EXTERNAL FACTORS. 419 



upon things. Doubling a creature s activity, quadruples the 

 area that comes within the range of its excursions : thus 

 augmenting in number and heterogeneity, the external 

 agencies which act on it during any given interval. 



By compounding the actions of these several orders of 

 factors, there is produced a geometric progression of changes, 

 increasing with immense rapidity. And there goes on on 

 equally rapid increase in the frequency with which the com 

 binations of the actions are altered, Knd the intvicaciep of 

 their co-operations enhanced. 



