on the lower plane. In all their gliding experiments they
studied safety first. They knew that the business they had embarked on
was of necessity a long and dangerous one; that they were bound to
encounter many dangers, and that each of them had only one life. They
took no avoidable risks. Gliding seemed to them, at first, to have been
discredited by the deaths of Lilienthal and Pilcher, so they planned to
try their machine by tethering it with a rope and letting it float a few
feet from the ground, while they practised manipulation. The wind proved
to be not strong enough to sustain the weighted machine, and they were
compelled to take to gliding. All their early glides were made as near
the ground as possible. The machine had no vertical rudder, but they
fitted it, in front, with what they called a horizontal rudder, that is,
an elevator. By the use of this they could bring it to the ground at
once when the wind was tricky and their balance was threatened. The
lateral balance they attempted to control by warping the wings, but with
no satisfactory results. They made glides longer than any on record, but
while the problem of stability was still unsolved, there could be no
real progress. At the end of 1901, Wilbur Wright made the prediction
that men would some time fly, but that it would not be in their
lifetime.

They returned to Dayton, and spent the winter in experiment and
research. They had taken up aeronautics partly as a sport; they were now
drawn deeper and deeper into the scientific study of it. They made a
wind-tunnel, sixteen inches square and about six feet long, and tested
in it the lift and drag of model wings, made in various sizes and with
various aspect ratios. The tables which they compiled from these
experiments were continually used by them thereafter, and superseded
the tables of Lilienthal and Langley, which took no account of the
aspect ratio. When they returned to Kitty Hawk, in the autumn of 1902,
they took with them a greatly improved glider. The aspect ratio of the
planes was six to one, instead of about three to one, as in their second
glider. Further, while preserving the horizontal vane, or elevator, at
the front of the machine, they added a vertical vane, or rudder, at the
rear. It was their failure to control the lateral balance in the
experiments of 1901 that suggested this device to them. From the first
they had discarded the method, practised by Lilienthal and Pilcher, of
adjusting th