I left Châteauroux for the reserve at Plessis-le-Belleville with a certain feeling of uneasiness, yet with the certainty that in case of emergency I knew almost instinctively what to do. In addition, I had become thoroughly familiar with the perils of the air which pilots are called upon to meet most often. These dangers are the same as those encountered on the high seas by sailors: fog, fire, and a lee shore. Take fog, for example. The most difficult operation in flying is the "atterrissage" (landing). Now, in a fog you must land almost by chance. You cannot see the ground until it is too late for your eyesight to be of any use. Your altimetre is supposed to register your height above the ground, but no altimetre is delicate enough to keep up with the rapid descent of an aeroplane. It is always from fifteen to twenty yards behind your real height. Nor is this all. The altimetre "begins at the ground"; it registers your height above the altitude from which you started. Now, since all ground is more or less irregular, you may be coming down on a spot lower—or, much worse, higher—than that from which you started. Besides, when a fog comes up the atmospheric pressure changes and, as the altimetre is a barometer, it becomes from that moment unregulated. Then, of course, on landing you may strike bad ground—houses or shrubbery or fences, all of which adds to the uncertainty and risk. The danger from fire has never been entirely eliminated, although it is not to-day as great as it was before aeroplane engines reached their present perfection. The greatest danger lies in the propeller. The slightest obstacle will break it, and if the motor cannot be stopped instantly the increased revolutions are certain to force the flame back into the carburetor and you are "grillé" before you can land. Aviators are from the first instructed to leave nothing loose about the machine or their clothing. Many pilots have been killed because their caps blew off, caught in the propeller, and broke it. So fast and powerful is the motion of the propeller that I have seen machines come out of a hail-storm with the blades all splintered from striking the hailstones. There have been experiments made with fire-proof machines, but none have yet proved successful. Fireproofing is apt to make a machine too heavy and cumbersome.