cannot be made much lower. It is a common mistake to assume that
complete stability will be secured by hanging the center of gravity very
low on the principle of the parachute. An aeroplane depends upon rapid
horizontal motion for its support, and if the center of gravity be far
below the center of support, every change of speed or wind pressure will
cause the machine to turn about its center of gravity, pitching forward
and backward dangerously.

Preserving Longitudinal Balance.

"The birds maintain longitudinal, or fore and aft balance, by elevating
or depressing their tails. Whether this action is secured in an
aeroplane by means of a horizontal rudder placed in the rear, or by
deflecting planes placed in front of the main planes, the principle is
evidently the same. A horizontal rudder placed well to the rear as in
the Antoinette, Bleriot or Santos-Dumont monoplanes, will be very much
safer and steadier than the deflecting planes in front, as in the Wright
or Curtiss biplanes, but not so sensitive or prompt in action.

"The natural fore and aft stability is very much strengthened by placing
the load well forward. The center of gravity near the front and a
tail or rudder streaming to the rear secures stability as an arrow is
balanced by the head and feathering. The adoption of this principle
makes it almost impossible for the aeroplane to turn over.

The Matter of Lateral Balance.

"All successful aeroplanes thus far have maintained lateral balance by
the principle of changing the angle of incidence of the wings.

"Other ways of maintaining the lateral balance, suggested by observation
of the flight of birds are--extending the wing tips and spilling the air
through the pinions; or, what is the same thing, varying the area of the
wings at their extremities.

"Extending the wing tips seems to be a simple and effective solution of
the problem. The tips may be made to swing outward upon a vertical axis
placed at the front edge of the main planes; or they may be hinged to
the ends of the main plane so as to be elevated or depressed through
suitable connections by the aviator; or they may be supported from a
horizontal axis parallel with the ends of the main planes so that they
may swing outward, the aviator controlling both tips through one lever
so that as one tip is extended the other is retracted.

"The elastic wing pinions of a bird bend easily before the wind,
permitting the gusts to glance off, but presentin