A bird's-eye observation is much more accurate than any that can be obtained from the ground. Even before this war, some observations were taken by sending a man up in a kite, particularly a kite towed from a ship, and even as far back as the Civil War captive balloons were used to raise an observer to a good height above the ground. They were the ordinary round balloons, but the observation balloon of to-day is a very different-looking object. It is a sausage-shaped gas-bag that is held on a slant to the wind like a kite, so that the wind helps to hold it up. To keep it head-on to the wind, there is a big air-bag that curls around the lower end of the sausage. This acts like a rudder, and steadies the balloon. Some balloons have a tail consisting of a series of cone-shaped cups strung on a cable. A kite balloon will ride steadily in a wind that would dash a common round balloon in all directions. Observers in these kite balloons are provided with telephone instruments by which they can communicate instantly with the battery whose fire they are directing. But a kite balloon is a helpless object; it cannot fight the enemy. The hydrogen gas that holds it up will burn furiously if set on fire. In the war an enemy airplane had merely to drop a bomb upon it or fire an incendiary bullet into it, and the balloon would go up in smoke. Nothing could save it, once it took fire, and all the observers could do was to jump for their lives as soon as they saw the enemy close by. They always had parachutes strapped to them, so they could leap without an instant's delay in case of sudden danger. At the very first approach of an enemy airplane, the kite balloon had to be hauled down or it would surely be destroyed, and so kite balloons were not very dependable observation stations for the side which did not control the air. As stated in the preceding chapter, just before the fighting came to an end, our army was preparing to use balloons that were not afraid of flaming bullets, because they were to be filled with a gas that would not burn. MAKING MAPS WITH A CAMERA Because airplanes filled the sky with eyes, everything that the army did near the front had to be carefully hidden from the winged scouts. Batteries were concealed in the woods, or under canopies where the woods were shot to pieces, or they were placed in dugouts so that they could not be located. Such targets could seldom be found with a kite balloon. It was the task of airplane observers to search out these hidden batteries. The eye alone was not depended upon to find them. Large cameras were used with telescopic lenses which would bring the surface of the earth near while the airplane flew at a safe height. These were often motion-picture cameras which would automatically make an exposure every second, or every few seconds. [Illustration: (C) Underwood & Underwood British Anti-aircraft Section getting the Range of an Enemy Aviator]