Shaw 
164 MR. DARWIN'S CRITICS 
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, 
whethera 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 
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 notior 
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? In what manner can 
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 — 
T can of what takes place when the motion 
