Comparisons of Magnetic Standards, 1915-21 



425 



Table 6C. Results of Inclination Comparisons at the Greenwich Observatory, 1915} 



1 Twelve additional comparisons were obtained on August 19 and 20, 1915, with C. I. W. magnetometer No. 26 set 

 up at the tent station with the Greenwich earth inductor on its pier; since there are no available data to determine station- 

 difference, if any, these sets have been omitted. The resulting mean value of (I. M. S. at the tent station Greenwich at 

 the inductor pier) was l'.O. 



! It is assumed that the station-difference between the intensity and inductor piers is negligible since they are only 

 4 feet apart and the comparisons made with No. 26 at the tent station and the Greenwich inductor at the inductor pier, 80 

 feet from the tent station, indicate an approximate station-difference between tent station and inductor pier of less than 0'.5. 



Series II, 1919. 



Advantage was taken of the opportunity before Observer F. Brown's departure for 

 field work in Cameroun and in Angola, Africa, to obtain during April 5 to 7, 1919, a 

 second series of comparisons at Greenwich. Because of the very short time at Mr. 

 Brown's disposal and because of other demands upon the time of the Observatory 

 personnel a complete set of intercomparisons with interchange of stations was not 

 feasible. The stations were as in 1915 except that in place of the tent station of 1915 

 a new tent station, designated Tent 1919, was occupied. This station was in the in- 

 closure around the absolute house 20 paces south-southeast of the southeast corner of 

 the latter; the north end of the northernmost and lowest building between the 28-inch 

 dome and the tower of the Observatory was used as an azimuth mark, its true bearing, 

 as determined by Mr. Brown, being 92 25'. 1 west of south. Declination and inclination 

 observations were made at the tent station by Mr Brown; simultaneous inclination 

 observations only were obtained by Mr. W. W. Bryant, Superintendent of the Magnetic 

 Department, on the inductor pier at the south end of the absolute house. The C. I. W. 

 horizontal-intensity observations were made on the center of the intensity pier as in 

 1915. It is assumed that any station-differences are negligible as the locality of the 

 absolute house had been tested by the Observatory authorities and found free of local 

 disturbance. 



The absolute instruments of the Observatory were as for the 1915 series, and the 

 Observatory data given for declination and for horizontal intensity were deduced from 

 the magnetograms standardized by them. The C. I. W. instruments were magnetometer 

 No. 13 and dip circle No. 177 with needles 13X and 16X. The behavior of the dip 

 circle was not altogether satisfactory, values by different needles being erratic; the 

 results given in Table 6E must, therefore, be regarded only as a general confirmation 

 of those obtained in 1915. The corrections on International Magnetic Standards 

 applied to the C. I. W. results are those tentatively adopted pending return and restand- 

 ardization at Washington, probably some time in 1922. 



