fluid.

"Oh, get away, and let us do it!" cried Tom at last. "I know what you--"

"Easy!" cautioned Mr. Petrofsky, with a warning look, and Tom subsided.

Finally the tanks were full, the man was paid, and he started to drive
away.

"Now to make a quick flight!" cried Tom, as he took his place in the
pilot house, while Ned went to the engine room. "Full speed, Ned!"

"Yes, and we'll need it, too," said the Russian.

"Why?" asked Tom.

"Look!" was the answer, and Ivan Petrofsky pointed across the field
over which, headed toward the airship, came the man who had sought a
quarrel with Tom. And with the spy were several policemen in uniform,
their short swords dangling at their sides.

"They're after us!" cried Mr. Damon. "Bless my chronometer they're
after us!"

"Start the motor, Ned! Start the motor!" cried Tom, and a moment later
the hum of machinery was heard, while the police and the spy broke into
a run, shouting and waving their hands.

CHAPTER XV

PURSUED

Slowly the airship arose, almost too slowly to suit those on board who
anxiously watched the oncoming officers. The latter had drawn their
short swords, and at the sight of them Mr. Damon cried out:

"Bless my football! If they jab them into the gas bag, Tom, we're done
for!"

"They won't get the chance," answered the young inventor, and he spoke
truly, for a moment later, as the big propellers took hold of the air,
the Falcon went up with a rush, and was far beyond the reach of the
men. In a rage the spy shook his fist at the fast receding craft, and
one of the policemen drew his revolver.

"They're going to fire!" cried Ned.

"They can't do much damage," answered Tom coolly. "A bullet hole in the
bag is easily repaired, and anywhere else it won't amount to anything."

The officer was aiming his revolver at the airship, now high above his
head, but with a quick motion the spy pulled down his companion's arm,
and they seemed to be disputing among themselves.

"I wonder what that means?" mused Mr. Damon.

"Probably they didn't want to risk getting into trouble," replied the
Russian. "There are strict laws in France about using firearms, and as
yet we are accused of no crime. We are only suspected, and I suppose
the spy didn't want to get into trouble. He is on foreign ground, and
there might be international complications."

"Then you really think he was a spy?" asked Tom.

"No doubt of it, and I'm afraid this is only the beginn