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Special Reports 



The stations are so well distributed that the graphs show beyond question the relative 

 corrections for the several needles. 



A third example involving a more extended expedition and short-period variations 

 for several of the needles is shown in Figure 6 from the work of Observer F. Brown with 

 circle No. 177 using needles Nos. 1, 2, 5, and 6. This expedition, beginning from a point 

 northwest of Peking, China, in August 1915 and terminating at Pehtaiho east of Peking 

 in July 1916, gave a complete circuit, crossing isoclinics +52 to +67 on the outward 

 journey and recrossing them later on the return. The values of inclination, when arranged 

 in order of magnitude, he very close together at intervals separated by some months and 

 afford favorable conditions for investigation. Mr. Brown, the observer, was more than 

 usually alert to note and to verify any apparently abnormal values given by any needle, 

 and thus the danger that any conclusions may be seriously affected by accidental or 

 observational errors is reduced to a minimum. The correction-curves for the four 

 needles as finally adopted and given in Figure 6 show, besides several small undulations, 

 the amplitudes of which are of the order that might be expected from purely accidental 

 causes, others which present striking peculiarities. With the exception of the large 

 variation shown in the curve for needle No. 1 (which will receive special consideration 



Fkj. 6. Correction-Curves for Needles used with Circle No. 177 during August 1915 tojjuly 1916. 



