410 THE INTERPRETATION OF EVOLUTION". 



ence of force, the re-distribution of matter and motion neces- 

 sarily proceeds in such way as to produce them; and by 

 doing this we shall unite them as co-relative aspects of one 

 law, at the same time that Ave unite this law with the fore- 

 going simpler laws. 



§ 148. Before proceeding it will be well to set down 

 some principles that must be borne in mind. In interpreting 

 Evolution we shall have to consider, under their special 

 forms, the various resolutions of force that 4 accompany the 

 re-distribution of matter and motion. Let us glance at such 

 resolutions under their most general forms. 



Any incident force is primarily divisible into its effective 

 and non-effective portions. In mechanical impact, the en- 

 tire momentum of a striking body is never communicated to 

 the body struck: even under those most favourable condi- 

 tions in which the striking body loses all its sensible motion, 

 there still remains with it some of the original momentum, 

 under the shape of that insensible motion produced among 

 its particles by the collision. Of the light or heat falling on 

 any mass, a part, more or less considerable, is reflected ; and 

 only the remaining part works molecular changes in the 

 mass. Xext it is to be noted that the effective 



force is itself divisible into the temporarily effective and the 

 permanently effective. The units of an aggregate acted on, 

 may undergo those rhythmical changes of relative position 

 which constitute increased vibration, as well as other 

 changes of relative position which are not from instant to 

 instant neutralized by opposite ones. Of these, the first, 

 disappearing in the shape of radiating undulations, leave the 

 molecular arrangement as it originally was; while the sec- 

 ond conduce to that re-arrangement characterizing com- 

 pound Evolution. Yet a further distinction has 

 to be made. The permanently effective force works out 

 changes of relative position of two kinds — the insensible 

 and the sensible. The insensible transpositions among the 





