Comparisons of Magnetic Standards, 1915-21 



Table 10G. Summary of Corrections on Standards for Kew Observatory. 



441 



1 Compilation of comparisons of 16 dip circles at Kew, 1902-1915. 



Indirect comparison obtained through magnetometer C. & G. S. No. 40 at Kew and at Cheltenham. 

 3 Value adopted tentatively pending redetermination of constants and correction of C. I. W. instrument (see p. 43'J). 



Whence we obtain weighted mean values as follows: 



(10) I. M. S.-Kew (Jones magnetometer) = +0'.3 (1908-1919). 



(10a) I. M. S.-Kew (Jones magnetometer) =- 00008H (1908-1910). 



(106) I. M. S.-Kew (Jones magnetometer) =- 0.00046// (1914-1915). 



(10c) I. M. S.-Kew (Jones magnetometer) = -0.001 09H (1919). 



(10J) I. M. S.-Kew (Barrow dip circle No. 33, needles 1, 2)=-0'.8 (1902-1919). 



NO. 1 1 ,-LOANDA OBSERVATORY, ANGOLA. 



During March 10 to 12, 1920, comparisons were secured by Observer F. Brown at 

 the Loanda (Joao Capello) Observatory in the upper city of Loanda. Because of the 

 scant time available comparisons were made only for declination and inclination. There 

 being no available space within the Observatory grounds suitable for a secondary 

 station, the work was done on the single large pier (section 45 cm. by 90 cm.) of the 

 absolute house. Declination observations were made with C. I.W. magnetometer on 

 small raised platform, designated B, near center of pier about 25 cm. north of point, 

 designated C, on the pier over which the Observatory magnetometer is mounted for the 

 determination of declination and horizontal intensity. Inclination observations with 

 both C.I.W. and Observatory instruments were made on north end of the pier at a 

 point designated A ; this is the station regularly used by the Observatory for inclination 

 determinations. The Observatory mark, west corner of Fort Miguel, was used, its 

 bearing as supplied by Commandant Rebelho, Acting Director of the Observatory, 

 being from C and from B 175 Sl'.O west of south. 



The Observatory instruments used were Elliott magnetometer No. 200 and dip 

 circle No. 115 (needle No. 1), both by Negretti and Zambra. The dip circle is an old 

 instrument, and needle No. 1 has been in use for 20 years and is somewhat corroded. 

 The C.I.W. instruments were magnetometer No. 13 and dip circle No. 177 with needles 

 13X and 14X. Throughout, the method of comparison by alternate observations was 

 followed. The observations reported upon were all made by Mr. Brown, who followed 

 with the Observatory instruments the Observatory procedure as instructed by Com- 

 mandant Rebelho. The I. M. S. values given depend upon the corrections finally adopted 

 for C.I.W. magnetometer No. 13 and dip circle No. 177. 



