“No! I did not want to have myself overhauled in public. I saw no use in that. I made my preparatory experiments in secret and was satisfied. 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 Manœuvring.—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 aëronaut, 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.
“You saw me bring on board with the car several cases or receptacles, the use of which you may not have understood. They are five in number.