ut narrow planes; and
these do not beat, like the wings of a bird, but are fixed rigidly on
either side of its body. How is the weight of machine and man borne
through this element we cannot see, and which appears intangible?

The secret is speed--the sheer pace at which an aeroplane passes
through the air. As a craft stands on the ground, its planes are
inoperative. Power lies dormant in the air, but only when it is in
motion, or when some object or apparatus is propelled through it at
high speed. Have you stood on a height, in a gale, and felt an air
wave strike powerfully against your body? The blow is invisible; but
you yield a step, gasping; and, had you wings at such a moment, you
would not doubt the power of the wind to sweep you upward. This is the
force the aeroplane utilises.

If, on a calm day, you accelerate your motor-car to 60 miles an hour,
the air sweeps past you in a powerful stream; just as it would if you
were standing still, and there was a gale of wind. Instead of the wind
possessing the speed, in this instance, it is you who provide it. The
motor of an aeroplane, driving the propeller of the machine, turns
this at 1000 or more revolutions a minute, and causes its curved
blades to screw forward through the air as they turn, like those of a
ship's propeller through water--or a gimlet into wood. The propeller,
as it bores its way into the air, draws or pushes the aeroplane across
the ground; and the speed grows rapidly until the air, sweeping with
an increasing pressure beneath the planes, becomes sufficient to bear
the craft in flight.

But the wing of an aeroplane would not sustain its load unless
designed specially to act upon the air. A man, if he is unlucky enough
to fall from a tall building, passes through the air at a high speed.
His body obtains no support from the air; so he crashes to the ground.
This is because his body is heavy, and presents only a small surface
to the air. To secure a lifting influence from the air, it must be
struck swiftly with a large, light surface.

Men go to Nature when building wings for aeroplanes, and imitate the
birds. The wing of a bird arches upward from front to back, most of
the curve occurring near the forward edge; and this shape, when
applied to an aeroplane wing, is known as its camber. With an
aeroplane wing, if its curve is adjusted precisely, the air not only
thrusts up from below as a machine passes through it, but has a
lifting influence also