The O₁ component of the geomagnetic lunar daily variation is examined at 4 Indian equatorial stations for the active sun years from 1958 to 1961 following the Chapman-Miller method generalized by Winch. Clear geomagnetic O₁ tides are found at every station and are favourably considered as due to an ionospheric current like the equatorial electrojet.

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The perturbation of alternating geomagnetic fields by a three-dimensional conductivity model is studied by a numerical technique. The model is a nonsymmetric island structure embedded in a layered half-space. Linearly polarized source fields of two different directions as well as a circularly polarized source field are studied. Three source field frequencies are considered. The results are presented as amplitude contours of the various field components over the surface plane. It is found that the perturbations in the fields are greater for shorter period. Also, the various maxima and minima in the amplitude contours associated with the island structure are dependent on the orientation of the source field. The results for the different polarization fields are compared, and the amplitude contours for the circularly polarized source field vary considerably from the linearly polarized cases.

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Complex magnetic interactions in specimens containing single-domain and/or multidomain grains of one or more ferromagnetic components will not cause non-ideal behavior in the Thelliers' method if the TRM and the induced magnetization are statistically stable, isotropic and linear with field, and if a single TRM distribution function which depends only on temperature applies to both the acquisition and the thermal demagnetization of TRM. These are physically reasonable, sufficient conditions which are fulfilled closely enough for paleointensity purposes by many, and perhaps most, volcanic rocks in fields of 0 to 1 oe.

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The maximum entropy method (MEM) of BURG (1968, 1970, 1972) has been applied to 2300 years of mean daily D, H, and Z data. Composite spectra and line counts, aside from the fundamental annual (mainly P₂⁰ mode) and semiannual (P₁⁰ mode) lines, show harmonics at periods 365/(n+1), n=1, 2, …, 6 days. In this range the geomagnetic spectrum consists of a P₂⁰ mode line structure superposed on a background P₁⁰ mode continuum. Mode mixing may have adversely affected previous Earth response estimates (BANKS, 1969) and must be considered in future studies. Finally, the ‘27-day peak’ is shown to be a broad band signal from 24 to 31 days, confirming results of RASSSACH et al. (1966).

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Preliminary Mössbauer spectroscopy data support the “x-phase” theory of Ishikawa and Syono, which explains reversed thermoremanent magnetization in the ilmenite-hematite series. Heat-treated samples of 50, 55, and 60mole% ilmenite show long-range magnetic order above their Curie points; quenched samples do not. The “x-phase” constitutes about seven percent of the 60mole% sample. Part of the x-phase has a Curie temperature at least 200°C higher than the bulk sample.

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X-ray, chemical and thermomagnetic analyses were made on ferromagnetic minerals separated from six submarine basalts of various ages, which are dredged from seamounts and ridge or drilled from sea floor. Lattice parameters, Curie temperatures and oxidation parameters are determined for these samples. From a comparison between K-Ar or Ar39-Ar40 ages and the magnetic properties, it is evident that major ferromagnetic minerals in young submarine basalts are titanomagnetites, whereas older submarine basalts contain essentially titanomaghemites. We conclude that the primary titanomagnetites have undergone maghemitization in suboceanic environment. The maghemitization process is estimated to have a time constant of a few tens of millions of years and maghemitized depth may extend to a few tens of meters in older (say older than 5×10⁷y) oceanic crust.
NRM of several maghemitized submarine basalts are subjected to a-f, pressure and low temperature demagnetization, hoping to see if any of the demagnetization techniques could discriminate a secondary magnetization which might be acquired during the maghemitization. Although the demagnetization techniques erased considerable portion of the NRMs, none of them was successful to demagnetize preferentially a remanent magnetization carried by titanomaghemites.

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