Magnetic Storms

Abstract

IN his letter (NATURE, November 11) Dr. Simpson raises an argument as to the absence of corresponding changes in the electrical potential gradient during magnetic storms which, if admitted, would, I imagine, prove a serious difficulty in the “electron stream” theory of magnetic disturbances. On the assumption that the arriving stream induces an opposite charge which resides at the earth's surface, we can agree with Dr. Simpson's calculation, except that, since there are two current sheets of opposite sign, the potential gradient ought to be half what he finds.