problem of flight had long been a subject of interested
speculation with him. Ten years later he wrote:

"Nature has made her flying-machine in the bird, which is nearly a
thousand times as heavy as the air its bulk displaces, and only those
who have tried to rival it know how inimitable her work is, for the "way
of a bird in the air" remains as wonderful to us as it was to Solomon,
and the sight of the bird has constantly held this wonder before men's
minds, and kept the flame of hope from utter extinction, in spite of
long disappointment. I well remember how, as a child, when lying in a
New England pasture, h watched a hawk soaring far up in the blue, and
sailing for a long time without any motion of its wings, as though it
needed no work to sustain it, but was kept up there by some miracle.
But, however sustained, I saw it sweep in a few seconds of its leisurely
flight, over a distance that to me was encumbered with every sort of
obstacle, which did not exist for it.... How wonderfully easy, too, was
its flight! There was not a flutter of its pinions as it swept over the
field, in a motion which seemed as effortless as that of its shadow.
After many years and in mature life, I was brought to think of these
things again, and to ask myself whether the problem of artificial
flight was as hopeless and as absurd as it was then thought to be"...
In three or four years Langley made nearly forty models. "The primary
difficulty lay in making the model light enough and sufficiently
strong to support its power," he says. "This difficulty continued to be
fundamental through every later form; but, beside this, the adjustment
of the center of gravity to the center of pressure of the wings, the
disposition of the wings themselves, the size of the propellers, the
inclination and number of the blades, and a great number of other
details, presented themselves for examination."

By 1891 Langley had a model light enough to fly, but proper balancing
had not been attained. He set himself anew to find the practical
conditions of equilibrium and of horizontal flight. His experiments
convinced him that "mechanical sustenation of heavy bodies in the air,
combined with very great speeds, is not only possible, but within the
reach of mechanical means we actually possess."

After many experiments with new models Langley at length fashioned a
steam-driven machine which would fly horizontally. It weighed about
thirty pounds; it was some sixteen