1. S.-I, Akasofu, , B., Fogle, , B., Haurwitz, , Sydney Chapman, Eighty, University of Colorado Press, Boulder, 1967,
2. Waldmeier, M., , The Sunspot Activity in the Years 1610–1960, Schulthess and Co., A. G., Zurich, 1961,
3. Waldmeier, M., , , Annual Sunspot Reports, , Swiss Federal Observatory, , Zurich, , 1961– 1967, .