1. The sunspot period;Clayton;Smithsonian Misc. Coll.,1939
2. Forecasting sunspot and radio transmission conditions;Durkee;Bell Lab. Rec,1937
3. Note on the epoch of the next sunspot maximum;Gleissberg;Astrophys. J.,1944
4. Solar cycle data for correlation with radio propagation phenomena;IRPL-R23,1945
5. Prediction of next sunspot maximum;Linder;Pop. Astron.,1945