TrtECyRTES OF CRYSTA'LXOGRAFMV, ^l 



" But what we confider as the mod important part of that Laws ^ftlie 

 philofopher's labours, is the method which they point out ofcryftals, and 

 difcovering the figure of the integrant particles of cryftals ;theory thence 

 becaufe it may pave the way for calculating the affinities oi^^ ii"in&» 

 bodies, which is certainly by far the raoft important part of 

 chemiflry. This part of the fubje6t, therefore, ddferves to 

 be inveftigated with the greateft care." 



But I return to the point whence this digreffion carried me, 

 to the vacuities left between the integrant particles in the con- 

 ftru6tion of a primitive form. The Abb^ confiders them as 

 filled either by the water of cryflallization or by fome oth^r 

 iubftance. It is not an admiffible fuppotidon that this other 

 fubftance is compofed of the fame elements as the integrant 

 particles, but in different proportions? At leaft, fuch is the 

 conclufion I fliould be tempted to draw after reading Berthol- 

 Jet's excellent Refearches on Affinities. 



I fliall now proceed to the laws of formation in fecondary 

 cryftals. It is eafy to deduce them from thefe two fa6ts : viz. 

 1(1, That the tides of the fecondary cryflals are planes ; 2dly, 

 That they divide by fmooth fe6tions parallel to the fides of 

 their primitive form. 



Let us take a rhomboid of carbonate of lime for example. 

 If on one of the (ides of the rhomboid I wilbed to raife a 

 pyramid, I fliould lay laminae of rhomboidal particles upon 

 each otlier.^ Thefe laminas would decreafe in furface until 

 the laft is reduced to a tingle rhomboid. Thus the fecond. 

 lamina contains fewer particles than the firfl, the third fewer 

 than the fecond, and fo on. As the faces of thefe pyramids 

 are always to be planes, the fucceffive decrements of the la-* 

 minae muft be eqtial ; that is to fay, the fecond lamina is lefs 

 by one range in every dire6tion than the firft, and the third 

 than the fecond, &c. If the decrement is more rapid ; that 

 is to fay, if two or three ranges are fubtrafted in the fecond 

 lamina, the fame number will be fubtra61ed from the third, 

 -and fo on fucceffively till the pyramid is completed. As the 

 fe6^ions are to be fmooth, the joints muft form one continued 

 plane ; therefore the ranges and even the particles at the 

 joints muft not encroach on each other: hence it follows Mai 

 the number of ranges fuccejjlveli/ fubtra6ied from each lamina can 

 "never he incotnmenfurahle ; that is to fay, the decrement, naay 

 'bel,2, 3, 4, &:c.; but never <y/ 2, v^3, &c. 

 ';. Vol. IX.— October, 1804. G Tijefe 



