wherein mechanical flight is supposed to be analogous
to bird flight.

SPEED AND SURFACE.--Birds which poise in the
air, like the humming bird, do so because they
beat their wings with great rapidity. Those
which soar, as stated, can do so only by moving
through the atmosphere rapidly, or by having a
large wing spread relative to the weight. It will
thus be seen that speed and surface become the
controlling factors in flight, and that while the
latter may be entirely eliminated from the problem,
speed is absolutely necessary under any and
all conditions.

By speed in this connection is not meant high
velocity, but that a movement, produced by power
expressed in some form, is the sole and most necessary
requisite to movement through the air with
all heavier-than-air machines.

If sufficient power can be applied to an aeroplane,
surface is of no consequence; shape need
not be considered, and any sort of contrivance
will move through the air horizontally.

CONTROL OF THE DIRECTION OF FLIGHT.--But the
control of such a body, when propelled through
space by force alone, is a different matter. To
change the machine from a straight path to a