lowered as desired.

With the aid of Jupe, the gas bag was inflated to a point where only a
slight additional quantity of gas would cause the craft to shoot
upward to the sky. When all was ready a test of the instruments was
made and they were found to be working perfectly. The powerful
alternator on the Wondership was, of course, worked by the same motor
that drove the big propellers.

"Well, I guess there's nothing to keep you back now," said Mr.
Chadwick, who looked pale and ill after his long days and nights of
work on his invention.

"No, we're as ready as we ever will be," said Jack, making ready to
climb into the machine above which the big yellow balloon bag was
billowing and sending impatient quiverings through the Wondership.

"I want you to promise me one thing, dad," said Jack, when he had
climbed into the driver's seat, in front of Tom, whose duty it was to
look after the engine.

"What is that, my boy?" asked the inventor.

"That after this test, whatever the result may be, you will take a
long rest."

"Yes, I will, I must," agreed his father. "I've been working too hard,
I guess, but in the excitement of perfecting the radio telephone I
hardly noticed it. But recently I've had dizzy spells."