Structurally the wing of a bird is a screw. It twists in opposite directions during the up and down strokes, and describes a figure of 8 in the air. The bird throws its wings forward and downward. The air is forced back and compressed in the cup-shaped hollows of the wings, and these latter, by the recoil thus obtained, drag the body forwardThis resistance of the air is absolutely essential to flight. We who think that, but for the buffetings of hard fate, we, too, might soar high and fly free in the upper realm of endeavor, should watch the efforts of the birds in a calm. We shall scarcely see them flying. If impelled to flight, by necessity, the process isa most laborious one. There being no resisting wind on which to climb (birds always fly against the wind) the climber must, by the rapid action of his wings, establish a recoil that will send him along. Watch the little mud-hen, flying close to the surface of the water, ready to dive the instant its timidity takes fright. Its wings vibrate swiftly, unceasingly, for it rarely rises high enough above the water to have advantage of the air currents. For it there are no long, soaring sweeps through the air; no freedom from the labors of its cautious flight. It is a very spendthrift of effort because of the timidity that never lets it rise to the sustaining forces just above its head. To climb the sky is not for him who hugs cover.