FARM IRRIGATION 249 



by steam are quite commonly used up to 40-horse 

 power and sometimes larger. Most of the smaller 

 pumps are run by gasoline. These pumps draw 

 water easily from a depth of 100 to 400 feet. This 

 method is practicable chiefly in the humid and sub- 

 humid regions and for small operations, but rarely 

 in an aria country and for large operations. Gaso- 

 line engines are often used to supplement wind 

 power, Deing used to run the pump on still days. 



Water-wheels. One of the oldest and still one 

 of the most useful means of carrying water to 

 thirsty land is by utilising the force of flowing 

 water. When a stream has sufficient fall to de- 

 velop water power this is one of the cheapest and 

 most satisfactory methods of irrigating small 

 areas. There are thousands of water-wheels on 

 the edge of swift-flowing streams in the arid West, 

 and hundreds of thousands in Europe and Asia. 



The undershot is one of the oldest and best of 

 water-wheels. This is a paddle wheel carrying 

 buckets on its rim, so that when the current turns 

 the wheel the buckets are filled, raised to the top 

 and emptied automatically into a wooden flume 

 which carries the water into the irrigation ditch. 

 These undershot wheels are of many patterns, and 

 may be as much as 35 feet in diameter. The largest 

 may supply nearly 120 acres with 2 inches of water 

 every ten days. 



On the other hand, the' water-wheel may be used 

 to drive a centrifugal pump which develops power 

 to lift other water out upon the land. This method 

 is especially useful when the stream has a high 

 bank along which canals could be built only at 

 great expense. The Wyoming Experiment Station 

 describes a wheel 10 feet in diameter and 14 feet 

 long, which is connected by a sprocket wheel and 



