448 



Special Reports 



Table 13D. Summary of Corrections on Standard for Pilar Observatory. 



Pilar standards in 1911 were Dover magnetometer No. 13S and mean of dip circle No. 216 and Toepfer inductor No. 

 Z, and hoi Dover magnetometer No. 175 and Toepfer inductor No. 3 as in 1913 to 1917. 



Hence we obtain weighted mean values as follows: 



(13) I. M.S. -Pilar (Dover magnetometer No. 138) = +-0'.4 (191 1). 

 (13a) I. M. S.-Pilar (Dover magnometer No. 138)= -0.00101// (1911). 

 (136) l.M. S.-Pilar (Dip circle No. 216 and inductor No. 3) = +-0'.3 (1911). 

 (13c) l.M. S.-Pilar (Dover magnetometer No. 175)= -0'.6 (1913-1917). 

 (13a 1 ) I. M. S.-Pilar (Dover magnetometer No. 1 75)= -0.00033// (191 3-191 7). 

 (I3e) I. M.S. -Pilar (Toepfer inductor No. 3)=- 0'. I (1917). 



NO. 14. RIO DE JANEIRO OBSERVATORY AT VASSOURAS, BRAZIL. 



The comparisons of 1915 were obtained by Observer D. W. Berky, and those of 

 1919 by Observer A. Sterling. The stations used for the comparisons of 1913," the 

 concrete piers A and B in the non-magnetic house for absolute observations at Vas- 

 souras, were reoccupied, and for the inclination work in 1919 the pier C was also used; 

 pier A is 3.3 meters east 5.2 of true north of pier B, and pier C is 3.3 meters south- 

 southeast of pier A. As it was thought there might possibly be, because of the short 

 distances between piers, a disturbing effect of one instrument on the second instrument, 

 special tests were made during the work in 1919; these tests showed there were no sensible 

 disturbing effects. At A the center of pin on the Observatory azimuth mark was used, 

 the azimuth as supplied by Dr. Morize, Director of the Observatory, being 140 40'. 7 

 west of true south. At B the azimuth mark in 1915 was the left edge of a white house 

 on a hill about one mile (1.6 kilometers) distant, its azimuth as supplied by Dr. Morize 

 being 174 55'. 9 west of true south; in 1919 the near corner of a house about one mile 

 (1.6 kilometers) distant was used, its azimuth as determined by Observer Sterling's 

 angular measurements to the Observatory mark being 175 16'. 2 west of true south. 

 The Observatory determinations of 1915 were made by Dr. A. C. Lemos, now chief of 

 the Section of Terrestrial Physics, and those of 1919 by Observer G. M. Soares. 



The Observatory instruments used in the comparisons were magnetometer No. 25 

 by Cooke and Son in 1915 and 1919, dip circle No. 8075 with needles 1 and 2 in 1915, 

 and dip circle No. 221 with needles 1 and 2 and needle 2 of 8075 in 1919. It should be 

 noted that these are not the same instruments as those used by the Observatory for 

 the comparisons of 1913. ' The C. I. W. instrument used in 1915 was universal magnet- 

 ometer No. 19 with dip needles 1 and 2 of C. I. W. magnetometer No. 21, and in 1919 

 magnetometer No. 16 and dip circle No. 242 with needles 1, 2, 5, and 6. Dip observa- 

 tions were also made in 1915 by Mr. Berky, using needles 2 and 6 of magnetometer li), 

 but the results by those needles had to be rejected because of development of rust on 

 pivots. 



The I. M. S. values given depend upon the constants finally adopted for the C. I. W. 

 instruments. When magnetometer 19 was returned from the field in September 1915, 

 it was found that there had been an appreciable decrease in the moment of inertia for 

 magnet 19L and its suspension. Examination of the comparisons with standards for 



" See li( !> 



Mag., Vol. II. pp. >:,.\ 254. 



