  We present a study of the rotation measure (RM) obtained from a sample of
extra-galactic radio sources either embedded in or seen in projection through a
sample of seven southern galaxy clusters (declination less than 30 degrees). We
compare our results with those obtained previously through similar statistical
studies and conclude there is a statistically significant broadening of the RM
signal in galaxy clusters when compared to a control sample. Further, we concur
with the findings of Clarke (2000) that the typical influence of the cluster on
the RM extends to around 800 kpc from the cluster core and that the RMs
determined are on average consistent with a 1-2 micro G field.
