In previous reports, the author performed the observations of tidal strain of the earth's surface in some or several directions by means of the extensometers at Osakayama observatory, Kishu mine and Matsushiro observatory, and obtained the tide-constituent (M₂, O₁ etc.) of the observed strains.
According to the results, the phase lags of M_2- constituent are nearly zero, and the upper and lower limit of them are 43° and 29° respectively. That is the coefficients of cos 2t-term are the positive values in all the azimuths, and the coefficients of sin 2t-term are far smaller than the ones of cos 2t-term, where t is an hourly angle of the hypothetical heavenly body at the observatories. And so, it is most probable that the secondary effect (due to the oceanic tide) is far smaller than the primary effect (due to the astronomical tide), and also the Love's number h is more than about five times of Shida's number l.
Now, the precise observations of the tidal strains in the prime vertical and in the meridional directions have been performed once more with heighly sensitive extensometers of which sensitivities are 0.37×10^-8/mm and 0.57×10^-8/mm respectively at Osakayama.
From the present observations, the value of h-3l, relating to areal strain is obtained as follow
h-3l= 0.448 ± 0.003
And the amplitude ratio of O₁-costituent vs. M₂-constituent are obtained as follows
(O₁/M₂)_φφ=0.85 in the prime vertical direction,
and (O₁/M₂)_θθ = 0.48 in the meridional direction.
If the secondary effect is as large as the primary effect, the ratio of amplitude, (O₁/M₂)_φφ and (O₁/M₂)_θθ should be almost equal to each other. But, on the contrary, both ratios are widely different each other. Hence we may neglect the secondary effect against the primary effect in the following process to calculate the tidal constants. The propriety of the result is shown by the comparison of the strains due to the Chile tsunami at Kishu and Osakayama. And the amplitude of M_2-costituent of the eθθcomponent vs. one of the eφφ-component is obtained as follow
(eθθ/eφφ)_M2 =1.69,
where eθθ and eφφ are the strain components in meridional and in the prime vertical directions respectively. From these results, the ratios of h and l are calculated as follows h =11.1l from (O₁/M₂)_φφand h =10.6l from (eθθ/eφφ)_M2
And from the value of h-3l and the ratio (O₁/M₂)_φφ the value of constant h and l are, calculated at 0.618 and 0.056 respectively.

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The bifilar surface ship gravity pendulum No. 2 was newly built. Though the new apparatus is quite similar to No. 1 as a whole many improvements have been introduced. First, the gimbal suspension was improved in order to keep an accurate horizon against horizontal accelerations of 50100 gals. Two horizontal accelerometers were placed on the gimbal in longitudinal and transverse directions of the ship and large rotatory inertia masses were attached to the gimbal. These rotors are driven by torque motors, and the angular ccelerations of the rotors are adjusted to be proportional to corresponding horizontal accelerations. The gimbal keeps its horizon even under large horizontal accele rations, because the gimbal recieves rotational reactions from the rotors, and the torque produced is equal in magnitude and opposite in sign to the torque due the horizontal acce lerations acting at the center of gravity of the gimbal. With the aid of electronic devices, the whole gimbal system is adjusted in such a way that the gimbal behaves like a long period pendulum against horizontal acceleration of 5.20 sec. period and behaves like a short period pendulum against horizontal acceleration of period of 20 sec. or more. The second improvement is in electronic equipments. Almost all the electronic part of the instument was wholly been transistorized. The test by this instrument was carried out on board "Takuyo" (700 tons), the Maritime Safety Agency, at Sagaminada on January 1960. The vertical acceleration of the boat always exceeded 100 gals and the results obtained in the test were not good. This is be lieved to be due to the fact that the damper which has been desighned for 10 gal vertical accelerations did not work satisfactorily. The damper was replaced by a large one and the measurements across the Pacific Ocean was carried out on board a cago boat "M/S MEIRINSANMARU" (7700 tons), MITSUISENPAKU Co. Ltd.. The boat sailed along the 38 N latitude with an average speed of 14 nautical miles. The vertical acceleration was almost always more than 50 gal ran ging between 200 gals at maximum and 20 gals at minimum. The accuracy of measure ments was about 10-4 under favorable conditions, except in San Francisco Bay where much better results were obtained.

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Many papers have been published which discuss Bouguer anomalies, from the viewpoint that they give equivalent anomalies "ΔgD" at a certain depth and that they therefo e give important informations about the underground construction of the earth. In these discussions, almost always Bouguer anomaly itself was used. The spectrum of Bouguer anomalies which has the same information, may more conveniently be used, and by doing so, the spectrum of equivalent underground "ΔgD" can be obtained more easily and will gives us the same information about the underground equivalent " ΔgD". If we take suchstand point of view, the first problem will be to see, whether the spectrum of underground equivalent "ΔgD" does converge or not. If we are to obtain equivalent "ΔgD" at a certain assumed depth, it is necessary that the spectrum of "Δg" at that depth is convergent. The spectrum must become gradually small according as the degree of the spectrum increases. In this paper, the spectrum of surface "Δg" was deduced for central and southern part of Japan. The spectrum intensity corresponding to these areas are approximately represented by e^-ωD. This means that the spectrum of "ΔgD" becomes approxi mately white at a depth D. Thus we can concider D as the limit of the depth where the equivalent "ΔgD" is reasonably accepted. This limit of depth has been obtained for many section in that area, and is shown in the Fig. 7. In the case of section No. 0, from the results of the explosion studies, we know the depth of the Mohorovicic layer. The limit of the depth as determined by the above method coincides well with the result of the explosion studies. This means that at this depth the spectrum of the equivalent "dg" is white. That is, the undulation of the interface of the Mohorovicic layer has a white spe ctrum.

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All the geodetic triangulations and the base line measurements have been executed by the Geographical Survey Institute (G.S.I.). The first order triangulation has been carried out on the basis of the revision survey program of the Japanese first order triangulation. The revisio surveys of the second and the third order triangulations have been carried out in the areas where the earth's surface has been deformed as a result of earthquakes and mining.

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Almost all of the levelling has been carried out by the Geographical Survey Institute. The Earthquake Research Institute of Tokyo University and the Disaster Prevention Research Institute of Kyoto University have also executed the survey on local lines.

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As a continuation of the astronomical survey in the whole land of Japan, the field work was carried out mainly by the Geographical Survey Institute (G.S.I.), and the latitude observations have been continuously carried out at the International Latitude Observatory of Mizusawa.

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While theoretical and observational studies on earth tides have been continued for many years in Japan, much progress in these branches was attained in the course of I.G.Y., 1957-58.

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