How Windmills Work. 169 



CHAPTER XVI. 



WINDMILLS. 



i. Here is a windmill (pointing to it on the 

 chart). This is a machine by means of which 

 we take hold of the wind, that we cannot see, 

 and make it do work that we can see. Wind- 

 mills are often used in this country to grind 

 wheat into flour, and corn into meal. 



Black-board Drawing-. Cog-wheels. Draw them by means of 

 chalk and a piece of cord. 



2. The large sails of the windmill turn a large 

 shaft with a cog-wheel that is, a strong iron 

 wheel with teeth, called cogs, all around it. 

 These teeth, or cogs, fit into the cogs of other 

 wheels and make them go around, so that you 

 can change in any way that is necessary the di- 

 rection of the moving wheels. Thus a very 

 large, round, and flat stone with a hole in the 

 middle is made to turn around above another 

 stone and very close to it. 



3. If wheat is poured into the hole in the 

 upper millstone it gets down between the stones., 



