114 



TOPOGRAPHIC SURVEYING 



of inclination determined. When the spirit level is set parallel 

 to the main tube it can be used as a hand level. 



If the horizontal distance of a slope is h and the angle of 

 slope a, the difference in elevation between the top and the 

 bottom of the slope, e, is 



e=h tana 



Also, h = ecota 



Example of Cross-Sectioning With Hand Level. Fig. 4 

 represents the right slope at Station 108 of a railroad survey. 

 The topographer, having determined that his eye is 5.1 ft. 

 above the ground, stands at the station and the rodman holds 

 the rod at B, where the slope changes. The topographer, by 



FIG. 4 



means of the hand level, finds that 10.4 ft. on the rod is level 

 with his eye. From this is deducted 5.1 ft., the height of his 

 eye, and the remainder, 5.3 ft., is recorded as the difference 

 in elevation between the points A and B. The distance from 

 A to B is measured and found to be 62 ft. and the slope, is 



5.3 

 recorded ~~a^~> minus meaning a descending slope. 



The topographer then proceeds down the slope to C, where 

 his eye is about level with the bottom of the rod at B. The 

 rod reading on B is .6 ft. The rodman proceeds to D, where 

 the slope again changes. The topographer turns around at C 

 and obtains the rod reading on D. which is 11.7. The differ- 

 ence of these rod readings, 11.7 .6 = 11.1, is the difference 



