In the presence of a large number of positive and negative ionic species, an analytical expression for the effective recombination coefficient of electrons in the D region is derived in the same from, α′=‹α_e›+λ‹α_ion›, as is customarily used in the upper regions. Here, ‹α_e› is the electronic recombination coefficient averaged with weights proportional to the abundance of various kinds of positive ions, and ‹α_ion› is the weighted mean of the various ionic recombination coefficients according to the composition of positive and negative ions. The effective loss rate of electrons are given as (1+λ)α′ in which the negative ion-electron ratio λ changes in a wide range as a function of altitude. Under the assumption of a model atmosphere containing eight minor constituents, this paper calculates the density distributions of thirteen species of positive ions and seven species of negative ions as well as of electrons. Based on the result, the effective recombination coefficient is estimated to be 4.2×10^-7cm³sec^-1 at the 80km-level, 1.5×10^-6cm³sec^-1 at 70km, and 1.9×10^-5cm³sec^-1 at 60km, while λ increases rapidly with decreasing height, being about 5.3×10^-3 at 80km, 7.9×10^-1 at 70km, and 1.0×10^-1 at 60km in a daytime condition. The effective loss rate estimated in this paper is shown to be consistent with the results derived from observations of solar eclipse, SID, and PCA events.

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The electromagnetic coupling between the earth's core and the mantle is studied during periodical variations in the geomagnetic dipole field. Based on archemagnetic data, it was revealed recently that the geomagnetic dipole has been changing its moment over a period of about 8000 years, its amplitude amounting to 50% of the present dipole moment. Small fluctuations with shorter periods seem to be superposed on it. These variations may possibly produce a considerable amount of change in the toroidal field both in the core and the conducting mantle. Nontidal variations in the earth's rate of rotation are then expected in association with the change in the coupling between the toroidal and the dipole field.
The electromagnetic coupling has been calculated for a simplified model of the earth. The core is approximated by a rigid sphere and a concentric spherical shell, both rotating around the same axis with different angular velocities. The electrical conductivity is assumed to be 3×10^-6emu for the entire core. The conducting mantle of 10^-9emu is considered to be covered with an insulating shell of about 400km thickness.
The result is that oscillation of the dipole moment as revealed by archeomagnetism is capable of causing a fluctuation of 10^-11rad/sec in the angular velocity of the mantle. The angular velocity increases with a decrease in the dipole moment. Since the dipole moment has been decreasing during the past 2000 years, the rotational speed of the mantle is supposed to have been accelerating.
Superposed on the gradual decrease in the dipole moment, there was a small maximum around 1800 A. D. amounting to about 5% of the present dipole moment. If it is assumed to be due to an oscillation with a period of 400 years, a change in the angular velocity of 5×0^-13rad/sec can be easily produced. This is approximately the same order of magnitude as would be expected from Newcomb's great empirical term in the observed longitude of the moon. From these, it may well be concluded that electromagnetic coupling plays an important role not only in decade variations but also in phenomena having such long periods as hundreds and thousands of years.

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The paleomagnetism of the Deccan Trap lavas in the western Ghats were studied in detail. Several stability tests were performed but the most effective one seemed to be progressive alternating field demagnetization. The direction of stable remanence was determined in 28 Mahabaleshwar and 5 Amboli lavas. It was noted that there is a good correlation between the stability of remanence and certain properties of magnetic minerals. Most rocks with evidence of high temperature oxidation are magnetically more stable than others.
As there is no significant serial correlation nor systematic large movement in directions of NRM in Mahabaleshwar lavas, the directions of the NRM may well represent the secular variation in the geomagnetic field in Eary Tertiary. The present data show a scatter of directions larger than the Quaternary paleomagnetic results, suggesting a bigger secular variation at that time. A statistical method to determine the upper limit of the time interval of volcanism was applied to the Mahabaleshwar section with the result that their activity had not lasted more than 5m.y. at 5% significance level. The mean pole position for all the lavas in this study shows a good agreement with the hypothesis that India moved northward in the Cenozoic era with great speed.

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A comprehensive study of the magnetic properties of nonstoichiometric (cation-deficient) titanomagnetites is described. Measurement of the saturation magnetization of synthetic samples provides information about the mechanism by which increasingly nonstoichiometric states evolve. It is concluded that in the spinel structure the inherent availability for oxidation of Fe²⁺ ions on tetrahedral sites is about 20% of that of Fe²⁺ ions on octahedral sites. Curie temperature increases with degree of oxidation, showing that the increasing vacancy concentration is offset by the greater number of strongly interacting Fe³⁺ ions. Comparison of calculated and observed Curie temperatures of highly oxidized compositions indicates that such materials have nonideal u-parameters. Thermomagnetic curves of the oxidized samples are of the “anomalous” type, but none was found having compensation temperatures. Coercivity and anisotropy decrease with decreasing Fe²⁺ ion concentration. Finally, contours of equal cell edge and Curie temperature are constructed for spinels in the FeO-TiO₂-Fe₂O₃ ternary system. These contours may be useful in the identification of naturally occurring samples, provided they do not contain appreciable amounts of other cations. An extrapolated value of 695°C is found for the Curie temperature of γ-Fe₂O₃.

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Some micropulsation field observations which were recorded on the Darling Downs (Queensland) above a wedge-shaped basaltic structure were initially inexplicable. One important observed anomaly was a great increase in the amplitude the telluric electric field near the tip of the wedge. In an attempt to obtain informanion about the local micropulsation source, the observations were compared with measurements from an analogue magnetotelluric model which simulated the relevant geological and magnetospheric situations. Agreement between field and model results adequately explained the anomaly mentioned above, thus enabling a general deduction to be made concerning the source. The experiment serves to illustrate the value of magnetotelluric modelling in research related to micropulsation.

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Observations of Zeeman tansitions in Rb⁸⁷ vapor can be used to make accurate measurements of the earth's magnetic field provided that the resonance lines are narrow enough so that the separate components of the transitions are resolved. However, the resulting relatively low signal-to-noise ratio makes it difficult to follow rapid chages in the field. Self-oscillating magnetometers have rapid response to magnetic field changes and high sensitivity, but poor long-term stability. The advantages of both approaches can be obtained with a compound magnetometer in which a self-oscillating magnetometer is locked with a long time constant to a narrow and well-resolved Zeeman transition. We designed and built two prototype optically pumped Rb⁸⁷ magnetometers of this kind, and carried out a stability test on them. Half-hour means of the magnetic field difference between the two were obtained for a period of nine and a half days. During this time local magnetic field activity ranged from quiet to disturbed and a sudden commencement occurred. The standard deviation of the individual half-hour difference values was 0.02γ(=0.02 nanoteslas, or 0.2 microgauss).

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