362 IRRIGATION FARMING. 



power. An eight-mile velocity of wind an hour gives 

 a force equal to one-third pound to a square foot, and 

 a fifteen-mile wind gives a force of one pound to a 

 square foot; a twenty-mile wind gives a force of .two 

 pounds to a square foot, and a twenty-five-mile wind 

 gives three pounds, while a thirty-mile wind gives a 

 force of about four and one-half pounds to a square 

 foot of wheel surface. Thus it will be seen that the 

 force of the wind increases or decreases in the ratios of 

 the squares of the velocities. A fifteen-mile wind gives 

 a force a little more than three times as great as an 

 eight-mile wind, and just twice as great as a ten-mile 

 wind, while a twenty-mile wind is nearly twice as great 

 as a fifteen-mile wind. The mean average velocity of 

 the wind throughout the United States is a little less 

 than eight miles an hour. In certain secflions, as along 

 the sea-coast and throughout the plains and table-lands, 

 the velocity is much greater, while in other secflions it 

 is less than the general average. It is, as a rule, safe 

 to figure on eight to ten hours' work out of the twenty- 

 four for the windmill, when the wind velocity will be 

 eight to fifteen miles an hour. At certain seasons, and 

 again in some localities, the velocity will equal fifteen 

 to twenty miles an hour for eight to twelve hours or 

 more out of the twenty-four. 



Pumping windmills of the solid wheel type are 

 usually adjusted by regulating their governor, so as to 

 govern w^hen the velocity of the wind reaches fifteen 

 miles an hour. This is to avoid injury to the pump 

 by preventing too rapid ac5lion of the pump valves. 

 Back-geared mills are an exception to this rule, being 

 geared back for the purpose of reducing the number of 



