New surface meter is designed with the analogous principle to measure the resolving power of lens. The images of test pattern reflected by polished surfaces diffuse according to their roughness. If the clearness of the images (the degree of diffusion of reflected light) is determined with certain measure, the surface roughness can easily be classified numerically.
Two methods are considered to realize the surface meter based on above principle. One of them is to vary the distance between the test pattern and reflecting surfaces and the other to adopt the test pattern with variable pitch of black and white stripes at a constant distance from reflecting surfaces. To simplify the mechanism of the apparatus logarithmic variable pitch is adobted to the practical purpose because it needs no moving part. As the results of experiments, electropolished surfaces, grinding or cutting ones, etc. are measurable, especially the direction of polishing is easily and clearly determined. This new surface meter is considered to be suitable for quick determination of polished surfaces, etc., in plating shops.

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A New pyrheliometer was constructed for measuring the total radiation from sun and sky falling on a horizontal plane. It consists of a special symmetrical type thermopile mounted in a case under a hemispherical glass cover. Characteristics of the pyrheliometer are as follows ; (1) the change of sensitivity according to the direction of radiation follows cosine low; (2) the drift of zero point due to selfheating is within 1% of the indication; (3) the sensitivity is 120 millivolto per watt per centimeter square. (=8.37 millivolts per gram calorie per minute per centimeter square.) As the result of calibrations of the thermopile by our large black body furnace, the sensitivity of the thermopile changed slightly according to the temperature of the black body. In order to established the standard of solor radiation, the sensitivity of thermopiles at the color temperature of the sun was determined from the extrapolation of the certificated value by the black body arid the standard pyrheliometer was calibrated in sunshine against above thermopiles.

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The optimum of indicating instruments should be distinguished from the optimum of recording instruments. General1y, "no overshooting and quickest response to the step input" will be best for the former, and "minimum wave distortion in response to the specified or random input signals" will be most adequate for the 1atter.
It will be convenient if we could evaluate the dynamic characteristics of measuring systems in frequency domain. Part III proposes a new criterion for the evaluation of indicating instruments which is represented by following equation;
whereε is the dynamic error, is squared error area weighted on duration of error, are added to give weight to the overshooting and cycling.
The author defines A_I as the Figure of Merit of the indicating instruments and in Figs. 5, 6, 9, and 10 shows the optimum adjustment of the typical systems by minimizing A_I. The evaluations of A_I are performed in frequency domain by Laplace transform.

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