Models to Aid in Visualizing the Optical Properties of Crystals

The study of crystal optics is largely a matter of solid geometry, and demands clear visualization of optical properties in their three-dimensional relations. To aid students in visualizing these relations, numerous models of wood, wire, glass, and plaster have been devised,¹ and have proven to be of definite value. The models described in this paper were designed, in part to supplement, and in part to substitute for standard types already in use. Following the precedent of Wright² and Rogers,³ emphasis is placed on the indicatrix, or index ellipsoid, and its relations to crystallographic directions and to common optical phenomena. Relations heretofore shown only by two-dimensional drawings, by solid opaque models, or by elusive wire “bird cages” are clearly represented in three dimensions by transparent models made of sheet celluloid.