The balloon is made of long strips of silk, sewn together, and
rendered air-tight by means of a coating of caoutchouc. A valve
is fitted to the top, and by means of it the aeronaut can descend
to the earth at will, by allowing some quantity of the gas to
escape. The car in which he sits is suspended to the balloon by
a network, which covers the whole structure. Sacks of sand are
carried in this car as ballast, so that, when descending, if the
aeronaut sees that he is likely to be precipitated into the sea
or into a lake, he throws over the sand, and his air-carriage,
being thus lightened, mounts again and travels away to a more
desirable resting-place. The idea of the valve, as well as that
of the sand ballast, is due to the physician Charles. They
enable the aeronaut to ascend or descend with facility. When he
wishes to mount, he throws over his ballast; when he wants to
come down, he lets the gas escape by the valve at the roof of the
balloon. This valve is worked by means of a spring, having a long
rope attached to it, which hangs down through the neck to the
car, where the aeronaut sits.
The operation of inflating a balloon with pure hydrogen is
represented in the engraving on the next page.
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