358 Mr. William Phillips on the OxydofTin. 



First Modification.^ 



This modification is represented by fig. 19. PI. 16. and consists 

 In a decrease on the four lateral solid angles of the primitive form, 

 by which each is replaced by a plane, perpendicular to the axis 

 passing through those angles. 



Fig. 20. shews this modification in a more advanced state, and 

 has been added not because it has been thus observed, but in order 

 that the combination of the planes of this modification with those 

 of the primitive form, may be the more readily traced in fig. 21 . 

 in which it occurs, though but rarely. In the fine collection of 

 tins, in the possession of Mr. Sowerby, there is a specimen of 



to adopt it as the integrant molecule. Indeed, It may fairly be doubted, whether, 

 considering the present state of mineralogical knowledge, much benefit has accrued from 

 the attempts that have been made to determine that of many other substances. 



* The crystals of this substance, when on the matrix, have so greatly the appearance 

 of being confusedly grouped, that little can be done towards describing them, on 

 account of their splendour and numerous facets, without first detaching them from the 

 matrix, which on account of their brittlcness requires considerable care. The mode best 

 adapted for preserving as well as for observing them, I first noticed in the scientific 

 collection of the Count de Bournon, in which, insulated crystals are placed on wax. 

 For this purpose I have used the common green taper cut into pieces of about an inch 

 in length, and placed the crystal at one end. There are between 4 and 500 crystals of 

 this substance so arranged in my collection, including every one described in the series 

 belonging to this paper, and, being placed in that series according to the method adopted 

 hy the Count de Bournon (that is, according to their modifications) little or nothing 

 need be said upon any of the individual crystals. 



But in order to render the series more perfectly intelligible, I have taken especial care 

 io place the drawing of every crystal throughout the scries in the same point of view, 

 except in a few instances, for the sake of illustration. I am aware that an attention to 

 this circumstance affords material facility to those w ho may desire to become acquainted 

 with the crystallization of the substance, in tracing the modifications through their 

 various combinations: and the same care has been observed, not to introduce in the 

 series of any modification, the figure of a crystal exhibiting the planes of any other 

 modification, that has not preceded it, ' 



