was driven
by the same aerial propellers that afforded her motive power on land
or in the air. She then became what may be called a hydromobile. If it
chanced to be rough weather, special hermetically sealed panels could
be drawn together, completely enclosing the body and making the craft
a water-tight "bottle." Ventilation was provided in such a case by a
hollow telescopic tube which reached twenty-five feet into the air. It
was divided in two. Fresh air was drawn by a fan down one section,
while the stale air in the "cabin" was forced out by a similar device
up the other part of the tube. Stability was afforded by hollow
pontoons, which worked on toggle joints, and could be raised or
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."

"Two weeks' rest will make you well," declared Jack, as he adjusted
the controls.

"Good-by and good luck," said his father.

Both boys waved their hands.

"All ready, Tom?" hailed Jack.

The other boy nodded and then turned on a valve so that with a hissing
sound additional gas rushed into the bag. Jack pulled a lever. The big
motors roared and a queer, sickly smell of burned gas filled the air.
The propellers began to revolve slowly and then increased their speed
till they became a mere blur.

"Dere she go! Gollyu