As I walked more leisurely back to my apartment by a less direct way, I found my analytical brain puzzling over the refreshing quality of the breezes that blew through those tunnel-like streets. With bits of paper I traced the air flow from the latticed faces of the elevator shafts to the ventilating gratings of the enclosed apartments, and concluded that there must be other shafts to the rear of the apartments for its exit. It occurred to me that it must take an enormous system of ventilating fans to keep this air in motion, and then I remembered the liquid air engine I had seen in the mine, and a realization of the economy and efficiency of the whole scheme dawned upon me. The Germans had solved the power problem by using the heat of the deeper strata of the earth to generate power through the agency of liquid air and the exhaust from their engines had automatically solved their ventilating problem. I recalled with a smile that I had seen no evidence of heating apparatus anywhere except that which the miners had used to warm their food. In this city cooling rather than heating facilities would evidently be needed, even in the dead of winter, since the heat generated by the inhabitants and the industrial processes would exceed the radiation from the exterior walls and roof of the city. Sunshine and "fresh air" they had not, but our own scientists had taught us for generations that heat and humidity and not lack of oxygen or sunshine was the cause of the depression experienced in indoor quarters. The air of Berlin was cool and the excess of vapor had been frozen out of it. Yes, the "climate" of Berlin should be more salubrious to the body, if not to the mind, than the fickle environment of capricious nature. From my reasoning about these ponderous problems of existence I was diverted to a trivial matter. The men I observed on the streets all wore their hair clipped short, while mine, with six weeks' growth, was getting rather long. I had seen several barber's signs but I decided to walk on for quite a distance beyond my apartment. I did not want to confront a barber who had known Karl Armstadt, for barbers deal critically in the matter of heads and faces. At last I picked out a shop. I entered and asked for a haircut. "But you are not on my list," said the barber, staring at me in a puzzled way, "why do you not go to your own barber?" Grasping the situation I replied that I did not like my barber. "Then why do you not apply at the Tonsorial Administrative Office of the level for permission to change?" Returning to my apartment I looked up the office in my directory, went thither and asked the clerk if I could exchange barbers. He asked for my card and after a deal of clerical activities wrote thereon the name of a new barber. With this official sanction I finally got my hair cut and my card punched, thinking meanwhile that the soundness of my teeth would obviate any amateur detective work on the part of a dentist.