Now they can see the river before
them and a bay of the sea which must be crossed or skirted.
The fog still lingers along the course of the river and between
the hills, but is fast rolling away in grey, ghost-like masses.
Out to sea it obscures the horizon, making it difficult to be
sure where water ends and fog begins, and creating a strange,
rather weird effect by which ships at a certain distance appear
to be floating in space.
Now the Aeroplane is almost over the river, and the
next instant it suddenly drops into a ``hole in the air.''
With great suddenness it happens, and for some two hundred
feet it drops nose-down and tilted over sideways; but the
Pilot is prepared and has put his craft on an even keel in
less time than it takes to tell you about it; for well he knows
that he must expect such conditions when passing over a
shore or, indeed, any well-defined change in the composition
of the earth's surface. Especially is this so on a hot and
sunny day, for then the warm surface of the earth creates
columns of ascending air, the speed of the ascent depending
upon the composition of the surface. Sandy soil, for instance,
such as borders this river produces a quickly ascending
column of air, whereas water and forests have not such a
marked effect. Thus, when our Aeroplane passed over the
shore of the river, it suddenly lost the lift due to the ascending
air produced by the warm sandy soil, and it consequently
dropped just as if it had fallen into a hole.
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