50 



AGRICULTURAL ENGINEERING 



depending somewhat upon whether the levels are to be taken 

 above or below the elevation of the bench mark. 



As for field surveying, a substantial field book should be 

 provided for level 

 notes. A book of the 

 same size as previ- 

 ously suggested is de- 

 sirable, with ruling as 

 showninFig.37. The 

 elevationof the bench 

 mark is placed in the 

 second column oppo- 

 site the entry B. M. 

 in the first column. 



Set the instrument up half way between the bench mark 

 and the first point whose elevation is desired in the line of 

 levels. This point is called Station A, and is entered as such 

 in the first column of the field book. After the instrument is 



Fig. 37. A form for level notes. 



10.00 



Fig. 38. Sketch illustrating the levels of Fig. 37. 



brought into a level position, the rodman holds the rod in a 

 vertical position over the bench mark, and the levelman takes 

 a reading by, over, or through the instrument to the rod. The 

 reading thus obtained is the distance of the line of sight 

 above the bench mark (B. M.), as the rod is graduated from 

 the bottom up and the line of sight is a level line. This 



