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On Some Special Variations of Earth-Current Potentials observed with Two Independent Base Lines in the Same Direction, E-W
In the present paper, the writer studies the earth-potential distribution around the observatory of some special short time variations which are simultaneously recorded on the magnetograph. The method of the investigation is to study the“Difference-Curve" defined by the difference E0-1−E1-5/n, where E0-1 and E1-5 are potential differences of east-west component of base length of 0.1 K.M. and 1.5 K.M. respectively, and n is approximately equal to the ratio of two base lengths. If the current flow is uniform around the observatory, the Difference-Curve does not show any deviation from a straight line, when other factors of potentials are constant. The main results of the present investigation are following. The Difference-Curve shows usually no appreciable deviations, justifying our expectation and throwing something to the fundamental problems of earth-currents, but some abnormal exceptions are found. These abnormal variations now investigated are Bay-Type variations, Mogel-Dellinger variations and some irregular short time variations occurred during the earth-current storm. The micropulsation of rather regular period of one minute or more does not show any abnormal variation.
From these investigations, the continuous record of two potential-differences with a single instrument, say, a differential-galvanometer, is desired. The writer shortly discusses the second derivative of earth-potential and proposes some possible explanations of these characteristic variations.
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