The Wrights did not at first think an elevator in front would provide inherent stability--that is, it would not give the machine the desired tendency to restore its own balance just from the arrangement of its fixed parts. But Wilbur shortly afterward developed a theory that led him to believe the machine would have that quality. Having read that the center of pressure moves toward the front edge of the wings whenever the wings are turned more nearly horizontal in flight, he thought inherent longitudinal stability could be obtained if the front elevator were set at a negative angle--that is, with its front edge lower than its rear edge. With such an arrangement of wings and elevator, every time the wings became more nearly horizontal in flight and met the air at a smaller angle on their under sides, the elevator would meet the air at a greater angle on its upper side. So, he reasoned, whenever, by becoming more nearly horizontal, the wings caused the center of pressure to move forward, tending to turn the machine upward in front, the front elevator would receive a greater downward pressure on its upper side and so counteract the disturbing pressure on the wings. Actual tests later proved that the negative angle of the front elevator did not provide the inherent stability expected. The explanation was that the center of pressure on cambered wings traveled in the opposite direction from that which Wilbur’s reading had led him to expect. The Wrights later were to discover that Wilbur’s reasoning was correct; but because the travel of the center of pressure was rearward instead of forward the elevator had to be set at a positive instead of at a negative angle. The Wrights’ elevator possessed three features not found in the gliders of any of the earlier experimenters. It was in front of the wings, where it was less liable to damage by striking the ground in take-off and landing; it was operable, instead of fixed as in other machines; and it flexed to present a convex surface to the air, instead of a flat surface. At this early stage of their work the Wrights considered this front elevator their most important invention, because, from their reading, they thought it was solving a problem more difficult than that of lateral control.