Shepherdstown register. [volume] (Shepherdstown, Va. [W. Va.]) 1849-1955, 1895-12-05
The Flight of Birds.

A4eA9 - 49, ~N@'+N :,
pressure as cold air, it follows that
these two layers of air are constantly
changing places, the relatively warm
air at the surface of the earth ascend
ing, expanding, doing work and be-
coming cooled, while the cold air from
above settles to the earth 10 take the
place of the warm air The velocity
with which these vertical currents
move is, say, from one mile to six miles
an hour, and their movement Is quite
independent of any other horizontal
current that the air may have as re-
lates to the earth at the same time.
These currents may be going on IN
valley surrounded by mountains with
out any other action of the atmosphere.
On plain, however, there Is also an
other action taking place at the same
time, but which does not in the least
interfere with the vertical action, that
is, the whole body of air may be pass
inc along over the surface Of the earth
at the rate, we will say, Of ten miles
an hour, while the vertical action Is
GOING nm at 4 velocity of. saw, four
miles an hour.
The soaring of a bird may be COM
pared with boy sliding downhill on
a sled.
ia hill is, say 100 feet high, and
the slides slope off in a horizontal d.
rection 1000 feet from the summit,
and if the snow is smooth, boy can
mount a sled and advance 1000 feet
while he Is falling, as relates to the
earth, 100 feet; that is, the sled with
the boy on it in falling through dis
tance of one foot develops sufficient
power to drive the sled forward 20
feet; but when the boy is at the bot
tom Of the hill and can develop no
more power while falling, the sled soon
comes to a state of rest Suppose now
that = hill could be made I'm such a
manner that it would constantly rise
at such velocity that the sled would
never reach the bottom of the hill
The boy would then be able to slide
forever, and this is exactly what oc-
ours with a bird. \ bird places Its
wings in such a position that, as 1t
falls in the air, say one foot, 1t moves
forward through the air 20 feet that
is, it slides along on the surface Of the
air underneath its wings in the same
manner that the boy slides down the
hill. Suppose now that the velocity
of the bird should be about 30 miles
an hour this would account for the
whole phenomenon Of soaring on an
upward current of only II miles an
hour. With an upward current Of 2
miles an hour the bird would rise, as
relates to the earth, one half mile an
hour while actually falling through the
air at the rate of II miles an hour
There is no doubt that a bird, by
some very delicate sense Of feeling and
touch, is able to ascertain whether it
is falling or rising in the air. In all
probability the numerous air cells
which are found in the body Of bird
are provided with delicate nerves,
which operate in similar manner to
those Of the swim bladder Of a fish, so
that as the bird is moving forward
through the air it is able to take adj
vantage Of rising column Of air. AS
a whole, We may consider that the ris-
ing columns of air would be half Of
the total area Of the earth s surface, so
that soaring bird would always have
a rising column of air which would
serve as a support. Referring to the
eagles which l saw in the Pyrenees,
on one occasion observed FIVE Of these
birds about 500 feet above the peak
Of a mountain, and they were balanc-
ing Themselves in stationary position
on an ascending column Of air pro-
duced by the wind blowing over the
peak, and seemed to be as much at
ease as if they were roosting upon a
tree. As ship passes through the
air, the air is divided exactly in the
same manner as water would be, and
as it comes together again at the stern
of the ship it produces an upward cur
rent, and it is on this ascending col
umn of air that the albatross and the
seagull find a resting place and follow
the ship for days at time without any
apparent exertion; but whenever they
find themselves in front Of the ship or
at ore side where there is no ascend
ing column Of air they have often to
work their passage very much as other
birds do.
But all birds do not soar. Ducks,
geese, partridges and pheasants are
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