Synchronous converters may be started up from the direct current side, being then synchronized in on the alternating current side, or they may be started up by auxiliary motors, and then synchronized in on the alternating current side, but these are not usual practice. They my be started from the alternating current side as induction motors, starting torque being provided by current, generaced by induction, in the damping bars. This method of starting is usual standard practice. Alihough this avoids the process of synchronizing, it has the disadvantage that the synchronism is ofen rea hod with wrong polarty.
In this paper, the writer discusses the various methods of correcting polarity, and the ins ant of polarity reversals. He also explains the switching in phenoment of converters after synchronism. This may be experienced by practical engineers that at the time of switch in on the high tension side of transformer taps after synchronism, the synchronism can be attained again very smoothly when the field is over excited, and the current at alternating current side will iucrease abruptly when the field is weak.
He concludes with the best condition of switching in on the high tension side taps of the transformer, and makes remarks on the polarity reversal, and the operation of automatic synchronizing by polarized relay.

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In general, a system which converts electric power into acoustic power is considered to be consisted of three transformers, that is to say, electrolectrical, electro-mechanical and acoustic. When both the terminal impedances, electric impedance of electric source and acoustic impedance of acoustic radiator, are given, the condition which makes the acoustic power maximum, can be derived, and the maximum acoustic power be comes larger the higher the electro-mechanical efficiency. When a moving coil type telephone receiver is used as the electro-mechanical transformer, the electro-mechanical efficiency reaches to its maximum at certain condition, and this maximum efficiency is limited by the degree of uniformity of acoustic power in the range of frequency required for faithful reproduction of speech.
A design procedure of electro-acoustic taansformer taking into account the efficiency and frequency distortion for reproduction of speech is proposed.

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In the present paper the theory of the characteristic of a triode valve for alternating current is based on the assumption that the alternating current of the grid and the plate can be expressed as complex linear functions of the alternating potential of these terminals. A general theory to determine the four valve constants is given. In a particular case the valve constant is reduced to three, i.e., input impedance, plate resistance and amplification constant. By measuring the amplification ratio by alternating current potentiometer, these three valve constants is determined. Direct potentiometrie method to determine the amplification constant is also given. The method is checked by experimental results.

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In double delta connection by three single phase transformers with two secondary windings, as shown in Fig. 1, we can derive simultaneous; loads from the full-voltage and half-voltage taps. The relaticn and limit of these loads for the safe operation of transformers are calculated and shown in curves of Fig. 5. And the equivalent network for this connection is given for the purpose of grasping the idea of voltage and current-distribution.

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The voltage amplification ratio of various types of audio frequency amplifiers is measured by an alternating current potentiometer. The result gives the amplification ratio in its magnitude as well as its phase angle for 1 to 3 stage amplifiers of resistance, reactance, and transformer coupling. The r frequency characteristic curves (the amplification ratio versus the frequency) and amplitude characteristic curves (the amplification ratio versus the amplitude of the input voltage) are given.
With resis ance and reactance am lifiers no distortion occurs due to the non-linear character in their frequency and amplitude characteristics.
With transformer amplifiers, these characteristics are far from ideal unless special atten tions be paid to the design of the transformers. A certain amount of the negative bias must be given to the grid of the triode is order to obtain the high amplification ratio. Withont the grid bias, the input impedance of the grid-filament decreases to a large amount to the detriment of the amplifying action of the set.
This deerease in the input impedance when the input voltage is too high is a'so the cause of the amplitude distortion. Various methods to prevent this distortion are suggested in the paper. The increase of the negative value of the grld bias is one of them. This me hod intoduces however another cause of distortion, as the working range of the triode is removed to the lower part of its characteristic. In such a case the "push-pull" arrangement may be employed with advantage.

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The impedance of audio-frequency amplifier transformers is measured by bridge method, and its polar diagram is given. The magntude of this impedance will be changed by the effect of the d.c. magnetiation of distributed capaeities at various parts and by the current flowing in the secondary of the transformer. The effect of the secondary current is the very important one, since in actual conditions the transformer is employed with its secondary conn cted to the grid circuit of a triode amplifier. The change in the impcdance due to this cause may be presented when the secondary grid circuit has a grid bias or a condenser shunted with high resistance.

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It is shown that the poynting vector
P=c/4π G-G0, H-H0
may be considered to represent the rate of flow of energy through unit area even when there is the phenomena of electric and magnetic hysteresis. The poynting vector is then decomposed into
Q=c/4π curl{V_??_Ω-VHi+ΩGψ}
and
R=Vi+Ωψ+c/4ψ[GψHi]
of which the latter may take the place of poynting vector to represent the surface denoity of the rate of flow of electromagnetic energy. The difference in conception of the actual state of flow of energy when we use either the Poynting vectors or the R vector is compared in the following three cases.
(a) superposed electrostatic and magnetostatie field.
(b) transmission line ecmposed of two parallel wires.
(c) eleetromagr etic wave field.
It is concluded that it is perhaps more proper to adapt R Vector instead of poynting vector to repre ent the surface density of the rate of flow of en rgy, at least in practical cases, and it is further explai edethat this conception will not be against the idea of continuity of lhenomena which is the basis of the Maxwell's theory. (May. 1925)

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[in Japanese]

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