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Special Reports 



the Observatory methods or arrangements were likely to be made in the near future, 

 it was decided, after consultation with the Astronomer Royal, to compare directly the 

 intensity results obtained with the C.I.W. magnetometer on the center of the intensity 

 pier with those obtained from the Observatory magnetograms. 



The Observatory absolute-instruments, viz, declinometer for declination, earth 

 inductor for inclination, and Gibson magnetometer No. 3 for horizontal intensity, were 

 used, and the data deduced from the Greenwich magnetograms depend upon base-line 

 determinations made with them. The C.I.W. instrument used was magnetometer- 

 inductor 26. The corrections on International Magnetic Standards" applied to results 

 obtained with magnetometer-inductor 26 were those finally adopted. 



Table 6A. Results of Declination Comparisons at the Greenwich Observatory, 1915. 1 



1 Fourteen additional comparisons were obtained: 8 on August 14, 16, and 17, 1915, with C. I. W. magnetometer 

 No. 26 at the tent station and 6 on August 23, 1915, with C. I. W. magnetometer No. 26 on the intensity pier, all with Green- 

 wich declinometer at its station, but since there are no available data to determine station-differences, if any, these sets have 

 been omitted. The resulting mean values of (I. M. S. at the tent station Greenwich at the declinometer station) and of 

 (I. M. S. at the intensity pier Greenwich at the declinometer station) were 0'.9 and 3'.1, respectively. The latter is 

 based upon a not especially trustworthy value for azimuth of mark. 



1 All values refer to the Greenwhich declinometer station. 



Table 6B. Results of Horizontal-Intensity Comparisons at the Greenwich Observatory, 1915. 1 



1 Four additional comparisons were obtained on August 14, 16, and 17, 1915, with C. I. W. magnetometer No. 26 at 

 the tent station and with the Greenwich magnetometer Gibson No. 3 at the intensity pier; since there are no data available 

 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 intensity pier) was 0.5t. 



' All values refer to the Greenwich intensity pier. 



" See Ret. Dep. Terr. Mag., Vol. II, pp. 270-278. 



