An ultrasonic thickness gauge is constructed which can be conveniently applied to the practical measurements of the thickness of plates and tubes. The instrument which indicates the spectrum of thickness resonances on the cathode ray oscillograph is composed of variable inductance sweep oscillator and vibrator of X-cut quartz plate, and equipped with measuring device to give measures of every 0.1mm for arbitrary materials. As the results of tests performed on the plates of mild steel, aluminum, brass and glass, accuracy of less than 0.01mm can be expected for those plates of nearly 5mm thick and with fair quality.
Abrupt change of thickness at the back and geometrical irregularities such as small holes and flaws cari be detected not only as the lowering of resonance intensity but as the decisive change of resonance spectrum. In suchjrregular position, resonances due to the lateral propagation of elastic wave is responsible for the spurious resonances. In practical inspection, ultrasonic thickness gauge can take charge of the ultrasonic flaw detector, provided the resonance spectrum can be carefully investigated.

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We already investigated experimentaly the electrical Polishing rate of plate anodes and gave out the results last year. This time electrolytic polishing with respect to cylindrical, ground steel parts was tried. In this case we aimed to succeed in the precision polishing, which was expec-ted to be a practical method of polishing away the required thiCkness layer from the parts which were needed high accuracy and were in the course of mass production.
The temperatures at 5 points in the solution were measured and the mean temperature of those was calld "bath temperature" by the writers.
First 30minutes polishing was carried out with constant current that was regulated easily by the resistance.
The relation between the polished away quantities and the bath temperatures was plotted on the graph.
Secondly the parts were polished for 30minutes with the same current, and the temperature changes of the bath were measured in several cases where the starting temperature was different respectively. The relation between the bath temperature and the time was graphically plotted.
By using the upper two graphs the precision finishing that we aimed at could be done. The experimental data were shown and discussed.

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This pneumatic divice makes use of the variation in total resistance of a compressed gas leaving from two symmetrical orifices which are at an equal short distance (h) from the wall (its diameter D) of a workpiece to be measured. It is arranged so that the compressed air with constant initial pressure (P_A), passing through the fixed orifice, may part into two branches to jet out of two measuring orifices, and that the pressure of the air in the space between the fixed orifice and the branching point can be measured. The nondimensional amplification |dP_C/dD| (d_B/P_A). (d_B/d₂) and the suitable clearance (h/d_B).(d₂/d_B) are respectively represented theoretically as the functions of a characteristic parameter (dynamic similarity factor) consisting of Reynolds Number, d₂/d₁ and d_B/d₂ The results thus obtained fairly agree with those of the experiment. When two jetting clearances are not equal, errors in comparative checkingwhich are small in comparing with the symmetrically standard characteristics will appear. Such errors, however, can be eliminated only by keeping two jets with guide pieces, contacting very closely to the works, horizontal. We can plan through the rtsults obtained the checking of ID by air spindles, OD by air rings and thickness of plastics and foils by air snaps with any desirable sensitivity.

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