EXPERIMENT STATION BULLETINS. 



497 



I ig. 19a. Tile scoop. 



Fig. 19b. Tile scoop. 



1 



Fig. 20. Tile hook. 



GRADE BARS. 



We have determined Tiow deep the ditch must be dug at each grade 

 stake. It is necessary to provide some simple means (1) by which we 

 may know just how deep to dig at every point, and (2) by which we 

 may scoop out the bottom of the ditch so that the fall shall be constant 

 from one grade stake to the next above or below. In Figs. 21 and 22 

 are shown what are known as grade bars. These grade bars are set up 

 over each grade stake, and the top of every grade bar is set at the same 

 height above the proposed hottoni of the ditch, and horizontal. This 

 height is usually 5.5 ft. in our own practice. Some persons prefer to 

 make it 6 ft. 

 63 



