of people were
gathered together on the outskirts of Paris to witness the risky feat.
The balloon made a perfect ascent, and quickly reached a height of
about half a mile above sea-level. A strong current of air in the upper
regions caused the balloon to take an opposite direction from that
intended, and the aeronauts drifted right over Paris. It would have gone
hard with them if they had been forced to descend in the city, but the
craft was driven by the wind to some distance beyond the suburbs and
they alighted quite safely about six miles from their starting-point,
after having been up in the air for about half an hour.

Their voyage, however, had by no means been free from anxiety. We are
told that the fabric of the balloon repeatedly caught fire, which it
took the aeronauts all their time to extinguish. At times, too, they
came down perilously near to the Seine, or to the housetops of Paris,
but after the most exciting half-hour of their lives they found
themselves once more on Mother Earth.

Here we must make a slight digression and speak of the invention of
the hydrogen, or gas, balloon. In a previous chapter we read of the
discovery of hydrogen gas by Henry Cavendish, and the subsequent
experiments with this gas by Dr. Black, of Glasgow. It was soon
decided to try to inflate a balloon with this "inflammable air"--as
the newly-discovered gas was called--and with this end in view a large
public subscription was raised in France to meet the heavy expenses
entailed in the venture. The work was entrusted to a French scientist,
Professor Charles, and two brothers named Robert.

It was quickly seen that paper, such as was used by the Montgolfiers,
was of little use in the construction of a gas balloon, for the gas
escaped. Accordingly the fabric was made of silk and varnished with a
solution of india-rubber and turpentine. The first hydrogen balloon was
only about 13 feet in diameter, for in those early days the method of
preparing hydrogen was very laborious and costly, and the constructors
thought it advisable not to spend too much money over the initial
experiments, in case they should be a failure.

In August, 1783--an eventful year in the history of aeronautics--the
first gas-inflated balloon was sent up, of course unaccompanied by
a passenger. It shot up high in the air much more rapidly than
Montgolfier's hot-air balloon had done, and was soon beyond the clouds.
After a voyage of nearly an hour's duration i