242 



Reports on Special Researches 



'Half set; weight, 0.5. 



As the great majority of dip circles are made in England and are tested at the Kew 

 Observatory before purchase, and provided, when found satisfactory, with Kew certificates 

 giving the results of the comparisons, it will be a matter of interest, as well as of importance, 

 to determine, if possible, the absolute correctness of the Kew Inclination Standard (Barrow 

 dip circle No. 33, needles 1 and 2). The result from Table 14C would give r.2 for the 

 correction of the Kew standard on I. M. S. (see p. 273), i. e., the Kew instrument j'ields 

 values of dip apparently about 1' too high. As the results from series I and II are not in 

 satisfactory accord, it will be desirable to .secure further evidence. 



InTable 14D are given in the column "Circle Kew," the differences obtained by the 

 Kew Observatory for 10 new Dover dip circles purchased by the Carnegie Institution of 

 Washington (Department of Terrestrial Magnetism) during the period 1904-11; the quan- 

 tities are taken directly from the Kew certificates. These same circles were compared, as 

 soon as possible, at Washington, where the inclination is only about 3 greater than at Kew. 

 In the column "I. M. S. Circle" are given the results of the Washington comparisons as 

 referred to I. M. S., chiefly by means of the Schulze earth inductor No. 48 (see p. 273). 

 From the combined comparisons of the 10 dip circles at Kew and Washington, are obtained 

 the results in the last colunm. From this table we accordingly find that the mean value of 

 the difference (I. M. S.-Kew) = -1'.17. 



Table 14 D. Results of Indirect Inclination Comparisons between Kew Standard and I. M. S. 



No. 



Dover 

 D. C. 



1 

 2 

 3 



4 

 5 

 6 

 7 

 8 

 9 

 lU 



171 

 172 

 177 

 178 

 201 

 202 

 205 

 206 

 222 

 223 



Needles 



1,2 



1,2 



1,2 



1,2 

 1,2,5,6 

 1,2,5,6 

 1,2,5,6 



1,2 

 1,2,5,6 

 1,2,5,6 



Date of Kew 

 Certificate 



1904, Nov. . 



1905, Apr. . . 

 1905, Nov . . 

 1905, Nov.. 

 1909, Jan.. 

 1909, Jan... 

 1909, June. 

 1909, Aug . . 

 1911, Oct.. 

 1911, Nov. . 



Mean. 



Date of Washing- 

 ton Comparisons 



I.M.S.- 

 Circle 



1905-06 +1.0 



1907 -0.4 



1907 -0.2 



1906 -1.0 



1909-10 +0.3 



1909, Apr., May.: +0.9 



1910, Apr ' 0.0 



191U, July, Sept. -0.2 



1913-14 +0.2 



1912-14 0.0 



Means . 



+0.06 



I.M.S.- 

 Kew 



-1.0 

 -2.4 

 -2.1 

 -2.5 

 -0.7 

 +0.1 

 -1.2 

 -1.7 

 0.0 

 -0.2 



-1.17 



