to some gentle slope. In starting from a slope it will be found easier
to keep the machine afloat, but the experience at first is likely to be
very disconcerting to a man of less than iron nerve. As the glider sails
away from the top of the slope the distance between him and the ground
increases rapidly until the aviator thinks he is up a hundred miles
in the air. If he will keep cool, manipulate his apparatus so as to
preserve its equilibrium, and "let nature take its course," he will come
down gradually and safely to the ground at a considerable distance
from the starting place. This is one advantage of starting from an
elevation--your machine will go further.

But, if the aviator becomes "rattled"; if he loses control of his
machine, serious results, including a bad fall with risk of death,
are almost certain. And yet this practice is just as necessary as the
initial lessons on level ground. When judgment is used, and "haste made
slowly," there is very little real danger. While experimenting with
gliders the Wrights made flights innumerable under all sorts of
conditions and never had an accident of any kind.

Effects of Wind Currents.

The larger the machine the more difficult it will be to control its
movements in the air, and yet enlargement is absolutely necessary as
weight, in the form of motor, rudder, etc., is added.

Air currents near the surface of the ground are diverted by every
obstruction unless the wind is blowing hard enough to remove the
obstruction entirely. Take, for instance, the case of a tree or shrub,
in a moderate wind of from ten to twelve miles an hour. As the wind
strikes the tree it divides, part going to one side and part going to
the other, while still another part is directed upward and goes over
the top of the obstruction. This makes the handling of a glider on
an obstructed field difficult and uncertain. To handle a glider
successfully the place of operation should be clear and the wind
moderate and steady. If it is gusty postpone your flight. In this
connection it will be well to understand the velocity of the wind, and
what it means as shown in the following table:

Miles per hour Feet per second Pressure per sq. foot
10 14.7 .492
25 36.7 3.075
50 73.3 12.300
100 146.6 49.200

Pressure of wind increases in proporti