80 



K. HONDA, T. TERADA, Y. YOSHIDA, AND D. ISITANI. 



mean deptli by mechanical integration.* Tlie velocities of pro- 

 pagation of the long waves along these paths were then cal- 

 culated from the depths. The time of transmission of the wave 

 along these paths was compared, and the path of the minimum 

 time was taken to correspond to the actual path. From the 

 path thus found and the actual time of transmission, we found 

 the mean velocity of propagation of the sea wave, as given in 

 the following table. As tlie time of occurrence of the sea wave 

 in its origin, we took the time of the earthquake. 



Hitherto it has been customary to measure the path along 

 the great circle of the earth ; but the actual distribution of the 

 depth being complicated, this is not a proper method. 



The value Vgk of the fourth column in the above table 

 represents the theoretical velocity of a long wave. Strictly 

 speaking, the mean velocity should be deduced from the dis- 

 tance s along the path and the time interval /f given by 



J\/gh 



*) The chart pnbHshed by " Deutschen Seewarte," 1896, -was used. One of the authors 

 CYaUiated the mean depths by Berghaus' Physikalischen Allas and obtained considerably 

 large values (Proc. Tokyo Matb.-Phys. Soc. 3, p. 1G5.). 



t) C. Davison, Phil. Mag. 50, p. 579, 1900 ; H. Nagaoka, Proc. Tokyo Math.-Pbys. Soc, 

 p. 12G, 1902. 



In deducing the above formula, no account is taken of the curvature of the earth; 

 if this is taken into account, the general tendency is to reduce the velocity from that given 

 ^^y \/y/r. Of course there is some dependence on the wave length and the configuration 

 of the sea. H. N. 



