aerostatic experiments.

The doctor, according to very accurate calculations,
found that, including the articles indispensable to his
journey and his apparatus, he should have to carry a weight
of 4,000 pounds; therefore he had to find out what would
be the ascensional force of a balloon capable of raising such
a weight, and, consequently, what would be its capacity.

A weight of four thousand pounds is represented by
a displacement of the air amounting to forty-four thousand
eight hundred and forty-seven cubic feet; or, in other
words, forty-four thousand eight hundred and forty-seven
cubic feet of air weigh about four thousand pounds.

By giving the balloon these cubic dimensions, and filling
it with hydrogen gas, instead of common air--the former
being fourteen and a half times lighter and weighing
therefore only two hundred and seventy-six pounds--a
difference of three thousand seven hundred and twenty-four
pounds in equilibrium is produced; and it is this
difference between the weight of the gas contained in the
balloon and the weight of the surrounding atmosphere
that constitutes the ascensional force of the former.

However, were the forty-four thousand eight hundred
and forty-seven cubic feet of gas of which we speak, all
introduced into the balloon, it would be entirely filled;
but that would not do, because, as the balloon continued
to mount into the more rarefied layers of the atmosphere,