Before the professor, who had felt the craft rear upward, could reach the pilot-house, the dirigible had shot up five hundred feet or more. Behind the professor came the others, except Matco, who was sent into a fresh paroxysm of fright by the strange and sudden upward leap of the airship.
“Good heavens!” cried the professor, as he jerked over the descending lever, “we have risen to a height of more than eight thousand feet.”
As he spoke they suddenly noticed that the air had grown bitterly chill.
“Just like Joe to make a break like that,” said Nat, with a good-natured laugh that took the sting out of his speech; “we’d better get down to earth once more as quickly as possible. It’s too cold to be comfortable up here.”
“We’ll soon drop now,” said Mr. Tubbs confidently.
But as the minutes passed and it grew colder, his face became grave.
“We’re rising,” cried the professor, glancing at the barograph.
“That’s right,” cried Nat. “What can be the matter?”
“Have you got the descending planes set at their sharpest angle?” demanded the professor.
“Yes,” was the response, “but they seem to have no effect on her at all.”