Some methods deriving the anomalies of geomagnetic components from observed values of the anomaly of total force are proposed by one (N.F.) of the writers [1]. Between the anomaly of total force and the geomagnetic potential at grid points in a plane the following equation holds.
2πs F₀/Z₀ ΔF(i, j)=∞Σμ=-∞∞Σν=-∞Φ(μ, ν)W(i+μ, j+ν),
where s is the spacing of grid points and Φ(μ, υ) is the weighting function given by (19). The anomalies of geomagnetic components are obtained from (7), (8) and (9). The following assumptions are involved in this method.1) W-surface considered as the group of small planes.2) W=O outside the area of grid points.3) The normal values Xo, Yo, Zo and Fo are approximately known and the approximation shown in (7) is adopted. In the actual procedure, the density of grid points is determined considering the pattern of ΔF observed. The surveying area is divided into blocks with suitable size and these blocks are overlapped to some extent. From the results (Figs 2.-4) of computation using the model combined two dipoles, it is clarified that the anomalies of geomagnetic components can be computed in almost the same accuracy of dF observed. In the southern part of Kanto district where the total force is only measured in the aeromagnetic survey (Fig. 5), the anomalies of geomagnetic components are obtained as shown in Fig. 6.

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The problem of dynamo action of tidal stream or ocean current in the earth's magnetic field has a long history of research. I investigated the effect of magnetic field induced by this action on geomagnetic observations. This problem seems very important to assure the accuracy of geomagnetic observations, because Japan islands are surrounded by sea and high speed ocean currents such as Kuroshio and Oyashio flows. The vertical component observed at Shimosato shows a remarkable seasonal variation. The relation between this phenomena and Kuroshio has been expected to be its origin. I calculated the induced magnetic field for a simple model of ocean current which flows straight with semi-elliptic cross section. This field is restricted in water and amounts to about 37 r/knot in magnitude. However, possible leakage of flux of this field which approaches near peninsura or encounters island is so small that ordinary magnetic measurement on land is not practically influenced. Seasonal variation at Shimosato can hardly be explained by this line of thought. The magnetometer in water may be disturbed by this induced field to the order of ten gammas according to circumstances. We may obtain information about the path of ocean current to a certain degree, with a suitable distribution of magnetometers in water.

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An experimental temperature observation of lower atmospheric layer was made for the purpose of improving the accuracy of electro-optical distance measurement near Mt. Kano, Boso peninsula in summer 1969. The instrument consists of a thermister sensing head suspended by a Kytoon of 15 m³ in volume, the altitude of which is 300 m in maximum and transistorized transmitter. The temperature signal from the sonde is received at the ground and recorded continuously with the accuracy of 0.2°C. The temperature difference between 200 m altitude and the ground shows clear local time dependence of which amplitude is about 3-4°C. The calculated temperature values at the middle point of the sight line by using the meteorological data at the two end stations has a discrepancy of about 2-3°C against the values obtained directly by means of Kytoon, which corresponds to the error of 2-3x 10^-6 in distance measurement. Using the observed temperature gradient, the refraction coefficient was also calculated, the value being almost same as the result obtained by Hopcke.

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In 1958, Prof. I. Tsubokawa proposed a gravity meter with three strings intersecting at right angles to one another as shown in Fig. 1. The principle of measurement is as follows [1]. Let the components of gravity along three strings be g₁, g₂ and g₃, and the frequencies of the strings 1, 2 and 3 be f₁, f₂ and f₃ respectively, then
g²=g₁²+g₂²+g₃²
g₁=a₁f₁², g₂=a₂f₂², g₃=a₃f₃²}(1)
where a₁, a₂ and a₃ are the coefficients which depend on the dimentions, linear density and elasticity of the strings and the weight. Let the respective angles between the strings be α₁₂, α₂₃ and α₃₁, where α₁₂=90°-ε₁₂, α₂₃=90°-ε₂₃ and α₃₁=90°-ε₃₁.
g=√a₁²f₁⁴+a₂²f₂⁴+a₃²f₃⁴+2a₁a₂f₁²f₂²sinε₁₂+2a₂a₃f₂²f₃²sinε₂₃+2a₃a₁f₃²f₁²sinε₃₁ (2)
We assume construction accuracies of gravity meter as follows;
1) ε₁₂, ε₂₃, ε₃₁<1×10^-3
2) a₁, a₂ and a₃ are equal in the accuracy of 1×10^-3
By integration Eq. (2) from time O to T, the value of the gravity difference between the starting and observation stations Δg can be expressed as
The suffix 0 corresponds to the starting station and s the observation station. In this equation, gh is the horizontal acceleration due to the ship's movement and the last term is the Eötvös correction, in which V is the speed of the ship in knot, ψlatitude and A the azimuth of the course. Gravity survey was carried out on the sea around Japan during the period from April to June in 1969 on the board "Hakuhop-maru" belonging to the Ocean Research Institute, the University of Tokyo. The ships' tracks are shown in Fig. 4 with profile No. of gravity anomaly. The plofiles of free air and Bouguer anomalies are shown in P. 1-17 with bottom topography.

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In this paper, the writers discussed the effects of the oceanographic conditions to the yearly mean sea level along the Pacific coast in the south-western part of Japan. As the elements of the oceanographic conditions, the mean water temperature from sea surface to 200 meters depth and the situation of the axis of Kuroshio-current were considered. In order to correct these effects to the yearly mean sea level, the relations between the sea level and these oceanographic conditions were investigated. The main conclusions resulted from above investigations are as follows. (1) The greater part of the fluctuation of sea level is due to the effect of the variation of sea water temperature. Particularly this effect is conspicuous at Aburatsubo and Mera. (2) The variation of the situation of the current-axis is also an element that fluctuates largely the sea level. The fluctuations of sea levels at Nagoya, Shimizu-minato, Aburatsubo, and Mera seem to be affected by the latitude of the most southern part of the current-axis of Kuroshio on the offing Enshu-nada. On the other hand, the fluctuations of sea level at Kushimoto and Kochi seem to relate with the longitude of the current-axis. These facts may be caused by the fluctuations of water temperature in the sea near the tidal station and of the current along the coast which are due to the variation of meandering Kuroshio-current. (3) The fluctuations of the yearly mean sea levels at the tidal stations may contain the effects of the sea water temperature and of the situation of the current-axis. At the tidal stations, Mera, Aburatsubo, Shimizu-minato, Nagoya and Kushimoto, these effects amount to about 70 percents of the fluctuations of yearly mean sea levels, and the standard deviations of the yearly mean sea levels from the linear variations are reduced about 10 millimeters.

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Since 1955, continuous geomagnetic observation has been conducted by the Geographical Survey Institute at the Kanozan Geodetic Observatory (latitude: 35°15'11"N and longitude: 139°57'32"E) in order to obtain epoch reduction data for geomagnetic surveys mainly. However, the electrification of the West-Boso line, the distance of which from the obser-vatory is only 7 km, was recently planned so that magnetic contamination of about 2-3 gammas due to the artificial disturbance became unavoidable on the geomagnetic record. Therefore, the institute constructed a new magnetic observatory named the Mizusawa Geodetic Observatory (latitude: 39°06'30"N and longitude: 141°12'26"E) on an eastern hill of Mizusawa City, Iwate Prefecture in 1968. On this occasion, magnetic instruments were improved so as to obtain digital record of the three components for saving routine duties as well as their analogue record in the new observatory. In principle, proton precessional method enables to make digital processing of not only the total force F but also any other components by using bias coils of known direction and size. At the Kanozan Observatory, for example, since 1960 analogue record of the horizontal component H has been obtained by means of the proton magnetometer combined with a set of Fanselau-Braunbek coils for eliminating the geomagnetic vertical component[1]. In the case of the declination observation, however, the proton precessional method may not be so convenient, while the ordinary suspension magnet type D-variometer is much favorable because of its simplicity in principle. Then, in the Mizusawa Observatory, digital records of the three components are composed of the improved D-valiometer with A-D converter, and proton magnetometers for F and H.

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The data for the mean sea levels at Lagos (Lisbon), Portugal, during the period from October 1908 to December 1958, were taken from Publication Scientifique, Monthly and Annual Mean Height of Sea Levels. The investigation was made with the intention of finding some evidences, if there exist abnormally large changes in the height of yearly mean sea levels preceding the occurrence of great earthquakes similarly ac :n the cases of the Kwanto Earthquake in 1923, the Nankaido Earthquake in 1946, the Niigata Earthquake in 1964 and others in Japan, concerning the problem of predicting the occurrence of great earthquakes. The analysis was made similarly as in the cases of San Fransisco[2] and Los Angeles [3] in United States of America, as there are no data for sea water density and barometric pressure in my hand.

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