All this time the brothers were solving problems and correcting faults, but in 1904 and 1905 their chief endeavour was to keep their machines from tipping sidewise when they turned. Only the most technical study and the final development of their wing-warping device solved the problem. Perhaps the strangest part was the lack of interest shown in their work by the world and even by their own townsmen, for, though there had been several newspaper accounts of their test flights, no great enthusiasm was aroused. They were not wealthy and they had spent more on their experiments than they could afford, so all this time they had proceeded without attracting any more attention than necessary. They desired to perfect their patents before letting the world know the secret of their inventions, and spent the next two years in business negotiations. Meanwhile, the French inventors were making much progress and soon brought out several successful aeroplanes. Why was this? Why was it that the art of air navigation sought by man since the earliest times should have been discovered and mastered so quickly? The answer lies in the putting together of two things by the Wright brothers--that is, their discovery of the kind of a plane that would stay aloft with the air passing under it at a swift enough clip to give it support, and their adaptation of the gasoline engine to the use of driving the plane forward with enough speed. When they began work, the gasoline engine was just coming to its real development. It was light, developed a high power, and its fuel could be concentrated into a small space. These things were essential to the success of the aeroplane--light weight, high power, and concentrated fuel. And these were things that the early inventors lacked. Sir Hiram Maxim equipped his machine with a steam engine, while Langley used steam engines in most of his models. These were very heavy, cumbersome, gave slight power in comparison to their weight, and could carry only a little fuel with them. Undoubtedly the adaptation of the gasoline engine to the use of the aeroplane marked the difference between mechanical flight and no flight, but it also is not to be doubted that those aviators, who are more mechanical than scientific, have overrated the importance of the engine in aeroplane construction. Before engines ever were used, the Chanute type of biplane had to be worked into a state of reliability, if not perfection. Now the scientific leaders in aviation are giving every bit as much attention to the perfection of their planes, their gliding possibilities, and the scientific rules governing their action as they are to their engines.