The preserving of an even keel is accomplished in the Curtiss machine by small planes hinged between the main planes at the outer ends. They serve to prevent the machine from tipping over sideways. They are operated by arms, projecting from the back of the aviator’s seat, which embrace his shoulders on each side, and are moved by the swaying of his body. In a measure, they are automatic in action, for when the aeroplane sags downward on one side, the pilot naturally leans the other way to preserve his balance, and that motion swings the ailerons (as these small stabilizing planes are called) in such a way that the pressure of the wind restores the aeroplane to an even keel. The wires which connect them with the back of the seat are so arranged that when one aileron is being pulled down at its rear edge the rear of the other one is being raised, thus doubling the effect. As the machine is righted the aviator comes back to an upright position, and the ailerons become level once more. [Illustration: Starting a Wright machine. When the word is given both assistants pull vigorously downward on the propeller blades.] There are other controls which the pilot must operate consciously. In the Curtiss machine these are levers moved by the feet. With a pressure of the right foot he short-circuits the magneto, thus cutting off the spark in the engine cylinders and stopping the motor. This lever also puts a brake on the forward landing wheels, and checks the speed of the machine as it touches the ground. The right foot also controls the pump which forces the lubricating oil faster or slower to the points where it is needed. The left foot operates the lever which controls the throttle by which the aviator can regulate the flow of gas to the engine cylinders. The average speed of the 7-foot propeller is 1,100 revolutions per minute. With the throttle it may be cut down to 100 revolutions per minute, which is not fast enough to keep afloat, but will help along when gliding. Obviously, travelling with the wind enables the aviator to make his best speed records, for the speed of the wind is added to that of his machine through the air. Again, since the wind is always slower near the ground, the aviator making a speed record will climb up to a level where the surface currents no longer affect his machine. But over hilly and wooded country the air is often flowing or rushing in conflicting channels, and the aviator does not know what he may be called upon to face from one moment to the next. If the aeroplane starts to drop, it is only necessary to push the steering wheel forward a little--perhaps half an inch--to bring it up again. Usually, the machine will drop on an even keel. Then, in addition to the motion just described, the aviator will lean toward the higher side, thus moving the ailerons by the seat-back, and at the same time he will turn the steering wheel toward the lower side. This movement of the seat-back is rarely more than 2 inches.