om such experiences as these the
philosopher who speaks of the concomitance of physical and mental
phenomena must draw the whole meaning of the word.

Let us here sharpen a little the distinction between sensations and
things. Standing at some distance from the tree, I see an apple fall
to the ground. Were I only half as far away, my experience would not
be exactly the same--I should have somewhat different sensations. As
we have seen (section 17), the apparent sizes of things vary as we
move, and this means that the quantity of sensation, when I observe the
apple from a nearer point, is greater. The man of science tells me
that the image which the object looked at projects upon the retina of
the eye grows larger as we approach objects. The thing, then, may
remain unchanged; our sensations will vary according to the impression
which is made upon our body.

Again. When I have learned something of physics, I am ready to admit
that, although light travels with almost inconceivable rapidity, still,
its journey through space does take time. Hence the impression made
upon my eye by the falling apple is not simultaneous with the fall
itself; and if I stand far away it is made a little later than when I
am near. In the case in point the difference is so slight as to pass
unnoticed, but there are cases in which it seems apparent even to the
unlearned that sensations arise later than the occurrences of which we
take them to be the report.

Thus, I stand on a hill and watch a laborer striking with his sledge
upon the distant railway. I hear the sound of the blow while I see his
tool raised above his head. I account for this by saying that it has
taken some time for the sound-waves to reach my ear, and I regard my
sensation as arising only when this has been accomplished.

But this conclusion is not judged sufficiently accurate by the man of
science. The investigations of the physiologist and the psychologist
have revealed that the brain holds a peculiar place in the economy of
the body. If the nerve which connects the sense organ with the brain
be severed, the sensation does not arise. Injuries to the brain affect
the mental life as injuries to other parts of the body do not. Hence,
it is concluded that, to get the real time of the emergence of a
sensation, we must not inquire merely when an impression was made upon
the organ of sense, but must determine when the message sent along the
nerve has reached some part