Use of Drainage Levels 



473 



feet, at station 1-1, it gives 10.2 feet, or the 

 elevation of station 1-2 above the same plane. The 

 difference, .2 feet, between stations 1-2 and 1-3 added 

 to the elevation of 1-2, gives 10.4 feet, or that of 

 station 1-3. In this manner the instrument is moved 

 forward step by step until measurements from e have 

 been made, when the level is next set at /, and back- 

 and fore -sights taken and entered, as shown in the 

 table, so as to connect the observations of the first 

 line with those of the second line of stations. 



Proceeding to g, the steps described are repeated 

 by moving back through &, i, j, Jc and I to m, and so 

 on until the elevations of all the stations have been 

 determined and entered in the table. It will be 



Fig. 154. Method of leveling. 



observed that when proceeding from higher to lower 

 levels it is necessary to subtract the value in the 

 column of differences from the elevation of the station 

 preceding it, in order to obtain the elevation of the 

 station for that difference. 



In Fig. 154 is shown the method of leveling 

 described where the different positions of the level 

 and of the target along one line are shown in ele- 

 vation. 



