, high up, they must
come--"

His words were drowned by another great concussion, but farther off. The
ground trembled, but there was no sign of flying debris.

"Another!" cried the _gendarme_. "There goes the gun again!"

"I didn't hear any gun," observed Jack. "What we heard was the explosion
of the shell. Look up, Tom, and see if there's a Hun plane in sight. If
there is, pity we haven't our machines right now."

The boys carried, slung over their shoulders, powerful binoculars, and
with these they swept the sky. Others about them were doing the same. By
this time the most seriously injured had been carried to the hospitals,
and the dead had been removed, while those only slightly hurt, as well
as those in the factory not at all injured, were telling their
experiences. The second explosion seemed to create great terror.

"There isn't a sign of a hostile plane," said Tom, as he swept the sky
with his glasses.

"I can't see any either," observed Jack. "And yet--"

There sounded the unmistakable roar of an aircraft's propeller.

"There she is!" cried some one.

But it was one of the first of a series of French planes that had
hastily ascended to search the heavens for a sight of the supposed
German craft that had dropped the bombs.

"What a chance we're missing!" murmured Jack.

"Yes," agreed Tom. "But they're going to have some flight before they
locate that Hun. There isn't so much as a speck in the sky except the
French craft."

"Let's go and see where that other explosion was," suggested Jack, when
they had observed several of the French planes scurrying to and fro over
the city, climbing higher and higher in search of the enemy.

"I'm with you," announced Tom. "I wonder what dad thinks of this?"

"It'll be something new for him," said Jack. "He'll have a good chance
to see how his stabilizer works, if they're using it on these planes
here. And maybe he can invent a better one."

"Perhaps," returned Tom. "But, Jack, do you know I'm worried about one
thing."

"I have more than that on my mind, Tom. There are mighty serious times
all about us, and it's terrible to think of those poor women and girls
being killed like rats in a trap. I'd just like to be in my plane, and
with a full gun, and then have a go at the Hun who did this."

"So would I," agreed Tom, as they made their way out of the crowd and in
the direction in which many of the populace were hurrying to go to the
scene of the second explo