bag into which the smoke was induced permitted of escape through
its pores; finding this method a failure the brothers desisted
until Priestley's work became known to them, and they conceived
the use of hydrogen as a lifting factor. Trying this with paper
bags, they found that the hydrogen escaped through the pores of
the paper.

Their first balloon, made of paper, reverted to the hot-air
principle; they lighted a fire of wool and wet straw under the
balloon--and as a matter of course the balloon took fire after
very little experiment; thereupon they constructed a second,
having a capacity of 700 cubic feet, and this rose to a height
of over 1,000 feet. Such a success gave them confidence, and
they gave their first public exhibition on June 5th, 1783, with
a balloon constructed of paper and of a circumference of 112
feet. A fire was lighted under this balloon, which, after
rising to a height of 1,000 feet, descended through the cooling
of the air inside a matter of ten minutes. At this the Academie
des Sciences invited the brothers to conduct experiments in
Paris.

The Montgolfiers were undoubtedly first to send up balloons, but
other experimenters were not far behind them, and before they
could get to Paris in response to their invitation, Charles, a
prominent physicist of those days, had constructed a balloon of
silk, which he proofed against escape of gas with rubber--the
Roberts had just succeeded in dissolving this substance to
permit of making a suitable coating for the silk. With a
quarter of a ton of sulphuric acid, and half a ton of iron
filings and turnings, sufficient hydrogen was generated in four