the wing, it causes the body to rock, so that at the
point where the wing joins the body, an elliptical
motion is produced.

_Fig. 10. Evolution of Humming-Bird's Wing._


HOW BIRDS POISE WITH FLAPPING WINGS.--This
is shown in Fig. 10, in which eight successive positions
of the wing are shown, and wherein four
of the position, namely, 1, 2, 3, and 4, represent
the downward movement, and 6, 7, 8, and 9, the
upward beat.

All the wing angles are such that whether the
suspension point of each wing is moving downwardly,
or upwardly, a support is found in some
part of the wing.

NARROW-WINGED BIRDS.--Birds with rapid flapping
motions have comparatively narrow wings,
fore and aft. Those which flap slowly, and are
not swift flyers, have correspondingly broader
wings. The broad wing is also typical of the
soaring birds.

But how do the latter overcome gravitation
without exercising some sort of wing movement?

INITIAL MOVEMENT OF SOARING BIRDS.--Acute