only by possessing the scientific knowledge borne of
experience. But it is not all.

One Hundred and Fifteen Zeppelins Built and Operated

From the day Count Zeppelin built his first ship until the last in 1919,
a total of 115 Zeppelins were built and operated. The first three were
experimental. Nine Zeppelins were successfully operated commercially in
the transportation of passengers. Forty were delivered to the German
army and 63 to the navy.

Scientific Comparison

There exists in the field of engineering an impartial, positive and
unswerving means of determining the relative merits of things; and that
is by a technical analysis of their success. By it one may recognize the
values of the principles and construction methods involved. It is
commonly said that nothing succeeds like success; and this is virtually
true of the Zeppelins. Their record for efficiency remains unsurpassed,
as a matter of fact, unequalled. It has never been denied that they were
superior to contemporary craft or that they failed to maintain an
increasing advantage over them.

This comparison is justified by the following figures which we will
first attempt to explain.

It will be noted that there are three kinds of efficiency, (1) Speed
(the aerodynamical figure), (2) Lift (the constructional figure) and (3)
All-around efficiency (the combined quality figure).

The first relates to the efficiency of airship propulsion as effected by
degrees of refinement in form, lessening of resistance, conservation of
power, etc. It is simply the relation between the speed and engine
power. Inasmuch as higher speed with the same power or the same speed
with less power means economy of operation; therefore, the higher figure
indicates superior quality.

[PLATE 26: Zeppelin-Dornier "Dolphin" Monoplane All Metal
Flying Boat Type DoCsII, 1920 Model.

Zeppelin-Dornier "Dolphin" Monoplane All Metal Flying Boat Type
DoCsII, 1921 Model.

Carries six passengers besides pilot and mechanician. Speed 93
miles per hour, 185 horsepower motor. Gasoline consumption 11.9
gallons per hour. Weight empty 3200 pounds.]

Secondly, referring to the lift, this constructional figure indicates
the relative useful or pay loads carried with the smallest amount of
material used in the ship itself, because the ship, which must also be
carried is "dead weight." As we must consider all ships equal as far as
structural safety is concerned, the t