miles an hour (8.80 feet per second),
then we have as the trend of the "relative wind" encountered:

6
-- = 0.353, or the tangent of 19 degrees 26'.
17

which brings the case into the category of rising wind effects. But the
bird was observed to have a negative angle to the horizon of about 3
degrees, as near as could be guessed, so that his angle of incidence to
the "relative wind" was reduced to 16 degrees 26'.

The relative speed of his soaring was therefore:

Velocity = square root of (17 squared + 6 squared) = 18.03 miles per
hour.

At this speed, using the Langley co-efficient recently practically
confirmed by the accurate experiments of Mr. Eiffel, the air pressure
would be:

18.03 squared X 0.00327 = 1.063 pounds per square foot.

If we apply Lilienthal's co-efficients for an angle of 6 degrees 26', we
have for the force in action:

Normal: 4.57 X 1.063 X 0.912 = 4.42 pounds.

Tangential: 4.57 X 1.063 X 0.074 = - 0.359 pounds,
which latter, being negative, is a propelling force.

Results Astonish Scientists.

Thus we have a bird weighing 4.25 pounds not only thoroughly supported,
but impelled forward by a force of 0.359 pounds, at seventeen miles
per hour, while the experiments of Professor A. F. Zahm showed that the
resistance at 15.52 miles per hour was only 0.27 pounds,

17 squared
or 0.27 X ------- = 0.324 pounds, at seventeen miles an
15.52 squared
hour.

These are astonishing results from the data obtained, and they lead to
the inquiry whether the energy of the rising air is sufficient to make
up the losses which occur by reason of the resistance and friction of
the bird's body and wings, which, being rounded, do not encounter air
pressures in proportion to their maximum cross-section.

We have no accurate data upon the co-efficients to apply and estimates
made by myself proved to be much smaller than the 0.27 pounds resistance
measured by Professor Zahm, so that we will figure with the latter as
modified. As the speed is seventeen miles per hour, or 24.93 feet per
second, we have for the work:

Work done, 0.324 X 24.93 = 8.07 foot pounds per second.

Endorsed by Prof. Marvin.

Corresponding energy of rising air is not sufficient at four miles per
hour. This amounts to but 2.10 foot pounds per second, but if we assume
that the air was rising at the rate of seven miles per hour (10.26 feet
per second), at which the pressur