The day on which we were required to begin our altitude flights the captain assigned three machines to our équipe—that is, one aero-biplane for each pair. My chum, a sous-lieutenant, and I were assigned to the same machine. We matched to see which one of us should use it first. He won and I helped him prepare for the test. I fastened on his recording barometer, which indicates the altitude reached by a machine, and he climbed in. Waving us a cheery "Au revoir," he started off. His machine climbed fast. To us he seemed to be going too steeply. We felt like shouting to him to be careful, but we knew it was useless. Suddenly his machine slipped off on the wing. For some unknown reason he failed to shut off his motor. His biplane engaged in the fatal spiral. There was a loud report, like a cannon-shot, and the machine collapsed. The strain had been too great. The top plane fell one way, the lower another, while my friend and the motor dropped like stones. I would have given anything to put off my own test for a few days, but within twenty-four hours I received orders that my turn had come; and orders were orders. I made up my mind to be very careful and to take my time about the climb. That first flight at six thousand feet gave me a thrilling sensation. I remembered my first flight alone, when I had barely reached two hundred feet. It seemed now as if I was going to mount to an indescribable height. Since that day I have had to go up that high often, and even higher; but it has all become commonplace, for familiarity breeds contempt in the air as well as on land. I was so very cautious about mounting that twenty minutes elapsed before the needle on my registering barometer marked six thousand feet. It was very cold. The wind struck my face with icy blasts, but I was so excited that I did not really mind it. After a while I shut off the motor and started to volplane to earth. I came down a little too rapidly and made a very bad landing. In fact, for a moment I thought that I had broken my machine. I was wet all through from the sudden rise in temperature and stone-deaf. It was ten minutes before I could hear again. Then I received my call-down. It seems that when a pilot has been up to a very great height, he loses his sense of altitude—his "sens de profondeur," as the French call it. When approaching the ground he cannot tell whether he is twenty-five or fifty feet in the air. He must take every care, before making contact, to train his eye for "depths" again by flying a few minutes fairly close to the ground. It is only a question of a few moments, but it is a necessary precaution.