Three days of quiet diurnal magnetic variation have been analysed as recorded by an array of three-component variometers sited stretching inland from the coasts of Southeast Australia. Particular attention has been paid to the anomalous variations in the vertical component of magnetic field: before this can be studied properly a regional normal vertical field must be estimated and subtracted vectorially from that which is observed. A possible correlation between anomalous and normal vertical

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... iations may indicate large scale induction in the oceans by the vertical variation field, as described by Bullard and Parker. However, comparison with estimates based on the calculations of Richards suggests that, whilst this inductive mechanism may give suitable values at the basic diurnal frequency, it does not appear to account for the coast effect observed at the second and third diurnal harmonics. The misfit of theory and observation is especially marked in the phase values. By contrast, the amplitudes and phases of the anomalous vertical variations of the first four diurnal harmonics all appear consistent with them being caused by the horizontal variation component at right angles to the coast line. If this is so it would require an electrical conductivity contrast between ocean and continent extending to depths sufficient to affect variations of 24-hour period.