Following a given classi®cation of geomagnetic activity, we obtained aa index values for the Maunder minimum (1645±1715). It is found that the recurrent and¯uctuating activities were not appreciable and that the shock activity levels were very low. The aa index level was due almost entirely to the quiet days. Calculated average solar-wind velocities were 194.3 km s )1 from 1657 to 1700 and 218.7 km s )1 from 1700 onwards. Also, the coronal magnetic ®eld magnitude and southward interplanetary

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... netic ®eld component Bz were lower. It is concluded that the nearly absent levels of geomagnetic activity during this period were due to lower coronal and Bz magnetic ®eld magnitudes as well as to the continuous impinging on the Earth of a slow wind.