As They Glided
Close Over My Head, I Intently Watched From An Oblique Position,
The Outlines Of The Separate And
Great terminal feathers
of each wing; and these separate feathers, if there had been
the least vibratory movement, would have
Appeared as if
blended together; but they were seen distinct against the
blue sky. The head and neck were moved frequently, and
apparently with force; and the extended wings seemed to
form the fulcrum on which the movements of the neck, body,
and tail acted. If the bird wished to descend, the wings
were for a moment collapsed; and when again expanded
with an altered inclination, the momentum gained by the
rapid descent seemed to urge the bird upwards with the
even and steady movement of a paper kite. In the case of
any bird soaring, its motion must be sufficiently rapid so
that the action of the inclined surface of its body on the
atmosphere may counterbalance its gravity. The force to
keep up the momentum of a body moving in a horizontal
plane in the air (in which there is so little friction) cannot
be great, and this force is all that is wanted. The movements
of the neck and body of the condor, we must suppose,
is sufficient for this. However this may be, it is truly
wonderful and beautiful to see so great a bird, hour after hour,
without any apparent exertion, wheeling and gliding over
mountain and river.
April 29th. - From some high land we hailed with joy
the white summits of the Cordillera, as they were seen
occasionally peeping through their dusky envelope of clouds.
During the few succeeding days we continued to get on
slowly, for we found the river-course very tortuous, and
strewed with immense fragments of various ancient slate
rocks, and of granite.
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