for
again the bombarding of the city began.

Meanwhile the air scouts did their best to find the place of the firing.
Hundreds of photographs were taken, and brave scouts risked death more
than once in flying low over suspected territory. But all to no purpose.
Several were killed, but others took their places. Jack was hit and so
badly wounded that he was two weeks in the hospital. But when he came
out he was again ready to join Tom in the search.

No word came as to the whereabouts of Bessie and her mother, nor did Tom
hear anything of his father. The lack of information was getting on the
nerves of both boys, but they dared not stop to think about that, for
the army needed their best efforts as scouts of the air, and they gave
such service gladly and freely.

Every possible device was tried to find the location of the German gun,
and numerous battles above the clouds resulted at different times during
the scout work.

On the whole the advantage in these conflicts lay with the armies of the
Allies, the Germans being punished severely. Once a German plane was
brought down within the French lines, and its pilot made a prisoner.

It was hoped that some information might be gotten out of the German
airman that would lead to the discovery of the big gun, but, naturally,
he did not reveal the secret; and no more pressure was brought to bear
on him in this matter than was legitimate. The hiding place of the gun
remained a secret.

Its possible size and the nature of its shooting was discussed every day
by Tom, Jack and their comrades. In order to make a cannon shoot a
distance of about eighty miles it was known that it was necessary to get
the maximum elevation of forty-five degrees. It was also calculated that
the shell must describe a trajectory the highest point in the curve of
which must be thirty-five miles or more above the earth. In other words
the German cannon had to shoot in a curve thirty-five miles upward to
have the missile fly to Paris. Of course at that height there was very
little air resistance, which probably accounted for the ability of the
missile to go so far. That, and the sub-calibre shell, made the
seemingly impossible come within the range of possibility.

"What are you going to do, Tom?" asked Jack one evening, after an
unsuccessful day's flight. For Tom was going toward his hangar.

"Going up."

"What for?" Jack went on.

"Oh, no reason in particular. I just feel like flying. We didn't