x.] MR. DARWIN S CRITICS. 251 



capable of being expressed in terms of one another. 

 Whether we shall ever be able to express consciousness 

 in. foot-pounds, or not, is more than I will venture to 

 say ; but that there is evidence of the existence of some 

 correlation between mechanical motion and conscious 

 ness, is as plain as anything can be. Suppose the poles 

 of an electric battery to be connected by a platinum 

 wire. A certain intensity of the current gives rise in 

 the mind of a bystander to that state of consciousness we 

 call a &quot;dull red light&quot; a little greater intensity to 

 another which we call a &quot; bright red light ; &quot; increase 

 the intensity, and the light becomes white ; and, finally, 

 it; dazzles, and a new state of consciousness arises, which 

 we term pain. Given the same wire and the same 

 nervous apparatus, and the amount of electric force re 

 quired to give rise to these several states of consciousness 

 will be the same, however often the experiment is re 

 peated. And as the electric force, the light-waves, and 

 the nerve-vibrations caused by the impact of the light 

 waves on the retina, are all expressions of the molecular 

 changes which are taking place in the elements of the 

 battery ; so consciousness is, in the same sense, an ex 

 pression of the molecular changes which take place 

 in that nervous matter, which is the organ of con 

 sciousness. 



And, since this, and any number of similar examples 

 that may be required, prove that one form of conscious 

 ness, at any rate, is, in the strictest sense, the expression 

 of molecular change, it really is not worth while to 

 pursue the inquiry, whether a fact so easily established 

 is consistent with any particular system of molecular 

 physics or not. 



Mr. &quot;Wallace, in fact, appears to me to have mixed up 

 two very distinct propositions : the one, the indisputable 

 truth that consciousness is correlated with molecular 



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