The rotation of the earth causes the seaward movement of less dense river water upon leaving the Mouth of river to deflect to the right side of its initial direction in the northern hemisphere and to the left side in the southern hemisphere.

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From the recent several tsunamis in the Pacific Ocean, we can derive the remarkable directivity. Consideration about this character of the tsunami is necessary when one may make the warning. Of course, the data are too scarce, but we can attribute this character to that of the origins themselves. Only the energy of the tsunami of November 4, 1952 seems to have been radiated almost symmetrically. The Hawaiian Islands and the shallows around them seem to have had the convex-lens effect on the orthogonals of the tsunami wave, and the origin of this tsunami and Talcahuano (Chile) were perhaps the conjugate foci concerning this lens.

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The gas pressure of Myojin Reef is estimated at 100-200 atm. at the most. At this pressure or so, shock waves may exist in the atmosphere and may not exist in sea water. And the transformation of the energy of ordinary explosion wave into heat energy is negligible in water. So we will once attribute theformation of the water dome to underwater explosion wave. Finally, entrance of explosion wave energy into the sound channel can be explained either by the diffraction or by the reflection of waves. The latter explana-tion seems to be more hopeful.

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The tide-gauge records obtained at several tidal stations in Japan (Hanasaki, Kushiro, Miyako, Tomisaki, Urakami, Kushimoto and Oshima) situated on the Pacific coast were investigated by the present author for the days of 1st and 27th of March, 26th of April and 5th of May, 1954, on which the “H-bomb” tests would have been carried out at Bikini Atoll, and for the days before and after the days of assumed explosion, and the following facts were found.
(1) At Hanasaki (Hokkaido Island), somewhat' anomalous fluctuations in the height of sea level with periods of about 7 minutes and with a maximum range of about 25 cm were recorded for several hours from about 9h 20m a. m. (135°E Standard Time) of May 5.
(2) At Kushimoto (Wakayama Prefecture), on March 27, April 26 and May 5, remark-able rises and falls of sea level with a period of about 12 minutes were recorded for about two and a half hours from about 8h 40m on each of these days. The maximum ranges of oscillations were about 30 cm, 20 cm and 35 cm which occurred at 10h 15m a. m. on March 27, 10h 20m a. m. on April 26 and 10h Om a. m. on May 5, respectively.
(3) At the stations other than the two above-mentioned tidal stations, nothing unusual especially was found in the tide-gauge records.
Moreover, occurrence of a weak tsunami at Cape Erimo on the south coast of Hokkaido Island on the morning of May 5 was observed by fishermen in the vicinity of the cape.
Although it is not quite certain at present whether or not these anomalous oscillations were really caused by the effect of “hydrogen bomb” tests at Bikini Atoll, it may be probable, because the date and the time of explosion estimated from the atmospheric oscillations observed at many places in Japan coincided fairly well with that inferred from the unusual oscillations of sea level so far as they were observed.

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On July 28th 1955, while 200 schoolboys and 188 schoolgirls were training in swimming at Nakagawara beach, Tu city, about 76 girls were drowned, and 36 girls of them died.
At that place, it is expected that if the seaconditions were normal, the speed of the tidal current would be only 5.0cm/sec or less. On the other hand, the speed of the current which caused the tragic case was estimated at about 15-30cm/sec or more.
This abnormal current can be explained as the longshore current, having the speed of 23-32 cm/sec, produced by the swell coming from the Typhoon No. 13.

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A new method has been described for the analysis of transient phenomena of a hydrodynamic system having a free surface, taking the case of the Bay of Nagasaki as an example. The main operation of the analysis was carried out by an electric network being analogous to the hydrodynamic system and by an electric analogue computer designed for this purpose. In this method, some newly designed techniques for the hydraulic experi-ments have been used to determined the constants of the above network, and these techni-ques themselves may be applied independently to the general hydraulic experiments.

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It is shown by the electron microscopic method that the large forms of the suspended organic matter in the sea is formed of microplankton after its death. Examining a process of origination of the suspended matter, the author could detect that protoplasm of diatom was spread out through the areolae of the frustule of diatom, and recognize that granular structure of the suspended organic matter was made from protoplasm of plankton cell. The author assumes that such structural features as organic granules take a part of turbidity factor of sea water. It is said that one cell or a colony of microplankton is the structural unit in origination of the suspended organic matter.
The author expresses his hearty thanks to prof. S. Nomura of the Tohoku University, Sendai, for a number of valuable advice and to Messrs. M. Takahara and H. Takahara of the Zeshinkai Hospital who let me kindly use their electron microscope, for their continued hospitality of collaboration.

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