1866.] Prof. W. H. Miller on Graphitoidal Silicon and Boron. 13 



nexed 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 : — 



€ C 



o 



39 



14 



eJc 



90 



em 



58 



31 



k m 



90 



e w 



19 



28 



kh 



60 



ex 



40 



19 



e a 



54 44 



en 



43 



21 



es 



62 4 



eh 



54 



44 



eg 



70 32 



e V 



C2 



4 



et 



76 44 



ef 



70 



32 



ez 



79 59 



e u 



76 



44 



eh 



90 



Besides the two forms already mentioned, Wohler and Deville obtained 

 boron in extremely thin scales, which were supposed to be a different modi- 

 fication of boron, and was accordingly called graphitoidal. Sella, however, 

 relying apparently upon the evidence afforded by the lustre and colour of 

 the scales, for he was unable to obtain any measurements, expresses his 

 conviction that they are not different from pure boron. Some scales of this 

 substance, for which, as well as a supply of crystals of pure boron, I am in- 

 debted to Dr. Matthiessen, have faces on their edges, but so narrow that 

 the reflected image of the bright signal is diffracted into a line of consider- 

 able length, and therefore difficult to bisect. For this reason it is not pos- 

 sible to determine the positions of the faces with accuracy. 



One of them, about 2 millims. wide and 0*014 millira. thick, of the 

 shape of half a hexagon divided by a line at right angles to two opposite 

 sides, exhibited faces agreeing in position very fairly, considering the un- 

 avoidable errors of observation, with two of the faces ky two of the faces p, 

 c, m, three of the faces 5, two of the faces Xy qy three of the faces h, and 

 four of the faces a. Another, smaller and thinner, of the shape of a 

 hexagon, had faces coinciding with two of the faces ky two of the faces e, c, 

 m,f, V, and four of the faces h. The agreement in position of so many of 

 the faces with those of pure boron appears to leave but little doubt of the 

 identity of the forms of the two substances. 



