nd for
which they insist upon implicit obeyance, is: "If your machine gets more
than 30 feet high, or comes closer to the ground than 6 feet, descend at
once." Such men as Wright and Curtiss will not tolerate a violation of
this rule. If their instructions are not strictly complied with they
decline to give the offender further lessons.

Why This Rule Prevails.

There is good reason for this precaution. The higher the altitude the
more rarefied (thinner) becomes the air, and the less sustaining power
it has. Consequently the more difficult it becomes to keep in suspension
a given weight. When sailing within 30 feet of the ground sustentation
is comparatively easy and, should a fall occur, the results are not
likely to be serious. On the other hand, sailing too near the ground
is almost as objectionable in many ways as getting up too high. If the
craft is navigated too close to the ground trees, shrubs, fences and
other obstructions are liable to be encountered. There is also the
handicap of contrary air currents diverted by the obstructions referred
to, and which will be explained more fully further on.

How to Make a Start.

Taking it for granted that the beginner has familiarized himself with
the manipulation of the machine, and especially the control mechanism,
the next thing in order is an actual flight. It is probable that his
machine will be equipped with a wheeled alighting gear, as the skids
used by the Wrights necessitate the use of a special starting track.
In this respect the wheeled machine is much easier to handle so far as
novices are concerned as it may be easily rolled to the trial grounds.
This, as in the case of the initial experiments, should be a clear,
reasonably level place, free from trees, fences, rocks and similar
obstructions with which there may be danger of colliding.

The beginner will need the assistance of three men. One of these should
take his position in the rear of the machine, and one at each end. On
reaching the trial ground the aviator takes his seat in the machine and,
while the men at the ends hold it steady the one in the rear assists in
retaining it until the operator is ready. In the meantime the aviator
has started his motor. Like the glider the flying machine, in order to
accomplish the desired results, should be headed into the wind.

When the Machine Rises.

Under the impulse of the pushing movement, and assisted by the motor
action, the machine will gradually rise