Free nuclear induction technique is widely used in measuring weak magnetic field. In the socalled Packard-Varian method, it is the problem how the design of the polarizing coil relates to the S/N ratio and how the transfer of the polarizing coil from the polarizing power supply to the amplifier relates to keep the coherency of the magnetization. This is the report along this line in the experimental and theoretical aspects. The experiment has been carried out in the earth's field, but extension to the higher field may be secured by the theoretical consideration given in this paper. The various results described in the report may present the general idea to design and construct a proton magnetometer of proper performance.

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Described in this paper is the tuning fork for self-excited oscillation to be used for accelerometer calibration up to acceleration of 1500g.
This equipment is composed of a tuning fork, capacitor as mechano-electrical transducer, Inoue's circuit, amplitude limiting circuit, power amplifier and electro-magnetic vibration exciter. Each fork is equipped with an accelerometer to be calibrated and a balancing mass.
In calibration operation, first the tuning fork vibrates when it is tapped and then a capacitor picks up the electric signal having a frequency only of vibration. The electric signal is amplified up to specified value and then sent to the electro-magnetic exciter coil. As its result, the tuning fork makes a self-excited oscillation in a constant amplitude value.
This equipment is very good for use in accelerometer calibration because this tuning fork always resonates independent of the weight of accelerometer.

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This paper has heen written to deal with the fundamental theory on which a mercury filled thermometer is based. In analyzing the flat-oval type spiral tube, the writer has first introduced the Wuest's theorem. As the system is filled with uncompressible fluid, the expansion occurred at thermobulb by temperature increase has proved to be equal to the volumetric expansion of the spiral tube. Then he obtained the following equation:
Δθ=ΔV/3abr₁{1-r03/(r1+r0)(r12+r02)}
Δθ: Angular displacement of spiral tube
ΔV: Volumetric expansion of mercury
r1: Radial coordinate of fixed end of spiral tube
r0: Radial coordinate of free end of spiral tube
2a: Length of long axis of tube section
2b: Length of short axis of tube section
In addition to this, the writer has found that the equation is affected neither by Young's modulus nor by wall thickness of the tube.
Also discussed is a working principle of force-balanced temperature transmitter. Maximum tube stresses are shown first as the value equivalent to that of ordinarily filled system, secondly as the additional caused by additional tube bulging by pneumatic feed-back and lastly as the subtractive by restriction of tube tip-movement by pneumatic feed-back.

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