SEGREGATION. 479 



of unlike matters, is also made manifest by the phenomena 

 of refraction: since adjacent and parallel beams of light, 

 falling on, and passing through, unlike substances, are made 

 to diverge. 



§ 164. On the assumption of their nebular origin, stars 

 and planets exemplify that cause of material segregation 

 last assigned — the action of unlike forces on like units. 



In a preceding chapter (§ 150) we saw that if matter 

 ever existed in a diffused form, it could not continue uni- 

 formly distributed, but must break up into masses. It was 

 shown that in the absence of a perfect balance of mutual at- 

 tractions among atoms dispersed through unlimited space, 

 there must arise breaches of continuity throughout the ag- 

 gregate formed by them, and a concentration of it towards 

 centres of dominant attraction. "Where any such breach of 

 continuity occurs, and the atoms that were before adjacent 

 separate from each other; they do so in consequence of a 

 difference in the forces to which they are respectively sub- 

 ject. The atoms on the one side of the breach are exposed 

 to a certain surplus attraction in the direction in which they 

 begin to move; and those on the other to a surplus attrac- 

 tion in the opposite direction. That is, the adjacent groups 

 of like units are exposed to unlike resultant forces; and ac- 

 cordingly separate and integrate. 



The formation and detachment of a nebulous ring, illus- 

 trates the same general principle. To conclude, as Laplace 

 did, that the equatorial portion of a rotating nebulous 

 spheroid, will, during concentration, acquire a centrifugal 

 force sufficient to prevent it from following the rest of the 

 contracting mass, is to conclude that such portions will 

 remain behind as are in common subject to a certain differ- 

 ential force. The line of division between the ring and 

 the spheroid, must be a line inside of which the aggregative 

 force is greater than the force resisting aggregation; and 

 outside of which the force resisting aggregation is greater 



