CUBIC SYSTEM. 11 FIG. 9. FIG. 8. 3-1. If we suppose h to be tlie greatest, and I the least of the three unequal indices hkl, fig- 8, will represent the distribution of thepoles of the form hkl, on the surface of the sphere of projection. Big. 9 exhibits the poles of the forms ob tained by making one of the indices zero, or by making two of them equal. Both figures show the poles of the forms loo, m,nnd 101. 35. The form bound ed cither by all the faces of the form hkl, whichhave an oddnum- ber of postive indices, or by all the faces which have an odd number of negative indices, is said to be hemihedral with inclined faces, and will bo denoted by the sym bol Md, where hkl is the symbol of any one of its faces. The upper and lower halves of the table in (33) contain the symbols of the faces of kIiM, i;hkl respectively. If the surface of the sphcro of projection be divided into eight triangles by zone-circles through every two of the poles of the form 100, tiie poles of xhkl will be found in four alternate triangles, and those of Md, in the remaining four alternate triangles. The form bounded either by all the faces of the form hkl, the indices of which stand in the order hklhk, or by all the faces the indices of which stand in the order Ikhlk, is said to be hemihedral with parallel faces, and will be denoted by the symbol whkl, where hkl is the symbol of any one of its faces. The right and left halves of the table in (33) contain the symbols of the faces of nhkl, irlkh respectively. If the surface of tho sphere of projection bo divided into B G
