The atmospheric potential gradient was observed on the summit of Mt. Fuji (3778m), at 5.5 go (2800m) and Gotemba (460m), each during two or three days in August, 1947, and January, 1948. For this purpose, a polonium-collector was attached to one side of Shimizu's unifilar electrometer opposite to the side the microscope is fixed. This instrument was made by the Institute of Physical and Chemical Research of Japan, and it was so designed that it can be mounted on a tripod. The visual observation was made hourly or half-hourly to investigate the diurnal variation of the atmospheric potential gradient. According to the observational results, the ordinary semi-diurnal variation (i. e. two maxima and two minima) prevails at Gotemba but at Tarobo the diurnal variation is not so conspicuous, whereas at 5.5 go and at the summit the potential is greater in the daytime and smaller during the night. Thus it was made clear that the large semidiurnal variation of the atmospheric potential gradient shows a change in character also in the vertical direction besides the local influences due to surrounding conditions.
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