Means for Leveling. 



313 



carpenter's square mounted on a horizontal arm on which 



a plumb bob is suspended, 



with which to set the 



square with its long arm 



level. 



387. leveling a Field 



In determining the differ- 

 ences of level, in different 

 parts of a field it is desired 

 to drain, the simplest 

 method for the inexper- 

 ienced person is to lay out 

 the field into squares of 

 100 or more feet, driving 

 short stakes at the coiners. 



Set the instrument at a, 

 Fig. 133, midway between 

 the stations 1-1 and !-:> 



i j ,-, -,. U 1 iG. 1S2.- Show ing cue form of water level. 



and record the reading 01 

 the target placed upon the 



stake at 1-1 in the table in the column headed "back-sight" 

 which is assumed for illustration to be 4 feet. Next turn 

 the instrument upon stake 1-2, when its distance below the 

 level is found to be 3.8 feet and is entered in the column 

 headed "fore-sight." This shows that the ground at 1-2 is 



4ft. 3.8ft. =.2 ft. 



higher than station 1-1. 



In the column headed "Elevation" the first station is 

 given arbitrarily a hight of 10 feet above an assumed 

 datum plane to avoid minus signs. The level is now trans- 

 ferred to b and the distance of 1-2 below the instrument 

 found to be 4.2 feet which is entered in the column "back- 

 sight" as before. Turning now upon 1-3, its reading is 

 found to be 4 feet and this is entered in th^ column "fore- 

 sight." 



The difference in level between the back sight and fore 

 sight shows the difference in level between the two stations 



