26 



REPORT ON 



Double Altitudes of the Sun for Time, observed at La Playa, San Diego Bay, California, 



June I5//4, 1866. 



Index correction. 



359 



30" 



35 

 20 



14' 5' 

 3 



5 



Ex. ther. 71 

 Refraction = 37". 4 

 Parallax = + 4-7 



At. ther. 



359 ii 28.3 o 14 43.3 



Correction = + 16' 5 4". 2 



72 Bar. 30.12 inches. 



Sun's declination +23 20' 22" 

 Latitude + 32 41 58 



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 



112 15' 0".0 



2 h 27 m 47'. 3 



-f o 11.3 



2 27 58.6 



5 18 3I- 1 



2 50 32.5 



7 48 52.6 



4 58 20.1 



Double Altitudes of the Sun for Time, observed on Yerba Buena Island, San Francisco Bay, 



California, June 2dth, 1866. 



Index correction. 



Correction = + 16' 53". 4 



Ex. ther. 67 

 Refraction = 7 2". 5 

 Parallax = + 6.6 



At. ther. 



Bar. 



Sun's declination 

 Latitude 



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 fast of Greenwich mean time . 



The chronometer used in making this observation was T. S. and J. D. Negus* No. 1287. 



True bearings were determined by measuring with a sextant the angle between 

 the sun's limb and some well-defined terrestrial object, the time being noted at 

 the instant the angle was observed. If the terrestrial object was much elevated 

 above the horizon its angular altitude was also measured. Knowing the latitude 

 of the place of observation, the local time, and the sun's declination, the sun's 

 zenith distance and true bearing were calculated. Then, having the zenith dis- 

 tance of the sun, the zenith distance of the terrestrial object, and the measured 

 angle between the sun and the terrestrial object, the horizontal angle between them 



