eculation. We begin with the captive balloon.
Against that the navigable balloon will presently operate. I am inclined
to think the practicable navigable balloon will be first attained by the
use of a device already employed by Nature in the swimming-bladder of
fishes. This is a closed gas-bag that can be contracted or expanded. If
a gas-bag of thin, strong, practically impervious substance could be
enclosed in a net of closely interlaced fibres (interlaced, for example,
on the pattern of the muscles of the bladder in mammals), the ends of
these fibres might be wound and unwound, and the effect of contractility
attained. A row of such contractile balloons, hung over a long car which
was horizontally expanded into wings, would not only allow that car to
rise and fall at will, but if the balloon at one end were contracted
and that at the other end expanded, and the intermediate ones allowed to
assume intermediate conditions, the former end would drop, the expanded
wings would be brought into a slanting condition over a smaller area of
supporting air, and the whole apparatus would tend to glide downwards in
that direction. The projection of a small vertical plane upon either
side would make the gliding mass rotate in a descending spiral, and so
we have all the elements of a controllable flight. Such an affair would
be difficult to overset. It would be able to beat up even in a fair
wind, and then it would be able to contract its bladders and fall down a
long slant in any direction. From some such crude beginning a form like
a soaring, elongated, flat-brimmed hat might grow, and the possibilities
of adding an engine-driven screw are obvious enough.

It is difficult to see how such a contrivance could carry guns of any
calibre unless they fired from the rear in the line of flight. The
problem of recoil becomes a very difficult one in aerial tactics. It
would probably have at most a small machine-gun or so, which might fire
an explosive shell at the balloons of the enemy, or kill their aeronauts
with distributed bullets. The thing would be a sort of air-shark, and
one may even venture to picture something of the struggle the deadlocked
marksmen of 1950, lying warily in their rifle-pits, will see.

One conceives them at first, each little hole with its watchful,
well-equipped couple of assassins, turning up their eyes in expectation.
The wind is with our enemy, and his captive balloons have been
disagreeably overhead all throu