RESULTS OF LAND MAGNETIC OBSERVATIONS, 1905-10. 



Explanatory Remarks. 



Few can realize the work involved in making a general magnetic survey of the 

 Earth and the many questions which must be settled, at times wholly arbitrarily, 

 not only in the work of organization, observation, and computation, but also in 

 the final presentation and publication of the derived results in such a manner that 

 all the varied purposes will be adequately served. Thus, for example, it has not 

 been deemed advisable to attempt at present to apply corrections to the observed 

 results on account of the numerous variations of the Earth's magnetism, e. g., diurnal 

 variation, secular variation, magnetic i)erturbations, etc. Instead, it is believed 

 to be better to publish the observed results as obtained with no corrections applied 

 except the reductions to the magnetic standards of the Department as fully ex- 

 plained in the section on this subject; thus undue delay is avoided in the promul- 

 gation of the results. The reduction to a common epoch can be undertaken more 

 advantageously later, probably after 1913, when additional data have been secured. 

 The reader will notice, however, that opposite the magnetic elements as tabulated 

 in the Table of Results the precise date and local mean time of each observation 

 are given; he is thus supplied with the required information in case, for some 

 purpose of his own, it is necessary to reduce the observed values to some mean time. 



Another question which had to be settled was the adoption of some sufficiently 

 elastic scheme of tabulation. The following main divisions have been adopted 

 for this volume: Africa, Asia, Australasia, Europe, North America, South America, 

 Islands Atlantic Ocean, and Islands Pacific Ocean. Under each main division there 

 are broad subdivisions; see Africa for example. The tabular entries under these 

 subdivisions are in the order of decreasing north or increasing south latitude; that 

 is to say, in the order of increasing co-latitude counting from the North Pole to the 

 South. When there are stations of the same latitude, their order will be according 

 to increasing east longitude, counting continuously from the standard meridian of 

 Greenwich or zero to 360 degrees. 



It seemed highly desirable not to have the complete entries for a station extend 

 over one page; hence condensation and restriction to essential data became 

 necessar\'. The question arose whether to give values of the horizontal intensity 

 exclusively, or values of total intensity exclusively. While from a theoretical 

 standpoint, it may appear preferable, if restriction must be made, to give the 

 total intensity rather than the horizontal, the choice for practical reasons had to be 

 made in favor of the latter. In the vast majority of cases, the horizontal intensity 

 rather than the total was observ^ed, and most likely will continue to be for some 

 years at least. Only in high magnetic latitudes, where the horizontal intensity 

 is small and hence its observation more or less difficult, were total intensities 

 generally obtained. In the present publication rather than give total intensities, 

 as derived by computation with the aid of the observed horizontal intensity and 

 inclination, it was thought a better procedure to compute, in the considerably 



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