While Paul had been telling this, Mr. Giddings had been busy jotting something down in shorthand in a notebook.
"Pardon me, Paul," he said, looking up with a smile, "but this is so mighty interesting that, before I knew it, my old-time reportorial instinct had gotten the best of me, and I found my pencil at work. If you have no objection I should like to use this in the columns of the Daily Independent some time when it seems to fit in."
"No objection at all, sir," assured Paul.
Mr. Giddings began twirling the little twelve-inch two-bladed propeller at the nose of the model airplane. "What do you use for power to turn this propeller?" he asked, after admiring its perfect proportions for a moment. "I don't see any rubber-bands, such as Robert here has always used on his little machines."
John deftly lifted off the thin veneer hood of the airplane, and disclosed a very small four-cylindered rotary pneumatic engine of bewitching simplicity and lightness, which a baby could have held out in its pudgy palm.
"Paul has worked this little motor out of aluminum and brass and steel, from odds and ends," said John.
"With more or less help on the part of my elder brother," interjected
Paul.
"Well, perhaps with a little," admitted John, "more suggestive than otherwise."
"What sets it going?" questioned Bob, curiously.
"The fuselage is divided into three sections," said Paul. "The forward section contains the engine here; the rear section is an airtight chamber containing helium; and the central section is also an airtight chamber, but contains ordinary air which has been pumped into it through a valve, using the bicycle pump John is carrying, until it is under strong pressure. When I turn this little valve an outlet is opened for the air to escape by a tube into branches communicating with each of these four cylinders. This works the tiny pistons, much the same as gas in a gasoline-motor, and they turn the little crank-shaft to which they are connected, and the crank-shaft in turn revolves the propeller on its end."