1. With the aid of parallel and divergent beams of Mo Kα rays, the effects of the surface treatment such as grinding on the mode of reflexion were examined for various crystals such as calcite, quartz, topaz, sodium chlorate, sulphur, iron pyrite and zinc blende. 2. It was found that the exarnined crystals, from their respective behaviour against the treatment, can be classified into at least three classes, namely, the calcite class, the quartz class including quartz, topaz and sodium chlorate, and the sulphur class including sulphur, iron pyrite and zinc blende. 3. Four groups of the state of crystallization, named (aα), (aβ), (bα) and (bβ), are conceived from the standpoint of Bragg and Darwin's theory of mosaic crystals, assuming that the primary and secondary extinctions operate almost independently. In (aα) both extinctions are operative, in (aβ) mainly the primary and in (bα) mainly the secondary. In (bβ) the effects of both extinctions are very small. 4. Comparing this theoretical classiffication with the experimental one, there seems to be a general agreement., if not perfect, between the two, such that the calcite class may belong to (bα), the quartz class to (aβ) and the sulphur class to (bβ). It is probable that the group (aα) includes such a perfect crystal as diamond, for which we have as yet no chance of investigation. In conclusion, the author wishes to express his best thanks to Professor S. Nishikawa for his encouragements and Valuable advices throughout the work

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1) The reflecting spectra of high voltage eathode-rays were obtained by means of a bent miea spectrograph and they showed that simple Bragg's law does not hold. 2) The deviations from the law was attributed to the consequence of refraction of the catlunlc rays in mica, and the refractive indices ware determined for the rays of different wave-lengths ranging from λ0=0.0474 to 0.1027 A. 3) Using a relation between the inner potential of a crystal and its refractive index, with the relativity correction, the inner potential of mica was calculated, and it way found to be nearly constant independent of wave-lengths, its mean value being 10.6 volts. In conelusion the writer expresses his sincere thanks to Professor S. Nishikawa for hi kind guidance throughout this work

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