"You've guessed it," he replied. "And I'm sorry I can't explain more
to you."

"We understand," said Jack. "And no doubt this machine is a
super-catapult."

"True," was the answer. "Of untold use to the scientific world. For
the present I shall confine testing its efficiency right in this place.
Now is my chance."

"But of what advantage will it be to our flying machine to start it
in this way?" "Stop and think, my boy," said the professor. "Just as
an aeroplane can literally be shot into the air within a very short
space, so can your airship. Of course, this is not necessary, but we
will be able to start the ship much faster that way than we could
withjust the motors."

"You'll make history, Professor," added Jack. "Exciting headlines for
the papers."

"Sure enough," said Mark enthusiastically.

"The publicity doesn't interest me," replied the scientist. "Moreover,
my super-catapult must remain a secret, as I told you a while ago."

"So you really propose to launch the _Snowbird_ in this way?" asked
Jack.

"We will be shot into the air. If you are sure of your machine, I am