it appears as the motion of the molecules of a little globule of
nerve-matter in the brain. In a rough way we might thus say that
the chemical energy of the food indirectly produces the motion of
these little nerve-molecules. But does this motion of
nerve-molecules now produce a thought or state of consciousness?
By no means. It simply produces some other motion of
nerve-molecules, and this in turn produces motion of contraction
or expansion in some muscle, or becomes transformed into the
chemical energy of some secreting gland. At no point in the whole
circuit does a unit of motion disappear as motion to reappear as
a unit of consciousness. The physical process is complete in
itself, and the thought does not enter into it. All that we can
say is, that the occurrence of the thought is simultaneous with
that part of the physical process which consists of a molecular
movement in the brain.[9] To be sure, the thought is always there
when summoned, but it stands outside the dynamic circuit, as
something utterly alien from and incomparable with the events
which summon it. No doubt, as Professor Tyndall observes, if we
knew exhaustively the physical state of the brain, "the
corresponding thought or feeling might be inferred; or, given the
thought or feeling, the corresponding state of the brain might be
inferred. But how inferred? It would be at bottom not a case of
logical inference at all, but of empirical association. You may
reply that many of the inferences of science are of this
character; the inference, for example, that an electric current
of a given direction will deflect a magnetic needle in a definite
way; but the cases differ in this, that the passage from the
current to the needle, if not demonstrable, is thinkable, and
that we entertain no doubt as to the final mechanical solution of
the problem. But the passage from the physics of the brain to the