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.
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