e the various
simultaneous reactions. Contemplation of it was confusing. After long
arguments we often found ourselves in the ludicrous position of each
having been converted to the other's side, with no more agreement than
when the discussion began.

'It was not till several months had passed, and every phase of the
problem had been thrashed over and over, that the various reactions
began to untangle themselves. When once a clear understanding had been
obtained there was no difficulty in designing a suitable propeller, with
proper diameter, pitch, and area of blade, to meet the requirements of
the flier. High efficiency in a screw-propeller is not dependent upon
any particular or peculiar shape, and there is no such thing as a "best"
screw. A propeller giving a high dynamic efficiency when used upon one
machine may be almost worthless when used upon another. The propeller
should in every case be designed to meet the particular conditions of
the machine to which it is to be applied. Our first propellers, built
entirely from calculation, gave in useful work 66 per cent of the power
expended. This was about one-third more than had been secured by Maxim
or Langley.'

Langley had made his last attempt with the 'aerodrome,' and his splendid
failure but a few days before the brothers made their first attempt at
power-driven aeroplane flight. On December 17th, 1903, the machine was
taken out; in addition to Wilbur and Orville Wright, there were present
five spectators: Mr A. D. Etheridge, of the Kill Devil life-saving
station; Mr W. S.Dough, Mr W. C. Brinkley, of Manteo; Mr John Ward, of
Naghead, and Mr John T. Daniels.[*] A general invitation had been given
to practically all the residents in the vicinity, but the Kill Devil
district is a cold area in December, and history had recorded so many
experiments in which machines had failed to leave the ground that
between temperature and scepticism only these five risked a waste of
their time.

[*] This list is as given by Wilbur Wright himself.

And these five were in at the greatest conquest man had made since James
Watt evolved the steam engine--perhaps even a greater conquest than that
of Watt. Four flights in all were made; the first lasted only twelve
seconds, 'the first in the history of the world in which a machine
carrying a man had raised itself into the air by its own power in free
flight, had sailed forward on a level course without reduction of
speed, and had fina