
quality of lift. Certain kinds of beetles, and particularly
the common house fly, disprove that theory,
as their wings are perfectly flat.

FEATHER STRUCTURE CONSIDERED.--Then the
feather argument is advanced, which seeks to
show that as each wing is made up of a plurality
of feathers, overlapping each other, they form a
sort of a valved surface, opening so as to permit
air to pass through them during the period of
their upward movement, and closing up as the
wing descends.

It is difficult to perform this experiment with
wings, so as to show such an individual feather
movement. It is certain that there is nothing in
the structure of the wing bone and the feather
connection which points to any individual feather
movement, and our observation is, that each
feather is entirely too rigid to permit of such an
opening up between them.

It is obvious that the wing is built up in that
way for an entirely different reason. Soaring
birds, which do not depend on the flapping motion,
have the same overlapping feather formation.

WEBBED WINGS.--Furthermore, there are numerous
flying creatures which do not have
feathered wings, but web-like structures, or like the
house fly, in one continuous and unbroken
plane.

That birds which fly with flapping wings derive
their support from the air, is undoubtedly true,
and that the lift produced is due, not to the form,
or shape, or area of the wing, is also beyond question.
The records show that every conceivable
type of outlined structure is used by nature; the
material and texture of the wings themselves differ
to such a degree that there is absolutely no
similarity; some have concaved under surfaces,
and others have not; some fly with rapidly beating
wings, and others with slow and measured
movements; many of them fly with equal facility
without flapping movements; and the proportions
of weight to wing surface vary to such an extent
that it is utterly impossible to use such data as a
guide in calculating what the proper surface
should be for a correct flying machine.

THE ANGLE OF 