FOR BETTER CROPS IN THE SOUTH 



99 



become filled with silt or sediment, thus decreasing the efficiency 

 of the tile. When the amount of money, time, and labor invested 

 in laying a tile system is taken into account, it is easy to see 

 the importance of being absolutely certain that the tile is laid 

 to grade, and that the grade is properly established. This can 

 be done only by using a surveying instrument. 



The Target System — All that is necessary in the target 

 system of grading is to make two or three targets as shown in 

 Figure 7, and one sighting rod, which should be about four and 

 a half feet in length, depending upon the height of the man 

 doing the grading. 



Fig. 7. Grading the ditch 



The targets may now be set as follows: We will say that 

 the tile at a certain station are to be laid thirty inches deep. 

 The sighting rod is fifty-four inches long. The target should 

 be set so that it is two feet above the hubs. In other words, 

 the depth of the ditch and the height of the target should equal 

 the length of the sighting rod. 



Digging the Ditch— Start at the outlet in digging the ditch. 

 The top twenty-four inches should be removed, leaving the last 

 six inches to be thrown out by the man doing the grading. 



i — r 



) ) ) 



I =a=3HSEEZE 



T T) } > j 



Fig. 8. Sags in tile line soon become filled with silt 



Start at the outlet when doing the grading, so that the sight- 

 ing rod will just reach the top of the target. Work back to 

 Station 1, keeping the top of the sighting rod in line with the 

 top of the two targets. Work this way until you have passed 

 Station 2. Then remove the target at Station 0, and place it at 

 Station 2, setting it the right distance above the hub. Continue 

 until the ditch is finished. By a little practice you will be able 

 to grade a ditch properly, giving it a uniform grade from end 

 to end, which will insure proper laying of the tile, and prevent 

 the loss due to sags and variation in the grade of the tile. 



To lay stress upon the danger of poor grading, you will 



