18 ART. 9. — S. KUÖAKABE. 



seismic centre. It is a matter of daily experience with us who 

 live in an earthquake country located in the ' girdle of fire of 

 the Pacific, that observers in some districts feel all shocks as if 

 coming from one particular direction even when the seismic centre 

 lies in an entirely different direction. 



As another consequence, there may exist seismic shadows ; 

 or, in other words, seismic waves may be partially shielded by a 

 vein or dike of old rocks. Earthquakes originating in one region 

 may always be well observed in the station while those originating 

 in another region may fail to be observed in the station. In 

 Prof. F. Omoei's paper* we find a most interesting example to 

 support the above consideration. Of the earthquakes which hap- 

 pened between Sept. 1889 and July 1886 in Central Japan, those 

 whose origins were situated within certain boundaries were never 

 felt in Tokyo, though the weaker ones of more distant origins 

 were clearly felt there. 



The frequency of earthquakes as related to the geological 

 distribution of rocks will be fully discussed in a following paper 

 under a special title. 



In conclusion, I wish to express my great indebtedness to 

 Mr. FuKUCHi for valuable information concerning the geological 

 characters of the specimens. My best thanks are due to Professor 

 H. Nagaoka, under whose kind guidance I have carried out this 

 experiment. 



* F. Omori. The Pub. of the E. I. C. in F. L. No. 11. 1902. 



