Reductions to Standard Instrxjments 77 



Land dip-circle 178. — Circle 178, manufactured by Dover, was used during Cruises 

 II and III. The adopted inclination-corrections are given by the formulse 



Needle 1 FA7 = -liS + S^l cos 7 - o:2 sin / 



Needle 2 FA/ = -1 .7 + 2.3 cos 7 + 0.7 sin 7 



Needles 7^A7 = -3.0 + 3.4 cos 7 



Needle6 FA7 = -1 .4 + 0.9 cos 7 



The correction adopted for observed declinations by the compass attachment is +1 '2. 



Land dip-circle 4655. — Circle 4655, manufactured by Casella and loaned by the United 

 States Coast and Geodetic Sm-vey, was used at one station only. The adopted inclination- 

 correction for the mean of observed values by needles 3 and 4 is ' 0. 



Sea dip-circles, 35, 169, and 189. — The adopted inclination-corrections for the sea 

 and shore work during Cruises I, II, and III are given on pages 66, 68, and 69. 



The corrections adopted for observed dechnations by the compass attachments are : 



For circle 35 -|-7!5 when mark readings are made with peep sights, and —9' 2 

 when mark readings are made with telescope; 



For circle 169 —2' 5 for observations in 1905; —2' when mark readings are 

 made with peep sights, and 4-3' when mark readings are made 

 with telescope, for observations subsequent to 1905; 



For circle 189 -\-S'.b when mark readings are made with peep sights. 



MAGNETIC STANDARDS ADOPTED. 



The Department's extensive intercomparisons of magnetic instruments at Washington, 

 in the field, and at magnetic observatories in all parts of the Earth, have made it possible 

 to refer its data to "International Magnetic Standards" within an error, in general, on the 

 order of the observational error (see Volume II, pp. 211-278). Since the adopted constants 

 for the sea instruments were made to depend upon the standardized data at shore stations, 

 (see pp. 105-110), the results derived from the magnetic observations on board the Galilee, 

 after being corrected for ship's deviations, are on the basis of the adopted magnetic 

 standards. 



The magnetic standards adopted for reduction to a common basis of the results con- 

 tained in the present volume are the so-called "C. I. W. Standards" as defined in Volumes I 

 (p. 42) and II (p. 16). These are: In decUnation, C. I. W. magnetometer 3 without cor- 

 rection; in horizontal intensity, C. I. W. magnetometer 3 with a correction of -|-0.000157f 

 applied to observed values of the horizontal intensity, H, computed by the constants given 

 for magnetometer 3 in Table 21; in inclination, earth inductor 48 with a correction of 

 — 0'.5 apphed to observed values of inclination. A detailed discussion of the relations 

 between the "C. I. W. Standards" and the "International Magnetic Standards" is given 

 in Volume II (pp. 270-278). It is shown there that the corrections of the originally selected 

 standards are so small as to be negUgible here. Accordingly, the values of the magnetic 

 elements, given in the Tables of Results on pages 97-110, may be regarded as based on Inter- 

 national Magnetic Standards. 



