1. A representation of the sunspot cycle;Anderson;J. Geophys. Res.,1939
2. Bartels , J. Collection of geomagnetic planetary indices K p and derived A p and C p for the years 1932 to 1961, IAGA Bull. 18 IUGG Publications Office Paris V 1962
3. Discussion of time variations of geomagnetic activity, indices Kp and Ap, 1932-1961;Bartels;Ann. Geophys.,1963
4. Bartels , J. A. Romana J. Veldkamp Geomagnetic data, 1961, indices K and C , IAGA Bull. 12 1 IUGG Publications Office Paris V 1964