He explained the difficulties of the airship builder, the expense and tendency to "pinholes" of gold-beaters' skin, the curious fact that chemists had so far failed to discover a gasproof varnish. "But of course," he said, "those things will come. The airship is the machine of the future. Its stability, its power to carry great weights, point to that. The difference between an airship and an aëroplane is the difference between a battleship and a submarine. Each has its own field of usefulness." All round lay great cylinders of pure hydrogen, used for inflating the balloon. Smoking in the hangar was forbidden. The incessant wind rattled the great canvas curtains and whistled round the rusting crane. From the shop next door came the hammering of machines, for the French Government has put the mill to work again. We left the hangar and walked past the machine shop. Halfway along one of its sides a tall lieutenant pointed to a small hole in the land, leading under the building. "The French government has sent here," he said, "the men who are unfit for service in the army. Day by day, as German aëroplanes are seen overhead, the alarm is raised in the shop. The men are panic-stricken. If there are a dozen alarms they do the same thing. They rush out like frightened rabbits, throw themselves flat on the sand, and wriggle through that hole into a cave that they have dug underneath. It is hysterically funny; they all try to get in at the same time." I had hoped to see the thing happen myself. But when, late that afternoon, a German aëroplane actually flew over the station, the works had closed down for the day and the men were gone. It was disappointing. Between the machine shop and the administration building is a tall water tower. On top of this are two observers who watch the sky day and night. An anti-aircraft gun is mounted there and may be swung to command any portion of the sky. This precaution is necessary, for the station has been the object of frequent attacks. The airship itself has furnished a tempting mark to numerous German airmen. Its best speed is forty miles an hour, so they are able to circle about it and attack it from various directions. As it has only two ballonets, a single shot, properly placed, could do it great damage. The Zeppelin, with its eighteen great gasbags, can suffer almost any amount of attack and still remain in the air. "Would you like to see the trenches?" said one of the officers, smiling. "Trenches? Seven miles behind the line?" "Trenches certainly. If the German drive breaks through it will come along this road." "But I thought you lived in the administration building?" "Some of us must hold the trenches," he said solemnly. "What are six or seven miles to the German Army? You should see the letters of sympathy we get from home!"