non-rigid made thoroughly reliable, are the most valuable types
for future development. The larger non-rigids, with the possible
exception of the North Sea, do not appear to be likely to fulfil
any very useful function.

Airship design introduces so many problems which are not met with
in the ordinary theory of structures, that a whole volume could
easily be devoted to the subject, and even then much valuable
information would have to be omitted from lack of space. It is,
therefore, impossible, in only a section of a chapter, to do more
than indicate in the briefest manner a few salient features
concerning these problems. The suspension of weights from the
lightest possible gas compartment must be based on the ordinary
principles of calculating the distribution loads as in ships and
other structures. In the non-rigid, the envelope being made of
flexible fabric has, in itself, no rigidity whatsoever, and its
shape must be maintained by the internal pressure kept slightly
in excess of the pressure outside. Fabric is capable of
resisting tension, but is naturally not able to resist
compression. If the car was rigged beneath the centre of the
envelope with vertical suspensions it would tend to produce
compression in the underside of the envelope, owing to the load
not being fully distributed. This would cause, in practice, the
centre portion of the envelope to sag downwards, while the ends
would have a tendency to rise. The principle which has been found
to be most satisfactory is to fix the points of suspension
distributed over the greatest length of envelope possible
proportional to the lift of gas at each section thus formed.
From these points the wires are led to the car. If the car is
placed close to the envelope it will be seen that the suspensions