A glider is an aeroplane without a propeller. With it one can cast off into the air from a great height and sail slowly to the ground. Before attempting to use a motor and propeller, the Wrights learned to control the glider perfectly. They had to learn how to prevent its being tipped over by the wind, and how to steer it in any direction. This took years of patient work. But the problem was conquered at last, and they attached a motor and propeller to the glider, and had an air-ship under perfect control and with the speed of an express-train. Their flyer of 1905, which made a flight of twenty-four miles at a speed of more than thirty-eight miles an hour, carried a twenty-five-horse-power gasolene motor, and weighed, with its load, 925 pounds. Figs. 94 and 95 show the Wright air-ship in flight. Fig. 97 shows the mechanism. [Illustration: FIG. 94--IN FULL FLIGHT] [Illustration: Copyright, 1908, by Pictorial News Co. FIG. 95--WRIGHT AIR-SHIP IN FLIGHT Rear view, showing propellers.] [Illustration: FIG. 97--THE SEAT AND MOTOR OF THE WRIGHT AEROPLANE Photo by Pictorial News Co.] How the Wright Aeroplane Is Kept Afloat The Wright aeroplane is balanced by a warping or twisting of the planes 1 and 2, which form the supporting surfaces (Fig. 96). If left to itself the machine would tip over like a kite when the string is cut and drop edgewise to the ground. Suppose the side _R_ starts to fall. The corners _a_ and _e_ are raised by the operator while _b_ and _f_ are lowered, thus twisting the planes, as shown in the dotted lines of the figure. The side _R_ then catches more wind than the side _L_. The wind exerts a greater lifting force on _R_ than on _L_, and the balance is restored. The twist is then taken out of the machine by the operator. A ship when sailing on an even keel presents true unwarped planes to the wind. [Illustration: FIG. 96--HOW THE WRIGHT AIR-SHIP IS KEPT AFLOAT This picture represents a glider. The motor-driven aeroplane is balanced by the warping of the planes in the same way as the glider.]