[Illustration: FIG. 28.--The 1900 Wright Glider (operator’s position).] Their first glider was a biplane, with 165 square feet of lifting surface, as illustrated in Fig. 28; several of its features need explanation. First there is the position of the operator; he can be seen lying prone across the centre of the lower plane. This attitude was adopted by the Wrights to minimise wind-pressure. Should a man be upright in his machine, they calculated that his body would, as the glider passed through the air, offer an appreciable resistance; while, in lying flat, he would offer scarcely any resistance at all. A small horizontal plane will be noted in front of the main-planes; this was to govern the rising and descending of the machine. The Wrights came to the conclusion that any body-moving method for controlling their craft, such as Lilienthal had adopted, would not be sufficiently powerful in a wind. Lilienthal, it will be remembered, had found his control weaken when he used a machine of large surface. So the Wrights decided that, instead of altering the centre of gravity of their machine when gusts struck it, they would leave the centre of gravity immovable and shift the centre of pressure upon their planes. This was done partly by the elevating plane, as it came to be called. Tilted upward, this had the effect of raising the front of the glider, and causing the centre of pressure to travel backward upon the planes. Tilted down, it made the planes dip forward, and brought the centre of pressure nearer their front edge. When he wanted to rise, the pilot raised the elevator; when he wished to glide earthward, he inclined it down. Here, indeed, was the method such as was described in Fig. 13, when dealing with the machine Sir Hiram Maxim built; and this system of the lifting plane is worthy of special mention. In one way or another, fitted in front of the planes or behind them, it is the recognised method for controlling the rise or descent of an aeroplane.