Magnetic Surveys¹

Abstract

THE importance of magnetic survey work has been recognised for a long time. Many of the most eminent scientific men of the century now about to close have devoted much time and thought to magnetic observation and the reduction of results, and their labours have not been without fruit. To them we owe all that is known with certainty as to the magnetic state of the earth and its changes; and though observations have no doubt to some degree outpaced the work of reduction and the construction of theory, much has been done to construct from observational data a general theory of terrestrial magnetism. We have the great mathematical theory of Gauss based on the results of Sabine, Barlow, Homer, and others, with the answer it gives to the question of the locality of the magnetic distribution which gives rise to the ordinary phenomena of terrestrial magnetism. Also, and founded to some extent on Gauss's theory, we have now that of Schuster on the daily changes of the magnetic forces and their causes, which has yielded most important results, as to the locality of the sources of this periodic disturbance. As a consequence of Schuster's theory there have lately been published some important discussions of the diurnal changes and their theory by von Bezold and others.