398 



Royal Society. 



tion that they belong to the oblique system, and that the angle be- 

 tween the oblique axes differs but little from 90°. 



The forms observed by Sella, considered as belonging to the 

 oblique system, are : — 



£10 0, eOOl, c013, m 2 3, £ 1 1,_ rc 5 4,_p 5 8, ? 2 3, 

 /201, A110, t-2 10, g 1 1 1, a 1 1 2, d 2 1 1, Z2 12. 



Of these, I have since reobserved all, with the exception of «, d, 

 I, and perhaps p, the corresponding reflexion being too faint to 

 enable me to affirm the existence of that face in the crystals I exa- 

 mined. I have also observed the following forms in which the dis- 

 tribution of the faces is in most cases, probably in all, the same as in 

 the prismatic system, or as if the oblique form hkl were always ac- 

 companied by the oblique form hkl: 

 w30 1, wl0 4, v40 3, #30 5, s22 3, £33 2, *22 1. 



On the same supposition regarding the distribution of the faces, 

 the annexed figure represents an octant of the sphere of projection, 

 the poles of some of the faces not wanted for comparison with those 

 of graphitoidal boron being omitted. The principal angles taken 

 or computed from the angles provisionally adopted by Sella, are : — 



ec 



39 14 



ek 



90 



em 



58 31 



km 



90 



ew 



19 28 



kh 



60 



ex 



40 19 



ea 



54 44 



eq 



43 21 



es 



62 4 



eb 



54 44 



eg 



70 32 



ev 



62 4 



et 



76 44 



ef 



70 32 



ez 



79 59 



eu 



76 44 



eh 



90 



Besides the two forms already mentioned, Wbhler and Deville ob- 

 tained boron in extremely thin scales, which were supposed to be a 

 different modification of boron, and was accordingly called graphitoi- 



