Crystallography
the science describes or delineates the form which describes or delineates the form of crystals. In A. D. 1672, Romé de Lisle published his "Essay on Crystallogon Crystallog raphy," but the honor of being regarded as the founder of the science is given to the Abbé René-Just Haüy. He was born at St. Just, in what is now called the department of Oise, and, among other works, published his "Essay on the his "E "Essay on the Structure of Crystals," in 1784, as also his "Treatise on Mineralogy" and his "Treatise on Crystallography," both in CTESIPHON 1822-the year of his death. His view was that all the varieties of crystals which a particular mineral may assume are derivable from one simple form, which is the type of the mineral. That Essentially the same form he attempted to ascertain in each individual case. Essentially the same to ascertain in each individual case. view is still held. Imaginary lines may be supposed to be drawn through a simple crystal longitudinally from end to end, transversely from side to side, or in either of those ways, or obliquely from angle to angle, around which imaginary lines all the particles of matter composing the crystal may be supposed to arrange themselves. Such imaginary lines are called the axes of the crystal. If skillfully chosen they become somewhat more than imaginary lines, for they may coincide with the optical axes of the the the optical axes of the crystal if it possess double refraction.
According to the number, relative length, position, and inclination to each other of these lines depends the outward form of the crystal.
Dana enumerates the following "systems of crystallization" : (1) Having the axes equal-the Isometric system. (2) Having only the lateral axes equal - the Tetragonal and Hexagonal systems. (3) Having the axes unequal - the orthorhombic, monoclinic, and triclinic systems. See