EQUILIBRATION. 503 



ances to change in that direction : leaving behind only those 

 movements which compensate each other, and so form a 

 moving equilibrium. Kespecting the structural 



state simultaneously reached, it must obviously be one pre- 

 senting an arrangement of forces that counterbalance all 

 the forces to which the aggregate is subject. So long as 

 there remains a residual force in any direction — be it excess 

 of a force exercised by the aggregate on its environment, or 

 of a force exercised by its environment on the aggregate, 

 equilibrium does not exist ; and therefore the re-distribution 

 of matter must continue. Whence it follows that the limit 

 of heterogeneity towards which every aggregate progresses, 

 is the formation of as many specializations and combina- 

 tions of parts, as there are specialized and combined forces 

 to be met. 



§ 171. Those successively changed forms which, if the 

 nebular hypothesis be granted, must have arisen during 

 the evolution of the Solar System, were so many transitional 

 kinds of moving equilibrium ; severally giving place to more 

 permanent kinds on the way towards complete equilibration. 

 Thus the assumption of an oblate spheroidal figure by con- 

 densing nebulous matter, was the assumption of a temporary 

 and partial moving equilibrium among the component parts 

 — a moving equilibrium that must have slowly grown 

 more settled, as local conflicting movements were dis- 

 sipated. In the formation and detachment of the 

 nebulous rings, which, according to this hypothesis, from 

 time to time took place, we have instances of progressive 

 equilibration ending in the establishment of a complete mov- 

 ing equilibrium. For the genesis of each such ring, implies 

 a perfect balancing of that aggregative force which the 

 whole spheroid exercises on its equatorial portion, by that 

 centrifugal force which the equatorial portion has acquired 

 during previous concentration: so long as these two forces 

 are not equal, the equatorial portion follows the contracting 



