medal
to Stephen, the younger brother. It was to heated or rarified air that
these balloons owed their ascending power; but the Montgolfiers, in the
paper in which they communicated their discovery to the Royal Academy,
erroneously attributed the ascending power, not to the rarified air in
the balloon, but to a peculiar gas they supposed to be evolved by the
combustion of chopped straw and wool mixed together, to which the name
of Montgolfiers' gas was given, it being believed for a time, even by
the members of the Academy, that a new kind of gas, different from
hydrogen, and lighter than common air, had been discovered.

Hydrogen gas, or, as it was also called, inflammable air, whose specific
gravity was first discovered in 1766, by Henry Cavendish, though the gas
itself had been known long before to coal-miners, from its fatal
effects, was, from its being the lightest gas known, early taken
advantage of for inflating balloons. It indeed occurred to the ingenious
Dr. Black of Edinburgh, as soon as he read Mr. Cavendish's paper, which
appeared in the Philosophical Transactions for 1766, that if a
sufficiently thin and light bladder were filled with this gas, the
bladder would necessarily ascend in the atmosphere, as it would form a
mass lighter than the same bulk of atmospheric air. Not long after, it
suggested itself to Tiberius Cavallo, an Italian philosopher, when he
first began to study the subject of air, that it was possible to
construct a vessel which, when filled with hydrogen gas, would ascend in
the atmosphere. In 1782, he actually attempted to perform the
experiment, though the only success he had was to let soap balls, filled
with that gas, ascend by themselves rapidly in the air, which, says he,
were perhaps the first sort of inflammable air balloons ever made; and
he read an account of his experiments to the Royal Society at their
public meeting on June 20, 1782. But, during the later part of the year
1783, two gentlemen in the city of Philadelphia actually tested the
value of hydrogen gas as a means of inflating balloons. The French
Academy, guided by the suggestion of Dr. Black, and the experiments of
Cavallo, also concluded to make the experiment of raising a balloon
inflated with the same gas. To defray the expense of the undertaking, a
subscription was opened, and so great was the enthusiasm excited by the
design among people of all ranks and classes, that the requisite sum was
speedily subscribed for