Two types of photoelectric polarimeter, one of which is a direct reading polarimeter and the other an automatic polarimeter, have been developed to meet the requirement for rapid and continuous measurement of the optical rotation of optically active solution.
In the direct reading polarimeter, each of two plane-polarized beams passes through either a standard liquid container or a sample container and a rotary analyzer, and finally impinges on a photomultiplier. Each of the two photomultipliers receives a flash of light modulated sinusoidally and generates a.c. signals, which are amplified and fed to the phasemeter. The output of the phasemeter indicates the optical rotational angle of the sample.
The automatic polarimeter has two fixed analyzers and CdS cells. Each output of the cells is connected differentially and fed to a balancing motor which is connected mechanically to the polarizers. At first, the outputs of the two cells are balanced. When the samples are inserted into two optical paths, the motor rotates the polarizers until balance is restored. Each of the rotational angles of the polarizers indicates the optical rotational angle of the sample.
The direct reading polarimeter and automatic polarimeter have an over-all accuracy within about±1% and are handy so that they are suitable for the use in the factory.

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The alternating generator used for testing watt-hour meters is wanted to stabilize its terminal voltage within 0.1% for any load change. For this purpose, the automatic voltage regulators employing vacuum tubes have been used. In DC generators, the terminal voltage is kept exactly constant by this method, while in AC generators, automatic regulating operation is abnormal for some kinds of load change. Such phenomena are due to waveforms of the generators. Therefore, when high constancy of voltage is wanted, the circuits free from the influence of waveforms are needed.
Described in this paper are two kinds of automatic voltage regulator for AC generators without influence of waveforms:
(1) Heater of vacuum tube is used as detector of regulator according to effective value of AC voltage and compensating circuits are added for its time lag.
(2) The regulation is also obtained by employing the smoothing circuits-for converting AC vol tage (output voltage) into DC voltage of detector-the elements of which are chosen not to be influ enced by waveforms. Therefore, the relations are sought between the circuits and higher harmonics.
As far as the loads do not generate much distortion in ordinary alternating generators, bothmethods are useful, but the latter is simpler and more practical.

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The differential transformer has various advantages as the mechano-electric transducer of displa-cement, but there is an obstacle in its use especially for the measurement of small displacement. It is the residual voltage at the balance point. The linearity of transduction and the phase characteristics are impaired by it.
In Chapter 1 of this paper, the reason of its occurrence is revealed. The mutual inductances between L₁ to L₂ and L₁ to L_2' (Fig. 1) can not be equal, for the errors are not null in the course of making the bobbin and winding the coils. The difference of the two mutual inductances is denoted as ΔM. On the other hand, the internal loss in the core material causes the phase lag of the magnetic flux to the input current. This lag angle is denoted as δ. ΔM and δ make up the rdsidual voltage. By the superposition of the two voltages differing in phase, the output characteristics is formulated. This formula was experimentally verified by using the fine drive mechanism and calibrating the displacement of the core by the interference comparator, the accuracy of which is better than 0.1μ (Fig. 3). There are ways to decrease the residual voltage using some means, which are developed in Chapter 2. One is to insert a resistor between the neutral points in the external compensating circuit so as to decrease the output current (Fig. 10). Another is to cancel the residual voltage by the induced voltage in the ternary winding. In both cases, good results are obtained adjusting the resistance or the induced voltage (Fig. 14). These methods are more effective than the conventional ones as seen in Figs. 13 and 14.The differential transformer has various advantages as the mechano-electric transducer of displa-cement, but there is an obstacle in its use especially for the measurement of small displacement. It is the residual voltage at the balance point. The linearity of transduction and the phase characteristics are impaired by it. In Chapter 1 of this paper, the reason of its occurrence is revealed. The mutual inductances between L1 to L2 and L1 to L2' (Fig. 1) can not be equal, for the errors are not null in the course of making the bobbin and winding the coils. The difference of the two mutual inductances is denoted as ΔM. On the other hand, the internal loss in the core material causes the phase lag of the magnetic flux to the input current. This lag angle is denoted as δ. ΔM and δ make up the rdsidual voltage. By the superposition of the two voltages differing in phase, the output characteristics is formulated. This formula was experimentally verified by using the fine drive mechanism and calibrating the displacement of the core by the interference comparator, the accuracy of which is better than 0.1μ (Fig. 3). There are ways to decrease the residual voltage using some means, which are developed in Chapter 2. One is to insert a resistor between the neutral points in the external compensating circuit so as to decrease the output current (Fig. 10). Another is to cancel the residual voltage by the induced voltage in the ternary winding. In both cases, good results are obtained adjusting the resistance or the induced voltage (Fig. 14). These methods are more effective than the conventional ones as seen in Figs. 13 and 14.

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