The artillery lieutenant smiled. "This war has certainly proved as nothing else ever did the wonderful ability of mankind to adapt itself to every sort of condition, no matter how difficult or unusual. It has given tremendous impetus to inventive genius all over the world, particularly in connection with the science of aeronautics. The conquest of the air is almost complete." "My father is an aviator in the American army," declared Don, proudly. "Formerly he served with a French squadron. Some day I hope to be an airman myself." "Ah, indeed!" exclaimed the lieutenant, evidently very much pleased. "But ma foi! You are very young." "Yes. I've no objection to that, however," laughed Don. "I suppose, Monsieur le Lieutenant, there are plenty of guns around here?" "Do you see any?" "No; and I don't expect to unless I should happen to find a muzzle sticking right in my face." "Ah! The art of camouflage is another thing I might have mentioned. But, to change the subject, the Americans have proved themselves very great friends of the French, and to show that I am among those who are appreciative of it I am going to invite you all to pay a visit, whenever it is convenient, to the battery to which I am attached. You accept, n'est-ce pas?" "I should say so!—eh, mes camarades?" exclaimed Don, enthusiastically. He turned toward his companions. The art student assented heartily, though Chase, who still looked pale and haggard, merely muttered his thanks and shrugged his shoulders non-committally. As the Americans proceeded they became more and more surprised at the immense number of men and dugouts to be seen on every side—indeed they were passing over the top of a veritable underground village, with little lanes running in all directions, so as to afford access to the various quarters. "Naturally, there isn't always so much life and activity on this hill," said the lieutenant, when Don mentioned the subject. He pointed to the surrounding forest. Many of the trees had been snapped in twain by high-explosive shells, while others lay prostrate on the ground; indeed, but very few had escaped being scarred, gashed or broken by the various bombardments. "Sometimes it is just as dangerous as you