propellers, in front, and that is the tractor type. The other has
the propeller in the rear, and that is the pusher type. Both good
as far as they go, but I have something better."

"What?" asked Tom with a smile.

"It's a Whizzer," said the eccentric man. "Bless my gold tooth!
but that is the best name I can think of for it. And, really, the
propeller I'm thinking of inventing does whiz around."

"But are you going to use a tractor or pusher type?" Tom wanted
to know.

"It's a combination of both," answered Mr. Damon. "As it is
now, Tom, you have to get an aeroplane in pretty speedy motion
before it will rise from the ground, don't you?"

"Yes, of course. That's the principle on which an aeroplane
rises and keeps aloft, by its speed in the air. As soon as that
speed stops it begins to fall, or volplane, as we call it."

"Exactly. Now, instead of having to depend on the speed of the
aeroplane for this, why not depend on the speed of the propeller
--in other words, the whizzer?"

"Well, we do," said Tom, a bit puzzled as to what his friend
was trying to get at. "If the propeller didn't move the airship
wouldn't rise--that is, unless it's of the balloon type."

"What I mean," said Mr. Damon, "is to have an aeroplane that