90 



AGRICULTURAL ENGINEERING 



grading ditches are in vogue. One is to stretch a cord or 

 line above the surface parallel to the grade line, using a 

 measuring stick to locate the grade. This is generally known 

 as the "line and gauge method." The other, the "target 

 method/' consists in locating a line of sights or targets above 

 the ditch, parallel to the required bottom, and the depths at 



all points are gauged by 

 sighting over these sights 

 and using a measuring 

 stick to determine the 

 proper depth. 



When the line is used 

 it must first be decided 

 how far above the bottom 

 of the ditch to place it, 

 and a measuring rod of 

 this length provided. 

 Five or seven feet are 

 convenient distances for 

 the usual depth of dig- 

 ging. The line may be 

 stretched directly over the 

 ditch or to one side. The 

 first instance requires that 

 a yoke be constructed 

 over the ditch, while the 

 latter requires only a 

 single standard or stake. 



Some tilers object to the line stretched over the ditch, 

 as it is more or less in the way, but there is no doubt that 

 more accurate measurements can be made when the line is 

 so placed. If the line be stretched at one side of the ditch, 

 a measuring stick with a bracket must be used. To obtain 



Fig. 57. 



The target method of grading 

 tile ditches. 



