his distance from the ground, while the others are utilised by the observer, as he turns to look from side to side. This biplane, and many others, is balanced against sideway roll by ailerons, and not by warping the wings. Constant warping, such as is necessary in the everyday use of machines, has been declared to strain a plane and render it weak; therefore the use of ailerons is now favoured. [Illustration: FIG. 64.--Scouting Monoplane, with occupants below the wings. A. Engine and propeller; B. Plane raised above hull; C. Seats for pilot and passenger; D. Rudder; E. Elevating-plane.] To meet the demand for a purely scouting machine, in which pilot and passenger shall have a clear field for observation, both above and below, a monoplane has been designed which is called the “parasol.” This machine, a Morane-Saulnier, is shown in Fig. 64. The two sustaining wings, forming a single surface, are raised above the body so that its occupants have nothing to impede their view earthward; and they can also see above them--an advantage of course in time of war, seeing that an enemy might be hovering overhead. [Illustration: FIG. 65.--The Control of a Biplane. A. Pilot’s seat; B. Hand-wheel (pushed forward or backward operates elevator; twisted sideways works ailerons); C. Foot-bar actuating rudder; D. Compass; E. Dial showing number of revolutions per minute that engine is making; F. Gauge showing pressure in petrol tank; G. Speed indicator; H. Dial showing altitude; I. Clock; J. Switch for cutting off ignition.] The driver of a modern-type aeroplane, sitting snugly within its hull, has a wheel and instrument-board before him, as sketched in Fig. 65. As he flies across country he has many things to think of. Holding the control-wheel in both hands, his feet resting upon the rudder-bar, his eyes rove constantly among the instruments on the dashboard before him. He glances at the compass often, for it is by this that he steers; and when the air is clear, and the earth below plainly seen, he will every now and then glance over the side of the hull, so as to be on the look-out for a landmark that may tell him he is on his course.