The morning news. [volume] (Savannah, Ga.) 1887-1900, 1897-09-05
WIND AS AN AID TO FLIGHT.
How Birds Understand the Air Cur
rents and Make Use of Them.
From knowledge.

From knowledge.
Birds understand wind and all its vaga-
ries, and they turn them all to account.
Many problems which men Of science are
compelled TO class among those which they
hope to solve some day, or, perhaps. des-
pair OF solving, young bird begins to
work out directly he Is fledged. / will take
some typical cases in which bird derives
help from the wind. 1t will be found that
the wind, II IL Is to lift bird, supplement-
ing the work of his wings, or even doing
all the lifting, must either move in an up
ward direction, or, If it does not deviate
from the horizontal, it must be of unequal
velocity A wind that is unequal or nos
uniform, may either be made up of cur
rents moving at unequal rates, or 1t may
blow now gently. now strongly. A uniform
horizontal breeze cannot lift or maintain a
heavy body in the air unless that body
has momentum of its own IL is no better
than still air, since the bird-we must try
to put ourselves in his observation-disclosures
part of the moving current The momen-
tum required he derives either from his
own wing-beats or from the inequalities
of the wind
When a bird rises with wings outspread
and motionless, there must be inequality
supposing that the wind is horizontal. A
lark, when he is flying upward-always
singing in spite of the steepness of the in
cline as If to show how easy It is-nVari-
ably faces the wind. When he turns away
from il he ceases to rise ana generally
loses elevation. When he wishes again to
rise, he turns his head towards the wind
To take another instance; a cormorant
stated at last, wishes TO join his comrades
who are drying their wings on a rock not
far off. The wind is blowing towards the
rock in question; accordingly, he begins by
flying in the opposite direction, 50 that the
wind may assist him as he struggles to
rise from the water. This feat accomplish
ed he turns round and makes all sail for
his destination The lark and the cormo-
rant are quite right in thinking that the
wind will help TO lift them, but it does so
only because it increases in velocity as
they rise. Near the surface of the land or
the sea it is retarded by friction.
An thermometer reveals a very marked
increase in velocity at successive eleva-
tons not far from the ground. BY means
of kites experiments have been made up
to hight of 1000 feet, and even there the
increase continues, 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. It would not lift him any more
than it would a balloon from which the
gas had escaped. But perpetually passing
from a slower to a more rapid current Gin
theory it is convenient 10 divide the air
into definite strata), he hag always an in
ertia which enables the Wind to lift him
He Is still. so to speak, part OF the slowly
moving stratum below when he energies
into the rapidly moving stratum above. In
fact he illustrates the principle of the kite
Inertia which is equivalent 10 momen-
tum, taking the place OF the string. As