361^ Mr. Whelpley on the Idea of an Atom. 



diminution of these nuclei, the ' cooHng' of the two atoms by 

 radiation will bring them nearer and nearer, their slight excess 

 of attraction gradually overcoming their repulsion. Bat if they 

 be such gases as oxygen and nitrogen, and therefore not con- 

 densable by the cold of space, this diminution will cease before 

 they can become liquid. 



The cohesion of liquids gives minute drops of them a spherical 

 shape, showing that their attractions are equal in all directions, 

 in the manner of gravitation : nor should this attraction be any 

 other than the mutual gravity o{ single nuclei, grown more pow- 

 erful by their near approach. (The sizes of liquid drops will 

 therefore measure the intensity of the attractions of their single 

 nuclei, (i. e. will measure the weights of the atoms,) supposing 

 they are all of equal size.) 



But when two gaseous nuclei are cooled in contact, their re- 

 pellent spheres do not actually interpenetrate, so that one en- 

 croaches upon the other ; for, when a gas is condensed, bodies 

 in ■contact with it become heated, (i. e. expanded,) showing that 

 the gaseous nuclei have contracted, and that the solid surface in 

 contact with them expanded proportionately, to sustain the equi- 

 librium of temperature. 



The middle n and p' continue, therefore, to coincide, as long 

 as the nuclei may be in contact, through all changes of tempe- 

 rature. 



Since, then, the attraction of liquid atoms differs in no respect 

 from gravity, there remains only one other species of attraction 

 to be considered, namely, the crystalline, giving rise to solidity. 



Crystalline attractions are stronger in certain lines and planes, 

 an inorganic solid being always more fragile in some directions 

 than in others. These directions are indicated by " planes of 

 cleavage," which form certain angles with each other; and these 

 angles of fracture are invariable, in crystals of the same substance, 

 at the same temperature. 



To account for crystallization, (i.e. solidity,) let it be suppo- 

 sed, that there are but two modes of aggregation, one, that of 

 liquids, and of gravitant atoms in general, the other that o£ solids. 

 Since, in any atom, the two forces, into which C has resolved 

 itself, are related to each other as positive and negative, they 

 tend always to an equilibrium, or equal diffusion, so that the 

 same degree of each shall be potentially present in any part of 



