Comparisons of Magnetic Standards, 1915-21 



423 



Table 5C. Results of Inclination Comparisons at the Eskdalemuir Observatory, 1915. 



i The times given apply for the C. I. W. observations; the Eskdalemuir observations were not strictly simultaneous 

 but the intervals between the mean times for corresponding sets are not large enough to affect materially, because of the 

 diurnal variation in inclination, the values for (I. M. S. Eskdalemuir). 



All values are referred to pier 6; pier 6 = pier S0'.0. 



Assembling the results, we have : 



(5) I. M. S.- Eskdalemuir (Elliott magnetometer No. 60)= -0'.8 (1915). 

 (5a) I. M.S. -Eskdalemuir (Elliott magnetometer No. 60) = - 0.00097/Y (1915). 

 (5b) I. M.S.- Eskdalemuir (Schulze inductor No. 103)= -0U (1915). 



NO. 6. GREENWICH OBSERVATORY, ENGLAND. 

 Series I, 1915. 



The comparisons of 1915 were obtained by Messrs. H. S. Jones and W. W. Bryant 

 of the Observatory staff and Observer E. Kidson of the Carnegie Institution of Washing- 

 ton. The observations were made at 3 stations in the absolute house, viz, the decli- 

 nometer station, the intensity pier, and the inductor pier, and at a tent station which 

 was 74 feet true south 31 29' east of the southeast corner of the absolute house. Since 

 the Observatory instruments were used at only their usual places in the absolute house, 

 and there was no exchange of stations, it was not possible to determine any station- 

 differences which may exist. Observations with C.I.W. instrument could be made at 

 only the declinometer station and at the intensity pier in the absolute house. The 

 adopted results for the comparisons in declination and horizontal intensity, therefore, 

 are based only upon the observations made with the C.I.W. instrument at the decli- 

 nometer station and at the intensity pier and the corresponding data deduced from the 

 Observatory magnetograms. The adopted results for the inclination comparisons 

 depend only upon the observations with the Greenwich earth-inductor on its pier 

 and with the C.I.W. magnetometer-inductor on the intensity pier The latter pier is 

 4 feet distant from the inductor pier; that the station-difference in inclination between 

 the 2 piers is probably negligible is indicated by the comparison? made betweeen the 

 Greenwich inductor on its pier and the C.I.W. instrument at the tent station (see Table 

 6C). For the work at the declinometer station a mark mounted on a fence-post about 

 200 yards distant was used; its true bearing, supplied by the Observatory authorities, 

 was 354 41'.8 west of south. 



Subsequent to the work in April and prior to the comparisons in October, Mr. 

 Bryant made some preliminary observations to test for magnetic impurity the slate 

 cap of the intensity pier by making oscillation experiments at different points on the cap. 

 These did not indicate any great disturbance. An observation on the dip-circle pier 

 indicated some disturbance or difference between the two piers, but the observations 

 were not conclusive. It appears probable, however, that, while the effect from the 

 slate cap itself is very small, some disturbance exists in the region. As no changes in 



