Geomagnetic data 1957 : indices K and C, rapid variations
by J. Bartels, A. Romana and J. Veldkamp
(IAGA bulletin, no. 12 l)
International Association of Geomagnetism and Aeronomy , Disbributed by North-Holland Publishing Co., 1961
At head of title: International Union of Geodesy and Geophysics. Association of Geomagnetism and Aeronomy (formaly Association of Terrestrial Magnetism and Electricity)
"Published with financial assistance from UNESCO"
IUGG Publication Office