Up to the time the derrick catapult was ready for its first trial on September 7, less than forty starts had been made and many of them failed for lack of speed. But now the length of the flights increased rapidly. The shorter flights had been in almost a straight line, but as the lengths of the flights increased it was necessary to make turns to stay within the field. Then a new trouble--or rather an old one that supposedly had been overcome at Kitty Hawk--began to bother the Wrights. Often in making a short turn they suddenly found themselves in a tail-spin which ended in a crash requiring days, or even weeks, for repairs. They soon learned what it was in making the turn that caused the tail-spin; but they found it difficult to avoid, because they had no way of knowing at what angle the air was striking the machine. This led to the “invention” of the first instrument for guidance of a pilot in flying. They simply attached a short piece of string to the crossbar beneath the front elevator. When the machine traveled directly forward the string trailed straight backward; but when the machine slipped to either side the string blew to one side or the other and indicated approximately the amount of the side slip. By close observance of this string it was possible to avoid entirely the danger of tail-spins, but the pilot learning to fly had so many things to attend to, so it seemed to him, that he sometimes neglected to watch the string closely enough. After it was found that the derrick permitted the plane to be launched at any time, the Wrights often let the machine stand on the track during the day with the weights raised, ready to start at a moment’s notice. One day in early November, while idly strolling in front of the track, Orville thought he saw a slight movement of the plane on the track. A more careful look did not confirm his first impression; nevertheless he turned and leisurely walked towards the plane. When within a few steps of it he saw that it actually _was_ in motion. The wire that held it against the pull of the 1,600-pound weight was attached to a stake driven into the soft ground several feet. That stake was slowly coming out of the ground! By leaping upon one of the skids, Orville reached the elevator control lever in time to prevent the machine from rising as it rushed down the track. A strained shoulder was the principal damage, though the machine suffered a few slight breakages. Not until the 51st flight in 1904, when the machine stayed in the air one minute and one second, did the Wrights beat their best Kitty Hawk record of 59 seconds. The first complete circle was not made until September 20. But toward the end of the 1904 experiments, there were two five-minute flights. In each of these the machine circled the field four or five times without stopping.