62 



Ocean Magnetic Observations, 1905-16 



Standard Ritchie compass 29499 with azimuth circle 481-1 II (ESC).— The adopted 

 periodic corrections to observed card-readings of compass R3C, used on Cruise III, are 

 given in Table 8. 



Table 8. — Periodic Corrections to Card Readings oj Compass B3C. 



The vaUie adopted for the correction, A,,, to observed card-readings by the prism 



method is for all altitudes 



A„ 



+ 0?28 



The adopted correction to observed card-readings by the alidade method, deduced from 

 a least-square adjustment of all available data, varies with the Sun's altitude, h, and is 

 given by the formula (see p. 140) 



A^= +0?06-l?68 tan /i-l?17 tan h tan^ +1?75 tan h sec2 



Negus compass 31974 with Negus azimuth circle (Dl). — Declinations obtained by this 

 compass and azimuth cu-cle during Cruises I, II, and III (to July 18, 1907) were used only 

 as checks upon values by compasses RIA, RIB, and R3C. 



Ritchie compass 33566 xnth azimuth circle 483-1 II {D2). — The adopted periodic cor- 

 rections to observed card readings of compa.ss D2, used on Cruise III beginning August 

 1907, are given in Table 9. 



T.\BLE 0. — Periodic Corrections lo Card Readings of Compass D2. 



The adopted correction. Ape, to observed card-readings by the prism method is for 

 all altitudes 



Ap, = - 0?54 



The adopted correction, A„, to card readings by the alidade method, deduced from 

 a least-square adjustment of all available data, varies with the Sun's altitude, h, and is 

 given by the formula 



Aac= -i-0?06-l?63 tan /i-f0?91 tan h tan 2 +1?33 tan h sec 2 



