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Reports on Special Researches 



by an earth inductor (C. I. W. No. 4) constructed in the workshop of the Department of 

 Terrestrial Magnetism; the correction of this inductor (C /. W. No. 4) on I. M. S., accord- 

 ing to the comparisons at Washington in January 1913 {see Table 27E, p. 264), was found 

 to be -\-0'.3. As the results with the Observatory dip circle were exceedingly irregular, it is 

 not worth while to give them in detail. The mean result from 8 sets on August 14-15, 191 1, 

 is: C. I. W. Mauritius dip circle =+4'.4; if referred to I. M. S. (see p. 273), we have 

 /. M. S. Mauritius dip circle = +4'-5. 



The C. I. W. instruments used by Dr. H. M. W. Edmonds were: C. I. W. magnetometer 

 No. 4 and Toepfer earth inductor No. 2. The method of comparisons was that of simul- 

 taneous observations and exchange of stations. Director A. Walter made the observations 

 for decUnation and horizontal intensity with the Observatory magnetometer. Two sta- 

 tions were occupied and designated as A and B. A was the central pier in the old paviUon, 

 this pier being used by the Observatory for the D and H observations. B was a temporary 

 station, 6.41 meters south of A and placed in Une with A and the former azimuth mark 

 (azimuth 1'.3 W. of S.). Owing to the pronounced local disturbance' near these stations, 

 the attempt was made to have the magnets of both magnetometers at the same level above 

 the ground at each station, viz, 1.53 meters at A and 1.32 meters at B. This could not 

 be done precisely, as the suspended magnets during deflections and oscillations with the 

 Kew magnetometer of the Observatory are at different heights, the average being taken; 

 the Kew declination magnet was, in conseqtience, 1 inch above the adopted height. 



Table 15 A. Results of Declination Comparisons at the Mauritius Observatory, 1911. 



'All results are referred to A; A = Bi2'.^. 

 Table 15 B. Results of Horizontal-Intensity Comparisons at the Mauritius Observatory, 1911. 



'All results are referred to -4; A =B-\-\7Zy. 



-Weight 3 assigned if observations consisted of 1 set of oscillations, 1 set of deflections, and again 1 set of oscillations; 

 if one set of oscillations had to be omitted, the weight 2 was given to the result. 



Referring the chief results to I. M. S. (see p. 273), we obtain: 



(15) I. M. S.- Mauritius (Elliott magnetometer No. 24)= +0'.4 (1911). 

 (15a) I. M. S.- Mauritius (Elliott magnetometer No. 24)= -0.00065// (1911). 

 (15i) I. M. S.- Mauritius (C. I. W. earth inductor No. 4)= +0'.3 (Washington, 1913). 



'See Terr. Mag-, vol. 16, 1911, pp. 243-246. 



