EARTHQUAKE MOTION DEDUCED FROM OBSERVATION. 9^3 



velocity must have been about 6,000 feet per second. If 

 we assume that the indications of direction obtained from 

 seismographs and other sources give to us by this intersec- 

 tion a proper origin, the velocity in some directions may 

 have been as much as 1 7,000 feet per second. 



An origin thus determined, or even if determined by 

 the method of circles, is in discord with the fact that 

 places like Nemuro, in the north-east of Yezo, were nearer 

 to the origin than any of the other places which have been 

 mentioned. 



The conclusion which we are therefore led to with 

 regard to this shock, assuming of course that the time 

 observations are tolerably correct, is that the velocity of 

 propagation was variable, being greater when measured 

 between points near to the origin than between points at 

 a distance. The velocities estimated vary between 4,000 

 and 9,000 feet per second. 



In the case of the earthquake which has just been 

 discussed, we have an example of a disturbance which must 

 have passed between Tokio and Yokohama in what was 

 almost a straight line from the origin. As this direction 

 ought to give the maximum time of transit if all earth- 

 quakes are propagated with the same velocity, the fol- 

 lowing table is given of the interval between the time of 

 observation of several shocks at these two stations : — 



From Yokohama to Tokio. Feom Tokio to Yokohama. 



1880 December 20th 



36 seconds 



1882 October 25th 



. 21 seconds 



1881 January 7th ] 4 



-31 



1) 



1883 February 6th 



. 23 „ 



„ March 8th 



60 



)> 



„ March 1 



53 „ 



„ ,, 17th . 



66 



»» 



>i » »j 



•63 „ 



„ November 15th 



31 



M 



„ „ 8th 



27 „ 



1882 February 16th 



22 



» 



„ 11th 



26 „ 



As these are observations which have been made with 

 the assistance of a telegraphic signal daily employed to 



