The Evolution of Mind. 257 



But within the knowable Mr. Spencer rejects the 

 rnonist doctrine : he holds that the immanent energy 

 is conditioned in two modes; it is conditioned in 

 matter otherwise than in mind. He must, therefore, 

 bring the manifestations thus distinctively conditioned 

 into a unity of relation such that mental activity may 

 be interchanged with physical action. If we look 

 closely at the correlation assumed to exist, it will be 

 seen to be impossible, unless on a Unitarian basis, 

 either that of sheer materialism or thorough -going 

 idealism. 



The use of steam as a driving power furnishes a 

 good example of correlation. Coal generates steam; 

 steam produces motion. The coal is expended in 

 raising the steam, and the steam in causing the 

 motion: the one form of force passes into the other 

 the amount expended being balanced by the work 

 done. The principle of correlation involves (a) the 

 expenditure of force which passes into a new form, 

 (6) equivalence in the amount of the force under both 

 forms. If mental activity be brought within the 

 correlation of physical forces, there must be (a) the 

 passing of physical force into intellectual force, and 

 vice versa ; and (6) the amount of physical force 

 expended must balance the mental force produced. 

 When a nerve-thrill passes into the sensorium, and a 

 cognitive act ensues, has the physical force operating 

 in the molecular motion in the brain passed into the 



cognition and been wholly, or in part, expended in 



K 



