Recognize. To know; seeing, hearing, or feeling, and having knowledge therefrom. Reflection. Considering; judging one thing by the examination of another. A beam of light, or an object, leaving a surface. Refraction. That peculiarity in a beam of light, which, in passing through water at an angle, bends out of its course and again assumes a direct line after passing through. Reflex. Turned back on itself, or in the direction from which it came. Requisite. Enough; suffieient for all purposes. Relegate. To put back or away. Rectangular. Having one or more right angles. Reservations. Land which is held by the Government for various purposes. Resistance. That which holds back; preventing movement. Retarding. Preventing a free movement. Revoluble. The turning or swinging motion of a body like the earth in its movement around the sun. See Rotative. To cause to move as in an orbit or circle. Resilient. Springy; having the quality of elasticity. Reversed. Changed about; turned front side to the rear. Rotative. That which turns, like a shaft. The movement of the earth on its axis is rotative. Saturation. Putting one substance into another until it will hold no more. For instance, adding salt to water until the water cannot take up any more. Security. Safety, assuredness that there will be no danger. Segment. A part eut off from a circle. Distinguished from a sector, which might be likened to the form of one of the sections of an orange. Sexagonal. Six-sided. Sine of the Angle. The line dropped from the highest point of an angle to the line which runs out horizontally. Sinuous. Wavelike; moving up and down like the waves of the ocean. Simulates. To pattern or copy after; the making of the like. Skipper. A thin flat stone. Spirally-formed. Made like an auger; twisted. Stability. In airships that quality which holds the ship on an even and unswerving course, and prevents plunging and side motions. Structural. Belonging to the features of eonstruetion. Strata. Two or more layers; one over or below the other. Stream line. In expressing the action of moving air, or an aeroplane transported through air, every part is acted upon by the air. Stream lines are imaginary lines which act upon the planes at all points, and all in the same direction, or angle. Stupendous. Great; important; above the ordinary. Substitute. One taken for another; replacing one thing by something else. Supporting. Giving aid; helping another. Synchronous. Acting at the same time, and to the same extent. Thus if two wheels, separated from each other at great distances, are so arranged that they turn at exactly the same speed, they are said to turn synchronously. Tactics. The art of handling troops in the presence of an enemy. It differs from strategy in the particular that the latter word is used to explain the movements or arrangement of forces before they arrive at the battle line. Tandem. One before the other; one after the other.