Comparisons of Magnetic Standards, 1915-21 443 



The Observatory instruments used in these comparisons were the same as used in 

 the comparisons of 1911, viz, Elliott magnetometer No. 49 and Schulze earth inductor 

 No. 42. Unfortunately owing to a mishap on August 20, 1917, with the magnet used 

 for the declination observations it had been found necessary to remagnetize it not long 

 before the comparisons; thus the values obtained for the differences of magnetometer 

 No. 49 on International Magnetic Standards are not comparable with former values. 

 The C.I.W. instruments were magnetometer No. 9 and dip circle No. 206 with needles 

 1 and 2 of 206 and needles 5 and G of 178. The comparisons for D and H were obtained 

 by the method of simultaneous observations and exchange of stations. The observations 

 for the inclination comparisons were made with No. 42 and No. 206 alternately, the dip 

 needles being removed during observations with No. 42 and the coils of the latter being 

 kept stationary while No. 206 was in use. A complete inclination intercomparison 

 consisted of: (1) Observations with the earth inductor according to usual method of 

 the Observatory; (2) inclination with one pair of needles of No. 206, ends "A" or "B" 

 down; (3) earth inductor same as (1); (4) inclination with second pair of needles of No. 

 206, ends "A" or "B" down; (5) earth inductor same as (1) ; (6) second half of inclination 

 with second pair of needles of No. 206, ends "B" or "A" down; (7) earth inductor same 

 as (1); (8) second half of inclination with first pair of needles of No. 206, ends "B" or 

 "A" down; (9) earth inductor same as (1). Thus the mean of earth-inductor observa- 

 tions (1), (3), (5), (7), and (9) corresponded with the mean of the dip-circle observa- 

 tions (2), (4), (6), and (8). Any station-difference between D b and D c had to be con- 

 sidered as negligible. The Observatory observations were made under the direction 

 of Reverend de Moidrey by Mr. Zi with the assistance in earth-inductor work of Mr. 

 Lee, both of Observatory staff; the C.I.W. observations were all made by Mr. Brown. 



The I. M.S. values depend upon the corrections finally adopted for C.I.W. mag- 

 netometer No. 9 and dip circle No. 206. It is to be noted that both needles 5 and 6 of 

 circle 178 were somewhat erratic in behavior for inclinations between +45 and +46; 

 two values with needle 6 had therefore to be omitted from the tabulation of results. 



Except for November 3, there was steady rain during the comparisons and the 

 weather was extremely dull and gloomy. This fact may account partly for the ap- 

 parently erratic values obtained for D with magnetometer No. 49 since a silk fiber was 

 used for suspension. For this reason Reverend de Moidrey has also supplied the mag- 

 netogram scalings for declination which depend on base-line determinations made prior 

 to the accident of August 20, 1917, and these are incorporated in the tabulation of 

 results; as will be noted, the value thus derived for (I. M.S. Lukiapang) = 1'.3 is 

 substantially in agreement with the value obtained in 1911, viz, 1'.5, while the value 

 derived from the magnetometer comparisons is +0'.8, indicating that the accident 

 caused a substantial change in the declination correction of magnetometer No. 49. 

 The result obtained from the inclination comparisons is identical with that obtained in 

 1911. 



The horizontal-intensity comparisons show a decided change in value of (I. M. S. 

 Lukiapang) since the comparisons of 1911 which may arise in part from the accident 

 above referred to. When transmitting the values of H for the Observatory Reverend 

 de Moidrey made the following notes : 



"It was at first supposed that the distribution coefficient had not been much affected by the 

 accident of August 20 but this did not prove to be correct. We therefore took for P the mean 

 of 43 determinations made during the period September 11 to December 5, 1917, which gave for H 

 the values herewith sent you, but these values differ considerably from those of Mr. Brown. We 

 also compared each series with the magnetograph at 18 and determined base-line values as follows: 

 For Mr. Brown 33141.7-y with a mean error 9.37, and for Mr. Zi 33083.87 with a mean error of 9. 27. 

 These values therefore amount practically to equal precision, but I am at a loss to explain the groat 



