the Able Haiufs Theories of Crystallography. £39 



particles are not in close contact with each other, and the 

 .constancy of the crystalline forms equally proves that they 

 are in equilibrio. We will now proceed to the construc- 

 tion of a crystal with these crystalline particles. That the 

 constancy of the form in the large crystal be preserved, the 

 particles must be in equilibrio. That the equilibrium be 

 preserved, the forces that solicit the particles to motion must 

 mutually destroy each other. That the mutual destruction 

 of these forces be effected, those forces after having been 

 .decomposed into other relatively parallel to three axes perr 

 pendicular to each other, and having a common point of in- 

 tersection, must each meet in its direction another force 

 equal and diametrically opposed to it. This will be obtained 

 if the similar particles are arranged on straight lines parallel 

 two and two at equal opposite distances from the common 

 centre, and bisected by lines passing through that centre; 

 but if the particles are thus arranged they must produce 

 symmetrical solids bounded by planes; and they are thus 

 arranged : for if a foreign force, an excess of caloric for 

 example, does not impede the free arrangement of the par- 

 ticles in the formation of the crystal, their exterior dispo- 

 sition will follow as much as possible their interior arrange- 

 ment ; but their interior arrangement must be on straight 

 lines, or the crystal would cease-to be homogeneous; their 

 exterior disposition will therefore be on straight lines. 



As the circumstances giving rise to the approach of the 

 particles may be in the highest degree variable, it must fol- 

 low that the forms produced may be diversified in the ex- 

 treme. Such, sir, is the answer I should submit for the 

 solution of the question proposed. 



When speaking of the approach of the proper particles, 

 I said that it might be occasioned by the subtraction of 

 certain interposed particles which obstructed the approach 

 of the proper particles. The former are generally water, 

 caloric, or any fluid elastic or not. Their exit may perhaps 

 make place for others, such as light, electricity, &c &c. 

 But the essential point is, that whatever these particles may 

 be, they are in perfect equilibrio with the proper particles, 

 otherwise they would become perturbing forces. Hence 

 it follows, that not only the integrant particles of the crys- 

 tal, but all those that are mixed with them, the chemical or 

 component particles, and even the vacuities, must follow 

 the same laws. It also follows, that if each species of par- 

 ticle (even the chemical) that enters into the formation of 

 the crystal be separately considered, each species will have 

 its distinct symmetrical and polyedral form. The forms 



Vol. 19. No. 75. August 180-1.' R will 



