LEVELLING 



193 



into the ground, driving in the high stake until the 

 plumb-line is about in, the middle of the board (bd). 

 Then mark just where the point of the plumb bob comes 

 Reverse the apparatus upon the stakes, without chang- 

 ing them and mark where the point of the plumb-bob 

 comes. Exactly halfway between the two marks is the 

 proper place to put the level mark. When the apparatus 

 is placed so that the plumb-bob comes to this mark the 

 bottom stick is level. 



Sometimes a certain slant is wanted, as when ditches 

 are being dug to carry water. In this case a block is 

 placed at (ce), having a length according to whatever 

 drop, as it is called, is wanted for each eleven feet. Then 

 the apparatus is used as in levelling, but instead of being 

 level the ground has the slant which is desired. 



Cut supplied through United States Department of Agriculture. 



Elern. Sci. 13 



