MAGNETIC OBSERVATIONS. 



15 



a = true geocentric altitude of sun's centre. 

 d = sun's polar distance, measured from the elevated pole. 

 <£ = latitude of place where observation is made. 

 t = hour angle at the pole. 

 t = equation of time. 



dt = correction of chronometer to reduce the reading of its face to 

 local mean time. 



Double Altitudes of the Sun, for Time, observed at the flagstaff in the Navy-yard at Portsmouth, Va., 



October 29th, 1865. 



5l m 7 , 





49" 



27 



50" ' 





51 42 







3« 



20 





52 22 



53 23 





5° 



49 

 7 



3° 

 40 



1- 2 



53 5^-5 







17 



50 





54 47 





50 



32 



20 





55 50 





49 



47 









56 25 







57 



20 





56 57-5 





5° 



6 



20 



► 2O 



57 59-5 







24 



50 





58 32-5 







34 



3° 





59 13-5 







45 



5° J 





Ex. ther. 50 









At. 



ther. 92 



Refraction = 



— 



«5" 









Parallax = 



+ 



3 









Index correction, 

 = + 15' 42" 



Bar. 30.40 inches. 

 Sun's declination — 13 35' 16" 

 Latitude + 36 49 32 



Mean of observed double altitudes 

 Local apparent time . 

 Equation of time 

 Local mean time 

 Mean of chronometer times 

 Chronometer fast of local mean time 

 Longitude west .... 

 Chronometer slow of Greenwich mean time 



Double Altitudes of the Sun for Time, observed at the flagstaff in the Navy-yard at Portsmouth, Va. 



5°' J 



7 



27 



9 h 



6 m 



4o 8 .8 





16 



10.6 



8 



5° 



30.2 



8 



55 



"•3 







4 



41. 1 



5 



5 



9.8 



5 







28.7 



October 29th, 1S65. 



jjU] 



55 3 



12 



54 



I 3 



3 2 -5 



14 



9-5 



14 



5i 



15 



36-5 



16 



52-5 



17 



37 



18 



z 4-5 



19 



1. 6. 5 



4o u 



10 



10 



39 



5i 



20 





38 



3° 



40 



3° 



30 





17 









2 



20 



39 



37 



3° 





2 3 



10 





8 



3° 



37 



46 









3i 



3° 





20 



10 



20 



Index correction, 

 = + 15' 42" 



20 55-5 



Ex. ther. 55 

 Refraction = — 1 70". 1 

 Parallax =4- 8.0 



I 2O 



At. ther. 



Mean of observed double altitudes 

 Local apparent time . 



79 Bar. 30.36 inches. 



Sun's declination — 13 40' 42". o 

 Latitude 4- 36 49 32. 



■ 39° l6 ' 2 f-3 

 3 h 2 7 m 5i"-9 



