3 8 THE POPULAR SCIENCE MONTHLY. 



units of like kinds tend to gather together, and the units of unlike 

 kinds to separate, everywhere cooperates in aiding Evolution. Yet a 

 further universal law is recognized and developed the law of equili- 

 bration. The question is asked, " Can these changes which constitute 

 Evolution continue without limit ? " and the answer given is that they 

 cannot ; but that they universally tend in each aggregate toward a 

 final state of quiescence, in which all the forces at work have reached 

 a state of balance. Like the other universal processes, that of equili- 

 bration is traced out in all divisions of phenomena. But the most 

 important development given to the doctrine of Evolution in this vol- 

 ume was its affiliation upon the ultimate principle underlying all sci- 

 ence the persistence of force. It was shown that from this ultimate 

 law there result certain universal derivative laws, which are dealt 

 with in chapters on " The Correlation and Equivalence of Forces," 

 " The Direction of Motion," and " The Rhythm of Motion," and it 

 was demonstrated that these derivative laws hold throughout all 

 changes from the astronomical to the psychical and social. It is then 

 shown that " the Instability of the Homogeneous," " The Multiplica- 

 tion of Effects," " Segregation " and " Equilibration," are also dedu- 

 cible from this ultimate principle of the persistence of force. So that 

 Evolution, having been first established inductively as universal, is 

 further shown to be universal by establishing it deductively as a re- 

 sult of the deepest of all knowable truths. 



The first edition of " First Principles " was published, but another 

 important step in elucidating the philosophy of Evolution required to 

 be taken. In dealing with the classification of the sciences, from the 

 point of view to which his philosophy has brought him, Mr. Spencer 

 had occasion to seek for that aspect of all physical phenomena which 

 forms the most general division of physical science. He found that 

 what he sought must be some general fact respecting the redistribu- 

 tion of matter and motion. The law was soon arrived at that inte- 

 gration of matter results from decrease of the contained motion, while 

 disintegration of matter results from increase of the contained motion. 

 It is at once manifest that the law thus reached was deeper than the 

 principle of Evolution, for it is conformed to by mineral bodies which 

 do not exhibit the phenomena of Evolution as Mr. Spencer had inter- 

 preted them. In short, it became clear that a law had been reached 

 holding of all material things whatever, whether they are those which 

 do, or those which do not, increase in heterogeneity. It was now first 

 possible to judge of the relative value and importance of the several 

 factors of the evolutionary process. In Von Baer's conception of or- 

 ganic development, it is made to consist essentially and solely in the 

 change of increasing heterogeneity in the evolving body. But Mr. 

 Spencer had shown that Evolution is a double process a tendency to 

 unity as well as to diversity, an integration as well as a differentia- 

 tion. It was now found that the process of integration, as it applies 



