MAGNETIC OBSERVATIONS. 



15 



a = true geocentric altitude of sun's centre. 

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

 (> = latitude of place Avhere 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 zgth, 1865. 



r 20 



Index correction, 

 = + 15' 42" 



Ex. ther. 50. 

 Refraction = 125" 

 Parallax = + 8 



At. ther. 92 



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 



Bar. 30.40 inches. 

 Sun's declination 13 35' 16" 

 Latitude +36 49 32 



. - 5 7' 27" 



9 h 6 m 4o".8 



. 16 10.6 



8 50 30.2 



. 8 55 11.3 



o 4 41.1 

 559-8 



5 o 28.7 



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



October 2<)th, 1865. 



Index correction, 



42 



20 



Ex. ther. 55 

 Refraction = 1 70". i 

 Parallax = + 8.0 



At. ther. 79 



Bar. 30.36 inches. 



Mean of observed double altitudes 

 Local apparent time . 



Sun's declination 13 40' 42".o 

 Latitude + 36 49 32. 



39 1 6' 23". 3 



