The Chinese and Japanese people have a kite-flying day. Most of their kites are made in the shapes of birds and butterflies, with wide-spread wings. They make them of hollow bamboo, the lightest and strongest wood known, and cover them with thin, tough rice-paper or silk. Very likely, many of them think no other kind of kite could stay up in the air. But really they stay up because their weight is spread out so that a great deal of air can get under them to support them. A bar of iron rolled into a sheet and pressed into a boat floats.

If all the material in a kite were crumpled into a lump, it would sink or drop through the air. Aeroplanes or flying machines are built much like kites—light, strong and spread out, giving a great deal of surface to the air. The chief difficulty in making use of them is that they must carry an engine, and at least one man to operate them. A balloon can carry men because it is filled with a gas that makes it lighter than the air, for a time.

Now a bird is like a balloon and a kite and a flying machine. Its wings give it the surface spread of the kite. Then it has air spaces in its body, and even in its bones and feather quills, like the strong, light, hollow frame-work of bamboo. Its feather dress is as light as paper or silk. No engine ever made is as powerful, in proportion to its weight, as the living, beating heart of a bird; no propellers as strong as the bird's wing-muscles, no rudder as flexible as a bird's tail. The shape of a bird's body is that of a little boat or a fish. It is sharply pointed in front and rear, with softly curving sides. The close-lying feathers are oiled so as to offer the least resistance to the air. The legs, being of no use in flying, are light and slender, and are folded back out of the way. With its wings a bird beats the air downward.

The bird knows very well that it is heavier than the air. When it wants to come down, it folds its wings and drops. Near the ground or perch, it raises its wings for a parachute, to break its fall. The aeronaut who jumps from a balloon uses a parachute. You see how much men have learned from birds in making kites, balloons and flying machines.

The first flying machines that men tried to make were really cigar or boat or bird-shaped, gas-filled balloons, with an engine to drive them in any direction through the air. That borrowed the light, air-filled body of the bird, the rudder tail and the beating-heart engine, but it made no use of the wing-power. The aeroplane or true flying machine of today, uses the wing-spread idea of the bird and the kite, with the engine heart and the rudder tail. (See Aeronautics.)