efficiency, and it should be possible for ample warnings to be
received of depressions to be met with during a voyage, and these
will be avoided by the airship flying round them. In the
northern hemisphere, depressions generally travel from west to
east and invariably rotate in a counter-clockwise direction with
the wind on the south side blowing from the west and on the north
side blowing from the east. Going west, the airship would fly to
the north of a depression to take advantage of the wind
circulating round the edge, and going east the southern course
would be taken.

Lastly, the vulnerability of the airship must be taken into
account. Hydrogen is, as everyone knows, most highly inflammable
when mixed with air. The public still feels uncomfortable
misgivings at the close proximity of an immense volume of gas to
a number of running engines. It may be said that the danger of
disaster due to the gas catching fire is for peace flying to all
intents and purposes negligible. At the risk of being thought
hackneyed we must point out a fact which has appeared in every
discussion of the kind, namely, that British airships flew during
the war some 21 million 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