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The sun may have been magnetically even weaker during the Maunder Minimum than the lack of sunspots for 70 years implies. This report that during the Maunder Minimum the sun was more profoundly quiet than it has ever been since was made at the 1978 AGU Spring Meeting by Miriam A. Forman of the State University of New York at Stony Brook.

Forman presented evidence that the enhanced amounts of radioactive carbon in tree rings which grew about 300 years ago are due to unusually high cosmic ray intensity, probably a result of extremely low solar magnetic activity during the ultralong sunspot minimum at that time. The amount of radiocarbon deposited in tree rings which grew in the late seventeenth and early eighteenth centuries is about one or two percent higher than that in nineteenth-century tree rings, the increase occurring during the 70-year-long sunspot minimum discovered in the 1890s by the English astronomer E. W. Maunder.