DE VEL OP ME NT OP SEISMOL OGY IN JAPAN 269 



Shida^^^ gives a design of a special horizontal pendulum with 

 which he proposes to study the possible free vibration of tlie earth. 

 He also constructed recently an extremely sensitive seismometer with 

 Avhich he is now continuing a special investigation in his Kamigamo 

 Observatory^^^. 



Imamura^"' lately introduced several points of improvement in 

 the registering mechanism of Omori^s tromometer and succeeded in 

 obtaining tine records of those minute vibrations which had hitherto 

 escaped our observation. With this instrument, it is hoped that it 

 will become practicable to determine the epicentres of minor earth- 

 quakes. 



Lastly, the recent investigation by S. Takaj'a and K. Tanabasi^'^^ 

 on the coefficient of the damping of the tromometer and its dependence 

 on the period is worth notice. 



(b) Velocity of propagation of seismic waves; duration of pre- 

 liminary tremor. The velocities of the propagation of the different 

 phases of 'seismic waves have been investigated by Omori^^^ and 

 Imamura^^^ from the earliest days. The former early noticed the dif- 

 ference of the velocities for continents and oceans. Velocities of waves 

 due to artificial shocks have also been investigated. 



Omori's formula"^^^ giving the relation between the duration of the 

 preliminary tremor and the ejDicentral distance is very well known. 

 The great service rendered by this formula for the advancement of 

 seismology in this country can scarcely be overestimated. It has its 

 own merit on account of its utmost simplicity and practical ap{)lica- 

 bility at least for the first approximation, though indeed its physical 



(1) Nagaoka Anniversary Volnnie (1925), 109. 



(2) Communicated to a Meeting of the E.I.C. ; still unpublished. 



(3) Eead before the Colloquium of the Earthquake Research Inst., 24 Feb., 1926 ; 

 not yet published. 



(4) U. t. S., 6 (1926), 31. 



(5) Ho., 3 (1895); 4 (1895); 21 (1898); 29 (1899); SO (1905); 73 (1911); Pub., 

 5 (1901); 13 (1903); 24 (1907); Bull., 1, No. 1 and No. 2 (1907); 2, No. 2 (1908); 3, 

 No. 2 (1909); T.S.B.K., 1 (1903), 207, 218; 2 (1905), 193. 



(6) Ho., 21 (1898); 32 (1900); 53 (1906); 70 (1910); Pub., 7 (1902); 16 (1909); 

 18 (1904); Seism. N., 6 (1924); T.S.B.K., 1 (1903), 261; 2 (1905), 151, 159. 



(7) Journ. Coll. Sci. Tok., 11 (1899), 147 ; Ho., 29 (1899) ; 50 (1905) ; 88A (1918) ; 

 Pub., 5 (1901); Bull., 1, No. 1. (1907); 2, No. 2 (1908); Seism. N., 1 (1921) ; T.S.B.K., 

 2 (1905), 290. Also Imamura, Ho., 82 (1915) ; 95 (1922) ; S. Nakamura, J.M.S., 35 

 (1916) e- 



