Mr. William Phillips on the OxydofTin. 353 



prism, but have in vain attempted it in a direction perpendicular to 

 its Dlanes. 



In pursuing this subject, it occurred to me that the exposure of 

 the crystals of this substance to the action of heat, might possibly- 

 lead to some further discoveries. Accordingly, some were placed in 

 the centre of a common fire during an hour or two, and being after- 

 wards left to cool I found that a slight touch with a, hammer imme- 

 diately reduced them into small pieces : a research among these 

 afforded very many of the above cited cleavages, which I had pre- 

 viously obtained from crystals that had not been subjected to the 

 action of heat. 



Let fig. 1. PI. 15. represent the cleavages, which are easily obtained 

 parallel with the faces of the prism, and fig. 2 its diagonal cleavages. 

 By a combination of all these in fig. 3, it will be seen that the prism 

 is divisible into right-angled triangular prisms, of which I have 

 numerous instances. 



In pursuing a research among the fractures, I found several qua- 

 drangular prisms with oblique terminal faces, parallel with each 

 other, as represented by fig. 4, and others similar to fig. 5 ; which it 

 will be obvious differ only from each other in these respects, that the 

 edges fg and b c are replaced by the planes a and b, and that the 

 two other edges, a d and e h^ are also replaced by similar planes, all 

 which planes are parallel with one or other of the diagonals of 

 fig. 4. 



I have other fractures described by fig. 7, which are the result of 

 a mechanical division of fig. 4 in the direction of its diagonal a b 

 and c d, and along the edges b c and a d. It follows that fig. 7 is 

 a right-angled triangular prism with oblique terminal faces, which 

 in some of these fragments are perfectly brilliant. 



If also a section of fig. 4 be made in the direction of its other 



Vol. II. 2 y 



