idered a monoplane. The box kite presents two such surfaces joined together at the sides by the ends of the "box," and may therefore be called a biplane.
When the boy flies his kite he first determines the direction of the wind and runs in that direction. In other words he flies his kite against the wind. The pressure of the moving current against the under surface keeps the kite aloft. When the boy runs against the wind, moving the kite forward with him, this pressure is increased and the kite tends to rise higher and higher. If instead of the long string and the boy there could be placed with the kite itself a very light motor that would give to it the same forward impulse, the kite would float through the air without boy or string and we would have a small aeroplane flying machine--a monoplane. If there were two kites, with parallel surfaces a few inches apart, united with light framework so that the air would pass between them, we should have a biplane. For many years the great problem in aviation