Geomagnetic secular‐change impulses

Secular-change impulses in magnetic declination, dip, and horizontal intensity derived from world-wide observatory data, tend to congregate around certain years (epochs). This tendency is examined statistically. As indications of the character of secular change, the impulses are well suited for use in the development of isoporic charts. Using a selected group of observatories, precise impulses were determined. These promise to be of value in investigations of the nature of secular change.