In this paper, the effect of magnetic interaction between coexisting minerals in the course of development of thermo-remanent magnetism (TRM) was examined. Various combinations of minerals in the ternary system FeO-Fe₂O₃-TiO₂ were derived by heat treating the natural ferromagnetic ilmenites. Coexisting phases produced by oxidation, reduction and phase transformations during heat treatments were found in parallel alternating structures. The main results were: (1) When both of the two phases are ferromagnetic, magnetic interaction acts negatively and the TRM of the composite system tends to be reverse TRM (RTRM). RTRM of the Haruna-type is the most typical example of this case, where the two phases are both ferromagnetic ilmenites. Intensification and artificial production of RTRM of this type were interpreted by the hypothesis of “partial exsolution” during the heat treatment at 600°C-700°C. Another type of RTRM where the two phases are titanomagnetite (Ti-Mt) and ferromagnetic ilmenite was produced by reduction. As for the case of combination of two Ti-Mts, the anomalous increase of TRM and the reversal of natural remanent magnetism, studied by other investigators, were referred to. (2) When non-ferromagnetic minerals, such as titan-hematite, rutile, non-ferromagnetic ilmenite or ulvöspinel, coexist with ferromagnetic ilmenite or Ti-Mt, the TRM and coercive force of the composite system are intensified remarkably: a linear relation J_tr(T₀)/J_s(T₀)∝H_c(T₀) was obtained for the composite of ferromagnetic ilmenite and titan-hematite and rutile.
As by-product of the present study, some information on the oxidation-reduction properties of ferromagnetic ilmenite was obtained: for example, oxidation was found to proceed in two distinct steps as the treatment temperature is raised.

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A remarkable 27-day recurrence tendency of cosmic-ray neutron intensities was noticed through the observation at Nagoya (geomagnetic latitude 25°N, sea level) from October, 1954 to July, 1955. This tendency is completely in the same phase with that of the solar activity during the same period. This phenomenon seems to show that some part of low energy cosmic rays are usually emitted from the sun.

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In order to investigate the geomagnetic variaton due to the Solar Eclipse of June 20th, 1955, the S_q-field at 13^h30^m of this day is expressed by a simple, and the current-system of the additional field due to the eclipse is drawn, using the present data and a quantitative result on the bygone eclipse.

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Considering the instability of electrically cocducting fluid heated below when a uniform magnetic field and Coriolis acceleration are both present, we find the instability first sets in oscillation of increasing amplitude when a temperature gradient, however small, exists, under astrophysical condition κ>>1/4πτ>>ν where κ, σ and ν are the thermal diffusivity, electrical conductivity and kinematic viscosity. Two critical frequency of oscillation are obtained depending on the ratio between Coriolis force and electromagnetic force.

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