THE DRAINAGE OF FARM SOILS 215 



is determined with the aid of a measuring rod, 

 which has an arm at a right angle and long enough 

 to reach to the line. 



A Sighting Method. Brooks recommends a 

 simpler and scarcely less accurate device for secur- 

 ing the right grade. Drive two stakes at the outlet, 

 one on each side of the position of the ditch, 

 so that when firm their tops are a little over six 

 feet above the level of the drain at the outlet. Thus 

 if the outlet must be 3 feet 8 inches deep the tops of 

 the stakes will be a little over 2 feet 4 inches above 

 the level of the ground. Nail a light, narrow board 

 from stake to stake so that the top of it will be level 

 and exactly six feet above the bottom of the drain. 

 Go to the upper end of the drain and place a similar 



frade board just 6 feet above the bottom of the 

 itch there; if the drain is 300 feet long, and a 

 grade of 3 inches in 100 feet can be secured, this 

 grade board will be nailed 9 inches above the sur- 

 face. 



At intervals of 50 feet on the line of the 

 drain set similar pairs of stakes. The height at 

 which to nail the grade boards on these is deter- 

 mined by sighting from the lower to the upper 

 grade boards, or vice versa. Dig the ditch nearly 

 to the desired depth. Now stretch a stout cord 

 very tightly from the top of the grade board at the 

 outlet to the top of the grade board at the upper 

 end of the drain, and midway between the stakes, 

 where the centre of the drain should be. Brace 

 the upper and lower grade boards to prevent the 

 line from sagging. When the ditch is completed 

 the bottom at all points should be exactly six feet 

 below the cord. 



The success of this device depends upon the 

 accuracy with which the sighting is done and the 



