Military photography is one of the most fascinating of the side issues of the war. Before the day of the airplane it was the scout or spy who worked his way secretly into the enemy's lines and at great personal risk,--and often after many thrilling adventures, if the story books are to be believed--brought back to his commanding officer news of the disposition of troops, etc., in the opposing camp. To-day the spy's job has been taken away from him. No longer is it necessary for him to creep under cover of night past the guard posts of the enemy. A big, comfortable and efficient airplane flies over the ground by broad daylight and collects the necessary information a great deal better than the spy ever could have secured it. [Illustration: _Copyright Underwood and Underwood_ AN AIRPLANE VIEW OF THE CITY OF RHEIMS, SHOWING THE CATHEDRAL] A reconnaissance camera has very little in common with a kodak. The observer does not tilt it over the edge of the machine, focus it on some interesting object and "snap" his picture. As a matter of fact it works more after the manner of a gun. It is fixed in the bottom of the airplane, facing downward. The observer has been instructed before leaving the ground that a certain area or trench is to be photographed. Straight to the beginning of that trench line the pilot heads his machine. The observer compares the country over which he is flying with the chart or map which he carries. Just as a gunner sights a target, he locates the beginning of the trench line to be photographed through a bull's eye, and immediately pushes the button which sets the camera working. From that point the camera operates automatically, taking a series of overlapping pictures of the country it looks down upon. With calm determination the pilot holds his machine to the course laid out, in spite of any opposition that may arise in his path, for the slightest deviation from that fixed line of flight will mean a gap in the reconnaissance report which the pictures represent. But once he has covered the required area, he turns and flees. In less time than it takes to tell that magazine of films is being developed in a dark room. From there the printed pictures are rushed to an expert interpreter who reads the secret meanings of the things he sees--this or that dark blotch or peculiar looking speck suggests to his trained mind a machine gun nest, a railroad center, an observation post, a barbed wire entanglement, a camouflaged battery, an ammunition dump, or what-not. Pasted together so that they give a continuous view of the foe's territory, the printed pictures are hurried to headquarters, where in a few brief moments their message has been turned into a command to the troops. By the word that those pictures bring the battle is directed, and the blow is aimed straight at the enemy's vital spots.