[Illustration: Fig. 1.]

The first subject is caught with his legs stretched in a stride, the
remarkable length of which arrests our attention. The sole of the right
foot is almost vertical. By the action of the muscles of the calf it has
_rolled off_ from the ground like a portion of the tire of a wheel, the
heel rising first, and thus the body, already advancing with all its
acquired velocity, and inclined forward, has been pushed along, and, as
it were, _tipped over_, so as to fall upon the other foot, now ready to
receive its weight.

[Illustration: Fig. 2.]

In the second figure, the right leg is bending at the knee, so as to
lift the foot from the ground, in order that it may swing forward.

[Illustration: Fig. 3.]

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,