Ixii 



GEODESY. 



Survey for 1876. Table 12 taken from the same source gives values of log p 

 needed for use in (3) and (4). 



For less precise work one may use equation (4) in the form 



H^ — IT\^^ s cot Zi-\- c s^. 



(5) 



wherein, if we make in = 0.07 and use for p its average value, or \j p,„ p,„ for 

 latitude 45°, 



log r = 2.313 — 10 for s in feet, 

 = 2.829 — 10 for s in metres. 



Thus, for a distance (s) of 10 miles the value of the term cs- in (5) is 57.3 feet. 



If altitudes a,, say, are observed in the place of zenith distances z^, it is most 

 convenient to write (5) thus : — 



!/._, — 7/i = ± s tan a^ -\- c r, (6) 



