XL ] MR. DARWIN'S CRITICS. 285 



changes in the organ of consciousness ; the other, that 

 the nature of that correlation is known, or can be con- 

 ceived, 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 imaginable 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 col- 

 lision is precisely correlated with the masses of both 

 balls and the amount of motion of the first. But how 

 does this come about ? 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 particles of my nervous matter, 

 caused by the impact of a similar ball, gives rise to the 

 state of consciousness I call pain. In ultimate analysis 

 everything is incomprehensible, and the whole object 

 of science is simply to reduce the fundamental incom- 

 prehensibilities to the smallest possible number. 



But to return to the Quarterly Eeviewer. He admits 

 that animals have " mental images of sensible objects, 

 combined in all degrees of complexity, as governed by 

 the laws of association." Presumably, by this confused 

 and imperfect statement the Eeviewer means to admit 

 more than the words imply. For mental images of sen- 

 sible objects, even though " combined in all degrees of 

 complexity," are, and can be, nothing more than mental 

 images of sensible objects. But judgments, emotions, 

 and volitions cannot by any possibility be included 

 under the head of " mental images of sensible objects." 



