"Puzzled?" and Ned raised his eyebrows to indicate how
surprised he was that anything should puzzle his friend.

"Yes, genuinely puzzled."

"Has anything gone wrong?" Ned asked. "No one is trying to take
any of your pet inventions away from you, is there?"

"No, not exactly that, though it is about one of my inventions
I am puzzled. I guess I haven't shown you my very latest; have I, Ned?"

"Well, I don't know, Tom. Time was when I could keep track of
you and your inventions, but that was in your early days, when
you started with a motorcycle and were glad enough to have a
motorboat. But, since you've taken to aerial navigation and
submarine work, not to mention one or two other lines of activity,
I give up. I don't know where to look next, Tom, for something new."

"Well, this isn't so very new," went on the young inventor, for
Tom Swift had designed and patented many new machines of the air,
earth and water. "I'm just trying to work out some new problems
in aerial navigation, Ned," he went on.

"I thought there weren't any more," spoke Ned, soberly enough.

"Come, now, none of that!" exclaimed Tom, with a laugh. "Why,
the surface of aerial navigation has only been scratched. The
science is far from being understood, or even made safe, not to
say perfected, as water and land travel have been. There's lots