"Cycles." . . "Radiación solar." . . "Promieniowanie słoneczne pomiary." . . "Smithsonian Institution. Roebling Fund." . . . . . . . . . . . "Periodic solar variation. (Roebling fund.)"@en . . . . . . . . . . . . "Periodic solar variation"@en . "Periodic solar variation" . "Periodic solar variation, by C. G. Abbot" . . . . . . . "Periodicity in solar variation" . "Periodicity in solar variation"@en . . . . . . . . . "Solar radiation." . . . . "Meteorology Periodicity." . .