34 



Ocean Magnetic Observations, 1905-16 



dependent on card-graduation errors and Sun's altitude, are applied to the mean settings, 

 both for prism and alidade, as explained on page 62. Thus for heading west, the mean 

 observed setting by prism is N 50?26 E ; the value after applying the instrumental correc- 

 tion (+0?33) is N 50?59 E. Similarly, the mean observed setting by aUdade is N 50?68 E; 

 the corrected setting is N 50?79 E. Accordingly, the mean corrected setting for prism and 

 alidade is, N 50?69 E, which is finally the quantity entered onFonn 22, opposite the mean 

 local apparent time: ^ (2" 12'"14?6 + 2" 12" 48'0) + 3'' W" 20« = 5^ 28"' 5P. In this way 

 are filled out the columns: "Local Apparent Time," and "Sun by Compass." 



Magnetic Observations on Swing: Declination (D) 



Station: San Francisco Bay 

 Dale: May 25, 1908, A. M. 

 Compass: Ritchie 29499 (R3C) 

 Weather: b 

 Sea: S 



(Form 21) 



Lai: 37° 51' N 

 Vessel: Galilee 

 06s V; W. J. P. 

 Wind: 

 Roll: 0° 



Long: 122° 23' W 

 Com'd'r: W. J. P. 

 Rec'd'r: D. C. S. 

 Temp: 13° C. 

 Helm: Port 



Knowing the latitude of the place of observation and the local apparent time, the 

 entries in the next column, "Sun's Azimuth," are computed with the aid of a conveniently 

 arranged abstract from published azimuth tables, e. g., those of the Umted States Hydro- 

 graphic Office. • 1 , • J u u 



The observed magnetic declination, entered in the fifth column, is obtained by sub- 

 tracting the Sun's magnetic azimuth ("Sun by Compass") from the true or computed azi- 

 muth. The + sign means that the magnetic decUnation is east of north. The values m 

 this column are affected by the ship's magnetism, the correction of which varies from head- 

 ing to heading. The mean value of the 8 equidistant headings, -f 17?96, is free from the 



