in order to attain flight. This impulse is
acquired either by running along the ground, or
by a leap, or in dropping from a perch. Soaring
birds cannot, by any possibility, begin flight,
unless there is such a movement to change from a
position of rest to one of motion.

_Fig. 9. Wing Movement in Flight._

In the diagram, therefore, the bird, in moving
forwardly, while raising the wing upwardly, depresses
the rear edge of the wing, as in position
1, and when the wing beats downwardly the rear
margin is raised, in relation to its front margin,
as shown in position 2.

A WEDGING MOTION.--Thus the bird, by a
wedge-like motion, gives a forwardly-propelling
action, and as the rear margin has more or less
flexure, its action against the air is less during its
upward beat, and this also adds to the upward lift
of the body of the bird.

NO MYSTERY IN THE WAVE MOTION.--There is
no mystery in the effect of such a wave-like motion,
and it must be obvious that the humming
bird, and like flyers, which poise at one spot, are
able to do so because, instead of moving forwardly,
or changing the position of its body horizontally,
in performing the undulatory motion of