d6 



A defective knowledge of refraction does not seriously 

 affect the accuracy of the work. For even if the altitude is 

 in error by 15", the resulting error in azimuth is only about 

 three-quarters of a second of arc. 



The following example illustrates the method of reduc- 

 tion. It will be seen that the calculations are simple, and 

 the method is undoubtedly capable of much greater accuracy 

 than the ordinary methods of making elongation observa- 

 >tions: — 



Star ohserved^-a^ Crucis. 



Right Ascension — 12h. 21m. 54s. 



Declination— m° 37' 47" S. 



Date — March 5, 1915. 



Place — Bu rnside . 



Latitude— M° 55' 38" S. 



Longitude — 9h. 14m. 36s. E. 



Standard Meridian — 9h. 30m. E. 



Computed Values. 

 Standard time at elongation — 9h. 13m. 18s. p.m. 

 J.o = 34° 06' 25" 

 2o-49° 51' 22" 



Mean Veruier 



Readings on 



Horizontal 



Circle. 



Observed 



Zenith 

 Distance. 



= Observed 

 ; Zenith 

 j Distance 

 i Corrected for 

 i Refraction. 



o 



1 



II 



o 



1 



II 



o 



; ■ 



II 



/ 



II 



360 























76 



56 



30 



50 



53 



00 



50 



54 



10 



62 



48 



76 



m 



30 



50 



26 



00 



50 



27 



09 



35 



47 



76 



55 



00 



49 



57 



15 



49 



58 



23 



7 



01 



76 



55 



15 



49 



36 



00 



49 



37 



07 



14 



15 



76 



55 



45 



49 



13 



45 



49 



14 



51 



36 



31 



76 



57 



00 



48 



38 



30 



48 



39 



34 



71 



48 



360 























34-36 

 11-15 



0-43 



1-77 



11-63 



44-92 



6 ) 104-26 



Mean value of m ... 17-38 

 Mean observed angle between star and R.M. = 76° 55' 50" 



B = 



cotp tan 62° 37' 47" 



sinz., sin 49° 51' 22" 



- 2'527 



Therefore mean value of angle between R.M. and star at 

 elongation 



= 76° 55' 50" -2-527 x 17-38" 

 = 76° 55' 50" -44" 

 = 76° 55' 06" 



