Kansas City journal. [volume] (Kansas City, Mo.) 1897-1928, 1898-02-20
HOW WELL KNOWN BIRDSFLY
THEIR USE OF THE FORCE OF THE
WIND.
Young Birds Work Out the Problem,
or Inherit Its SoIution-GuIls Fol-
low n Ship Without Seeming
to Use Their Wings.

/
Birds understand wind and all its va
carries, and they turn them all to ac-
count, says F. W. Headley in knowledge. |
Many problems, which men of science are
compelled to class among those which they |
hope to solve some day, or. perhaps. de-
spair of solving, a young bird begins to
work out directly he is fedged. L will
take some typical case in which a bird de-
rives help from the wind. 1t will be found
that he wind. If it is to lift a bird. sup
plementing the work Of his wings, or even
doing all the lifting. must either move
In an upward direction, or II 1t does not
deviate from the horizontal. it must be Of
unequal velocity. A win that Is unequal:
or not uniform, may either be made up of
currents moving at unequal rates, or 1t
may blow now gently, now strongly: A
maintain a heavy body in the air unless
that body has momentum of its own. 1t
Is no better than still air, since the bird
I'VE must try to put ourselves in his po-
eition) becomes part of the moving current.
The momentum required he derives either
from his own wing beats or from the
inequalities Of the wind. When a bird
rises. with wings outstretched and notion
less, there must be inequality. supposing
A lark when he is flying upward in
variably faces the wind. When he turns
again to rise he turns his head toward
the wind. To take another instance: A
cormorant. stated at last. wishes to join
wings on a rock not far off. The wind
is blowing toward the rock in question;
opposite direction, SO that the wind may
assist him as he struggles TO rise from
the water. This feat accomplished he
turns round and makes all sail for his
destination. The lark and the cormorant
are quite right in thinking that the wind
will help to lift them, but 1t does so only
because 1t Increases in velocity as thew
rise. Near the surface of the land or
the sea 1t Is retarded by friction. An
crease In velocity at successive elevations
not far from the ground:
By means of kites experiments have
been made up to a height of a thousand
feet, and even there the increase con-
tinues. though 1t is much more. gradual.
Were it not for this increase Of velocity
with altitude the lark, after. his first
jump from the ground. would. but for his
own efforts, move backward with the wind.
would a balloon from which the gas has
escaped. But perpetually passing from a
slower TO a more - ra dpI1de eu IRE H. uh Int tne 1Wo
which enables the wind to lift him. He is
stratum below which he energies into the
rapidly moving stratum above. In fact.
he illustrates the principle of the kite
inertia, which Is equivalent to momentum,
taking the place of the string. As long as
the kite is held by the string 1t will rise:
cut the string and the wind will wi, at once
We see then that If the lark wishes the
wind to help him to rise, he must face it
inclined. and further that the inequality
of the wind must give him inertia. or mo-
mentum or else his wings will have to
raise him without assistance. When gulls
advance to right angles with the wind
without any beating of the wings, the prin-
ciple applied is the same. From some slight
near the ground or the surface of the sea,
then POSSIBLY by a twist at the waist
lifts them to their former elevation; after
which the process begins again. 1t may
be that when birds soar. i. e.. rise in spirals
availing themselves at each upward step
of the increasing velocity of the wind
But they sometimes attain an elevation of
a mile or more. and there the increase must
be a neglible quantity, II it has not at
length reached the vanishing, point; and.
therefore, We have to look elsewhere for
an explanation of soaring.
This brings US to the subject of up
currents, obviously much to be desired if
wing labor is to be saved, and birds. when
ever such assistance is to be had, are al
ways ready to profit by it; When the wind
fecsed a ,snMsrd a s GliH, e ii u.s. nav 81 c eomefim aes
be seen enjoying the fun of being lifted
like a foam bubble Of the up-current. then
may be- Seen en- sc Soaring over cliffs or hills
near the shore ascending in noble spirals
without a motion Of their wings. The
L iIc III NiIc up"dio ldi vi NIic Win
But soaring may be seen under quite
different circumstance. The adjutant
bird: one of the noblest of ~soarers. rises
till he looks a mere speck or vanishes al
together. over the plain of Burmah. Can
there be upcurrents there? 1t is possible
heated by the sun, there may be such
currents here and there. But in Egypt I
have seen kites soaring over fields where
green. and where. consequently. the earth's
surface was not much heated. Probably
the adjutant depends on the irregularity
Even what we call a steady wind. we
know by Professor Langley's expert
mously in velocity from one moment to
another. This fact. the adjutant may
make use of deriving the indispensable
offer resistance to the breeze, not being
carried by 1t like a balloon. but feeling
!, VIII Pio Continue IN to h,s lift hace h;im so iT %Sen nee pre fbe
wind freshens he will turn and face it
and will rise like a kite. When it slackens
Obviously. there will be a good deal Of
leeway, a phenomenon vouched for by good
observers. but there will be a gain in alti-
tude. And thus the grand bird. making
even the wind, that Chartered libertine."
his slave. rises higher and higher. often.
on the earth below. but often. probably.
delighting only in the cool upper air and
in the exercise of his own skill:
To descend now to a humber but very
wonderful performance. Gulls may often
be seen following in the wake Of a steamer
without a motion Of their wings, though
the wind is blowing strong in their faces.
They are taking advantage of the up-cur-
rent. As the steamer advances. the air
at the stern rushes down to prevent a
vacuum being left and this down-draft re-
bounds off the surface of the sea and a
strong up-draft is formed. The. gull puts
himself in this up-draft. which lifts him
like a feather weight. and then he glides
downward and onward at a great pace.
Meanwhile. the point at which the up-draft
is formed advances. He soon finds himself
in It again, is raised to his former eleva-
ton. and the process is repeated. But
often a gull will hover over the stern, in
reality steadily advancing with the steam
er. Here, too. there must be an up-cur-
rent, the wind blowing at a slight angle
TO the steamer being DETECTED upward when
It strikes her side. This buoys the gull up.
In rising he loses way: when advancing
he descends. But he does not descend
or rise rapidly. as in the case last de-
.cribed. Like a consummate artist. the
gull conceals the art which he EMPLOYS.
For the solution and other flight prob
lens more observations are needed. The
interest of the subject will amply repay
any one who will devote time and ener-
A. ~ slKT ~