EXPERIMENT STATION BULLETINS. 



471 



tice. See Fig. 4. In any system of tile, that line which receives the 

 water from all the other parts of the system is called the main and 

 all the lines receiving water directly from the soil and conveying it to 

 the main are called laterals. If there should be more than one sys- 

 tem of laterals, each sj^stem flowing into another line than the main, 

 which in turn carries the water to the main, this other line we call a 

 sub-main. Figure 4 illustrates this point. 



OUTLET. 



The point at which the main discharges its water is called the outlet. 

 The efficiency of a tile system and the expense of installing such a 

 system Avill depend vei-y much upon the location and the construction 



Fig. 4. A combination of the systems shown in Fig. 1 and Fig. 2, 

 in operation on the college farm. 



of the outlet. Generally the outlet should be so located that the main 

 shall extend through the loAvest portion of the area to be drained and 

 that the main can be placed with the least amount of digging, and have 

 the fewest possible angles in its course. It should be so located that 

 ordinary outside water should not stand as high as the bottom of the tile. 



DEPTH. 



It is desirable that tile drains shall lie about three feet below the 

 surface. It sometimes happens that in fields with uneven surfaces, or 

 where it is difficult to get the proper amount of fall, the tile must be 

 laid in places as close 1o Hie surface as eighteen inches. Tile placed too 



