354 Mr. William Phillips on the Oi<yd of Tin. 



diagonal, shewn by the dotted lines e f and g h, and along the 

 edgesy^ and e h^ it will be divided into four parts, one of which 

 will be represented by fig. 8, which is a right-angled triangular 

 prism with inclined terminal faces : several of these are in my 

 possession. 



The fractures represented by figs. 5, 7, 8, prove the mechanical 

 division of the crystals of this substance, in the direction of both 

 diagonals ; and what has before been said of that in a direction 

 parallel with the faces of the prism, would suffice without further 

 proof. If however evidence were wanting, the cleavage described 

 by fig. 6, decides its practicability beyond a doubt. Having placed 

 in the fire a made represented by the dotted lines of that figure, 

 and of about the same size, I afterwards obtained from it a nucleus 

 similar to the fig. a b c d^ represented within it, and of about the 

 same size, with faces well defined and very brilliant ; it is now in 

 my collection. This nucleus, it will be seen, is of the same form 

 as that of the made described by fig. 208, Pi. 25, and resulted 

 from a cleavage of fig. 6, (which is of the same form as fig. 209) 

 in a direction parallel with each of its six larger faces ; and, as 

 hereafter will be shewn in describing the formation of those macles, 

 consequently parallel with the faces of the prism. 



Among the fragments obtained from crystals that had been placed 

 in the fire, I found some quadrangular prisms having one terminal 

 face similar to that of the upper one of fig. 4, but with indications 

 of the lower terminal face in the opposed direction as represented 

 by fig. 9. 



On applying the goniometer to the face P and along the edge h c 

 of fig. 9, I was somewhat surprized at finding that there is no per- 

 ceptible difference between their incidence on each other and that 

 of the plane P, and along the edge ^ r of a crystal similar to fig. 1 1 j 



