establish a hard and fast rule against
incorporating in an airship's design any inclosed space in which
waste gas might gather. This rule and its reason were known to Count
von Zeppelin and by ignoring both he lent new colour to the charge,
already current in scientific circles, that he was loath to profit
by the experiences of other inventors.

Whether this feeling spread to the German Government it is
impossible to say. Nor it is easy to estimate how much official
confidence was shaken by it. The government, even before the war,
was singularly reticent about the Zeppelins, their numbers and
plans. It is certain that orders were not withheld from the Count.
Great numbers of his machines were built, especially after the war
was entered upon. But he was not permitted longer to have a monopoly
of government aid for manufacturers of dirigibles. Other types
sprung up, notably the Schutte-Lanz, the Gross, and the Parseval.
But being first in the field the Zeppelin came to give its name to
all the dirigibles of German make and many of the famous--or
infamous--exploits credited to it during the war may in fact have
been performed by one of its rivals.

It would be futile to attempt to enumerate all these rivals here.
Among them are the semi-rigid Parseval and Gross types which found
great favour among the military authorities during the war. The
latter is merely an adaptation of the highly successful French ship
the _Lebaudy_, but the Parseval is the result of a slow evolution
from an ordinary balloon. It is wholly German, in conception and
development, and it is reported that the Kaiser, secretly disgusted
that the Zeppelins, to the advancement of which he had given such
powerful aid, should have recorded so many disasters, quietly
transferred his interest to the new and simpler model. Despite the
hope of a more efficient craft, however, both the Gross and the
Parseval failed in their first official trials, though later they
made good.

The latter ship was absolutely without any wooden or metallic
structure to give her rigidity. Two air ballonets were contained in
the envelope at bow and stern and the ascent and descent of the
ship was regulated by the quantity of air pumped into these. A most
curious device was the utilization of heavy cloth for the propeller
blades. Limp and flaccid when at rest, heavy weights in the hem of
the cloth caused these blades to stand out stiff and rigid as the
result of the centrifugal forc