as ascertained by watching thistledown, and rising
fogs alongside of trees or hills of known height. Everyone will readily
realize that when walking at the rate of four to eight miles an hour in
a dead calm the "relative wind" is quite inappreciable to the senses and
that such a rising air would not be noticed.

2nd.--That the buzzard, sailing in an apparently dead horizontal calm,
progressed at speeds of fifteen to eighteen miles per hour, as measured
by his shadow on the ground. It was thought that the air was then
possibly rising 8.8 feet per second, or six miles per hour.

3rd.--That when soaring in very light winds the angle of incidence of
the buzzards was negative to the horizon--i. e., that when seen coming
toward the eye, the afternoon light shone on the back instead of on the
breast, as would have been the case had the angle been inclined above
the horizon.

4th.--That the sailing performance only occurred after the bird had
acquired an initial velocity of at least fifteen or eighteen miles per
hour, either by industrious flapping or by descending from a perch.

An Interesting Experiment.

5th.--That the whole resistance of a stuffed buzzard, at a negative
angle of 3 degrees in a current of air of 15.52 miles per hour, was 0.27
pounds. This test was kindly made for the writer by Professor A. F. Zahm
in the "wind tunnel" of the Catholic University at Washington, D. C.,
who, moreover, stated that the resistance of a live bird might be less,
as the dried plumage could not be made to lie smooth.

This particular buzzard weighed in life 4.25 pounds, the area of his
wings and body was 4.57 square feet, the maximum cross-section of
his body was 0.110 square feet, and that of his wing edges when fully
extended was 0.244 square feet.

With these data, it became surprisingly easy to compute the performance
with the coefficients of Lilienthal for various angles of incidence
and to demonstrate how this buzzard could soar horizontally in a dead
horizontal calm, provided that it was not a vertical calm, and that the
air was rising at the rate of four or six miles per hour, the lowest
observed, and quite inappreciable without actual measuring.

Some Data on Bird Power.

The most difficult case is purposely selected. For if we assume that the
bird has previously acquired an initial minimum speed of seventeen miles
an hour (24.93 feet per second, nearly the lowest measured), and that
the air was rising vertically six