The morning news. [volume] (Savannah, Ga.) 1887-1900, 1892-07-18
HOW BIRDS Fly.
When an Eagles Wings Are still His
Toll is at Work.

Toll is at Work.
From the Vienna Stein der Weisen.
An eagle circling in the air maintains his
wings rIgidly motionless, but he spreads his
tail as wide as possible and works it like a
quarter revolution Of a screw. The reao-
tionary force Of the air which he thus dis
places drives him forward, and.by exerting
more force Of pressure with one side OF his
tail than with the other, he diverts his course
to right or left The change Of position of
the bird is attended with short, quick mo-
tions, as the point Of one wing is stretched
forward, while that Of the other wing is
turned correspondingly backward. These
short. convulsiYe movements first caught
my attention, and was guided by them TO
look for the energetic action 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 OBJ
served it in action for the construction of
the side tail feathers, like the primary feath-
ers Of the wings, sdapts them for propulsion,
so that the tail Is evidently, from its struct-
ure. subsidiary wing.
0atke's falcon that went up like a bal
loon, turned himself against the wind, and -,
raising himself some what forward, worked
himself in such manner as to neutralize
the pressure OF the wind, 30 that the bird,
driven upward, just as sailboat Is driven
across the stream.
The direct ascent have observed in rap
torres only, never In storks; their tails have
not the necessary development; storks con-
sequently rise by circling, and so also do
gulls and albatrosses. None Of these birds
are capable Of rising directly from the
ground or water
The direct upward ascent OF the falcon Is
nothing more than vertical sailing, or SAIL
ing dlagonally across a wind, as ravens 50
frequently do.
Under the apparently rigid wings a sus-
tanning current Of air is constantly rushing.
column OF air which, by its motion under
the wings, produces the same effect as IL
the air were still and the wings were beaten
against it.
To illustrate my meaning as 10 the atmos-
pherio irregularities produced by resistance,
let me cite a fact communicated to me by
Mr.. Meyer Of Hamburg, and observed by
him at Heligoland. There the wind beat
ing against the cliffs gets caught ia the In
lets OF the rocky shore wall. producing the
upward currents of such force that the boys
aInuse themselves by leaning over the top
OF the cliffs, resting on the support of the
ascending current, while ladies standing n
yard behind them have the feathers 10 their
bonnets unruffied. The upward pillar Of
air completely arrests the horizontal cur
rent.
Such rigid ARRIVAL Is produced by every
sailing bird under his wings, through their
own movement, and by the bird resting on
point Of air, by allowing current Of air
to stream through under his motionless
wings, in either case he is upheld by the
supporting power Of a circulating pillar of
air under the wings.
In my work, "The Mechanical Principle
Of Flight, 7" it was laid down as scientifically
demonstrated that birds possess relatively
no more strength than other creatures OF
flesh and blood, and that the bird is capable
of transporting his own body with such
ease Is possible only because in the horizon
tally extended wings there resides aforcs es-
pecially favorable to horizontal flight.
This is especially evident in the case of
storks, albatrosses and other birds with i'm
perfectly developed tails which although
capable of sustaining flighs of hundreds of
leagues, are, from their incapacity to soar
directly, unable to escape from a small in
closure with walls five or six feet high.
AS a consequence Of the law Of gravita-
tion, less force is required to raise a body a
yard high than to move it yard horizon
tally A raven which l observed hoped q
meter high and then sailed eighty yards
after pillow without motion Of his wings !;
he converted meter Of lifting power into
eighty meters of horizontal transport
power; but there was, Of course, an expen-
diture OF scullips power also.
By raising water 100 feet high, I can
transports it In an incline trough at least fifty
times the distance. And so it is exactly In
bird flight. The elastic oblique surface ten
sion of the quill feathers is the shallo w
trough in which she power expanded In
raising the bird q yard is converted into
horizontal flight.