SIMPLE AND COMPOUND EVOLUTION. 299 



centration going on there go on other re-distributions. 

 Contrariwise, where the parts have approached within such 

 small distances that what we call the attraction of cohesion 

 is great, additional actions, unless intense, cease to have 

 much power to cause secondary re-arrangements. The 

 firmly-united parts no longer readily change their relative 

 positions in obedience to small perturbing influences; but 

 each small perturbing influence usually does little or noth- 

 ing more than temporarily modify the insensible molecular 

 motions. 



How may we best express this difference in the most 

 general terms? An aggregate that is widely diffused, or but 

 little integrated, is an aggregate that contains a large quan- 

 tity of motion — actual or potential or both. An aggregate 

 that has become completely integrated or dense, is one that 

 contains comparatively little motion : most of the motion its 

 parts once had has been lost during the integration that has 

 rendered it dense. Hence, other things equal, in propor- 

 tion to the quantity of motion which an aggregate contains 

 will be the quantity of secondary change in the arrangement 

 of its parts that accompanies the primary change in their 

 arrangement. Hence also, other things equal, in proportion 

 to the time during which the internal motion is retained, will 

 be the quantity of this secondary re-distribution that accom- 

 panies the primary re-distribution. It matters not how these 

 conditions are fulfilled. Whether the internal motion con- 

 tinues great because the components are of a kind that will 

 not readily aggregate, or because surrounding conditions 

 prevent them from parting with their motion, or because 

 the loss of their motion is impeded by the size of the aggre- 

 gate they form, or because they directly or indirectly obtain 

 more motion in place of that which they lose; it through- 

 out remains true that much retained internal motion must 

 render secondary re-distribution facile, and that long re- 

 tention of it must make possible an accumulation of such 

 secondary re-distributions. Conversely, the non-fulfilment 



