CRYSTALLOGRAPHY

science of form, structure, and properties of crystals. Nicol a us Steno was the ‘first record (1669) that, although the faces different quartz crystals varied in size shape, the angles (as measured by goniometer, the Contact form being for large crystals) between corresponding faces are constant. This fact corroborated by Bar tholi nus and Huygens, who agreed with R. Hooke's suggestion that crystals were built up spheroids. Cappeler, of Lucerne, published the earliest treatise on c’s (1723), but the science was not properly founded till 1783-84, when Romé de and Hautiy discovered the symmetry of crystals to certain planes, and derived all crystals from six ‘primitive forms.’ C. S. Wei (1809) studied crystal lin e forms from a‘ geometrical standpoint, and introduced a new Sys5of cla ification, Lévy, Naumann, Miller (1839) devised methods of notation which refer the planes of crystals three axes, correspon ding in directo three edges. In 1830 He e proved that 32 types of symmetry are po ible in_ crystals, which are now grouped in 32 correspon ding cla es, belonging to 6 systems. The importance the optical properties of crystals was recognized by Sir D. Brewster 1828. E. von Fedorow showed (1912) that when the crystals of any substance are correctly set up and measured on the theodolite goniometer they furnish an adequate means of identification without further analysis. Numerous discoveries in the allied sciences of chem., physics, and mineralogy have done ae towards furthering the progre of c