inches, the lift of 1,000 cubic feet of hydrogen at 98 per cent
purity is 69.6 lb. Under same conditions at 80 per cent purity
the lift of 1,000 cubic feet of hydrogen is 56.9 lb., a resultant
loss of 12.9 lb. per 1,000 cubic feet.

The whole of this statement on "lift" can now be condensed into
three absolute laws:

1. Lift is directly proportional to barometric pressure.

2. Lift is inversely proportional to absolute temperature.

3. Lift is directly proportional to purity.


AIRSHIP DESIGN

The design of airships has been developed under three distinct
types, the Rigid, the Semi-Rigid, and the Non-Rigid.

The rigid, of which the German Zeppelin is the leading example,
consists of a framework, or hull composed of aluminium, wood,
or other materials from which are suspended the cars, machinery
and other weights, and which of itself is sufficiently strong to
support its own weight. Enclosed within this structure are a
number of gas chambers or bags filled with hydrogen, which
provide the necessary buoyancy. The hull is completely encased
within a fabric outer cover to protect the hull framework and
bags from the effects of weather, and also to temper the rays of
the sun.