WATER WHEELS AND WINDMILLS 



205 



wheel to rotate. The principle of the windmill is the 

 same as that of the turbine water wheel ; the moving sub- 

 stance or fluid strikes the blades of the wheel at an angle 

 in each case and thus imparts mechani- 

 cal energy to the wheel. The axle of 

 the wheel of the windmill is rigidly 

 fastened to the wheel. The axle has 

 fastened to it a cogwheel that turns 

 another wheel with a crank attached 

 which moves the piston of the pump up 

 and down as the wheel turns around. 



The wheel of a windmill will not turn 

 when it stands edgewise to the wind. 

 It must stand perpendicular to the 

 wind, that is, face the wind, in order to 

 rotate. A tail -like fan is used to cause 

 the wheel to face the wind. When the 

 fan is perpendicuar to the wheel the 

 wheel will face the wind and rotate, but 

 when the fan is pulled so that it stands 

 edgewise with the wheel, the wheel will 

 not rotate. By shifting the fan the 

 wheel is thrown in or out of action. Most windmills 

 are constructed so that they throw themselves out of 

 action when the wind blows extremely hard. 



Windmills are used mostly for pumping water. The 

 water is kept out of the lowlands of Holland by wind- 

 mills which are very numerous and work while the wind 

 blows. Many farmers use windmills for pumping water 

 for their live-stock and for their homes. The water is 

 generally pumped into an elevated tank. From these 

 tanks it is piped into the house for use in the various 

 rooms and sometimes piped into the barn for the stock. 



WINDMILL 



