great, Tom! Great!" he yelled.

"Yes, I guess it will do, Ned. I'm satisfied. If there was an
international meet now I'd capture some of the prizes. As it is--"

Tom stopped suddenly. His voice which had been raised to overcome the
noise of even the muffled motor, sounded unnaturally loud, and no
wonder, for the engine had ceased working!

"What's the matter?" gasped Ned.

"I don't know--a breakdown of some kind."

"Can you get it going again?"

"I'm going to try."

Tom was manipulating various levers, but with no effect. The aeroplane
was shooting downward with frightful rapidity.

"No use!" exclaimed the young inventor. "Something has broken."

"But We're falling, Tom!"

"I know it. We've done it before. I'm going to volplane to earth."

This, it may be explained, is gliding downward from a height with the
engine shut off. Aeroplanists often do it, and Tom was no novice at the
art.

They shot downward with less speed now, for the young inventor had
thrown up his headplanes to act as a sort of brake. Then, a little
later they made a good landing in a field near a small house, in a
rather lonely stretch of country, about ten miles from Shopton, where
Tom lived.

"Now to see what the trouble is," remarked our hero, as he climbed out
of his seat and began looking over the engine. He poked in among the
numerous cogs, wheels and levers, and finally uttered an exclamation.

"Find it?" asked Ned.

"Yes, it's in the magneto. All the platinum bearings and contact
surfaces have fused and crystallized. I never saw such poor platinum as
I've been getting lately, and I pay the highest prices for it, too. The
trouble is that the supply of platinum is giving out, and they'll have
to find a substitute I guess."

"Can't we go home in her?" asked Ned.

"I'm afraid not. I've got to put in new platinum bearings and contacts
before she'll spark. I only wish I could get hold of some of the better
kind of metal."

The magneto of an aeroplane performs a service similar to one in an
automobile. It provides the spark that explodes the charge of gas in
the cylinders, and platinum is a metal, more valuable now than gold,
much used in the delicate parts of the magneto.

"Well, I guess it's walk for ours," said Ned ruefully.

"I'm afraid so," went on Tom. "If I only had some platinum, I could--"

"Perhaps I could be of service to you," suddenly spoke a voice behind
them, and turning, the youths saw a tall, bearded man, wh