Another idea is that
when a bird seems to be floating on unmoving wings there is really a
rapid fluttering of the feathers of the wings, by which a sustaining
power is obtained. But no one who knows anything of the anatomy of
the bird will adopt this idea for an instant, and no one who has ever
watched with a good field-glass a floating bird of the albatross or
buzzard kind will suppose they are fluttering their feathers in this
way, even though he should be utterly ignorant of the anatomy of the
wings. Moreover, any one acquainted with the laws of dynamics will know
that there would be tremendous loss of power in the fluttering movement
imagined as compared with the effect of sweeping downward and backward
the whole of each wing.
There is only one possible way of explaining the floating power of
birds, and that is by associating it with the rapid motion acquired
originally by wing flapping, and afterward husbanded, so to speak, by
absolutely perfect adjustment and balancing. To this the answer is often
advanced that it implies ignorance of the laws of dynamics to suppose
that rapid advance can affect the rate of falling, as is implied by the
theory that it enables the bird to float.
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