special paper bags. In these latter the gas escaped,
and Cavallo was about to try goldbeaters' skin at the time that the
Montgolfiers came into the field with their hot air balloon.

Joseph and Stephen Montgolfier, sons of a wealthy French paper
manufacturer, carried out many experiments in physics, and Joseph
interested himself in the study of aeronautics some time before the
first balloon was constructed by the brothers--he is said to have made
a parachute descent from the roof of his house as early as 1771, but
of this there is no proof. Galien's idea, together with study of the
movement of clouds, gave Joseph some hope of achieving aerostation
through Galien's schemes, and the first experiments were made by passing
steam into a receiver, which, of course, tended to rise--but the
rapid condensation of the steam prevented the receiver from more than
threatening ascent. The experiments were continued with smoke, which
produced only a slightly better effect, and, moreover, the paper 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