cu.xv.] TRE COMPOSITION OF MIND. 131 



^rind is composed, a simple psychical skoc\ answering to 

 that simple 'physical pulsation which is the ultimate unit of 

 nervous action. By the manifold and diverse compounding 

 of myriads of such primitive psychical shocks, according 

 to the slight structural differences of different nerves, are 

 formed innumerable elementary sensations, which appear 

 to be genei-ically different ; just as aquafortis and laughing- 

 gas, which seem generically different, yet differ really only 

 in the proportions of nitrogen and oxygen which compose 

 them. By a similar differential compounding of these 

 elementary sensations, we get complex sensations of blue- 

 ness and redness, warmth, pressure, sweetness, roughness, 

 and of various kinds of timbre and degrees of pitch. Carry- 

 ing still farther the same process of differentiation and inte- 

 gration, we rise step by step to perceptions of greater and 

 greater complexity, to conscious classifications, and to rea- 

 soning in its various forms, from the crude inferences of the 

 child, barbarian, or boor, to the subtle and indirect combina- 

 tions of the artist and the scientific discoverer. Thus, amid 

 all their endless diversities, we discern, though dimly, a 

 fundamental unity of composition throughout all orders of 

 psychical activity, from the highest to the lowest. 



Near the close of his first edition of the " Origin of 

 Species," Mr. Darwin predicted that the establishment of 

 his theory would eventually place the science of psychology 

 upon a new basis — that of the acquirement of each mental 

 faculty by slow gradations.^ We seem now to have fairly 

 started upon the path which leads to this desired goal. For, 

 while, among the mental operations above analyzed, some 

 are peculiar to the highest human intelligence, there are 

 others which are shared by the highest and the lowest human 



* Mr. Darwin has since recognized that this new basis is already well laid 

 by Mr. Spencer. See Origin of Species, 6th edit., p. 428. Indeed the 

 'Principles of Psychology," upon Avliich the present chapter is almost 

 /utirely founded, was first published in 1855, four years before the "Origin 

 at' Species." 



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