The equatorial ring current postulated by Chapman and Ferraro to explain the main phase of terrestrial magnetic storms is analyzed with respect to its effect on the intensity of the cosmic radiation. For mathematical convenience, the ring current is replaced by a current sheet located on the surface of a sphere concentric with the earth, in accordance with a suggestion due to Chapman. A simple expression is then obtained relating the variations in magnetic field at the equator with the corresponding variations to be expected in the intensity of cosmic radiation measured by an arbitrary detector located at any latitude and atmospheric depth.

• Received 25 August 1952

DOI:https://doi.org/10.1103/PhysRev.89.130