Comparisons of Magnetic Standards, 1905-14 



253 



rncJination. Since manj' of the earth inductors of the Wild-Eschenhagen pattern, 

 made by Toepfer or by Schulze, are tested at Potsdam, it will be desirable to get another 

 check upon the quantity found in Table 20 C. This is afforded by means of Table 20 D. 



Table 20 D. Results of Inclinalion Comparisons between the Standard Earth Inductors at Potsdam and Cheltenham, 



1906-12. 



|The standard earth inductor at the Potsdam Observatory is Schulze No. 1 (Wild-Eschenhagen pattern) and at the Chelten- 

 ham Observatory in Maryland the standard is the large AVild-Edelmann earth inductor No. 20. The earth inductors, 

 the comparison-results of which at Potsdam and Cheltenham are given in the table, are all of the Wild-Eschenhagen 

 pattern as made by Schulze of Potsdam. It will be seen that, with the exception of No. 4S, they were purchased by the 

 United States Coast and Geodetic Survey, which organization courteously communicated its results to us.) 



Maker and 

 number 



Owner of Earth 

 Inductor 



Date of Cheltenham 

 Comparisons 



Cheltenham - 



Earth 



Inductor 



Potsdam Cheltenham 



AI 



Weight 



Schulze 43 j U. S. C. & G. S . , 



48 i C. I. W 



63 I U. S. C. &G. S.. 



89 ! U. S. C. &G. S. . 



1906, Aug . . . 



1907, Feb. . . 



1911, Apr... 



1912, Aug. . . 



-0.29 

 -0.27 

 -0.03 

 -1-0.10 



! 1906 



I 190S, Mar., Apr. 



1911, June 



1912, Nov 



-0 91 

 -U.o4 

 -0.36 

 -0.26 



-fO.62 

 -1-0.27 

 -t-0.33 

 -1-0.36 



Weighted mean value of (Potsdam Cheltenham) . 



-f-0.36 



Hence we have from the table: 

 (g) Potsdam - Cheltenham =+0'.36 (1906-12). 



From the C. I. W. comparisons 1908-10 (Table 7C, series I, II, and III, p. 229) we 

 find: 



(h) C. I. W.- Cheltenham =+0'.06. 

 Combining (g) and (/i) we get: 



{i) C. I. W. - Potsdam =-0'.30 (1908-10), which agrees well with the directly- 

 observed quantity 0'.34, in Table 20 C. 



Weighting the various results according to their reliability and referring them to 

 I. M. S. (see p. 273), we obtain: 



(20) I. M. S.-Potsdam (Wanschaff magnetometer) = +0'.2 (1910). 

 (20a) I . M. S. - Potsdam (Wanschaff magnetometer) = + 0.00008// ( 1 9 1 0). 

 (20i) I. M. S.-Potsdam (Schulze Inductor No. 1)= +0'.2 (1910). 



NO. 21. RIO DE JANEIRO OBSERVATORY, AT VASSOURAS, BRAZIL. 



The comparisons of 1913 were obtained by Observer H. F. Johnston, in the course of 

 his field work, at Vassouras, the new site of the magnetic observatory belonging to the 

 National Observatory of Rio de Janeii'o. The site is in the suburbs of the little city of 

 Vassom-as, wliich is distant 3 hours by rail from Rio de Janeiro, and is located in a district 

 where the danger of disturbing influences from electric lines in the near future is not to be 

 feared. The stations occupied, designated A and B, are the two concrete piers, 10.9 feet 

 (3.32 meters) apart, in the non-magnetic house for absolute observations. Pier .4 is the 

 larger one and is to the north of pier B. 



At A the mark used was the left edge of a brass pin in the Observatory azimuth mark, 

 about 90 meters from the building, the azimuth, as suppUed by Dr. Morize, Director of the 

 Observatory', being 146 40'.4 west of true south. At B the azimuth mark was the left edge 

 of a white house on a hill about 1 mile (1.0 kilometers) distant; its azimuth, as suppUed by 

 Dr. JNIorize, is 174 58'. 8 west of true south. 



The Observatory instruments used in these comparisons were magnetometer No. 20 

 by Cooke and Son, Survey of India pattern, and Negretti and Zambra dip circle No. 1 14, 

 with needle No. 2. The C. I. W. instrument used by Mr. Johnston was universal magne- 

 tometer No. 19, with dip needles 1 and 2; unfortunately, it was found necessary to reject 



