188 EARTHQUAKES. 



they could always work in conjunction with each other, to 

 determine the origins more accurately. By knowing the 

 origin from which a set of shocks spring we know the 

 general direction in which we may expect the most violent 

 disturbances, and we can arrange our seismometers accord- 

 ingly. 



Approximate determination of origins, — In 1880 I 

 obtained a tolerably fair idea of the distribution of seismic 

 energy throughout Japan, by compiling the facts obtained 

 from some hundreds of communications received from 

 various parts of the country respecting the number of 

 earthquakes that had been felt. 



The communications were replies to letters sent to 

 various residents in the country and to a large number of 

 pubHc officers. By taking these records, in conjunction 

 with the records made by instruments, it was ascertained 

 that in Japan alone there were certainly 1,200 shocks 

 felt during the year, that is to say, three or four shocks 

 per day. The greater number of these shocks were felt 

 along the eastern coast, commencing at Tokio, in the 

 south, and going northwards to the end of the main island. 

 These shocks were seldom felt on the west coast. It 

 appeared as if the central range of mountains formed a 

 barrier to their progress. Similarly, ranges of mountains 

 to the south-west of Tokio prevented the shocks from 

 travelling southwards. Proceeding in this way the con- 

 clusion was arrived at that the west coast, the southern 

 part of Japan, and the islands of Shikoku and Kiushiu, 

 had" their own local earthquakes. 



Earthquake-hunting. — These preliminary enquiries 

 having shown that the northern part of Japan was a better 

 district for seismological observations than the southern 

 half, the next step was to subject the northern half to a 

 closer analysis. This analysis was commenced by sending 



