s capital was
exhausted.

So he put the money into a bank whence he could draw it out as he
chose, and withdrew himself from the world to work out the ideal of
his life.

Year after year passed, and still success did not come. He found
practice very different from theory, and in a hundred details he met
with difficulties he had never seen on paper. Meanwhile his money
melted away in costly experiments which only raised hopes that ended
in bitter disappointment. His wonderful machine was a miracle of
ingenuity, and was mechanically perfect in every detail save one--it
would do no practical work.

Like every other inventor who had grappled with the problem, he had
found himself constantly faced with that fatal ratio of weight to
power. No engine that he could devise would do more than lift itself
and the machine. Again and again he had made a toy that would fly, as
others had done before him, but a machine that would navigate the air
as a steamer or an electric vessel navigated the waters, carrying
cargo and passengers, was still an impossibility while that terrible
problem of weight and power remained unsolved.

In order to eke out his money to the uttermost, he had clothed and
lodged himself meanly, and had denied himself everything but the
barest necessaries of life.

Thus he had prolonged the struggle for over five years of toil and
privation and hope deferred, and now, when his last sovereign had
been changed and nearly spent, success--real, tangible, practical
success--had come to him, and the discovery that was to be to the
twentieth century what the steam-engine had been to the nineteenth
was accomplished.

He had discovered the true motive power at last.

Two liquefied gases--which, when united, exploded spontaneously--were
admitted by a clockwork escapement in minute quantities into the
cylinders of his engine, and worked the pistons by the expansive
force of the gases generated by the explosion. There was no weight
but the engine itself and the cylinders containing the liquefied
gases. Furnaces, boilers, condensers, accumulators, dynamos--all the
ponderous apparatus of steam and electricity--were done away with,
and he had a power at command greater than either of them.

There was no doubt about it. The moment that his trembling fingers
set the escapement mechanism in motion, the model that embodied the
thought and labour of years rose into the air as gracefully as a bird
on the wing, and sailed rou