40 A MANUAL OF TOPOGRAPHIC METHODS. 



The following is an example of these computations: 



Example of the computation of (he azimuth at elongation, and the local mean times of both 

 elongations of Polaris. 



[ Latitude = </, =40°. Meridian of Washington. November 28, 1891.] 



Sine Azimuth ;it elongation - sec. c/> cos 6. 

 log. 860. 40° =0.1157460 



log. COS I 88 44 05.5 =8. 3439803 



log. sine A 1 39 05. 8 =8. 4597203 



Cos. hour angle at elongation, t e , =tan * cot 6. 

 log. tan 40° = 9.9238135 



log. COtS 88 44 05.5 =8.3440862 



log, cos t, 88 56 17. 5 =8. 2678997 



ft. m. s. 

 U — 5 55 45. 2. 



Sidereal time western elongation, Ts = K. A. Polaris + t*. 

 ft. m. *. 

 R. A. Polaris 



Mean interval before noon 

 Local mean time, western elongation = 



h. m. a 



Sidereal time eastern elongation = 24 b + a — te = 19 23 50. 



a, = 10 29 11.1 



Sideral interval after noon, I = 2 54 35.6 



Correction sidereal to mean interval = 28. 6 



Local mean time eastern elongation 



Local mean time western elongation 



s. 



For longitudes west of Washington decrease times of elongation 0.66 for each degree. 



