Every student of crystals is aware how frequently they fall short of the ideal perfection which theory ascribes to them. With regard to the development of the simple forms, the irregularities are most prominent on the crystals which are subject to certain laws of symmetry. In consequence of the differences of size presented on the same crystal by planes belonging to the same form, the most manifold distortions ensue, resulting at one time in the imitation of forms of a lower degree of symmetry, at another in the complete absence of symmetry. Moreover, as long as the faces constituting the distorted form remain the same, i.e. as long as the cause of the distortion is without influence on the development of the combination, so long will the angles of inclination of the circumscribing elements of the individual remain the same, and thus the degree of symmetry can be determined by measurement of the crystal notwithstanding the distortion.