miles, and there is only one case
of an airship catching fire in the air. This was during a trial flight
in a purely experimental ship, and the cause which was afterwards
discovered has been completely eliminated.

For airships employed for military purposes this danger, due to the use
of incendiary bullets, rockets and various other munitions evolved for
their destruction, still exists.

Owing to its ceiling, rate of climb and speed, which we take to be from
70 to 80 miles per hour in the airship of the future, the airship may
be regarded as comparatively safe against attack from the ordinary type
of seaplane. The chief danger to be apprehended is attack from small
scouting seaplanes, possessing great speed and the power to climb to a
great height, or from aeroplanes launched from the decks of ships. If,
however, the airship is fitted to carry several small scout aeroplanes
of high efficiency in the manner described in the previous chapter, it
will probably be able to defend itself sufficiently to enable it to
climb to a great height and thus make good its escape.

The airship, moreover, will be more or less immune from such dangers if
the non-inflamable gas, known as "C" gas, becomes sufficiently cheap to
be used for inflating airships. In the past the expense of this gas
has rendered its use absolutely prohibitive, but it is believed that
it can be produced in the United States for such a figure as will make
it compare favourably with hydrogen.

The navigation of an airship during these long voyages proposed will
present no difficulty whatever. The airship, as opposed to the
aeroplane, is reasonably steady in the air and the ordinary naval
instruments can be used. In addition, "directional" wireless
telegraphy will prove of immense assistance. The method at present in
use is to call up simultaneously two land stations which, knowing their
own distance apart, and reading the direction of the call, plot a
triangle on a chart which fixes the position of the airship. This
position is then transmitted by wireless to the airship. In the future
the airship itself will carry its own directional apparatus, with which
it will be able to judge the direction of a call received from a single
land station and plot its own position on a chart.

We have so far confined our attention to the utilization of airships
for transport of passengers, mails and goods, but there appear to be
other fields of activity which can be