A determination of the constants of elliptic polarization of light reflected from a fresh cleavage surface of antimonite enabled Professor P. Drude to calculate two of the indices of refraction of this substance as 5.17 and 4.49 respectively. Instead, however, of the symmetry-axes of the crystal, regarded as belonging to the orthorhombic system, coinciding with the principal vibration directions in the plane (010), he found that the latter were inclined to the former lines at angles which varied in different observations between 2.6° and 15.4°. These observations, which indicate that the symmetry of antimonite is of the oblique or anorthie type, stand in opposition to those of Professor O. Mügge, who found that exceedingly thin flakes of antimonite placed between crossed nicols in direct sunlight transmitted sufficient light of a deep red colour to enable him to determine the extinction as straight.