On Crystallography. 345 



not result a picture too much overcharged. Our method 

 being founded on analysis, it is only as it were bv accident 

 that certain divisions suit an assortn)ent of characters which 

 fiiost frequently vary in a resjx!ct quite dift'erent from that 

 to which the combination of the component principles i$ 

 subjected. After all, if we examine the sy^^tcms in which 

 arbitrary terms most prevail, those in which the characters 

 themselves have led the way for the distribution of bodies 

 instead of following it, we shall perceive thiU it will oftea 

 "happen that general divisions are therein clearly circum- 

 scribed. Alntost continually we find substances eirtergmg 

 from the limits within which they were supposed to have 

 been confined. The important pouU is, that the species 

 are well determined ; because, as we have remarked, the 

 number not being considerable, it is much easier to study 

 the system, and to render it always sufficiently present to 

 our minds, to apply it easily as occasion may require, par- 

 ticularly when on the one hand the progress is traced ac- 

 cording to fixed principles, which second the efforts of the 

 memory bv connecting it with the understanding, and 

 when on the other hand the methods which it emplovs for 

 /characterizing the bodies belong lo interesting observations 

 or experiments, which leave upon the mind durable traces 

 of what has once spoken as it were to the eyes. 



We hav-e collected under one and the same point of view 

 the principal characters which may serve for the description 

 of a mineral, and we have formed ft tabic of them, v^hich 

 will be foimd prefixed to the plates. We have arranged 

 this table according to the methodical order oi the different 

 branches of knowledge to which it refers; this order hav- 

 ing appeared more favourable for assisting us in seizinc; the 

 whole at a glance, and to render it present to the me- 

 piory. 



VVe shall here subjoin a series of annotations, intended 

 to give a more developed idea of certain characters, or 

 details relative to the method of verifynig those which, in 

 order to become evident, require experiments. 



These annotations will be followed by several distinct 

 tables, which wilj present successively the indicarion of the 

 specific gravities of minerals reduced to their limits, that 

 of their hardness, the enumeration ot the substaiices which 

 possess double refraction, of those which are electrical by 

 beat, of those which have for their primitive form a rhom- 

 hoi'd, an octahedron, or a solid of another kind. &c. These 

 various tables will serve as a kind of supplement to the 

 ?y$iemj pa|-tic«larly with ;espect to the second class, 



uhich 



