抄録
The present World Magnetic Survey is described and discussed in relation to defining the earth's main field and secular change. Some effects dependent on geomagnetic noise levels affecting the survey are indicated. Difficulties incident to the extrapolation of faulty surface-field data to the surface of the core are noted. The extrapolated results of previous surveys are used to indicate the possible principal descriptive features of surface fluid motions that are derived for the outer core.
