As soon as the electric current had been switched on again the captain returned. He seemed surprised at my "enthusiasm." "Just like you Americans," he said smiling. "A man en permission, however, should never look for trouble." He then explained that this night guarding required special training. Even had he needed my services, I would have been helpless, as I had never before flown after sundown. One by one the defenders of Paris returned. At two thousand feet they were invisible, though we could hear the humming of their motors. Then, as they came nearer and nearer we saw little indefinite lights moving in the mist above us, and finally the machines, their dimmed search-lights yet staring like two great eyes. About fifty aeroplanes are in the air around Paris all the time. Each pilot remains up three hours, when he is relieved by another flier. When the Zeppelins are known to have crossed the front, some eighty miles away, the whole defense squadron of two hundred takes to the air. The organization of the aerial defense of Paris is admirable, and it is this, together with the efficient anti-aircraft posts in the environs, which prevents the "Boches" from raiding Paris more often. I was allowed to examine everything at my leisure, and took advantage of this opportunity to gain as much information as I could about the lighting systems and the new models of small cannon which had recently been installed on the aeroplanes. Presently I was greeted by one of the pilots who had just landed. He proved to be an old acquaintance. It seems that the Zeppelin had profited by the mist to slip by our watchers at the front, and had reached the very outskirts of the city before it was sighted by the air guards of Paris. The Boches dropped several bombs near the Gare du Nord and in the vicinity of Le Bourget. Then they had vanished into the mist. "How could they ever find the railway-station in the dark?" I asked. "That’s easy," he answered. "The Zeppelins are equipped with a small observation-car that hangs down on a long cable. It is built something like an aeroplane and travels about five thousand feet below the dirigible. This evening the raider flew at an altitude of seven thousand feet, while the car moved along only two thousand feet from the ground. Its passenger could, therefore, locate everything easily and telephone the directions to the commander above." "But," I insisted, "how did they ever locate the freight-yards in the dark?" "Easily," replied my companion; "their spies had arranged all that. They simply hung a series of blue lights in the chimneys of houses and laid out a path directly to the spot." These spies in all probability had been already caught, but I was angry, very angry, to realize that their "espionage" was still so efficient.