THE USE OF PIPES ON THE SURFACE. 55 



fig. 23. ) This distance, however, will depend altogether 

 upon the force with which the water is discharged or upon 

 the amount of head given to the supply reservoir. The 

 operation of this system is illustrated herewith. It has 

 the disadvantage of increased cost, but the merit of econ- 

 omy of application. One acre is irrigated at a time and 

 during one hour. The irrigation is done, as it always 

 should be, at night, or between the afternoon and the 

 morning. The apparatus is self -operating and needs only 

 the turning on and off of the water by an attendant, who 

 can be occupied with other work in the intervals. A plan 



Fig. 23. IRRIGATING BY SURFACE PIPES. 



of subsoil irrigation by means of drain tiles has been in 

 operation for many years, although a recent patent has 

 been granted in the United States for the invention. The 

 patent only refers to perforated tiles. But the common 

 drain tiles will answer every purpose that the perforated 

 pipes can or will. The plan is very simple. It is exactly 

 the reverse of draining by tiles. Large pipes the size 

 being chosen to suit the system tributary to them are 

 laid down, a foot beneath the surface, at the highest part 

 of the tract to be irrigated. From these, smaller pipes 

 branch as the secondary channels of supply, and from 

 them one-inch pipes again branch as distributing chan- 



