For convenience in explaining the action, the planes E are placed at right angles to their regular positions, F being the forward margin of the plane, and G the rear edge. Wires H connect the ends of the frame B with the respective planes, or ailerons, E, and another wire I joins the downwardly-projecting arms of the two ailerons, so that motion is transmitted to both at the same time, and by a positive motion in either direction. _Fig. 65. Action of the Gyroscope._ In the second figure, 65, the frame of the aeroplane is shown tilted at an angle, so that its right side is elevated. As the gyroscopic wheel remains level it causes the aileron on the right side to change to a negative angle, while at the same time giving a positive angle to the aileron on the left side, which would, as a result, depress the right side, and bring the frame of the machine back to a horizontal position. FORE AND AFT GYROSCOPIC CONTROL.--It is obvious that the same application of this force may be applied to control the ship fore and aft, although it is doubtful whether such a plan would have any advantages, since this should be wholly within the control of the pilot. Laterally the ship should not be out of balance; fore and aft this is a necessity, and as the great trouble with all aeroplanes is to control them laterally, it may well be doubted whether it would add anything of value to the machine by having an automatic fore and aft control, which might, in emergencies, counteract the personal control of the operator. ANGLE INDICATOR.--In flight it is an exceedingly difficult matter for the pilot to give an accurate idea of the angle of the planes. If the air is calm and he is moving over a certain course, and knows, from experience, what his speed is, he may be able to judge of this factor, but he cannot tell what changes take place under certain conditions during the flight. For this purpose a simple little indicator may be provided, shown in Fig. 66, which is merely a vertical board A, with a pendulum B, swinging fore and aft from a pin a which projects out from the board a short distance above its center. The upper end of the pendulum has a heart- shaped wire structure D, that carries a sliding weight E. Normally, when the aeroplane is on an even keel, or is even at an angle, the weight E rests within the bottom of the loop D, but should there be a sudden downward lurch or a quick upward inclination, which would cause the pendulum below to rapidly swing in either direction, the sliding weight E would at once move forward in the same direction that the pendulum had moved, and thus counteract, for the instant only, the swing, when it would again drop back into its central position. _Fig. 66. Angle Indicator._