wasting fuel in a hundred or more places where it should be saved.
This is _not_ concentration. Concentration means the focussing of a
force; and when the mathematical faculty of the brain alone should
be at work, the force is not focussed if it is at the same time
flying over all other parts of the body in useless strain of
innumerable muscles. Tell another man, one who works naturally, to
solve the same problem,--he will instinctively and at once "erase
all previous impressions" in muscle and nerve, and with a quiet,
earnest expression, not a face knotted with useless strain, will
concentrate upon his work. The result, so far as the problem itself
is concerned, may be the same in both cases; but the result upon the
physique of the men who have undertaken the work will be vastly
different.

It will be insisted upon by many, and, strange as it may seem, by
many who have a large share of good sense, that they can work better
with this extra tension. "For," the explanation is, "it is natural
to me." That may be, but it is not natural to Nature; and however
difficult it may be at first to drop our own way and adopt Nature's,
the proportionate gain is very great in the end.

Normal exercise often stimulates the brain, and by promoting more
vigorous circulation, and so greater physical activity all over the
body, helps the brain to work more easily. Therefore some men can
think better while walking.

This is quite unlike the superfluous strain of nervous motion,
which, however it may seem to help at the time, eventually and
steadily lessens mental power instead of increasing it. The
distinction between motion which wholesomely increases the brain