Page:Science vol. 5.djvu/519

 A RECENT JAPANESE EARTHQUAKES

An unusually great eariliquake was felt in and about Tokio on OcL 15, 1SS4. Tlic annexed nuto- - graphic record ol it comes, with the following par- ticulars, from my formeraaiiatant, Mr. K. Seklya, who is DOW in charge of ths aeismological observatory of theUniveisityof Tokio. Itwasgiren by a horlEontal penilulnm seismograph of the kind recently described in Science (ir. 516), and it has many features in com- mon with the examples of records shown on p. G17 of

��ground lasled for about five minnles. During the Grst half-dozen Hconds, while both components were being registered, there is a tolerably close agreement of phase between the two, showing that the displace- ments were then not very far from rectilinear. The greatest motion in this part of the disturbance U>ok place five seconds from the start. At that point the actual motion of the ground was:t.7 centimetres from ea>t to west, and 2.2 centimetres from south to

��the B

�� ��But i

��the present i

tude of the earth's lioriion-

tal movement far exceeds

any thing that has been re-

C0Tde<3 since observationa of

this kind were instituted, in

1880.

The Rgure shows the rec- ord reduced to about one- third its actual size. The undulations on the inner circle have lieen traced by a pointer which registered the north to so'Ulh component of motion, and those on the other circle by another pointer, which registered east to west motion. The pointers are prolongations of horizontal pendulums, and trace their records on a revolving sheet of smoked glass, which In this example was started into motion by theearlhquakeilseif, through the agency of a delicate elec- tric contact-maker. The plate is driven by a clock- work train, which, af(«r starling, quickly reaches a steady rate under the control of a fluid friction governor. The speeil of rotation was one revolution in eighty- two seconds. The short radial lines mark seconds during the first part of the disturbance. The record on the outer, or east to west, circle, has been turned round so aa to bring it into synchronism with the inner, or north to south, record; and the earliest wo- liona are distinguished in the cut by the use of a somewhat heavy line. The records l>eglii at a and if, and are traced in the direction of the arrow, which is opposite to the direction of motion of the glass plate. At 6 thseastlo west record comes to an abrupt stop, owing to the displacement there having been so great as to carry that pointer off the plate altogether. The inner record extends over nearly four complete revolutions, showing that visible motions of the

���k

��' From liah

��, April M,

��north. The displacement of the ground is mul- tiplied four times in the original record, or about one and a thl.-d times in the reduced copy given here. The two components taken together represent a move- ment of the ground, from one side to the other, of no less than 4.3 centimetres, — a quantity which is in striking contrast to the "6 or even 7 mi Hfmi^fre* ' which, after three years' experience, 1 named as the amplitude to which in a Yedo earthijuake the dis- placement from the mean position ' occasionally

So far 09 can be judged from the north to south component alone, the most violent motions were over In about ten seconds; but tor some minutes afterwards, the oscillationa, though very much re-

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