Suprathermal electrons of energies between 5keV and 10keV were found to exist in the altitude range 200-800km at geomagnetic latitude 20°N, the L-value ranging from 1.17 to 1.25. The electrons were detected with proportional counters of thin plastic windows on board a sounding rocket L-3H-7 launched at 21:00 Japanese Standard Time on September 3, 1971, when solar and geomagnetic activities were quiescent. The angular distribution of the electrons was peaked in the direction perpendicular to the magnetic line of force at altitudes above 500km, indicating that the electrons are trapped in the geomagnetic field. The altitude dependence is in essential agreement with that expected from the collision loss of electrons in the upper atmosphere. The extrapolation of the measured altitude dependence to the radiation belt gives an electron flux much lower than that observed inside the belt.

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Electrons of energies between 6.5 and 23keV have been observed from a sounding rocket with a thin-window (37μg/cm² polypropylene) proportional counter in the altitude range between 140km and 326km at the geomagnetic latitude of 20°N, the L-value at the apogee being 1.17.
The directional dependence of the electron flux with respect to the magnetic line of force indicates that these electrons consist of two components, the one peaked perpendicular to the line of force and the other being isotropic in the upper hemisphere. The former is considered to be geomagnetically trapped and the latter to be precipitating along the line of force. The flux ratio of the trapped to the isotropic components is 0.77±0.12 and 1.7±0.2 at 200km and 300km, respectively. The isotropic component does not change between these altitudes, while the trapped component increases nearly twice as much. The observed intensities of the trapped and the isotropic electrons at 300km are (310±20) electrons·cm^-2·sec^-1·(4π sterad)^-1 and (27±4) electrons·cm^-2·sec^-1·sterad^-1, respectively.

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A detailed investigation on the diurnal variation of ionospheric absorption over Calcutta at various frequencies (over Calcutta) shows that the absorption fits better with the relation L∝cosⁿ χ rather than with L=A+Bcos χ, with the n values lying between 0.9 to 1.9 for different frequencies and seasons. The frequency dependence of the exponent n depends critically on the relative amount of the deviative and non-deviative losses.
The diurnal variation of absorption also shows some asymmetry between the forenoon and afternoon values, the index n for the forenoon values being always greater than the afternoon values. The possibility of geomagnetic control over at least a part of the absorbing region has been invoked.

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Simultaneous observations of the ionospheric drift and anisotropy parameters of the ground diffraction pattern at Thumba (0.6°S dip) using the spaced receiver technique were conducted at two adjacent receiving aerial systems of different sizes. It is shown that though the apparent drift speed V_a shows very little dependence on the size of the triangle, the true drift speed V increases to some extent with the increasing E-W separation of the receiving aerials. The random drift speed V_c shows slight decrease with increasing E-W separation while the true and apparent drift directions φ and φ_a show almost no dependence. The axial ratio ‘r’ of the characteristic ellipse shows a positive dependence on the N-S separation of the aerials while the transverse size ‘b’ shows a small increase with the E-W separation. The orientation of the characteristic ellipse φ tends to be more close to magnetic N-S with increasing N-S separation of receiver aerials.

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The theoretical island effect relevant to Miyake-jima Island as calculated on the basis of electromagnetic induction in a thin sheet representing the sea does not agree with observations when the coupling effect between the sea and an underground conducting layer is ignored. It is shown that the electrical conductivity structure beneath Miyake-jima Island can be estimated by examining the coupling effect in detail.
It is concluded that a highly conducting layer having a conductivity of 10^-12emu or thereabout must lie close to the earth's surface beneath Miyake-jima Island and that this layer is likely to be underlain by a poorly conducting layer, 10^-14emu extending from 50km to about 400km in depth. The highly conducting layer at the top seems to have an important bearing on the thermal state at the northern part of the Izu-Bonin arc.

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A method of eliminating noises from geomagnetic observations for detecting local anomalous changes is proposed. Unlike the simple or weighted difference methods hitherto proposed, the method is based on an idea that most fluctuations in the geomagnetic total intensity are caused by those of equatorial ring current which produces the Dst field. It is possible to correct the observed values of the total force at a station for the Dst, that is to obtain the values that should have been observed when the equatorial Dst is zero.
Applying the above method to the proton precession magnetometer data as obtained by the geomagnetic research group for earthquake prediction, isoporic lines of the total force over Japan are obtained for epoch 1970. 0. The pattern of the isoporic lines is completely different from those obtained for epoch 1965. 0.
An anomalous secular change in the total intensity has been found at stations on Oshima Island, a volcanic one about 100km south of Tokyo. The change seems likely to have something to do with the volcanic activity there.

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Relation between changes in the dipole field and those in the earth's rate of rotation has been examined for three different periods, 8000, 400 and 65 years, based on such various kind of data as those of archeomagnetism, observation of moon's longitudes and recent instrumental observations. It has been confirmed that fluctuation exists in the rate of rotation corresponding to the dipole change for these periods. The magnitude of the variation in the rotation to be related to the dipole change increases as the period decreases.
Time variation in the drift velocity has also been examined for several features of the geomagnetic secular variation. It is very probable that a change in the drift velocity accompanied the 400 year period fluctuation in the earth's rotation.
The results thus obtained are compared with a theoretical result. Except for the phase of the angular velocity of the mantle for 65 year period and the magnitude of the geomagnetic westward drift for 400 year period, the observed results are well accounted for by an electromagnetic coupling caused by a dipole change at the core-mantle boundary, provided that the electrical conductivity of the lower mantle is as large as 10^-8emu.

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Preisach diagrams for soils derived from sedimentary geological strata and for synthetic samples containing dispersed magnetite grains are presented and are used as the basis for distinguishing between superparamagnetic, stable single domain and multidomain grains. In particular it is established that between 10 and 20 percent of the total magnetic constituents in a typical soil are well-dispersed stable single domain grains with diameters of about 250Å, the majority of the remainder being superparamagnetic grains with slightly smaller diameters.
The Preisach-Néel theory for interacting single domain grains is extended so that the associated magnetic viscosity phenomena can be represented on the Preisach diagram in terms of a fluctuating viscosity field and experimental results justifying the introduction of this concept are included. This presentation provides a clear indication of those areas of the Preisach diagram, and hence the components of the overall magnetic grain distribution in the sample, that are associated with any particular viscosity process. It is thus shown that the value for the coefficients for the decay of viscous remanent magnetism can be used for comparing the magnetic grain size distributions in different samples.

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