We used a strong (r = 0.96) correlation between Ii-year averages of su
nspot number (SSN) and the geomagnetic aa index to infer that the mean
level of geomagnetic activity during the Maunder Minimum (1645-1715)
was approximately a third of that observed for recent solar cycles (si
milar to 7 nT VS. similar to 24 nT). We determined the variation of Ii
-year averages of solar wind speed (v) and the southward component of
the interplanetary magnetic field (B-s) with cycle-averaged SSN for th
e two most recent cycles and also compared cycle-averaged variations o
f v(2)B(s) and aa for the same interval. We then extrapolated these ob
served solar wind variations to Maunder Minimum conditions (mean SSN o
f similar to 2 and mean aa value of similar to 7 nT) to deduce that, o
n average, the solar wind during that period was somewhat slower (v =
340 +/- 50 km s(-1)), and the interplanetary magnetic field much smoot
her (B-s = 0.3+/-0.1 nT), than at present (similar to 440 km s(-1) and
similar to 1.2 nT). Various lines of evidence (including Be-10 data)
suggest that, despite the virtual absence of sunspots that characteriz
ed the Maunder Minimum, the 11-year geomagnetic (solar wind) cycle per
sisted throughout this period.