318 Irrigation and Drainage 



Number of acres a first-class windmill may irrigate to a depth of 10 inches 

 and 20 inches in 100 days 



Lift 10 feet Lift 15 feet Lift 20 feet 



Diam. of 10 ins. per 20 ins. per 10 ins. per 20 ins. per 10 ins. per 20 ins. per 

 wheel 100 days 100 days 100 days 100 days 100 days 100 days 



In computing this table for other sizes of wheels, we have 

 used the ratios calculated by Wolff ; * but as our observed work 

 is about 12 per cent less for the 16 -foot wheel than he com- 

 putes for this size, the values in the table are correspondingly 

 lower than his table would give. It is the writer's conviction, 

 however, that the results he has observed for the 16 -foot 

 wheel are quite as high as will be likely to be realized by 

 average practice with the pumping devices of to-day. 



NECESSARY CONDITIONS FOR THE HIGHEST SERVICE 

 WITH A WINDMILL 



In order that the largest service may be secured from a 

 windmill, there are certain essential conditions which must be 

 observed. First among these is a good wind exposure. It is 

 useless to purchase a windmill and then set it up in such a 

 manner that the wind cannot have free access to it. Strong 

 towers, having a height of 70 to 90 feet, should usually be 

 used, and these placed where hills, groves or other obstructions 

 cannot break the jforce of the wind. 



Second in importance to a good exposure of the mill is a 

 pumping outfit thoroughly adapted to the power of the mill. It 

 should not be so heavy as to force the mill to stand idle in winds 

 of 9 miles per hour, and yet it should be capable of utilizing 

 the full power developed in a 25- to 30 -mile wind. 



*A. R. Wolff, the Windmill as a Prime Mover. 



