"During the late 1880s, first Gustav F.W. Sporer and then E. Walter Maunder reported that the l7th-century solar anomaly coincided with a cold spell in Europe. That astonishing observation lay neglected for almost a century, with many astronomers assuming that their predecessors had not been competent enough to count sunspots. It was only in l976 that John A. Eddy of the University Corporation for Atmospheric Research in Boulder, Colo., reopened the debate by examining the Paris archives and establishing the validity of what came to be known as the Maunder minimum.

Eddy also noted that the amount of carbon l4 in tree rings increased during the dearth of sunspots. This radioactive element is created when galactic cosmic rays transmute nitrogen in the upper atmosphere. Eddy's finding suggested that when the magnetic fields in the solar wind--the blast of particles and energy that flows from the sun--are strong, they shield the earth from cosmic rays, so that less carbon l4 forms; the presence of excess carbon l4 indicated a low level of magnetic activity on the sun during the Maunder phase. Eddy thus reinforced the connection between the paucity of sunspots and a lull in solar activity." [See chart ]

Scientific American, 7/96, p 49.

The Stellar Dynamo, Elizabeth Nesme-Ribes, Sallie L. Baliunas and Dmitry Sokoloff.