which requires no artificial
motor, and many workers believe that success will first come by this
road. I refer to the soaring flight, by which the machine is permanently
sustained in the air by the same means that are employed by soaring
birds. They spread their wings to the wind, and sail by the hour, with
no perceptible exertion beyond that required to balance and steer
themselves. What sustains them is not definitely known, though it is
almost certain that it is a rising current of air. But whether it be a
rising current or something else, it is as well able to support a flying
machine as a bird, if man once learns the art of utilizing it. In
gliding experiments it has long been known that the rate of vertical
descent is very much retarded, and the duration of the flight greatly
prolonged, if a strong wind blows up the face of the hill parallel to
its surface. Our machine, when gliding in still air, has a rate of
vertical descent of nearly six feet per second, while in a wind blowing
26 miles per hour up a steep hill we made glides in which the rate of
descent was less than two feet per second. And during the larger part of
this time, while the machine remained exactly in the rising current,
there was no descent at all, but even a slight rise. If the operator had
had sufficient skill to keep himself from passing beyond the rising
current he would have been sustained indefinitely at a higher point than
that from which he started.

* * * * *

[Illustration]

In looking over our experiments of the past two years, with models and
full-size machines, the following points stand out with clearness:--

1. That the lifting power of a large machine, held stationary in a wind
at a small distance from the earth, is much less than the Lilienthal
table and our own laboratory experiments would lead us to expect. When
the machine is moved through the air, as in gliding, the discrepancy
seems much less marked.

2. That the ratio of drift to lift in well-balanced surfaces is less at
angles of incidence of five degrees to 12 degrees than at an angle of
three degrees.

3. That in arched surfaces the center of pressure at 90 degrees is near
the center of the surface, but moves slowly forward as the angle
becomes less, till a critical angle varying with the shape and depth of
the curve is reached, after which it moves rapidly toward the rear till
the angle of no lift is found.

4. That with similar