“The tall one in the center.  Yes, that’ll suit us.”

They inspected the tree and then made a long circuit about it, finding nobody near.  John, full of zeal and enthusiasm, volunteered to climb the tree and fasten the flag to its topmost stem, and Weber, after some claims on his own behalf, agreed.  John was a good climber, alert, agile and full of strength, and he went up the trunk like an expert.  It was an uncommonly tall tree for France, much more than a sapling, and when he reached the last bough that would support him he found that he could see over all the other trees and some of the low hills.  At a little distance ran the Marne, a silver sheet, and he thought he could discern faint puffs of smoke on the hills beyond.  No human being was in sight, but although high in the tree he could still feel the vibrations of the air beneath the throb of so many great guns.  Several aeroplanes hovered at points far distant, and he knew that others would be on the long battle line.

Reaching as high as he could he tied the flag with a piece of twine that Weber had given him—­the Alsation seemed to have provided for everything—­and then watched it as it unfolded and fluttered in the light breeze.  He felt a certain pride, as he had done his part of the task well.  The flag waved above the green leaves and any watcher of the skies could see it.

“How does it show?” he called to Weber.

“Well, indeed.  You’d better climb down now.  If the Germans come from the air they’ll get you there, and if they come on land they’ll have you in the tree.  You’ll be caught between air and earth.”

“That being the case I’ll come down at once,” said John, and he descended the tree rapidly.  At Weber’s advice they withdrew to a cluster of vines growing near, where they would be well hidden, since their signal was as likely to draw enemies as friends.

“I think Lannes will surely see that flag,” said Weber.

“Why do you have such great confidence in his coming?” asked John.

“He inspires confidence, when you see him, and there’s his reputation.  I’ve an idea that he’ll be carrying dispatches between the two wings of the French army, dispatches of vast importance, since the different French forces have to cooperate now along a line of four or five score miles.  Of course the telephone and the telegraph are at work, too, but the value of the aeroplane as a scout and dispatch bearer cannot be over estimated.”

“One is coming now,” said John, “and I think it has been attracted by our flag.  I take it to be German.”

“Then we’d better keep very close.  Still, there’s little chance of our being seen here, and the aviators, even if they suspect a presence, can’t afford to descend, leave their planes and search for anybody.”

“I agree with you there.  One can remain here in comparative safety and watch the results of our signal.  That machine is coming fast and I’m quite sure it’s German.”