xiv.] ON DESCARTES' "DISCOURSE! 1 33 ( .> 



Let mo try to explain what I mean. I hold, with the 

 Materialist, that the human body, like all living bodies, 

 is a machine, all the operations of wliieli will, sooner or 

 later, be explained on physical principles. I believe that 

 we shall, sooner or later, arrive at a mechanical equivalent 

 of consciousness, just as we have arrived at a mechanical 

 equivalent of heat. If a pound weight falling through a 

 distance of a foot gives rise to a definite amount of heat, 

 which may properly be said to be its equivalent ; the same 

 pound weight falling through a foot on a man's hand gives 

 rise to a definite amount of feeling, which might with equal 

 propriety be said to be its equivalent in consciousness. 1 

 And as we already know that there is a certain parity 

 between the intensity of a pain and the strength of one's 

 desire to get rid of that pain ; and secondly, that there 

 is a certain, correspondence between the intensity of the 

 heat, or mechanical violence, which gives rise to the pain, 

 and the pain itself; the possibility of the establishment 

 of a correlation between mechanical force and volition 

 becomes apparent. And the same conclusion is sug- 

 gested by the fact that, within certain limits, the inten- 

 sity of the mechanical force we exert is proportioned to 

 the intensity of our desire to exert it. 



Thus I am prepared to go with the Materialists wher- 

 ever the true pursuit of the path of Descartes may lead 

 them ; and I am glad, on all occasions, to declare my 

 belief that their fearless development of the materialistic 

 aspect of these matters has had an immense, and a most 

 beneficial, influence upon physiology and psychology. 

 Nay more, when they go farther than I think they are 

 entitled- to do — when they introduce Calvinism into 



* For all the qualifications which need to be made here, I refer the reader 

 to the thorough discussion of the nature of the relation between nerve-action 

 and consciousness in Mr. Herbert Spencer's "Principles of Psychology/' 

 P> 115 et scq. 



