THE WINDMILL 



185 



which rise, as the kite does, because of the resistance 

 (inertia) of the air (Fig. 190). Only, while the kite uses 

 the inertia of air in motion (wind), the plane airship uses 

 air as matter which resists being pushed out of the way. 



The explanation of the action of the air upon the aeroplane is prac- 

 tically the same as if the aeroplane were still, and the air were in rapid 



FIG. 190. 

 A Modern Wright Flyer. Courtesy of Dr. Orville Wright. 



motion. When the engine forces the planes rapidly forward, the force 

 (resistance) of the air acts in two parts, as with the kite. One of these 

 parts opposes the forward movement of the planes, and must be over- 

 come by the engine. The other portion of the air's resisting force acts 

 vertically upward, and raises the planes, against gravity, into the air. 



210. The Windmill. One of the reasons why farming 

 has developed so rapidly in recent years is that windmills 



