48 



A MANUAL OF TOPOGRAPHIC METHODS. 



Reduction to sea level. 



log K (metres) . 



I«-L. r A nili'tirsi. 



Co log E 



. = 4. 05956 

 . = 2. 87599 

 . 3. 19660 



4. 448 feet 0. 64814 



Spearville base : Summary by section/). 

 [Corrected for temperature.] 



Mean of '- measurements = *37, 806. 645 



Reduction from S. W. liase to A - 168.235 



Reduction from N. E. base to A - 2.864 



Correction for inclination — 0.179 



Reduction to sea level - 4. 448 



Corrected length = 37,630.919 



PRIMARY TRIANGULATION. 



The base line having been measured, the next step is the expansion. 

 This work, as well as the body of the triangulation, consists in the selection 

 of stations, the erection of signals, and the measurement of angles. Each 

 triangle proceeding from the base line outward will, when the angular meas- 

 urement is completed, have one side and the three angles known, from which 

 the other two sides can be computed by means of a simple trigonometric 

 formula. 



The expansion differs from the body of the triaugulation only in the 

 fact that the average length of the sides of the triangles is less. As the 

 expansion progresses away from the base line, the sides of successive triangles 

 become gradually longer, until the average length of side of the triangula- 

 tion is reached. Since the sides are increasing in length, and hence since any 



* Corrected for temperature. 



