=Wire, Cross Bracing=--A bracing wire, the position of which is diagonal
from right to left when viewing it from the front of an aeroplane. [49]

=Wire, Control Bracing=--A wire preventing distortion of a controlling
surface. [50]

=Wire, Control=--A wire connecting a controlling surface with the pilot's
control lever, wheel, or rudder-bar. [51]

=Wire, Aileron Gap=--A wire connecting top and bottom ailerons. [52]

=Wire, Aileron Balance=--A wire connecting the right- and left-hand top
ailerons. Sometimes termed the "aileron compensating wire." [53]

=Wire, Snaking=--A wire, usually of soft metal, wound spirally or tied
round another wire, and attached at each end to the framework. Used to
prevent the wire round which it is "snaked" from becoming, in the event
of its displacement, entangled with the propeller.

=Wire, Locking=--A wire used to prevent a turnbuckle barrel or other
fitting from losing its adjustment.

=Wing=--Strictly speaking, a wing is one of the surfaces of an
ornithopter. The term is, however, often applied to the lifting surface
of an aeroplane when such surface is divided into two parts, one being
the left-hand "wing," and the other the right-hand "wing."

=Wind-Tunnel=--A large tube used for experimenting with surfaces and
models, and through which a current of air is made to flow by artificial
means.

=Work=--Force x displacement.

=Wind-Screen=--A small transparent screen mounted in front of the pilot
to protect his face from the air pressure.

Types of Aeroplanes.

[Illustration: Plate I.]

The first machine to fly--of which there is anything like authentic
record--was the Ader "Avion," after which the more notable advances were
made as shown above.

[Illustration: Plate II.]

The Henri Farman was the first widely used aeroplane. Above are shown
the chief steps in its development.

[Illustration: Plate III.]

THE AVRO.--The aeroplane designed and built by Mr. A. V. Roe was the
first successful heavier-than-air flying machine built by a British
subject. Mr. Roe's progress may be followed in the picture, from his
early "canard" biplane, through various triplanes, with 35 J.A.P. and 35
h.p. Green engines, to his successful tractor biplane with the same 35
h.p. Green, thence through the "totally enclosed" biplane 1912, with 60
h.p. Green, to the biplane 1913-14, with 80 h.p. Gnome.

[Illustration: Plate IV.]

THE SOPWITH LAND-GOING BIPLANES.--The earliest w