of gliding machines, some of which
had as many as half a dozen planes arranged one above another. His best
results, however, were obtained by the two-plane machine, resembling to
a remarkable extent the modern biplane.

CHAPTER XVII. The Aeroplane and the Bird

We have seen that the inventors of flying machines in the early days of
aviation modelled their various craft somewhat in the form of a bird,
and that many of them believed that if the conquest of the air was to be
achieved man must copy nature and provide himself with wings.

Let us closely examine a modern monoplane and discover in what way it
resembles the body of a bird in build.

First, there is the long and comparatively narrow body, or FUSELAGE, at
the end of which is the rudder, corresponding to the bird's tail. The
chassis, or under carriage, consisting of wheels, skids, &c., may well
be compared with the legs of a bird, and the planes are very similar
in construction to the bird's wings. But here the resemblance ends: the
aeroplane does not fly, nor will it ever fly, as a bird flies.

If we carefully inspect the wing of a bird--say a large bird, such as
the crow--we shall find it curved or arched from front to back. This
curve, however, is somewhat irregular. At the front edge of the wing
it is sharpest, and there is a gradual dip or slope backwards and
downwards. There is a special reason for this peculiar structure, as we
shall see in a later chapter.

Now it is quite evident that the inventors of aeroplanes have
modelled the planes of their craft on the bird's wing. Strictly
speaking, the word "plane" is a misnomer when applied to the supporting
structure of an aeroplane. Euclid defines a plane, or a plane surface,
as one in which, any two points being taken, the straight line between
them lies wholly in that surface. But the plane of a flying machine is
curved, or CAMBERED, and if one point were taken on the front of the
so-called plane, and another on the back, a straight line joining these
two points could not possibly lie wholly on the surface.

All planes are not cambered to the same extent: some have a very small
curvature; in others the curve is greatly pronounced. Planes of the
former type are generally fitted to racing aeroplanes, because they
offer less resistance to the air than do deeply-cambered planes. Indeed,
it is in the degree of camber that the various types of flying machine
show their chief diversity, just as the work