The boys looked at each other in amazement and the words of Captain
Hazzard flashed across Frank's mind.
"WE HAVE SOME VERY UNDESIRABLE NEIGHBORS AT CLOSE QUARTERS," the captain had said. Undoubtedly he was right.
"What did you make it out for?" asked Harry at length.
"A dirigible and no small one," was the reply, "and you?"
"Same here. You can't mistake the sound of an airship's engine. The question is what is the explanation of it all?"
"Simple."
"Simple, well I—"
"That aeroplane is the one which was bought in Europe. It is specially provided with radiators which electrically heat its gas, allowing it to navigate in these regions without fear of the gas condensing and causing the ship to descend."
"Yes, but whose is it? What are they doing in it?"
"The first question is easy to answer. That ship is the ship of the rival expedition."