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
