278 T. Teeaua and T. MATUiJAWA 



stations. K. Suda^^^, in a series of papers, proposed to distinguish the 

 physical source, i.e. the seat of energy stored up for the occurrence of 

 the earthquake, from the apparent origin of disturbance, as is usually 

 determined by the geometrical construction. In these papers, he also 

 adduced some theoretical consideiations on the mechanism of the 

 origin, similar to that treated by Nahano and Matuzawa, and suggested 

 a new mode for the classification of earthquakes. 



(e) Pulsations. The fact that the pulsatory motion of the earth 

 is intimately connected with the appearance of conspicuous cyclones 

 or typhoons has bt^en early recognized by Omori*^^^ and confirmed by 

 N. Simono'^^^ and others. The former noticed also that the pheno- 

 menon appears most conspicuous when the centre of atmospheric 

 disturbance lies on the sea, especially on the Pacific side. He invest- 

 igated later the relation between the periods of ocean waves and 

 those of tlie pulsations and found some common periods in these two 

 kinds of waves. 



The seasonal variation'^''^ of the frequency of occurrence of the 

 pulsations shows generally a maximum in December and a minimum 

 in September. The daily variation*^^^ shows a maximum in the 

 daytime. 



The frequency is markedly great on alluvial plains and less in 

 mountainous regions'^''\ The frequency of waves with different dura- 

 tions, or degi'ees of coherence, shows maxima near 6 and 10 

 waves'^ '^^ 



The comparisons*^ of observations made at two stations in Tokyo, 

 one in Hongo, situated on tertiary ground at a height of 16 m, from 

 the sea-level, and the other at Hitotubasi, situated on the low alluvial 

 plain, has revealed that the identification of waves for the two stations 

 is not easy. Eecently, Imamuva'^^^ made, with his improved tromo- 

 meter already mentioned a comparison of the pulsations observed at 



(1) U.I.S., S (1925), 46, 64, 80. 



(2) Ho., 43 (1903); 50 (1905); 89 (1918j ; 94 (1921); Bull 3, No. 1 (1909); 5, 

 No., 3 (1913). 



(3) J.M.S., 27 (1908), 317 ; 28 (1909), 85. 



(4) Omori, Ho., 50 (1905). 



(5) Omori, Ho., 50 (1905); Bull., 2, No., 1 (1908). 



(6) Omori, Ho., SO (1905). 



(7) Omori, Bull., 3, No. 1 (1909). 



(8) Omori, Pub. 13 (1903); 18 (1904); Bull., 2, No. 1 (1908); 3, No. 1 (1909). 



(9) Not yet published. 



