The professor welcomed them cordially and at their request gave a thorough scrutiny to the various mechanical contrivances that went to the make-up of the flying machine. He pronounced it, as far as could be known before a practical test, a perfect mechanism. "And we will try it to-morrow morning, boys," he said, with almost as much enthusiasm as Jack and Mark themselves displayed. "You have completed the machine in excellent time, and I 'un likewise ready to make the experiment." "What experiment, Professor?" asked the boys in chorus. "Haven't you noticed what I was tinkering on at the other end of the shop?" queried Professor Henderson, in surprise. "Why, I see that you have a long steel plank there, with some kind of a compressed air contrivance at one end," said Jack. "Is that what you mean, Professor?" queried Mark. "That, boys," said the scientist, with some pride, "is a modern catapult--an up-to-the-minute catapult which, had it been known to the ancients, would have enabled the hosts of Joshua, for instance, to batter down the walls of Jericho without the trouble of marching so many times around the city." "And what has a compressed air catapult got to do with the _Snowbird_?" queried Jack. "You propose launching your flying machine in the usual way," said the professor. "I see you have wheel trucks all ready to slip under her. We will not use those wheels, boys. I have a better plan. We will launch the _Snowbird_ into the air from my catapult." "Great goodness, Professor!" cried Mark. "Is that practicable?" "We'll know after we have tried it," retorted Professor Henderson, drily. "How did you happen to start working on this catapult idea?" asked Jack. "Well, I can't tell you everything," replied the inventor, "for it is partly a secret." "Huh," laughed Mark. "You're mysterious. You haven't joined forces with some department of our government, or with another country?" The professor smiled, thinking how keen this young man always proved himself to be. "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."