the former the entering edge of the plane would be twelve times
as great as in the latter, and the lifting power would
necessarily be much greater. Thus, though both machines have
planes of the same area, each plane having a surface of 144
square feet, yet there is a great difference in the "lift" of the
two.

But it is not to be concluded that the back portion of a plane is
altogether wasted. Numerous experiments have taught aeroplane
constructors that if the plane were slightly curved from front to
back the rear portion of the plane also exercised a "lift"; thus,
instead of the air being simply cut by the entering edge of the
plane, it is driven against the arched back of the plane, and
helps to lift the machine into the air, and support it when in
flight.

There is also a secondary lifting impulse derived from this
simple curve. We have seen that the air which has been cut by
the front edge of the plane pushes up from below, and is arrested
by the top of the arch, but the downward dip of the rear portion
of the plane is of service in actually DRAWING THE AIR FROM
ABOVE. The rapid air stream which has been cut by the entering
edge passes above the top of the curve, and "sucks up", as it
were, so that the whole wing is pulled upwards. Thus there are
two lifting impulses: one pushing up from below, the other
sucking up from above.

It naturally follows that when the camber is very pronounced the
machine will fly much slower, but will bear a greater weight than
a machine equipped with planes having little or no camber. On