At the beginning of the war the artillery-fire of the Allies was directed for the most part by airplanes. Their work, however, left much to be desired. Though the plane observers could locate targets fairly well, they frequently lost touch with their batteries through the difficulty of sending and receiving wireless or visual signals from the swiftly moving craft. Thus there came into use the captive balloon, which by the end of the war had practically replaced the airplane as a director of gun-fire wherever possible, thus making the artillery infinitely more efficient than ever before. Sitting comfortably aloft, the observer in the basket of a kite-balloon had the whole panorama of his particular station spread beneath him like a map in bas-relief, being able to detect, with the aid of powerful glasses, anything transpiring within a radius of ten miles or more. He was constantly in touch with his batteries by telephone and could not only give the gunners, by means of co-ordinated maps, the exact location of their target and the effect of their bursting shells, but could keep the staff informed of enemy troop movements, airplane activities, and preparations for impending attacks. The balloonist became, indeed, a veritable sentinel of the skies, hovering over the battle-lines with the persistency and the keen, long-range vision of a hawk. He played a less spectacular part in the great drama than the airplane scout or fighter in the latter’s free and dazzling flights, but his duties were scarcely less important. Nor did he suffer from ennui during his stays aloft. When a kite-balloon went up along the battle-front it at once became the subject of the keenest attention by the enemy because it was known to be up on business and was certain to be the cause of damage unless it was forced down. Long-range, high-velocity guns were trained on it and, from the upper levels of the air, planes came swooping down upon it in their attempts to dash through the screen of shells from the antiaircraft guns and put an incendiary bullet into the sausage-shaped, elephant-colored gas-bag which so insolently defied them. And a bullet which got home meant the instant ignition of the highly inflammable hydrogen, the quick destruction of the balloon and, perhaps, the occupants of the basket as well, unless they could get away in their parachute. From the moment the gas leaped into flame until the fall of the balloon was rarely over fifteen or twenty seconds, so quick thinking and quick work was called for if the men in the basket were to jump to safety. The pilot of the airplane could dodge and swerve and slip away from the guns by a hundred shrewd devices; not so the pilot of the kite-balloon anchored to its windlass. He had to carry on his abstruse mathematical calculations unconcernedly, his spare moments being enlivened by watching the flash of an enemy gun on a distant hill and then waiting twenty or thirty seconds for the whining messenger of death