and very convex in aquatic mammals and diving birds ; in fishes it is almost spherical. This most important re- fracting structure of the eye is imbedded in the anterior portion of the vitreous humor, and is enclosed in a membranous capsule, to which it is prevented from adhering by the " liquid of Morgagni." Its structure is com- plicated, but it consists, when fully formed, of fibres arranged side by side, and united into laminae by serrations of their edges; the fibres originate in cells ; the vessels are confined to the capsule, and are derived from the central artery of the retina ; when hardened in spirit, it may be split into three sections, composed of concentric laminae ; it is made up of 58 parts of water and 42 of soluble albumen ; the cen- tral parts are the densest, and this property increases with age. Besides its refractive power, necessary for distinct vision, it is gen- erally believed that a change in its curvatures, by means of the ciliary muscle and the elasticity of its own tissue, is the mechanism by which the eye is adapted to distinct vision at varying distances ; besides the anatomical arrangement of the parts, this view is rendered more prob- able by the development of this muscle in pre- daceous birds which have a great range of vision, and by the loss of this power of adapta- tion when the lens of the human eye is re- moved or displaced in the operation for cataract. For the diseases of the lens and its capsule, and their treatment, see CATARACT. CRYSTALLOGRAPHY, the science of form and structure in the inorganic kingdom of nature. In the organic kingdoms, the animal and ve- getable, each species has a specific form and structure evolved from the germ according to a law of development or growth. In the in- organic kingdom also, which includes all in- organic substances, whether natural or arti- ficial, a specific form and structure belong to each species, and the facts and principles in- volved therein constitute the science of crys- tallography. The forms are called crystals; so that animals, plants, and crystals are the three kinds of structures characterizing spe- cies in nature. As the qualities of crystals depend directly on the forces of the ultimate molecules or particles of matter, crystallogra- phy is one of the fundamental departments of molecular physics, and that particular branch which includes cohesive attraction. Cohesive attraction in solidification is nothing but crys- tallogenic attraction, for all solidification in in- organic nature is crystallization. The solidi- fication of water, making ice, is a turning it into a mass of crystals ; and the word crystal is appropriately derived from the Greek npia- ra/Uof, ice. The solidification of the vapors of the atmosphere fills the air with snow flakes, which are congeries of crystals or crystalline grains. Solid lava, granite, marble, iron, sper- maceti, and indeed all the solid materials of the inorganic globe, are crystalline in grain; so that there is no exaggeration in the statement that the earth has crystal foundations. The elements and their inorganic compounds are, in their perfection, crystals. Carbon crystal- lized is the diamond. Boron is little less bril- liant or hard ; and could we reduce oxygen to the solid state, it would probably (as we may infer from its compounds) have no rival among nature's gems. Alumina is the constituent of the sapphire and ruby, and silica of quartz crys- tals. Magnesia also has its lustrous forms. The metals all crystallize. Silica and alumina com- bined, along with one or more of the alkalies or earths, make a large part of the mineral in- gredients of the globe, its tourmaline, garnet, feldspar, and many other species, all splendent in their finer crystallizations; and limestone, one of the homeliest of all the earth's mate- rials, as we ordinarily see it, occurs in a multi-. tude of brilliant forms, exceeding in variety every other mineral species. The general prin- ciples in the science of crystallography are the following: I. A crystal is bounded by plane surfaces, symmetrically arranged about certain imaginary lines, called axes. II. A crystal has an internal structure which is directly related to the external form, and the axial lines or directions. This internal structure is most obviously exhibited in the property called cleavage. Crystals having this property split or cleave in certain directions, either parallel to one or more of the axial planes, or to diag- onals to them ; and these directions are fixed in each species. In some cases, cleavage may be effected by the fingers, as with mica and gypsum ; in others, by means of a hammer with or without the aid of a knife blade, as in galena, calcite, fluor spar ; in others it is indis- tinguishable, as in quartz and ice. In all spe- cies, whether there be cleavage or not, crys- tals often show a regular internal structure through the arrangement of impurities, or by internal lines, striations, or imperfections ; and, when there has been a partial solution or ero- sion of the crystal, there is often a develop- ment of new lines and planes, indicating that the general symmetry of the exterior belongs