was greater than the weight of tire covering of the balloon.
Therefore the balloon mounted.

And, seeing that air diminishes in density the higher we ascend,
the balloon can rise only to that stratum of air of the same
density as the air it contains. As the warm air cools it gently
descends. Again, as the atmosphere is always moving in currents
more or less strong, the balloon follows the direction of the
current of the stratum of air in which it finds itself.

Thus we see how simply the ascent of Montgolfiers, and their
motions, are explained. It is the same with gas-balloons. A
balloon, filled with hydrogen gas, displaces an equal volume of
atmospheric air; but as the gas is much lighter than the air, it
is pushed up by a force equal to the difference of the density of
air and hydrogen gas. The balloon then rises in the atmosphere
to where it reaches layers of air of a density exactly equal to
its own, and when it gets there it remains poised in its place.
In order that it may descend, it is necessary to let out a
portion of the hydrogen gas, and admit an equal quantity of
atmospheric air; and the balloon does not come to the ground till
all, or nearly all, the gas has been expelled and common air
taken in. Balloons inflated with hydrogen gas are almost the
only ones in use at the present day. Scarcely ever is a
Montgolfier sent up. There are aeronauts, however, who prefer a
journey in a Montgolfier to one in a gas-balloon. The air
voyager in this description of balloon had formerly many
difficulties to contend with. The quantity of combustible
material which he was bound to carry with him; the very little
difference that there is between the density of heated and of