Entirely apart from any advantages to be gained from the use of the tail, the first trials of the new machine were highly encouraging for another reason. It was soon evident that by disregarding all tables of air pressures used by their predecessors and building according to the figures obtained from their wind-tunnel experiments, the Wrights had made a big advance toward flight. Because of the knowledge they now had, not possessed by any previous experimenter, of how the wings should be shaped, this 1902 machine was of just about twice the “dynamic efficiency” of any other glider ever built; it could have been flown with probably less than half the power required for any other glider. Altogether the Wrights made more than one thousand gliding flights in September and October, 1902. Several glides were of more than six hundred feet, and a number of them were against a thirty-six-mile-an-hour wind. No previous experimenter had ever dared to try gliding in so stiff a wind. That the Wrights were successful at such feats gave proof of the effectiveness of their devices for control. Some of their flights lasted more than a minute and at times it was possible to soar in one spot without any descent. So impressive were such exhibitions that Bill Tate’s brother Dan solemnly offered the opinion: “All she needs is a coat of feathers to make her light and she will stay in the air indefinitely.” About one time in fifty, however, the machine behaved in a manner quite mysterious. It would turn up sidewise and come sliding to the ground in spite of all the warp the operator could give to the wing tips. At one trial the lateral control would work perfectly and then the next time, under conditions that seemed to be about the same, it was impossible to prevent one wing end from striking the sand with a kind of spinning movement that the brothers called “well-digging.” This new problem, that had not occurred in their previous gliders, came from the fact that the machine had a tail. Those “well-digging” accidents were tail-spins--though that term did not come into use until several years afterward. But even after it was evident that the tail had something to do with the machine’s peculiar behavior, neither brother was prepared to explain _why_. Then one night Orville drank more than his customary amount of coffee. Instead of going to sleep as usual the moment he got into bed, he lay awake for several hours. Those extra cups of coffee may have been important for the future of practical flight for, as he tossed about, he figured out the explanation of the phenomenon caused by the tail. Here it is, as he eagerly gave it to Wilbur, and to their brother Lorin, who was visiting them, at breakfast the next morning: