Comparisons of Magnetic Standards, 1905-14 



Table 29 B. Results of Horizonlal-Intcnsity Comparisons at the Liikiapang Ohserrntnry, 1011. 



267 



'AH values are referred to D^; Da= f 8.57. 



Table 29 C- Results of Inclinaiion Comparisons al the Lukiapang Observatory, 1911. 



Assembling the results and referring them to I. M. S. (see p. 273), we obtain: 



(28) I. M. S.-Zikawei (Elliott magnetometer No. 49)= - IM (1907). 

 (28a) I. M. S.-Zikawei (Elliott magnetometer No. 49)= +0.00042// (1907). 

 ClU) I. M. S.-Zikawei (Dover dip circle No. 33. needle 14)= -0'.4 (1907). 



(29) I . M. S. - Lukiapang (Elliott magnetometer No. 49) = - 1 '.5 ( 1 9 1 1 ). 

 (29a) I. M. S.- Lukiapang (Elliott magnetometer No. 49)= +0.00084// (1911). 

 (1%) \. M. S.- Lukiapang (Schulze earth inductor No. 42)= O'.O (1911). 



NO. 30. SPECIMEN FIELD COMPARISONS. 



The comparisons in 1910 at Rumeh Hissar, near Constantinople, by Observers J. C. 

 Pearson and W. H. Sligh, will serve as a specimen of field comparisons such as the observers 

 of the Department of Terrestrial Magnetism seek to obtain whenever opportunity affords. 

 In this particular case Mr. Pearson was homeward bound after two years' field work and 

 Mr. Sligh was sent to meet him at Constantinople, and after intercomparing instruments 

 with him, to continue the magnetic survey in Turkish countries. 



The instruments used by Mr. Pearson were C. I. W. magnetometer No. 5 and Dover 

 dip circle No. 177 (needles 1, 2, 5, and 6), whereas Mr. Sligh observed with C. I. W. magne- 

 tometer No. 7 and Dover dip circle No. 202 (needles 1, 2, 5, and 6). 



The comparisons were made at two stations, A and B, in the grounds of Robert College, 

 about 6 miles northward from Constantinople. B is 88.5 feet south and 84.5 feet west of A. 

 Adverse weather conditions were experienced at the time of the comparisons, a continuous south 

 wind, which at times came in very severe gusts, rendering observations in the observing tents very 

 difficult. 



The method of comparisons was that of simultaneous observations and exchange of 

 stations. 



Since Mr. Pearson's instruments were used in comparisons with the magnetic standards 

 at Kew in March 1908 and March 1910, at Helwan in April 1908, at Tiflis in June 1908 and 

 July 1909, at Pola in February 1910, and at Potsdam in February 1910, it will be of interest 

 to see what control the above field comparisons gave over the corrections of his instruments 

 on the C. I. W. standards. (See Table 30 D.) 



