he earth, as falls a bird with a broken wing.

CHAPTER XX

QUEER MARKS

"What happened?" cried Jackson to Tom, as he leaned forward in his seat
which was in the rear of the young inventor's.

"Don't know, exactly," was the answer, as Tom quickly shifted the
rudders to correct the slanting fall of his craft. "Sounded as though
there was a tremendous back-fire, or else the muffler blew up. The
engine is dead."

"Can you take her down safely?"

"Oh, yes, I guess so. She's a bit out of control, but the stabilizer
will keep her on a level keel. Good thing we installed it."

"You're right!" said Jackson.

Now they were falling earthward with great rapidity, but, thanks to the
gyroscope stabilizer, the "side-slipping," than which there is no
motion more dreaded by an aviator, had nearly ceased. The craft was
volplaning down as it ought, and Tom had it under as perfect control as
was possible under the circumstances.

"We'll get down all right if something else doesn't happen," he said to
Jackson, with grim humor.

"Well, let's hope that it won't," said the mechanic. "We're a good
distance up yet."

They were, as a matter of fact, for the explosion, or whatever had
happened to the craft, had occurred at a height of over two miles, and
they at once began falling. As yet Tom Swift was unaware of the exact
nature of the accident or its cause. All he knew was that there had
been a big noise and that the engine had stopped working. He could not
see the silencer from where he sat, as it was constructed on the
underside of the motor, but he had an idea that the same sort of mishap
had occurred as on the occasion when the test machine had sailed
through the roof of his workshop.

"But, luckily, this wasn't as bad," mused Tom. "Anyhow the motor is out
of business."

And this was very evident. The young inventor had tried to start the
apparatus after its stoppage by the explosion, but it had not responded
to his efforts, and then he had desisted, fearing to cause some further
damage, or, perhaps, endanger his own life and that of Jackson.

Down, down swept Silent Sam--doubly silent now, and Tom began looking
about for a good place to make a landing. This was nothing new for
either him or his mechanician, and they accepted the outcome as a
matter of course.

"Not a very lively place down there," remarked Jackson, as he looked
over the side of the cockpit.

"If we have to depend for help on any one down there,