The young captain of the airship pointed up to it.

“My apartments!” he said.

“Do you mean to say that you sleep here?” I asked.  For the building was bitterly cold; one end had been knocked out to admit the airship, and the wall had been replaced by great curtains of sailcloth to keep out the wind.

“Of course,” he replied.  “I am always within call.  There are sentries also to guard the ship.  It would be very easy to put it out of commission.”

The construction of the great balloon was explained to me carefully.  It was made of layer after layer of gold-beater’s skin and contained two ballonets—­a small ship compared to the Zeppelins, and non-rigid in type.

Underneath the great cigar-shaped bag hangs an aluminum car which carries a crew of three men.  The pilot sits in front at a wheel that resembles the driving wheel of an automobile.  Just behind him is the observer, who also controls the wireless.  The engineer is the third man.

The wireless puzzled me.  “Do you mean that when you go out on scouting expeditions you can communicate with the station here?” I asked.

“It is quite possible.  But when the airship goes out a wireless van accompanies it, following along the roads.  Messages are picked up by the van and by a telephone connection sent to the various batteries.”

It may be well to mention again the airship chart system by which the entire region is numbered and lettered in small squares.  Black lines drawn across the detail map of the neighbourhood divide it into lettered squares, A, B, C, and so forth, and these lettered squares are again subdivided into four small squares, 1, 2, 3, 4.  Thus the direction B 4, or N 2, is a very specific one in directing the fire of a battery.

“Did you accomplish much to-day?” I inquired.

“Not as much as usual.  There is a ground haze,” replied Colonel M——­, who had been the observer in that day’s flight.  “Down here it is not so noticeable, but from above it obscures everything.”

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 aeroplane 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.