abstract
Absolute observations of the geomagnetic Z component done on Marion Island on two consecutive quiet days in May 1971 showed a phase reversal in the daytime variation of this component when compared with the expected Sq variation for the latitude of the Island. The results are compared with theoretical approximations for the "island effect" and with experimental results obtained by other workers who found the "island effect" only for periods much shorter than that for which the effect is observed at Marion Island.