Measuring of the top edge radius of blade has hitherto been made by several workers. The method devised by Schmerwitz is most reliable although it is of ruinous nature and gives only the maximum top edge radius. The writer's method, which is optical and not ruinous, gives the mean top edge radius. The experiment shows that, with a few exception, the smaller the top edge radius, the smaller the string cutting value.
The top edge radius of safety razor blades obtainable on the market is found to be about 1μ.
The method is simple yet very effective; it can be used for measuring the radius of curvature at any point on the blade edge surface.

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Of late, very short pulse signal technique has been well developed and has opened up a wide field in the study of experimental physics. For measuring the electron mobility in alkalihalide single crystals, a set of distributed amplifiers with the total gain of 10⁵ and the band width of 100 MC is devised for the purpose of amplifying short signals of 0.5 mV in amplitude and 10 mps in rise time. The set consists of four groups: pre-amplifier, main amplifier, impedance converter and output amplifier. The total number of tubes used is about 60. Two types of output amplifier are made: one is of conventional push-pull using 16 6CB6 tubes and the other of dynode push-pull using 6 EFP60 tubes. These types of amplifier suffer from thermal noise due to input impedance and shot noise in the first tube limiting the threshold value of the input signal for amplification. The writers' system has a noise input voltage of the order of 50 μV which is considered tolerable for their purpose. Use of these amplifiers enabled the analysis of induced current patterns in specimens bombarded by high energy electrons. The electron mobility in NaCI single crystal was estimated to be about 100 cm²/sec. V at -179◊C.

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In order to ascertain the dynamic viscoelastic behavior of baked coating films during deformation process at a room temperature, the frequency dependence of rigidity modulus G and viscosity η of the films are measured by using a torsional pendulum of improved design consisting of a horizontal steel rod with two equal load disks fixed symmetrically with respect to the rod center at which the lower end of a sample film strip is attached. As the samples, phenol-cresol formaldehyde resin films of thermo-setting type unplasticized and plasticitized with P. V. B. or Epon _??_1009 and Fuji film of thermo-plastic type for the sake of contrast are used. The period of the pendulum is varied within the range of 1.5-17 sec. by shifting the load disks. The frequency dependence of G and η at 20_??_21°C is found as follows:
(1) With all the film examined, G values remain nearly constant but η values change considerably.
(2) η-period relation of Fuji film is of an approximate straight line passing through the origin whereas that of all the other films are of curves of third degree intercepting 7) axis.
(3) η-period relation for all the films is explained satisfactorily by the model of Voigt 4 elements.
(4) The relaxation time τ2=η2/G2 of films plasticized with P. V. B. or Epon _??_1009 is longer than that of unplasticized although η2 and η3 values of the former are smaller than those of the latter.

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Reverse characteristics of Ge p-n junctions are studied in detail, and useful and predictable relations obtained. These relations are applicable to actual diodes, alloyed on thin Gewafers.
The two most important findings are:
(1) the design center of the base width should be about 0.55mm for junction diodes alloyed on base materials of _??_sec., _??_, and S_??_200 cm/sec. in the case of P+-N-R structure, and
(2) In the case of n-type Ge wafers of nearly 20Ωcm and 0.5mm thick, it is possible to maintain V_B above 500 volts by keeping _??_ sec., and S>500 cm/sec.
The behavior, _??_., is observed for junction diodes made from a small lifetime starting materials of _??_>300μ sec. and nearly 20Ω cm resistivity.

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A new method of measuring photoconductive time constant is described. The basic principle of this method is to match the output waveform of a photoconductive cell with that of a vacuum phototube provided with time constant elements which are adjusted. Detailed explanation is given of the experimental apparatus that has been built to measure the time constant of a Sb₂S₃ photo-conductive cell used as a target of vidicon. The time constant thus measured is a combination of photoconductive time constant and circuit time constant; the paper deals with how to discriminate the photoconductive time constant and determine it.

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Assuming that Bartlett's and Walsh's theorems are applicable to a hollow cylindrical black body with perfect diffusive internal surface kept at a uniform temperature, the effective emittance of the cylinder bottom can be calculated approximately by Rossmann's principle.
1. The case of free opening
The effective emittance of the bottom is given by ε_α+ε_α' where ε_α is the original emissivity of the bottom and ε_α' the increment in emissivity resulting from multiple reflections between the bottom and the walls. If the free end is imagined to be closed by a lid of the emissivity 1, and if ε₁" be the increment in emissivity of the bottom by direct radiation from this imaginary lid and ε₁''' that by indirect radiation reflected by the walls, then it would be _??_ The problem is then reduced to the calculation of ε₁" and ε₁'''.
If l is the length of the cylinder measured by its radius as the unit, ε₁" is given as
_??_
where _??_
In evaluating ε₁''', if only the primary reflection on the walls is considered, we have
_??_
where _??_
2. The case of the opening being closed by a lid with a circular hole in its center
The effect of the lid is to increase the effective emittance of the bottom given in the case 1 by the amount ε_α"+ε_α''' where ε_α" is the increment due to mutual radiations emitted and reflected directly between the lid and the bottom, and ε_α''' to those indirectly through reflections on the walls.
If p is the length of the radius of the hole in the lid measured by the cylinder radius as the unit, and k=1-p², ε_α" and ε_α''' are given as
_??_
_??_
where _??_
For l=1, 2, 3, ••••10, and k=0, 0.75, the calculated results are shown in tables and figures with some other data as reference.
The author's plots are closely in agreement with Nakaji's who used a digital computor for numerical solution of Buckley's equations.

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In brazed boundary, the movement of atoms of metal are studied by using isotopes as tracer. The behaviour of the isotope used in a filler metal at the boundary is observed by autoradiographic method. As the first step, solid solutions, eutectics and peritectics, which are supposed to be formed when the metals are brazed, are studied. Zn 65 was sandwiched between two crystals of a brass of 30% and 15% in content. The diffusion was faster in the former than in the latter. This phenomenon is explainable by the theory of Johnson and Wagner. When copper is brazed with Ag 110, it is found that the atoms of the filler metal move more readily along a special direction in a crystallographic plane of foreign metal. For example, it is always faster in [110] direction than in any of other directions.
Behaviours of Zn 65 in silver and tin are observed by “specific contact autoradiography” with a considerable resolving power. The results by autoradiography are in fair agreement with microphotographic structures.

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Residual strain in injection molded specimens of linear polymer (polystyrene) is photoelastically analyzed.
In the samples, isochromatic patterns of high orders are observed. The retardation observed seems to be based upon two types of residual strains: (1) frozen molecular orientation caused by the flow of molten linear polymer in molding process, and (2) that by thermal stress as the result of quenching in dies. This is ascertained by the fact that isochromatic patterns are scarecely changed when sliced at an ordinary temperature, and that a remarkable decreasing of isochromatic fringe order occurs accompanying shrinkage and deformation of the samples when annealed at temperatures higher than the secondary transition point.
Principal stress trajectories derived from isoclinic patterns seem to coincide with thedirection of flow in molten linear polymer. Therefore, photoelastic analysis may also be applied to study the state of flow of molten polymer in molding process.
A few results on the relations between the maximum isochromatic fringe orders in molded specimens and molding conditions were obtained.

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Using the apparatus and methods previously reported by the author^{1), 2)}, reflection characteristics of several kinds of ground glass, prepared by rubbing with alundum of 100 to 300 mesh, are measured. The results obtained are as follows:
1. The distribution of the relative area of mirror facets having various inclination to the mean surface resembles normal distribution, but the kurtosis index is somewhat larger.
2. When the incidence or reflecting angle is larger than 50°, the maskings of mirror facets occur and the coarser the roughness of the surface, the larger the magnitude of the maskings.
3. If the distribution of mirror facets is represented by the normal distribution function having the standard deviation of about 18° and the masking of them by the exponential function, the reflection characteristics of ground glass can be approximately explained by the combination of these two functions.

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The authors presented previously a graph showing the mutual relation between aberrations and central obstruction of reflecting microscope objectives.
Results of further scrutiny of this graph are described. Best solutions for aspherical objectives lie on a straight line. These solutions have a small central obstruction (0.3>R>0.2) and no comatic aberration but a large negative spherical aberration. Plane parallel glass plates have a large positive spherical aberration and cancel this negative aberration. The residual aberrations are eliminated by aspherising a concave mirror. As a practical example, an objective of NA=0.65, R=0.26 for visible light is illustrated.

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