ds and developed
one horse-power, which served to drive two airscrews, revolving in
opposite directions. The best flight of this machine was more than
three-quarters of a mile, and was made over the Potomac river. When, on
its first flight, it had flown for a minute, 'I felt', says Professor
Langley, 'that something had been accomplished at last, for never in any
part of the world or in any period had any machine of man's construction
sustained itself in the air before for even half of this brief time'.
His flying machines were called by Langley 'aerodromes', and the word
'aeroplane' was used by him, as it is used in the _New English
Dictionary_ of 1888, only in the sense of a single plane surface used
for aerial experiments. But no usage, however authoritative, can
withstand the tide of popular fashion; the machine is now an aeroplane,
while aerodrome is the name given to the flying-ground from which it
starts.

The success of his machine became widely known, and in 1898 the War
Department of the United States, having ascertained that Langley was
willing to devote all his spare time to the work, allotted fifty
thousand dollars for the development, construction, and test of a large
'aerodrome', big enough to carry a man. The construction was long
delayed by the difficulty of finding a suitable engine. This difficulty
hampered all early attempts at flight. The internal-combustion engine
was by this time pretty well understood, and, with the will to do it,
might have been made light enough for the purpose. But it was almost an
axiom with engineering firms that a very light engine could not wear
well and was untrustworthy in other ways. One horse-power to the
hundredweight was what they regarded as the standard of solid merit.
Further, they were prejudiced against that extremely rapid movement of
the parts which is necessary if the crank-shaft is to revolve more than
a thousand times a minute. They were asked to depart from all their
cherished canons and to risk failure and break-down in order that man
should achieve what many of them regarded as an impossibility. It was
with Langley as it was with Pilcher and the Wrights; he had to make his
own engine. By 1901 he had completed with the aid of his assistants an
engine of fifty-two horse-power, weighing, with all its appurtenances,
less than five pounds to the horse-power. A year and a half more was
spent in adapting and co-ordinating the frame and appliances, and in
carry