WRITINGS OF JAMES SMITHSON. 39 



The importance of a knowledge of the true quantity in 

 which matters combine, is too evident to require to be dwelt 

 upon ; but this importance will be greatly augmented, if it 

 should prove that this quantity is, as has been suggested, 

 expressive of the forces with which they attract each other. 

 It is perhaps in the form of matters that we shall find the 

 cause of the proportions in which they unite, and a proof, 

 a priori, of the system here maintained. 



I have examined some of the grey ores of copper in 

 tetraedral crystals ; but the notes of my experiments are in 

 England. I can, however, say, that they do contain anti- 

 mony, and that they do not contain iron in any material 

 quantity. With respect to the proportions of the constitu- 

 ent parts, I cannot now speak with any certainty ; but, I 

 think, that at least some species of fahlertz contain a smaller 

 portion of sulphuret of antimony, than the fahlertz does 

 which exists as an element in the foregoing compound one. 



Of the Form of this Substance. 



Of the seventeen figures which have been given, as of the 

 crystals of this compound sulphuret, in Part II. of the 

 volume of the Transactions for 1804, great part are ac- 

 knowledged to have no existence, nor are indeed any of 

 them consistent with nature. 



This substance seems to have yet offered but one form, 

 and which is represented in the annexed Plate under its 

 two principal appearances ; that is, having the primitive 

 faces, the predominant ones of the prism ; and having the 

 secondary ones such, and which will be fully sufficient to 

 make it known. In the first infancy of the study of crys- 

 tals, it might be necessary to attend to every, the most 

 trifling, variation of them, to trace each of their changes, 

 step by step, to, as it were, spell the subject ; but in the 

 state to which the science has now attained, to continue to 

 do so would be not only superfluous, but most truly puerile. 



