"And why so, if you please?"

"Because you can ascend only by throwing out ballast;
you can descend only after letting off gas, and by these
processes your ballast and your gas are soon exhausted."

"My dear sir, that's the whole question. There is the
only difficulty that science need now seek to overcome.
The problem is not how to guide the balloon, but how to
take it up and down without expending the gas which is
its strength, its life-blood, its soul, if I may use the
expression."

"You are right, my dear doctor; but this problem is
not yet solved; this means has not yet been discovered."

"I beg your pardon, it HAS been discovered."

"By whom?"

"By me!"

"By you?"

"You may readily believe that otherwise I should not
have risked this expedition across Africa in a balloon. In
twenty-four hours I should have been without gas!"

"But you said nothing about that in England?"