April 23, 1885] 



NA TURE 



A RECENT JAPANESE EARTHQUAKE 



AN unusually great earthquake was felt in and about 

 Tokio on October 15, 1SS4. The annexed auto- 

 graphic record of it comes, with the following particulars, 

 from my former assistant, Mr. K. Sekiya, who is now in 

 charge of the seismological observatory of the University 

 of Tokio. It was given by a horizontal pendulum seismo- 

 graph of the kind recently described in NATURE (vol. xxx. 

 p. 150), and it has many features in common with the 

 examples of records shown on pp. 174 and 176 of the 

 same volume. But in the present case the amplitude of 

 the earth's horizontal movement far exceeds anything that 

 has been recorded since observations of this kind were 

 instituted in 1880. 



The figure shows the record reduced to about one-third 

 its actual size. The undulations on the inner circle have 



been traced by a pointer which registered the north to south 

 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, 1 and 

 trace their records on a revolving sheet of smoked glass, 

 which in this example was started into motion by the 

 earthquake itself, through the agency of a delicate electric 

 contact-maker. The plate is driven by a clockwork train 

 which, after starting, quickly reaches a steady rate under 

 the control of a fluid friction governor. The speed of 

 rotation was one revolution in 82 seconds ; the short 

 radial lines mark seconds during the first part of the dis- 

 turbance. The record on the outer, or east to west circle, 

 has been turned round so as to bring it into synchronism 

 with the inner or north to south record, and the earliest 

 motions are distinguished, in the cut, by the use of a 

 somewhat heavy line. The records begin at a and "[a 1 



and are traced in the direction of the arrow, which is 

 opposite to the direction of motion of the glass plate. At 

 b the east to 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 ground lasted for about five 

 minutes. During the first half-dozen seconds, while 

 both components were being registered, there is a toler- 

 ably close agreement of phase between the two, showing 

 that the displacements were then not very far from recti- 

 linear. The greatest motion in this part of the disturb- 

 ance took place five seconds from the start ; at that point 

 the actual motion of the ground was 37 centimetres from 

 east to west and 2 - 2 centimetres from south to north. 

 [The displacement of the ground is multiplied four times, 



in the original record, or about one and a third times], in 

 the reduced copy given here.] The two components 

 taken together represent a movement 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 " 5 or even 

 7 millimetres" which, after three years' experience, I 

 named as the amplitude to which in a Yedo earthquake 

 the displacement from the mean position "occasionally 

 rises" (vol. xxx. p. 175). So far as can be judged from 

 the north to south component alone, the most violent 

 motions were over in about ten seconds, but for some 

 minutes afterwards the oscillations, though very much 

 reduced, continued to exceed in amplitude almost any 

 that I have recorded. 



1 See "Measuring Earthquakes" (Nature, vol. xxx. p. 150), or a 

 " Memoir on Earthquake Measurement" (Tokio, 1883, p. 22). 



