In this paper a brief summary will be given of the historical development of geomagnetism as a science in southern Africa and particularly the role played by Hermanus Magnetic Observatory in this regard. From a very modest beginning in 1841 as a recording station at the Cape of Good Hope Hermanus Magnetic Observatory is today part of the South African National Space Agency (SANSA), where its geomagnetic field data are extensively used in international research projects with a wide range.

In this study we performed a wavelet and Lomb-Scargle analysis of the geomagnetic activity K-index at Lerwick (LER), Hermanus (HER) and Canberra (CNB) for the period between 1960 and 2010, overlapping with solar cycles 20 to 23. Daily mean K indices are used to identify how several harmonics of the 27.0-day recurrent period change during each solar cycle when comparing high- and mid-latitude geomagnetic activity, applying a 95% confidence level.