Ader, Maxim, and others, lay principally in
the fact that these latter either did or did not succeed in rising into
the air once, and then, either willingly or by compulsion, gave up
the quest, while Langley repeated his experiments and thus attained to
actual proof of the possibilities of flight. Like these others, however,
he decided in 1896 that he would not undertake the construction of a
large man-carrying machine. In addition to a multitude of actual duties,
which left him practically no time available for original research, he
had as an adverse factor fully ten years of disheartening difficulties
in connection with his model machines. It was President McKinley who, by
requesting Langley to undertake the construction and test of a machine
which might finally lead to the development of a flying machine
capable of being used in warfare, egged him on to his final experiment.
Langley's acceptance of the offer to construct such a machine is
contained in a letter addressed from the Smithsonian Institution on
December 12th, 1898, to the Board of Ordnance and Fortification of the
United States War Department; this letter is of such interest as to
render it worthy of reproduction:--

'Gentlemen,--In response to your invitation I repeat what I had the
honour to say to the Board--that I am willing, with the consent of the
Regents of this Institution, to undertake for the Government the further
investigation of the subject of the construction of a flying machine
on a scale capable of carrying a man, the investigation to include the
construction, development and test of such a machine under conditions
left as far as practicable in my discretion, it being understood that my
services are given to the Government in such time as may not be occupied
by the business of the Institution, and without charge.

'I have reason to believe that the cost of the construction will come
within the sum of $50,000.00, and that not more than one-half of that
will be called for in the coming year.

'I entirely agree with what I understand to be the wish of the Board
that privacy be observed with regard to the work, and only when it
reaches a successful completion shall I wish to make public the fact of
its success.

'I attach to this a memorandum of my understanding of some points of
detail in order to be sure that it is also the understanding of the
Board, and I am, gentlemen, with much respect, your obedient servant, S.
P. Langley.'

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