nowise
"suspended" or "defied" when a man lifts his arm; but that, under such
circumstances, part of the store of energy in the universe operates on
the arm at a mechanical advantage as against the operation of another
part. I was simple enough to think that no one who had as much
knowledge of physiology as is to be found in an elementary primer, or
who had ever heard of the greatest physical generalisation of modern
times--the doctrine of the conservation of energy--would dream of
doubting my statement; and I was further simple enough to think that
no one who lacked these qualifications would feel tempted to charge me
with error. It appears that my simplicity is greater than my powers of
imagination.

The Duke of Argyll may not be aware of the fact, but it is
nevertheless true, that when a man's arm is raised, in sequence to
that state of consciousness we call a volition, the volition is not
the immediate cause of the elevation of the arm. On the contrary, that
operation is effected by a certain change of form, technically known
as "contraction" in sundry masses of flesh, technically known as
muscles, which are fixed to the bones of the shoulder in such a manner
that, if these muscles contract, they must raise the arm. Now each of
these muscles is a machine comparable, in a certain sense, to one of
the donkey-engines of a steamship, but more complete, inasmuch as the
source of its ability to change its form, or contract, lies within
itself. Every time that, by contracting, the muscle does work, such as
that involved in raising the arm, more or less of the material which
it contains is used up, just as more or less of the fuel of a
steam-engine is used up, when it does work. And I do not think there
is a doubt in the mind of any competent physicist, or physiologist,
that the work done in lifting the weight of the arm is the mechanical
equivalent of a certain proportion of the energy set free by the
molecular changes which take place in the muscle. It is further a
tolerably well-based belief that this, and all other forms of energy,
are mutually convertible; and, therefore, that they all come under
that general law or statement of the order of facts, called the
conservation of energy. And, as that certainly is an abstraction, so
the view which the Duke of Argyll thinks so extremely absurd is really
one of the commonplaces of physiology. But this Review is hardly an
appropriate place for giving instruction in the element