92 EARTHQUAKES. 



we assume that the shock, after having reached Hakodate, 

 travelled on at the same rate as it did between Tokio and 

 Yokohama in order to reach Saporo, where the shaking 

 was felt eighteen seconds after Hakodate, it must have 

 had about thirteen geographical miles to travel after 

 Hakodate was shaken before Saporo felt its effect. 



Drawing from Hakodate a tangent to the eastern side 

 of a circle of thirteen nailes radius described round 

 Saporo, the origin of the disturbance must be on the line 

 bisecting this tangent at right angles. As it also lies on 

 a line drawn through Tokio and Yokohama, it lies in a 

 position about 41 N. lat. and 144° 15' E. long., which 

 is a position somewhat nearer to Nemuro than Hakodate, 

 as we should anticipate. If this be taken as approximately 

 indicating the origin, then the shock, after reaching 

 Hakodate from the Hakodate koTrioseist, travelled about 

 218 miles to reach Tokio in 128 seconds, which gives a 

 velocity of 10,219 feet per second. 



The method here followed is equivalent to that of the 

 hyperbola and one direction (see p. 204). The hyperbola 

 is described on the assumption that the velocity deduced 

 from the time taken to travel between Tokio and Yokohama 

 is correct, and also that the earth waves travelled with 

 approximately the same velocity in the vicinity of Saporo 

 as near Tokio. The probability, however, is that they 

 travelled more quickly. If this be so, then the origin is 

 thrown somewhat to the south-east and the velocity 

 between the Hakodate homoseist and Tokio reduced. 

 Thus, if the velocity in the Saporo district be double that 

 observed in the Tokio district, the origin is shifted about 

 twenty-eight miles to the south-west, and the last-men- 

 tioned velocity is reduced to about 9,000 feet per second. 



If we work by the method of circles, and assume the 

 velocity to have been constant in all directions, then this 



