The brothers, like all inventors, seem to have had enquiring minds.
They were for ever asking the why and the wherefore of things. "Why
does smoke rise?" they asked. "Is there not some strange power in the
atmosphere which makes the smoke from chimneys and elsewhere rise in
opposition to the force of gravity? If so, cannot we discover this
power, and apply it to the service of mankind?"

We may imagine that such questions were in the minds of those two French
paper-makers, just as similar questions were in the mind of James
Watt when he was discovering the power of steam. But one of the most
important attributes of an inventor is an infinite capacity for taking
pains, together with great patience.

And so we find the two brothers employing their leisure in what to us
would, be a childish pastime, the making of paper balloons. The story
tells us that their room was filled with smoke, which issued from the
windows as though the house were on fire. A neighbour, thinking such
was the case, rushed in, but, on being assured that nothing serious was
wrong, stayed to watch the tiny balloons rise a little way from the thin
tray which contained the fire that made the smoke with which the bags
were filled. The experiments were not altogether successful, however,
for the bags rarely rose more than a foot or so from the tray. The
neighbour suggested that they should fasten the thin tray on to the
bottom of the bag, for it was thought that the bags would not ascend
higher because the smoke became cool; and if the smoke were imprisoned
within the bag much better results would be obtained. This was done,
and, to the great joy of the brothers and their visitor, the bag at once
rose quickly to the ceiling.

But though they could make the bags rise their great trouble was that
they did not know the cause of this ascent. They thought, however, that
they were on the eve of some great discovery, and, as events proved,
they were not far wrong. For a time they imagined that the fire they had
used generated some special gas, and if they could find out the nature
of this gas, and the means of making it in large quantities, they would
be able to add to their success.

Of course, in the light of modern knowledge, it seems strange that the
brothers did not know that the reason the bags rose, was not because of
any special gas being used, but owing to the expansion of air under the
influence of heat, whereby hot air tends to rise. Every schoolb