248 IRRIGATION FARMING. 



is called a tilting tower. This tower supports a mast 

 pivoted in the center. On one end of this mast is placed 

 the wheel, while the other end is weighted to the weight 

 of the wheel. When oiling is needed the foot of the 

 mast is unlocked and the wheel drawn to the ground. 

 The latest plan introduced to overcome the necessity of 

 oiling is to have all bearing parts made of graphite, 

 which is a composition of brass and black lead, the latter 

 in itself a great lubricator. The makers of these bear- 

 ings claim that they will last from twenty to twenty-five 

 years. All bolt work on a frame and about the gearing 

 should be carefully watched, and where joints become 

 loosened they should be tightened promptly, as in this 

 way serious loss may often be averted. 



Power of Wind Engines. The velocity of the 

 wind and the diameter of the wheel determines the 

 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 sur- 

 face. 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 cer- 

 tain sections, as along the sea coast and throughout the 

 plains and table-lands, the velocity is much greater, 

 while in other sections it is less than the general aver- 

 age. It is, as a rule, safe to figure on eight to ten hours' 

 work out of the twenty-four for the windmill, when the 



