258 Mr. William Phillips on the 



other way (M on the opposed plane) 62°. 56'. The Count de 

 Bournon however considers the primitive crystal to be a rectangular 

 tetrahedral prism with square bases. This determination arose on 

 •his part from having cleaved in directions parallel with the planes 

 of that solid, some crystals in the form of square laminae, which 

 are often extremely thin, and which always yielded in those di- 

 rections. These crystals, he adds, are found in Derbyshite, in the 

 Bannat, and in Siberia.* 



From an amorphous specimen of this substance I succeeded in 

 extracting a solid in the form of an octohedron almost entire, and 

 having more or less of every plane brilliant enough for the use of 

 the reflecting goniometer. The results of measurements taken in 

 the same directions as those given by Haiiy were, for the first 

 71°. 40', being 1°. 10' more ; and for the second, 62°. 42', being 

 14' less ; and not only did this fragment yield each of these mea- 

 surements twice, but also the complementary numbers of 108°. 20' 

 (P on P) and 117° 18'. (M on M), each also twice. Several 

 other fragments gave perfectly coinciding results. 



This substance may be split with about equal ease by the assist- 

 ance of a sharp knife, whether it be held in the hand or placed on 

 a table ; provided the blade of the knife be carefully placed in the 

 direction of the laminae, and the back gently struck by a light 



hedron, its substractive crystal an obtuse rhomboide, and its integrant molecule an irre- 

 gular tetrahedron. I obtained solids not only in these forms, but also others in the form 

 of an octohedron of 90° over the summit, and of a plane of one pyramid on the adjacent 

 plane of the other, and of 120° of one plane of either pyramid, on the adjacent plane of 

 the same pyramid ; I procured also others in the form of an acute rhomboid of 60° and 

 120°. These measurements were obtained by means of the reflecting goniometer, which 

 also gave those of the obtuse rhomboid 60° and 120°, which by Haiiy, are said to be 

 70°, 31'. 44" and 109°. 28'. 16". Hence blende may be split into five different solids. 



* Catalogue, p. 339. 



