164 MR. DARWIN'S CRITICS y 



examples that may be required, prove that one 

 form of consciousness, 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. Wallace, in fact, appears to me to have 

 mixed up two very distinct propositions : the one, 

 the indisputable truth that consciousness is corre- 

 lated with molecular changes in the organ of 

 consciousness ; the other, that the nature of that 

 correlation is known, or can be conceived, which 

 is quite another matter. Mr. Wallace, presumably, 

 believes in that correlation of phenomena which 

 we call cause and effect as firmly as I do. But if 

 he has ever been able to form the faintest notion 

 how a cause gives rise to its effect, all I can say is 

 that I envy him. Take the simplest case imagin- 

 able suppose a ball in motion to impinge upon 

 another ball at rest. I know very well, as a matter 

 of fact, that the ball in motion will communicate 

 some of its motion to the ball at rest, and that 

 the motion of the two balls, after collision, is 

 precisely correlated with the masses of both balls 

 and the amount of motion of the first. But how 

 does this come about f In what manner can we 

 conceive that the vis viva of the first ball passes 

 into the second ? I confess I can no more form 

 any conception of what happens in this case, than 

 I can of what takes place when the motion of 



