I
have not been able to time the continuance of the longest flights during
which the wings have not once been flapped, for the simple reason that,
in every case where I have attempted to do so, the bird has passed out
of view either by upward or horizontal traveling. But I am satisfied
that in many cases the bird sweeps onward or about on unflapping wings
for more than half an hour.
Now, many treat this problem of aerial flotation as if it were of the
nature of a miracle--something not to be explained. Explanations which
have been advanced have, it is true, been in many cases altogether
untenable. For instance, some have asserted that the albatross, the
condor, and other birds which float for a long time without moving
their wings--and that, too, in some cases, at great heights above the
sea-level, where the air is very thin--are supported by some gas within
the hollow parts of their bones, as the balloon is supported by the
hydrogen within it. The answer to this is that a balloon is _not_
supported by the hydrogen within it, but by the surrounding air, and in
just such degree as the air is displaced by the lighter gas. The air
around a bird is only displaced by the bird's volume, and the pressure
of the air corresponding to this displacement is not equivalent to more
than one five-hundredth part of the bird's weight.
Pages:
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169