In the _Zeppelin_, a sliding weight could be moved along the keel so as
to cause the center of gravity to coincide with the center of upward
pressure in spite of variations in weight and position of gas, fuel,
and ballast. In the German balloon _Parseval_, the car itself was
movable on a longitudinal suspending cable which carried supporting
sheaves. This balloon has figured in recent press notices. It was
somewhat damaged by a collision with its shed in March: the sixteen
passengers escaped unharmed. A few days later, emergency deflation by
the rip-strip was made necessary during a severe storm. In the ordinary
non-rigid balloon, the pumping of air between the ballonets aids in
controlling longitudinal equilibrium. The pump may be arranged for
either hand or motor operation: that in the _Clément-Bayard_ had a
capacity of 1800 liters per minute against the pressure of a little
over three-fifths of an ounce. The _Parseval_ has two ballonets. Into
the rear of these air is pumped at starting. This raises the bow and
facilitates ascent on the principle of the inclined surface of an
aeroplane. After some elevation is attained, the forward ballonet is
also filled.
[Illustration: CAR OF THE ZEPPELIN
(From the _Transactions_ of the American Society of
Mechanical Engineers)]