I have no occasion,
then, to learn any thing more from them."
"Well! doctor, would it be proper to ask what is
your secret?"
"Here it is, gentlemen--the simplest thing in the
world!"
The attention of his auditory was now directed to the
doctor in the utmost degree as he quietly proceeded with
his explanation.
CHAPTER TENTH.
Former Experiments.--The Doctor's Five Receptacles.--The Gas Cylinder.--
The Calorifere.--The System of Manoeuvring.--Success certain.
"The attempt has often been made, gentlemen," said
the doctor, "to rise and descend at will, without losing
ballast or gas from the balloon. A French aeronaut, M.
Meunier, tried to accomplish this by compressing air in an
inner receptacle. A Belgian, Dr. Van Hecke, by means
of wings and paddles, obtained a vertical power that would
have sufficed in most cases, but the practical results
secured from these experiments have been insignificant.
"I therefore resolved to go about the thing more directly;
so, at the start, I dispensed with ballast altogether,
excepting as a provision for cases of special emergency,
such as the breakage of my apparatus, or the necessity of
ascending very suddenly, so as to avoid unforeseen obstacles.
"My means of ascent and descent consist simply in dilating
or contracting the gas that is in the balloon by the
application of different temperatures, and here is the
method of obtaining that result.
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