Take a sheet of stiff paper and cut it in the shape shown in the diagram above, but considerably larger. Be very careful to have the two sides alike, so that they shall balance each other. Now fold up the front margin of each wing, along the dotted lines a, a, a, a, to form a stiff rim to represent the rim of bone along the front edge of a bird's wing, and cut out a small strip of wood, about as thick as a match and twice as long, and run this through the two slits, b, b, to represent the body of the bird. If you hold this model about three feet from the ground, and allow it to fall gently, you will see that, instead of falling straight to the ground, it will slide forward, and strike the ground two or three feet ahead of you. It is really its weight which causes it to do this, so that the statement that a bird flies by its own weight is strictly true.
This is true, also, of insects and bats. They all have wings with stiff front edges, and flexible hind edges which bend and allow the air to pass out, so that flying is nothing but sliding down a hill made of air. A bird rises, then, by flapping its wings, and it flies by falling back toward the earth and sliding forward at the same time. At the end of each stroke of its wings it has raised itself enough to make up for the distance it has fallen since the last stroke, and accordingly it stays at the same height and moves forward in a seemingly straight line. But if you watch the flight of those birds which flap their wings slowly, such as the woodpecker, you can see them rise and fall, and will have no trouble in seeing that their path is not really a straight line, but is made up of curves; although most birds flap their wings so rapidly that they have no time to fall through a space great enough to be seen. Birds also make use of the wind to aid them in flight, and by holding their wings inclined like a kite, so that the wind shall slide out under them, they can sail great distances without flapping their wings at all. They are supported, as a paper kite is, by the wind, which is continually pushing against their wings, and sliding out backward and downward, thus lifting or holding up the bird, and at the same time driving it forward.
A SKILLFUL FLYER.
The birds are not compelled to face the wind while they are sailing, but by changing the position of the wings a little they can go in whatever direction they wish, much as a boy changes his direction in skating by leaning a little to one side or the other. Some birds are very skillful at this kind of sailing, and can even remain stationary in the air for some minutes when there is a strong wind; and they do this without flapping their wings at all. It is a difficult thing to do, and no birds except the most skillful flyers can manage it. Some hawks can do it, and gulls and terns may often be seen practicing it when a gale of wind is blowing, and they seem to take great delight in their power of flight.
Of all birds the albatross is the most skillful in the art of sailing in the air. It is a large sea-bird, about the size of a swan, and has very long and powerful wings. It lives far out upon the open ocean, hundreds of miles from land, and spends nearly all of its life in the air, very seldom alighting upon the water. It flies almost entirely by the aid of the wind, and sometimes does not flap its wings for an hour at a time. Albatrosses often follow a ship clear across the ocean, or, rather, they keep company with the ship, for as they are able to fly one hundred miles an hour with ease, the rate at which a ship travels is much too slow for them; so they make long journeys ahead and behind, like a dog taking a walk with his master, returning occasionally to the ship to pick up any food which may have been thrown overboard.
[NANCY CHIME.]
By S. Smith.