e wind until the two vanes again secured equal
pressures, which would be at approximately 30 and 50 degrees. But the
vane performed in this very manner. Further corroboration of the tables
was obtained in experiments with the new glider at Kill Devil Hill the
next season.

'In September and October, 1902 nearly 1,000 gliding flights were made,
several of which covered distances of over 600 feet. Some, made against
a wind of 36 miles an hour, gave proof of the effectiveness of the
devices for control. With this machine, in the autumn of 1903, we made
a number of flights in which we remained in the air for over a minute,
often soaring for a considerable time in one spot, without any descent
at all. Little wonder that our unscientific assistant should think the
only thing needed to keep it indefinitely in the air would be a coat of
feathers to make it light!'

It was at the conclusion of these experiments of 1903 that the brothers
concluded they had obtained sufficient data from their thousands of
glides and multitude of calculations to permit of their constructing
and making trial of a power-driven machine. The first designs got out
provided for a total weight of 600 lbs., which was to include the weight
of the motor and the pilot; but on completion it was found that there
was a surplus of power from the motor, and thus they had 150 lbs. weight
to allow for strengthening wings and other parts.

They came up against the problem to which Riach has since devoted so
much attention, that of propeller design. 'We had thought of getting the
theory of the screw-propeller from the marine engineers, and then, by
applying our table of air-pressures to their formulae, of designing
air-propellers suitable for our uses. But, so far as we could learn, the
marine engineers possessed only empirical formulae, and the exact action
of the screw propeller, after a century of use, was still very obscure.
As we were not in a position to undertake a long series of practical
experiments to discover a propeller suitable for our machine, it seemed
necessary to obtain such a thorough understanding of the theory of its
reactions as would enable us to design them from calculation alone.
What at first seemed a simple problem became more complex the longer we
studied it. With the machine moving forward, the air flying backward,
the propellers turning sidewise, and nothing standing still, it seemed
impossible to find a starting point from which to trac