u 



THEORIES OF CRYSTALLOGRAPHY, 



Laws of the 

 ftrufture of 

 ciy'ftals, and 

 theory thence 

 refultirig. 



no other force than that which they exercife on each other, 

 are in equilibrio, thej are in the clofeft poffible union that 

 concomitant circumftances will permit. If the particles were 

 in equilibrio previous to their leaving the flate of reft, fome- 

 thing niuft have obftru6led their approach. Let us fuppofe 

 that fomeihing to be the interpofition of another fubftance, and 

 that fo long as the interpofition remains equilibrium is main,- 

 "taihed. But this can only be the cafe, in as much as the whole 

 of the particles of the interpofed fubftance are in equilibrio 

 with the whole of the particles diflblved and about to leave the 

 ftateof reft, which in the future I ftiall call the proper particles. 

 If by any caufe which a6ls uniformly on the whole furface of 

 the diflblving fluid any of the interpofed particles are fub- 

 tracted, the proper particles muftceafeto be in equilibrio. A 

 ftep toward aggregation will immediately take place, and the 

 equilibrium will be reftored, A further fubtra6lion will pro- 

 duce a further ftep toward aggregation, and a confequent 

 equilibrium; and thefe operations will be repeated fo long as 

 the caufe of fubtradion continues, and the longer its duration 

 the larger will be the refulting cryftalline mafs. If the above 

 mode of reafoning be admitted, it will fuffice to apply the 

 laws of equilibrium to deduce the laws of cryftalH«e forms. 

 The laws of equilibrium to which I allude, are thofe of the 

 equilibrium of fluids, with certain modifications which ftiall 

 hereafter be explained. According to thefe laws, that the 

 preceding conditions may take place in the formation of a 

 cryftal, it will be neceHary that they take place in the forma- 

 tion of each and every part of it, whatever may be the figure 

 or the fmallnefs of thofe parts. They muft alfo take place in 

 thofe laft cryftals which contain the leaft poflible number of 

 particles; and as thefe particles are in equilibrio, and in the 

 greateft poflible ftate of proximity to each other which cir- 

 cumftances will permit, it muft follow, to fulfil all the condi- 

 tions, that thefe particles form a fymmetrical polyedron. This 

 peculiar difpofition of the cryftalline particles conftitutes the 

 modification, to which I alluded, in the laws of the equili- 

 brium of fluids ; it being neceflary in this cafe to lake the num- 

 ber of cryftalline particles into account, which is not the cafe 

 when treating of the particles of a fluid. In a fluid, the par- 

 ticles and their reciprocal diftances are fuppofed infinitely 

 imall J but the cryftalline particles and their diftances to each 



other 



