The project of a general magnetic survey of the globe, undertaken by the Department of Terrestrial Magnetism of the Carnegie Institution of Washington, and co‐operating organizations, makes necessary the determination of possible instrumental differences existing between the standards used in different countries. The pioneer work of van Rijckevorsel, Solander, Rücker and Thorpe, Moureaux, Palazzo, Bauer, and others, called attention to the need of such instrumental comparisons, and so various resolutions on this subject were passed by the Magnetic Commission of the International Meteorological Committee, which have recently been put into effect by various countries. The present contribution records the results obtained by the Carnegie Institution of Washington in the course of its magnetic operations, and under the direction of Dr. Bauer. The accuracy here striven for is that which, in general, will be amply sufficient for ordinary magnetic survey purposes.