From the analysis of the external components of the equinoctial geomagnetic daily variation in Peru it follows that they are generated by a complex current system. In this work it is found that in addition to the global current system and the main electrojet, with I₀=0.124Amp/m, it is necessary to include two secondary lateral currents parallel to the main electrojet. Their intensities are I₁=0.38I₀ and I₂=0.03I₀, north and south of the dip equator, respectively.

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A unique large magnetic shield room of the spherical type has been constructed on the new campus of the Institute of Space and Astronautical Science. A spherical shield room is theoretically of good design to produce a nice uniform field inside it. The purpose of the magnetic shield room is to test the magnetic characteristics of spacecraft, satellite, sounding rocket payload and their subsystems, the calibration of magnetometer and others. The present shield room is also used as an electric shield room. Therefore, it is quite useful to check the electro-magnetic interference of payload system and to calibrate the high sensitive electronic circuit. The present paper describes the design and the shielding characteristic of the room. The authors wish that the shielding room can be used effectively by many investigators in the space science field and others. It is the authors desire that the shielding room will be utilized effectively by numerous investigations, not only in the space science field but also that of other fields of research.

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High temperature oxidation of titanomagnetite Fe_3-xTi_xO₄ commonly observed in subaerial volcanic rocks also proceeds in laboratory when the rocks are heated in air. Changes in magnetic hysteresis properties were traced by heating small samples of basalt in air at 640°C for various intervals. The ferromagnetic mineral contained in this basalt is titanomagnetite with a composition of x=0.4. The largest changes occurred at about 10 minutes heating time. The oxidation increases single domain (SD) like regions characterized by large values of coercive force (H_c), remanence coercivity (H_rc), and saturation remanence to saturation magnetization ratio (J_r/J_s), and by low H_rc/H_c ratio. As these changes are accompanied by the increase of high Curie temperature component close to that of magnetite, the SD-like region can be interpreted as magnetite-ilmenite intergrowths formed by high-temperature oxidation.

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As part of the “Basic Maps of the Sea” project and partly for the “Earthquake Prediction Program”, detailed magnetic, hydrographic, seismic and gravity surveys were carried out by the Hydrographic Department, Maritime Safety Agency, Japan, in the southern part of the Japan trench during the period from 1976 to 1977. Using these results, magnetic anomalies over two seamounts, Daiiti kasima and Katori, were analyzed by means of Talwani's method. Besides, further studies based on two-dimensional modeling were conducted for Daiiti-kasima with special reference to the hypothesis of subduction of this seamount.
As the results of above analyses, the author presents a magnetic structure of Daiiti-kasima and suggests “an accretional model” of the seamount during the subduction of an oceanic plate to explain the geomagnetic and topographic features of Daiiti-kasima.
In addition to the above results, the following have also been concluded.
1) A considerable part of the top of Daiiti-kasima must be non-magnetic, and the depression of the magnetized layer of Daiiti-kasima should be taken into account to explain the long distance between the positive and negative magnetic anomaly peaks for the size of the seamount.
2) The VGP (virtual geomagnetic pole) for Daiiti-kasima is located at N62°, E349° and the VGP for the top portion of Katori at N60°, E354°. These results which are consistent with the mean VGP from Cretaceous Pacific seamounts support the hypothesis of the northward drift of the Pacific plate.
3) As for Katori seamount, magnetization of the top (4200m to 4750m) and that of the bottom (4750m to 7500m) seem to be considerably different in their directions and magnitudes.

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It has long been considered that anomalous behavior of short-period geomagnetic variations in the Kanto Plain (the Kanto anomaly) reflects a mantle conductivity anomaly and the sedimentary layer as thick as 3, 000m or more plays a rather minor role, only as local perturbation superposed on a regional anomaly. The complicated surface conductivity structure in this region, characterized by the sea existing to the east and the south and the thick sedimentary layer in the central part, has hampered quantitative discussion on the effects of seawater and sediments on short-period geomagnetic variation anomalies. It is shown, however, that such surface effects can be estimated approximately by considering two different polarization cases separately; one for a northwestward geomagnetic variation and the other for a northeastward geomagnetic variation. In the former case, the sea effect is striking as disclosed by numerical calculations of the peninsula effect. In the latter case, the so-called channeling effect due to the presence of the sedimentary layer seems to be a predominant factor. It is concluded that the Kanto anomaly is primarily accounted for by these surface effects, although no significant information on the crustal and mantle conductivity structure could be derived.

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Electromagnetic induction by a uniform magnetic field in a semi-infinite medium of finite conductivity having a sinusoidal undulation at the surface is studied. The source field is assumed to be parallel to the mean surface. The apparent resistivity (ρ_a) vs. period of variation (T) relation is obtained at various points over the undulating surface by means of conventional magneto-telluric technique. The phase vs. T and the transfer function vs. T relations are also obtained from the electric and magnetic fields studied in this paper.
It turns out that the ρ_a-T relation is little affected by the surface undulation. The order of magnitude of ρ_a value at various points over the surface does not vary although ρ_a for a longer period variation takes on a relatively lower value at a depressed portion of the undulatory surface. On the other hand, the transfer function vs. T relation differs from observation point to observation point depending upon the position of observation point on the undulatory topography.

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