472 



Special Reports 



The standard instruments at Eskdalemuir in 1915, when comparisons were made there 

 by the Department, were Elliott magnetometer No. 60 and Schulze earth-inductor 

 No. 103; the latter instrument replaced dip circle No. 74 in 1914. From the data given 

 in the British Meteorological and Magnetic Year Book for 1914 by the graph of vertical- 

 irtensity base-line values determined, during January to September 1914, by inductor 

 No. 103 and by circle No. 74, respectively, we compute the relation 



(4) Eskdalemuir (Schulze inductor No. 103) Dover dip circle No. 74= I'. I. 



which was used to refer the inclination results reported by Mr. Richardson to the Obser- 

 vatory standard in 1915. 



Table 21 A gives a summary of the data obtained from Mr. Richardson's compari- 

 sons and of the resulting, differences on I. M.S. for the various observatories visited as 

 determined by the relations determined at Eskdalemuir in 1915 (see pp. 422^23). The 

 values for the observatories were generally taken from the magnetograms and were for 

 the periods of observation by Mr. Richardson except at Valencia and Falmouth. At 

 Valencia absolute observations were made by the Superintendent. At Falmouth, owing 

 to loss of magnetograms, it was necessary to use observations made preceding and follow- 

 ing the comparisons and deduce values corresponding to the times of comparison by 

 reference to diurnal-variations on magnetically quiet days. 



Table 21A. Comparisons on I. M.S. Resulting Indirectly from Comparisons between Eskdalemuir Magnetic Standards 



and Certain Observatory Standards. 



[The results as published in Mr. Richardson's report have been modified here as follows: (a) the signs of the declination 

 differen"es (A.D) have been reversed in order to correspond with east declination taken as positive; (6) the horizontal- 

 intensity differences (A//) have been expressed in parts of H with the aid of the values of H, as given in the report, 

 for the observatories and referred to Eskdalemuir by formula (2) above: (c) the inclination differences (A/) have been 

 referied to Schulze inductor No. 103, the 1915 standard instrument at Eskdalemuir, by formula (4) above] 



'The values given depend upon number of sets as foMows; AD. two at each observatory except for Kew and Val 

 Joyeux where only one each; AH, one each at Greenwich and Kew, two each at Valencia, De Bilt, and Val Joyeux. three at 

 Potsdam, and four at Falmouth; A/, two each at Falmouth, Valencia, and Potsdam, and one each at Greenwich, Kew, De 

 Bilt, and Val Joyeux. 



These data taken from publication of each observatory for 1913. 



1 The declinations are observed with a special declinometer. 



Mr. Richardson states "A chip f-om one of the bricks of the observing pier at Falmouth was tested at Eskdalemuir 

 and found to have a magnetic susceptibility (per unit volume) of about 1.2 x 1(T C. G S. unit. As magnetometer 40 and 

 dip circle 120 were almost identical in size and form with those used by the Observatory the pier would affect both equally 

 and be without influence on difference between them." 



Declinometer used for declination. 



" Magnetograms were seriously disturbed by building operations. 



7 See page 473. 



According to data given on page 72 of the British Meteorological and Magnetic Year Book, part IV, section 2, for 

 1914, the mean value at Potsdam (probably sometime in 1913) from three determinations for (Potsdam Schulze inductor 

 No. 103) was O'.Oo; thus we have indirectly, since (I. M. S. Eskdalemuir) = 0'. 10. (1. M. S. Potsdam) = 0'.0 which is 

 in substantial agreement with the directly observed value of +0'.2 determined in 1910 (see Vol. II, p. 253). 



