As a result of increased survey activities by satellites and marine vessels, it is likely that more geomagnetic data have been recorded in the past 4 years than in any previous 4-year interval.

From marine magnetic surveys, measurements of total intensity have provided data that have contributed significantly to the newer concepts of sea-floor spreading and continental drift [Allan, 1969]. Magnetic measurements in the oceans will continue to be a major tool in the exploration of the sea floor and its underlying crust and mantle.