342 



AGRICULTURAL ENGINEERING 



and also as the square of the diameter of the wheel. A later 

 investigator found that the power varied more nearly as the 

 square of the wind velocity and about the 1.25th power of 

 the diameter of the wheel. The following table, reproduced 

 from the work of Mr. E. C. Murphy, indicates in a general 

 way the amount of power furnished by different kinds of mills 

 under different conditions. 



Power furnished by windmills under different conditions. 



Towers. Like the windmill proper, the tower may be 

 built either of wood or steel. With the increase in the cost 

 of wood the steel tower has come into more general use. The 

 usual height of tower for a pumping mill varies from 20 to 

 60 feet. The wooden tower usually has four posts made of 

 4x4 or 5x5 material. The steel tower is made up of three or 

 four posts of angle irons. The steel tower is now almost 

 universally galvanized for protection against corrosion. This 

 is also true of the steel windmill. It is desirable to have the 

 wheel placed well above all obstructions to the wind, in the 

 way of trees, buildings, or embankments. A small wheel 

 on a high tower is regarded as better than a large wheel on a 

 lower tower which does not permit the wind to reach the 

 wheel with full force. 



