Flexure. The capacity to bend and yield, and return to its original position. Flexible, That which will yield; springy. Fore and Aft. Lengthwise, as from stem to stern of a ship. Formation. The shape or arrangement of an article or thing. Formulated. Put into some eonerete form, or so arranged that it may be understood. Frictionless. Being without a grinding or retarding aotion. Fulcrumed. A resting place for a lever. Function. The duty or sphere of action in a person, or object. Glider. An aeroplane, without power, adapted to be operated by an aviator. Governing. An element which is designed to control a machine in a regular manner. Graduated. A marked portion, which is regularly laid off to indicate measurements or quantities. Gravity. The attraction of mass for mass. The tendency of bodies to move toward the earth. Gravitatior The force with which all bodies attract each other. Gyratory. Having a circular and wheeling as well as a rotary motion. Gyroscope. A wheel, designed to illustrate the laws of motion, which freely revolves in gimbals within a ring, and when set into motion, objects to change its plane of rotation. Hemispherical. The half of a sphere. The half of an apple would be hemispherical. Hazardous. That which is doubtful; accompanied by danger. Helicopter. A type of flying machine which has a large propeller, or more than one, revolubly fixed on vertical shafts, by means of which the machine is launched and projected through the air. Horizontal. Level, like water. Hydroplane. A term used to designate an aeroplane which is provided with pontoons, whereby it may alight on the water, and be launched from the surface. The term hydroaeroplane is most generally used to indicate this type of machine. Impact. The striking against; the striking force of one body against another. Immersed. Placed under water below the surface. Impinge. To strike against; usually applied where air strikes a plane or a surface at an angle. Imitation. Similarity; the same in appearance. Incompatible. Without harmony; incapable of existing together. Incurved. Applied to a surface formation where there is a depression, or hollow. Inequalities. Not smooth, or regular; uneven. Infinitely, Boundless; in great number, or quality; without measure. Initial. The first; that which is at the beginning. Indestructibility. Not capable of being injured or destroyed. Influenced. Swayed; to be induced to change. Inherent. That which is in or belongs to itself. Initiating. To teach; to instill; to give an insight. Indicator. A term applied to mechanism which shows the results of certain operations and enables the user to read the measure, quantity, or quality shown. Inconceivable. Not capable of understanding; that which cannot be understood by the human mind. Institute. To start; to bring into operation. Insignias. Things which are significant of any particular calling or profession.