e with the Langley coefficient would be
0.16 pounds per square foot, we have on 4.57 square feet for energy of
rising air: 4.57 X 0.16 X 10.26 = 7.50 foot pounds per second, which
is seen to be still a little too small, but well within the limits of
error, in view of the hollow shape of the bird's wings, which receive
greater pressure than the flat planes experimented upon by Langley.

These computations were chiefly made in January, 1899, and were
communicated to a few friends, who found no fallacy in them, but thought
that few aviators would understand them if published. They were then
submitted to Professor C. F. Marvin of the Weather Bureau, who is well
known as a skillful physicist and mathematician. He wrote that they
were, theoretically, entirely sound and quantitatively, probably, as
accurate as the present state of the measurements of wind pressures
permitted. The writer determined, however, to withhold publication until
the feat of soaring flight had been performed by man, partly because he
believed that, to ensure safety, it would be necessary that the machine
should be equipped with a motor in order to supplement any deficiency in
wind force.

Conditions Unfavorable for Wrights.

The feat would have been attempted in 1902 by Wright brothers if the
local circumstances had been more favorable. They were experimenting on
"Kill Devil Hill," near Kitty Hawk, N. C. This sand hill, about 100
feet high, is bordered by a smooth beach on the side whence come the
sea breezes, but has marshy ground at the back. Wright brothers were
apprehensive that if they rose on the ascending current of air at the
front and began to circle like the birds, they might be carried by the
descending current past the back of the hill and land in the marsh.
Their gliding machine offered no greater head resistance in proportion
than the buzzard, and their gliding angles of descent are practically as
favorable, but the birds performed higher up in the air than they.

Langley's Idea of Aviation.

Professor Langley said in concluding his paper upon "The Internal Work
of the Wind":

"The final application of these principles to the art of aerodromics
seems, then, to be, that while it is not likely that the perfected
aerodrome will ever be able to dispense altogether with the ability
to rely at intervals on some internal source of power, it will not be
indispensable that this aerodrome of the future shall, in order to go
any distance--even