In considering the vibration of diaphragms which are arranged in drum shape (as shown in Fig.1), the author replaced them by a shell in the form of a very flat oblate spheroid (as shown in Fig. 2), thus avoiding heavy calculations. The effect of surrounding water upon the vibration of this shell in form of oblate spheroid has been studied. And obtained simple formula for the value of so-called effect of virtual mass. Some considerations on relation of phase of vibration to virtual mass, etc. are also given.

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The lateral vibration of an elastic bar, supported at two arbitrary :points is analysed and calculating the natural frequency, its characteristic variation and the nature of the extreme values that appedr during the transferring of the supports are made clear. As for the extreme values there exists a general rule which holds for all kinds of supporting conditions or any distribution of the cross section and the mass of the bar. But in this paper, the meaning and reality of this general rule are shown partially by the concrete analysis of the subject, leaving the more complete description of the rule to another study.

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The author cunsidered on the influence of the frictional resistance upon the rolling of a ship when she stopped or advanced slowly. The result was obtained that 0% of the attached moment of inertia which was composed of various factors, was due to the frictional resistance.

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