The Cecil Whig. [volume] (Elkton, Md.) 1841-current, 1892-09-17
HOW BIRDS FLY.
When an Eagles Wings are Still His Tail
is at Work.

An eagle circling in the air main
tans his wings rigidly motjoniess, but
he spreads his tail as wide as possible
and works it like the quarter revolu-
ton OF screw. The reactionary force
of the air which he thus displaces
drives him forward, and by exerting
more force of pressure with one side of
his tail than with the other, he dverts
his course TO right or left. The change
of position of the bird Is attended
with short, quick motions, as the point
of one wing is stretched forward, while
that of the other wing is turned cor
respondingly backward. These short,
convulslve movements first caught my
attention, and l was guided by them
to look for the energetic acton of the
tail which | at once recognized. And,
indeed, the part played by the tail
could not have escaped me even if |
had not so often observed it In action,
for the construction OF the side tail
feathers, like the primary feathers of
the wings, adapts them for propulsion,
so that the tail IS evidently, from its
structure, subsidiary wing.
Gatke's falcon that went up like
balloon, turned himself against the
wind, and raising himself somewhat
forward, worked his tail in such a
manner as to neutralize the pressure of
the wind, so that the bird, instead of
being driven away before it, was driven
upward, just as sail boat is driven
across the stream.
This direct ascent | have observed
in raptores only never l.. sstUlks their
| tails have not the necessary develop
ment; storks consequently rise by
circhng, and so also do gulls and al.
batrosses. None of these birds are
capable of rising directly from the
ground or water.
The direct upward accent of the
falcon IS nothing more than vertical
sailing, or sailings diagonally across
wind, as ravens so frequently do.
Under the apparently rigid wings a
sustaining current of air is constantly
rushing, a column of air which, by its
motion under the wings, produces the
same effect as if the air were still and
the wings were beaten against 1t.
To illustrate my meaning as to the
atmospheric irregularities produced by
resistance, let me cite fact comuni-
Gated to me by Mr.. Meyer, of Ham,
burg, and observed by him at Heligo-
land. There the wind beating against
the cliffs gets caught IN the inlets of
the rocky shore wall, producing up
ward currents of such force that the
boys amuse themselves by leaning
over the top of the cliffs, resting on
the support of the ascending current,
while ladies standing a yard behind
them have the feathers in their bonnets
unruffled. The upward pillar Of air
completely arrests the horizontal cur
rent.
Such rigid air wall is produced by
every sailing bird under his wings,
through their own movement, and by
the bird resting on point of air, by
allowing a current of air to stream
through under his mo:ionless wings; in
either case he is upheld by the support
ing power of a circulating pillar of air
under the wings.
In my work, The Mechanical Prin-
ciple of Flight, 1t was laid down as
scientifically demonstrated that birds
possess relatively no more strength
than other creatures OF flesh aud blood,
and that the bird is capable CT trans
porting his own body with such ease is
possible only because in the horizon,
tally extended wings there resides a
force especially favorable to horizontal
flight.
This is especially evident in the case
Of s,orks, albatrosses and other birds