Comparisons of Magnetic Standards, 1905-14 



275 



Table 31 F. Comparkons of C. I. \V. MagtielomeUir No. 7 with Standard at Washington, 1908-13. 



Another equally interesting exliibit is afforded by C. I. W. magnetometer No. 13, used by 

 Observer D. W. Berky in West Africa in 1912 and on his Trans-Saharan expedition of 1913. 



Table 31 G. Comparisons of C. I. W. Magnetometer No. 13 with Standard, 1912-14- 



'As derived from previous comparisons. 



EXPLANATIONS OF TABLES A, B. AND C. 



Table A (p. 278) gives the corrected results derived (see p. 273) for all magnetic observato- 

 ries (21), at which direct comparisons have been obtained by the observers of the Department 

 of Terrestrial Magnetism, in the course of their field work. Three observatories have been 

 omitted from the list for the reason that their instruments at the time were not such as to 

 meet the demands of accurate magnetic work. The Samoa Obser^'atory at Apia has been 

 omitted for the reason that the instruments have been changed from time to time and also 

 because they are all referred ultimately to the Potsdam standards ; there is also some uncer- 

 tainty in the data supplied us. For some of the observatories those results regarding 

 which, for one reason or another, there may be some doubt, are found omitted in the table. 

 Furthermore, 4 observatories had to be omitted enth-ely, pending receipt of desired data. 



Although the quantities aH, H have been retained to the fifth decimal, no claim, of 

 course, is made as to the correctness of the last figure; indeed, some of them may be in 

 error 10 units or more in this decimal, but it is hoped that, in general, the error may not 

 exceed a unit in the fourth decimal. While the sD and ^I quantities are given to the 

 nearest O'.l, no claim to tliis accuracy is made. Nevertheless, whenever the conditions for 

 accurate comparisons were good, it is not believed that the error in these quantities will be 



