OEVILLE WEIGHT 575 ■ obtained, they perfected their appaxatus until it gave them identical results as often as they repeated the experiment, and by comparing figures they learned how to plot the shape of a surface so that it would do what they wanted it to do. They hit upon a fundamentally different principle from any which they found already set forth. They made the machine as inert as possible to the effects of change of direction or speed, and thus reduced the effects of windgusts to the mini- mum. They did this in the fore-and-aft stability by giving the aeroplanes a peculiar shape ; and in the lateral balance by arching the surfaces from tip to tip : just the reverse of what their predecessors had done. Then they sought some suitable contrivance, actuated by the operator, which would regulate the balance. The method of balancing the machine by shift- ing the weight of the operator's body was deemed impractic- able for use under large conditions. By means of their tests they learned the angles to which the wings would need to be warped or turned in order to maintain equilibrium. Then they made the wings capable of being warped by the operator, who also adjusted the supplementary surfaces or rudders. A device was discovered whereby the apparently rigid system of superposed surfaces, invented by Wenham, and improved by Stringfellow and Chanute, could be warped in a most un- expected way, so that the aeroplanes could be presented on the right and left sides at different angles to the wind. This, with an adjustable, horizontal front rudder, formed the main feature of the first glider. The gliding experiments were begun in October of 1900, at Kitty Hawk, North Carolina. The place was extremely dif- ficult of access, but they were told by the weather bureau that there the winds were the strongest and steadiest of any part of the United States. They made no great mystery of their work but invited the members of the life-saving crew, and others who lived near, to watch the flights. Only when spies or photographers were known to be near did they cease their activities. They calculated by Lilienthal's tables that the glider, which had a surface of 165 square feet, should be sus- tained by a wind of twenty miles an hour. Instead of hours
