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Transactions of the Asiatic Society of Japan (1881)
Transactions of the Asiatic Society of Japan - 1881 Author:Asiatic Society of Japan Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: 40 NOTES ON SOME EECENT EARTHQUAKES. By J. A. Ewing, B. Sc., F. K. S. E. [Bead December 14, 1880.] The earthquakes which are the subject of the follo... more »wing notes took place during the month of November, 1880, and were of the usual slight kind familiar to residents in Tokiyo. Whatever interest they may have is due to the fact that they formed the first tests to which a new seismograph of the writer's design was exposed, and that, by its means, a complete record of the horizontal movement of the earth's surface was obtained from the beginning to the end of each shock. The new seismograph, a fuller account of which will soon be published elsewhere, consists of two horizontal levers pivoted on vertical axes which are rigidly fixed to posts stuck in the earth. At the short end of each lever there is a heavy bob of metal, whose inertia keeps it at rest during the earthquake. The long end of each presses very lightly upon a smoked-glass plate, which is kept revolving continuously by clock-work. The construction of the levers is such that the axis on which each of them is pivoted is the centre of percussion relatively to the centre of the bob, which is the corresponding centre of oscillation. The effect is, that when any small horizontal movement of the earth's surface takes place at right angles to either lever, the bob of that lever remains stationary while the axis moves, and consequently the long end moves on the revolving plate through a distance which is a certain multiple of the earth's motion. The two levers are placed at right angles to each other, so as to record two rectangular components of a displacement in any horizontal direction. In the instrument now in use, theratio which the recorded motion bears to the actual motion is six to one. During an earthquake the ...« less