14() 0> CRYSl A L LOCK A PHY. 



which makes them attract one part of another particle and repel 

 the other parts. This polarity would e.xpluin the regularity of 

 crystallization ; hot it is itself inexplicable. 



It is remarkable that crystals not only assume regular (i^u; 

 but are always bounded by plane surfaces. It is very rarely in. 

 deed that curve surfaces are observed in these bodies ; and when 

 they are, the crystals always give unequivocal proofs of imperfec- 

 tion. But this constant tendency towards plane surfaces is incon. 

 ceivable, unless the particles of which the crystals are composed 

 are themselves regular figures, and bounded by plane surfaces. 



5. If the figure of crystals depends upon the figure of their in. 

 tvgrant particles, and upon the manner in which they combine, it 

 is reasonable to suppose that the same particles, wlu n at full liber. 

 ty, will always combine in the same way, and consequently that 

 the crystals of every particular body will be always the same. 

 Nothing at first sight can appear farther from the truth than this. 

 The different forms which the crystals of the same body assume are 

 often very numerous, and exceedingly different from each other. 

 Carbonate of lime, for instance, has been observed crystallized in 

 no fewer than forty different forms, fluate of lime in eight differ, 

 c-nt forms, and sulphate of lime in nearly an equal number. 



But this inconsistency is not so great as might at first sight ap- 

 pear. Rome de Lisle has shewn that every body susceptible of 

 crystallization has a particular form which it most frequently as. 

 sumes, or at least to which it most frequently approaches. lierj;. 

 man has demonstrated, that this primitive form, as Hauy has call- 

 ed it, very often lies concealed in those very crystals which ap- 

 pear to deviate farthest from it. And Hauy has demonstrated, 

 that all crystals either have this primitive form, or at least contain 

 it as a nucleus within them ; for it may be extracted out of all of 

 them by a skilful mechanical division. 



These primitive forms must depend upon the figure of the inte- 

 grant particles composing these crystals, and upon the manner in 

 which they combine with each other. Now, by continuing the 

 mechanical division of the crystal, by cut ing off slices parallel to 

 each of its faces, we must at last reduce it to so small a size that 

 it shall contain only a single integrant particle. Consequently 

 this ultimate figure of the crystal must be the figure of the inte- 

 grant particles of which it is composed. The mechanical division, 

 , cannot be continued so far; but it may be continued till it 



