eriment, we cast it all aside, and decided to rely entirely
upon our own investigations. Truth and error were everywhere so
intimately mixed as to be undistinguishable. Nevertheless, the time
expended in preliminary study of books was not misspent, for they gave
us a good general understanding of the subject, and enabled us at the
outset to avoid effort in many directions in which results would have
been hopeless.

The standard measurements of wind-pressures is the force produced by a
current of air of one mile per hour velocity striking square against a
plane of one square foot area. The practical difficulties of obtaining
an exact measurement of this force have been great. The measurements by
different recognized authorities vary 50 per cent. When this simplest of
measurements presents so great difficulties, what shall be said of the
troubles encountered by those who attempt to find the pressure at each
angle as the plane is inclined more and more edgewise to the wind? In
the eighteenth century the French Academy prepared tables giving such
information, and at a later date the Aeronautical Society of Great
Britain made similar experiments. Many persons likewise published
measurements and formulas; but the results were so discordant that
Professor Langley undertook a new series of measurements, the results
of which form the basis of his celebrated work, "Experiments in
Aerodynamics." Yet a critical examination of the data upon which he
based his conclusions as to the pressures at small angles shows
results so various as to make many of his conclusions little better
than guesswork.

To work intelligently, one needs to know the effects of a multitude
of variations that could be incorporated in the surfaces of flying
machines. The pressures on squares are different from those on
rectangles, circles, triangles, or ellipses; arched surfaces differ
from planes, and vary among themselves according to the depth of
curvature; true arcs differ from parabolas, and the latter differ
among themselves; thick surfaces differ from thin, and surfaces
thicker in one place than another vary in pressure when the positions
of maximum thickness are different; some surfaces are most efficient
at one angle, others at other angles. The shape of the edge also makes
a difference, so that thousands of combinations are possible in so
simple a thing as a wing.

We had taken up aeronautics merely as a sport. We reluctantly entered
upon the scien