Spectral energy distributions of several radiation sources for ultraviolet region are briefly discussed. In practice, as the standard of spectral energy, the Krafft's standard lamp seems to be the most useful source at present. With the appearance of the photomultiplier as a high sensitive detector, the ribbon filament tungsten lamp would become useful source emitting continuious spectrarn in U. V. region.
As for the qualtz enveloped low pressure mercury discharge lamp, caution is necessary for its weak fluorescence in same cases. The high wattage X_e-arc lamp is the strongest source emitting continuious spectrum in U. V. region. The hot cathode hydrogen discharge lamp can be easily stabilized in its radiation intensity with application of vacuum tubes, so that it is a quite suitable source for measuring absorption transmission etc.

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In connection with servo-mechanizm, a study and discussion have been made for the purpose of filling up gas with the pressure which fluorescent lamp needs. In that case, about the control system adopting glow discharge tube, a description is given as to its trial make, working and analysis of working condition. l n the glow discharge tube, the gas pressure is for function of temperature and the tube voltage corresponds to function of pressure.
Now put together 2 discharge tubes of same structure to make electrical bridge circuit. Of the 2 tubes, one is taken as reference and the voltage variation will be picked up from the another tube. Under such voltage pressure picked up, the control of gas pressure at same temperature makes the value which being corrected necessary pressure at reference temperature.
In actual use, as to the size of discharge tube, in case electrical source and ballast resistance, etc. are fixed, it should hold a suited size.
Besides, filling pressure should be corrected against position between discharge tube and fluorescent lamp and also for difference in temperature. In doing such operation, timely variation of control voltage is automatically to be recorded so that this system has become very convenient in regulation.
At the last, this system is considered as electric equivalent circuit in order to catch theoretically the foundation as for the working and regulation.

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