CHAPTER V 

 LEVELING 



LEVELING is a process by which the heights or elevations 

 of definite points in a line or in an area above an arbitrarily 

 adopted plane are determined. This is called the datum 

 plane, and is usually so located as to lie lower than the 

 lowest point whose elevation is sought. In the ordinary 

 practice of leveling, for drainage purposes, this plane is 

 so established that the point at which the leveling begins 

 lies just 10 feet above it, " 10 feet above datum." 



It will be seen that if the datum plane is itself level, 

 and if the height of each point is determined, in a line or 

 in an area, above the datum plane, it is then an easy matter 

 to determine the difference in elevation between any point 

 and any other point, or to determine the fall between 

 any two points. 



124. The level. The level shown in Fig. 36 con- 

 sists of a telescope mounted on a spindle, which is in 

 turn mounted on a tripod. The telescope carries a spirit 

 level which is so carefully adjusted that when the bubble 

 stands in the center the telescope stands level for that 

 direction. When the tripod is set, the spindle can be ad- 

 justed so that the telescope swinging upon the spindle is 

 always level. 



As one looks through the telescope, one sees apparently 

 near the far end two lines one horizontal and the other 

 perpendicular crossing each other at the center of the 



94 



