Using the model magnetosphere of the Mead's type, periods of self oscillation of the magntosphere are calculated for the cases of weak or strong dependence of its amplitude on longitude. It is shown that the transverse wave can exist when the periods of these two modes are equal. This condition is satisfied at latitudes near the auroral zone. The oscillations with a longitudinal dependence in form of Gauss-function are also considered, and the values of Ne/T² are calculated. The plasma density Ne in the magnetosphere is estimated using the period T of observed geomagnetic pulsations; the result is in agreement with the data of other methods.

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It has already been reported by one of the authors that electron temperature can be calculated from the ratio of the two floating potential shifts caused by the rf signals of different amplitude which is successively applied to the Langmuir probe. However, conventional type of electron temperature probe which is based on the above principle detects v×B voltage induced by geomagnetic field and rocket velocity as well as any other noise.
In order to get rid of the effects of v×B and random noise, an improved type of electron temperature probe is developed with sufficient results. At the same time, the instrument is made compact and light-weighted to some extent.

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Assuming the distributions of minor constituents in the upper mesosphere, an estimate is made of the negative ion densities in chemical equilibrium with the observed electron density. The result shows that the negative ion composition in the region above 80km is essentially same as in the E-region. But in the region below 70km, negative ions, such as CO₃^-, NO₂^-, and NO₃^-, of high electron affinities are shown to be relatively abundant, especially during the night. The result may possibly account for the characteristic growth of the D-region electron density at sunrise. A discussion of the sequences of negative ions in the D region leads to the conclusion that O₃ and CO₂ play an important role in determining the abundance of these negative ions of high electron affinities.

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During extremely quiet magnetic times, transient magnetic signals have been observed which differ significantly from any previously reported. They can be interpreted as being due to a travelling bunch of charged particles (for which two models are discussed), or to meteors.

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Plane electromagnetic waves are assumed to be incident normally on an ocean surface, overlying a sea floor of uniform slope. Berdichevskii's method of images is used to extend the computations of surface fields for a basement with non-zero conductivity, at sites remote from the coastline. The vertical magnetic field is enhanced over shallower depths while the horizontal electric field shows a transition from the polarization behaviour on the landward side of a continental shore to that on the seaward side. The fields are computed for slopes of 3° and 10° and compared with those over an ocean with a horizontal floor. The calculations are applied to three sets of measurements on iceislands in the Arctic Ocean; no disagreement is found, although quantitative explanation cannot be made owing to the difficulties of controlling the experimental conditions, or of simulating them precisely in a mathematical analysis.

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Runcorn has shown that a moving magnetic source in the earth's core can cause the north pole of the magnetic vector at a fixed observatory on the earth's surface to rotate clockwise (when viewed along the vector toward its north-seeking end) for a westward motion of the source and counter-clockwise for an eastward motion of the source. Examination of the terrestrial magnetic record, which contains evidence of such vector rotations at many observatories, reveals no obvious contradictions to Runcorn's rule. Numerical calculations based on radial dipole source models of the non-dipole field show the theory can also account for the magnitude of the effect observed in the terrestrial record and, together with the results of simple tests with a spherical compass and a magnetic dipole, these calculations indicate that exceptions to the rule are rare, if indeed they exist at all. The theory therefore presents a potentially powerful tool for the analysis of the geomagnetic secular variation from paleomagnetic and archaeomagnetic data obtained from a single locality. As an example, it is shown that paleomagnetic results from Pleistocene sediments in Japan indicate the non-dipole field may have been drifting westward around 50, 000 years ago.

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The thermomagnetic records of natural pyrrhotite were interpreted on the basis of two phases differing in magnetic properties. The chemical composition of these phases as deduced from these records agrees with the microprobe results obtained for suitable unheated specimens. The thermomagnetic method requires heating the specimens to about 310°C, but the microprobe results show that loss of sulphur is confined to the surface of the specimens when heated in argon at the rate of 5°C/minute. The results obtained with both methods of analysis indicate homogenization of the specimens at 400°C which may be due at least in part to appreciable loss of sulphur. The thermomagnetic method has the advantage that finely dispersed mixtures of the phases can be analysed and that their relative abundance can be easily estimated.

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Magnetic properties of four groups of natural monomineralic clays were studied by means of thermomagnetic analysis, reflecting microscope, X-ray diffractometer, X-ray flourescence analyser and electron probe microanalyser. All samples were heated up to 700°C in air and in vacuum and it was found in many cases that a new magnetic phase appeared after heating. The new magnetic phase is thought to originate from colloid, amorphous iron impurities and/or hydroxidse of iron.

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Archeomagnetically determined values of inclination and declination are commonly reduced to a base location, the regional geomagnetic field being approximated either by the axial dipole or by a virtual dipole. We investigate the error in these approximations by using the spatial variations of the 1965 IGRF to simulate the temporal secular variation. The virtual dipole approximation is found to be significantly more accurate than the axial dipole approximation, particularly when the archeomagnetic site is at the same latitude as the base. Inclination error and declination error each have a normal distribution, but the directional dispersion is not circular-normal (Fisherian). Tables are presented by which the statistical error in reduction of archeomagnetic directions to a base site can be readily estimated.

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The natural remanent magnetization (NRM) of three Apollo 11 lunar materials, i. e. a crystalline rock and two kinds of microbreccia, is examined in detail with special attention to the possible effect of viscous magnetization acquirable in the terrestrial magnetic field.
The intensity of stable NRM (I_n), the critical AC-demagnetization field (H*) which represents the upper limit for keeping approximate invariance of NRM direction, and the effective demagnetization field (H₀) which reduces the intesity of NRM to (1/e) of the initial value are determined as follows; (a) I_n=8.9×10^-6emu/gm, H*=30Oe, H₀=25Oe for a crystalline rock (NASA No. 10024.22): (b) I_n=1.50×10^-5emu/gm, H*=40Oe, H₀=35Oe for a weakly impacted microbreccia (No. 10021.32): (c) In=1.50×10^-4emu/gm H*>500Oe, H₀≅1400Oe for a strongly impacted microbreccia (No. 10085·16).
The intense and extremely stable NRM of the strongly impacted lunar microbreccia may suggest that a strong impact of lunar materials can cause an acquisition of a particularly stable remanent magnetization even in a very weak magnetic field.
A certain portion of metallic irons in the lunar materials are very fine particles of several hundreds of Ångström in mean diameter. These particles behave almost superpara-magnetically. Saturated viscous remanent magnetization acquired in the geomagnetic field being denoted by ΔI_v, the ratio of 44 to the stable remanence I_n is determined to be 0.015, 8.4 and 0.23 respectively in cases of (a), (b) and (c).
The larger value of the ratio ΔI_v/I_n indicates that the larger portion of fine particles of metallic irons. The relaxation time of the viscous magnetization at 20°C ranges from 2×10 to 7×10⁴sec., which implies that the grain size of the find iron particles is 170-180Å in diameter.

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All the data of paleomagnetic and archeomagnetic studies made in these two decades in Japan are presented as three tables. Two of them give the paleomagnetic and archeomaghetic direction studies and the other table gives results of intensity studies from the recent to the geological past.

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