256 Ocean Magnetic Observations, 1905-16 



Land dip-circle 201.— Circle 201, manufactured by Dover, was used during Cruises I 

 and II. The adopted inclination-corrections are as follows: 



Cruises I and II (to December 1910) : 



Needle 1 FM = -0^4+0:9 cos / -0'.3 sin / 

 Needle 2 FM = -1.9+2.6 cos 7 +0.4 sin 7 



Cruise II (from January 1910) : 



Needle 1 FA7 = -0:3+o:8 cos 7 -0:4 sin 7 

 Needle 2 FA7 = -1 .6+1 .9 cos 7 +0.2 sin 7 

 Needle 5^ A7 = -1 .3 for 7 = - 5° 



A7 = +2.0 for 7 = -30° to -45° 

 Needle 6^ A7 = +2.3 for 7 = - 5° 



The adopted correction for observed declination by the compass attachment is -4(6 



for Cruises I and II. 



Sea dip-circles 189 and 203.— The adopted inclination-corrections for the sea and shore 

 work durmg Cruises I, II, and III, are given on pages 251-252. 



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



For circle 189 on Cruises I and II +6' when mark readings are made with peep sights. 

 For circle 203 on Cruise I +1' when mark readings are made with telescope or 



with peep sights. 

 For circle 203 on Cruise II - 1' when mark readings are made with telescope. 



Earth-Inductor Corrections. 



The numerous comparisons made with earth inductors by the observers of the Depart- 

 ment of Terrestrial Magnetism, in various regions of the globe, have indicated that the 

 correction of an earth inductor on standard is subject to practically no change with change 

 in magnetic field. The adopted inchnation-corrections for the inductors are given sepa- 

 rately for each instrument; they are to be applied algebraically, inclination of the north- 

 seeking end of the needle below the horizon being regarded as positive, and vice versa. 



Earth inductor ^.—Inductor 2 of the Wild-Eschenhagen pattern, manufactured by 

 Toepfer und Sohn, and modified somewhat by the Department of Terrestrial Magnetism, 

 was used on Cruise II from September 1910. The adopted mclination-correction is -0'7. 



Marine earth-inductor 3.— Values at shore stations by inductor 3, designed and con- 

 structed by the Department of Terrestrial Magnetism, were used to strengthen inclination 

 determinations for some stations. The adopted inclination-correction is the same as that 

 used for the sea work, viz, — 1!0. 



Magnetometer-inductor 25.— The inductor attachment of magnetometer-inductor 25, 

 designed and constructed by the Department of Terrestrial Magnetism, was used at shore 

 stations on Cruises III and IV . The adopted inclination-correction is -0!5. 



'Needles 5 and 6 were used only at 2 stations. 



