Recent development of Schwalzschild type reflecting microscopes are reviewed. Especially Grey's, Norris' and the auther's own designes are compared. Third order aberrations and central obstructions are analysed. In addition a short note on the application of reflecting microscopes is given.

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The narrow pass band interference filters are divided into two typeson principle, the summation type and the product type of the series of trigonometric functions. The principal analogy of these two types are discussed. The principle and the several devices for improving of the polarization interference filter are also reviewed. Furthermore, the possibilities of the tunable filter or high-resolving polarizing interferometer filter are described.

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As the result of an colorimetrical analysis of the phenomena called sensitive color, it was made clear that tbe sensitive color occurs when the two primaries have nearly equal intensity and increase in inverse direction each other. By usingtwo fight sources whose distance on the chromaticity diagram is the possible largest value, we were able to produce very high sensitivity.
An outline of this analysis and the application of this high sensitivity to the phasemicroscope-sensitive color microscope is described.

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The two layer reflection reducing coating for glass whose Ist and 2nd layer are respectively and approximately λ/4 and λ/2 thick optically (λ being the appropriate wave-length), when satisfying some conditions, is knownto have relatively good spectral reflection characteristics.
Theauthor determined the refractive indices of two layers of this type of reflection reducing coating in order that the reflection may be zero at the given opticalthicknesses, made it experi-mentarilly through the use of centrifugal and evaporation processes, and got expected results.

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An equation for ultimate pressure of oil diffusion pump is derived from Gaede's principle which is modified in physical meaning.
This equation is sufficient to explain qualitatively the relation between the ultimate pressureand the operating temperature. In lower temperature range, the ultimate pressuredecreases with. increase of operating temperature which increases the sealing effect of jet. In moderate temperature range, it remains constant and is in equilibrium with the vapour pressure of the oil film near the gauge. In higher temperature range, it increases with decrease of the intrinsic speed of the pump which is exhausting the gases caused by desorption from the wall and decompostion of oil vapour at the ionization gauge. The third mechanism becomes more complicated when the decomposition of oil is occured in the boiler.
These mechanism and the relation between the minimum ultimate pressure and oil impurities are discussed on experiments made with a onestage glass pump, in terms of fore pressure, lagging effect on the condensing wall, cold trap effect and thermal decompositionof oils.

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The quantitative electron density at the focusing surface on the anode of an X-ray tube (10 kW, line focus type) is measured using an ordinary X-ray pinhole-camera with the aid of the relation between X-ray intensity and the blackness of X-ray image on film.
It is found that the electron density J(mA/mm₂) can be calculated by J=X/DI, where D stands for total. X-ray intensity due to total focused surface, X for X-ray intensity due to an arbitrary point on the same surface and I for current of X-ray tube.
An X-ray film was divided into several parts, and one part is used for obtaining the blackness vs. X-ray intensity relation, and the other parts are used for taking pinhole-photographs under various focusing conditions. All photographs were developed simultaneously so as to exclude error. Microphotometer is used to obtain point to point X-ray intensity on the focusing surface with the aid of the blackness vs. X-ray intensity relation.
From these measurements a conclusion is arrived at that the input wattage at any point on the focusing surface on anode is, within the normal range, namely the saturated range expressed by the multiplication of tube voltage and tube current at that point, because the trajectory of elelectrons emitted from cathode of the X-ray tube is unrelated to the variation in the tube current and tube voltage.

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MgO-smoke particle has a cubic crystal habit and its crystallites always rest ona substrate with their [001]-axes normal to the surface. Thé smoke particle deposited on a perfectly flat surface such as a cleavage face, therefore, gives a spot pattern when examined by electron diffraction. The smoke particles on an uneven surface, however, will give an arc pattern and the length of thearc will depend on the degree of unevenness of the surface.
We have examinedvarious finished surfaces by this method and have studied the intensity distribution along (004)-arc of MgO diffraction pattern. By the analysis of the data thus obtained, more or less quantitative results on the unevenness of surface were obtained.
Since the size of the MgO-smoke crystallites is 1000 Å or so, the new method gives an ultramicroscopic topography of a surface.

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