The next stage of movement is shown in the _left_ leg of figure 3. This
leg is seen suspended in air, a little beyond the middle of the arc
through which it swings, and before it has straightened itself, which it
will presently do, as shown in the next figure.

[Illustration: Fig. 4.]

The foot has now swung forward, and, tending to swing back again, the
limb being straightened, and the body tipped forward, the heel strikes
the ground. The angle which the sole of the foot forms with the ground
increases with the length of the stride; and as this last surprised us,
so the extent of this angle astonishes us in many of the figures, in
this among the rest.

The heel strikes the ground with great force, as the wear of our boots
and shoes in that part shows us. But the projecting heel of the human
foot is the arm of a lever, haying the ankle-joint as its fulcrum, and,
as it strikes the ground, brings the sole of the foot down flat upon it,
as shown in figure 1. At the same time the weight of the limb and body
is thrown upon the foot, by the joint effect of muscular action and
acquired velocity, and the other foot is now ready to rise from the
ground and repeat the process we have traced in its fellow.

No artist would have dared to draw a walking figure in attitudes like
some of these. The swinging limb is so much shortened that the toe never
by any accident scrapes the ground, if this is tolerably even. In cases
of partial paralysis, the scraping of the toe, as the patient walks, is
one of the characteristic marks of imperfect muscular action.

Walking, then, is a perpetual falling with a perpetual self-recovery. It
is a most complex, violent, and perilous operation, which we divest of
its extreme danger only by continual practice from a very early period
of life. We find how complex it is when we attempt to analyze it, and
we see that we never understood it thoroughly until the time of the
instantaneous photograph. We learn how violent it is, when we walk
against a post or a door in the dark. We discover how dangerous it is,
when we slip or trip and come down, perhaps breaking or dislocating our
limbs, or overlook the last step of a flight of stairs, and discover
with what headlong violence we have been hurling ourselves forward.

Two curious facts are easily proved. First, a man is shorter when he is
walking than when at rest. We have found a very simple way of showing
this by having a rod or yardstick placed hori