80 Ocean Magnetic Observations, 1905-16 



For Vertical Intensity 



A, = kZ + R = Z{ii-l) (24) 



B, = gZ cot / (25) 



C, = - hZ cot / (26) 



M = A; + 1 + | (27) 



From the usual observations at the positions (see Fig. 1, p. 27, and Plate 2, Fig. 1) of 



the various instruments on the Galilee's observing-bridge, we may derive combinations of 

 the quantities above mentioned. Thus 



For Standard-Compass Position (Declination) 



l/'a-e\bcdfP ,Q 

 x(^' X' X' X' X' X' ^^^ X 



For Sea-Deflector Position (Declination and Horizontal Intensity) 



X, a, b, c, d, e, f, P, and Q 



For Sea-Dip-Circle Position (Inclination and Total Intensity) 



X, a, c, e, f, g, h, k, P, Q, and R 



DEVIATION-COEFFICIENTS FOR CRUISES I, II, AND III. 



Forms 23, 23a, pages 36 and 39, give, respectively, specimens of derivation of deviation- 

 coefficients for declination and horizontal intensity. Those for inclination are derived 

 in a similar manner (see pp. 43-45). The values of the coefficients, resulting from the vari- 

 ous swings and for the three magnetic elements, D, I, H, are given separately for each 

 cruise in Tables 23-28, pages 81-85. The column-headings and explanatory remarks will 

 make clear the entries and conditions under which the quantities were derived. The same 

 general designations for instruments, as given on pages 28-32 and 94 have been used in 

 these tables. For interpretation of symbols appearing in columns of "Remarks," see page 

 95. The colunms, "Headings," give the number of headings on port swing (p) and the 

 number on the starboard swing (s). 



The probable-error colunms give the probable errors of an observed de\dation on a 

 single heading; they have been computed as showii in Forms 23 and 23a, pages 36 and 39. 

 The intensity unit used for the deviation-coefficients and probable errors, which appear in 

 Tables 24, 26, and 28, is the fourth decimal c. G. s. In these same tables, the letters S, L, 

 appearing in the columns "Dip Circle" and "Deflector (Defl'r)," stand, respectively, for 

 short deflecting-distance and for long defiecting-distance. 



On the various cruises, the Galilee was swung about every fifth or sixth day, the average 

 distance between swing-stations being somewhat over 600 miles. An inspection of the 

 quantities in the probable-error columns shows a steady improvement in accuracy of 

 observation for all the magnetic elements as the work advanced and the various diffi- 

 culties caused by ship conditions and imperfection of sea instruments were more or less 

 successfully overcome. Only occasionally did the probable error reach a magnitude, 

 because of conditions encountered, such as to warrant either total rejection of the results 

 of the swing, or giving them diminished weight in the final adjustments, explained in 

 the next paragraph. 



