Mr. J. F. Daniell on Crystallization. 41 



It would be easy to show how all the regular solids of the 

 octohedral series, and their modifications, might be produced by 

 either of these principles of arrangement ; but enough has 

 been premised to introduce the additional argument in favour 

 of the spheroidical hypothesis of crystallization, which may, I 

 think, be unexpectedly derived from the experiments of Pro- 

 fessor Mitscherlich. 



We have hitherto considered the arrangement of our atoms 

 as due solely to their mutual powers of attraction let us now 

 contemplate it as the result of a balance of the attractive 

 power of the atoms, and of the repulsive power of an elastic 

 atmosphere, with which we may conceive each to be sur- 

 rounded, and which will represent the repulsive power of heat. 

 The atoms we suppose attractive of each other and of the par- 

 ticles of the hypothetical atmosphere, but the latter highly 

 repulsive of each other. 



Upon these postulates, each spherical atom would 

 be surrounded by a stratum of equal depth in all its 

 parts, uniformly distributed over its surface ; which, 

 preventing the actual contact of the particles, would 

 nevertheless allow them to arrange themselves according to the 

 laws of the predominant attraction. 



We may suppose the figure a to represent a section of the 

 tetrahedral arrangement of spheres in simple contact ; and the 

 figure b of the same spheres with their atmospheres ; an 



arrangement essentially the same with regard to structure and 

 external figure. 



Any addition or diminution of the repulsive aura would 

 cause the atoms to recede from or approach towards each 

 other equally ; and if we were to heat a solid so constructed, 

 it would expand equally in all directions. 



But what would be the case with the structure of oblate 

 spheroids, instead of spheres ? 



In the first place, as the force of their attraction must, from 



