Soaring Power of Birds.
The writer of this paper published in the
"Aeronautical
Annual" for 1896 and 1897 an article upon the sailing
flight of birds, in which he gave a list of the authors who
had described such flight or had advanced theories for its explanation,
and he passed these in review. He also described his own observations
and submitted some computations to account for the observed facts. These
computations were correct as far as they went, but they were scanty. It
was, for instance, shown convincingly by analysis that a gull weighing
2.188 pounds, with a total supporting surface of 2.015 square feet, a
maximum body cross-section of 0.126 square feet and a maximum
cross-section of wing edges of 0.098 square feet, patrolling on rigid
wings (soaring) on the weather side of a steamer and maintaining an
upward angle or attitude of 5 degrees to 7 degrees above the horizon, in
a wind blowing 12.78 miles an hour, which was deflected upward 10
degrees to 20 degrees by the side of the steamer (these all being
carefully observed facts), was perfectly sustained at its own "relative
speed" of 17.88 miles per hour and extracted from the upward trend of
the wind sufficient energy to overcome all the resistances, this energy
amounting to 6.44 foot-pounds per second.
