The Doctrine of Evolution. 457 



Darwinism and other Essays.* Their purport is, that in 

 tracing the correlation of motions into the organism through 

 the nervous system, and out again, we are bound to get an 

 account of each step in terms of motion. Unless we can 

 show that every unit of motion that disappears is trans- 

 formed into an exact quantitative equivalent, our theory of 

 correlation breaks down ; but when we have shown this we 

 shall have given a complete account of the whole affair 

 without taking any heed whatever of thought, feeling, or 

 consciousness. In other words, these psychical activities do 

 not enter into the circuit, but stand outside of it, as a seg- 

 ment of a circle may stand outside a portion of an entire 

 circumference with which it is concentric. Motion is never 

 transformed into thought, but only into some other form of 

 measurable (in fact, or, at any rate, in theory measurable) 

 motion that takes place in nerve-threads and ganglia. It is 

 not the thought, but the nerve-action that accompanies the 

 thought, that is really " transformed motion.' 1 '' I say that, if 

 we are going to verify the theory of correlation, it must be 

 done (actually or theoretically) by measurement ; quantita- 

 tive equivalence must be proved at every step ; and hence 

 we must not change our unit of measurement ; from first 

 to last it must be a unit of motion : if we change it for a 

 moment, our theory of correlation that moment collapses. 

 I say, therefore, that the theory of correlation and equiva- 

 lence of forces lends no support whatever to materialism. 

 On the contrary, its manifest implication is that psychical 

 life can not be a mere product of temporary collocations of 

 matter. 



The argument here set forth is my OAvn. When I first 

 used it I had never met with it anywhere in books or con- 

 versation. AVhether it has since been employed by other 

 writers I do not know, for during the past fifteen years I 

 have read very few books on such subjects. At all events, 

 it is an argument for which I am ready to bear the full 

 responsibility. Some doubt has recently been expressed 

 whether Mr. Spencer would admit the force of this argu- 

 ment. It has been urged by Mr. S. H. Wilder, in two able 

 papers published in the New York Daily Tribune, June 13 

 and July 4, 1890, that the use of this argument marks a 

 radical divergence on my part from Mr. Spencer's own posi- 

 tion. 



It is true that in several passages of First Principles 



* See also Excursions of an Evolutionist, 1883, pp. 274-282. 

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