plants were put down.
Hydrogen was also found to be the bye-product of certain industries,
and considerable supplies were obtained from commercial firms, the
hydrogen being compressed into steel cylinders and dispatched to the
various stations.

Before concluding this chapter, certain words must be written on
parachutes. A considerable controversy raged in the press and
elsewhere a few months before the cessation of hostilities on the
subject of equipping the aeroplane with parachutes as a life-saving
device. In the airship service this had been done for two years. The
best type of parachute available was selected, and these were fitted
according to circumstances in each type of ship. The usual method is
to insert the parachute, properly folded for use, in a containing case
which is fastened either in the car or on the side of the envelope as
is most convenient. In a small ship the crew are all the time attached
to their parachutes and in the event of the ship catching fire have
only to jump overboard and possess an excellent chance of being saved.
In rigid airships where members of the crew have to move from one end
of the ship to the other, the harness is worn and parachutes are
disposed in the keel and cars as are lifebuoys in seagoing vessels.
Should an emergency arise, the nearest parachute can be attached to the
harness by means of a spring hook, which is the work of a second, and a
descent can be made.

It is worthy of note that there has never been a fatal accident or any
case of a parachute failing to open properly with a man attached.

The material embodied in this chapter, brief and inadequate as it is,
should enable the process of the development of the airship to be
easily followed. Much has been omitted that ought by right to have
been included, but, on the other hand, intricate calculations are apt
to be tedious except to mathematicians, and these have been avoided as
far as possible in the following pages.

CHAPTER II

EARLY AIRSHIPS AND THEIR DEVELOPMENT TO THE PRESENT DAY

The science of ballooning had reached quite an advanced stage by the
middle of the eighteenth century, but the construction of an airship
was at that time beyond the range of possibility. Discussions had taken
place at various times as to the practicability of rendering a balloon
navigable, but no attempts had been made to put these points of
argument to a practical test.

Airship history may be said to date from J