74 LEVELING 



LEVELING 



SPIRIT LEVELING 



Leveling is the process of determining the relative elevations 

 of a series of points. There are three general methods of 

 determining elevations, namely, gravity leveling, commonly 

 called spirit leveling, and also designated as direct leveling; 

 trigonometric leveling, also called indirect leveling; and baro- 

 metric leveling. 



The most highly developed form of the spirit level is the 

 engineers' level. It consists essentially of a telescope, having a 

 very accurate spirit level attached, mounted on a tripod and 

 controlled by leveling screws in such a manner that the line of 

 sight can be made truly horizontal. There are two general 

 classes of engineers' levels, namely, the wye level, also written 

 Y level, in which the telescope rests in Y-shaped supports from 

 which it can be removed, and the dumpy level, in which the 

 telescope is fixed. The wye level is much the more popular 

 with American engineers because of the facility with which it 

 can be adjusted, while the dumpy level is favored in Europe. 



THE WYE LEVEL 



An engineers' wye level is shown in Fig. 1. The telescope 

 A B rests in the Y-shaped supports Y, in which it is held 

 firmly by semicircular clasps, commonly called clips; these are 

 hinged at one end, and passing over the telescope are held 

 at the other end by small pins. The lower ends of the wyes 

 pass through the ends of the horizontal bar CD, sometimes 

 called the level bar, and are adjustable vertically by means of 

 the capstan-pattern nuts shown at C and D, which bear against 

 the upper and lower surfaces of the bar. The bar CD is 

 attached rigidly to the center or spindle, which turns in the 

 socket V, permitting the telescope to be revolved in a hori- 

 zontal plane. The spindle can be clamped by the screw K 

 and the telescope then revolved slowly by means of the tangent 

 screw t, which operates against a short projecting arm having 



