228 Parallel of a; me de l y Isle's cmd 



terposed substance are its cquilibrio with tht? whole of the 

 particles dissolved and about to leave the state of rest, which 

 in the future I shall call the proper particles* If by any 

 cause which acts uniformly on the whole surface of the dis- 

 solving fluid any of the interposed particles are subtracted, 

 the proper particles must cease to be in cquilibrio. A step 

 toward aggregation will immediately take place, and the 

 equilibrium will be restored. A further subtraction will 

 produce a further step toward aggregation, and a consequent 

 equilibrium; and these operations will be repeated so long 

 as the cause of subtraction continues, and the longer its 

 duration the larger will be the resulting crystalline mass. 

 If the above mode of reasoning be admitted, it will suffice 

 to apply the laws of equilibrium to deduce the laws of crys- 

 talline forms. The laws of equilibrium to which I allude 

 are those of the equilibrium of fluids, with certain modifica- 

 tions which shall hereafter be explained. According; to these 

 laws, that the preceding conditions may take place in ,the 

 formation of a crystal, it will be necessary that they take 

 place in the formation of each and every part of it, what- 

 ever may be the figure or the smallness of those parts. They 

 must also take place in those last crystals which contain the 

 least possible number of particles; and as these particles are 

 in equilibrio, and in the greatest possible state of proximity 

 to each other which circumstances will permit, it must fol- 

 low, to fulfil all the conditions, that these particles form a 

 symmetrica! polyedron. This peculiar disposition of the 

 crystalline particles constitutes the modification, to which I 

 alluded, in the laws of the equilibrium of fluids; it being 

 necessary in this case to take the number of crystalline par- 

 ticles into account, which is not the case when treating of 

 the particles of a fluid. In a fluid, the particles and their 

 reciprocal distances are supposed infinitely small ; but the 

 crystalline particles and their distances to each other must 

 be supposed finite. This material difference will neces- 

 sarily cause a difference between the forms of their ag- 

 gregates. Those formed with the particles of a fluid will 

 be bounded by curved lines : the crystalline aggregates, on 

 the contrary,will be terminated by straight lines; and when 

 these straight lines are not too small, the boundaries will be 

 sensibly rectilinear. 



To ascertain what the power is that holds the particles 

 in the state c; rest, though not in close contact, is not the 

 question ; but the form of the polyedrons which they pro- 

 duce. The closer adhesion of the particles to be obtained by 

 the subtraction of caloric sufficiently demonstrates that the 

 3 particle* 



