The acquisition of piezo-remanent magnetization (PRM) of igneous rocks under uniaxial compression is experimentally studied. It has been found that the rate of acquisition of PRM is several times as large as that of assemblages of magnetic minerals. This is in remarkable contrast to another observed fact that the rate of decrease of magnetic susceptibility owing to an increase of uniaxial compression in rocks is about one order smaller than that in magnetic minerals.
The rate of acquisition of PRM is larger in a smaller magnetic field than in a larger magnetic field, and it is larger for rock samples which are magnetically harder, having a larger value of magnetic coercive force and a slower rate of decrease by AC-demagnetization.
It is qualitatively shown that all these experimental results can be consistently explained based on a simple model of configuration of magnetic domains of magnetic minerals under the effect of inverse mangetostriction.

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Three magnetic classes of ocean basalts are defined on the basis of thermomagnetic and microscopic analysis. Moderate heating of Class I basalts results in an anomalous increase in Curie point, magnetization intensity, the ratio TRM to NRM, and magnetic susceptibility. The same thermal treatment of Class II rocks results in an anomalous decrease in all magnetic parameters except the Curie point. Class III rocks are stable. Several Class I and II ocean basalts possess the property of self reversal. Class I and II rocks contain metastable magnetic minerals and readily transform into stable Class III rocks when heated. The transformation mechanisms are described and the characteristics of each class are tabled. It is concluded that in situ cores are necessary to discover the composition of the ocean crust, and the distribution of the different magnetic classes of ocean basalts within the ocean crust. Otherwise, little faith can be placed in any interpretation of ocean magnetic anomalies.

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Irreversible changes of the remanent magnetization of fine grains of ferromagnetics under uniaxial compression have been experimentally examined in a systematic way. The compression of a sample in a magnetic field results in a remanent magnetization which is greater than that obtained without compression in the same field. The pressure remanent magnetization PRM produced by removing uniaxial compression in a magnetic field increases with increasing compressional stress. The dependence of the PRM of a fine grain assemblage of titanomagnetite upon pressure P and a magnetic field H_ex can be expressed by a·f(p)·H_ex, where f(p) increases monotonically with respect to pressure, reaching some limitting value at pressures higher than 2kb, and a is a numerical constant systematically dependent on grain size. The ratio of PRM/IRM in a weak magnetic field for homogeneous bulk specimens with grain size larger than about 0.1mm varies from 1 to 5, whereas specimens containing fine grains with diameters less than 0.1 microns have ratios of 20 to 40. A similar grain size dependence is found for Cu-Co superprecipitates containing homogeneously dispersed ferromagnetic fine grains in a non-ferromagnetic matrix. Stability of the PRM of a fine grain assembalge of titanomagnetite has been examined through ac field demagnetization. The decay of PRM with respect to increasing peak intensity of an ac field resembles that of IRM rather than that of ARM.
The intensity of various types of remanent magnetization, such as TRM, IRM and ARM, decreases irreversibly as the specimen is compressed uniaxially in a non-magnetic space. The observed hyperbolic decay of remanent magnetization with increasing compressional stress can be accounted for by a PRM induced by the demagnetizing field of the specimen itself in a reverse sense to the initial remanent magnetization. It is shown that the PRM vector deviates from the direction of an external magnetic field toward a plane perpendicular to the compressional axis when the magnetic field is not parallel or perpendicular to the axis of compression. The maximum deflection angle is calculated to be 10 degrees and occurs when the angle between the magnetic field and the compressional axis is about 45 degrees.
The mechanism of acquisition of PRM is briefly discussed. A more detailed discussion of the problem will be given in a future paper.

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Two basalt samples with homogeneous titanomagnetites as the only ferrimagnetic component, have been investigated, to find out about the influence of uniaxial compression on coercive force and saturation remanence at different temperatures and on thermoremanent magnetization. The samples have been investigated in natural state and after a heat treatment of 30h at 700°C in air. Caused by this heat treatment the original homogeneous titanomagnetites are transformed into an inhomogeneous mineral aggregate. The natural samples show a strong dependence of all measured values on uniaxial compression: At room temperature and a compression of 1kbar for example, the coercive force increases by about 100% and the saturation remanence decreases by about 50%. These variations are reversible. The behaviour of thermoremanence is distinctly different depending upon whether uniaxial compression and applied magnetic field are parallel or perpendicular to each other. In the first case a decrease of about 50%, in the second case an increase of about 50% is observed.
In contrast to these results the heat treated samples show only a very slight dependence of their magnetic parameters on uniaxial compression.

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Large coercivities of some ilmenohematite minerals are probably due to magnetostrictive effects associated with exsolution.

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For consideration of magnetomechanical effects in rock magnetism, it would be desirable to have a criterion for the influence of directed stress on magnetization. A technique is outlined for determining the theoretical uniaxial stress required to impose magnetization rotation and dominate the arrangement of a pattern of magnetic domains. It involves an appropriate balance of magnetocrystalline and magnetoelastic anisotropy energies. Calculations for magnetite agree with reported experimental results obtained from domain observations. Results for nickel further support the method as a quantitative measure for determining the stress sensitivity of a magnetic crystal.

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Simultaneous magnetic total field measurements have been obtained over a span of seventeen months with a proton magnetometer and with a series of self-oscillating single-cell rubidium magnetometers. Their comparison indicates variation in frequency response of the rubidium magnetometers to a fixed absolute magnetic field. These variations can be as much as 7γ between different sensors, can be 6γ when a sensor is retuned, and can be time-variable over a 2γ range in the case of an undisturbed sensor. However, approximately two-thirds of the absolute field values computed from a mean of calibration factors, redermined each week, lie within ±0.2γ of the “true” value.

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The theory of multipoles is applied to the main field and secular variation field in order that the spherical harmonic coefficients of the secular variation field may be subdivided precisely into parts associated with the westward drifting, polewards drifting and nondrifting components of the main field.

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Basaltic rocks from twenly-three lava flows of late Pliocene in New Mexico and Arizona, U. S. A., were studied by means of Thellier's method and seventeen intensity estimates were obtained. It was observed for both originally normal and reversed samples that the field intensity at the time of lave-flowing was not greatly different from that of the present geomagnetic field at the sampling locality. Seventeen estimates of the intensity of the geomagnetic field in the late Pliocene range from 0.35oe to 0.82oe, the mean valve being 0.53±0.14oe. It has been confirmed that the direct comparison of the magnitude of natural remanent magnetization with that of total thermoremanent magnetization produced in laboratory could not give reliable intensity values in many cases, because most samples show some changes in magnetic properties during the heating process. According to the results obtained from Rio Grande lavas which cover about one million years in the late Pliocene, the intensity fluctuations of the geomagnetic field seem to have a much shorter period than the duration time of a geomagnetic polarity epoch.

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The phenomenon of excess point discharge which reports anomalous values of point-discharge for the after-discharge potentials during rapid field-changes, is explained by the development of a transient local potential around the point during such changes. Magnitude of this local potential has been calculated from the concentration of space charge in the field-region of the point. The local potential is found to be -V-V₀/4 where V is the pre-discharge potential and V₀, the critical potential to start point discharge. The theoretical and observed values of point-discharge currents at after-discharge potentials have also been compared.

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A theory of one of several possible mechanisms responsible for micropulsations is presented. It is shown that hydromagnetic waves generated by an instability of the interface between solar wind and magnetosphere are transmitted through the magnetosphere and received on the surface of the earth as micropulsations. The bandwidth of the micropulsations essentially determined by the source mechanism is found to be a few tenths of a second to hundreds of seconds. The important role of the path in the magnetosphere, including that in the outer exosphere in determining the transmission characteristics of micropulsations is analyzed. The crucial role of the slightest variation of the path length in the outer magnetosphere (due to variations in the solar wind) in masking out the resonances of lower exosphere and upper ionosphere is discussed. The resonances in transmission due to the path in outer magnetosphere are seen to be more likely than those of the lower exosphere and upper ionosphere.

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The amplitude spectrum of micropulsation signal at the surface of the earth is essentially determined by the resonances of the transmission path. On the other hand the power spectral density depends both on the squared amplitude of transmission and the occurrence or persistence probability. This latter probability is a function of the sensitivity of the overall transmission on the variation of the path length in the outer magnetosphere. A crude analysis based on this sensitivity yields spectral peaks at time periods of approximately 2.5, 6, 11 and 20 seconds with a slope of 6 db/octave at long time periods only.

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The Pc 1 events with amplitudes over -1/2γ recorded at College, Alaska, over a 6 1/2 year interval, were studied. Their general characteristics are described. Sonagram displays and polarizations are similar to those for smaller events, but there is typically more ionospheric cosmic noise absorption accompanying the large events, and the large events are usually observed at only one station. It is proposed that large amplitudes observed on the ground are at least partially due the presence of unusually welldefined wave guides of enhanced ionization along magnetospheric field lines.

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Solar cosmic-ray flares are always followed by intense sudden ionospheric disturbances (SID). By examining the developing process of SID's, some problems such as the characteristics of cosmic-ray flares and associated X-ray emissions and the generation of high-energy particles are investigated.
The nature of cosmic-ray flares is closely related to some observed characteristics of solar cosmic-rays and the developing process of SID's.
The emission process of solar flare X-rays and its relation to the acceleration of energetic particles are considered.

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