o to speak, a kind of physical
ideas, which are retained in the central organs, constituting what might
be called physical memory, and may be combined in a manner which answers
to association and imagination, or may give rise to muscular
contractions, in those "reflex actions" which are the mechanical
representatives of volitions.

Consider what happens when a blow is aimed at the eye.[75] Instantly,
and without our knowledge or will, and even against the will, the
eyelids close. What is it that happens? A picture of the rapidly
advancing fist is made upon the retina at the back of the eye. The
retina changes this picture into an affection of a number of the fibres
of the optic nerve; the fibres of the optic nerve affect certain parts
of the brain; the brain, in consequence, affects those particular fibres
of the seventh nerve which go to the orbicular muscle of the eyelids;
the change in these nerve-fibres causes the muscular fibres to change
their dimensions, so as to become shorter and broader; and the result is
the closing of the slit between the two lids, round which these fibres
are disposed. Here is a pure mechanism, giving rise to a purposive
action, and strictly comparable to that by which Descartes supposes his
waterwork Diana to be moved. But we may go further, and inquire whether
our volition, in what we term voluntary action, ever plays any other
part than that of Descartes' engineer, sitting in his office, and
turning this tap or the other, as he wishes to set one or another
machine in motion, but exercising no direct influence upon the movements
of the whole.

Our voluntary acts consist of two parts: firstly, we desire to perform a
certain action; and, secondly, we somehow set a-going a machinery which
does what we desire. But so little do we directly influence that
machinery, that nine-tenths of us do not even know its existence.

Suppose one wills to raise one's arm and whirl it round. Nothing is
easier. But the majority of us do not know that nerves and muscles are
concerned in this process; and the best anatomist among us would be
amazingly perplexed, if he were called upon to direct the succession,
and the relative strength, of the multitudinous nerve-changes, which are
the actual causes of this very simple operation.

So again in speaking. How many of us know that the voice is produced in
the larynx, and modified by the mouth? How many among these instructed
persons understand how the voice is p