SIMPLE AND COMPOUND EVOLUTION. 307 



ons 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 apj^roaching 

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

 distributions can still be made, though much less easily; 



