A.G. McNish , Department of Terrestrial Magnetism, Carnegie Institution of Washington, "Magnetic Storms," page 361, Edison Electric Bulletin, July 1940.
2.
Dr. Clifford N. Anderson, Bell Laboratories Publication. Notes on the time relation between solar emission and terrestrial disturbances. Nov. 1940. A representation of the sun spot cycle. June 1939.
3.
Glen Ireland, Bell Telephone Quarterly, July 1940—Sun Spots and Telephone Service.
4.
L.W. Germaine , "The Magnetic Storm of March 24, 1940—Effects in the Communication System," Ed. Elec. Inst. Bull., page 367, July 1940.
5.
G. Wascheck , "Earth Resistivity Measurements," Bell Laboratories Record, February 1941.
