imilar to those
used in the Fens for skating races. Upon those runners the machine
moved along the ground when starting to fly. In more modern machines the
chassis is equipped with two or more small rubber-tyred wheels on which
the machine runs along the ground before rising into the air, and on
which it alights when a descent is made.

You will notice that the pilot's seat is fixed on the lower plane,
and almost in the centre of it, while close by the engine is mounted.
Alongside the engine is a radiator which cools the water that has passed
round the cylinder of the engine in order to prevent them from becoming
overheated.

Above the lower plane is a similar plane arranged parallel to it, and
the two are connected by light upright posts of hickory wood known
as STRUTS. Such an aeroplane as this, which is equipped with two main
planes, known as a BIPLANE. Other types of air-craft are the MONOPLANE,
possessing one main plane, and the TRIPLANE, consisting of three planes.
No practical machine has been built with more than three main planes;
indeed, the triplane is now almost obsolete.

The Wrights fitted their machine with two long-bladed wooden screws,
or propellers, which by means of chains and sprocket-wheels, very like
those of a bicycle, were driven by the engine, whose speed was about
1200 revolutions a minute. The first motor engine used by these clever
pioneers had four cylinders, and developed about 20 horsepower. Nowadays
engines are produced which develop more than five times that power.

In later machines one propeller is generally thought to be sufficient;
in fact many constructors believe that there is danger in a
two-propeller machine, for if one propeller got broken, the other
propeller, working at full speed, would probably overturn the machine
before the pilot could cut off his engine.

Beyond the propellers there are two little vertical planes which can
be moved to one side or the other by a control lever in front of the
pilot's seat. These planes or rudders steer the machine from side to
side, answering the same purpose as the rudder of a boat.

In front of the supporting planes there are two other horizontal planes,
arranged one above the other; these are much smaller than the main
planes, and are known as the ELEVATORS. Their function is to raise or
lower the machine by catching the air at different angles.

Comparison with a modern biplane, such as may be seen at an aerodrome
on any "exhibi