^ CUBIC SYSTEM. twenty-four triangles by zone-circles passing through every two of the poles of the form m, the poles of nhkl will be found in twelve alternate triangles, and the poles of wlJch in the remaining twelve alternate triangles. •nrifU ?i Um ^ er of bolohedral forms may occur in combination p C °,, er ’ ai ? "/^h an y hcmihedral forms with inclined hedrnl for ^ T f ° rm8 with P arallel fa « e8 - Hemi- combtlZ 8 ^?^ 6 ? f ? C / S baVe 11 been observed in ombination with hemihedral forms with parallel faces. 38 To find the position of the pole of any face. pole of Ml’ °J e rl t P ° leS ° f i 00 ’ ° 10 ’ ° 01 ’ and lefc p be the P 01 BC > ca, ab are quadrants. cospa = cospb = cosPC = PIG. 10. + k* + 1‘) h >/(A a + /c 2 + V) I V(*’ +~/fc s + 1‘) tanPAB = I tanPBC = * tanPCA = \. 39 To find the distance between the poles of any two faces. Let p be the pole of hkl, q the pole of pqr. Then COSPQ = hp + icq -|- l r \/{h? + k 1 + V) ^ ^ • respect to zorm °'^ ^ are 8 y m metrically arranged with 7!’,*™ « f “» poles xif the The poles of Ml are a ^ r° °f, e P (des of the form ill. the zone-circles thromd/w™ 6 rlca % arranged with respect to ill; and the poles of H/* 7 ® l )oles of the form respect to zone-circles throne^ 6 s f m ™ etricall y arranged with form loo. every two of the poles of the faces,derived fTOm^e^am^holoh^cialf^ ° F of the form loo, the poles of JIV 1 * 0 two 0 PP 08lte P olcs poles of Ml, and thiols ofIT™ the I )kcc8 J tho poles of Mh. But a combination of 2End° ^ pkCCS °l n° different from a combination nf n, a l u Lw r 18 e88 entmlly compination of Ml an d mr ; and acombina-
