The Wrights were not sure they would ever build another glider. But their curiosity, their passion for getting at truth, had now been too much aroused for them to quit studying the problem of air pressures. They decided to build another wind-tunnel, less crude than the one Orville had hastily used, and continue their experiments. The new tunnel consisted of an open-ended wooden box about sixteen inches square on the inside by six feet long. Into one end would come a current of air and the draft thus created would be “straightened,” as well as made uniform, by having to pass through a set of small pigeon-holes. It would have been a great convenience to use an electric fan for sending the air into the tunnel. But the Wrights had no electric current in their shop--still lighted by gas--and the fan was driven by a one-cylinder gas engine they had previously made. They attached the fan to a spindle that had held an emery wheel. A new measuring device, or balance, was built of wire intended for bicycle spokes, and pieces of hacksaw blades. These experiments were now done with much more refinement than at first, and the measurements were for both “lift” and “drift.” But as each curved surface measured was balanced against the pressure on a square plane, exposed at ninety degrees to the same air current, it was not necessary to know the precise speed of the air current. During that autumn and early winter of 1901, the brothers tested in the wind-tunnel more than two hundred types of wing surfaces. They set these at different angles, starting with the angle at which the surface begins to lift, and then at 2½ degree intervals, up to twenty; and at five degree intervals up to forty-five degrees. They measured monoplane, biplane, and triplane models; also models in which one wing followed the other, as used by Langley in his experiments. They measured the lift produced by different “aspect ratios”--that is, the ratio of the span of the wing to its chord. They found that the greater the span in proportion to the chord the more easily the wing may be supported. They measured thick and thin surfaces. One surface had a thickness of nearly one-sixth of its chord. Among other things, these experiments proved the fallacy of the sharp edge at the front of an airplane wing and the inefficiency of deeply cambered wings as then generally advocated by others. Sometimes they got a result so unexpected that they could hardly believe their own measurements--as, for example, when they discovered that, contrary to all previously published figures by students of the subject, a square plane gave a greater pressure when set at thirty degrees than at forty-five degrees.