ance 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_.

That with a _sufficient_ speed of rotation, the supporting power of
the inertia of air must _equal_ that of _water_.

That as mere speed of rotation of propeller _shaft_, minus blades,
must absorb but a small proportion of power of engine, the addition of
blades will not cause more resistance than that actually encountered
from inertia of air.

That this must be the measure of load lifted.

That without _slip_ of screw, the actual _power_ expended, will be
little in _excess_ of that required to support the machine in _water_,
with a slower rotation of screw.

That in case the same _power_ is expended in water or air, the only
difference will lie in the sizes and speed of engines or screws.

That the _greater_ the speed, the _less_ weight of engine, boiler, and
screw must be, and the stronger their construction.

That, in consequence, solid metal worked down, instead of bolts and
truss work, must be used.

That as the bird wing is a screw in action, and acts _directly_
between the inertias of the load and the air, the position and
operation of the screw, to the load, must imitate it.

That, in consequence, machines having wing planes, driven _against_
one inertia of air by screws acting in the line, of flight against
another inertia of air, lose fifty per cent. of useful effect, besides
exposing to a head wind the cross section of the stationary screw wing
planes and the rotating screw discs; and supporting the dead weight of
the wing