alian plane was not ready, it seemed, to be used, but it would
be soon, it was said.

Then came the day and the hour when certain members of the picked
squadron were to take the air to look for the gun. Tom and Jack, to
their delight, were selected to go.

"What a chance!" exclaimed Jack, as he climbed into his machine, and saw
that he had plenty of ammunition for the Lewis gun.

"I hope we can make good!" returned Tom.

Then they were away and up, seeking to find the monster cannon that was
bringing the war into the heart of Paris.

CHAPTER XVIII

A CLOUD BATTLE

For some little time the picked squadron that was intrusted with the
difficult and dangerous task of locating the big German gun flew over
the French lines. Below them Tom and Jack could make out various French
camps, the front and supporting lines of trenches, and various other
military works. They could see a brisk artillery duel going on at one
point. They noted the puffs of smoke, but of course could not hear the
explosions, as their own motors were making too much noise.

Tom and Jack kept within sight of one another, and also within view of
their comrades. Each plane was marked with a big number so it could be
distinguished, for the aviators themselves were so wrapped in
fleece-lined clothes, so attired in gauntlets, goggles and fur boots, as
protection against the terrible cold of the upper regions, that one's
closest friend would not recognize him at a near view.

It was the object of this first scouting expedition to make a
preliminary observation over as wide a range of the enemy's country as
possible. While it was hoped that the location of the big gun might be
spied out, it was almost too much to expect to pick out the spot at the
first trial. The Germans were keen and wary, and undoubtedly they would
have laid their plans well.

"Well, I don't see any of 'em coming out to dispute our passage,"
thought Tom, as he looked at his controls and noted by his height gage
that he was now up about two miles. "There isn't a Boche plane in
sight."

And the same thing was observed by Jack and the other fliers. The
Germans seemed to be keeping down, or else were higher up, or perhaps
hidden by some cloud bank.

That was another hazard of the air. Going into a cloud, or above it
might mean, on coming out, that one would find himself in the midst of
enemies.

It is a life full of dangers and surprises. It is this which makes it so
appeal