But do not imagine that he has lost his enthusiasm for the air. If that were the case then he would not be of the stuff of which aviators are made. At the worst reckoning he has acquired an intense ambition to some day "try it on the other fellow," and this in all probability he will do, when, in the course of time he has become an experienced and seasoned airman. In the meantime, however, he must first accustom himself to the "feel" of the air, and next he must learn the operation and control of the airplane in flight. After a few first trips as a "passenger," he will be allowed to try his hand at steering the machine. This is done by what is called a dual control system. Instead of the single control-stick and steering-bar of the ordinary airplane, the training machine has these parts duplicated, so that any false move on the part of the student flyer may be immediately corrected by the instructor. As long as his movements are the right ones, the instructor does not interfere, but the moment he makes a mistake the control of the airplane passes out of his hands. Gradually he becomes more and more adept at guiding the big bird through the air, and can get along nicely without any interference or correction. At each lesson he has mastered some new problem. He knows how to leave the earth at the proper angle after the first short run over the ground, and how to come down again, how to turn in the air, when to cut off the power in alighting and when to apply the brakes. He learns to listen for the rhythmic sound of the engine and to know when anything has gone wrong with it. By far the most difficult of his problems is the art of landing. As we have already seen the speed of an airplane cannot be reduced below a certain danger line if its wings are to continue to support it in the air. This danger line varies with different types of airplanes, but in all of them the engine must be kept running at a fairly high speed or the whole structure will come crashing to the earth. To bring an airplane to earth while it is traveling at a speed of 75 miles an hour is no mean accomplishment. It must not bump down heavily upon the ground, or its landing chassis will be broken, even if no more serious accident occurs. It must settle slowly until its wheels just touch, while all the time it is moving forward at the rate of a fast express train. This is an art that requires infinite practise to acquire, but it is one of the most important feats the student airman has to learn.