SIMPLE AND COMPOUND EVOLUTION. 307 



ous as quite to subordinate the primary motion. Sup- 



pose that presently, the loss of molecular motion has reached 

 that point at which the gaseous state can no longer be 

 maintained, and condensation follows. Under their more 

 closely-united form, the parts of the aggregate display, 

 to a considerable degree, the same phenomena as before. 

 The molecular motion and accompanying molecular mobil- 

 ity implied by the liquid state, permit easy re-arrangement ; 

 and hence, along with further contraction of volume, con- 

 sequent on further loss of motion, there go on rapid and 

 marked changes in the relative positions of parts local 

 streams produced by slight disturbing forces. But 



now, assuming the substance to be formed of molecules that 

 have not those peculiarities leading to the sudden inte- 

 gration which we call crystallization, what happens as the 

 molecular motion further decreases? The liquid thickens 

 its parts cease to be relatively moveable among one an- 

 other with ease; and the transpositions caused by feeble 

 incident forces become comparatively slow. Little by little 

 the currents are stopped, but the mass still continues modi- 

 fiable by stronger incident forces. Gravitation makes it 

 bend or spread out when not supported on all sides; and it 

 may easily be indented. As it cools, however, it continues 

 to grow stiffer as we say less capable of having its parts 

 changed in their relative positions. And eventually, further 

 loss of heat rendering it quite hard, its parts are no longer 

 appreciably re-arrangeable by any save violent actions. 



Among inorganic aggregates, then, secondary re-dis- 

 tributions accompany the primary re-distribution, through- 

 out the whole process of concentration, where this is gradual. 

 During the gaseous and liquid stages, the secondary re-dis- 

 tributions, rapid and extensive as they are, leave no traces 

 the molecular mobility being such as to negative the fixed 

 arrangements of parts we call structure. On approaching 

 solidity we arrive at a condition called plastic, in which re- 

 distributions can still be made, though much less easily; 



