That the swifter the wing beat, the more efficient its effect per unit
of surface, the greater the load carried, and the swifter the flight.
That the screw action being, in full flight, that of a screw propeller
whose axis of rotation forms a slight angle with the vertical, the
distance of flight per virtual "revolution" of "screw" wing far
exceeds the pitch distance of said "screw."
That consequently a bird's flight answers to an iceboat close hauled;
the wing _force_ answering to the _wind_, the wing _angle_ to the
_sail_, the bird's _weight_ to the leeway fulcrum of the _ice_, and
the passage across direction of the _wing_ flop to the fresh _moving_
"inertia" of the wind, both yielding a maximum of force to bird or
iceboat.
That the speed of _reciprocation_ of a fly's _wing_ being equivalent
to a _screw rotation_ of 9,000 per minute, proves that a _screw_ may
be run at this speed without losing efficiency by centrifugal vacuum.
That as the _object_ of wing or screw is to mount upon the inertia of
the particles of a mobile fluid, and as the rotation of steamship
propellers in water--a fluid of many times the inertia of air--is
_already_ in _excess_ of the highest speed heretofore tried in the
propellers of moderately successful flying machines, it is plain that
the speed employed in _water_ must be many times exceeded in _air_.
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