e homewards.

On our way back Mr Sedgwick expatiated on the powers and beauty of the
frigate-bird. "See," he observed, "these feathers are not of that
coarse and downy texture peculiar to aquatic birds; indeed, its graceful
form and all the internal arrangements seem especially adapted--I was
almost going to say for eternal flight. See these wings, twelve feet
from tip to tip. Observe this forked tail, these short legs, the thighs
not more than an inch in length. Unless perched on some rocky pinnacle,
it is unable to take flight. Neither, you will observe, is it adapted
for living on the waves. See its feet; they are unlike those of
water-fowl, being but partially webbed. Now, when I come to show you
the interior of the creature, you will see with what surprising
arrangements it is furnished for flight without fatigue in the loftiest
regions of the air, where it can even sleep without the danger of
descending. See beneath its throat this large pouch; it communicates
with the lungs, and also with the hollow and wonderfully light bone-work
of its skeleton. When it wishes, therefore, to rest in air, it first
spreads out its mighty wings, which are almost sufficient to float its
light body. It then fills its enormous pouch with air, from whence it
is forced into all its bones, and even into the cavities between the
flesh and the skin. Now this air enters cold, but in a short time, from
the heat of the bird's circulation, which is greater than that of other
animals, it becomes rarified, and will consequently swell out both the
pouch and every cavity I have spoken of, thus giving the bird a
wonderful buoyancy, even in the highest regions of the atmosphere. We
saw how high those birds went just now, but they probably have gone far
higher. In the same way, when the weather is stormy near the earth, the
frigate-bird rises into the higher and calmer regions, where, with
outspread wing, it remains suspended, motionless, and at rest. There it
might remain for days together, unless compelled by hunger to descend.
When this is the case, it expels the rarified air from its body and
pouch, and drops swiftly towards the ocean. It never, however, dives,
or even swims, but as it comes within a few feet of the waves, it
instantly brings itself to a stop, and skimming along, catches the
flying-fish with its hawk-like bill or talons, holding its neck and feet
in a horizontal direction, striking the upper column of air with its